Nutrition during late pregnancy – the foundation to flock profitability
Late pregnancy and early lactation is the most traumatic time during the year for pregnant ewes. Inadequate nutritional management at this time increases labour requirement and lamb mortality. Researcher Tim Keady has information and advice on nutritional managment at this critical time.
- Digestibility (DMD) is the most important factor influencing silage feed value
- Each 5 percentage point increase in silage DMD increases ewe weight post lambing by 6.5 kg and increases lamb birth weight by 0.25 kg.
- The level of supplementation offered to ewes in late pregnancy should be based on lambing date, forage quality and expected litter size.
- Inadequate nutritional management (under or excess nutrition) increases lamb mortality due to birth weight issues, thus increasing labour requirement.
The periparturient period (late pregnancy and early lactation) is the most traumatic time during the year for pregnant ewes because the lambs are growing rapidly in utero, birth occurs and lactation is initiated. Under nutrition during late pregnancy results in ewes in poor body condition at lambing and lambs of low weight and poor vigor whilst over nutrition results in oversized lambs that require assistance at birth. Therefore inadequate nutritional management increases labour requirement and lamb mortality. My objective in this article is to summarise results from the many studies at Athenry on the effects of the grass silage feed value offered to ewes during late pregnancy on ewe and lamb performance.
Impact of grass silage feed value
Digestibility (DMD) is the most important indicator of the feed value of grass silage when offered to ewes. At farm level DMD of grass silages can vary from 52 to 82%, average DMD of silage produced in Ireland is 70%. Consequently, when developing a nutritional plan for housed ewes in late pregnancy it is essential to know the feed value of the silage been offered.
The results from studies undertaken at Athenry on the impact of silage digestibility on the performance of pregnant ewes, and that of their progeny are summarized in Table 1. Increasing silage DMD increased ewe live weight and body condition score (BCS) at lambing and increased lamb birth and weaning weights by 0.3 and 1.2 kg, respectively. Each 5 percentage-point increase in silage DMD increases ewe weight post lambing by 6.5 kg and increases lamb birth weight by 0.25 kg.
Table 1. The effects of grass silage feed value in late pregnancy on ewe and subsequent lamb performance
|Ewe weight post lambing (kg)||58.7||66.7|
|Lamb – birth weight (kg)||4.4||4.7|
|- weaning weight (kg)||30.5||32.7|
*Average DMD of silages in Ireland is 70% DMD
Silage feed value and concentrate requirement
The effects of concentrate feed level and silage feed value (DMD) on lamb birth weight and BCS at lambing are presented in Table 2. Note for ewes offered silage with 70 % DMD increasing concentrate feed level allowance above 25 kg yielded no real gain in lamb birth weight but the ewes were clearly fatter (higher BCS); for ewes on 75% DMD silage – increasing concentrate allowances above 15 kg yielded a minimum change in lamb birth weight. Therefore the increased energy intake from feeding excess concentrate to ewes during late pregnancy is converted to body fat.
Table 2. The effects of concentrate feed level in late pregnancy on lamb birth weight and ewe body condition score (BCS)
|15||4.7 (3.1)*||5.0 (3.7)|
|25||5.2 (3.3)||5.1 (3.8)|
*BCS of the ewe
Level of concentrate to offer
The effects of silage feed value on the concentrate requirement of twin-bearing ewes in late pregnancy are presented in Table 3. It is assumed that the silage is been offered using good feeding management, i.e., ewes have access to fresh silage 24 hours daily and that any silage residue is removed twice weekly. The main factor influencing concentrate requirement during late pregnancy is silage DMD. For example, for silages at 79 and 64% DMD an additional 3 and 10 kg concentrate, respectively, are required for long chop silages, compared to precision chop silages, respectively. The concentrate requirements per ewe presented in Table 3 can be reduced by 5 kg in the case of single-bearing ewes, whilst concentrate supplementation should be increased by 8 kg for ewes carrying triplets.
Table 3. Effects of silage quality on total concentrate requirements (kg) of twin-bearing ewes during late pregnancy
|Big bale/Single chop||13||24||35|