This is the research that I presented at the New Zealand Society of Animal Production conference in July this year. The aim of this research was to determine if the change in body condition score (BCS) had an effect on sheep production as measured by the number of lambs scanned at pregnancy diagnosis, the number of lambs weaned and the total litter weaning weight.
Key Points
There is no benefit in exceeding a body condition score of 3.5.
Farmers should ensure that ewes are increasing in body condition score leading up to mating.
Ewes that lose body condition score between mating and weaning are associated with greater production.
Body condition score (BCS) is an on-farm subjective measurement used to inform feed management decisions in sheep.
This study determined the relationships between BCS, changes in BCS and production in 2500 Romney ewes aged from 1 to 5.
Production was measured as:
Number of lambs scanned (NLS)
Number of lambs weaned (NLW)
Average weight of lambs weaned (WWT)
Total weaning weight of lamb (TLW)
BCS was recorded 4 times annually as can be seen in the graph below. Beginning of the mating period (mating), pregnancy scanning (scanning), two weeks prior to lambing or set stocking (lambing), weaning.
BCS was grouped into 5 groups as follows:
Total litter weaning weight
The graph below shows the effect of BCS group on total litter weight. The different letters indicate significant difference. There is a slight difference between the different BCS groups at scanning. The greater the BCS at lambing and weaning, the lower the total litter weight weaned.
Ewes with a BCS ≤2.5 at weaning were associated with the greatest TLW, suggesting these ewes had utilised their stored body fat to achieve high milk yields. This means that the fat ewes at weaning are the ones most likely to have reared singles or smaller multiple lambs. Therefore, above a BCS of 3.5 there seems to be no production benefits.
Number of lambs scanned
The graph below shows the change in BCS from previous weaning to mating and from mating to scanning on the number of lambs scanned. An increase in BCS from weaning to mating was associated with a greater number of lambs scanned. However, the opposite relationship was observed with a loss in BCS from mating to scanning associated with a greater number of lambs scanned. This means that farmers should be feeding ewes well up until mating, however, after mating they may return to maintenance feeding allowances.
Number of lambs weaned.
The next BCS change graph looks at the number of lambs weaned (NLW). As you can see there was no relationship on the BCS change from mating to scanning on NLW. A similar relationship for NLS and NLW of BCS change from weaning to mating. A gain in BCS from scanning to lambing and lambing to weaning resulted in less lambs weaned.
Total litter weaning weight
The following graph shows the change in BCS between each BCS measurement and the effect this has on the total litter weaning weight. Ewes that decreased BCS between lambing and weaning produced greater total litter weaned compared with ewes which maintained or gained BCS indicating their body reserves were acting as a buffer to provide milk to the lambs.
Although a loss in BCS from lambing to weaning seems like this results in a greater number of lambs weaned and thus total litter weight weaned. It could be that the ewes that rear and wean multiple lambs have a greater energy demand, therefore, resulting in the loss of BCS, not the loss resulting in the greater lamb production. Even though we are not sure of this relationship, this study did confirm that it is important to 'flush' ewes prior to mating, meaning to feed above maintenance requirements to result in a gain in BCS.
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