Abstract
The objective of this study was to characterize the association between body condition score (BCS) and BCS change (ΔBCS), determined by an automated camera system at multiple time points, and the subsequent pregnancy per first artificial insemination (P/AI1) of Holstein cows. A retrospective observational study was completed using data collected from 11,393 lactations in 7,928 Holstein cows calving between April 2019 and March 2021 in a commercial dairy operation located in Colorado. Cows were classified as primiparous or multiparous. Scores generated by BCS cameras at dry-off, calving, 21 days in milk (DIM), 56 DIM, and first artificial insemination were selected for the analyses and subsequently categorized as low (≤lower quartile), moderate (interquartile range), and high (≥upper quartile). Changes in BCS were calculated by periods of interest as change from dry-off to calving (multiparous cows); change from calving to 21 DIM; change from calving to 56 DIM; and change from calving to first artificial insemination and assigned into categories as large loss of BCS (top 25% of cows losing BCS); moderate loss (bottom 75% of cows losing BCS); no change (ΔBCS = 0); or gain of BCS (ΔBCS > 0). Data were examined in primiparous and multiparous cows separately using logistic regression and time-to-event analyses. Initial univariable models were followed by multivariable models that considered calving season, occurrence of disease, and milk yield up to 60 DIM as covariables. The logistic regression analyses indicated that in both parity groups the associations between BCS category and P/AI1 were more evident at 21 DIM, 56 DIM, and first artificial insemination, with lower odds of P/AI1 in cows in the low BCS category. Likewise, cows with large loss in BCS between calving and 21 DIM, calving and 56 DIM, and calving and first artificial insemination had lower odds of P/AI1 compared with other categories of ΔBCS within the same period of interest. Similarly, survival analyses evidenced that cows in the low BCS category required more time to get pregnant. In agreement, differences in the dynamics of the average daily BCS during the first 90 DIM were evident when cows were grouped by first AI outcome (pregnant vs. nonpregnant) and by their time to pregnancy category (<90 DIM; 91-150 DIM; or >150 DIM), with cows with reduced fertility showing lower BCS up to 90 DIM. Overall, low BCS and more pronounced reductions in BCS occurring closer to first artificial insemination resulted in lower odds of pregnancy per artificial insemination.
Highlights
The peripartum of dairy cows is characterized by an increased demand for nutrients to support the initiating lactation, followed by slower increments in DMI (Gross et al, 2011)
Body condition scores are an indirect measure of the level of subcutaneous fat in dairy cattle (Ferguson et al, 1994), where body condition score (BCS) at a time point are an indication of energy status, whereas BCS gain or loss, and rate of change are considered as a proxy for the evaluation of energy balance (Roche et al, 2009)
Considering the known physiological effects of energy status and energy balance on the duration of anestrous postpartum and the likelihood of a successful pregnancy, multiple studies have tested the associations among BCS and cow fertility
Summary
The peripartum of dairy cows is characterized by an increased demand for nutrients to support the initiating lactation, followed by slower increments in DMI (Gross et al, 2011). Due to the detrimental effect of pronounced and extended periods of negative energy balance, the evaluation of the energy reserves by body condition scoring is a frequent monitoring practice implemented in dairy farms. Body condition scores are an indirect measure of the level of subcutaneous fat in dairy cattle (Ferguson et al, 1994), where BCS at a time point are an indication of energy status, whereas BCS gain or loss, and rate of change are considered as a proxy for the evaluation of energy balance (Roche et al, 2009). Considering the known physiological effects of energy status and energy balance on the duration of anestrous postpartum and the likelihood of a successful pregnancy, multiple studies have tested the associations among BCS and cow fertility.
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