Effects of dry period length on milk yield and content and metabolic status of high-producing dairy cows under heat stress.

The objective of the present study was to investigate the effects of shortening dry period (DP) on milk yield, milk composition, and blood parameters in cows under heat stress. For this purpose, three DP groups were considered (30, 45, and 60 days), and 14 heat-stressed high-producing dairy cows (7 primiparous and 7 multiparous) were assigned to each DP group. The results showed that shortening the DP (from 60 to 30 days) decreased a 305-day milk yield in subsequent lactation. The difference in milk yield between 30- and 60-day DP groups was significant in the second 100 days of lactation. Accounting for additional milk yield before calving completely compensate for the loss of milk production resulting from shortening the DP. Milk protein, lactose, and solids non-fat percentages were significantly lower for cows with a 60-day DP compared to cows with a 45- or 30-day DP. Serum BHBA and urea concentrations were significantly higher, and serum glucose concentration was significantly lower for cows with a 60-day DP compared to cows with a 30-day DP. In conclusion, results showed that shortening the DP improved the metabolic status of heat-stressed transition dairy cows without decreasing total milk yield.