SUBSTITUTION OF MILK PROTEIN WITH SOYFLOUR OR MEAT-SOLUBLES N CALF MILK REPLACERS

Abstract

Five Holstein male calves were fitted with ileo-cecal re-entrant cannulae. Calves were fed five milk replacers according to a 5 × 5 Latin square design. The control milk replacer (SM-100) was formulated so that 80% of the crude protein originated from skim milk powder and the remainder from whey proteins. In the test milk replacers, 40 or 60% of the skim milk protein was replaced by protein from soyflour (SF-40; SF-60) or meat-solubles (MS-40; MS-60). Diets were supplied at a rate of 50 g dry matter per unit metabolic body size (BWkg0.75) d−1. Average daily gain (ADG) and protein efficiency ratio (PER) decreased when SM was replaced by SF or MS. This depression was greater (P < 0.05) with higher levels of substitution and more marked for MS than SF. Plasma methionine concentration was lowest in calves fed the SF-60 and MS-60 diets. Average ileal digestibilities of the total of the indispensable amino acids were highest in SM-100 (94.6%), intermediate in MS-40 (88.0%) and MS-60 (86.8%) and lowest in SF-40 (83.8%) and SF-60 (82.1%). Fecal amino acid digestibilities did not differ between diets (P > 0.05). In summary, there was a decrease in ADG and PER when milk protein was replaced by protein from SF or MS. The inferior performance of calves fed SF- or MS-containing milk replacers is, in part, related to a lower digestible amino acid supply as measured in digesta collected from the distal ileum. Key words: Calf, milk replacers, soyflour, meat-solubles, amino acid digestibility