The Effects of Graded Abomasal Glucose Infusion on Milk Yield and Composition in Lactating Goats

Four non-pregnant multiparous lactating goats were used in a 4 × 4 latin square experiment in the present study. The four treatments were abomasal infusion of 0, 50, 100, and 150 g d-1 glucose. The results showed that graded glucose infusion increased milk yield (P < 0.01). The highest milk yield was observed when 50 g d-1 glucose was infused. An infusion of glucose at 100 or 150 g d-1 failed to increase milk yield further and milk yield of the 100 g d-1 glucose infusion treatment was even significantly lower than that of the 50 g d-1 treatment (P < 0.01). Though milk fat content was gradually decreased by graded glucose infusions and milk fat yield of the 100 and 150 g d-1 treatments were lower than that of the control (P < 0.01); milk fat yield of the 50 g d-1 treatment was not depressed and was higher than that of the control (P < 0.01). Graded glucose infusion did not change the contents of milk protein and non-fatty solids. Yields of milk protein (P < 0.05), lactose (P < 0.01), non-fat solids (P < 0.01), and lactose content (P < 0.01) of the 50 g d-1 treatment were higher than those of the control but had no difference among the other three treatments. Contents of those de novo synthesized fatty acids in milk fat remained unchanged or increased and those preformed fatty acids remained unchanged or decreased by graded glucose infusion. Glucose infusion decreased the total yields of C16 + C16:1 and > C16 fatty acids and had no influence on the yield of C4-C14:1 fatty acids (P < 0.05). Results of the present study implied that increased glucose supply had positive effects on the production of milk, milk protein, milk fat, and lactose only when glucose was a limiting factor for milk synthesis. Excessive glucose supply had no further beneficial effects and might depress milk fat synthesis.