Genetic associations between mastitis, milk electrical conductivity, and milk flow rate in temperate dairy cows in tropics

Abstract

Milk electrical conductivity and milk flow rate are potential indicators in selection targeting mastitis resistance. This study aimed to estimate the genetic parameters for clinical mastitis, average daily milk electrical conductivity (EC), milk flow rate (FR), and milk yield (MY) for the first lactation of imported Jersey and Jersey-Friesian dairy cows in Sri Lanka. Genetic parameters for mastitis traits, the prevalence of clinical mastitis in each cow, the duration of clinical mastitis treatment, and the number of episodes of mastitis were estimated using univariate sire models with permanent environmental effect of the cow added to models for prevalence of clinical mastitis in each day of milk over the whole lactation, or within the first 100-days of milk. The genetic parameters for the traits EC, FR, and MY over the whole lactation and for these traits defined for 30-day intervals were estimated using univariate animal models. For all mastitis traits, a zero heritability was estimated under both normal and logit scales. Heritabilities of EC and FR ranged from 0.02 to 0.11 and from 0.02 to 0.14, respectively. Genetic correlations between MY and EC and between MY and FR around peak milk yield were 0.25 ± 0.46 and 0.46 ± 0.29, respectively. Based on the heritability estimates for mastitis, dairy cows in this study cannot be directly selected for mastitis resistance, but indirect selection via EC and FR is feasible. Recording all cases of both sub-clinical and clinical mastitis in subsequent lactations is recommended to aid selection of dairy cows for mastitis resistance.