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Association of feed intake with body condition loss during the dry period.

R. R. Daros



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Association of feed intake with body condition loss during the dry period.
R. R. Daros*1,2, C. D. Havekes3, T. J. DeVries3. 1Animal Welfare Program, Faculty of Land and Food Systems, University of British Columbia Vancouver, BC, Canada, 2Graduate Program in Animal Science, School of Life Sciences, Pontif�cia Universidade Cat�lica do Paran� Curitiba, Paran�, Brazil, 3Department of Animal Biosciences, University of Guelph Guelph, ON, Canada.

Body condition loss during the dry period has been associated with a myriad of transition cow diseases. Further, over conditioned cows at dry-off are those that suffer the greatest BCS loss. We used data from 2 studies to assess the relationship between BCS loss during the dry period (DBCS), DMI, and BCS at dry-off. One hundred cows at the University of Guelph (Elora, ON, Canada) were enrolled in 2 studies to investigate the effects of different diets on feeding behavior during the dry period. In both studies BCS and BW were recorded at dry-off and biweekly up to calving. DBCS was calculated by subtracting BCS at dry-off from the BCS at calving. Feed intake data were collected using electronic feed bins. DMI was calculated as % of BW (DMI%BW). BCS at dry-off was categorized as over-conditioned (BCS ≥3.5) and normal (BCS <3.5); no cows had BCS <2.75. Parity and milk production in the previous lactation were considered. Data sets were split into far-off and close-up periods, wk 8 to 4 and 3 to 0 before calving, respectively. To evaluate the associations between DMI and BCS at dry-off in each period, mixed linear regression models were built using DMI%BW as the outcome variable. For each model the following covariates were included: parity, previous lactation milk yield, study, and diets that the cows were enrolled on in each study. Experimental day was included as random slope and cow as random intercept. We used mediation analysis to evaluate the potential causal direct effect of BCS at dry-off on DBCS and the potential indirect effect mediated by differences in DMI. Independent of diet, parity, and previous lactation milk production, BCS at dry off was associated with differences in DMI%BW; over-conditioned cows had lower daily DMI%BW during the far-off (normal: 2.1 � 0.1 vs over-conditioned: 1.8 � 0.1%; P < 0.01) and close-up (normal: 1.9 � 0.1 vs over-conditioned: 1.5 � 0.1%; P < 0.01) periods. DBCS was only partially mediated by DMI%BW (10%; lower CI = 2% - upper CI = 27%; P = 0.02), while BCS at dry-off still had a direct effect on DBCS (P < 0.01). Overall, these results suggest that mechanisms in addition to feed intake are associated with body condition loss during the dry period.

Keywords: fat mobilization, eating behavior, mediation analysis.