ANTIGENICITY AND DIGESTIVE UTILIZATION OF 4 SOYA PRODUCTS BY THE PRERUMINANT CALF

A study was conducted to study the utilization by preruminant calves o f commercial or experimental soya products variously treated and to as certain whether differences among products for nitrogen digestibility could be linked with their in vitro antigenicity. Four milk replacers containing a mixture of skim milk powder and soya products (40:60, pro tein basis) were fed to 3-week old calves for 102 days at a rate incre asing progressively from 1050 to 2700 g DM/day. Two heated soyabean fl ours (antigenic: ASF, or non-antigenic: NASF) and two soyabean protein concentrates (water extracted, antigenic: ASC or protein hydrolyzed, non-antigenic: NASC) were compared. Antigen immunoreactivity in vitro was high in ASF and ASC, low in NASF and not detectable in NASC. Growt h performance and antisoya antibody production were recorded throughou t the trial. Digestibility and nutrient retention were measured betwee n 16-21 and 55-60 day of the experiment. Live weight gain was lower (1 6%, P<0.05) with ASC than with NASF and NASC. Apparent digestibility o f total nitrogen increased with age (P<0.05) and the mean values were 78, 84, 75 and 88% for ASF, NASF, ASC and NASC, respectively. Values c alculated by difference for soyabean nitrogen were 66, 76, 61 and 83%. Antisoya antibody titres at the end of the trial were 6.3, 2.7, 7.8 a nd 0.8 respectively. In the present study, the apparent digestibility of nitrogen appeared to be inversely related to the in vitro and in vi vo antigenicity of the soya products. However, other factors including soya batch, protein structure and contents in various antinutritional factors, but apparently not trypsin inhibitors, may also have played a role. Additionally, soyabean protein hydrolysis appears to be partic ularly interesting to decrease antigenic activity and improve digestiv e utilization by calves.