Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2006
Publication Date: April 1, 2007
Citation: Kuhn, M.T., Hutchison, J.L., Norman, H.D. 2007. Dry Period Length in US Jerseys: Characterization and Effects on Performance. Journal of Dairy Science. 90(4):2069-2081. Interpretive Summary: Characterization of dry period lengths (the number of days between lactations when a cow is not being milked) for US Jerseys as well as determining the effects of days dry on subsequent lactation milk, fat, and protein yield, fat and protein percentages, somatic cell score, and days open for US Jerseys were the objectives in this study. This research is useful not only on a farm level, but also throughout the industry because there is very little research comparing breeds and their variations in dry period length; virtually all research has been conducted using only Holsteins.
Technical Abstract: The objectives of this research were to characterize dry period lengths for US Jerseys, determine effects of days dry (DD) on subsequent lactation actual milk, fat, and protein yield, fat and protein percentages, somatic cell score (SCS), and days open (DO), and to determine the dry period length that maximizes yield across lactations. Field data, collected through the Dairy Herd Improvement Association, on US Jersey cows first calving between January 1997 and November 2004 were utilized. Characterization of DD included a frequency distribution of dry period lengths as well as factors affecting US Jersey DD. Of the factors considered in this research, the primary ones affecting dry period length were DO, milk yield, and SCS. Cows with longer DO, lower milk yield, and higher SCS receive longer dry periods. Actual lactation records calculated from test-day yields using the test-interval method were used to determine the effects of DD on subsequent lactation traits. The model for analyses included herd-year of calving, year-state-month of calving, parity of calving, previous lactation record, age at calving, and DD as a categorical variable; records were pre-adjusted for cow effects. There were a total of 123,032 records from 73,797 cows in 808 herds used for estimation of DD effects on subsequent lactation actual milk yield. Jersey milk, fat, and protein yield in subsequent lactation is maximized with 60 DD. Dry periods of 30 d or less result in especially large reductions in subsequent lactation production. A short dry period was beneficial for fat and protein percentages in subsequent lactation. Short dry periods also resulted in fewer DO in the subsequent lactation; however, this was entirely due to the lower milk yield associated with shortened dry periods. By far the biggest difference between Jerseys and Holsteins was a much larger, detrimental effect on SCS in Jerseys for dry periods of 30 d or less. Jersey SCS increased 10%, relative to the overall mean, for dry periods of 20 d or less and 4.6% for DD between 21 and 30 d. Jersey producers, especially, should be skeptical of dry periods less than 30 d, since the value of the milk will be reduced in the following lactation due to substantially higher SCS. Dry periods of 45 to 70 d maximized yields across adjacent lactations. A dry period length, after first lactation, of 45 to 70 d maximizes actual milk yield across lactations 1, 2, and 3. The final recommendation to Jersey producers is to avoid dry periods < 45 d. Long dry periods (> 70 d) should also be avoided as these are even more costly to total yield than dry periods < 30 d.