During the peripartum, dairy cows face an increased demand for nutrients to support the initiating lactation. As this demand is followed by slower increments in dry matter intake (DMI), the levels of energy consumption do not meet the energetic requirements of the starting lactation.
In response, the resulting negative energy balance (NEB) triggers fat and labile protein mobilization from body energy reserves, conducing to significant alterations of the carbohydrate, lipid, protein and mineral metabolism. This environment of metabolic changes around calving results in loss of body condition and increased serum concentrations of fatty acids, ketone bodies and acute-phase proteins, accompanied by compromised innate immunity and impaired health status.
Assessing the impacts: Body condition scoring
Due to the detrimental impact of pronounced and extended periods of negative energy balance, the evaluation of the energy reserves by body condition scoring (BCS) is a monitoring practice implemented in dairy farms. Body condition scores are considered an indirect measure of the level of subcutaneous fat, assessed on a 1 (severe underconditioning) to 5 (severe overconditioning) point scale with 0.25-point increments.
The detrimental effects of inadequate energy balance during the peripartum on cow fertility have been widely explored, and research highlights the impact of low body condition scores at calving, as well as the negative effect of significant loss in body condition following dry-off and during the transition period. In addition, cows that lose body condition during early lactation have more health events than cows that gain or maintain body condition. Moreover, cows with the greatest body condition score loss during early postpartum display worsened embryo development during the first week of gestation.
Remarkably, although the interest in body condition scores is increasing, it is estimated that only one-third of the dairy farms have implemented this scoring into their management practices. Limitations such as subjectivity and significant use of time are proposed as the main reasons for low levels of application at the farms and, as a response, new automated technologies such as the use of 3D have been developed.
The extra challenge of disease
The interrelationship between loss in body condition score and occurrence of disease during the transition period is complex, and establishing precise cause-and-effect associations is challenging. Increased risk of milk fever, ketosis, fatty liver, metritis, digestive disorders and mastitis in cows with greater loss of body condition score after calving has been reported. Conversely, diseases associated with reduced feeding time and decreased DMI would result in increased loss of body reserves and deviation of energy resources for the immune response.
To better understand these associations, our group has explored the dynamics of the changes in body condition score in cows affected by different health disorders around calving. As evidenced by use of daily automated body condition scoring (DeLaval BCS cameras), cows that remained healthy and calved with intermediate body condition scores were able to maintain the greatest body condition scores after 30 days in milk (DIM) (Figure 1).
Interestingly, cows with ketosis started with the greatest body condition scores at calving but had a more pronounced drop in body condition scores than healthy cows after calving. Also, cows with left displacement of the abomasum dropped to the lowest body condition scores after the second week postpartum, and the affected cows continued losing body condition until day 50.
In a recently published study from our group, we observed a significant impact of both change in body condition scores from calving to 40 DIM and disease on multiple reproductive measures, including resumption of ovarian cyclicity, pregnancy at first artificial insemination and early pregnancy loss. Fertility was clearly impacted by body condition score loss, especially when the change was greater than three-quarters of a point (excessive loss), while reproductive diseases (dystocia, twins, retained fetal membranes, metritis and clinical endometritis) had greater impact than non-reproductive diseases (subclinical ketosis, left displaced abomasum, lameness, clinical mastitis and respiratory disease) on reproductive outcomes. Specifically, the odds of resumption of ovarian cyclicity in cows with excessive body condition score loss were half the odds of cows that gained body condition score. The odds of pregnancy at 150 DIM (P150) in cows that gained body condition score were 1.61 times greater than the odds of P150 in cows with severe body condition score loss.
When health status was analyzed, cows with reproductive or non-reproductive disorders had smaller odds of resumption of ovarian cyclicity compared with healthy cows (Or = 0.65 and 0.79, respectively). For pregnancy outcomes, cows with reproductive disease had smaller odds of pregnancy at the first A.I. and at 150 DIM compared with healthy cows (Or = 0.70 and 0.73, respectively). As expected, both loss of body condition score and health status had a significant effect on culling and death.
Interestingly, when cows are grouped combining the categories of body condition score change and their health status, the impact of these variables on fertility increases. Figure 2 presents fertility measures by body condition score change within health groups.
The detrimental effect of body condition score loss appears consistent across health groups, but it seems worsened when cows have concurrent disease, especially reproductive disorders.
The use of information on body condition score change and health status, which is accessible in modern dairy farms, could assist in making more informed decisions regarding management or culling during early lactation.
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