The correlated response in health cost accompanying selection for milk yield in Jerseys

Health data were recorded for 567 and 193 cows in selection and control herds, respectively. Health costs were expenses due to drugs, labor, and veterinary charges. Health expenses were grouped into one of six health functions: 1) mammary, 2) locomotion, 3) respiration, 4) reproduction, 5) digestion, and 6) other. Costs were summed across lactation and discounted to birth at rates of 0%, 3%, and 6%. Data were analyzed using a model that included year-season, parity, line, sire (line), and lactation length. Selection cows had significantly (P<.001) higher health costs at all three discount rates. Differences were mainly due to higher (P<.01) mammary costs. Differences between lines for other individual function costs were not significant, but were higher in selection cows. Parity, year-season, and stage of lactation were significant (P<.001) non-genetic sources of variation in health costs. Costs were greater for third and later parities and during the first 30 days of lactation. Results indicate that health costs are likely to increase with selection for milk yield; however, additional revenues from increased yield would offset added costs. Increased management in early lactation and later parities may decrease health expense.