Effects of feeding monensin to lactating goats: acetyl coenzyme A carboxylase, hormone-sensitive lipase, plasma glucose, and circulating hormones.

These trials explored metabolic events associated with monensin-induced changes in milk composition. In trial 1, diets containing 0 or 33 ppm monensin sodium were fed ad libitum to separate groups of 7 mature lactating goats. In trial 2, diets containing 0 or 18 ppm monensin sodium were fed ad libitum to two groups with 5 mature (greater than 2 yr) and seven young (less than 2 yr) lactating does in each group. Blood was sampled at 1200 h and at 3 min after morning milking in both trials. Diets containing 33 ppm monensin increased serum growth hormone and plasma glucagon. Monensin (33 ppm) increased growth hormone from 13 to 60 ng/ml in samples taken 3 min after milking. Monensin (33 ppm) decreased insulin in these postmilking samples from 432 to 317 pg/ml but increased midday insulin in the samples taken between milkings from 279 to 349 pg/ml. Monensin did not affect plasma glucose or serum prolactin concentrations. Monensin fed at 18 ppm did not affect growth hormone, glucagon, adipose acetyl CoA carboxylase activity, hormone-sensitive lipase, or glucose concentrations. Young animals had higher growth hormone, glucose, and glucagon than mature does. The results indicate that effects of milk production intensity can be more important than monensin treatment on milk composition and circulating hormone concentrations.