The effect of level of feeding and grain type on the milk production of cows grazing ryegrass / prairie pastures in a subtropical environment.

Abstract

1A The effect of level of feeding and grain type on the milk production of cows grazing ryegrass/prairie pastures in a subtropical environment B.C. Granzin NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar NSW 2477 brad.granzin@agric.nsw.gov.au It is recognised that milk fat yields can fall when cows fed ryegrass_based diets are supplemented with high levels of grain_based concentrates (Stockdale et al. 1987). This occurs primarily because of a reduction in acetate supply to the udder due to a fall in rumen concentrations of acetate and butyrate (AB) relative to propionate (P). Feeding slowly fermentable grains (e.g. maize) have been shown to increase rumen AB:P as opposed to rapidly fermentable grains (e.g. barley; Nocek and Tamminga 1991). Therefore, feeding supplements based on maize as opposed to barley could be an option to increase milk fat yields of cows grazing ryegrass. An experiment (23 August to 29 October 1999; 14 d adjustment period, 56 d observation period) was conducted at Wollongbar with forty_eight cows (32 early lactation, 16 mid_late lactation) grazing annual ryegrass (Lolium multiflorum cv. Concord)/prairie grass (Bromus wildenowii) pastures. Cows were fed daily either 4.5 or 8.1 kg DM of a barley or maize_ based concentrate. Both concentrates were rolled, isonitrogenous and isoenergetic. The average rumen availabilities of starch of the maize and barley_based supplements were 32 and 80% respectively. The results in Table 1 show that cows fed a maize_ based supplement had higher concentrations of milk fat and milk protein, and higher milk fat yields compared to cows fed a barley_based supplement. Rumen acetate concentrations were higher in cows fed the maize_based concentrate which could explain the increase in milk fat yield. Financial assistance from Dairy Research and Development Corporation is acknowledged. Nocek, J.E., and Tamminga, S. (1991). Site of digestion of starch in the gastrointestinal tract of dairy cows and its effect on milk yield and composition. Journal of Dairy Science 74, 3598_3629. Stockdale, C.R., Callaghan, A. and Trigg, T.E. (1987). Feeding high energy supplements to pasture_fed dairy cows. Effects of stage of lactation and level of supplement. Australian Journal of Agricultural Research 38, 927_940. Table 1 The effects of feeding either a bar ley or maize_based concentrate on milk production, liveweight change (LWC) and rumen concentrations of acetate and acetate+butyrate:propionate (AB:P). Barley kg DM/cow/day Milk yield (l/day) Fat % Protein % Fat yield (kg/day) LWC (kg/cow/day) Acetate (mmol) AB:P 1 ab Maize 8.1 22.1 4.5 20.3 b Probability of effect 8.1 SEM 0.46 c 4.5 20.1 3.65 a GR*L 0.096 0.023 0.638 0.869 0.692 0.802 0.810 Grain1 0.217 0.001 0.004 0.015 0.251 0.030 0.541 Level2 0.013 0.231 0.054 0.863 0.758 0.015 0.004 20.7 c 3.25 3.02 0.72 0.28 55.6 3.4 4.04 3.07 0.80 0.42 58.9 4.1 4.17 3.19 0.112 0.483 0.032 0.093 0.62 0.16 2.95 0.72 0.34 57.6 4.0 0.81 0.43 57.3 3.5 Overall effect of barley versus maize; 2 Overall effect of level of feeding of supplement Means with different superscripts indicate significant differences Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)