Evaluation of Heifer Management Criteria for Improved Lactation and Reduced Dystocia: A Systematic Analysis of Body Weight, Average Daily Gain, and Age

Decisive heifer management for improved lactation and reduced dystocia requires a systematic analysis of age, body weight (BW), and average daily gain (ADG) using an adequately large sample size. The objective of this study was to determine effects of BW and age at first breeding and ADG until pregnancy on yields of milk, milk fat, and milk protein in the first lactation and the occurrence of dystocia in Holstein heifers. Production, reproduction, and growth data for 3208 heifers from three large Holstein herds were recorded and used. Heifers were divided to four groups based on ADG including 1) < 700 g/d, 2) 700-750 g/d, 3) 750-800 g/d, and 4) > 800 g/d. Based on BW at the commencement of pregnancy, heifers were divided to three groups of 1) < 350 kg, 2) 350-380 kg, and 3) > 380 kg. Based on age at the start of pregnancy, heifers were divided to three groups of 1) < 14 mo, 2) 14-15 mo, and 3) > 15 mo. Results demonstrated that weight and age at first breeding affected (p < 0.05) milk production in the first lactation, such that heifers with > 380 kg body weight (11499 kg milk) and > 15 mo age (11430 kg milk) at breeding had the highest milk production. Heifers with > 800 g/d ADG tended (p < 0.10) to have higher milk and milk protein production during the first lactation compared to other ADG groups. Heifers with 700-750 g/d ADG had the highest milk fat production among ADG groups. Heifers with > 380 kg BW at first breeding had higher milk fat production (349 kg) in their first lactation compared to heifers with > 350 kg BW (334 kg) and 350-380 kg BW (336 kg). Heifers with > 800 g/d ADG (24.4%) had higher (p < 0.05) occurrence of dystocia compared to heifers with ADG of < 700 g/d (14.2%), 700-750 g/d (11.3%), and 750-800 g/d (20%). Heifers with < 350 kg BW at first breeding had higher occurrence of dystocia than did the other BW groups (p < 0.05). In conclusion, greater heifer BW (>380 kg) and age (>15 mo) at first breeding were associated with greater productive performance during the first lactation, but heifers with the age of < 23 mo at first calving had decreased milk production and increased occurrence of dystocia. Thus, ADG prior to conception and BW and age at first breeding all affect production performance in the first lactation and dystocia incidence rate at first calving.