Stephanie Patel BVetMed MRCVS
With the growing concern around the global impact of farming and the production of farm animals on the environment, the topic of efficient production is even more important to ensure we are doing what we can to reduce our carbon footprint.
Efficient growth in our animals, and in particular our lambs, not only ensures that we are fulfilling our ecological duty through lowering our carbon output, but also has a positive economic impact on the individual farm as animals are reared and sold more quickly.
There are different growth stages during the life cycle of the lamb, with the most efficient growth occurring pre-weaning, whilst the lamb is still on milk. During this period growth rates of greater than 250g/day should be the target.
Crucially, weighing lambs at 8 weeks old will provide a wealth of information, it can help to determine when to wean and also provides a good indication of the growth that has taken place whilst that lamb has been nursed, which is influenced by the following factors: age of the dam, litter size and nutrition during pregnancy. With the latter playing a significant role and impact on a lamb’s birth weight.
Work in Ireland has shown that for each 0.5kg increase in lamb birth weight, weaning weight increased by 1.7kg. Birth weight is determined by many factors which include: litter size, dam size, nutrition during late pregnancy and body condition at tupping, which for a lowland farm should be at 3.5. The ideal birth weights for lambs are between 4-4.5kg, depending on the breed of ewe. It has been shown that lambs that fall either side of that weight can be at a greater risk of a difficult delivery for larger lambs, or of neonatal mortality for smaller lambs.
During the first 3-4 weeks of the lamb’s life the ewe will reach peak lactation, and therefore her body condition can be assessed. It is important to do this at this stage as her body condition will reflect her feed supply and, subsequently, her milk production as this will be represented in the growth of the lamb. For lowland sheep farmers, the ewes body condition should be 2.5 at weaning. If she is below this during the 8 week weigh-in, then the nutrition needs to be assessed and the decision made as to whether you should wean earlier and allow her to recover and regain condition prior to tupping. Typically it will take her 6-8 weeks to recover one point on the body condition score.
When to wean will change annually, but consistently depends on several factors including:
- Feed availability
- Body condition of the ewe
- Lamb growth rates
Typically, most farms will wean between the ages of 12-14 weeks. Lambs should be weaned on leys that they are already familiar with, as the rumen will take several weeks to adapt to a new source of feed, at weaning they should be put onto pasture away from the sight/sound of their mothers to minimise stress.
Age of weaning will vary from farm to farm, by 8 weeks of age the lamb is more reliant on forage than milk as a source of energy, so long as the lamb has a functional rumen. If at 8 weeks they are lighter and have not achieved an average of 250g/day, then it may be worth creep feeding to accelerate rumen development. At weaning, weights should be recorded and thereafter every couple of weeks a small proportion ie 10-20% of the flock should be weighed to determine daily live weight gain.
Post-weaning growth potential drops compared to when they are on milk, 200g/day should be the target, but commonly less than 100g/day is achieved. A drop in daily live weight gain can be caused by a number of factors from nutrition, to disease and parasitism. If it is taking longer to reach finishing weights of approximately 40kg then you should speak to your vet and who can investigate the cause.
In summary, the body condition of the ewe and her nutrition are key to lamb growth, and so particular attention needs to be paid to this to ensure maximum profit.
For further advice and information on growth rates and weaning of lambs, including nutritional guidance, you can get in touch with the Molecare Farm Vets team by emailing [email protected] or call the office on 01392 872934 to speak to one of the team.
References: Gascoigne E, Lovatt F Lamb growth rates and optimising production. In Practice 2015; 37:401-414 EBLEX Sheep BRP Manual 5: Growing and Finishing Lambs for Better Returns