Mid-Pregnancy Feeding Drives Lamb Crop

5 November 2019

A close focus on ewe feeding in mid-pregnancy has a huge bearing on lamb numbers, lamb viability and potential returns per ewe, according to Laura Drury, Ruminant Technical Advisor with Trouw Nutrition GB.

“The future of the British sheep industry remains uncertain, so producers should be taking every opportunity to maximize lamb outputs to improve gross margins. The mid-pregnancy period is a critical period for ensuring the production of strong, viable lambs to improve margins but is often seen as less important than feeding immediately pre-and post-lambing.  Months two and three of pregnancy actually set the foundations for the lamb crop.”

She says there are two crucial objectives at this stage.  The first is to manage ewe condition, feeding to achieve the target lambing BCS of 3.0-3.5 for lowland ewes condition and 2.5 for hill ewes. Target lambing BCS should be achieved before ewes enter the late pregnancy period, therefore any required body condition score change must managed during mid-pregnancy.

“You need to avoid weight loss in thin ewes, below BCS 2.0, while encouraging weight loss in overfat ewes (>4.0 BCS).  Overfat ewes will have a lower DMI during late pregnancy, leading to increased fat mobilization and a higher susceptibility to twin lamb disease.

“You need to set targets for ewe lambs too and you should be aiming to increase their bodyweight by 5% in months 2-3 of pregnancy, since they are still growing to reach a mature weight”.

The second key objective is ensuring optimal development of the placenta to support lamb growth throughout pregnancy.  Ms Drury explains that as it supplies all the nutrients to growing lambs, placental development is important for optimal lamb birthweights and survival. Poor placental growth can have a detrimental effect on lamb birthweight, increasing susceptibility to hypothermia, reducing colostrum intake leading to poor growth rates and lower survival.

“The placenta plays a crucial role in setting the size of the lamb crop influencing lamb survivability and subsequent growth rates”.

“Most sheep farmers know that 75% of lamb growth is put on in the last 6 weeks of pregnancy. Fewer know that at month three of pregnancy, the products of conception of a twin-bearing ewe average 5.7kg, and 80% of this weight will be the placenta representing a significant proportion of eventual placental size.

“If placental growth is compromised during this period, it cannot be compensated for in late pregnancy and may result in smaller, weaker and less viable lambs which will require more feed for growth and will take longer to finish. This will reduce the opportunity to finish lambs earlier when prices are higher.”

To achieve these objectives, she says an ME intake of 10MJ/day with 85g/day of metabolisable protein is sufficient to meet maintenance requirements of a 70kg ewe, which can usually be supplied from average quality grazing if a dry matter intake of 1kg/day is achieved, but she advises allowing a 30% greater grazing allowance for thin ewes.

“The AHDB sheep KPI project has also highlighted the benefits of gaining condition in mid-pregnancy where appropriate. Preliminary data indicates improvements in scanning percentages when ewes continue to gain condition through to scanning, so a small increase in nutritional supply over maintenance should be considered and factored into grazing allowances.”

Minerals are also key to the establishment of a strong lamb crop. Although they only make up a small proportion of the diet, they have essential roles in energy metabolism, immunity, and hoof integrity just to name a few. She advises providing supplementary minerals at grass for optimal ewe health and performance as the TNGB 5 year average forage mineral analysis shows levels of zinc, cobalt, iodine and selenium in fresh grass are inadequate to meet requirements of ewes throughout mid-pregnancy.

“We would also advise all sheep producers to scan ewes at around 60 days pregnant as it has many benefits. Early detection of empty ewes will allow them to be removed from the in-lamb group saving on feed costs, while pregnant ewes can be grouped and fed according to the number of lambs being carried and BCS.

“The mid-pregnancy period is a good time to plan ahead for the pre-lambing phase. Get forages analyzed for their nutritional and mineral content and select the appropriate pre-lambing supplements to balance forage in the run up to lambing.”