Sixteen rumen-fistulated Holstein Friesian cows in early lactation were offered 40 kg herbage dry matter (DM)/cow/day (to ground level). The objective of the experiment was to investigate the economics of feeding cereal grain supplements to cows grazing highly digestible ryegrass herbage in spring and determine the impact of grain feeding on rumen conditions and milk composition. Six kilograms DM of cereal grain were offered to eight cows, while the other 8 cows did not receive grain. Superimposed on these grain supplementation rates were 0 or 300 g sodium bicarbonate in a 2x2 factorial design. The inclusion of grain in the diet reduced herbage intake (from 16.7 - 12.7 kg DM/day, P<0.01) and the neutral detergent fibre concentration of the total diet (from 410 g/kg - 325 g/kg DM). Grain feeding reduced milk fat concentration (from 41.7 - 34.3 g/kg, P<0.05) and increased milk protein concentration (from 32.8 - 34.6 g/kg, P<0.05). Grain feeding depressed the rumen fluid concentration of acetic acid and increased that of propionic acid, resulting in a lipogenic:glucogenic ratio (acetic + butyric:propionic acid ratio) below 3:1 for both grain treatments. The milk responses from cows consuming concentrates with highly digestible herbage in spring were low (-0.4 - 0 kg 4% fat corrected milk/kg DM grain consumed) and did not improve the returns to farmers during the period of feeding. The most profitable use of concentrates is likely to come after spring calving cows have reached their peak and herbage quality begins to decline.
Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 224-228, 2001
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