Low levels of condensed tannins enhance lactation performance in dairy cows

This study was conducted to determine the effects of relatively low doses of supplemental condensed tannins (CT) on nutrient intake and apparent total-tract digestibility, feed particle sorting index, ruminal fermentation parameters, milk yield and composition, serum concentrations of glucose and urea-N, nitrogen use, and urinary purine derivatives excretion in dairy cows. Twenty-four Holstein cows (171 ± 26 days in milk, 33.8 ± 1.16 kg/d milk yield), of which 4 were ruminally cannulated, were blocked according to the presence of cannulas, parity number, milk yield, and days in milk. Cows were assigned to a 4 × 4 Latin square experimental design, with cows within blocks randomly allocated to a sequence of treatments, which included the following: control (CON), or a feed additive with CT (73.5 g/kg minimum guarantee of CT) supplemented at 0.06, 0.12, and 0.18 % diet DM (CT1, CT2, and CT3, respectively). The feed additive was mixed into the concentrate. Experimental periods consisted of 21 d, with the last 7 days designated for sampling and data collection. Differences among treatments were evaluated using linear and quadratic contrasts. Dry matter intake (DMI) tended to be quadratically affected by CT doses (27.6, 27.0, 26.3, and 27.0 kg/d, for CON, CT1, CT2, and CT3, respectively). Feed sorting index or apparent total-tract digestibility of nutrients were not affected by treatments. Ruminal pH and concentrations of NH₃-N and total volatile fatty acids were not influenced by treatments. Milk yield (32.7, 32.8, 32.8, and 33.6 kg/d, for CON, CT1, CT2, and CT3, respectively), fat-corrected milk yield (FCM), and yields of fat and protein linearly increased with CT. Milk urea nitrogen concentration tended to be quadratically affected with CT doses. Feed efficiency (FCM/DMI) exhibited a quadratic response according to CT dose (1.24, 1.27, 1.33, and 1.26 kg/kg, for CON, CT1, CT2, and CT3, respectively). Serum concentrations of glucose and urea-N were similar across groups. CT tended to linearly increase the efficiency of consumed N converted into milk N. Urinary purine derivatives excretion was not affected by treatments. Relatively low dietary doses of CT (up to 0.18 % diet DM) linearly increased FCM yield, without affecting the apparent total-tract digestibility of DM, ruminal fermentation parameters, or markers of microbial protein synthesis. Lower doses of supplemental CT than traditionally used can improve milk fat yield of lactating cows.