Giving greater consideration to nutrition of pregnant ewes may help reduce worm concerns, according to New Zealand-based researcher John Donaldson
PARASITE control programmes for sheep systems must place greater emphasis on an integrated approach, and rely less heavily on the use of chemical drenches.
With continued incidence of drench failure as worms become resistant to chemical treatment, and growing concern over chemical residues in animal products, the need to reconsider control measures is paramount.
Few researchers would advocate a complete abandonment of anthelmintic treatment, but rather advise aiming towards minimal strategic use as part of an integrated programme.
Alternative control methods, which include utilising the animals natural immunity to worms and minimising larval challenge to susceptible stock have, in the past, taken second place to highly effective chemical drenches. Now, the balance is changing and the animals natural resistance to worms and its follow-on effect on pasture contamination is being reassessed.
Young lambs in their first grazing season have little natural immunity to worm infection picked up from pasture. When grazing heavily contaminated areas they will require several drenches to maintain productivity. Research in New Zealand is looking at ways of reducing this contamination and so cut down on the number of drenches required.
Recent work has shown that most larval contamination of pasture around lambing comes from the mature breeding ewe.
As sheep mature and are exposed to worms they develop immunity to worm infection.
But mature ewes, at lambing, experience a temporary relaxation of immunity to infection. This results in a massive increase in the number of worm eggs passed out in faeces. These develop to infective larvae on pasture, just as the worm-naive lambs begin grazing.
This is compounded by increased faecal output of ewes at this time due to consumption of large quantities of feed to meet nutrient demands of the rapidly growing foetus and milk production.
The reasons for this relaxation in immunity have been investigated for many years, and until recently little progress had been made. But research at Lincoln University, New Zealand has found a link between ewe nutrition in late pregnancy and her parasite status around lambing time.
Development and maintenance of resistance to worm infection in growing animals is closely related to feed intake, and particularly the protein component of the diet. The ewes nutrient requirements in late pregnancy and shortly after lambing, when demand for milk is high, reach similar levels to that of the growing animal in terms of protein to energy ratio and protein requirement/kg body weight.
Trials at Lincoln monitored parasite status of groups of ewes on diets which varied in both energy and protein content. It also compared infection levels in single and twin bearing sheep – the assumption being that if there was a nutritional basis to breakdown in resistance it would be more evident in twin bearing sheep than in singles.
Sure enough, twin bearing ewes were found to have faecal egg concentrations more than double those of single bearers. Worm burdens backed up this finding. Twin bearing sheep were found to have more than three times as many worms in their stomachs and intestines than single bearing ewes.
In terms of feed supply, results indicated that there was little, if any, effect on ewe parasite status from altering energy supply.
This was in marked contrast to the effect of increasing protein supply. Faecal egg concentrations were 10 times higher in ewes fed a basal metabolisable protein level – 100g/head/day – compared to those on a supplemented protein ration of 120g/head/day.
Again, this was backed up by worm counts. Sheep on basal protein diets had worm burdens almost eight times greater than those on the supplemented ration.
Basal diets were levels recommended to meet nutrient requirements of single and twin bearing ewes around this time in pregnancy and lactation. That meant the sheep were not protein deficient.
This suggests influencing the immunity of livestock may require a nutritional allowance above that for production.
But what do these findings mean for producers? At present, feeding additional protein may be uneconomic in comparison to anthelmintic treatment – particularly in the southern hemisphere where drenches are cheap to buy, and supplementary feeding is far less common. However, this may change depending on future availability of effective drenches, and advances in the ability to manipulate protein supply from pasture.
Trials have looked at protein supply from different forage species, and results are encouraging. In particular, plants containing condensed tannins, which influence protein supply to the animal, appear to improve performance of animals facing parasitic challenge. But it has yet to be determined whether this is protein effect, some anthelmintic effect of the condensed tannins, or simply a reflection of low larval concentration on these forages.
Although in the early stages, results suggest that potential exists to reduce pasture contamination by consideration of nutrient requirements of breeding ewes. This would appear to be particularly important in prolific flocks, where twin suckling lambs face greater worm challenge at the same time as receiving less milk than their single suckled counterparts.n
Ewe immunity to worm infection breaks down around lambing. The worm eggs passed in faeces develop to infective larvae on pasture just as worm-naive lambs begin grazing, warns researcher John Donaldson.
Feeding higher levels of protein to breeding ewes may help avoid the breakdown in worm infection immunity which occurs around lambing.
EWE WORM RISKS
• Immunity relaxed at lambing.
• Prolific ewes provide greatest risk to lambs.
• Feeding more protein may reduce risks.