The winter feeding of beef cows represents a high, proportion of the costs of calf production. Attempts to minimise cost include the use of beef (♂) x dairy cows (♀) which have the ability to suckle two calves and to mobilise body reserves during periods of underfeeding in early lactation. Khan and Topps (1985) observed that cows in good condition at calving could maintain milk production and raise two good calves when given 110 MJ ME/day in a diet which included a source of undegradable protein. Subsequently a preliminary experiment was carried out with three single suckled and nine double suckled cows to examine the effect of energy level on the performance of cows and calves.
Three single suckled cows and nine double suckled cows i.e. six with a natural plus foster calf and three with twin calves produced by embryo transfer were used in this experiment. The levels of energy that were examined were 70 or 90, 80 or 100 and 90 or 110 MJ ME/day for single and double-suckled cows respectively, supplied in diets containing ammonia treated straw, barley and fishmeal. Nine of the cows were placed into trios according to calving date and age, with a trio consisting of a cow with a natural calf, a cow with a natural and foster calf, and a cow with twin calves. Each trio was allocated at random to one of the three levels of energy. Similarly, the remaining three cows with a natural and foster calf were allocated at random to 90, 100 or 110 MJ ME/day. The calves were given good quality hay ad libitum and free access to a concentrate mixture up to a maximum intake of 2 kg/head/day. The concentrate mixture consisted of (g/kg) 800 barley, 150 soyabean meal and 50 molassine meal. The experiment started on the 22nd day of lactation and was of 20 weeks duration for most of the cows.