Effects of an exogenous enzyme, Roxazyme® G2 Liquid, on milk production in pasture fed dairy cows

A study was conducted to determine effects of a predominantly xylanase and endoglucanase exogenous enzyme (EE) product, Roxazyme® G2 Liquid, on milk production of early lactation (80 ± 18.2 days in milk) dairy cows grazing pastures in a subtropical environment. Holstein Friesian cows (n = 72) were allocated to one of six treatments in a 2 × 3 factorial design comprising either dry-rolled barley or sorghum grain supplements (6.7 kg dry matter (DM)/day) treated with one of three levels of applied EE (i.e., 0, 2.15 or 4.30 ml/kg DM, Control, Low and High levels, respectively) diluted with water to 20 ml/kg DM concentrate. Cows (549 ± 47.9 kg live weight (LW)) grazed irrigated prairie grass (Bromus willdenowii cv. Matua) and biennial ryegrass (Lolium multiflorum cv. Concord) pastures during the 75-day treatment period, with individual feeding of supplement occurring at the morning (4.0 kg DM) and evening (2.7 kg DM) milkings. Rumen fluid samples were collected 2 and 6 weeks after supplementation commenced prior to (05:00–06:45 h) and 6 h after (10:40–13:00 h) the morning feeding. The EE application caused a linear decline (P<0.05) in LW gain of cows fed the sorghum supplement, but not in cows fed the barley supplement. There were no effects of EE supplements on body condition score changes. Milk yield (28.6 l/day) and composition were unaffected by grain type or EE supplementation, although milk fat yields were numerically (P=0.112) lower for cows on the High EE supplementation level versus unsupplemented cows (960 g/day versus 1010 g/day, respectively). EE treatment had no effect on supplement intake or estimated pasture intake. Despite some grain-specific effects on rumen fermentation, including NH3-N and VFA concentration changes, we conclude that there are no beneficial effects of supplementing dairy cows grazing C3 dominant pastures with the fibrolytic enzyme Roxazyme® G2 Liquid.