Statistical comparison of milk fat depression metabolic incidence between progeny of local and exotic Holstein bulls and between grade and pure Holstein cows

In order to study the effect of sperm type (internal and external) and cow genotype (grade and pure) on probability of milk fat depression (MFD), a number of 938,047 test day records belonging to 108,077 first-parity Holstein cows calved during 1995-2009 in 427 herds were used. For data analysis, statistical methods of Pearson's chi square and logistic generalized linear model were utilised. In the model, fixed effects of production season, sperm type used for dam insemination, first calving age, herd, animal genotype, calving year, and stage of lactation as well as random effect of sire were included. Based upon fat to protein ratio for each test day record and with respect to threshold point of -0.12, dependent variable was defined as a binary (zero code for lack of MFD and unit code for incidence of MFD) character. Incidence of MFD was not significantly associated with sperm type while it was significantly related to the cow genotype. Estimate of odds ratio (OR) for the grade as compared to the pure cows was found to be 0.949 indicating that the former are less sensitive to MFD.