Replacement of skim milk with soya bean protein concentrates and whey in milk replacers for veal calves

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Two experiments were conducted at a 1 year interval to study the nutritional utilization by veal calves of milk replacers containing either milk protein (skim milk powder and/or whey) as the only sources of protein in controls or a mixture of whey protein and various commercial soya bean protein concentrates (SPC). A water-extracted SPC (SPC 1) and a SPC treated with hot aqueous ethanol (SPC 2) were incorporated at 65% (crude protein basis) in formulas studied in Experiment 1. The SPC 1 was highly antigenic in vitro while SPC 2 was not. Recently, in vitro antigenicity of SPC 1 was drastically reduced by extra treatments. The new product obtained (SCP 3) provided 72% of protein in the formula of Experiment 2. All these milk replacer diets were given to 4- to 5-week-old veal calves for 101–103 days. Apparent digestibility of feed constituents and nitrogen retention were measured between 9–14 (Experiments 1 and 2) and 51–56 (Experiment 1) or 65–70 (Experiment 2) days from the beginning of dietary treatment. The SPC adversely affected final live weight (LW), LW gains and feed conversion ratios over the experimental period. Digestibility of feed constituents was also most often significantly reduced with SPC-based diets, regardless of age. For example, N digestibility was 16% and 9% lower with the SPC 1 and SPC 2 diets, respectively (Experiment 1), and 10% lower with the SPC 3 diet (Experiment 2) than with the control diet. Digestibility of N in SPC products was calculated to be 71%, 81% and 81% for SPC 1, SPC 2 and SPC 3, respectively. Thus, reducing the antigenic activity of SPC 1 increased the digestibility of its N by 14%. Nitrogen retention was also usually lower with diets containing SPC than with controls. In terms of immunogenicity, calves given the SPC 1 and SPC 3 diets displayed low antibody titres. This was unexpected from in vitro data found with SPC 1. Calves given the SPC 2 diet had no detectable anti-soya antibodies. It is concluded that the SPCs tested in the present study could not replace so high a proportion of dairy protein without adversely affecting calf performance. This may have resulted mainly from a lower digestibility of soya N rather than from adverse reactions to soya since specific antibody titres remained low to moderate.