Changes in piglet tissue composition at birth in response to increasing maternal intake of long-chain n-3 polyunsaturated fatty acids are non-linear

Addition of marine oils containing long-chain n-3 polyunsaturated fatty acids to the diet of pregnant sows may reduce piglet mortality. In previous experiments, when marine oils have been fed to pregnant sows, improvements in piglet tissue 22 : 6n-3 status have been accompanied by potentially undesirable decreases in 20 : 4n-6. The objective of the present experiment was to establish an amount of dietary salmon oil which would enhance piglet 22 : 6n-3 status while minimising reductions in 20 : 4n-6. Twenty-four pregnant multiparous sows were used in the experiment which began on day 60 of pregnancy (gestation length 115 d). To give four diets, salmon oil was added in increasing amounts (0, 5, 10 and 20 g/kg diet) to a basal diet; the diets were made isoenergetic by adding palm oil to each diet to give a total of 20 g oil/kg diet. Diets were offered to the sows in fixed amounts (2.5 kg/d) until parturition. Piglet tissue samples (brain, liver and retina) were obtained at birth before consumption of colostrum. The greatest increase in piglet tissue 22 : 6n-3 proportions occurred between 0 and 5 g salmon oil/kg diet, with only small increases between 10 and 20 g salmon oil/kg diet. In contrast, tissue 20 : 4n-6 proportions declined progressively as the amount of salmon oil fed to the sow increased. In brain, the change in the value 22 : 6n-3/22 : 5n-6 was greatest between 0 and 5 g salmon oil/kg diet, whereas in liver the value increased linearly with added salmon oil. In addition, piglet brain weight (g/kg live weight) increased to a maximum at 10 g salmon oil/kg diet. The optimum amount of supplementary salmon oil in the current experiment, defined as that which gave the greatest response in brain 22 : 6n-3 proportions with minimum reduction in 20 : 4n-6,was 10 g salmon oil/kg diet. This corresponds to an intake of approximately 2.4 g 20 : 5n-3 plus 3.6 g 22 : 6n-3/d or 0.6 % digestible energy.