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The endocrine control of compensatory hypertrophy was investigated in 12 Morgan stallions, four each at one, two and three years of age. Half were assigned to be unilaterally castrated (UC) in January and half to remain intact (IN). Nine blood samples were taken from each stallion at half-hour intervals 30, 90, and 150 d after unilateral castration for radioimmunoassay of serum concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone. Mean serum LH concentration was greater (P<0.06) in UC than IN stallions; however, the difference was greatest at 30 d and least at 150 d. Serum LH was greater (P<0.01) in two- and three-year-olds than in one-year-olds. The mean log(10) for serum FSH concentration was greater (P<0.06) in UC than IN stallions. Mean serum testosterone concentrations were similar in UC and IN stallions for all sample days, suggesting that the single testes of the UC stallions produced as much testosterone as the two testes of the IN stallions. Two- and three-year-old stallions had greater (P<0.01) serum testosterone than one-year-old stallions. Unilateral castration of stallions was associated with a significant increase in serum LH and FSH concentrations and, perhaps, higher intratesticular testosterone, which may explain, in part, the compensatory hypertrophy noted in the remaining testis.

A two-phase study was conducted to evaluate the effect of controlled daily exercise on semen characteristics of 2-yr-old stallions. Eight nonexercised, sexually inexperienced 2-year-old Morgan stallions were randomly assigned to one of two groups. In Phase 1, four stallions were randomly assigned to receive daily controlled exercise for 16 wk. In Phase 2, these stallions were confined to box stalls for 16 wk. The remaining four stallions were confined to box stalls for 16 wk during Phase 1 and received daily controlled exercise for 16 wk during Phase 2. Individual semen collections were obtained from all stallions every 14 days. Daily sperm output (DSO) was determined by daily semen collections for seven consecutive days on Wk 0, 8, 16, 24, and 32. Mean DSO (10(9)) in Phase 1 was 3.52+/-.62 and 2.79+/-.75 for Wk O and 3.12+/-.39 and 2.61+/-.68 for Wk 16 for exercised and nonexercised stallions, respectively. Mean DSO (10(9)) in Phase 2 was 2.61+/-.68 and 3.12+/-.39 for Wk 16 and 2.48+/-.69 and 3.95+/-.51 for Wk 32 for exercised and nonexercised stallions, respectively. No effect (P>.05) of treatment was observed in either phase when parameters of spermatozoa concentration, total spermatozoa per ejaculate, DSO, total volume, gel-free volume, gel volume, percentage motility, percentage live, pH, and percentage normal were measured and analyzed.

Transcervical diagnostic techniques may alter the length of the equine estrous cycle and affect subsequent luteal function. Therefore, nine mares were used to determine the effect of cervical dilation on plasma 13, 14-dihydro, 15-keto-prostaglandin F(2) (PGFM), progesterone (P(4)) and posttreatment duration of luteal function. Mares were given a daily score of 0 to 4 based on sexual receptivity. Five days following the end of receptivity, mares were randomly assigned to one of three, 3 x 3 latin squares. Control mares received no cervical dilation. Cervically stimulated mares recieved cervical dilation for 60 sec. Cervically stimulated plus inhibitor mares were dilated similarly to cervically stimulated mares, but received a prostaglandin synthetase inhibitor 30 min prior to treatment. Each mare completed all three treatments in three consecutive estrous cycles. Plasma PGFM and P(4) were determined by RIA. Plasma PGFM was lower (P<0.05) in cervically stimulated plus inhibitor than control and cervically stimulated mares. In addition, plasma P(4) was lower (P<0.10) in cervically stimulated plus inhibitor than in control and cervically stimulated mares. Luteal function following treatments did not differ. These data indicate that neither plasma PGFM and P(4) nor the duration of luteal function were affected by cervical dilation. However, administration of a prostaglandin synthetase inhibitor prior to cervical dilation decreased plasma PGFM and P(4) concentrations.

Twelve non-pregnant, non-lactating mares were randomly assigned to four treatment groups using a 2x2 factorial arrangement with three replicates per group. Mares were administered PGF(2alpha) (10 mg, IM) on days -14 and 0, followed by HCG (3000 IU, IM) on day 5. The following treatments were administered: Group A received PMSG on days 2 (4000 IU, IM) and 5 (1000 IU, IV); Group B received PMSG (4000 IU, IM) on day 2; Group C received PMSG (1000 IU, IV) on day; Group D received no PMSG. Mares received progesterone (25 mg, IM) on days 1 through 4. Reproductive tracts were recovered at necropsy on day 16 (10 days post-ovulation). Ovaries were weighed, CL number and weight determined, follicles counted and measured, and volume of follicular fluid quantified. Mean ovarian weight (g) and number of CL per mare, respectively were: Group A, 100.0+/-15.6, 1.7+/-.7; Group B, 128.6+/-40.4, 1.3+/-.7; Group C, 92.4+/-21.0, 2.0+/-.0; Group D, 93.3+/-12.3; .3+/-.3. Mean number of follicles >10 mm and total volume (ml) of follicular fluid per mare, respectively, were: Group A, 9.4+/-2.0, 21.8+/-10.9; Group B, 1.3+/-.3, 32.2+/-28.9; Group C, 4.3+/-1.8, 5.4+/-2.3; Group D, 6.0+/-4.5, 24.0+/-10.3. There was no difference (P>.05) in mean ovarian weight, CL number, CL weight, follicular fluid volume, number of follicles, or size of follicles between treatment groups. These results show no significant effect on ovarian activity in progesterone treated mares following administration of exogenous PMSG.

Twelve pregnant mares were used in a switchback design with two groups of six mares each. On day 255 of gestation, group A was administered repository progesterone (250 mg, IM) and group B progesterone in sesame oil (250 mg, IM). Jugular vein plasma was taken 15 min pre-injection and post-injection at 30 min, 1, 3, 6, 9, 12, and 24 hours. Additional samples were taken on days 2, 3, 4, 6, and 8. Both groups were then assigned to the opposite treatment on day 270 of gestation. Concentrations of plasma progestogens after injection with progesterone in sesame oil were not different (P>.05) from values obtained using repository progesterone through the 8 days studied. Mean progestogen concentrations after injection of progesterone in sesame oil were, however, consistently higher through 48 hr than those given repository progesterone. Concentrations of progestogens were not different (P>.05) from pre-injection concentrations by day 6 post-injection using either vehicle.

The effects of unilateral castration on testicular compensatory hypertrophy were measured in 12 Morgan stallions, four each at one, two, and three years of age. They were randomized within age to intact (IN) or unilaterally castrated (UC) groups. Allotment and surgery were in January 1983 and total castration was in June 1983, 150 d after unilateral castration. Testis weight increased linearly with age (P < 0.01) and was increased by unilateral castration (P < 0.07). Epididymal weight also increased linearly with age (P < 0.05) and was heavier in UC animals (P = 0.15). Tubule diameter (P < 0.10) and epithelial height (P < 0.03) were greater in UC than in IN stallions. In conclusion, testes of stallions underwent compensatory hypertrophy after unilateral castration.

Ten sexually inexperienced Thoroughbred stallions, ranging in age from 4 to 7 yr, were used to determine the relationship between available extra-gonadal reserves (AEGR) and daily sperm output (DSO). Ejaculates were obtained during the months of June through December. Each stallion was ejaculated at 0700, 0800, and 1700 h on Day 1 and 0700, 1200, and 1700 h on Days 2 and 3. A single ejaculate was collected at 0700 h on Days 4 through 7. DSO was calculated by averaging the total spermatozoa obtained on Days 5, 6, and 7. A minimum of 14 d was allotted to each stallion between trials to allow replenishment of AEGR. Weekly trials were classified as 1) primary: ejaculates taken from sexually inexperienced stallions; 2) normal: all weekly ejaculated in which the total spermatozoa in the second ejaculate (0800 h on Day 1) divided by the total spermatozoa in the first ejaculate (0700 h on Day 1) yielded percentages >20 and <70%; and 3) all: all weekly trials. Regression analysis yielded an equation of estimated DSO=0.18 (total spermatozoa in first ejaculate) + 0.93. Measured DSO, mean of total spermatozoa collected on Days 5, 6, and 7, divided by total spermatozoa in the first ejaculate of normal weekly trials averaged 27.5+/-1.9%. When 27.5% was multiplied by the total spermatozoa found in the first ejaculate (0700 h on Day 1) in primary, normal, and all trials, correlation coefficients between measured and estimated DSOs of 0.95, 0.95, and 0.92, respectively, were obtained. In conclusion, there appears to be a relatively stable relationship between AEGR and DSO in Thoroughbred stallions aged 4 to 7 yr. This relationship allowed a famrly accurate (82%) estimation of DSO when the total number of spermatozoa found in the first ejaculate of sexually rested stallions is multiplied by 27.5%.

Estrus synchronization trials with mares were carried out using progesterone impregnated vaginal sponges and pregnant mare serum gonadotropin (PMSG) injections. In Phase 1, 10 non-pregnant, non-lactating mares were administered 1 g progesterone via vaginal sponges (5 x 6 cm) without regard to stage of estrous cycle. Sponges were replaced on day 7 of trial for an additional seven days. On day 12, PMSG (1000 IU, IM) was administered to five mares (Group A); five control mares (Group B) received no injections. There was no difference (P>.05) in estrus synchronization between Group A and Group B. Total sponge retention was 75%. In Phase 2, 11 non-pregnant, non-lactating mares were administered 2 g progesterone via vaginal sponges (10 x 6 cm) without regard to stage of estrous cycle. Sponges were replaced on day 7 of trial for an additional seven days. Estrus behavior was exhibited in 54.5% of mares by day 19. Total sponge retention was 95.4%. There was no difference (P>.05) in estrus synchronization or sponge retention between Phase 1 and Phase 2. The larger Phase 2 sponges showed less (P<.01) posterior movement within the vagina than the smaller Phase 1 sponges.