Abstract

Post-ruminally infused casein has increased milk and milk protein yield in post-partum cows. We theorised top dressing (TD) higher amounts of soybean meal (SBM) might mimic these effects. Fifty-one multiparous Holstein cows 1 day after calving were assigned to 3 dietary treatments: a base total mixed ration (CON) with 196 g/kg crude protein and 329 g/kg neutral detergent fibre; 17 cows TD with l kg of SBM (SBM1); and 17 cows TD with 2 kg of SBM (SBM2) for 30 days. Milk and milk components were measured at days 9, 18, and 27. Rumen and urine samples were collected on day 27; blood samples were obtained on day 30. Statistical inference was by JMP software (Version 10.0.2, 2012) with production variables analysed as a repeated measures design. Cows fed SBM increased milk yield (P = 0.02; 35.4, 36.6, and 42.6 kg/day for CON, SBM1, and SBM2, respectively). Yield of milk true protein was notdifferent among treatments. Cows fed SBM had lower serum n on esterified fatty acids  concentrations at day 30 (1.35, 1.13, and 0.59 mM/l; P < 0.01). We conclude that SBM TD beginning immediately after calving may increase milk yield rapidly and decrease dependence on fatty acids for energy.