Interesting, also, was the impact of hot temperatures on liveweight gains on these “rocket fuel” feeds. Despite such good feed, in temperatures of over 38C day after day, the cattle intakes were low, as were the weight gains. Of course in the barns this did not happen, but at a feed cost of over 40c/kg/DM in those barns there had to be significant benefits over the rocket fuel of about 15c/kg/DM.
I had a fascinating discussion in France with a scientist who has been working on lamb survival and ewe lactation. He had decent data on causes of lamb death, which included diseases that we do not see here. He also had data showing the close link between ewe body condition score at lambing on both lamb survival and lamb weaning weight.
I asked him how he extended such messages and he replied that it was through farmer meetings. My next question was about the uptake of these messages. For farmers that lambed ewes for their lambs (like most of New Zealand sheep farmers) the uptake was poor. For farmers who lambed ewes so that they could milk them (there are plenty of these flocks) the uptake was good. Just as dairy farmers can see daily the impact of things they do, for these French sheep farmers their milk yields gave them direct feedback on their management. They could see that better condition ewes gave more milk.
Even though the lamb producers got the same benefit, why were they not as responsive to the condition score message? I saw similarities with NZ sheep farmers. Is it because several other factors affect lamb weaning weight? Maybe it is because the most important ones are not obvious enough. Even though the amount of high-quality pasture that a suckling lamb can eat has a big impact on its weaning weight, the start and support that it gets from milk is a significant contributor to that weight.
The weaning decision is looming and planning or defining the decision-making process for when to wean is not common enough. A frustration I have is how often the time of weaning is driven by the need to shear ewes. This in no way enables weaning to be timed to maximise lamb weaning weight and/or ewe condition and/or market opportunity.
That shearing date either advances or delays the ideal weaning date.
Once the amount of quality pasture becomes limiting there is competition between the ewe and the lamb. The ewe will always win and at that stage of lactation there will be no lift in the milk supply. Once the lamb has restricted access to quality pasture its weight gain will drop. Using changes in ewe condition in that weaning decision is not really a valid tool. That assessment of change will be visual, so by the time it is obvious the lamb weight gains will have really dropped off.
Ideally being able to measure lamb weight gains would enable the best decisions, but realistically that is not on. This is one time when that highly perceptive eye of a good stockman is really valuable.
Before weaning millions of lambs will have been yarded and drenched. In my opinion in many or even most of those cases there will have been no productive benefit and the whole process would have been a cost. We know that drenching those suckling lambs will make them cleaner, but that does not mean faster growth. In a spring in which there is feed, as many farms are enjoying, and ewes are gaining condition the potential growth responses to that drench will be limited.
We know also that suckling lambs get a lot of worm protection from the milk, so this should come into the decision about the need to yard ewes and lambs for drenching. The Nematodirus threat for southern lambs is always used to justify this intrusion and no doubt it is valid for many farms, but there are many farms down there on which suckling lambs are not drenched and they wean plenty of heavy enough lambs.
This is an area of worm management in which we have poor tools for decision-making. If we put alongside this the cost of mustering and yarding ewes and lambs, maybe that decision could be more discerning. But what is that cost?
- Trevor Cook, veterinarian, Manawatu.
