Systems of concentrate allocation for dairy cattle 2. A comparison of two patterns of allocation for autumn-calving cows offered two qualities of grass silage ad libitum

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Abstract
In a 25-week experiment beginning at week 3 post partum, grass silages of 10·5 (H) and 8·9 (L) MJ metabolizable energy per kg dry matter (DM) were offered ad libitum to two groups of 24 autumn-calving dairy cows. Within each silage-quality group, two patterns of concentrate allocation were compared, a flat-rate (F) and a variable rate (V). All four treatment groups, HF, HV, LF and LV, received on average 1575 kg fresh weight per cow of a concentrate containing 170 g crude protein per kg during the 25 weeks. The cows on treatment F were all individually given 9 kg concentrate per day throughout. Individuals on the V treatments received different levels of concentrate, based initially on their 14-day milk yield and then reduced by 1 kg/day at 10, 15 and 20 weeks. For treatments HF, HV, LF and LV respectively, mean adjusted daily milk yields were, 24·4, 24·1, 21·6 and 22·1 kg; intakes of silage DM, 9·1, 8·7, 7·6 and 7·6 kg/day, and live-weight gains, 0·39, 0·31, 0·28 and 0·22 kg/day. The effects of silage quality were significant in each case, but the effects of pattern of concentrate allocation were not. Cows given the H silage produced milk with significantly greater lactose and solids-not-fat concentrations. During the residual period (2 weeks indoors and 14 weeks grazing) no significant differences in milk yield were observed. The 305-day yields of 6215, 6096, 5786 and 5824 kg for treatments HF, HV, LF and LV respectively, reflected the differences obtained during the indoor feeding period.