Effect of dry period length on milk yield, Body Condition Score, somatic cells count and health disorders in subsequent lactation in Italian Friesian cows

Effects of dry period length (DPL) on milk yield, body condition score (BCS), somatic cell count and health disorders in subsequent lactation were studied using 76399 test-day records from 7299 Italian Holstein cows reared in 115 herds of northern Italy from 1998 to 2001. Dry period length (DPL) was grouped in 4 classes: DPL1 (1-35 d); DPL2 (36-55 d); DPL3 (56-80 d) and DPL4 (81- 220 d). Milk yield, BCS and log-transformed SCC (SCS) were analyzed according to a mixed linear model accounting for herd-test day, parity, DPL, days in milk and animal effects. DPL affected milk yield of subsequent lactation, and DPL1 cows evidenced a reduction of milk yield at peak, of milk in 305 d and an increase in persistency with respect to other DPL classes. DPL did not affect change of BCS and SCS in the subsequent lactation. A logistic regression analysis was used for estimating the effect of DPL on the risk of contracting mastitis, lameness, retained placenta and mammary edema. Several models considering single or multiple health disorders were applied. DPL did not appear associated with the risk of health disorders occurrence, but some other factors (herds, parity, exposition time and cow breeding values) were important as predisposing factors.