An observational study of the relationships between time from calving to pregnancy, body condition score, and...

The transition period for dairy cattle from drying off to calving and subsequent return to estrus is crucial to health and productivity. Body condition scoring is used to monitor loss of body tissue that arises from a negative nutrient balance during this period. Over-conditioned cows (BCS ≥3.5) or those with a BCS <2.0 are at greater risk of ill health and reduced fertility, manifest by an increased calving-to-pregnancy interval (CPI). A low BCS also increases the risk of lameness, which is associated with an extended CPI. Body condition score and mobility scores are subjective assessments, so accuracy and reproducibility vary according to individual experience and training. Scoring also represents an additional labor cost. Automated video monitoring systems (AVMS) have the potential to provide low-cost, replicable, objective, and dynamic monitoring of BCS and mobility. In this retrospective longitudinal observational study, we analyzed BCS and mobility score data from 4 British dairy herds using a commercially available AVMS that captured 3-dimensional and 2-dimensional image data (HerdVision, Agsenze), to which fertility data including dates of service and pregnancy diagnosis were appended. We used Cox proportional hazard models to estimate associations between lameness, BCS at drying off (BCS1), BCS at calving (BCS2), BCS change between drying off and calving (BCS2 - BCS1), or greatest change in BCS between calving and pregnancy (dBCS) using CPI as our outcome. Lactation number was included as a fixed effect, and farm was included as a random effect. Lameness was significantly associated with increased days to pregnancy in all models. Body condition score at calving was not significantly associated with CPI, although it was strongly correlated with BCS2. The change in BCS between drying off and calving (BCS2 - BCS1) was strongly associated with an increased CPI. When considered independently, BCS2 was strongly associated with an increased CPI. A reduction in BCS (dBCS) between calving and pregnancy was weakly associated with a reduced CPI. Our results are consistent with the published literature and indicate the potential of an automated system for the early identification of change in BCS or lameness. Effective early intervention could improve animal welfare and productivity.