What affects the costs of raising replacement dairy heifers: a multiple-component analysis.

A DP model of a dairy replacement herd was developed to analyze the impact of different dairy and replacement herd variables on the cost of rearing replacements for a representative dairy herd of 100 cows. A model was developed with Pennsylvania and US average information as the basis for the parameters. We used age at first calving of 25 mo, calving interval of 13 mo, herd-culling rate of 25%, and preweaned calf death of 10% as the base for comparison. We examined the impact of factors including age at first calving, calving interval, PDR, and the number of replacements required. From the base model, the total cost of rearing sufficient replacements for a 100-cow herd was $32,344. A reduction in culling rate to 20%, holding all other factors fixed, caused the net costs of raising replacements for the dairy herd to fall by $7968 or 24.6%. Increasing the culling rate above 25% led to a deficit in replacements for maintaining constant herd size, assuming a closed herd. The average age at first calving also affected the net costs of raising replacement heifers; reducing the age at first calving by 1 mo lowered the cost of a replacement program by $1400 or 4.3%. Changes in the length of the calving interval or in the PDR had marginal impacts on the net costs of replacement programs when compared with either herd-culling rate or average age at first calving.