Enhancing immunity to nematode parasites in pregnant and lactating sheep through nutrition and genetic selection

Susceptibility to infection from nematode parasites in sheep is most pronounced in young animals and in periparturient ewes. The susceptibility of young animals is a consequence of an inability to develop effective acquired immune responses to nematode parasites. In the periparturient ewe, susceptibility arises from a temporary loss of acquired immunity. Loss of immunity is associated with a rise in faecal egg counts (FEC) and this can increase the number of infective nematode larvae on a given mass of pasture. Greater pasture–larval counts will increase nematode infection of lambs. Strategies to reduce the periparturient rise in FEC will be of benefit to the ewe and to her progeny and increase animal production. Protein requirements of young sheep and periparturient ewes are high in relation to other classes such as non–reproductive animals. Increasing the supply of protein to the intestines of young sheep has been shown to improve resistance to nematode parasites and consequently lower FEC. A similar response has been observed in the periparturient ewe. Genetic selection for increased resistance to nematode parasites has been demonstrated to reduce FEC and lower the extent of the periparturient rise. In this review, the effects of and interactions between genetic selection and nutrition on resistance to infection from nematode parasites are discussed. Given the current situation of endemic drench resistance, non–chemical approaches to control disease are of great value.