Effect of calflhood morbidity on age at first calving in New York Holstein herds

The effect of calhood morbidity on age at first calving was investigated in 948 heifer calves in 21 herds in the vicinity of Cornell University. Heifers were born from July 1983 to April 1985 and neither died nor were sold prior to 90 days of age. All calvings occurred on or before 31 May 1987.

The specific calfhood morbidity variables of interest were the first occurrences of the following clinical signs as diagnosed by farmers on check-off forms: scours/diarrhea within 14 days of birth and from 15 to 90 days of age; dull, listless, droopy ears, or off of feed within 90 days of birth; cough, runny nose or eyes, or trouble with breathing within 90 days of birth. The Kaplan-Meier product-limit life-table technique and Cox's proportional hazards model were used to evaluate the effect of calfhood morbidity on the age distribution of first calving. Season and year of birth were included (forced) into the Cox's proportional hazards model as possible confounding variables. The model was stratified on herd (allowing a different survival function for each herd) in order to account for herd effects.

The final Cox's proportional hazards model included season and year of birth, signs of respiratory illness within 90 days of birth and dullness within 90 days of birth. Heifers without respiratory illness as calves were twice as likely subsequently to calve and calved 6 months earlier when compared to those with respiratory illness as calves. Heifers with dullness as calves were 1.6 × more likely to calve and calved 2 months earlier when compared to calves without dullness as calves.