To treat or not for prelamb

The effect of parasites on production.

It is well known that parasites cause animal production losses. They do this in a myriad of ways including damaging the mucosal lining of the abomasum and intestine, sucking blood and inducing an immune response from the host animal. All these actions result in protein and production loss.

Much has been written on whether or not to drench ewes prelamb. Certainly there are pros and cons with any anthelmintic treatment.
The reasons not to treat may be;

  • concerns around resistance to the drench used
  • the cost
  • benefit of the treatment stress on ewes late in gestation associated with yarding and treatment.

However the treatment benefits, of which there are many, tend to outweigh these concerns. Trials have been conducted on in-lamb ewes to try to understand how significant the effects of parasites can be. One of the trials1, conducted at Lincoln University, found that parasitism reduced milk production by 10 to 59 per cent. The most significant reduction in milk production occurred in ewes from lambing until six weeks into lactation.

Blood pepsinogen levels (a measure of abomasal damage) were high throughout the trial after the animals were infected. This was in spite of mean egg counts dropping from 1330 eggs per gram (epg) 4 weeks prior to lambing, to 16epg 12 weeks after lambing. This highlights that low egg counts aren’t necessarily reflective of the damage occurring to ewes during this time.

The appetite of the ewes was not affected by infection in the four weeks prior to lambing, however the repercussion of this early parasite infection was a reduction in feed intake of 30 per cent after lambing. Another trial2 found there were no significant effects of infection during pregnancy on feed intake, body weight change, wool production or lamb birth weight. However during lactation, parasite infection reduced both feed intake and milk production by 16 per cent.

Interestingly, only three of the 32 infected sheep had positive faecal egg counts during pregnancy, but elevated plasma pepsinogen levels indicated substantial abomasal damage during both pregnancy and lactation.
These results indicate that:
breeding ewes may be affected by parasite larval intake, even though clinical signs may not be seen.
damage may occur during pregnancy which can affect performance of the ewe during lactation

It is apparent that intake of larvae during the prelamb-lambing periods has a marked and prolonged effect on the milk production of lambing ewes - which can then impact on the growth rates of lambs.

Treating ewes during the prelamb period would prevent much of the losses found in these trials. Using products that deliver longer protection from parasites rather than more conventional treatments can help offset these effects, thereby maximizing production from the ewe.

So, to drench or not to drench? Vets or animal health advisors can recommend what is the best option for individual farms. However, the trial data is clear. When ewes ingest infective worm larvae with pasture in the prelamb-lambing period, they do suffer from parasitism. Removing these parasites and protecting ewes from an ongoing challenge, will improve production and profit.

References :
1McAnulty R, Familton A, Sykes A, Proc NZSAP 1991, vol 51. Effects of daily larval challenge on the performance of breeding ewes from late pregnancy to weaning.
2Leyva V, Henderson A and Sykes A Proc NZSAP 1981, vol 41. The effect of daily infection with O circumcincta larvae on the performance of pregnant and lactating sheep