Effect of feeding different types of sugars on rumen fermentation and productivity of lactating dairy cows
The objective of this study was to investigate the effect of feeding different types of sugar (sucrose or lactose) on rumen fermentation and milk production of lactating dairy cows. Our hypothesis was that sucrose diets have lower rumen pH and milk fat yield compared with diets supplement with lactose. Twenty-eight multiparous lactating Holstein cows (141 ± 50 DIM; 614 ± 53 kg of BW) including 8 ruminally cannulated cows were used in this study. Cows were assigned to four dietary treatments in a 4 × 4 Latin square design. Two high sugar diets contained 27% starch and 9% sugar with sucrose (SUC) or lactose (LAC) as a supplemental sugar. In addition, high starch diet (STA) contained 32% starch and 4% sugar, and control diet (CON) contained 27% starch and 4% sugar. All diets were formulated to contain 17% crude protein. There was no significant difference in DMI between two high sugar diets, but it was higher for SUC than CON (27.8 vs. 26.2 kg/d; P < 0.01). In addition, both high sugar diets had higher DMI than STA diet (27.8 and 26.9 vs. 25.5 kg/d; P < 0.01). There was no difference in minimum rumen pH, duration and area of rumen pH < 5.8 among treatments, though LAC diet tended to have lower mean rumen pH than STA diet (6.17 vs. 6.32; P = 0.08). Milk yield and milk composition were not different between two high sugar diets, but STA diet had lower fat yield compared to CON, SUC and LAC diets (1.26 vs. 1.36, 1.32 and 1.33 kg/d; P < 0.01). Milk CP yield tended to be higher for SUC diet than STA diet (1.32 vs. 1.26 kg/d; P = 0.08), and both high sugar diets had higher CP concentration than CON (3.51 and 3.50 vs. 3.46%; P = 0.04). However, all STA, SUC and LAC diets had lower MUN concentration compared with CON (13.2, 12.9 and 13.3 vs. 14.5 mg/dL; P < 0.01), which was probably due to more carbohydrate fermentation in the rumen for high-starch or high-sugar diets compared with CON diet, providing more energy for microbes to capture NH3-N. These results suggested that feeding different type of sugar (sucrose or lactose) to lactating cows might not affect rumen fermentation and animal performance.
Keywords: sucrose, lactose, milk fat content