Validation of ultrasound procedures to measure body condition in preweaned calves and the relationship to performance

Abstract

Body condition scoring (BCS) is widely utilized in the dairy industry as both a management tool and a proxy for assessing animal welfare. However, BCS evaluations can be highly subjective, often exhibiting considerable inter-assessor variability, and remain largely invalidated in preweaned dairy calves. In adult dairy cattle, BCS has been correlated with objective measures such as backfat thickness (BFT) and muscle thickness (MT) via ultrasonography. These established associations in mature, lactating cows support the potential for adapting similar ultrasound-based methods to validate BCS in preweaned calves. The objective of the first study was to explore the use of ultrasonography for analyzing internal physical structures (BFT, MT, and total thickness [TT]) in preweaned dairy calves and their associations with BCS. Additional predictors such as hip height (HH), age, and body weight (BW) will be assessed for the relationship with BCS. We hypothesize that preweaned dairy calf BCS will be associated with the physical composition measurements obtained via ultrasonography. Because dairy calf BCS has not been widely explored, this preliminary study aims to provide insight into objective BCS assessments. Preweaned, female Holstein dairy calves (n = 202) were enrolled at arrival and evaluated every two weeks (biweekly) for BCS, BW, and ultrasound parameters. Ultrasound examinations were conducted in the area between the tuber ischii, the tuber coxae, and above the coxofemoral joint on the left side of the body. Ultrasound images were analyzed to determine BFT (area from the termination of the skin to the termination of the profound fascia) and MT (area from the termination of the profound fascia to the termination of the gluteal muscle) for each calf. Linear mixed models were utilized to estimate the relationships between BCS and ultrasound measurements and included the fixed effects of age group, BFT, and MT, and the random effects of animal and nutritional study. Visual BCS of preweaned dairy calves was associated with BFT and MT with regression coefficients of 0.096 ± 0.011 and 0.016 ± 0.006, respectively. Calves increased in BCS across the preweaning period, with the highest BCS (2.47 ± 0.07) recorded at greater than 56 d and the lowest between 0-27 d (2.09 ± 0.07). Age was highly correlated with BW (r = 0.91) which resulted in multicollinearity; therefore, BW was excluded from the initial analysis. A secondary model was fit that included BW and excluded age group. In the secondary model, BW was associated with higher BCS with a regression coefficient of 0.016 ± 0.001; however, MT was not associated with BCS when BW was included in the model. Our results suggest that BCS in preweaned calves is related to body composition, specifically BFT. In addition, we found strong associations between BCS and age or BCS and BW. Our results also suggest that a relationship between MT and BCS may exist. As increased attention is placed on preweaned calf performance, nutrition, and health, these results may be useful to determine if BCS is a relevant method of assessment specifically around the age of evaluation or if other measures of nutritional status such as BW and ADG targets are more beneficial. The objective of the second study was to examine how BFT, MT, TT, and BCS at weaning relate to management practices, health events, and performance metrics such as average daily gain (ADG) and dry matter intake (DMI). These types of associations have not been fully investigated in dairy calves. We hypothesize that calf body composition and BCS at weaning are influenced by early-life growth, management, and physical characteristics. Understanding the relationship between early-life events and physical composition at weaning could impact management strategies and support future cow success. Preweaned, female Holstein calves (n = 81) were enrolled in this study. Data on DMI, fecal scores, treatment costs, ADG, and hip heights were obtained from the heifer raiser. Ultrasound parameters (BFT, MT, TT) and visual BCS evaluations were collected once every two weeks (biweekly) by the researcher. Findings from this study demonstrate that ADG at day 56 was a consistent predictor of increased BFT, MT, TT, and BCS at weaning. DMI intake and hip height were significantly associated with body composition measures, while HMI and milk solids intake were positively associated with BCS. These results highlight the importance of ADG and nutrition for optimal calf development during the preweaning period.