With many ewes in the last trimester of pregnancy, what happens now will affect flock productivity , profitability and labour requirement.
long with silage feed value, concentrate supplementation has a significant impact on ewe and lamb performance
— as shown in a number of studies undertaken at Teagasc Athenry.
In one of these (whose results are presented in Table 1) the ewes were housed in mid-December, offered silage with either medium (70pc DMD) or high (75pc DMD) feed value, and lambed in early March.
In late pregnancy the ewes offered the medium feed-value silage received either 15kg, 25kg, 35kg or 45kg concentrate. The ewes offered the high-feed value silage received either 15kg or 25kg concentrate.
For ewes offered the high feed value silage, increasing concentrate feed level above 15kg had no effect on lamb birth weight or ewe body condition (BCS) at lambing.
The lack of response to the higher level of concentrate is associated with substitution rate. Studies at Athenry have shown that the substitution rate for high feed-value silages is as high as 0.75kg reduction in silage dry matter intake per 1kg of concentrate consumed.
This shows that concentrate was displacing the high feed-value silage in the diet so had little impact on total metabolisable energy intake.
For ewes offered the medium feed-value silage, increasing concentrate feed level during late pregnancy from 15kg to 25kg increased lamb birthweight.
However, increasing concentrate to higher levels had no significant effect on lamb birth weight but was partitioned to ewe body condition.
This shows that the ewes on the medium feed-value silage were not able to consume enough silage to meet their requirements.
The lower the feed value of grass silage, the greater the response to increased concentrate supplementation.
These results illustrate that feeding excess concentrate does not improve animal performance, so there will be a negative return on expenditure.
Concentrate supplementation
The effects of silage feed value on the concentrate requirement of twin-bearing ewes in late pregnancy are shown in Table 2.
It is assumed that the silage is offered using good feeding management practice: ewes have access to fresh silage 24 hours per day and any silage residue is removed at least twice weekly.
Concentrate requirement is influenced primarily by silage DMD, but also by chop length (harvest system).
For example, for silages at 79pc and 64pc DMD, an additional 4kg and 10kg concentrate, respectively, are required for long-chop silage compared to precision chop silage.
The concentrate requirements per ewe presented in Table 2 can be reduced by 5kg in the case of single-bearing ewes, while concentrate supplementation should be increased by 8kg for those carrying triplets.
Protein concentration
For prolific flocks the concentrate should be formulated to contain 19pc crude protein as the grass silage on many sheep farms has a low protein concentration.
Since low levels of concentrate supplement are offered during weeks 6 to 4 prior to lambing, there is little financial benefit from formulating low and high protein concentrates for most flocks in Ireland.
Concentrate ingredients
Ingredient composition of concentrate was examined in a recent study at Athenry.
Two concentrates were formulated to have the same ME and crude protein concentrations. The protein sources used were either soybean meal or a mixture of by-products (rapeseed, maize distillers and maize gluten).
The soya-based concentrate had higher digestible undegraded protein concentration — the proportion that escapes fermentation in the rumen and is absorbed in the small intestine.
Lambs born to ewes that had been offered the soyabean-based concentrate were 0.3kg and 0.9kg heavier at birth and weaning.
The increase in weaning weight of lambs from ewes offered the soyabean-based concentrate in late pregnancy (extra cost ~€0.70/ewe) is similar to the response from offering each lamb 6kg of creep concentrate until weaning (cost ~ €6/ewe per set of twins).
Another interesting finding was that lambs from ewes offered 16kg of the soya-based concentrate were the same weight at weaning as lambs from ewes offered 28kg of the concentrate containing the by-products.
So feeding concentrates made with good ingredients can reduce the quantity of concentrate required in late pregnancy.
The ingredient composition of the concentrate I have formulated for the ewes during late pregnancy at Athenry is presented in Table 3. It contains 19pc crude protein using good protein (soya, rapeseed), energy (maize, barley) and fibre (soya hulls, beet pulp) sources.
When buying concentrate, be aware of its ingredient composition rather than basing the decision solely on price. A reduction in concentrate price of €20/t equates to a saving equivalent to only 45c/ewe.
Pregnancy nutrition plan
To optimise the use of concentrate, a pregnancy nutrition plan should be prepared. You need:
■ Laboratory analysis of the silage feed value;
■ Ewes should be grouped according to predicted litter size (based on ultrasonic scanning) and expected lambing date (determined by information on raddle colour);
■ Supplementation should be stepped up weekly over the weeks prior to lambing to follow the known changes in ewe requirements.
The feed schedules required to deliver different concentrate feed levels, varying from 10-45kg/ewe in late pregnancy are given in Table 4.
During the week prior to lambing ewes receive up to 1kg daily, illustrating the benefits of penning ewes according to expected lambing date as well as expected litter size.
For example, for each extra week on the high level of concentrate supplementation, a flock of 100 ewes would consume ~700kg concentrate — dramatically increasing concentrate usage and expenditure (by approximately €350).
Science to practice
■ Develop a late pregnancy nutrition plan to provide the required amount of concentrate;
■ Use a concentrate with 19pc protein formulated using good-quality ingredients;
■ Buy concentrate based on ingredients, not solely on price;
■ Concentrate supplementation should be stepped up weekly immediately prior to lambing to meet ewe requirements;
■ Excess concentrate supplementation will not yield an economic response.
■ Implementing an effective nutrition plan during the ‘time of tranquillity’ in the shed will reduce stress for both ewe and farmer during the hectic lambing period.
Dr Tim Keady is a Teagasc researcher based at Athenry
