EFFECT OF INTRARUMINAL MONENSIN CAPSULES ON REPRODUCTIVE-PERFORMANCE AND MILK-PRODUCTION OF DAIRY-COWS FED PASTURE

Cows from three herds calving in spring that were fed on pasture were paired by herd, production index, predicted calving date, and age. One cow from each pair was allocated randomly to the treatment group and received a controlled-release capsule of monensin 1 mo prior to the st art of AI. A random sample of 20 matched pairs of cows was selected wi thin each herd to monitor BW and metabolic parameters. Treated cows pr oduced more fat, protein, and liters of milk per day during the 2nd mo of monensin activity and produced a greater total milk volume than di d control cows. Treated cows gained less BW during the Ist mo after tr eatment. No significant differences were identified in submission rate s, overall pregnancy rates, or pregnancy rate to first or second AI. B lood urea nitrogen was elevated in the treatment group as a main effec t, and NEFA were elevated in the 2nd and 3rd mo after treatment. There was no significant effect on blood concentrations of glucose, albumin , or BHBA.