Effects of Supplemental Carbohydrate Sources on Lactation Performance, Nitrogen Balance, and Ruminal Fermentation in Dairy Cows Fed Energy-Deficient Total Mixed Rations

摘要

The effects of supplemental carbohydrate (CHO) sources on milk yield and composition, nitrogen (N) balance,and ruminal fermentation were evaluated in lactating dairy cows fed energy-deficient total mixed rations (TMR) . Fifty-six lactating Holstein cows (36. 8 ± 3. 4 kg / d of milk yield; 152 ± 26 days in milk [DIM]) were randomly assigned to one of four diets: (1) basal TMR (control) ; (2) basal TMR + 1. 25 kg / d sucrose (SUC) ; (3) basal TMR + 2. 12 kg /d steam-flaked corn (SFC) ; (4) basal TMR + 2. 23 kg / d wheat (WHE) . The trial lasted 70 days,including the first 10 days of adaptation. Simultaneously, a 4 × 4 Latin square trial was conducted with four ruminally cannulated cows of similar DMI (Dry Matter Intake) fed on the above four diets. Each testing period lasted 18 days: 15 days for adaptation and 3 days for sampling. Cows fed SUC-,SFC-,and WHE-supplemented diets produced 1. 6,2. 9,and 0. 8 kg / d,respectively,more milk than those on the basal TMR control diet,but the difference was not significant (P = 0. 160) . However,the production of energy-corrected milk of cows fed CHO-supplemented diets improved significantly (P = 0. 020) ,and the yield of 4% fatcorrected milk tended to be higher (P = 0. 063) than in control animals. Percentages of milk protein,lactoseand solids-not-fat (SNF) increased significantly in cows fed CHO-supplemented diets (P 0. 10) . The average ruminal pH was lowest in cows supplemented with SUC,while that in cows supplemented with SFC and WHE was only slightly reduced (P = 0. 025) . Ruminal NH 3 -N concentration was highest with no supplementary CHO (P = 0. 017) ,and changes in postfeeding time were similar across the diets. Total volatile fatty acid concentration was significantly lower in control animals than in those on SUCand WHE-supplemented diets (P = 0. 001) ; significant dietary responses were observed in the concentrations of acetate,butyrate,and branchedchain fatty acids and in the acetate-to-propionate ratio (P <0. 001) . These results indicate that supplementation with different CHO sources in energy-deficient diets substantially improved the balance of energy and N in the rumen,altered ruminal fermentation,and improved lactation performance in dairy cows.