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 re placements for a representative dairy herd of 100 cows. A model was develop ed with Pennsylvania and US average information as the basis for the parame ters. We used age at first calving of 25 mo, calving interval of 13 mo, her d-culling rate of 25%, and preweaned calf death of 10% as the base for comp arison. We examined the impact of factors including age at first calving, c alving interval, PDR, and the number of replacements required. From the bas e model, the total cost of rearing sufficient replacements for a 100-cow he rd was $32,344. A reduction in culling rate to 20%, holding all other facto rs fixed, caused the net costs of raising replacements for the dairy herd t o fall by $7968 or 24.6%. Increasing the culling rate above 25% led to a de ficit in replacements for maintaining constant herd size, assuming a closed herd. The average age at first calving also affected the net costs of rais ing 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 o f 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 aver age age at first calving.