The effects of dietary soybean oil on milk-fat composition in the cow

Abstract

SummaryThe effects of the isocaloric replacement of starch in a low-fat concentrate mixture by 8% soybean oil on the yield and composition of milk fat were investigated in a feeding experiment with 6 cows in mid lactation. Two high-fat concentrate mixtures were given to the cows. In one the requisite amount of soybean oil was given by including 50% coarsely ground soybeans in the concentrate mixture. In the other an equal amount of soybean oil was added directly to the concentrate mixture. The concentrate mixtures were given with a high-roughage diet that supplied 5·5kg hay and 2·7kg of sugar-beet pulp/day.When the 2 high-fat rations were given to the cows there were reductions in the percentages and yields of 10:0, 12:0, 14:0, 14:1, 16:0 and 16:1 fatty acids and increases in the concentrations and yields of 18:0, 18:1 and 18:2 fatty acids in the milk fat. The direct addition of the soybean oil to the diet also reduced the percentage and yield of 6:0 and 8:0 whilst the inclusion of the soybeans increased the percentage of 4:0 and the yields of 4: 0 and 6:0 in the milk fat.When both high-fat rations were given to the cows there were increases in the yields and concentrations of as-9–18:1 in the milk fat, whilst inclusion of the soybean oil in the diet increased also the concentration and yield oftrans-11–18:1.The implications of these findings are discussed.