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2nd March 2021

Nutrition for Sheep 4: Energy


  1. The objectives of the sheep enterprise
  2. The concepts of sheep nutrition
  3. Feed intake
  4. Energy
  5. Protein
  6. Minerals & Vitamins
  7. Water
  8. Popular husbandry systems

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 the everyday housewife on a 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) instead!

For reference 1 Megajoule = 239 calories

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 35 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

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 need , 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 energy to 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.

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 flawed 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 using the Fermentable Metabolisable Energy, (FME) 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 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 are poorly constructed.

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 printout might look OK, but do they represent the complete story . Were they based on accurate information in the first place?

Unrealistic estimates are frequently put on the nutritive values of the feeds. This can be due to the inaccuracy of sampling.

Poor balancing by the trade, or other bodies, may be due to the inexperience of the advisors or failure to set realistic parameters.

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. He was right!

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 humping 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 a bit limiting.

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 sliming diets!

The tables in the appendix show energy requirements for sheep on Q 62.5 diets. It has been shown that as the value of Q drops the requirement of energy for maintenance and production increases.

Energy for Milk Production

The tables also show the energy allowances for lactating ewes. 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.

Rations which utilise poor quality forages or fall towards the “Q” 0.50 ration category will tend to require around 1.0 MJ per kilogram of milk more energy, and those aspiring to “Q” 0.70 will need 1.0 MJ per Kg milk, less energy.

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 its 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 4

(Taken from Mitchell, H, H. 1962)

Composition of Gain (g/Kg)

Animal Live-Weight (Kg) Age (Months) Water Protein Fat Ash Energy(MJ/Kg)
Lamb 9 1.2 579 153 248 22 13.9
Weaning 34 6.5 480 163 324 31 16.5
Sheep 59 19.9 251 158 528 63 20.8
Calf 70 1.3 671 190 84 7.8
Weaning 230 10.6 594 165 189 11.4
Cow 450 32.4 552 209 187 12.3

Referral to table 4 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.

Pregnancy also requires an allowance for energy.

The growth of the developing 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 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 required for pregnancy is used to support and grow the placenta and umbilicus, which is lost at lambing.

Recent work on feeding dry ewes 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 ewe.

In the mid 1980’s work done at the Rowett research institute near Aberdeen, showed that feeding the ewe extra undegradable protein, prior to lambing, helped to mobilise back fat and resulted in ewes producing better colostrum and more milk at lambing. Both fish meal, and protected soya seem to have similar effects.

Fish meal is very high in calcium, so it should be limited in its use for ewes near to lambing. Fish meal also contains some very beneficial fatty acids, which have been shown to have a significant effect on reproductive health.

Ewe with suckling lambs

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 contribute to the ME to the diet.

Some advisers seem to oversimplify the diets by placing the emphasis on supplying total energy requirements without worrying about how the energy is actually sourced. These diets do not work well compared to diets that contain a variety and balance of the main energy sourcesQuite often it is the neglect of this simple principle which accounts for poor animal performance.

Oils and 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, whereas poor winter hill pastures contain only about 2.5% fat.

Saturated Fat

Saturated fat is generally quite desirable but fairly expensive to buy in purified forms. In ewe rations in late pregnancy and early 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.

When peak yields are attained at about 4 weeks in the ewe and 9 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 the 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 some 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 helps to overcome the problem.

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 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.

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.

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 has to be a very important part of day-to-day management. The answer is to control feed intake by using pasture management and speciality diets for housed animals.

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, 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

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 bigger lowland sheep breeds also suffer from the same problem. in these situation the addition of saturated fat to the finisher diet in order to maintain this very high energy density is essential.

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 some of the essential fatty acids present in unsaturated marine oils can have a very significant effect on animal health. This group of fatty acids are collectively known as the “Omega 3’s”.

The size of the eggs in the ovary can be improved. The regression of the protective corpus luteum layer seems to be more effective as heat periods start; and the viability of the embryos is improved.

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.

Principle amongst these fatty acids are Stearic, Oleic, Linoleic, Linolenic (the C 18 fatty acids).

There are a lot more fatty acids, but these are the best-known group. 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.

There is also evidence that when fed to bulls and rams these fatty acids can improve the viability of sperm.

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 1% 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 1%. Remember excess will affect fibre digestion adverse 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, or bulling.
  • Use high Omega 3 inclusions 3 weeks before lambing or calving.
  • Use high Omega 3 inclusions in baby lamb or calf creeps.
  • Whilst fish meal will contain Omega 3 fatty acids, generally greater concentrations will be needed from specialist premixes.
  • Avoid excessive use of high oil by-products e.g.
    Full fat soya, linseed, rape, high oil corn distillers. 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 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.

Flock of Swaledale sheep on winter pasture


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, 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. So, 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.

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. Large single intakes of sugar are very dangerous and can result in acidosis. Rapid production of lactic acid by the frenzied activity of the rumen bugs on receiving the overload of sugar, causes an overload in lactic acid in the rumen. This effectively shuts the rumen down, and after a while the animal will die. Large daily fluctuations in the acidity of the rumen brought about by big single feeds of sugar or starch, can result in a subclinical acidosis which although is not particularly obvious or fatal; will reduce performance significantly due to the long periods where the rumen is trying to adjust ph back to normal and is thus not producing microbial protein at the optimum rate.

Ketosis (Acetonaemia) should not be confused with acidosis, it is sometimes referred to as “lambing sickness”, or “slow fever”. The condition is usually seen in high yielding animals. Symptoms are easy to recognise, first the animal reduces its intake of concentrates, it then becomes dull and lethargic, after a while the dung becomes very dry and hard, milk production falls and the animal becomes constipated. The best symptom is the smell of acetone on the animal’s breath.

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. This is in turn due 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 by ensuring that there is enough fermentable carbohydrate (starch & sugar)in the diet.

Lack of energy at lambing time can result in a serious condition known as “Pregnancy Toxaemia” or “Twin Lamb disease”.

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.

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.

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.

Rationing tips

  • High levels of fructose tend to be laxative, so it is necessary to restrict the use of molasses due to this side effect.
  • Glucose is probably the best source of sugar, but it is difficult to buy.
  • Some human food by-products can be excellent sugar sources:- Glucose syrup washings, marshmallow, toffee, recovered honey, biscuit meal, breakfast cereal waste, some confectionary wastes, are all made available from time to time.
  • 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 is able to deal more effectively with lower grade roughages like straw.
  • Sugar is directly linked to the efficiency with which the ruminant ca 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 its 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 is only 71% dry matter so even if it has 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, 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 tor twin and triplet bearing ewes where twin lamb disease is a real risk.


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.

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 30% is a good guide.) Forages and long fibre sources are responsible for maintaining the animals cudding ability and amongst other things this affects the animals 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)

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 happens 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, 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.

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.
  3. Crimping and acid treating.
  4. Rolling, bruising, or crimping. Fast
  5. Whole. No effect
  6. Caustic soda treating (3% caustic). Slower Buffered
  7. Caustic soda treating (5% caustic). 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.

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.

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 byproducts 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, though 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 in wet or 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 65 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 growing 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 byproducts, 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 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 animals’ milk straight into the abomasum,) opens and allows milk and other feeds to drop into the young rumen. This process initiates rumination, as te rumen takes over in supplying nutrients to abomasum, the young animal is weaned.

Longfibre plays an essential role in the weaning process. Early intakes of good palatable fibre feeds like molassed sugar beet pulp, 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.

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 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 30% 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 celluolytic 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. This 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 fermenters 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 one 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.
  • Try to use good sources of fairly low NDF feeds. Silages should be around 50% NDF, and hay around 55%. Concentrates are normally much lower, reflecting their limited fibre value.
  • Ensiling forages in order to preserve the crops with fermentation acids until off season feeding, is based on converting the sugars in the crop to lactic acid. This Acidity should turn off the fermentation and stabilize 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.

This section should have demonstrated why it is so important to consider the balance of energy in such a way that all of 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.