REPLACEMENT OF SKIM MILK WITH SOYA BEAN PROTEIN-CONCENTRATES AND WHEYIN MILK REPLACERS FOR VEAL CALVES

Two experiments were conducted at a 1 year interval to study the nutri tional utilization by veal calves of milk replacers containing either milk protein (skim milk powder and/or whey) as the only sources of pro tein in controls or a mixture of whey protein and various commercial s oya bean protein concentrates (SPC). A water-extracted SPC (SPC 1) and a SPC treated with hot aqueous ethanol (SPC 2) were incorporated at 6 5% (crude protein basis) in formulas studied in Experiment 1. The SPC 1 was highly antigenic in vitro while SPC 2 was not. Recently, in vitr o antigenicity of SPC 1 was drastically reduced by extra treatments. T he 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 (Experi ments 1 and 2) and 51-56 (Experiment 1) or 65-70 (Experiment 2) days f rom the beginning of dietary treatment. The SPC adversely affected fin al live weight (LW), LW gains and feed conversion ratios over the expe rimental period. Digestibility of feed constituents was also most ofte n significantly reduced with SPC-based diets, regardless of age. For e xample, 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 p roducts 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 incre ased the digestibility of its N by 14%. Nitrogen retention was also us ually lower with diets containing SPC than with controls. In terms of immunogenicity, calves given the SPC 1 and SPC 3 diets displayed low a ntibody 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 r eplace so high a proportion of dairy protein without adversely affecti ng calf performance. This may have resulted mainly from a lower digest ibility of soya N rather than from adverse reactions to soya since spe cific antibody titres remained low to moderate.