title: Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers.
abstract: Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh 27695-7621, USA. scott_whisnant@ncsu.edu
authors.forename: C S
authors.initials: CS
authors.lastname: Whisnant
authors.forename: P J
authors.initials: PJ
authors.lastname: Burns
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage; D004958:Estradiol / Q000008:administration & dosage*; D004971:Estrus / Q000187:drug effects*; D005260:Female; D008863:Microspheres; D010060:Ovulation / Q000187:drug effects; D011374:Progesterone / Q000008:administration & dosage* / Q000097:blood; D012741:Sexual Maturation / Q000187:drug effects*
chemical_list: D011374:Progesterone; D004958:Estradiol; D015237:Dinoprost