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Do biological and management causes of a short or long dry period induce the same effects on dairy cattle productivity?

K. E. Olagaray




Do biological and management causes of a short or long dry period induce the same effects on dairy cattle productivity?
K. E. Olagaray*1, M. W. Overton2, B. J. Bradford1. 1Kansas State University Manhattan, KS, 2Elanco Animal Health Greenfield, IN.

A retrospective observational study utilized 32,182 lactations from 16 farms to determine if management versus biological reasons for a short or long dry period have the same associations with subsequent lactation performance. Herd inclusion criteria were Holstein cows, herd size ≥900 cows, breeding by artificial insemination, and bimonthly milk testing. Dry period (DP) length and gestation length (GL) were each categorized as short (>1 SD below mean) or long (>1 SD above mean) and combined to generate the following 7 study groups: short DP, short GL (SDSG); short DP, average GL (SDAG); average DP, short GL (ADSG); average DP, average GL (ADAG); average DP, long GL (ADLG); long DP, average GL (LDAG); and long DP, long GL (LDLG). Continuous data were analyzed by mixed models and time to event data by Cox proportional hazard models, both accounting for clustering at the herd level. First test and whole lactation milk and component yields were least for SDSG. Within cows that experienced calving difficulty, time to first service was delayed 13 and 20% for SDSG and ADSG compared with ADAG. Hazard of leaving the herd by 60 DIM was 34% greater for ADSG than ADAG. Similar outcomes between SDSG and ADSG but not SDAG indicated short GL was a greater contributor to poor performance than DP length itself. Overall production was similar between ADAG and SDAG; however, first test somatic cell linear score was greater and milk yield was lesser for SDAG cows with greater milk at last test before dry-off. Long DP or GL did not impact early lactation or whole lactation milk yield. Cows with a long DP due to management factors (LDAG) likely experienced issues related to excessive lipid mobilization as milk fat concentration and fat:protein ratio at first test were greater and hazard of leaving the herd was 30 and 24% greater compared with ADAG by 60 and 365 DIM, respectively. In conclusion, deviations in DP length caused by biology (short GL) were associated with greater impacts than management causes of short DP, whereas management reasons for long DP were associated with more negative outcomes than long GL.

Keywords: gestation length, lactation, survival.