Evaluation by digestibility,growth and slaughter with young milk-fed calves of microbial cells as a source of protein

A comparison of two milk replacer diets, using Ayrshire bull calves, was undertaken. Calves were offered either a diet based on skim milk, fat and whey (diet CM) or one (diet DMC 10) in which 20% skim milk was replaced by equal quantities of dried microbial cells (DMC) and whey. The inclusion of DMC resulted in a reduction in energy digestibility but had little effect on the digestibility of nitrogen. The metabolisable energy (ME) value for diet DMC 10 was significantly lower than that for diet CM. Calves offered diet DMC 10 consumed more feed and grew faster than calves on diet CM. The gross efficiency of conversion of nutrients for growth was unaffected by treatment and the composition of the liveweight gains was similar on both diets. The efficiencies of tissue accretion were higher for the calves given diet DMC 10, particularly in relation to the efficiency of use of nitrogen for tissue gain.