The effects of dietary manipulation of polyunsaturated fatty acid intake on tissue fatty acid composition and immunity to infection with nematode parasites in the calf
Three experiments were carried out in calves to investigate the effect of changes in dietary PUFA supply on; the fatty acid composition of primary lymphoid organs and tissues, ex-vivo lymphocyte proliferation response, eosinophil and mucosal mast cell numbers in the gut and on immune response to nematode parasites Ostertagia ostertagi and Cooperia oncophora infection. In experiment 1, two groups of Jersey bull calves were fed on 25 g/day of either an n-3 enriched fish oil (FO) (n-3 group) or a binary mixture of palm/rapeseed oil (normal group) for a period of 21 days (n=10) or 42 days (n=12). In experiment 2, calves (n=40) were allocated at birth to 7 treatment groups, which received for 21 days oils supplements similar to experiment 1 in either whole milk or milk replacer. While in experiment 3, calves (n=24) were allocated to two dietary treatment groups (n=12) and fed oil supplements similar to experiment 1. Within each dietary treatment group, calves (n=8) were infected for 8 weeks (three times/week) with 2000 stage 3 larvae of Ostertagia ostertagi and Cooperia oncophora. The remaining calves (n=4) were uninfected controls. In experiments 1 and 3 calves were fed on 500 g/day of a standard milk replacer hay and calf weaner pellets (1.5 X maintenance of metabolizable protein (MP) and metabolizable energy (ME) requirements). 30-mg a-tocopherol acetate/kg PUFA was fed all the calves. In exp. 1 lymphocytes, plasma and tissue samples were collected for fatty acid analysis. In exp. 2 tissue samples were collected for fatty acid analysis, lymphocyte stimulation responses and determination of mucosal mast cells and eosinophils numbers. While in exp. 3 faeces samples were collected twice per week for faecal egg counts (FEC) and blood for plasma collection was sampled every week. At slaughter, tissue sample for fatty acid analysis were collected, while abomasal, duodenum and terminal ileum samples were collected for MMC and eosinophil counts. The gut contents from abomasum and intestine were washed and collected for worm counts. Tissue fatty acids reflected dietary fatty acid intake indicating that in young calf tissue fatty acids can be manipulated by dietary means. Tissues in the fish oil supplemented calves had a significantly (p<0.05) higher content of n-3 PUFAs and a lower n-6/n-3 ratio in most of the tissues examined. Ex-vivo peripheral blood mononuclear cells (PBMC), mesenteric lymph nodes (MLN) and spleen lymphocytes responses in the n-3 group were significantly (p<0.05) reduced. Mucosal mast cell (MMC) and eosinophil numbers were significantly (p<0.05) reduced in the n-3 group in both exp. 2 and 3 and were significantly increased (p<0.05) by infection in exp. 3. FEC were not significantly influenced by the oil supplement but were higher in the normal group.