Essential-fatty acid supply of weanling piglets

This thesis describes research on the essential-fatty acid supply of weanling piglets. Vertebrates require dietary sources of essential fatty acids. The polyunsaturated fatty acids (PUFAs), linoleic acid (LA, C18:2 n-6) and a-linolenic acid (ALA, C18:3 n-3) are considered the parent compounds of the n-6 and n-3 families of PUFAs, respectively. The products of desaturation and elongation arachidonic acid (AA, C20:4 n-6) and eicosapentaenoic acid (EPA, C20:5 n-3), are the precursors for eicosanoids, which play an important role in the immune response. Eicosanoids produced from n-3 PUFAs generally have effects opposite to those elicited by eicosanoids synthesized from n-6 PUFAs. Due to the competition between n-3 and n-6 PUFAs for the desaturase and elongase enzymes, the net response to eicosanoids depends on the amounts and on the ratio of n-3 and n-6 PUFAs present in the diet. The experiments described may be interpreted in that the addition of n-3 PUFAs to the weaner diet may be beneficial, but only when the piglets have a low status of n-3 PUFAs at weaning. Thus, a literature review was made to identify the factors determining the fatty acid status at weaning. The fatty acid composition of fat mobilized by the sow and that of the lactation diet influence the fatty acid composition of the sows milk which then determines the fatty acid status of piglets at weaning. The risk to develop post-weaning disorders and post-weaning feed intake are negatively related. To put the potential beneficial effects of the fatty acid composition of the weaner diet in perspective the final experiment was done. In an attempt to increase post-weaning feed intake, piglets were fed diets with increasing water contents. An increase in the water content of the diet was found to raise dry matter intake, total water intake and body-weight gain in a dose-dependent fashion. When the magnitude of the effect on feed intake seen in this study is compared with that in the previous studies using diets with different fatty acid compositions, it follows that the effect of PUFAs is relatively small. This thesis has focussed on the dietary provision of PUFAs to weanling piglets in relation to growth performance and small intestinal integrity. The status of n-3 and n-6 PUFAs in piglets at weaning might determine their susceptibility to the development of post-weaning disorders. In agreement with this statement, it was found that fish oil, which is rich in EPA, tended to have a positive effect on the clinical response in weanling piglets to a pathogenic E. coli. It is suggested that the status of n-3 PUFAs at weaning relates to the risk of post-weaning growth depression and development of diarrhoea. The status of PUFAs at weaning is determined by the fatty acid status of the sow and the fatty acid composition of the weaner diet. Depending on the fatty acid status of the piglet at weaning, there may be no change of the status after weaning in spite of the low feed intake. The requirement of ALA by weanling piglets to display maximum growth is not known, but it may be above 0.22% of metabolizable energy. Dietary fish oil might positively affect growth of weanling piglets, with low status of n-3 PUFAs, this effect not being mediated by counteracting the weaning-induced decrease in villus height. However, the addition of fish oil to a weaner diet adequate in ALA and fed to weanling piglets with high status of n-3 PUFAs may not enhance growth performance, faeces consistency and body condition. When put in perspective, it is concluded that the potential beneficial effect of the fatty acid composition of the weaner diet, at least under practical situations, may only be marginal and certainly is much smaller than that obtained by measures that raise post-weaning feed intake