Effect of forage/concentrate ratio and soybean oil supplementation on milk yield, and composition from Sarda ewes

Abstract

Sixteen lactating Sarda ewes were fed four diets differing in the forage/concentrate ratio (two diets 75/25, two diets 60/40, on a DM basis) and in soybean oil supplementation (two diets with 100 g·d-1 oil, two diets with no oil), in a 4 x 4 Latin square design. The inclusion of soybean oil in the diet resulted in a significant increase of both daily milk yield and fat corrected milk (P ≤ 0.01), while diets with higher concentrate content resulted in lower levels of milk production (P ≤ 0.05). Milk fat content did not differ among treatments, while milk fat yield was increased when ewes consumed oil added diets (P < 0.01). Milk protein content was lower when oil was added to the diet (P ≤ 0.01), which was attributed to a dilution effect, while milk protein secretion did not differ among treatments. Dietary soybean oil modified the milk fatty acid composition towards a lower level of medium chain and saturated fatty acid and a higher level of PUFA and CLA, confirming how an adequate dietary strategy can broadly modify sheep milk quality towards a more desirable composition for human health. In particular, soybean oil in the diet resulted in a significant increase of both rumenic acid (cis-9, trans-11 CLA) and vaccenic acid (trans-11 C18:1) in milk fat. Interactions among forage and oil resulted in a significant increase in rumenic acid and vaccenic acid with the HF/O diet and trans-10 C18:1 and trans-10, cis-12 CLA with the LF/O diet, probably due to a shift in rumen biohydrogenation of linoleic acid. © INRA, EDP Sciences, 2006.