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Luteolysis, Growth Hormone, Glucocorticoids, Prolactin and Milk Production in Lactating Dairy Cows Given Prostagland in F₂

Michigan State University⁴, East Lansing 48824

Abstract

Fifty-seven lactating Holstein cows 2 to 3 months postpartum were given 25 mg prostaglandin F₂ (PGF₂) intramuscularly 12 days before a treatment dose of 0, 5, 15, 25 or 35 mg PGF₂. Incidence of luteolysis in cows given 15, 25 or 35 mg PGF₂ (87%) was greater than those for cows given saline (0%) or 5 mg PGF₂ (40%). In cows which responded with luteolysis, average intervals from PGF₂ to onset of estrus, peak of the ovulatory surge of luteinizing hormone and ovulation were 73 ± 4, 80 ± 5 and 100 ± 4 hr, respectively. Progesterone decreased 50% within 6 hr, and to less than 1.0 ng/ml within 24 hr following a luteolytic dose of PGF₂±. Serum progesterone was reduced transiently from 5.5 to 3.3 ng/ml, but increased toward pre-injection values within 24 hr in cows given a nonluteolytic dose of PGF₂.

Blood serum growth hormone increased from 1.7 to 3.3 ng/ml within .5 hr after 35 mg PGF₂, but was not significantly changed after smaller doses; glucocorticoid increased from 3.1 to peaks of 22.3, 34.9 and 39.0 ng/ml at 1.0 hr after 15, 25 or 35 mg PGF₂, respectively; and prolactin increased from 38 to peaks of 57, 84 and 95 ng/ml at 1.0 hr after 15, 25 or 35 mg PGF₂, respectively. None of these hormones was affected significantly by 5 mg PGF₂. PGF₂ did not significantly affect daily milk yield, fat or total protein during the 7 days after treatment.

² Present address: Department of Animal Science, University of Florida, Gainesville, FL 32601.

³ Present address: Department of Animal Science, North Carolina State University, Raleigh 27607.

⁴ Department of Dairy Science.

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