Milk replacers for preruminant lambs: protein and fat interactions

Abstract

Seventy male crossbred lambs, aged between 2 and 5 days at the start of the experiment, were given milk replacers in which the source of protein was either dried skimmed milk (DSM) or isolated soybean protein (ISP). The diets provided either 0.10 or 0.25 of the total energy as protein. Fat provided either 0.80 or 0.50 of the total gross energy and was added as butter oil, olive oil, safflower oil, groundnut oil or coconut oil. When ISP replaced DSM there was a significant reduction in the apparent digestibiIities of nitrogen and fat, and in the digestibilities of the component fatty acids (corrected for metabolic fat losses) for all diets, irrespective of the source of dietary fat. When the protein energy concentration was reduced from 0.25 to 0.10, there was a reduction in the above digestibilities for all diets, except those containing butter oil. The corrected digestibilities of the saturated fatty acids invariably decreased with an increase in chain length. The digestibility of an unsaturated fatty acid was usually, but not always, greater than that of its saturated counterpart. The digestibility of any given fatty acid was independent of the concentrations of other fatty acids in the same fat.