DRY PERIOD LENGTH AS RELATED TO MILK YIELD AND SCC DURING THE FIRST MONTH OF SUBSEQUENT LACTATION

Analysis was made of the effect of dry period length in primiparous and multiparous cows on daily milk yield during the first month of subsequent lactation and on milk somatic cell count (SCC) on the basis of the information about the test-day milkings of 59 138 cows. The GLM and FREQ procedures of the SAS package were used in the statistical calculations. Dry period length in the primiparous and multiparous cows had a significant effect (P <= 0.01) on daily milk yield and udder health, determined based on SCC. In terms of milk yield, the most favourable dry period would be 51-70 days for both primiparous and multiparous cows. Depending on udder health, a dry period of 51-90 days can be suggested. Shorter dry periods had more undesirable effects than longer dry periods. Excessively shortened dry period (<= 10 days) caused the daily milk yield to decrease by 17% in primiparous and by 13% in multiparous cows while increasing the risk of clinical changes of the cow's udder, regardless of age. The proportion of milk samples that showed evidence of clinical mastitis also increased when the dry period was excessively long (>90 days), especially in multiparous cows.