Associations of growth rates during the first 2 months of life with feeding behavior, development, and first-lactation performance in Holstein heifers

Early-life growth and development are crucial for the future performance of replacement heifers. Optimizing growth enhances immediate performance and establishes the foundation for long-term productivity, improving overall efficiency in milk production. This study retrospectively investigated the associations between growth rates during the first 2 mo of life and feeding behavior during the preweaning period, overall growth, and first-lactation performance in Holstein heifers under a high milk allowance. In this study, 42 female Holstein calves were retrospectively grouped based on their ADG before weaning during an intensified milk replacer (MR) program (12 L MR/d for 8 wk, followed by gradual weaning until wk 14). Two clusters were obtained: (1) maximum daily gain (MAX; n = 21; 1.06 ± 0.06 kg/d, mean ± SD) and (2) moderate daily gain (MOD; n = 21, 0.84 ± 0.05 kg/d). The MAX calves had significantly higher preweaning MR intakes and 1.20-fold better feed efficiency (gain:feed ratio in kg/Mcal) during the first 2 wk of life (individual housing, 2 meals per d). During the subsequent group housing period, the calves had access to automatic feeders for both MR and concentrate. At weaning (wk 14), the MAX calves were 16 kg heavier than the MOD calves (MAX: 149 ± 9.3 kg; MOD: 133 ± 7.3 kg). Similarly, concentrate intake for MAX was greater in wk 10 to 12. During the MR-feeding period, MAX calves visited the MR-feeding stations more frequently than MOD calves, both in total and relative to their visits at the concentrate feeder. A random forest analysis showed that the ratio of visits to the MR and concentrate stations can serve as an indicator of growth rate during both the preweaning and weaning periods. The MAX heifers remained heavier than the MOD heifers, reaching the 400 kg of BW threshold for first insemination 42 d earlier than the MOD group. In all 3 stages (early, mid, and late) of their first lactation, the milk yield of MAX exceeded that of MOD. The daily milk yield of MAX heifers averaged 37.5 ± 4.7 L across lactation, which was 3.8 L/d more than MOD (33.7 ± 4.7 L/d). This also resulted in a higher 305-d milk yield for MAX, reaching 11,511 ± 821 kg (MOD: 10,242 ± 1,088 kg). Milk composition differed between the groups, with lower MUN and a trend toward higher lactose concentrations in MAX heifers. In this long-term study, preweaning ADG under an intensified MR-feeding program proved to be a robust predictor of subsequent growth, reproductive maturity, and milk yield in the first lactation, enabling data-driven selection of optimal replacement heifers. The integration of sensor data on automated feeding behavior enhances precision management of high-potential animals and supports sustainable improvements in herd productivity and profitability.