Factors associated with the time and magnitude of the nadir body condition score in early lactation and its subsequent effects on fertility of Holstein cows.

The objective of this study was to identify variables associated with the time and magnitude of nadir BCS (nBCS) during early lactation and to characterize the effects of these two measurements on the subsequent pregnancy at first artificial insemination (P/AI1) and pregnancy loss of Holstein cows. A retrospective observational study was completed using data collected from 12,042 lactations in 7,626 Holstein cows calving between April 2019 and January 2022 in a commercial dairy operation located in Colorado, USA. Scores generated by an automated BCS camera system at dry-off (BCSdry), calving (BCS1), nadir (nBCS; defined as the lowest daily BCS from calving to 100 DIM), and 21 d post nadir were selected for the analyses and subsequently categorized into quartiles (Q1 = lower nBCS). Changes in BCS were calculated from dry-off to calving (multiparous cows); from calving to nadir; and from nadir to 21 d post nadir and assigned into quartile categories considering Q1 as the 25% of cows with greater loss (pre nadir) or smaller gain (post nadir) of BCS. Data were examined using logistic regression, ANOVA, and time to event analyses. Initial univariable models were followed by multivariable models that considered parity category, calving season, BCS1, and average milk yield up to 30 DIM (M30) as covariables. Sick cows and high producing cows had increased DIM at nadir, while lower BCSdry, greater M30, and occurrence of disease were associated with lower nBCS. Cows that conceived at AI1 had their nBCS earlier (45.1 ± 0.32 d) than cows that remained open after first AI (46.4 ± 0.35 d). On the contrary, DIM at nBCS did not differ by pregnancy loss status. The logistic regression analyses reported smaller odds of P/AI1 in cows in the lower nBCS categories. Likewise, cows with larger loss in BCS between calving and nadir had smaller odds of P/AI1. Although cows that lost their pregnancy had lower nBCS, this association was not consistent across the analyses. The time to and magnitude of nBCS, together with the ∆BCS from calving to nadir could be useful measures to evaluate the transition and early lactation status of dairy cows.

The transition from gestation to lactation requires adjustments in nutrient consumption that are challenging for the postpartum dairy cow. As milk energy output increases more rapidly than energy intake, most cows mobilize fat and labile protein from body energy reserves, which results in reductions in body condition score during early lactation. The objective of this study was to identify variables associated with the extent of the lossin body condition score (BCS) during early lactation and to characterize the effects of the nadir BCS on the subsequent pregnancy at first artificial insemination and pregnancy loss in Holstein cows. Parity, disease presentation, and milk yield were associated with the time and magnitude of nadir BCS. Sick cows and high producing cows had increased DIM at nadir, while lower BCS at dry-off, greater milk yield, and occurrence of disease were associated with lower nadir BCS. Overall, cows with later and lower nadir BCS and greater loss of BCS between calving and nadir had poorer fertility. Monitoring nadir BCS could be a useful tool for evaluating the transition and early lactation status of dairy cows.

Prepartum factors associated with postpartum diseases in pasture-based dairy cows.

This cross-sectional observational study aimed to identify prepartum management, environmental, and animal factors associated with clinical -lameness, metritis, mastitis- and subclinical -calcium imbalance, magnesium imbalance- diseases in pasture-based dairy cows. A total of 565 cows from 25 commercial dairy farms in southern Chile were enrolled over four months. Data on prepartum management and environmental conditions were obtained through a survey and inspections of prepartum paddocks. Cows were evaluated two times. In the first evaluation, between 30 to 3 days before calving, cows were assessed for lameness, body condition score, and blood samples were collected to measure nonesterified fatty acid (NEFA), calcium (Ca), and magnesium (Mg). In the second evaluation, between 3 to 21 DIM, cows were assessed for metritis, lameness, and blood samples were collected and analyzed for total Ca and Mg concentration. Cows were considered as having Ca imbalance if Ca < 2.0 mmol/L, and Mg imbalance if Mg < 0.65 mmol/L. Postpartum clinical mastitis was diagnosed based on the foremilk's daily condition and udder assessed by the milker at each milking during the postpartum transition period. Multivariable logistic regression models, controlling for the farm as a random effect, were built to identify prepartum factors for each postpartum disease. The odds of postpartum lameness were higher for cows that were lame during the prepartum period, had elevated prepartum NEFA concentrations, had greater parity, and for cows that were kept in paddocks with no grass cover. The odds of metritis were higher in cows with lower parity, with increased prepartum NEFA, in cows that had dystocia, and farms with predominantly Holstein breed, and that did not have calving records. The odds of clinical mastitis were higher for cows lame during the prepartum period. The odds of Ca imbalance were higher in cows with a long dry period, dystocic calving, and in farms without prepartum anionic salts supplementation. The odds of Mg imbalance were higher in cows with lower prepartum Mg concentrations, higher prepartum Ca concentration, and higher parity. Our findings indicate that farmers could benefit from refining these areas to improve their cows' health and welfare.