Bulkiness and protein treated with zinc ions in concentrates for grazing dairy cows

Abstract

Conventional or high fiber concentrates, formulated with or without treated protein, were compared using 12 Holstein cows in a repeated 3 × 3 Latin square dice experiment, with periods of 21 days in a dry season. Rotational grazing was at a rate of 4.8 animals / ha in non-fertilized grass forage. As supplements, three commercial concentrates were used, with theoretical levels of 1.76 Mcal of net energy / kg and 13% of crude protein (CP) in dry matter (DM). Concentrates B and C contained protein protected against ruminal degradation by treatment with zinc ions, unlike A (control); C was bulky, but with 5.25 fat to adjust for energy value. Forage on offer was estimated at 20.2, 22.1 and 14.0 kg DM / cow-day during the three periods, with 5.68% CP and 46.0% digestibility in vitro. The molar ratios of acetate / propionate (A / P) formed in vitro were 2.29 with the forage and 1.93, 2.42 and 2.52 with three concentrates in that order. The average results obtained with treatments A, B, and C were: daily consumption of DM of concentrate 7.69, 7.61 and 7.78 kg; daily milk production corrected to 4% fat: 14.0, 13.5 and 14.2 kg; fat percentage, 3.21, 3.04 and 3.79; daily increase in live weight, 0.36, 0.46 and 0.51 kg. The bulky concentrate promoted a higher fat content in the milk, associated with a high A / P. The lack of a productive stimulus of the supplemental protected protein suggests that intestinal amino acid absorption was not limiting or that such absorption was not increased.