The effect of slow-release oral calcium bolus administration at calving on performance, blood calcium, and reproductive parameters of fresh cows in the summer season

The objective of this study was to evaluate the effect of feeding two oral Ca boluses at calving and 12 h later on feed intake, milk yield, body weight (BW) changes, blood calcium and some reproductive parameters of high producing dairy cows during summer season. Twenty-four Holstein cows with average parity of 2.8 ± 0.8 were selected and randomly assigned to one of two treatments including control or the group receiving slow-release oral Ca bolus at calving and 12 h post-calving. Row milk yield was greater in cows receiving Ca boluses compared to control treatments during 21 days of lactation (P = 0.02). The milk fat (P = 0.01) and solid non-fat percentage (P = 0.05) were greater in cows that received calcium bolus compared to control treatment. In addition, energy-corrected and fat-corrected milk yields increased in cows received Ca bolus (P = 0.03). Plasma glucose and serum calcium concentration as well as BW change were not affected by experimental treatments. The pregnancy per artificial insemination, days to first insemination and open days were not significantly different between the experimental treatments (P >0.05). The results showed that using oral calcium bolus at calving and 12 hours after calving improved milk production and composition, but had no effect on serum Ca, BW change during first 21 days of lactation, and reproduction parameters.