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Replacing alfalfa silage with birdsfoot trefoil silage varying in tannin content in lactating cow diets
Silages made from birdsfoot trefoil (BFT) containing 3 levels of condensed tannins (CT) were compared to alfalfa silage (AS) as the principal forage in the diets of lactating dairy cows. Thirty-five multiparous and 15 primiparous Holstein cows were fed a covariate diet for 2 wk then blocked by parity and DIM and randomly assigned to one of 5 diets in a trial of randomized complete block design. Experimental diets were fed as TMR for 12 wk and contained 48% (dry matter (DM) basis) AS, or 16% AS plus 32% BFT with low CT (BFTL), normal CT (BFTN), high CT (BFTH), or a mixture with equal DM from all 3 BFT silages. The BFTL, BFTN and BFTH contained, respectively, 5.1, 8.4 and 14.8 g CT/kg DM. The balance of dietary DM was fed as corn silage, high moisture shelled corn, soybean meal, soy hulls, Energy Booster<sup>®</sup>, macro and trace minerals, plus vitamins A, D and E. Diets were formulated to 16.5% CP and 30% NDF. Statistical analyses were performed using the mixed procedures of SAS. Intake and yield of milk, ECM, true protein, lactose and SNF were greater (P < ??) on BFTL and BFTN than on AS and BFTH, while BFT mix was intermediate. Apparent N-efficiency also was numerically higher (P > ??) on BFTL and BFTN than the other 3 diets; MUN was lower (P < ??) on all BFT diets than on AS. These results suggest that CT concentrations of approximately 5 to 8 g/kg DM in BFT improve utilization of forage nutrients for milk production.
Keywords: birdsfoot trefoil, condensed tannins, milk production