The influence of treatment with monensin capsules on milk production and reproductive performance of pasture fed dairy cows

Pasture fed cows from 3 spring-calving herds, were paired within herd on production index, predicted calving date and age. One cow per pair was randomly allocated to the treatment group and received a controlled-release capsule of monensin 1 month before the start of AI. A sample of 20 matched pairs from each herd was randomly selected for monitoring weight and metabolic parameters. Treated cows produced more fat, protein and milk per day during the second month of monensin activity and more milk for the total lactation. Treated cows gained less weight the first month after treatment. Submission rates, pregnancy rates, first and second AI pregnancy rates were similar. Blood urea nitrogen (BUN) was elevated in the treatment group and non-esterified fatty acids (NEFA) were elevated in the 2nd and 3rd months after treatment. There was no significant effect on blood glucose, albumin, or beta-hydroxybutyrate.