Nutrition for Sheep 3: Feed Intake – Lakeland Scottish Feeds & Services

Voluntary Feed Intakes and Dry Matter Intakes

The animals need for food is controlled by its appetite. The daily voluntary feed intake is defined as the amount of feed which is eaten when the animal has access to food on a truly ad-lib basis. This normally means that the animal is allowed the freedom to refuse some of the food on offer and is not forced into clearing up the less palatable remnants. Daily feed intake is expressed as the total daily consumption of food minus the water content of that food. This is referred to as “Dry Matter Intake”. (DMI). Sometimes other definitions are used, “Fresh Weight” or “Bulk” intake being the other most commonly used expressions.

DMI is directly proportional to the body weight of the animal. There are several factors which modify the animal’s consumption of food.

1. The relative level of production.

(Stage of Lactation, Milk Yield, or Daily Liveweight Gain)

The stage of lactation is very important. There is a lot of recent work that suggests that the management of the changeover from pre-lambing diet to the early lactation diet can have a very significant effect on the speed at which the animal can get up to her maximum dry matter intake during the early weeks of lactation, this will be covered in more detail later.

2. Food Conversion Efficiency (FCE) and the condition score of the animal.

” Condition score is more of a consequence of voluntary feed intake than a factor affecting intake”.

FCE is the measure by which we determine how efficiently the animal is utilising its food.

Example 1:-

If we take two tup lambs eating 500 grams DM per day and over the period of a week one grows by 700 grams and the other by 350 grams; the FCE is the number of grams of dry matter consumed divided by the number of grams of live weight gain.

ie Tup lamb number one eats 7 x 500 g DM and grows 500 g (3500 g / 500 g) = FCE 7:1

Tup lamb number two eats 7 x 500 g DM and grows 400 g (3500 g / 400 g) = FCE 8.75:1

Tup lamb number one produces more daily weight gain per kilo of dry matter intake and is more efficient than tup lamb number two.

Example 2:-

If we take two lactating ewes, one eating 1.9 kg DM and giving 2 kilo’s of milk, and the other eating 1.2 kg DM and giving 1 kilo of milk, if we assume that both ewes have a stable body weight the FCE is as follows:-

ie Ewe number one eats 1.9 kg DM and gives 2 kg milk (2.0 / 1.9) = 0.95:1 Kg DM/Litre

Ewe number two eats 1.2 kg DM and gives 1 kg milk (1.2 / 1) = 1.2:1 Kg DM/Litre

Ewe number one uses less dry matter intake to produce a litre of milk than ewe two and is thus more efficient.

There is often an understandable element of confusion with regard to the animals feed intake and body condition. Some fat ewes seem to have low levels of feed intake, others have high levels of intake so how can we make sense of this situation?

Ewes get fat for several reasons :-

1. They can be efficient food converters, some of the highest yielding ewes tend to put on condition very easily in late lactation simply because the intake which is not being used for maintenance, milk production or pregnancy is efficiently converted to body condition.

These animals can have high feed intakes.

If this is to be avoided the ewes need to be put on to poor pastures and allowed to lose some weight.

2. Thinner ewes have a tendency to eat more per unit of body weight than fat ewes but are more efficient at converting the nutrients into milk rather than growth. They can also have a higher metabolic rate. This means that the whole metabolic system is more active, and consequently needs a greater rate of nutrient throughput to drive it.

3. Genetic differences can affect appetite and the tendency to put on condition.

4. Breed has a definite affect. Hill sheep tend to carry less condition than lowland sheep breeds. Genetically they are also much smaller sheep.

5. Health. ewes suffering from Fatty liver syndrome, for example, over fat ewes at lambing, losing weight rapidly at say 100 g per day, can have lower feed intakes which is why they mobilise excessive body reserves when demand is high just after lambing.

This is thought to aggravate, problems like milk fever, metritis (whites) and mastitis.

Ewes with poor feet tend to be less efficient at grazing and consequently tend to be thin.

Ewes with incomplete sets of teeth also have a reduced intake. The practise of teeth clipping has been shown to improve intakes dramatically.

It is very important for the good stockman to keep a eye on body condition. With the obvious exception of high output pedigree tups, and finishing lambs, most animals thrive better if they are kept in a fit condition.

The use of distinctive “Grower” diets and “Finisher” diets designed to avoid these problems, will result in much more effective production from all classes of growing stock .

3. The palatability of the diet.

Well-made dry hay will always be more palatable than hay that contains moulds and yeasts associated with hay that has been baled damp or has been rained on.

Big Bale and clamp silages are becoming more popular as a source of winter forage, provided the bulk is reduced substantially near lambing, these conserved forages can be a better source of nutrients than most hay.

There are a number of nutrients which can improve palatability when they are already in short supply; these include, Sugar, Salt, and Lactic acid. These can combine to give high cluster indexed silage.

Note:- Well preserved silage with low levels of free, volatile acids (High PH and dry 25%+ ), are likely to be eaten faster than wetter lower PH silages which will require more buffering by Bicarbonate, either from the saliva , or added to the diet.

Equally there are a number of nutrients that will reduce palatability; these include, the volatile fatty acids like Butyric acid and Propionic acid; also, high levels of Non-Protein Nitrogen (NPN). These can combine to give a low silage cluster index.

Back in the early 1990’s The Scottish Agricultural College (SAC), has identified four main types of grass silage. The silages are characterised by the pattern and extent of the fermentation that has occurred.

The clusters are summarised in table 1 below: –

Table 1

SAC Cluster Index for silages (Offer et al, 1993)

C L U S T E R

	1	2	3	4
Fermentation	Bad	Moderate	Good	Very Good
Lactic Acid	Low	High	High	Low
Residual Sugar	None	Low	Low	High
VFA	High	Moderate	Low	Low
Amino N % of total soluble N	Low	Moderate	Moderate	High
Neutralising value	Low	High	Moderate	Low

4. The general quality of the diet or “Q” Factor.

This is a simple, but very important, measurement where Q is equal to the Metabolisable Energy (ME) of the total ingredient dry matter of the diet consumed each day, divided by the Gross Energy (GE) of total dry matter in the diet. For the most part it is reasonable to use a figure of 0.62.5 for high output systems and 0.50 for extensive systems.

Diets with a high Q value tend to encourage higher dry matter intakes

5. The “D” value of the diet

(The speed of passage of feed through the gut). The “D” value usually refers to a measurement of the digestible organic dry matter (DOMD) of a feed or a ration. The digestibility of a feedstuff is of fundamental importance in assessing the potential value of it as a source of useful nutrients; obviously the lower the “D” value the lower the potential value of the feed as a dietary ingredient. DOMD can be expressed as a percentage (1), in the Dry Matter content [DOMD], (2), in the corrected Dry Matter content [DOMDc], or in the Oven Dry Matter [DOMDo].The difference in the three measurements is usually quite small, so it isn’t particularly important which one is used.

6. The Neutral Detergent Fibre (NDF) level of the diet

Dry matter intake generally decreases as the NDF fraction of the diet increases, within an accepted normal range.

NDF is the cell wall lignin, cellulose and hemicellulose.

Lignin is virtually indigestible but this structural fibre is vital to maintain the scratch reflex and keep the rumen churning properly.

Cellulose has a very low utilisable energy value.

Hemicelluloses can contribute significantly to the energy supply.

Note:- TMR systems can increase DMI

It is important to try and keep NDF Levels, no lower than 400 g/kg DM even in high

performance diets, since low levels will impair cudding time and subsequently reduce voluntary intakes.

Most nutritionists now agree that keeping the target level of NDF at around 500 g/kg DM is desirable, though many hill sheep are expected to perform well on much higher levels. It is certain that some breeds of sheep are able to cope better under these conditions than others.

7. Rumen PH and stability.

The ideal Rumen PH is agreed to be 6.7, large meals of starch and sugar (Cereals and some compound pellets), will result in frenzied activity of the rumen micro flora. A by-product of this activity is the production of various common organic acids, the main one being Acetic Acid [Vinegar], this results in a dramatic and rapid drop in rumen PH if the level drops below PH 6 it becomes too acid for the fibre digesting cellulytic bacteria to survive so they die off or become dormant and this reduces DMI and productivity. If the PH drops below 5 the animal starts to suffer from rumen Acidosis. This can be fatal. Usually, the rumen recovers slowly after the rapid fermenting energy sources are used up and gradually the celluolytic bacteria re-establish themselves, for a few hours until they are hit again with the next highly fermentable meal. This cannot be sensible to feed regimes where high outputs are required.

8. Physical form of the diet.

Rations that are compressed or too finely ground with not enough structural, long fibre tend to depress appetite. Sheep in particular, prefer an open structure which is good for cudding and for large mouthfuls.

9. Feed System

TMR diets are generally eaten in larger quantities than when the concentrates are fed separately to the forages. This has been proved beyond doubt in dairy systems, and although research on intake effects on housed ewes and fat lambs is scarce, the effect is probably the same.

This is likely to result in much better rates of fibre digestion than the consequences of twice a day trough feeding of concentrates. It’s amazing how this system can depress intakes especially if the concentrates being fed consist of fine starches or sugar.

I have found that where possible starches and sugars should be fed mixed into the forages and the feeds should be balanced to include some digestible fibre(HDF) types in order to minimise the disturbing effect that commonly occurs when moderate or high starch cakes are fed.

The animals that get fed the largest amounts cake in single feeds, are actually the ones that suffer the most! )

DMI is easy to calculate, for most sheep it is around 1.5% of body-weight. This will vary according to the factors outlined above. Figures vary from about 1.0% up to 3.0% of body weight for big lowland sheep fed on high “Q”diets.

Table 2

Predicted Dry Matter Intakes Of Ewes (g DM/Day)

Ration Q value = > 0. 62.5

Body Weight (Kg)	8 weeks to lambing	4 weeks to lambing	2 weeks to lambing	6 weeks post lambing	12 weeks post lambing
55	1200-1300	1200-1300	1100-1200	1700-1800	1600-1700
75	1500-1600	1500-1600	1400-1500	2200-2000	2100-2000
95	1700-1800	1700-1800	1600-1700	2700-2400	2600-2400
115	1900-2000	1900-2000	1800-1900	3000-2700	2900-2600

Note DMI drops by around 20% for dry ewes and low yielders, on diets where “Q” drops to 0.45. This would be very much in line with the results expected from higher levels of NDF typical of moorland pastures.

“Q” 0.62.5 diets in theory , don’t have much effect on the top DMI in Table 2 but well-balanced diets can make a nonsense of these figures. Ewes will eat fully 2.0 Kg of dry matter with ease if the diets are both palatable and well presented.

Big tup lambs can eat huge amounts of dry matter. I have had good first-hand experience of lowland breed tup lambs eating 6 to 7 kilos of dry matter a day as they are pushed to reach optimum weight for the autumn tup sales.

Low “Q” value diets will not support high intakes so performance will only be moderate as a result. The “Q” value of typical mountain/moorland pastures will typically be not much more than about 40, except in spring when the new shoots of grass and heather may increase this dramatically for a few weeks in May & June. Most mountain sheep have evolved over thousands of years to cope with low “Q” diets. This probably explains why these breeds are small and tend to produce single rather than twin lambs, and lamb naturally in late spring when the grass is at its best and will allow the ewe to produce enough milk to feed one lamb.

The list of correction factors below should always be used in assessing a more realistic level of DMI.

In the same way, beef and dairy systems can also be affected. It is a fairly logical conclusion that the more palatable, higher quality, better presented and the less competition there is; the dietary intakes of all classes of ruminant will tend to be maximised.

Tip:- Don’t forget the importance of NDF, getting this one wrong will have serious effects.

Table 3

Correction Factors

It would be unrealistic to ignore the effects of the following list of husbandry situations.

Situation	Correction Factor Multiply By	Comment
Complete Diet	1.1 -1.3	Need well balanced diet
Feeding little and often	1.1 -1.5	Pedigree tups could eat twice the normal dry matter intakes.
Lowland	1.0 -1.3	Bigger gut capacity
Standard upland and cross breed	1.0	Standard sheep
Mountain	0.8	Check the actual weights
Mixed Forage Systems	1.05	Dependant on the balance
Easy feed silage / hay	1.0	Basic system
Self Feed Silage	0.95	Check head space
Gimmers	0.9	Smaller ewes
Broken mouthed sheep	0.7-0.9	Check the ease of access
Wet butyric to mouldy dry silage	0.75-0.9	Unpalatable appetite depressing
Night lighting of housed sheep	1.07	Helps intakes at night
Water at less than 4.0 deg C	0.95	Reduces DMI when too cold

Extensive fed mature animals like hill sheep and dry suckler cows, can eat as little as 1.5 % of body weight DMI per day just for maintenance.

Examples :-

1. The DMI of a 100 kg tup = 3% of 100 kg which = 3.0 kg per day.

This figure could be as high as 4.0% for a tup fed six times a day in preparation for the sales. These animals are more common than they used to be.

2. The DMI of a 30 kg intensive fed lamb is 2.5% of 30 kg = 0.75 kg.

3. The DMI of a 30 kg grass fed lamb is 2.0% of 30 kg = 0.60 kg

That! believe it or not, concludes the first, and some would consider, most important lesson in sheep rationing! As you can see, it is not a very precise science, so it is always advisable to check actual figures against the real conditions on the farm and adjust feeding where possible, in order to achieve the best results.

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