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

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 x 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 x L interactions ( P> 0.05) on pasture intake, neutral detergent fibre digestibility or rumen concentrations of ammonia or volatile fatty acids. There were G x 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.