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A Prospective Study of Calf Factors Affecting Age, Body Size, and Body Condition Score at First Calving of Holstein Dairy Heifers

¹ Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802
² Department of Biostatistics/School of Public Health, University of Washington, Seattle 98195
³ Department of Animal Science, University of Tennessee, Knoxville 37996
⁴ Department of Agricultural Education, University of Florida, Gainesville 32611

Corresponding author: A. J. Heinrichs; e-mail: AJH{at}psu.edu.

Data were collected prospectively on parameters related to first calving on 18 farms located in Northeastern Pennsylvania. This project was designed to study possible residual effects of calf management practices and events occurring during the first 16 wk of life on age, BW, skeletal growth, and body condition score at first calving. Multiple imputation method for handling missing data was incorporated in these analyses. This method has the advantage over ad hoc single imputations because the appropriate error structure is maintained. Much similarity was found between the multiple imputation method and a traditional mixed model analysis, except that some estimates from the multiple imputation method seemed more logical in their effects on the parameter measured. Factors related to increased age at first calving were increased difficulty of delivery, antibiotic treatment of sick calves, increased amount of milk or milk replacer fed before weaning, reduced quality of forage fed to weaned calves, maximum humidity, mean daily temperature, and maximum ammonia levels in calf housing areas. Body weight at calving tended to increase with parity of the dam, increased amount of grain fed to calves, increased ammonia levels, and increased mean temperature of the calf housing area. Body condition score at calving tended to be positively influenced by delivery score at first calving, dam parity, and milk or milk replacer dry matter intake. Withers height at calving was positively affected by treatment of animals with antibiotics and increased mean temperature in the calf area. This study demonstrated that nutrition, housing, and management factors that affect health and growth of calves have long-term effects on the animal at least through first calving.

Key Words: calf and heifer management • multiple imputations • longitudinal data analysis

Abbreviation key: AFC = age at first calving, ADG = average daily gain, BCSC = BCS at calving, BWC = BW at calving, MAR = missing at random, MCAR = missing completely at random, MI = multiple imputation, MNAR = missing not at random, MM = mixed models, WHC = withers height at calving