Ewe fertility, expressed through litter size and conception rate, is a critical aspect of production in hill sheep systems.
Previous research has shown that the Scottish Blackface breed is the most responsive of breeds in terms of breeding performance and having ewes in the optimum body condition score and liveweight at time of joining.
At the recent Teagasc virtual hill sheep conference, Dr Liz Genever, an independent sheep and beef consultant based in Lincolnshire, England, provided further thought on aspects that may be contributing to lower than desired breeding performance on hill sheep farms. Liz said that recent research carried out in the UK has shown that body condition score during lactation will affect the next season’s fertility.
“If ewes are thin at eight weeks of lactation it doesn’t matter how much feeding ewes receive after or how condition improves after this – fertility will be set at this stage.
This is linked with the development of follicles within sheep and therefore we need to take account more of energy in early lactation. That is what our research is telling us.”
Liz says that priority needs to be given to grass quality and quantity during lactation to ensure ewes don’t lose too much condition.
She says that for thin ewes falling below optimum body condition score these ewes need to be allocated good-quality feed and grazed on a sward with grass height ranging between 4cm and 8cm to ensure intake is not compromised and grass-quality is maintained in a digestible manner.
Performance from grass
It is important that performance is underpinned by the farm’s output potential rather than driving increased performance solely from feeding higher levels of concentrates.
This is due to the fact that maintaining a happy balance in output from hill breeds is critical in terms of limiting input requirements and optimally managing hill vegetation.
For example, if the litter size in hill sheep flocks increases too much it will result in a higher percentage of twin-suckling ewes that need to be retained on improved or upland grazing and influence the level of supplementary feed required.
If this number is too high then a possible knock-on consequence is hill and mountain-type vegetation being undergrazed and over time deteriorating in feeding quality. The optimum level of output will be based on the quality of grazing available and feed resources.
Table 1 details the optimum body condition score for different breed types at key time frames throughout the production cycle.
Hill ewes have a lower desirable body condition score compared to lowland ewes.
Liz says that hill breeds tend to carry more fat internally which can’t be felt through the standard body condition score technique but which acts as a resource for ewes if required.
The advice is to handle ewes each time tasks are being carried out to keep on top of condition and ideally to be able to pull out and segregate ewes falling behind target for preferential treatment.
Another important task to carry out on an ongoing basis is to assess the level of feed available and review if the system of production in place is making the best use of the farm’s resources.
For example, one question that should be asked is if the farm’s lambing date is in line with the normal onset of grass growth and spring feed availability. In this regard, body condition score is raised as an invaluable tool to assess if the production system is performing adequately as it links across all aspects of production.
Liz says the most sustainable farming systems on an economical, environmental or social focus are those that match production with the farm’s resources while using the simplest system of production.
Liz states that poor management during the rearing phase will affect lifetime performance.
She said that ideally young ewes would be maintained separate from mature ewes for as long as possible, with some systems now aiming to keep hoggets which have lambed at two years of age separate until they have weaned their lambs.
This will allow these animals to be prioritised in terms of feed quality and even where this is not possible then it is important to monitor the performance of these animals closely.
While ewe lambs are rarely mated to lamb as yearlings in hill sheep systems, Liz says there is evidence that getting these sheep to mating weight (60% to 65% of mature weight) and hitting puberty is important for future fertility even if sheep are not being joined to rams.