Effect of dietary soybean or sunflower seeds on milk production, milk fatty acid profile and yield of conjugated linoleic acid

Eight cows in mid-lactation were used to determine the effects of feeding diets containing soybeans (SBS) or sunflower seed (SFS) on conjugated linoleic acid (CLA) yield and concentration in milk during two 3-wk periods. All cows were fed a standard pre-trial diet for 2 wk, before assignment to treatment diets in both periods of the 2 x 2 cross-over design used in the study. The two treatment diets contained on a dry matter (DM) basis: (1) SBS: 20% barley silage, 34.7% barley grain, 30% alfalfa cube, 13% crushed soybean seed and 0.36% sunflower oil, and (2) SFS: 17% barley silage, 34.6% barley grain, 40% sunflower seed incorporated into alfalfa cubes (cubes comprised 18% whole sunflower seed and 82% alfalfa hay), and 6.5% heat-treated soybean meal. The ingredients in the two diets were adjusted so that they would provide similar levels of energy (1.5 MCal kg(-1)) and have similar nutrient composition with regard to protein (16.7%), ether extract (5.2%) and fibre components (41%). Milk samples were collected, on 2 d prior to initiation of treatment diets and on days 6, 7, 13, 14, 20 and 21 of each experimental period. Cholecystokinin and insulin concentrations in blood samples collected at the start and end of each experimental period indicated no significant differences. Dry matter and net energy intake of cows fed the SBS and SFS were 23.3 and 21.4 +/- 0.9 kg d(-1); 34.4 and 31.6 +/- 1.4 Mcal d(-1), respectively, and in vitro volatile fatty acid concentration after 24 h of incubation was 123.3 and 114.7 +/- 1.3 mM, respectively, and lower (P < 0.05) for the SFS diet. Milk, milk fat, protein and lactose yields from cows fed the SBS and SFS diets were similar (32.9 and 32.0 +/- 2.4; 1.10 and 0.97 +/- 0.07; 1.05 and 1.00 +/- 0.05; 1.46 and 1.39 +/- 0.12, respectively), but the CLA cis-9, trans-1l concentrations in the milk from cows fed the SBS and SFS diets were 4.05 and 7.28 mg g(-1) of lipid and resulted in 66% higher (P < 0.01) CLA yield (g d(-1)) in milk for cows fed the SFS diet. This study confirmed that feeding sunflower seeds as a component of a hay cube increased CLA yield in the milk of dairy cows without affecting yields of other milk components.