The influence of body condition at calving and dietary protein supply on voluntary food intake and performance in dairy cows

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Abstract
Four groups of 12 cows were fed from between 12 and 18 weeks before calving to achieve condition scores at calving of 2·0 (T) or 3·5 (F). For 20 weeks after calving all cows were offered 10 kg/day of a dairy concentrate (metabolizable energy (ME) 13 MJ/kg dry matter (DM)) containing 74 g undegradable dietary protein (UDP) per kg DM (groups TH and FH) or 45 g/kg DM UDP (groups TL and FL), 2 kg/day sugar-beet pulp, 5 kg/day brewers' grains and hay ad libitum.Milk yields were similar for all groups over the first 20 weeks of lactation, but slightly lower for cows in group FL than for other cows. Cows in group FH lost condition over the first 15 weeks and cows in group FL lost proportionally more condition over the first 12 weeks of lactation. Cows in groups TH and TL increased in condition slightly over the first 20 weeks of lactation. After calving, cows in groups TH and TL had significantly higher intakes of DM, digestible DM and ME than did cows in groups FH and FL (P < 0·001). Cows in group TL had higher intakes than did cows in group TH.Groups TH and FH were in negative energy balance until weeks 10 and 11 respectively. Group FL was in negative energy balance between weeks 4 and 7 and group TL was only in negative energy balance in week 5. The biological efficiency of milk production (energy output in milk/energy intake) was 0·37, 0·35, 0·40 and 0·38 for groups FH, FL, TH and TL respectively.It was concluded that cows which are thin at calving produce more milk directly from food than cows which are fat and are biologically more efficient; higher UDP levels in the diet led to increased negative energy balances but in thin cows this was due to lower food intakes whereas in fat cows this was due to higher milk yields which led to greater losses of condition.