Álvaro García
Dairy cows undergo physiological changes post-calving, that disrupt the balance between nutrient demand and dry matter intake, resulting in negative energy balance (NEB). This imbalance triggers metabolic adaptations affecting their immune system, increasing serum fatty acids and beta-hydroxybutyric acid (BHB), and causing body condition loss, which heightens susceptibility to health disorders. Simultaneously, acute-phase proteins like C-reactive protein and haptoglobin rise, part of the cow’s response to inflammation or tissue damage. Understanding these changes and their interactions is crucial for managing dairy herd health and optimizing productivity.
The body condition score (BCS) at calving significantly impacts subsequent milk yield and pregnancy rates, with low BCS linked to reduced outcomes, while over-conditioning raises the risk of metabolic diseases. Managing BCS changes from dry-off through the transition period is essential for fertility, overall health, and survival. Over-conditioning at dry-off reduces dry matter intake (DMI), increases BCS loss, lowers pregnancy rates per artificial insemination (AI), and hampers embryo development. Postpartum, cows are susceptible to health issues like uterine and metabolic disorders, reducing fertility and milk yield and increasing culling rates. Significant BCS loss post-calving increases the risk of milk fever, ketosis, fatty liver, metritis, digestive disorders, and mastitis. Cows mobilizing nutrients extensively exhibit higher serum fatty acids (FA) and BHB, along with lower milk yields. Diseases further diminish feeding time and DMI, exacerbating body reserve loss and feed inefficiency.
Recent research
A study conducted at Colorado State University (Manriquez et al., 2021) examined how decreases in body condition score (BCS) postpartum affected Holstein cows (n = 11,733) with specific health disorders. The research focused on reductions in BCS between 5 and 40 days in milk (DIM) and their impact on fertility (resumption of ovarian cyclicity, pregnancy at first artificial insemination [PAI1], pregnancy loss at 60 days, pregnancy at 150 days [P150], and pregnancy at 305 days [P305]), average daily milk yield in the first 90 DIM (M90) and culling or death after 40 DIM (CD). Cows were categorized into those with reproductive disorders, other health disorders, or healthy within 40 DIM. The voluntary waiting period ranged from 40 to 70 DIM, with breeding managed through timed AI and heat detection, and milking frequencies varied from 2 to 4 times per day. Cows were enrolled at calving, and 33% were primiparous. They were monitored weekly for disease, reproductive events, culling, and death.
Body condition was assessed at 5 (BCS5) and 40 DIM (BCS40) using a scale from 1 to 5 in 0.25-point increments. Cows’ BCS was categorized as low (<2.75), moderate (2.75 to 3.5), high (3.75 to 4.25), and excessive (>4.25). Based on the difference between these assessments, cows were classified into four categories: excessive loss (EL; BCS decrease ≤ -0.75), moderate loss (ML; BCS decrease = -0.5 to -0.25), no change (NC; BCS change = 0), or gain (GN; BCS increase ≥ 0.25).
Disease monitoring and BCS assessments were conducted weekly, with research personnel receiving periodic training on BCS. Health events, including calving-related issues, left displaced abomasum, mastitis, and respiratory disease, were recorded using on-farm software, and only those diagnosed within the first 40 DIM were included in the analyses. Health events were categorized into reproductive disorders (REP; dystocia, twins, retained fetal membranes, metritis, clinical endometritis), other disorders (OTH; subclinical ketosis, left displaced abomasum, lameness, clinical mastitis, respiratory disease), and healthy cows (HLT) with no disease events.
Overall, the mean BCS at 5 DIM (BCS5) and 40 DIM (BCS40) were 3.18 and 2.97 points, respectively, with a mean decrease of 0.21 points over the study period. Primiparous (PP) cows had higher BCS5 (3.22 vs. 3.15) and BCS40 (3.04 vs. 2.93) compared to multiparous (MP) cows. The BCS change was less in PP cows compared to MP cows (decrease of 0.18 vs. 0.23 points).
This study underscores the critical role of managing BCS changes and health status during early lactation to optimize dairy cow health, productivity, and longevity.
The study revealed that changes in body condition score (BCS) did not significantly interact with health group outcomes, emphasizing their independent effects. BCS change notably influenced ovarian cyclicity resumption and achieving pregnancy at 150 days in milk (P150); cows gaining BCS had higher odds of ovarian cyclicity and achieving pregnancy at 150 days compared to those with excessive BCS loss. Health status significantly affected ovarian cyclicity, pregnancy at first artificial insemination (PAI1), P150, and P305 within the first 40 days in milk; cows with reproductive disorders (e.g., dystocia, retained fetal membranes, metritis, clinical endometritis) or other health disorders (such as subclinical ketosis, left displaced abomasum, lameness, clinical mastitis, respiratory disease) showed lower odds of ovarian cyclicity and reduced pregnancy rates compared to healthy cows, except for those with other health disorders concerning PAI1, P150, and P305. Overall, the study underscores the impact of parity, BCS changes, and health status on reproductive and health outcomes in Holstein cows, with primiparous cows exhibiting higher BCS and reproductive disorders but lower rates of other health disorders than multiparous cows, indicating that healthier cows or those with less BCS loss show better reproductive performance.
Impact of Changes in BCS and Health Group on Milk Yield and Survival
The study found that changes in BCS and health status were significantly linked to average daily milk yield within the first 90 days of lactation (M90). Cows that experienced excessive or moderate BCS loss (EL: 87.0 ± 2.49 lb/day; ML: 85.8 ± 2.45 lb/day) tended to have higher M90 compared to those with no change (83.5 ± 2.47 lb/day) or gain (79.8 ± 2.47 lb/day) in BCS. This suggests that cows losing BCS tended to yield more milk on average per day during this early lactation period. Conversely, cows with reproductive-related events (81.6 ± 2.45 lb/day) showed lower M90 compared to those experiencing other health-related issues (85.4 ± 2.47 lb/day) or healthy cows (85.0 ± 2.45 lb/day). These findings highlight how changes in BCS and health status impact milk production early in lactation, with BCS loss potentially stimulating higher milk yields despite the associated metabolic challenges.
Implications
Effectively managing BCS and health post-calving is essential for optimizing dairy cow health, productivity, and longevity amidst the physiological challenges of negative energy balance and metabolic adaptations. Maintaining appropriate BCS at calving is critical as low scores correlate with reduced milk yield and fertility, while over-conditioning increases metabolic disease risks. The study from Colorado State University highlights that cows experiencing excessive BCS loss face elevated risks of health complications and diminished reproductive performance. Importantly, the interaction between changes in BCS and health status did not significantly affect milk yield, indicating independent impacts on productivity. This echoes existing literature on the detrimental effects of BCS loss and health disorders during early lactation, emphasizing their persistent influence on long-term productivity and culling risk. Understanding these dynamics informs improved management practices aimed at enhancing dairy herd health and profitability across diverse production environments. Recommendations include regular BCS monitoring, early detection of health issues, and tailored nutritional management during the critical transition period to mitigate postpartum challenges such as milk fever and mastitis. By integrating BCS management with proactive health protocols, dairy farmers can achieve healthier cows, higher productivity, and improved profitability, thereby supporting animal welfare and the sustainability of dairy operations.
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