Effects of supplement grain type and level of feeding on the milk production of early-lactation Holstein - Friesian cows grazing temperate and tropical pastures

Abstract

Two experiments were undertaken to examine the effects of supplement grain type (barley v. maize) and level of feeding [4.5 v. 8.1 kg dry matter (DM)/cow.day] on the milk production, nutrient intake and rumen fermentation of cows grazing swards of biennial ryegrass (Lolium multiflorum cv. Concord), prairie grass (Bromus willdenowii cv. Matua) (expt 1) or kikuyu (Pennisetum clandestinum cv. Common) (expt 2). There were no interactions (P>0.05) between grain type and level of feeding (G × L) on milk production, liveweight change or condition score in either experiment. When the main effects were examined, feeding maize as opposed to barley resulted in higher milk protein concentrations (P = 0.001) in both experiments (2.96 v. 2.83% and 2.91 v. 2.71% for expts 1 and 2, respectively), higher milk fat concentration (P = 0.001; 3.85 v. 3.36%) and daily milk fat yield per cow (P = 0.029; 875 v. 791 g) in experiment 1, and higher daily yield (P = 0.004) of milk protein in experiment 2 (618 v. 578 g). In both experiments, feeding increased supplement resulted in higher (P<0.05) daily yields per cow of milk (24.1 v. 22.0 L and 23.6 v. 20.1 L for expts 1 and 2, respectively) and milk protein (703 v. 637 g and 646 v. 550 g for expts 1 and 2, respectively), and lower (P<0.05) milk fat concentrations (3.46 v. 3.76% and 3.25 v. 3.57% for expts 1 and 2, respectively). In both experiments, there were no G × L interactions (P>0.05) on pasture intake, neutral detergent fibre digestibility or rumen concentrations of ammonia or volatile fatty acids. There were G × L interactions on organic matter digestibility (P = 0.019) in experiment 1 and on starch digestibility (P = 0.003) in experiment 2, with cows fed 4.5 kg DM/day of barley having higher organic matter digestibility, and cows fed either level of barley having higher starch digestibility. In both experiments, feeding more supplement reduced (P>0.05) daily pasture intake per cow (13.3 v. 11.3 kg DM and 9.9 v. 8.3 kg DM for expts 1 and 2, respectively). Feeding barley rather than maize caused higher starch digestibility (P = 0.006) in experiment 1 (93.0 v. 89.8%), and higher organic matter digestibility (P = 0.021) and neutral detergent fibre digestibility (P = 0.009) in experiment 2 (70.8 v. 69.3% and 62.9 v. 59.7%, for organic matter digestibility and neutral detergent fibre digestibility, respectively). Feeding maize rather than barley reduced (P = 0.034) rumen molar proportion of butyrate (16.1 v. 17.6 mol %) in experiment 1. These experiments show that feeding supplements based on maize, as opposed to barley can: increase the milk fat concentration and yield of cows grazing temperate pastures; increase the milk protein yield of cows grazing tropical pastures; and increase the milk protein concentration of cows grazing either temperate or tropical pastures.