Long-term effects of transition milk feeding on feed intake, growth performance, feeding behavior, and oxidative status of Holstein calves.

This study investigated the long-term effects of feeding 5-d transition milk (TRANS) compared with milk replacer (MR) on parameters including intake, growth, feeding behavior, and oxidative stress. Fifty Holstein calves (30 females and 20 males) were fed 12 L/d of either TRANS or MR for the first 5 d after an initial colostrum feeding of 3.5 L. Thereafter, all calves were fed with 12 L of MR/d (140 g/L) and were gradually weaned starting in wk 8 until wk 14. Throughout the 14 wk, the calves had unrestricted access to concentrate (up to 9.8 kg/calf per day), hay, and water. After weaning all heifers were fed a TMR for young cows. Oxidative status was assessed in blood samples from birth to first insemination. Parameters assessed included the ferric-reducing ability of plasma (FRAP) for antioxidant capacity and the concentration of reactive oxygen metabolites via detection of reactive oxygen metabolites (dROM) assay. In addition, the activity of glutathione peroxidase (GSHPx) and oxidative damage in the form of lipid peroxidation as thiobarbituric acid-reactive substances (TBARS) and as advanced oxidation protein products (AOPP) were measured. An oxidative stress index was calculated: dROM/FRAP × 100. Total protein concentration was also quantified via Bradford assay. The only significant difference in feeding behavior between the 2 treatment groups was a higher concentrate intake by the TRANS calves during the weaning phase. Body weight and ADG did not differ significantly between the TRANS and MR groups. The TRANS calves showed a trend for fewer cases of health disorders. Markers of oxidative status, including TBARS, AOPP, GSHPx, FRAP, and reactive oxygen metabolites, showed no treatment effects but varied significantly over time. Of note, the oxidative stress index, as ratio between pro- and antioxidants in both groups, peaked during weaning and then returned to baseline, suggesting an effective response to this transition phase. Overall, the results indicate that feeding TRANS during the first 5 d of life had no long-term effect on the parameters studied as compared with MR feeding under the present rearing conditions. These results provide insight into the changes of oxidative status with age and confirm that the relatively high milk feeding level, with slow and late weaning, enables calves to adapt well to solely solid feed.