Nutrition during late pregnancy – the key factor influencing flock profitability

Nutritional management during late pregnancy impacts: colostrum quality and quantity, ease of lambing, lamb survival, lamb birth weight and the formation of the ewe-lamb bond.

All of these factors impact lamb performance from birth to sale, flock productivity and labour requirement during the lambing period – the key factors influencing flock profitability and job satisfaction. Tim Keady discussed this in detail at this year's Teagasc Sheep Open Day in Athenry.

Silage feed value

The main factor influencing silage feed value is digestibility (DMD). The effects of the DMD of silage offered to ewes whilst housed on ewe and lamb performance are presented in Table 1. Increasing DMD increased silage intake. When concentrate supplementation was initiated (approximately six weeks pre-lambing) the intake of medium DMD silage remained relatively unchanged up to lambing, whilst that of the high DMD silage declined as concentrate feed level increased. Concentrate displaced high DMD silage in the diet.

Studies at Athenry have shown that increasing silage DMD increases ME (metabolisable energy) intake by up to 53% during late pregnancy. The ewes offered the high DMD silage were 10kg heavier and had a higher body condition score (BCS) at lambing. At pasture, between lambing and weaning, the ewes that had been offered the high DMD silage lost 0.5 units BCS (sacrificed body reserves in favour of milk production), whilst those offered the medium DMD silage gained 0.2 units BCS (partitioned energy intake to replenish their own body reserves rather than to milk production). The lambs from ewes offered the high DMD silage were: 0.5 kg heavier at birth, 1.9 kg heavier at weaning and 17 days younger at slaughter. A reduction of 17 days at slaughter is equivalent to the response expected from feeding 19kg concentrate per lamb from birth to slaughter. As each ewe in the study reared 1.75 lambs, this would equate to 33kg concentrate/ewe - equivalent to ~ €15/ewe.

Table 1.The effects of grass silage feed value and concentrate feed level on ewe performance

Concentrate supplementation

Whilst increasing concentrate intake to ewes offered the medium DMD silage yielded a small improvement in BCS at lambing, it had no impact on lamb performance (Table 1). Thus, feeding excess concentrate in late pregnancy does not improve lamb performance and will result in a negative return on concentrate expenditure. 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 ewes have access to fresh silage 24 hours daily. Concentrate requirement is influenced primarily by silage DMD (but also by chop length). The concentrate requirements per ewe can be reduced by 5kg for single-bearing ewes, and increased by 8kg for ewes carrying triplets.

Concentrate composition

An Athenry study evaluated two concentrates which were formulated to have the same ME and crude protein concentrations and used either soyabean meal or a mixture of by-products (rapeseed, maize distillers and maize gluten) as the main protein source. The concentrates were offered to ewes during late pregnancy. Lambs born to ewes that were offered the soyabean-based concentrate were 0.3kg and 0.9kg heavier at birth and weaning, respectively, than lambs born to ewes offered the concentrate containing by-products as the protein source.

The increase in weaning weight of 0.9kg (extra cost ~€0.60/ewe) is similar to the response obtained from offering each lamb 6kg of creep concentrate until weaning (cost ~ €6/ewe per set of twins). Lambs from ewes that were 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. Purchase concentrate based on ingredient composition rather than solely on price. A reduction in concentrate price of €20/t equates to a saving equivalent to only €0.50/ewe.

Pregnancy nutrition plan

To optimise the use of concentrate, ewes should be grouped according to predicted litter size (based on ultrasonic scanning) and expected lambing date (change raddle colour every 7-10 days during the joining season). Analyse your silage and base supplementation level on data presented in Table 2. Supplementation should be stepped up weekly over the weeks immediately prior to lambing to coincide with ewe requirements.

Table 2.Effects of silage DMD on concentrate requirements (kg) of twin-bearing ewes during late pregnancy

This paper was orginally published at the Teagasc Sheep Open Day 2022.