Effects Of Supplementation Of Soy Proteins In Milk Replacer On The Growth And Development Of Calves

Experiments were conducted to study the effects of supplementation of three soy protein (heated full-fat soybean flour, defatted soybean flour and extruded soybean flour) in milk replacers on the growth and development of calves.The first part was mainly conducted to study the effects of three different processed soy proteins on the growth and development of pre-ruminant calves. 24 Holstein male calves were randomly allotted to four groups randomly. Calves in the 4 treatments were fed milk (CK) or milk replacer supplemented with heated full-fat soybean flour (MR1), defatted soybean flour (MR2) and extruded soybean flour (MR3). After 6w's feeding, 4 calves from each group were slaughtered to collect samples. The results indicated that supplementation of soybean with different processing methods had the negative effects on growth and intestinal morphology of the pre-ruminant calves and decreased the intestinal trypsin and chymotrypsin activities. The average daily weight gain were 0.39kg/d, 0.26kg/d, 0.18kg/d and 0.26kg/d in CK, MR1, MR2 and MR3 group, respectively. The nitrogen retention rate of 20-25d calves with MR3 was 6.82g/d, significantly higher than that in MR1 and MR2(3.43g/d and 3.16g/d, respectively) (P< 0.01) ; whereas, 40-45d calves had the higher nitrogen retention rate in MR1 group (10.84g/d) and MR3group (10.60g/d ) ,respect to 40-45d calves in MR2 (6.98g/d) (P<0.05) . Intestinal villus were damaged severely in calves fed MR2 supplemented with defatted soy protein, accompanying with villous shrank and recess (C) hyperplasia. The average daily weight gains of calves were similar fed within MR1 and MR3, whereas lower than that of control group fed milk in CK. The results indicated that milk protein in milk replacer could be proportionally replaced by supplementing heated full-fat soybean flour and extruded soybean flour based on the damage to the digestive enzyme activities and the intestinal morphology.The second part evaluated the adaption ability of calves fed milk replacer after weaning. 48 Holstein male calves were assigned to two treatments randomly fed milk or milk replacer and weaned at 55d of birth abruptly. Starter feed were supplied restricted. The results indicated that: (1) Weaning stress decreased DMI and ruminal volatile fatty acids concentration, but plasma cortiol and acute-protein concentration increased rapidly (P<0.05) at the weaning day. (2) Ruminal mucosa color was darker and papilla length and density were better in calves in MR group than that in CK group. Honeycomb structures of reticulum were founded in 55-day calves in MR group, but it was unobvious in CK group. (3) Ruminal acetate concentrations were similar in both groups (P > 0.05) , but the ruminal concentrations of propionic acid , butyric acid and TVFA were significantly higher in 55d calves in all MR group than that in CK group (P<0.05)The results indicated that: (1) Adding different processed soy protein in milk replacer had the negative effects for pre-weaning calves, as for decreased the activities of trypsin and chymotrypsin and induced damage of intestinal morphology. (2) Calves fed with milk replacers containing heated full-fat soy protein and extruded soy protein flour had the similar growth performance, significantly higher than that containing defatted soy protein. Therefore, heated soy protein and extruded soy protein could substitute part of milk protein in milk replacer and had fewer negative effects on the growth performance of pre-weaning calves. (3) Although adding soy protein had the negative effects on the growth performance of pre-weaning calves, soy protein could enhance the development of pre-stomach and DMI in the weaning period, decrease weaning stress, fasten the calf breed. Thus, extruded soy protein could substitute part of milk protein in milk replacer.