ALTERATION OF MILK-FAT BY VARIATION IN THE SOURCE AND AMOUNT OF STARCH IN A TOTAL MIXED DIET FED TO DAIRY-COWS

The effect on milk yield and composition of the supplementation of the diets of dairy cows with wheat or potato peelings was studied at thre e different starch intakes (<5, 6, and >7.5 kg/d) for dry matter intak es around 20 kg/d. Starch supply was varied using different dietary co ncentrations of corn silage. Trials were conducted using Latin square designs, and all cows were fed a total mixed diet composed of corn sil age, grass silage, or both; soybean meal; a mixed meal with formaldehy de treatment; minerals; and one of the following energy concentrates: potato peelings or wheat. Dry matter and energy intakes varied signifi cantly only at the low starch concentration; higher intakes were obser ved when the potato peelings were fed. Body weight, milk yield, true p rotein content, lactose content, and protein yield were not affected b y treatment. Milk fat content was higher (+3.3 g/kg) when potato peeli ngs were fed at the high starch concentration but was unaffected at th e low and medium starch concentration. Slow degradation of starch from the potato peelings in the rumen could enhance a higher delivery of p recursors of milk fat synthesis in the udder. The effect on fat yield differed among starch concentrations. Milk fat content appeared to dec rease for cows fed diets containing quickly degradable starch at a sta rch intake >7 kg/d.