Supplemental document for Journal of Dairy Science article: Associations among body condition score, body weight and serum biochemistry in dairy cows

<b>Interpretive Summary: </b>Body condition score and body weight are different measures of body tissue reserves of dairy cattle that were explored separately and in combination with novel categorization in a large, multi-site, cross-sectional study. Serum albumin and glucose were consistently and positively associated with body measures. Urea, BHB, cholesterol, milk production and calcium were also associated with body measures. The BCS decreased and BW increased with increasing parity, with no interaction between metabolites and parity in these models. These findings suggest that greater insights into the metabolic physiology of cows could help to achieve optimal body condition and cow health.<b>Abstract: </b>Body condition score (BCS) and body weight (BW) yield insights into body tissue reserves and diet while serum biochemical measures reflect the metabolic status of cows. Associations between body composition measures and biochemistry are unclear and investigation may reveal important information on the metabolic and physiological status of cattle with varying levels of labile tissue reserves. Cohorts of 739 non-lactating, late pregnant, ‘dry’ cows (26.9d prepartum, 12.4SD) and 690 peak milk cows (58.0DIM, 14.5SD) were selected by stratified (parity: 1, 2, 3, &gt;3) random sampling from 30 farms (15 pasture, 15 TMR) in this cross-sectional study. A single serum, BCS (1-5 scale), BW and milk production datum were collected per cow, per cohort between Nov 2022 and Jul 2023. Eleven analytes were collected, analyzed and standardized within group (cohort/breed/farm). Mixed linear models for BCS and BW were specified, with random effect of group. A 6-point, unordered, categorical body-group classification that combined BCS (&gt;, equal, or &lt; group median; as High, Median or Low BCS) and BW (&gt; or &lt; group median; as High or Low BW) was analyzed by polytomous logistic regression. Effect sizes are listed for a 1 SD increase the specified analyte, keeping other covariables at their mean value. Dry BCS was positively associated with albumin (0.075BCS±0.014SE), urea (0.038BCS±0.014SE) and glucose (0.052BCS±0.014SE), and negatively with the interaction between cholesterol and days pre-calving. Dry BW positively associated with albumin (11.03kg±2.48SE) and negatively with cholesterol (-8.47kg±2.57SE). Peak milk BCS was positively associated with albumin (0.47BCS±0.015SE), β-hydroxybutyric acid (BHB: 0.048BCS±0.015SE) and glucose (0.051BCS±0.015SE). Peak milk BW was positively associated with albumin (6.94kg±2.35SE) and negatively with Ca (-7.02kg±2.33SE). Increasing BW and decreasing BCS was associated with increasing parity, except in dry 2nd parity cows that had low BCS. The dry polytomous model associated a 1 SD increase in albumin with a 4.89%±1.56SE decreased risk of being low BCS/low BW and 5.87%±1.46SE increased risk of high BCS/high BW. Risk change associated with 1 SD glucose was -5.61%±1.58SE for low BCS/high BW and 3.17%±1.58SE for high BCS/high BW. For the peak milk cohort, change in risk was associated with albumin for low BCS/low BW -3.67%±1.56SE, low BCS/high BW -3.22%±1.53SE. Risk change with 1 SD BHB was -3.36%±1.47SE for median BCS/low BW, 2.86%±1.44SE for high BCS/low BW and 2.69%±1.37SE for high BCS/high BW. Risk of low BCS/low BW was greatest in 2nd parity cows, while high BCS/high BW was greatest in &gt;3rd parity dry and 3rd parity peak milk. There were no interactions between parity and analytes. Albumin was consistently associated with BCS and BW, potentially reflecting innate differences in protein metabolism of cows.