Replacing alfalfa or red clover silage with birdsfoot trefoil silage in total mixed rations increases production of lactating dairy cows1

摘要

The objective of this study was to compare milk production and nutrient utilization in dairy cattle fed silage made from alfalfa (AL) or red clover (RC) versus birdsfoot trefoil (BFT) selected for low, normal, and high levels of condensed tannins. Condensed tannin contents of the 3 BFT silages were 8, 12, and 16 g/kg of DM by butanol-HCl assay. Twenty-five multiparous Holstein cows (5 fitted with ruminal cannulas) were blocked by days in milk and randomly assigned within blocks to incomplete 5 Χ 5 Latin squares. Diets contained [dry matter "(DM) basis] about 60% AL, 50% RC, or 60% of 1 of the 3 BFT; the balance of dietary DM was largely from high-moisture corn plus supplemental crude protein from soybean meal. Diets were balanced to approximately 17% crude protein and fed for four 3-wk periods; 2 wk were allowed for adaptation and production data were collected during the last week of each period. No differences existed in DM intake or milk composition due to silage source, except that milk protein content was lowest for RC. Yields of milk, energy-corrected milk, fat, protein, lactose, and solids-not-fat were greater for the 3 BFT diets than for diets containing AL or RC. Feeding BFT with the highest condensed tannin content increased yield of milk, protein, and solids-not-fat compared with BFT containing the lowest amount of condensed tannin. Moreover, milk-N/N-intake was higher, and milk urea nitrogen concentration and urinary urea-N excretion were lower for diets with normal levels of BFT than for AL or RC diets. Feeding RC resulted in the highest apparent digestibility of DM, organic matter, neutral detergent fiber, acid detergent fiber, and hemicellulose and lowest ruminal concentrations of ammonia and free amino acids. Ruminal branched-chain volatile fatty acid levels were lowest for RC diets and diets with high levels of BFT and highest for the AL diet. Overall, diets containing BFT silage supported greater production than diets containing silage from AL or RC. The results indicated that feeding BFT or other legume silages containing condensed tannins can enhance performance and N utilization in lactating dairy cows.