Dr Peers Davies MA VetMB PhD MRCVS
In most sheep systems profitability hinges on lambs reared per ewe far more than the scanning percentage because lamb survival varies enormously with many flocks scanning at 180% and above but only selling 120-130%.
There are many reasons for lambs failing to make it through to sale and even more factors influencing lamb growth rate and final carcase value. However, many of the most important factors are under our control as producers as they relate to the nutrition, genetics and management of the ewe prior to lambing influencing the development of the lamb in the uterus and the survival changes after lambing.
These can be broken down into the ewe reserves of energy and protein and the supplementation of specific trace elements, particularly selenium, iodine and biotin. Whilst these trace elements are normally the focus of a lot of attention there is more evidence for the energy and protein supply to the ewe being the real key factor.
We have good evidence from large Australian studies (Lifetime Wool Project) that ewe body condition in twin-bearing ewes at lambing should be at a score of 4 out of 5 in order to hit an average twin lamb birth weight of 4kg. This is important as lamb birth weight is the most important predictor of lamb survival. 4kg has been shown to be the optimum weight for twins with both lighter and heavier lambs more likely to succumb to a wide range of issues from hypothermia to dystocia.
Beyond lambing, the ewe body condition score of 4 means that ewes have sufficient reserves of energy to maintain her immune function and retain her immunity to roundworm infection so they release far fewer worm eggs onto pasture and therefore provide lambs with a lower parasite challenge and better live weight gain is the result.
Getting ewes into the correct condition score takes time and effort to group and monitor ewes appropriately throughout the whole production cycle. This regular use of manual body condition scoring is not a particularly common practice in the UK but it pays dividends as it allows the whole flock to perform at a higher level. In order to make the best use of available farm resources forage analysis is essential to allow farmers, with their nutritionist or vet to calculate the minimum energy and protein required to match that provided by the forage. This approach can mean either specific compounds, blends or home mix rations can be fed, cutting feed costs overall.
Protein levels are particularly important especially for the establishment of milk yield and good colostrum quality. The balance between different types of protein; digested in the rumen or abomasum, is crucial when feeding late pregnancy ewes as the levels of these vary enormously in different supplementary feedstuffs with a big impact on overall cost.
Further on in lactation, the role of high dietary protein has been shown to be critical in allowing lambs to fight off worm infestations and also in ewes to bolster milk yield and reduce mastitis rates. This can mean strategic feeding of ewes and creep feeding of lambs during the first 8 weeks is appropriate and profitable in some early production systems in particular.