Prevalence of and Risk-Factors for Intramammary Infection in Pasture-Grazed Dairy Heifers in Late Gestation

Mastitis is a common infectious disease in dairy cattle, and is among the most economically damaging animal health problem producers face. Mastitis in dairy heifers is recognised as a distinct problem from that in older cows because of the different pattern of disease (Barkema, Schukken et al. 999; Valde, Lawson et al. 004) and unique factors that determine its occurrence (Waage, Sviland et al. 998; Waage, Odegaard et al. 00 ). Data from New Zealand (Compton, unpublished) shows that heifers have amongst the highest age-specific incidence of clinical mastitis (CM) (up to 5%) and that the largest majority of cases are diagnosed in the first to weeks of lactation. Other NZ data (Compton, unpublished) shows that intramammary infection (IMI) between and weeks pre-calving is common but is not as high as at calving. But no data is available to define when most new infections occur pre-calving or what factors may be associated with them. Knowledge of both these factors is important for developing control programmes for heifer mastitis.