Álvaro García
The purpose of body condition scoring (BCS) is to provide a quick and cost-effective method for assessing a cow’s energy reserves. Cows with insufficient or excessive energy reserves often experience reduced fertility, particularly during rapid changes in energy status. Monitoring changes in BCS is crucial for effective fertility management, with recommended scoring intervals including the transition period, 60 days post-calving, approximately 100 days pre-drying off, and at drying off. It is essential to ensure that all farm staff are trained in BCS measurement by experienced observers and that scoring systems remain consistent across the farm for accurate assessment and trend identification. Additionally, variability between observers in BCS measurements can be a challenge. However, the introduction of 3D imaging technology has shown promise in reducing this variability by providing more objective data and minimizing the subjective element of traditional scoring methods. This enhancement in accuracy and reliability improves BCS assessment across different observers.
Excessive body condition score
Excessive BCS, particularly at calving, is strongly associated with diseases such as ketosis, leading to reduced fertility. This connection to disease arises because overweight cows have reduced appetites and more body fat to mobilize. Additionally, excessive BCS can detrimentally affect fertility even without apparent clinical disease. Excessively fat cows may experience longer intervals to ovulation, first heat, insemination, and conception, as well as reduced first-service conception rates. While significant issues typically arise when cows exceed the target by a considerable margin (e.g., scoring 4.5 on a 1-5 scale), cows with a BCS of 4 may still exhibit effects on the calving to first estrus interval.
The primary driver behind high BCS and poor fertility is the loss of body condition score. Cows with high BCS at calving often experience more significant condition loss between calving and the point of their lowest BCS (nadir). Greater and faster loss of body condition post-calving is associated with poorer fertility across various parameters, from the calving to first estrus interval to the proportion of cows culled due to infertility. This extensive impact of BCS loss on fertility stems from its effects on the ovary, uterus, and brain axis, which produces hormones controlling the estrus cycle. The precise impact of excessive BCS loss varies significantly between farms and depends on factors such as the voluntary waiting period, farm system, and underlying fertility. Research indicates that cows losing <0.5 body condition score between calving and BCS nadir ovulate and are served sooner than cows with ≥1 BCS loss. Research also suggests that cows gaining BCS show heats earlier than those losing BCS. These findings underscore the importance of minimizing BCS loss in early lactation to achieve fertility objectives. Excessive BCS loss not only affects a cow’s ability to conceive but also her ability to maintain pregnancy. Additionally, recent research has also determined that BCS loss between days 28 and 56 increased embryo losses. The graph below illustrates the case of cow 118, from a farm using 3D imaging technology to monitor its cows. She was inseminated on day 435 when she showed her first heat, with a body condition score (BCS) 0.5 points above her ideal BCS, and subsequently diagnosed as pregnant. It’s worth noting that her BCS was increasing at the time of insemination.
Low body condition score
While high BCS is directly and indirectly linked to poor fertility, the solution does not lie in keeping cows under-conditioned, as low BCS is also associated with reduced fertility. Like excess BCS loss, poor body condition (i.e., BCS below the targets outlined in Table 1) impacts fertility measures from estrus return to final pregnancy rates. However, these effects are less consistent than those observed for excess BCS loss. Nevertheless, cows with below-target BCS generally experience poorer fertility than those meeting the targets, along with reduced milk production. Research has reported that the calving-conception interval decreased by 6 days for every 1 unit change in BCS. In addition to these direct effects, cows with low BCS face an increased risk of uterine diseases such as endometritis. Therefore, as with high BCS, there is an indirect link from low BCS to poor fertility. Furthermore, although low BCS at calving tends to be associated with reduced BCS loss afterward, this is not a certainty. It remains vital to ensure that BCS loss is not excessive, even in cows failing to meet their BCS targets.
The graph below depicts cow 88, a very thin cow that began her lactation with a BCS of 3.2, declined to 2.6 by 30 days in milk, and remained below this value thereafter. She displayed no apparent estrus during her first 130 days in milk. Despite her production exceeding expectations, it has been highly erratic, characterized by intermittent peaks and valleys. This pattern suggests that she lacks sufficient energy reserves to consistently sustain higher productivity levels.
Managing Body Condition Score (BCS)
BCS data serves as a valuable ongoing information source, requiring not just recording but also continuous monitoring, issue identification, and implementation of solutions. Utilizing computer recording simplifies this process, facilitating the creation of useful outputs and the evaluation of management changes’ effectiveness. Avoiding excessive BCS change post-calving is crucial to optimize fertility. While increasing energy intake by feeding more high-energy-density feed may seem like a straightforward solution, it often has minimal impact on BCS loss or fertility. This is because cows fed high levels of concentrates primarily allocate the additional energy to milk production, offering limited benefits in reducing negative energy balance and BCS loss. Moreover, low-fiber diets can lead to reduced feed intakes due to fluctuations in rumen pH, affecting appetite. Properly formulated diets and effective transition from dry to lactating diets are essential for optimizing intake post-calving. Adequate bunk space is also critical, as insufficient space per cow can decrease intakes, particularly in less dominant cows. Ultimately, the focus of BCS management should be achieving the target BCS (2.5 to 3.0) at calving.
Achieving Target BCS at Calving
Drying off cows with excessively high BCS, necessitating BCS loss during the dry period, is suboptimal. Such cows are more likely to experience difficult calving (dystocia) and face a higher risk of culling during the subsequent lactation. Monitoring cows in late lactation, especially in the last three months, and adjusting feed (or increasing milk production) if BCS is too high can help avoid these issues. Increasing BCS is more feasible during the dry period due to higher plasma insulin concentrations and reduced energy partitioning into milk. However, prolonged dry periods, potentially caused by fertility problems, increase the risk of over-fat cows at calving. Conversely, a short dry period may not allow sufficient time for economical BCS increase. Therefore, the target is for cows to be dried off at the same BCS as they calve, with focus on maintaining rather than increasing or decreasing BCS during the dry period.
Implications
Effective management of body condition is critical for optimizing fertility and overall herd health in dairy cattle. Body condition scoring provides a valuable tool for assessing energy reserves, with the goal of achieving and maintaining BCS targets throughout lactation. While excessive body condition can lead to metabolic disorders and reduced fertility, under-conditioned cows also face challenges in conception and productivity. Utilizing innovative technologies like 3D imaging alongside traditional scoring methods enhances accuracy and reliability, overcoming challenges associated with observer variability. By implementing sound management practices, such as proper nutrition, adequate bunk space, and strategic dry period management, farmers can work towards achieving optimal BCS and ultimately improve fertility outcomes within their herds. Effective body condition management not only enhances reproductive success but also contributes to overall profitability and sustainability in dairy farming operations.
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