Thirty-two lactating Holstein cows were assigned to 1 of 4 groups in a randomized block design using a 2 X 2 factorial arrangement of treatments. Recombinant bovine growth hormone (rbSt; 25 mg/day) or placebo was administered beginning at Day 35 or 70 postpartum. All cows began treatment approximately 3 days post-estrus. Blood samples were collected at least once daily for a 70-day period to determine the concentration of progesterone and the duration of the luteal and follicular phases. During estrous cycles 1 and 3, frequent blood samples were taken (every 10 min for 8 h) 24 and 60 h after the onset of luteal regression. These samples were assayed for luteinizing hormone (LH), and samples coincident with the second LH pulse detected were assayed for estradiol. Ultrasonography was used to determine the size of the largest ovarian follicle from Day 17 until ovulation in estrous cycles 1 and 3. Luteal life span, length of the follicular phase, and diameter of the largest follicle were not affected by treatment with rbSt. Administration of rbSt increased the concentration of progesterone in plasma during the first two luteal phases (p less than 0.01). Progesterone was elevated during the mid-luteal phase of cycle 3 in rbSt-treated cows that began treatment about Day 35 postpartum but not in cows that began treatment on Day 70 postpartum (Treatment X Stage X Day, p less than 0.01). During the first follicular phase studied, LH pulse frequency was higher (p = 0.06) in rbSt-treated cows than in cows receiving the placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

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It was postulated that the induction of twin ovulations in cattle may require a combination of two appropriate stimuli. The first putative requirement is an increase in the circulating FSH concentrations and/or a decrease in inhibin concentrations to induce the development of additional potentially ovulatory follicles. The second putative requirement is an increase in LH pulse frequency during the follicular phase of the cycle to enhance the stimulus for follicle maturation and ovulation. On the basis of studies reported in the literature, it was suggested that such stimuli may be provided by immunization against inhibin and against a steroid hormone such as androstenedione, respectively. This experiment was designed to determine the effects of immunization against androstenedione and inhibin, either separately or together on the endocrine status of heifers and on the associated patterns of ovarian follicle development and ovulation rate.

Link to this article: http://journals.cambridge.org/abstract_S0003356100006607How to cite this article: S. M. Rhind, S. R. Schemm and B. D. Schanbacher (1993). Follicle populations, ovulation rates and proles of gonadotropins, inhibin and insulin-like growth factor-1 of heifers actively immunized against androstenedione and inhibin, separately or in combination. Abstract Four groups of 20 Simmental cross heifers were actively immunized against human serum albumin (control, (Q), androstenedione (A), a 30 amino acid synthetic fragment of porcine inhibin alpha (I) or A and I in combination (AI). At the time of the third and final antigen injection and again 2 weeks later, all animals were injected with synthetic prostaglandin F 2a (PG) to synchronize oestrus. Concentrations of LH, FSH, insulin-like growth factor-1 (IGF-1) and inhibin (C and A heifers only) in serum samples collected twice daily during 3 days before the second PG injection and at 15-min intervals from 24 to 32 h after PG injection were determined. Two weeks later, all heifers were administered PG and ovariectomized 24 h later.Ovarian follicles were dissected from the stroma, measured and cultured in medium 199 for 2h at 37°C. Numbers of small (3-0 to 7-9 mm diameter) and large (>8-0 mm diameter) follicles were not significantly altered by any of the immunization treatments. Intrafollicular concentrations and secretion rates of oestradiol, testosterone, progesterone and inhibin, determined in vitro, were not affected by immunization. Intrafollicular IGF-1 concentrations were not affected; this hormone was not detectable in the culture medium. Intrafollicular concentrations of oestrogen and testosterone and secretion rates of all three steroids were greater (P < 0-05) in animals which had regressing corpora lutea at the time of ovariectomy. Of the animals that had dominant follicles, one of 17, one of 13, four of 19 and six of 15 in the C, A, I and AI groups, respectively, had two or more. Only the difference between AI and C cows in the incidence of dominant follicles was statistically significant (P < 0-05). Mean circulating concentrations of LH, and inhibin (C and A groups only) and mean LH pulse frequency and pulse amplitude were unaffected by treatment but FSH concentrations were higher in A (P < 0-001) and lower in AI and I heifers (P < 0-001) compared with C animals while IGF-1 concentrations were lower in A heifers (P < 0-001) and higher in AI heifers (P < 0-05) compared with C heifers. It is concluded that immunization against inhibin, either alone or in combination with immunization against androstenedione increased the incidence of multiple dominant follicles in heifers but did not increase their ovulation rate.