Effect of delactosed whey permeate on lactation performance and total-tract nutrient digestibility on high-producing dairy cows.

The objective of this study was to evaluate the effects of forage fiber and starch sources replacement with delactosed whey permeate (DLP) on lactation performance and total-tract nutrient digestibility of high-producing dairy cows. Ninety-six multiparous Holstein cows (88 ± 36 DIM) and dietary treatments were randomly assigned to 12 pens of 8 cows for an 8-wk treatment period, after a 2-wk covariate period. Treatments were diets fed without DLP (CON), 5% replacement of corn silage with DLP (LCS), and 5% replacement of high-moisture corn with DLP (LHMC). Data were analyzed as a completely randomized design with data from the 2-wk covariate period used as a covariate using a mixed model with week of treatment as repeated measures. The model included treatment, week, and their interaction as fixed effects, and treatment within pen as a random effect. The CON diet tended to have 1.4 kg/d greater DMI than LCS but did not differ from LHMC. The CON diet had a greater milk yield compared with LCS by 2.2 kg/d and LHMC by 2.7 kg/d. Similarly, cows fed CON had 0.04 percentage units and 0.07 percentage units greater milk lactose concentration compared with LHMC and LCS, respectively. Milk fat yield tended to be greater for CON than LCS, but concentration did not differ between treatments. Diets with partial replacement with DLP had 0.05 percentage units greater milk protein concentration. However, no effects on feed efficiency were observed with replacement with DLP. Digestibility of DM, OM, and CP were greater for LCS diet compared with LHMC by 3.4 percentage units, 3 percentage units, and 3.8 percentage units, respectively. Ether extract digestibility tended to be 4.1 percentage units greater for LCS than LHMC. Additionally, NDF digestibility of the LCS diet was greater than CON and LHMC by 6.1%, on average. These findings suggest that replacing high-moisture corn or corn silage with DLP may decrease milk yield and milk lactose concentration but increase milk protein concentration. However, DLP can have positive effects on total-tract digestibility when replacing corn silage but not when replacing high-moisture corn.