Effects of altering dietary fatty acid composition on prostaglandin synthesis and fertility

Several studies over the past 20 years have demonstrated that subjects on d iets composed of substances with high levels of n-3 polyunsaturated fatty a cids (PUFAs) (e.g. fish) have a decreased incidence of heart disease. On th is basis, a recent report from the Department of Health has advised UK cons umers to decrease the proportion of saturated as opposed to unsaturated fat s in their diet and to increase the ratio of n-3 to n-6 PUFAs. This could b e achieved by altering the amounts of these constituents in milk and meat. n-3 Fatty acids can most easily be added to animal feed as either fish oil or linseed oil and can be increased in the blood and milk of ruminants foll owing protection to avoid hydrogenation in the rumen. In western countries the ratio of consumption of n-6 to n-3 PUFAs is greater than 10 and current evidence tends to suggest that a ratio nearer 5 would be more desirable an d compatible with cardiovascular well being. As fertility in the UK dairy h erd is already poor, it is important to establish whether alterations in di etary n-3 and n-6 PUFAs affects herd fertility before widespread changes in animal diets are recommended. Therefore, this review considers the role pl ayed by PUFAs and eicosanoids in fertility, with particular reference to th e implications for farm livestock production. The evidence reviewed shows that alteration of the concentration and ratio of n-6 and n-3 PUFAs in feeds can influence prostaglandin synthesis/metabol ism in a number of mammalian systems. The changed patterns of prostaglandin synthesis can as a consequence, affect the diverse functions (e.g. hormone secretion) that are normally mediated via prostaglandins. Similarly, chang es in prostaglandin synthesis effected through manipulation of PUFAs has a major bearing on fertility (as PGs affect many reproductive parameters, e.g . ovulation). Several studies in cattle and other mammals, show that feedin g or infusing different types of fat with varying PUFA content to females c an alter: the number and size of ovarian follicles, the ovulation rate, pro gesterone production by the corpus luteum, the timing of luteolysis and ges tational length. In the male most recent work has focussed on sperm product ion and experiments in fowl have demonstrated clear effects of dietary PUFA s on both the sperm membrane phospholipid composition and on fertilizing ab ility. (C) 1999 Harcourt Publishers Ltd.