Effect of corn and beet pulp based concentrates on sheep milk and cheese fatty acid composition when fed Mediterranean fresh forages with particular reference to conjugated linoleic acid cis-9, trans-11

Abstract

Sixty-four Sarda dairy sheep fed fresh forage based diets were allocated to eight groups in early lactation ( i.e., 44 days in milk, winter period, growing stage of the forages) and at mid-lactation ( i.e., 98 days in milk, spring period, reproductive stage of the forages) to evaluate effects of corn grain or beet pulp based supplementation on milk and cheese fatty acid (FA) composition. Four forage species were compared, being: annual ryegrass (RY; Lolium rigidum Gaudin), sulla (SU; Hedysarum coronarium L.), burr medic (BM; Medicago polymorpha L.) and crown daisy, (CD; Chrysanthemum coronarium L.). The supplements differed in carbohydrate composition consisting either of 600 g/kg (dry matter basis) corn grain (concentrate C) or 400 g/kg sugar beet pulp (concentrate BP) and were offered at a fixed rate (C, 500 g/day; BP, 530 g/day) to provide a similar metabolizable energy and crude protein supply. Forage species affected (P<0.05) all variables studied. In both experimental periods, CD and BM forage groups had higher levels (P<0.05) of conjugated linoleic acid and a lower atherogenicity index (an index of human health benefits) in milk and cheese relative to other groups. Oleic and linoleic acid were also influenced by forage species, with higher level in milks and cheeses of sheep fed crown daisy relative to the other groups. Concentrate source did not influence standard milk yield in winter (1347 ml/day) but BP fed ewes yielded more milk than C fed ewes in spring (1209 and 1099 ml/day, respectively; P<0.01). In winter, while the forages were at vegetative stage, concentrate supplementation did not affect milk fat content (52.0 g/kg versus 52.7 g/kg, respectively) but BP fed ewes had lower milk protein content than C ewes (47.6 g/kg versus 49.1 g/kg, respectively; P <0.01). In contrast, in spring forage at a reproductive stage, BP supplemented ewes had higher milk fat (59.1 g/kg versus 55.5 g/kg; P<0.01) and tended to have higher milk protein (47.4 g/kg versus 46.5 g/kg; P = 0.08) contents than C ewes, respectively. Proportion of VA (31.1 g/kg versus 27.5 g/kg; P<0.01) in cheese FA were higher in BP versus C supplemented ewes, whereas C ewes outperformed BP for cheese C18:2 (linoleic acid) (25.6 g/kg versus 28.4 g/kg; P<0.01) and C18:3 (linolenic acid) (16.4 g/kg versus 18.3 g/kg; P<0.01) in winter. In spring, PUFA cheese levels were higher in C versus BP groups when ewes were fed CD forage (60.6 g/kg versus 68.8 g/kg; P<0.05). Only small differences occurred between the FA profile of ripened cheeses and milks within dietary treatment. This study provides evidence that forage species, and to a lesser extent the source of carbohydrate in the concentrate, influence milk and cheese FA profiles.