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29th April 2020

Energy for Ruminants

Energy Definitions

Nutritionists define energy in several different ways, of course the main reason for this is just to confuse everyone!
No seriously, it is because the feeding system for monogastric species like Humans and Pigs, is defined differently to that of ruminants. After all Pigs have only got one stomach and ruminants have got four! The following definitions are included to try and clarify much of the confusion that surrounds them for the layman.
Energy itself is measured in Calories Kcals to us humans on a slimming diet! This is usually how you see energy referred to on food labels in supermarkets; but if your metricated, up to date and want to feed ruminants, then we use Megajoules (MJ’s).

Gross Energy (GE)

This is the total amount of energy contained within a feed.
Gross energy is measured by burning a sample of the feed in oxygen and measuring the heat produced. Carbohydrates contain around 17.5 MJ GE/Kg DM, protein is itself a source of energy at around 26 MJ GE/Kg DM, and fat is about 38 MJ GE/Kg DM.

Digestible Energy (DE)

If all the gross energy was digestible there wouldn’t be any passed out in the faeces. Unfortunately no ruminant is capable of digesting 100% of the gross energy of a feedstuff, although it can get pretty close with some of the protected fats.
The bit that gets Digested is called….. go on have a guess! Yes it’s Digestible Energy !
Therefore Gross Energy minus Faecal Energy = Digestible Energy (D E)
The DE varies from about 45% in poor quality feeds like straw to about 85% of the GE in good quality feeds like wheat.

Metabolisable Energy (ME)

There are further energy losses as energy leaves the body via the Urine, and Methane. The remaining energy is therefore all metabolisable. Metabolisable means, “used inside the body on the body’s side of the gut wall.”
Metabolisable Energy = Digestible Energy minus Urine Energy and Methane Energy.

Net Energy (NE)

This is the energy the animal uses to grow, produce milk, move around, or grow a foetus.
As the animal does all these things it also wastes some of the ME as heat.
Body heat is usually manufactured during the biochemical processes of getting all the energy in complex molecular form around the body. These energy cycles are responsible for converting the energy into the growth or milk that we require from the animal and they also release heat into the body and subsequently it is wasted into the atmosphere.
Net Energy = Metabolisable energy minus Heat Energy.

Fermentable Energy (FME)

“Fermentable Metabolisable Energy”. Just saying this, could be a very bad way of trying to impress your friends at parties! FME is a lot easier to say. It is particular to the Metabolisable Protein (MP) System which assumes that the fraction of energy available to supply the rumen microbes, is the FME.

The objective of maximising the output of rumen microbes, is essential to the high output animal, therefore particular care is needed to ensure that they get the correct amount of FME.
FME is calculated as the metabolisable energy minus the gross energy from the fat and oil fraction and the fermentation acids in the feed.


(Metabolisable Protein from Energy)

The “Feed into Milk” system replaces FME with MPE. It is effectively the same thing because it describes the potential output of metabolisable protein that is predicted can be generated from the rumen degradable energy supply.
It is split into S A B & C fractions where S is instantly available, A is slowly available, B is very slow and By-pass and C is the rate of rumen outflow.
This is the first value to check since it often falls short of allowance and should not be targeted at a level of less than 200 grams below the potential output from MPN (see below).

Energy Metabolism

I can remember sitting in the lecture theatre at college, in the 1970’s, thinking that the lecturers seemed to be in a bit of a quandary when it came to energy requirements for ruminants.
The problem was, “What system should be used?”
In the early part of the 20th century the scientists expressed energy as “Hay Equivalents!”, I wonder how many people can remember that system.
The hay equivalent system was replaced with a much better but still questionable Starch Equivalent System. In 1974 we had to learn how this system worked only to be told that after we had mastered it, we had to learn the system that is still the base for the one we use today, The Metabolisable Energy System, (M E System for short).
This system has been the subject of much debate and considerable research and the early form has now largely been modified by refining the Fermentable Metabolisable Energy (FME) to the MPE definition in the Metabolisable Protein system, (MP, System for short).
Unfortunately for the layman, the complicated sounding names of these systems is enough to put them off or to induce an instant and total deep sleep!
The good news or bad news, depending on which way you look at it, is that whilst the ME and the modern MP systems do indeed represent a much more accurate solution to the predictability of feeding ruminants, there are still a few situations where they can produce less than optimum results.
This is where salesmanship and artistry enter the equation. Most farmers are only too aware of the amount of sales pressure that goes into getting the animal feed order for the local feed rep.
There is now a massive array of impressive sales aids ranging from various glossy leaflets and folders to videos, fancy computer programs and computer software.
The quality of this approach is self evident but the degree of interpretation can sometimes leave a lot to be desired. As an independent nutritionist I am often called in to sort out diets that have been incorrectly balanced by the trade, or other bodies, this is often due to the inaccuracy of sampling or the inexperience of the advisors.
Whilst the trade and the independent advisory bodies try their best in good faith to balance up the rations; in truth some of the diets that result don’t live up to expectation. Usually this is due to failure to read between the lines. The figures on the print out might look okay, but do they represent the complete story, and were they based on accurate information?
I can remember after three years working in the trade for a big national compounder I was firmly put on the spot by a good customer in North Yorkshire.
He said to me that as far as he was concerned, the computer generated diet that I had spent hours balancing, was rubbish. The problem was that the energy system that we were using at that time didn’t do a very good job of evaluating the balance of energy from different sources.
This was a hard lesson at the time. In those days the use of the “portable” computer (these things were actually very cumbersome) was designed to look really impressive, so it was a bit of a blow to realise that the main reason for lugging this contraption from farm to farm was because it was nothing more than a useful sales aid!
To be fair, the diet programs that were in use at this time made a reasonable job of balancing compound feeds into the diet. They were certainly better than what had gone before, but when it came to rationing diets wholly composed of straights, they were moderate in their reliability.
Modern software is way ahead of the programs that were being used in the 1980’s and the new Feed into Milk rationing system represents a big advance in ration prediction, but we still have to be realistic about the accuracy of the figures that are used to balance the diets. Variability in the analysis of silage, fresh grass and many of the bought in feeds can soon make a complete nonsense of the resulting paper ration.
Metabolism is the process by which the body uses the nutrients it gets from the digestive system to do things.
Metabolisable energy can be used for keeping warm, moving about, scratching an itch, or more importantly for producing milk, growth or for growing foetuses.
The energy system that we use today expresses the daily needs of the animal using the energy unit known as the Megajoule (MJ). For our purposes it doesn’t matter exactly what a Megajoule is, just that in order to get the animals to perform we need to supply enough of them.
All animals need energy for maintenance. If they don’t get enough, they start to lose weight by mobilising the energy stored in the body fat. Just like human slimming diets!
FiM takes a blanket assumption that the energy required for maintenance is 80 MJ! This seems high but when the slight reduction in allowance for milk production is taken into account it is not so drastic. Modern Hybrid MP programs are, in my opinion, more accurate.
The tables below show just how much energy is needed by the animals to insure that they can produce enough for maintenance, milk or growth.
The tables are a good guide and although they are now quite old they do not seem to be far off the mark.
Table 6 is still worth a look since the influence of the Q value shows how the relative density of the ration can affect output. A quick look back to the Output vs Density graph in the previous section will endorse this point.

Energy for Maintenance

Table 6

The daily maintenance allowance of ME for Dairy & Beef Cows. (AFRC 1990)

Body weight (Kg) MJ per head per day
Q. 45 Q. 50 Q. 55 Q. 60 Q. 65 Q .70
100 17
150 22
200 27
250 31
300 36
350 40
400 50.1 48.8 47.6 46.4 45.3 44.2
450 54.5 53.1 51.7 50.5 49.2 48.1
500 58.7 57.2 55.7 54.4 53.1 51.8
550 62.8 61.2 59.7 58.2 56.8 55.5
600 66.8 65.1 63.5 61.9 60.4 59.0
650 70.8 68.9 67.2 65.5 64.0 62.5
700 74.6 72.7 70.9 69.1 67.5 65.9
750 78.4 76.4 74.4 72.6 70.9 69.2

Energy for Milk Production

Table 7 shows the energy allowances for milk production. The actual amount of energy needed to produce a kilogram of milk will vary in accordance with the amount of milk solids within that milk.
The solids consist of butterfat, protein, lactose and minerals.
At this point it is useful to show an example. by referring to table 7 we can see that the average black and white dairy cow producing milk of 4% butterfat and 3.3% Protein needs 5.15 Megajoules for each kilogram of milk she is producing. This will have to be added to the energy that she needs for maintenance and growth.
Using the figure 5.2 Megajoules per kilogram of milk will prove to be a good rule of thumb for most commercial animals.
FiM uses a blanket figure of 5 MJ per Kilo, many commercial programs have manipulated this figure. This is an effort to give a more reliable prediction model for their rationing purposes.
In the light of what we have just shown, this seems a bit harsh for the FiM system, but when we remember the generous allowance for maintenance of 80 MJ, it can be seen that high yielding cows would close the obvious gap between the MP and FiM allowances.

Table 7

Energy allowances for milk production. (Q= 0.60 Ration) (AFRC 1990)

FAT Content of Milk
Protein 3.00 3.25 3.5 3.75 4.0 4.25 4.5 475 5.0
2.8 4.32 4.48 4.64 4.80 4.96 5.12 5.28 5.44 5.60
2.9 4.36 4.52 4.68 4.84 5.00 5.16 5.32 5.48 5.64
3.0 4.39 4.55 4.71 4.87 5.03 5.19 5.35 5.51 5.67
3.1 4.43 4.59 4.75 4.91 5.07 5.23 5.39 5.55 5.71
3.2 4.47 4.63 4.79 4.95 5.11 5.27 5.43 5.59 5.75
3.3 4.51 4.67 4.83 4.99 5.15 5.31 5.47 5.63 5.79
3.4 4.54 4.70 4.86 5.02 5.18 5.34 5.50 5.66 5.82
3.5 4.58 4.74 4.90 5.06 5.22 5.38 5.54 5.70 5.86
3.6 4.62 4.78 4.94 5.10 5.26 5.42 5.58 5.74 5.90


From Tables 6 and 7 we can now calculate that a Holstein cow weighing 650 Kg and giving 35 Kg of milk at 4% Butterfat and 3.3% on a Q 0.60 ration will need to be supplied with the following amount of energy from her diet:-
Maintenance 650 Kg cow = 65.5 MJ.
Milk production 35 x 5.15 = 180.25 MJ
Total requirement is therefore, 65.5 MJ + 180.25 MJ = 245.75 MJ per day.
The calculation using FiM is as follows:
Maintenance for the 650 Kg Cow = 80 MJ
Milk Production 35 x 5 = 175 MJ
Total requirement is therefore 255 MJ!

Some cynical people would say that the FiM system has built in a lead feed of around 2 litres of milk. (Not bad if you are selling compound feeds).
The scientists would argue that we were under feeding by this amount when we use the MP system.
Personally, I reckon that the “extra energy is needed in early lactation to try and improve fertility responses.
Rations which utilise poor quality forages or fall towards the Q 0.50 ration category will tend to require around 0.3 MJ per Kilogram of milk more energy, and those aspiring to Q 0.70 will need 0.3 MJ per Kg milk, less energy.
This example doesn’t take into account the energy contribution from body weight loss experienced by most animals in early lactation, or the extra energy needed for live weight gain in late lactation.

Energy for Growth, Pregnancy and Weight Loss

One of the less obvious aspects of ruminant nutrition is that the seemingly simple idea of a Kilo of live-weight gain (LWG), is in fact far from simple! The trouble is that each Kilo could differ in it’s make up of water, protein, fat and ash and even the energy contained within.
The Table below is taken from some quite old research, but it shows the difference in the composition of an average Kilo of body weight of a sheep and a cow at different overall weights.

Table 8

(Taken from Mitchell, H, H. 1962)

Composition of Gain (g/Kg)
Animal Live-Weight (Kg) Age (Months) Water Protein Fat Ash Energy


Sheep 9 1.2 579 153 248 22 13.9
Sheep 34 6.5 480 163 324 31 16.5
Sheep 59 19.9 251 158 528 63 20.8
Cow 70 1.3 671 190 84 7.8
Cow 230 10.6 594 165 189 11.4
Cow 450 32.4 552 209 187 12.3

Referral to table 8 shows us that it is not unreasonable to suppose that the amount and balance of nutrients needed to produce a kilo of LWG for a young lamb is different to that of its mother. and similarly, a Kilo of LWG from a calf is completely different to that of its mother or its older sister.
There is also a difference in the composition of a Kilo of body weight between animals of the same age but of differing sex or breeds. The nutrient requirements for achieving targets set for LWG vary considerably as a consequence of these differences in composition.
Tables 9A and 9B shows the ME requirements for growth and from live-weight loss for dairy cows in milk and dry. I have included the tables for a more global assessment of nutrient requirements for growing cattle and sheep in the glossary.

Table 9 A

Metabolisable Energy Values (MJ of ME) of weight change in milking and pregnant dry cows on rations of varying quality (from AFRC 1990 and AFRC 1993)

Milking Cows

Q -1.00 -0.75 -0.50 -0.25 0.25 0.50 0.75 1.00
0.50 -23.3 -17.4 -11.6 -5.8 9.7 19.4 29.1 38.8
0.60 22.0 -16.5 -11.0 5.5 9.2 18.3 27.5 36.7
0.70 20.8 -15.6 -10.4 -5.2 8.7 17.4 26. 1 34.7

Note: – Now we can see that a kilo of liveweight loss from a dairy cow on a Q 0.70 (high density diet) is only worth 20.8 MJ whereas a kilo of gain requires 34.7 MJ.

Table 9 B

Dry Cows

Q -1.00 -0.75 -0.50 -0.25 0.25 0.50 0.75 1.00
0.40 -24.8 -18.6 -12.4 -6.2 17.3 34.5 51.8 69.0
0.50 -24.8 -18.6 -12.4 -6.2 13.9 27.7 41.6 55.4

Pregnancy also requires an allowance for energy.
The growth of the developing calf or lamb occurs mainly in the last third of the pregnancy. The initial stages of growth are tiny and can only be measured in milligrams per day, it is not until 10 weeks before calving and 6 to 8 weeks before lambing (dependant on the number of foetuses), that the extra nutrient requirements become significant enough to make real dietary allowances for.
Much of the energy and protein required for pregnancy is used to support and grow the placenta and umbilicus, which is lost at calving.
Recent work on feeding dry cows has highlighted the importance of feeding correctly. We now know that this should be viewed as a training period for the next lactation and not a rest from the last one. The advances in nutrition during this period have done much to improve the health and performance of the dairy cow. It is not unreasonable to suppose that some of these advantages in technique would also yield benefits if applied to Suckler cows and sheep.
Chapter 5 deals with the management of the dry ruminant in more detail.
Table 10 shows the differences in calf weights of common breeds of sire used on dairy herds.

Table 10

AFRC 1992

Breed of Sire Bull Calf Heifer Calf Average
Angus 27.0 25.1 26.1
Ayrshire 35.0 32.6 33.8
Charolais 44.0 40.9 42.5
Friesian 39.0 36.3 37.6
Guernsey 33.0 30.7 31.8
Hereford 36.0 33.5 34.7
Holstein 45.0 41.9 43.4
Jersey 26.0 24.2 25.1
Limousin 39.0 36.3 37.6
Simmental 44.0 40.9 42.5

The table is a fairly predictable data set because we all know that a Jersey cow is a lot smaller than a Holstein Friesian.
What may be surprising is that the Holstein calf is heavier than the big continental Charolais and Simmental breeds.
Table 11 shows the energy allowances to be made for a pregnancy resulting in a calf birthweight of 40 Kg.
The correction factor is linear so if we were trying to work out the energy requirement for a
Pure Bred Holstein it would be 43.4/40 = 1.085 x the ME requirement listed in table 11.
Tables for sheep are included in the glossary

Table 11

Metabolisable Energy requirements for Pregnancy (AFRC 1990)

Days Weeks MJ/ Day
35 5 0.3
70 10 0.7
105 15 1.4
140 20 2.8
175 25 5.5
210 30 11.1
217 31 12.7
224 32 14.6
231 33 16.8
238 34 19.2
245 35 22.1
252 36 25.4
259 37 29.1
266 38 33.5
273 39 38.4
280 40 44.1


Now we can complete the example from page 10, our Holstein cow weighing 650 Kg
giving 35 Kg of 4.0% Butterfat and 3.3% Protein Milk, on a Q = 0.60 diet, could have been in very early lactation and losing 0.50 Kg of body-weight per day. Now we can work out her actual energy requirement as follows:-
Maintenance from table 6……………………….. 650 Kg = 65.50 MJ
Production from table 7…………….. 35 Kg x 5.15 MJ = 180.25 MJ
Body-weight change from table 9 a…………….0.5 Kg = -11.00 MJ
Week 8 of pregnancy from table 11………………………= 0.50 MJ (0.05 x 1.085 = 0.5425)
Total Metabolisable Energy requirement……………….= 235.25 MJ

The Feed into Milk system retains the same lead in this calculation resulting in a total Metabolisable energy requirement of 244.25 MJ.

Balancing Energy Sources

Most animal feed stuffs contain some useful energy providing nutrients. The obvious exception to this is the inorganic minerals. Energy sources are broadly split into four main categories, or five if we include protein, which in times of severe under supply of the other four sources, can be broken down as an energy source.
The four sources are made up of Oils and Fats, Sugars, Starches, and Fibre. Each of these sources will make a contribution of ME to the diet.
Some advisers seem to over-simplify the diets by placing the emphasis on supplying total energy requirements without worrying about how the energy is sourced. These diets do not work well compared to diets that contain a variety and balance of the main energy sources Quite often it is the neglect of this simple principle which accounts for poor animal performance.

The Role of Insulin

The value of ‘Q’ is variable but typically around 65%. This means that only 65% of the energy in the diet is metabolizable, (often lower for sheep and extensively grazed animals). Dairy and sheep energy inputs are a moving target, fresh calving cows and immediate pre lambing sheep simply can’t get enough energy due to a reduced appetite.
In this situation, low blood sugar levels trigger a reduction of insulin which mobilises body fat and enables the cow to milk off her back, and the ewe to supply enough energy for her lambs just before and after lambing.
This release of body fat results in an eventual increase in blood sugars as glucose which is the body’s way of supplying demand for sugar when the diet cannot keep up or the liver is not processing enough sugar to meet energy demands.
In later lactation the intake of energy exceeds requirements and the cow and ewe will replace their depleted body reserves.
Cows in particular tend to fail to hold to service until the rate of body weight loss starts to slow down.
Insulin also controls the storage of excess circulating blood glucose as fat.
Diets that feature excessive quantities of starch and sugar raise insulin levels, so milk production falters and the cow gains weight.
Recent research has also shown that insulin increases the rate of release of Follicle Stimulating Hormone (FSH), and thus has a significant link to fertility.
This tells us that we must control the use of starch and sugar by ensuring that we supply the right amount for the desired production targets.
Too much circulating sugars and we get reduction in production (also probable sub-acute rumen acidosis) and cows getting fat.
Too little circulating sugars and we get cows milking off their backs, unable to release enough FSH for good conception rates, and possible sub-acute Ketosis due to fatty livers.
Setting appropriate nutrient parameters should be the first step in ration balancing.


Ketosis is a metabolic disease that occurs when the animal (usually newly calved or lambed) cannot mobilise enough blood sugar to cope with the demand to produce enough milk to feed a calf or lambs.
Ketosis is caused by the more general deficiency of starch and sugars, as opposed to just sugar. It occurs in early lactation with animals that are struggling to mobilise body fat to fuel increasing demands for milk production.
The mobilised of fat from body reserves is broken down to glucose in the liver by a complex metabolic cycle known as lipolysis.
Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and three fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes.
Lipolysis is induced by several hormones, including glucagon, epinephrine, norepinephrine, growth hormone, atrial natriuretic peptide, brain natriuretic peptide, and cortisol.
Fatty liver syndrome and other liver issues (ie: – Fluke) will ultimately lead to inadequate propionate production, (the main acid produced by the degradation of starch).
Ewes with triplets and very high yielding cows (especially those with chronic fatty liver syndrome); are the most susceptible.
Prevention is firstly by ensuring that the animals do not get too fat. Secondly by ensuring that there is enough fermentable carbohydrate (starch & sugar) in the diet.

Ketosis in Sheep

The foetal lamb maintains the sugar concentration of its own blood at a level which is higher that its mother. If the glucose supply of the mother is too low, her own blood glucose levels may fall so low that the nerve tissues (which rely on carbohydrate for energy) become affected.
This triggers the classic Twin Lamb disease or “Pregnancy Toxaemia”
The symptoms are that the ewes become dull, lethargic and lose their appetite. They then start to tremble and hold their heads at peculiar angles. Ewes often generate high levels of ketones in the blood and may show signs of metabolic acidosis accompanied by renal failure in the later stages of the disease.
Mortality rates can be as high as 90%.
The disease is usually prevalent in twin and triplet bearing ewes, where there is a food shortage, or there has been stress caused by transportation or dog worrying.
A more normal occurrence is that sheep in particular, will get too fat in late lactation and before tupping. Excess weight gain results in fat deposits in the liver the heart and the birth canal. These deposits result in liver and heart failure, and difficulties in lambing or calving respectively including pregnancy toxaemia which is normally treated by supplying glucose licks and drenching with mono-propylene glycol at lambing.
Prevention is by maintaining high enough intakes of starch and sugar. Glucose licks are particularly popular as a cure for this problem. Some farmers include molasses licks or feed molassed meals in order to ensure adequate sugar intakes.

Ketosis in Cows

Ketosis occurs at a time when the cow’s appetite is depressed after calving and energy intake cannot meet the increasing demand of the rising milk yield.
This period of ‘negative energy balance’ (NEB) is normal in all newly calved cows but it is the level at which this happens that is important.
To meet energy requirements, the cow loses weight by mobilizing “back fat” which is then transported (as NEFAs) to the liver and broken down to glucose to release energy.
During periods of high energy demand the liver cannot fully utilize the fat. Metabolites known as ketones, such as acetone and beta-hydroxybutyrate, are produced. If too much weight is lost, these ketones overflow into the blood resulting in a further depression of appetite and subsequently reduced milk yield.
This situation is made even worse when the liver itself contains fat deposits, effectively clogging up the system. “Fatty Liver Syndrome” is a key focus of both modern dry cow and “Close Up” ewe management.
Typically, cows will lose 0.5 in body condition score from calving to bulling and service but many cows will lose more than that; especially when suffering from fatty liver.
Fat cows already have lower dry matter intakes post calving and so their body condition score drops even more, taking them to the point of ketosis.
Cows that have been dry for a long period of time or cows that have some sort of metabolic disease during calving, or dystocia, are also more susceptible to ketosis.
Ketosis is a problem in UK dairy cattle, with approximately 30% having sub-clinical ketosis. The incidence has increased as the genetically driven increase in average yield has increased.
It is commonly characterized by anorexia, depression and reduced productivity, lower milk yields and poorer fertility.
Even when at sub-clinical level, cows are at higher risk of suffering a wide range of metabolic and reproductive diseases which can further reduce income and add extra cost.
The direct costs of ketosis include the input by the vet and herdsperson, drugs, discarded milk and reduced yield. Longer term problems are extended calving intervals, higher cases of cystic ovaries, LDAs, retained foetal membranes and metritis.
When peak yields are attained at about 4 weeks in the ewe and 8 to 10 weeks in the cow, appetite generally catches up and, the animal stops losing weight.
One area to watch is body condition at lambing or calving since if t
he animal is too thin it will not have enough fat to mobilise and will need to be fed on very high energy diets if it is to have any chance of producing its genetic potential output of milk. In many dairy herds even normal condition loss is not enough to prevent the animal achieving her yield potential.
The food conversion efficiency, of the individual animal can often be the deciding factor in these situations. As a rule of thumb, “The better the genetic potential, the better the F C E”, but it is only a rule of thumb.
The addition of saturated fat at this stage of the diet supplies a very rich energy source which we traditionally thought would help to overcome the problem.
Recent research supports the use of sugar sources in the first few weeks of lactation in preference to extra protected fat. This energy source is easier for the liver to metabolise than fats which go through lipolysis before they can be further metabolised. This highlights the need for rapidly available energy at the onset of lactation in order to reduce the nutritional stress that exists at this point.
The addition of too much starch and sugar provokes the onset of acidosis. The generally recognised bomb proof nutritional advice is to optimise the sugar content of the diet to between 6% and 8% and feed a sugar pre-cursor like glycerol or Mono Propylene Glycol.
This technique is very effective for most cows and ewes other than those with severe complications outlined above.
Much research has been done to find ways of preventing Ketosis and we now have much improved close-up and fresh diets for both dairy cows and sheep.
The supplement of late lactation diets with fat is generally pointless since the animal’s appetite normally exceeds requirements and the cow and ewe will quite happily put on condition.
The possible exception to this rule is the “super” Holstein cow. This animal can still be giving a high volume of milk in her late lactation. If she is to have any chance of recovering before her next lactation, she either needs to be allowed the luxury of a missed service interval or two in order to prolong the lactation, or she must be fed a very high density diet right through to drying off in the hope that there will be enough “extra” energy to allow for some condition recovery.
The late lactation and dry periods tend to result in excess weight gain even when saturated fat is not added top the diet.
Good stockmanship is an essential prerequisite of success, and condition monitoring should be a very important part of day to day management.
The answer is to control feed intake by using pasture management and appropriate diets for housed animals. Some larger herds now have the luxury of having a late lactation conditioning group where the priority is to manage cow condition not milk yield.
The addition of saturated fats to young lamb and calf rations is helpful in supplying energy to animals that have excellent food conversion efficiency.
There is no doubt that faster growing lambs and calves tend to be the most profitable since they finish earlier, have a lower carbon footprint and subsequently cost less to keep. Getting them off to a good start is therefore worthwhile and although saturated fat is expensive it is generally worth including a small amount in starter diets.
I do not believe that it is worth adding saturated fats to young stock and grower diets since the aim is to produce muscle rather than fat cover at this stage.
Fat lamb and beef rations work best at high energy densities, maximum daily liveweight gain will only be achieved on diets with energy densities of 12 to 13 MJ/Kg DM.
It is difficult to see how Barley based finisher diets when fed with low energy feeds like straw, can supply high levels of energy unless the cereal is very high quality, and the diet is helped by using some saturated fats. In this situation the finishing rate is controlled more by appetite than Food Conversion Efficiency (FCE).
Breed has a real effect on finishing rates with large continental types needing higher density than the smaller native and extensively managed breeds.
Market requirements for lightweight beef is at odds with the tendency for continental and especially Holstein beef that are trying to achieve a heavier mature weight. There is also evidence that some of the larger lowland sheep breeds also suffer from the same problem. in these situations, the addition of saturated fat to the finisher diet in order to maintain this very high energy density is desirable.


Blacks Veterinary Dictionary defines Acidosis as “A condition of reduced alkaline reserve of the blood and tissues with or without an actual fall in pH”.

This definition is straight forward for monogastric species.
The condition is probably best known in ruminants when animals die suddenly after gorging on grain or following a sudden changeover to a cereal based concentrate from a forage based diet.

The Blacks definition is clinical, but Ruminants have a more complex version based on how rapidly fermenting carbohydrate sources affect the microbial activity in the rumen.

Modern ruminant nutrition has a focus on balancing the fermentation rates of the different nutrient sources.

Most forage analysis will feature two sets of S.A.B.C. figures. One set is for the energy in the feed and the other set is for the protein. Balancing the first two S and A figures without over or under achieving the overall targets, will target an optimum fermentation with a minimum risk of acidosis.

The whole objective of this process is to optimise the rumen fermentation efficiency to generate as much microbial crude protein as possible.
Put another way: we want to grow as many rumen bugs as we can each day because they are a fantastic source of high quality amino acid balanced feed protein that the animal can consume each day, (This is what the rumen evolved over millions of years to do!)

Large intakes of sugar and starch are very dangerous and can result in acidosis. In this situation the rumen ph starts to drop as lactobacilli begin to dominate because their favourite starch and sugars are in plentiful supply.
The cellulolytic, proteolytic and archeo-bacteria start to lose the battle to dominate and fibre fermentation starts to slow down. Eventually as the ph drops below 6.2 and on to 5.5 these bugs become dormant or start to die. This situation is now known as SARA (Sub-acute Rumen Acidosis).
The cow’s normal response to this is to stop eating and go an lie down. She starts to chew the cud, as this happens she generates a powerful alkalai in saliva (sodium bicarbonate) and slowly begins to raise the rumen ph. This has the effect of suppressing the now dominant lactobacilli and allowing the cellulolytic, proteolytic and archeo-bacteria to recover their populations and re-start the breakdown and release of nutrients from the forage. Once the ph returns to neutral at 6.7. the animal is recovered and functioning at full efficiency.

The modern high output animal needs a nutrient supply that not only balances her forage intake but also allows for both fully efficient rumen function and enough rumen bi-pass nutrients to be digested in the hind gut and provide her with all she needs for elevated levels of productivity.

Acidosis is estimated to be prevalent at a sub-clinical level in around 30% of dairy cows. Mostly the condition is not serious but there are many effects on rumen fermentation efficiency.

There are some useful management techniques to minimise the effects of acidosis.

  • Feed a TMR or PMR (Total Mixed Ration or Partial Mixed Ration). By mixing all (TMR) or part (PMR) of the concentrates with the forage fraction of the diet; we can supply less fluctuation in the rumen ph.
  • Minimise sorting of the concentrates from the forages by compact feeding (pre-mixing water with the concentrates the night before adding to the forage). Or by adding some molasses to the less palatable ingredient fractions of the mix.
  • Where concentrates have to be fed separately to the forages, feed little and often. Robots and automatic out of parlour feeders should work on a 24 hour even split over the number of programmed visits.
  • Always target a minimum intake of 6 Kilos of NDF in the dry matter (25% of the diet dry matter and 65% minimum forage NDF for dairy cows.
  • Use buffer feeding at grass when the spring and autumn fibre levels in the grazing are at their lowest.
  • Feed artificial chemical buffers in high carbohydrate diets for Dairy, Beef and sheep diets.
  • Feed live yeast. There is a large body of proof showing how rumen ph is elevated as the yeast helps the reduction of lactic acid in the rumen and encourages more efficient fibre digestion and appetite.

Oils & Fats

There are essentially two types of fat, saturated and unsaturated. Each fat is constructed from a selection of fatty acids. Both oils and fats are not required in any great quantity in the diet but to put it into perspective; productive spring grass can contain as much as 8% fat, where as poor winter hill pastures contain only about 2.5% fat.

Saturated Fat

Saturated fat is generally quite desirable but tends to be fairly expensive to buy in purified forms. In ewe rations in late pregnancy and peak lactation; and lamb fattening diets it can help to bridge what is known as the “energy gap”.
The “energy gap”, exists when the appetite of the animal fails to supply enough dry matter and energy from the basic diet. When this occurs in high yielding cows, they will not hold to service.
In ewes feeding twins and triplets, there is a general failure to produce enough milk. the animals natural defence in this situation, is to mobilise some of its own body fat, this should be allowed for when calculating energy requirements.

Unsaturated Fats

Modern nutrition recognises that unsaturated fats are undesirable as a source of rumen available energy, due to their ability to cling to, and thus inhibit the digestion of fibre by the little cellulytic rumen bugs.
However, recent research has shown that two the essential fatty acids present in unsaturated marine oils can have “a very significant effect” on improving animal health. These form part of a group of fatty acids that are collectively known as the “Omega 3’s”.
The size and viability of the eggs in the ovary can be improved by the regression of the protective corpus luteum layer. This seems to be more effective as heat periods start when the requirements for EPA (Eicosapentaenoic Acid) & DHA (Docosahexaenoic Acid) are both met. Scientific evidence has made the link to the health and viability of the embryos which are also improved.
Feeding these essential oils from the point of ovulation and throughout the conception helps to ensure a successful pregnancy. Marine fish oil is a rich source of both EPA and DHA which are the two essential fatty acids that can only be supplied by nutrition.
These two essential fatty acids have been shown to regulate and suppress the PGF2? hormone (Prostaglandin F2). This has direct implication in improving the conception rate.
Farmers have known as long ago as the early part of the 20th century, that products like cod liver oil have always had a beneficial effect on animal health.
There is also an improvement in the efficiency of the circulatory system, particularly at the placenta. This alone helps to improve the supply of nutrients to the developing foetus.
Foetal development requires rich supplies of Omega 3′ fatty acids. This is known because there are concentrations found in the brain, eye and nervous tissues.
The principle fatty acids are: Stearic, Oleic, Linoleic, Linolenic (the C18 fatty acids).
There are other groups of fatty acid chains like the C16 palmitic acids which is known to directly improve butterfat content of milk.
The Omega 3’s, are probably the best known of the groups.
Human nutritionists are quite keen that heart patients consume diets that are low in saturated fats and have reasonable levels of unsaturated fats, because they are fully aware of the general beneficial effects that theses fatty acids have in lubricating the circulatory system.
Evidence shows these fatty acids improve the viability of sperm when fed to bulls and rams.
Omega 3’s can also increase the effectiveness of the immune system and hence provide a greater resistance to disease challenges.
The result of maintaining a supply of Omega 3’s to the pregnant animal and to the baby animal is an improvement in birth weight, viability, and vigour. Animals on flushing programs would benefit significantly from this technology.
Finally, one further observation is that animals that receive adequate levels of Omega 3’s seem to exhibit a more placid nature and are apparently more able to cope with stress. (perhaps there is a lesson for human beings here!)
Actual requirements are still a bit vague but as a guideline around 0.01% of dry matter intake should come from a source of Omega 3’s in late pregnancy, flushing and bulling, and for baby animal creep diets. Bulls and rams on service programs should also receive around 0.01%. Feeding excess has an adverse affect fibre digestion so it is best to err on the side of caution.

Rationing Tips

  • Use desirable saturated fats for high energy high output situations.
  • Use protected fats, to avoid upsetting rumen fermentation.
  • Use high Omega 3 inclusions at flushing for cows but not for sheep.
  • Use high Omega 3 inclusions 3 weeks before lambing or calving.
  • Use high Omega 3 inclusions in baby lamb or calf creeps.
  • Avoid excessive use of high oil by-products e.g.:- Full fat soya, linseed, rape, high oil corn distillers certain maize bi-products, vegetable and recycled cooking oils should be avoided at all costs.
  • Avoid any source that exhibits signs of rancidity.
  • When mixing on the farm, use dry fat meals, in preference to liquids, these are much easier to incorporate.
  • If liquids have to be used, either premix the liquid fat with other liquids in the mix

like molasses, or spray evenly into the mix during the actual mixing.


All ruminant diets should include sugar as one of the main sources of energy.
I do not intend to provide information on the biochemistry of sugar metabolism, but it will be helpful to be aware of the various different sugars from the simple to the more complex in structure.
Glucose is the fundamental simple sugar. Dextrose, sucrose, galactose fructose, maltose, and lactose are all commonly available sugar sources.
Sugar is an essential source of energy for the rumen micro flora. It represents the most readily available source. The rumen bugs use the dietary sugar and readily available protein and non protein nitrogen as nutrient sources to make more bugs, this process is known as “Microbial Protein Synthesis”. The bugs then go on to be digested by the sheep or cow in the abomasum and hind gut.
The logic of the situation is simple, if we can increase the yield of microbial protein from rumen fermentation then we can feed the animal better.
Microbial protein is the best source of protein in the cow’s diet because it contains a great level of essential amino and fatty acids.
Spring grass is a wonderful feedstuff. Good grass can be 20% dry matter, 20% sugar and 20% protein. This simple fact gives us a clue that high output diets should aim to be similar. Certainly, diets of about 40% dry matter are better, but around 16 to 20% protein and 16 to 24% carbohydrate are good targets to aim at.
The main requirement from feeding sugar supplements is that they are fed continuously.
Very recently Lactose has provided some fascinating research, strongly suggesting that dry cows fed on this sugar prior to calving can actually achieve double the rumen papillae surface area, when compared to animals fed on cereal starch.
This results in a much faster achievement of peak yields and better fertility due to lower rates of condition loss in early lactation.
Lactose is best described as a very slowly fermented sugar.

Rationing tips

  • High levels of molasses tend to be laxative, so it is necessary to restrict it’s use due to this side effect. Molasses contains mainly fructose, sucrose and high levels of potassium.
  • Glucose is probably the best source of sugar, but it is difficult to buy.
  • Some human food by-products can be excellent sugar sources:- Biscuit meal, breakfast cereal waste, some confectionary wastes, are common but I have had experience of glucose syrup washings, fondant icing, marshmallow, toffee, recovered honey and chocolate! Handling some of these products may be difficult.
  • Sugar is naturally palatable to all classes of stock and can be used to improve the intakes of less palatable mixes of food. This is a handy way of getting animals to eat poorer quality silage.
  • By using sugar to stimulate the activity of rumen micro flora, the ruminant can deal more effectively with lower grade roughages like straw.
  • The sugar content of the ration is directly linked to the efficiency with which the ruminant can utilise non protein nitrogen (N P N). This infers that there is a direct link with infertility caused by high blood urea levels, and certain foot problems.
  • Always buy sugar on the basis of it’s percentage expressed as dry matter. Many raw materials are sold as fresh weight, but the water element should be discounted before any judgement is made as to the true level of nutrient supplied in a tonne of fresh weight product. Eg: Molaferm 20 or Stockmol 20 are both only 71% dry matter so even if they have a sugar content of 56% this equates to 40% as fed. Pure Cane Molasses on the other hand is 75% dry matter and is 64% sugar so its analysis equates to 48% sugar as fed! This means that pure cane molasses has 20% more sugar than Stockmol 20 or Molaferm 20, so if the main reason for buying molasses is to buy sugar then it makes more sense to buy pure cane molasses than either of the other two products. It will also be cheaper per % of sugar since the price differential is rarely as high as 20%. Make sure you ask your supplier for accurate figures.
  • Some molasses based products are more viscous than others. Pure cane molasses is much thicker and more difficult to handle than molaferm or Stockmol. Marshmallow is almost as bad as chewing gum!
  • Conventional sugar rich feeds include the following:- Molasses, molasses blends and meals, fodder beet, sugar beet pulp, citrus pulp, some breakfast cereals, and carob.
  • As a rule, ruminant diets should contain a minimum of 8% sugar. Sheep diets will benefit from increasing this up to 15% or even 20% near lambing for twin and triplet bearing ewes where twin lamb disease is a real risk, provided fibre levels are optimum.
  • The minimum of 8% sugar can be quite difficult to achieve in winter TMR diets. The use of breakfast cereal meals and sweet mixes can be very useful in this respect.


Starch is probably the most commonly added energy source in ruminant diets, it is also the most misunderstood nutrient, since it is frequently poorly balanced into the ration.
Starches in rough terms, comprise a matrix of linked glucose molecules.

Starch and Fibre

The relationship between starch and fibre is well understood but getting the balance wrong tends to result in poor performance all round. Starch can be fermented quite well in the rumen between acid Ph levels of 7 (neutral) and 5.5 (quite acid). Fibre on the other hand can only be efficiently fermented between acid Ph levels of 7.0 and 6.2 (slightly acid).
Optimum fermentation of both starch and sugar needs to stay within the Ph limits for fibre.
The productive ruminant should always be supplied with adequate levels of forage in its diet. (Books vary a bit on the actual minimum amount but 40% is a good guide.)
Forages and long fibre sources are responsible for maintaining the animals cudding ability and amongst other things this affects the animal’s production of saliva. Saliva is the mechanism that the animal uses for chemically buffering and regulating the fermentation acids in the rumen.
Sheep probably only need to approach minimum fibre levels just prior to lambing or in intensive finishing diets. Dairy cows on the other hand could very easily have the forage fraction of the diet reduced to this level. In this situation it is vital to include a minimum of 12% structural fibre (Long Crude Fibre). Rations should be pitched at around 17% to 22% ADF.


If the starch/sugar content of the diet is too high and rumen Ph levels drop below 6.2, the fibre digesting cellulytic microbes start to die out. When this occurs, the rumen starts to become much less efficient due to a build up of lactic acid. The ruminant starts to show signs of acidosis, and performance starts to suffer as appetite levels drop.

Rumen Fermented Starch

This type of starch is the most common, it is supplied from feedstuffs like barley, wheat, maize, potatoes, and by-products like biscuit meal and dried processed bread.
The rate at which starches ferment are a good guide to how quickly acid is produced. This is much less of a problem for animals fed on a total mixed ration than it is for animals fed one or two feeds of concentrates a day. Rapid fermenting starches like barley will reduce digestive efficiency and turn out to be quite expensive unless they are used carefully.
Cereals are generally not fed whole except to growing lambs and small breeds of sheep, because they will pass through the gut undigested. Pre-processing the cereal is an essential part of feeding management.
The type and quality of the cereal, and the type of process used can have a dramatic effect on the rate of fermentation.
Firstly, wheat can be 70% fermented after 12 hours, oats and barley are 70% fermented after 16 hours. Maize takes 24 hours to be 70% fermented.
These figures will vary considerably in line with the processing method used.
Secondly, I have listed below the order of processing choices starting with those that increase the speed of fermentation and finishing with those that have a slowing or buffering effect on the fermentation process.

  1. Grinding or milling. Very Fast (Compound Feed Pellets)
  2. Jetsploding, micronising and cooking. Fast
  3. Crimping and acid treating and ensiling. Fast
  4. Rolling, bruising or crimping. Fast
  5. Whole. No effect
  6. Caustic soda treating (3% caustic). Slower Buffered
  7. Caustic soda treating (5% caustic). Slower (same as 6 above), Buffered
  8. Fermented (35%+DM) Whole Crop. Slow, Naturally buffered

These different treatments will vary the effectiveness with which fermentation acids are controlled.
Caustic soda treatment of cereal results in a sodium bi-carbonate residue, this chemical buffer is carried into the rumen where it helps to increase rumen ph in exactly the same way as bicarbonate from saliva.
The fermentation rates of both the 3% and 5% treatments are the same.
They tend to be slower than bruised, rolled and crimped cereal because the particle size is larger, not because of the Sodium Bicarbonate.
Note: Sodium bicarbonate buffers acidity it does not affect fermentation rate directly.

Rumen Bi pass Starch

This starch bypasses the rumen unchanged and gets digested in the abomasum and hind gut in the same way as monogastric species digest starch.
Most of the starch escaping rumen fermentation would be digested in the small intestine or fermented in the large intestine.
Bypass starch tends to be very efficiently digested so it is quite desirable to include around 30% of this starch in high output diets.

Recent work shows that bypass starch from maize helps to improve milk protein and daily liveweight gain. Maize contains about 30% to 40% bypass starch and is the most common natural source.
Some by-products contain bypass starch. Cooking can increase the proportion of bypass starch but over cooking can render it indigestible.

Rationing Tips

  • Always make sure that high output animals are fed with starch from more than one source. this will help to spread the rates of fermentation and more closely match the varying rates at which protein can be fermented.
  • Good combinations include equal parts of bruised wheat, maize and barley.
  • Whole cereals can be used for sheep, large lowland breeds do better on bruised cereal.
  • Oats are a very desirable sheep cereal and can form the greater part of the cereal fraction of the diet.
  • Avoid cereals that have been harvested damp conditions, moulds and fungus may be evident. Some moulds and fungi may induce health problems by introducing toxins.
  • Buy good quality cereal with high bushel weights. ie 72 for wheat and 64 for barley.
  • Cereal starch can vary dramatically, book values for barley are 54% and Wheat 64% but there are many occasions where disease affected crops can drop these figures to 20%. In these situations, the cereal will not supply enough nutrient and performance will suffer dramatically.
  • Where it is necessary to change diets from mainly forage to mainly concentrates, make sure that the changeover is gradual. This is a good rule for all changes of diet for all livestock groups. There is good evidence that the use of certain performance enhancing yeasts, can have considerable benefits in changeover situations.
  • Storage of cereals and starchy feeds needs to be carefully considered. Rodents and birds love cereals, bread, biscuit and other starchy by-products, even silos containing whole crop cereals are a target. Rising standards in farm storage are certainly minimising the risks of spoilage but I am afraid to say that damp, mould, insects, mites, heating, and rodents account for a huge amount of food waste on British farms every year. Stores should be regularly inspected (once a week) for signs of damage so that steps can be taken to minimise waste.
  • It is important to ask about starch quality and quantity when buying feeds. Always check dry matter contents before making the decision (see earlier section on buying sugar).


The role of crude fibre in ruminant nutrition can be split into two functions.
The first is a purely physical one. The rumen needs to “churn” its contents in order to assist fermentation and digestion. Churning is stimulated by a scratch reflex which is stimulated by long stiff fibre.
Young lambs and calves start life with a monogastric digestive pattern, pretty well like humans and pigs. As they get older, the oral groove, (A mechanism for directing the baby animal’s milk consumption straight into the abomasum,) opens and allows milk and other feeds to drop into the young rumen.
This process initiates rumination, as the rumen takes over in supplying nutrients to abomasum, the young animal is weaned.

Long fibre plays an essential role in the weaning process. Early intakes of good palatable fibre feeds like molassed sugar beet pulp and really clean very well made sweet hay, rich in digestible fibre, encourage the animal to start ruminating.

As the rumination process starts, the young animals start to decrease their intakes of milk and increase their intakes of dry creep feed. This changeover to dry feed is very desirable if lambs or calves are being reared on reconstituted artificial milk powders, since these are quite expensive.
The second function of fibre is as a supplier of energy rich nutrients. This might sound a bit odd to some people since traditionally the fibre declaration on the feed bag was used to signify the energy of the compound feed. the higher the fibre content the lower the energy of the feed inside, however high ‘D’ value fibre can be high in energy.
All fibre can be broken down into three constituents.

  • Lignin which is mature woody fibre and is indigestible.
  • Hemicellulose, slightly less complex fibre, partially digestible.
  • Cellulose. All ruminants have the ability to make good use of “anaerobic mesophilic cellulolytic” bacteria to break down cellulose into sugars which in turn increases the yield of rumen bugs.

Hay, silage, straw, stalks, and most important of all grass, contain cellulose. Milk fat is directly influenced by the fermentation characteristic of fibre.
Fibre fermentation produces acetate which is the main energy precursor for butterfat production.
All ruminants need to receive a minimum 35% of their diet as long fibre each day. Sheep, suckler cows and store cattle really only need to be fed on concentrates for specific purposes. If grazing management is good enough the provision of nutrients from forage sources will need very little help from concentrates in order to feed the animal during the grazing season.
As already noted in the starch section cellulolytic fermentation is optimum at a rumen Ph of 6.2 to 7. It is therefore important to make sure that if optimum performance is to be achieved from forage that the rumen conditions are maintained at this level.
Sometimes spring grass can be so young, lush and high in sugar that the animal needs to have long fibre added to the diet to prevent the young grass from passing through to quickly.
The fibre should be mature like straw or old clean hay in order to stimulate rumen motility and the churning effect.
This technique is called buffer grazing and serves to help to regulate rumen Ph.
As mentioned earlier, most nutritionists use NDF as the measure of useful digestible fibre, since this contains the cellulose and useful Hemicellulose.
Dairy farmers trying to optimise milk protein should look at the relationship between NDF and starch + sugar.
This ratio will give a good indication of how well balanced the different energy sources are. The ratio also gives an idea of how well balanced the diet will be for the optimum production of milk protein.
Starchy cakes have to be fed very carefully if they are not to upset rumen Ph the table below shows the relationship between NDF and starch + sugar and how the ratios can be used to describe the finished diet for dairy cows. Ratios should not drop below 1.5:1 or the rumen fermentation risks becoming too acidic

The finished diet shown as the NDF to Starch +Sugar Ratio

Whole Ration Cake Only
Starchy Less than 1.75:1 Less than 0.6:1
Average Between 1.75:1 and 3.0:1 Between 0.6:1 and 1.0:1
Fibrous More than 3.0:1 More than 1.0:1

Remember this table can be quite useful but starches and sugars vary considerably in their fermentation rates according to chemical structure and physical presentation.
If all the starch and sugars are rapid fermentors the lower ratio limits should be increased in order to avoid problems.
Similarly if all the NDF sources include high proportions of structural fibre, then the lower limits need to be pursued. Like all things, “moderation is the best rule”.

Rationing Tips

  • Diets containing more than one source of forage tend to show increased dry matter intake characteristics over diets containing a single source. This is irrelevant for sheep near lambing since rumen capacity is very reduced an optimum dry matter intake has to be balanced by the need for a more concentrated and less bulky ration. Bulky feeding at this point will only serve to encourage prolapse.
  • Dairy cows should be targeted at around 1% of body weight for NDF ie a 650 Kg cow should have a minimum of 6,500 grams of NDF in its diet. Most nutritionists target 7000 grams.
  • Use good sources of fairly low NDF feeds. Silages should be around 38% NDF, and hay around 50%. Concentrates are normally much lower, reflecting limited fibre value
  • Ensiling forages in order to preserve the crops with fermentation acids until winter feeding, is based on converting the sugars in the crop to lactic acid. This acidity should turn off the fermentation and stabilise the crop. Sometimes spoilage organisms, convert the lactic acid into volatile fatty acids, like acetic, and butyric. Apart from smelling awful, butyric silage has a much lower energy contribution than the well preserved lactic crop.
  • The best types of conserved forage are those which have had limited or no fermentation. Lucerne and barn dried grass hays are excellent.
  • The use of certain yeast cultures fed with fibre sources should be considered as advantageous. There is no doubt that certain specific strains of yeast are very capable of liberating more nutrients from dietary fibre than most naturally present strains.
  • Recent work has shown that the inclusion of certain strains of yeast will encourage the populations of lactic acid utilising bacteria. Lactic acid is a good source of energy but when present in large quantities as is found in wet low Ph silage, it will depress intakes and reduce productivity. The inclusion of these yeasts on a day to day basis in this situation will increase productivity by between 5% and 10%.

This section should have demonstrated why it is so important to consider the balance of energy in such a way that all the different nutrient sources are assembled in healthy proportion. Favouring one source over the others will result in failure of the ration to perform efficiently and in some cases pose a serious threat to the health status of the animal.