Spotlight on benefits of pre-lamb drenching

Latest research is challenging the popular belief that drenching ewes around the time of lambing will consistently provide production and financial benefit, AgResearch scientists say.

At the recent Beef + Lamb New Zealand AgInnovation conference in Palmerston North, AgResearch parasitologist Dr Dave Leathwick reviewed the science around the production benefits from drenching ewes at lambing, and showed some new data on the benefits of focusing drench treatments on ewes with low body condition scores.

“Around this time of the year farmers are bombarded with promotions about the benefits of treating ewes pre-lambing,” Dr Leathwick says.

“Reviewing all of the on-farm trials conducted in New Zealand since the 1960s, there is one common theme all the way through – there is no consistent production benefit from drenching ewes around lambing time. This applies whether you’re talking about an oral drench, a long-acting injection or a capsule.”

“That means that sometimes there is a measurable benefit and sometimes there isn’t. But it’s a bit more complicated than that, because many of the trials didn’t actually measure all the variables necessary to make a proper decision on the benefits of treatment.”

“This was clearly seen in the recent series of trials conducted by farmers in the Wairarapa, the ‘Wairarapa Anthelmintic Trial’. This study was largely run by farmers and was funded by a complex of industry agencies and companies. It was by far the most comprehensive study ever conducted in New Zealand on this topic.”

“The key outcome from this work was that in nearly 50 per cent of the trials, there was a net financial loss as a result of drenching ewes. This came about because while treated ewes and their lambs tended to be heavier at weaning, there tended to be fewer of them ie. ewes treated with long-acting drenches, on average, weaned fewer lambs.”

“The fewer lambs effectively cancelled out any benefit from the heavier ewes and lambs. Further, the financial analysis showed that the biggest driver of dollar return on investment, was, in fact, the number of lambs weaned, rather than ewe or lamb weaning weights. The results showed the biggest driver of financial benefit was lamb survival.”

Another interesting and unexpected result from the Wairarapa study was that the response to treatment was independent of ewe body condition score pre-lambing ie. all ewes responded the same regardless of their condition.

AgResearch scientists have been following up on this finding over the last year, and have further analysed data from both the Wairarapa study and other trials. Their recent findings show that over the period from pre-lambing to weaning, some ewes increase in condition, some lose condition and some stay the same.

“The proportions following this pattern are exactly the same whether the ewes were drenched or not, and the type of drench was irrelevant,” Dr Leathwick says.

“We interpret these data as telling us that low body condition in ewes at this time of year is unlikely to be caused by worms. Even when skinny ewes are given a long-acting drench, many of them don’t improve in condition, and some lose condition.”

“The take-home message seems to be that ill-thrift in ewes is probably due to other factors. Work from Massey University has suggested subclinical pneumonia and facial eczema are more likely to be involved. While the causes of ill-thrift remain uncertain, it does appear worms are not important. So, if you try and solve an ill-thrift problem in your ewes by drenching you will probably fail.”

“Therefore, while farmers may, in some situations, see some benefit from drenching ewes around lambing, they should be cautious, as a positive financial benefit is not certain. The benefits of treating ewes pre-lambing are not at all reliable or consistent, and there may be much better ways to spend your money.”

“Currently, the best recipe to maximise kg lambs weaned/ewe mated, seems to be to get as many ewes as possible to condition score 3 before lambing starts.”