Identify ill-thrift early to get to real cause of problem
You may well ask 'why is he on about ill-thrift' seeing as lambing has not even finished yet. However, farmers generally only notice ill-thrift or poor growth rate during July and August and only then because the lambs are not becoming fit for sale.
The number of complaints by farmers about ill-thrift is directly related to the trends in lamb price. When prices are falling and lambs are not being sold, there are generally a large number of complaints. When prices are holding or even rising, like last year, there are few complaints, even though lamb thrive was no better than the previous year.
In the majority of situations, when farmers do seek a remedy from their adviser or vet at this time of year, they are recommended a worm dose or trace element supplement without any real discussion or problem analysis. The adviser has collected his fee, the vet his sale and the farmer feels happy that it was not his management, or the lack of it, that caused the problem.
Poor lamb drafting means that there is a problem, but gives no indication as to when the problem started. In my view, many cases of poor lamb thrive occur before the lambs are 10 weeks old and sometimes before the lambs are born.
Ewes underfed during pregnancy will have lighter lambs that will take longer to finish. A reduction of 0.4kg in lamb birth weight can readily occur due to poor ewe nutrition and this becomes a disadvantage of 1kg at weaning time, resulting in the lambs taking an extra week to finish.
Pasture quality and digestibility are at their highest during March, April and May. Twin lambs have the potential to gain at least 300g/day (singles 350g/day) during this period. As pasture quality drops during June, lambs' growth rate will also decline to around 220g/day. Growth rates after weaning are generally in the region of 150g/day.
As can be seen, March-born lambs on grass have the potential to grow twice as fast during the first 10 weeks of life than after weaning. A loss of 30g/day (which does not seem a lot) in lamb growth rate during this early period means a loss of 2kg in weaning weight and two weeks' delay in finishing. It comes down to providing sufficient grass (sward height 5-6cm), first for the ewes so that they have adequate milk supplies, and then for the lambs as milk yield declines and lambs become increasingly reliant on pasture.
In general, nutrition and feeding have the highest influence on lamb growth rate, followed by diseases such as lameness, parasites and then trace elements. But there are exceptions to every rule. Where there is a long lambing spread, parasites become more important. Young lambs (1-2 weeks of age) grazed with older lambs (5-6 weeks or older) can become heavily contaminated with roundworms (eg, nematodirus and coccidia).
Unlike their older comrades, they have developed little immunity and probably will miss out on the first worm dose. Their growth rate will be impaired and they may suffer irreparable gut damage that will affect subsequent performance. Where there is a long lambing spread, the later-born lambs should be treated as a separate flock and avoid pastures grazed by their older comrades until after weaning.
Early observance of ill thrift is important. A large difference in the weight of single and twin-born lambs at the first or second worm dose will provide an indication that all is not well, but it is only an indication.
The only one real way of identifying it is by periodic weighing. One simple way is to tag about 50 lambs throughout the lambing period (15 singles and 35 individual lambs taken from pairs of twins) and record birth date and whether single or twin. Weighing these lambs at about 5-6 weeks of age (first worm dose), at 10 weeks (second worm dose) and at weaning will give invaluable information.
For instance, under performance at the 5-6 week dose would indicate a low lamb birth weight or ewe milk yield problem. Under performance between the first and second dose would indicate a problem with grass supply. The information would help discussions between you and your adviser or vet.
I believe in trace element supplementation where proven deficiencies occur but believe they do not solve the majority of ill-thrift problems. Many perceived trace element deficiencies may be the result of earlier mismanagement.
Andrew Kinsella is a Wicklow sheep farmer and a former Teagasc sheep specialist
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