Effects of feeding whole milk or milk replacer on the performance, gastrointestinal tissue development, and digestive enzyme secretions of Holstein calves

The purpose of the research was to compared the effects of the supplementation of whole milk or milk replacer on the performance, gastrointestinal tissue development, and digestive enzyme secretions of Holstein calves. Twelve newborn Holstein male calves (1.96 ± 0.99 d of age; 40.0 ± 4.37 kg BW) were blocked by arrival date and age, divided into two groups: whole milk group(WM) and milk replacer group(MR)(n=6) in One-way experimental design. The results showed that at 30 d, the WM group had significantly higher (P<0.05) pre-slaughter body weight (P<0.05), ADG (P<0.05) and average dry matter intake (ADMI) (P<0.05) than the MR group; and at 60 d, the ileocecal pancreatic amylase level of the WM group was significantly lower (P<0.05) than that of the MR group. Rumen development was better in the MR group than in the WM group, and small intestinal villus length development was different in each intestinal segment(P<0.05). The relative abundance of Proteobacteria in the WM group was significantly higher than that in the MR group on day 30(P<0.05) and the relative abundance of succinogens was significantly higher (P<0.05) in the MR group than in the WR group (P<0.05). At 60 d, the relative abundance of Bacteroidetes and Actinobacteria in the MR group was higher (P<0.05) than in the WM group, and the relative abundances of Prevotella (P<0.05) and Bacteroides in the WM group were greater than those in the MR group (P<0.05).Calves fed MR showed poorer growth performance early in lactation, but higher starter intake helped calves plateau in growth performance at weaning. Gastrointestinal digestive enzymes showed more positive amylase activity and more mature rumen development and teat growth. In addition, rumen microbes in MR-fed calves were more efficient at degrading starter intake.Therefore, feeding MR would improve calf digestion of solid feeds by increasing rumen development and small intestinal amylase levels. However, the evolutionary processes and specific mechanisms responsible for this outcome cannot be explained because the current study was limited to epiphenomena.