Associations between body weight estimated with three-dimensional cameras and milk yield in Holstein, Jersey, and Red...

Precision livestock farming technologies, such as three-dimensional (3D) imaging, offer novel opportunities for automated and real-time BW monitoring in dairy cows. This study examined the relationship between BW, BW changes, and 305-day energy-corrected milk (ECM) yield in Holstein, Jersey, and Red Dairy Cattle cows from commercial Danish herds. Using 3D cameras, daily BW was estimated in 7 750 complete lactations. Results showed that BW at calving was positively associated with ECM yield in primiparous cows, emphasising the importance of adequate BW at first calving for productivity. While higher average BW in primiparous cows was beneficial, this effect diminished in multiparous cows, suggesting that heavier cows do not necessarily produce more milk but instead allocate more energy to maintenance. Multiparous cows also experienced greater BW losses in early lactation and reached their minimum BW later than primiparous cows, indicating increased metabolic challenges with advancing parity. These patterns show that 3D imaging-based BW estimates reflected expected biological changes and were consistent with results from scale-based studies. In addition, an external comparison with independent slaughterhouse records showed strong correlations (r ≥ 0.89) between BW predicted using 3D imaging during the last 7 days on-farm before slaughter and slaughterhouse-recorded weights. This comparison provides supportive evidence from an independent dataset but should not be interpreted as a formal validation of individual-level prediction accuracy. Given its high-frequency and automated monitoring capabilities, 3D imaging presents a valuable tool for precision management that enables early detection of energy balance issues and supports improved heifer management through better monitoring of BW at first calving.