The effects of dietary energy on double-suckled cows, their calves' performance and behaviour
1. Autumn-calving beef cows and their single, natural plus foster or twin suckling calves have been studied in three trials which have been recorded as four experiments. The objective of the studies was to obtain basic information on milk production, nutrition and metabolism in relation to the performance of cows and performance and behaviour of calves. In the first trial 12 cows were used. Six cows received 80% of their energy requirements and a source of UDP and 6 cows received adequate energy to meet their requirements without a special source of UDP. The second experiment was part of this trial and two methods of estimating milk production were compared. In a second trial or third experiment 3 cows with a single calf, 6 cows with a natural plus foster calves and 3 cows with natural twin calves were studied in their response to three levels of dietary energy. In the final experiment 9 cows with natural plus foster calves and 9 cows with natural twin calves were used to study the effects of another ' three levels of dietary energy. 2. In the first experiment body weight losses were 0.28, 0.21 kg/d; milk yields were 14.3, 14.9 kg/d and calves growth rate were 1.05, 0.98 kg/d for the 80% energy and adequate energy group respectively. The calves on the cows receiving 80% energy group ate 13% more concentrate and 11% more hay than those in the adequate energy group, but these extra costs were compensated at least partly by the greater liveweight gain.3. In the second experiment the overall mean milk yields estimated by machine milking were less than those obtained by the calf suckling techniques, the difference being 1 kg/d. The calf suckling technique appeared to produce values which were a truer representation of the yield than the machine milking technique. 4. In the second trial or third experiment for the low (70 or 90), medium (80 or 100) and high (90 or 110 MJ ME/d) energy treatments mean weight losses of the cows were 0.57, 0.37, 0.13; mean daily yields of milk were 13.1, 13.5 and 11.1 and mean growth rates of calves were 1.13, 0.91 and 0.97 kg/d. For the single, natural plus foster and twin-suckling cows the mean weight losses of the cows were 0.26, 0.54, 0.10; mean daily yields of milk were 9.4, 14.2 and 12.7 and mean growth rates of calves were 1.07, 0.96 and 1.01 kg/d. The differences in suckling behaviour between natural plus foster and twin calves were small, but the presence of two calves instead of one approximately doubled the suckling activity per cow even though milk yield increased on average by 40% only. Three cows in this trial suffered from ketosis. 5. In the last trial or experiment for the low (105), medium (115) and high (125 MJ ME/d) energy treatments mean weight losses of the cows were 0.10, 0.06, 0.11; mean daily yields of milk were 13.2, 13.5 and 14.3 and mean growth rate of calves were 0.90, 0.92, 0.98 kg/d. The performance of double-suckled cows and calves was similar to that of twin suckled cows and calves. Twin calves had a growth rate comparable to that of a natural plus foster calf. Suckling behaviour of twin-suckling calves varied both diurnally and with stage of lactation. There were no significant effects of calf type, level of feeding or milk yield of the cow. 6. The results of the first trial indicated that cows calving in good condition and raising two calves may be given either a lower energy diet with a source of UDP or an adequate energy diet with no extra and special protein. The choice is dependent on the need to utilize the cow's body reserves and the cost of the dietary ingredients. The second trial was a preliminary trial, since relatively few cows were available. The results indicated that double-suckled cows that calve in good condition are able to maintain high milk yields and raise two good calves on levels of dietary energy as low as 90 to 100 MJ ME/d when the diets includes a source of undegradable protein. However, there may be a risk of ketosis in cows which lose weight rapidly. The results of the last trial did not fully support those of the second. Higher levels of dietary energy were used since the cows were in poorer condition at calving than those in the second trial. In addition they were younger. Cows in the last trial lost very little weight even though two groups were underfed to a significant extent.