Milk production and in sacco disappearance of pasture NDF in grazing Jersey cows receiving a barley based concentrate
The aim of the experiment was to determine the effect of feeding low (2.4 kg/d), medium (4.8 kg/d) and high (7.2 kg/d) levels of a barley-based concentrate on milk production and in sacco ruminal disappearance of dry matter (DM) and neutral detergent fibre (NDF) in Jersey cows grazing a Westerwold ryegrass pasture. Sixty Jersey cows in early- to mid lactation were randomly allocated to one of three treatments (n = 20). Milk production tended to increase when concentrate level was increased from 2.4 to 4.8 kg/day. Fat corrected milk yield, milk fat yield and milk fat percentage were not affected by treatment. Protein yield only increased when the concentrate level was increased from 2.4 to 4.8 kg/cow per day but there was no further increase when feeding the high level of concentrate. Live weight change and body condition score only increased when the concentrate was fed at 7.2 kg/cow per day. An additional 12 Jersey cows, fitted with ruminal cannulae, were randomly allocated to the High and Low concentrate treatments in a two-period crossover design. Rumen liquid samples were collected every four hours for the determination of rumen pH and volatile fatty acid (VFA) concentrations. Rumen pH was not affected by treatment while total VFA, acetate and isovalerate concentrations increased when the level of concentrate mixture was increased. Rumen NH3-N concentrations were not affected by treatment. The in situ nylon bag technique was used to determine DM and NDF degradation of the pasture. Pasture samples were incubated in the rumen for 0, 4, 8, 12, 20, 30, 48, 72 and 96 hours. Increasing the concentrate mixture did not affect in situ disappearance of pasture DM and NDF, or the rate of degradation. It was concluded that the supplementation of a barley based concentrate to pasture based Jersey cows does not improve animal response when fed at levels higher than 4.8 kg/cow per day.
South African Journal of Animal Science Vol. 37 (2) 2007: pp. 81-89