Effect of nutritional status and fat reserves on the periparturient immune response to Haemonchus contortus infection in sheep.

A study was made of the effect of body fat stored by ewes in early pregnancy on the subsequent immune response to gastrointestinal parasites around parturition. Pregnant ewes were given access to a lucerne pelleted diet either ad libitum (H) or at approximately 0.70 of their maintenance requirements (L) from the 42nd day of pregnancy in order to achieve a clearly differentiated level of body reserves by the 90th day of pregnancy. Then, all animals were put on the same plane of nutrition till 3 weeks after parturition. All ewes in both groups received 7,000 infective larvae of Haemonchus contortus per week for 7 weeks prior to lambing. The dietary treatments led to large differences between both groups of ewes in back-fat thickness that had a high correlation with mean plasma concentrations of leptin. In spite of the fact that animals were on the same plane of nutrition at infection time, host resistance, as measured by faecal egg counts, was significantly affected by the nutritional treatment established during early pregnancy. This effect produced noticeable differences in worm size and in worm burden at lambing. The response was accompanied by a marked increase in circulating eosinophils in better-fed ewes than in those maintained on a restricted diet in early pregnancy. Serum pepsinogen concentration, however, was inversely affected by the nutritional treatment till lambing, showing a maximum difference as early as 2 weeks after infection. The results support the view that higher levels of nutrition during early pregnancy enhance the expression of immunity against gastrointestinal parasites around parturition. Furthermore, the differences in the immune response appeared associated with serum leptin levels suggesting that leptin may be a key link between nutritional status and the protective immune reactivity against GI nematode infection.