Evaluation of classification modes potentially suitable to identify metabolic stress in healthy dairy cows during the peripartal period1

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Abstract
The transition of pregnancy to lactation, with the concomitant negative energy balance during early lactation, requires substantial adaptive performance of the cow. Apart from clinical disease problems, the identification of cows with suboptimal adaptation is relevant to be able to adequately treat these animals or modify the ration. Effective approaches are necessary to provide maximal information at the earliest time possible. We therefore aimed to identify a measurement that, when applied at a defined point in time relative to calving, was relevant as much as possible to other information on metabolic and health status during early lactation. Blood samples were collected weekly from 4 wk antepartum to 12 wk postpartum from 38 high-yielding Holstein-Friesian cows. Nonesterified fatty acids, beta-hydroxybutyrate, IGF-I, and leptin were measured in serum, and BCS was recorded. Health status was characterized using the concentrations of haptoglobin, the number of leukocytes and neutrophils, as well as the activity of glutamate dehydrogenase (GLDH) in blood to evaluate liver status. Using the factors related to fat mobilization, the animals were classified according to their values recorded at one defined point in time or time interval as being above or below certain thresholds. For each criterion, the groups classified were compared with regard to the time-course yielded from all recordings. From 7 criteria of classification, the most closely related to the variables of fat mobilization was obtained when using NEFA and IGF-I (thresholds of 0.5 mM and 39 ng/mL in wk 1 postpartum, respectively). Both items were then combined into to the criterion NEFA + IGF-I. Applying these criteria, the relations to indices of health and liver status were detectable on the basis of NEFA- and NEFA + IGF-I-classes, which yielded differences in both GLDH and leukocyte numbers. Animals with NEFA > 0.5 mM showed increased GLDH activity but decreased leukocyte numbers. The time and effort required for measuring the IGF-I-concentration in addition to NEFA is not justified for evaluating the metabolic status. Nonesterified fatty acid values ≥0.5 mM during the first week of lactation were considered as the most suitable criterion for identifying limited adaptive performance. Copyright © 2007. . Copyright 2007 Journal of Animal Science

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