ADDITION OF RUMINALLY DEGRADABLE CRUDE PROTEIN AND BRANCHED-CHAIN VOLATILE FATTY-ACIDS TO DIETS CONTAINING HYDROLYZED FEATHER MEAL AND BLOOD MEAL FOR LACTATING COWS

This study investigated the effects of amounts of RDP and branched-chain VFA on milk production and DMI by 32 early lactation Holstein cows fed diets based on corn silage and corn. All supplemental dietary protein was supplied by animal protein by-products and urea. Hydrolyzed feather meal and ring-dried blood meal served as sources of supplemental protein and were fed in a 3:1 ratio on a N basis. The experimental design was a completely randomized design with a 2 x 2 factorial arrangement of treatments. Main factors were percentage of RDP (8.0 vs. 9.5% of dietary DM) and amount of branched-chain VFA in the diet (0 vs. 90 g/d per cow). Urea was used to adjust the amount of degradable CP. Individual DMI, milk production, and milk composition were monitored during wk 5 to 19 of lactation. Ruminal fluid and blood were collected to examine the treatment effects on ruminal VFA patterns and plasma urea N concentrations. The DMI, total milk production, and milk component yield were unaffected by treatments. The molar percentages of isobutryate, isovalerate, and n-valerate increased when branched-chain VFA were fed, and concentrations of urea N in plasma increased with higher percentages of RDP. A combination of feather meal and blood meal can be used as supplemental protein to support high milk production (>37 kg/d) in early lactation. No production benefits were observed by increased dietary RDP or branched-chain VFA.