Managing ewe diets to maintain body condition can influence hormone production, fertilisation and early embryonic development.
This is a consideration for all sheep breeders, but none more so than those who invest in assisted reproductive technologies such as embryo transfer. David Thornton, Rumenco technical manager, says: “Pedigree breeders, and increasingly commercial breeders, are using techniques such as embryo transfer to produce consistent quality progeny for the markets they are targeting.
“Peer reviewed studies highlight and support the importance of a balanced ration to ensure donor ewes are in best condition to produce first class oocytes.”
A study at the University of Dakota, USA, compared the effects of over- and under-nutrition on the success of in vitro fertilisation (IVF) and early embryonic development in mature ewes, measuring fertility parameters of a control group fed a maintenance diet, an overfed group fed ad libitum, and an underfed group fed 60 per cent of the maintenance diet.
Although all ewes were fed a different daily quantity, the composition of the ration remained the same, consisting of 2.4Mcal metabolisable energy and 130g (13 per cent) crude protein per kg in terms of dry matter.
Mr Thornton says the study highlights how variation of daily intakes significantly influences body condition and body weight of the ewe, ultimately affecting the ewes’ ability to produce quality oocytes.
Over- and under-nutrition decreased the rate of cell division in the early embryo from 85 per cent in the control group to 51 per cent in overfed and 48 per cent in underfed ewes.
Subsequently, this reduced the number of blastocysts available for implantation to 2 and 6 per cent respectively.
Although the study focuses on IVF, Mr Thornton says the principle of controlling body condition score by maintaining a level plane of nutrition is transferable to all sheep farmers and will influence embryo quality and performance across the board.
He says: “Nutrition must correspond with the stage of pregnancy and many underestimate the importance of trace elements in the diet and focus on energy intakes alone. However, the importance of cobalt, copper, and selenium in particular, must not be overlooked.
“A lack of cobalt in pregnant ewes’ diets has been shown to have a negative effect on total number of lambs born; increasing rates of stillbirths and neonatal mortality. “Lamb health and vigour can also be affected where ewes are fed diets deficient in cobalt.
“This year, more than ever, it appears forage has not been performing as we would expect. As such, stimulating intakes and supporting diets through supplementation is vital.
“Maintaining optimum body condition pre-breeding and ensuring diets match nutritional demand will pay dividends in maximising ewe fertility, number of lambs on the ground, and the overall return from the flock – a primary focus for both commercial and pedigree breeders.”
|Final body condition score||3.0||4.2||1.8|
|Cleaved oocytes rates (percentage)||85||51||48|
Source: Dakota State University, USA