Control of the estrous cycle in the mare

All current approaches to manipulating the reproductive biology of the nonpregnant mare are discussed.     

Serum concentrations of prolactin, thyroxine and triiodothyronine relative to season and the estrous cycle in the mare

Studies were conducted to characterize circulating concentrations of prolactin, thyroxine (T4) and triiodothyronine (T3) relative to season and the estrous cycle, and to evaluate the ability of thyrotropin-releasing hormone (TRH) to induce prolactin secretion in the horse mare. The increase in serum prolactin following the iv injection of 0, 5, 50 and 500 micrograms TRH was dose-related, while all three doses of TRH induced a significant and comparable increase in serum T4. Seasonal variations in serum prolactin were directly correlated (P less than .001) with changes in photoperiod (r = .80) and temperature (r = .61). By comparison, concentrations of T3 were inversely related to temperature (r = -.49; P less than .001), while changes in T4 were less closely associated with photoperiod (r = -.29; P = .04). There were no significant fluctuations in prolactin, T3 or T4 at any stage of the estrous cycle. These results demonstrate that concentrations of prolactin in the mare are highest during the summer and lowest during the winter, but it is unknown whether this annual rhythm is controlled by photoperiod, temperature and(or) other environmental factors.     

Effect of intrauterine saline infusion during the late luteal phase on the estrous cycle and luteal function of the mare

The intrauterine infusion of 500 ml of warm sterile saline solution into mares on days 12, 13, or 14 after ovulation failed to alter the ovulatory interval, although intervals were shorter for days 12 and 13 (20.6 days) when compared with those in control mares (21.6 days). The IU fusion shortened luteal-life-span on days 12 (12.0 vs 13.8 days) and 13 (13.0 vs 14.4 days) (P is less than 0.05), but not day 14 (14.0 vs 13.5 days), when comparing the effects of IU infusion with an average of before and after base-line data. There was no effect on the interval from corpus luteum regression to ovulation, ie, the final follicular phases. The treatment average for days 12 and 13 combined was 7.7 days vs 7.3 days for controls. Also, no significant effect was observed for the duration of estrus in that the treatment average for days 12 and 13 was 5.1 days, and for controls, 6.0 days. The infusion of saline solution caused an immediate release of prostaglandin F(2alpha) within 5 minutes, with additional large releases occurring over the next 24 hours. Progestin concentrations decreased rapidly in relation to this prostaglandin release.     

Chelated mineral supplementation in the barren mare: A preliminary trial

Twenty-four Thoroughbred mares with breeding histories of having been barren for at least the previous 12 months were evaluated in a double-blind feeding trial to determine the effects of chelated mineral supplementation upon subsequent breeding performance. At the start of the trial (Day 0), mares were split into three dietary treatment groups of eight mares each and fed: (a) control diet with macro- and microminerals fed at NRC recommended levels for maintenance of the mature horse, (b) chelated minerals supplementation and (c) inorganic minerals supplementation at levels equal to Group B. Sixty days after initiation of the trial, there were no differences (P>0.05) between age, endometrial biopsy classification, calculated body weight and body condition score for mares between dietary treatment groups. A breeding performance trial was initiated at this time (Day 60). The number of first cycle and cumulative (i.e. over 3 estrous cycles) conceptions, number of first cycle and cumulative pregnancies and the number of total embryonic losses were not different (P>0.05) between the control and either the chelated mineral or the inorganic mineral groups. There were no harmful effects observed from feeding the chelated minerals 60 days prior to, and during, this breeding trial.     

Severe hypoglycemia attributable to surreptitious injection of insulin in a mare

A mare with signs of hypoglycemia had high serum insulin concentrations before it was euthanatized. High pressure liquid chromatography revealed that the insulin in the mare's blood was of commercial origin. Surreptitious insulin injection has been suspected as the cause of several suspicious deaths of insured horses. The use of high-pressure liquid chromatography should help put an end to this practice.     

Uterine motility during the estrous cycle: studies in healthy bitches

Natural and drug-induced uterine motilities (UM) were recorded via uterine-implanted catheter-tip pressure transducers in 5 bitches during proestrus and estrus and in 6 bitches during early (30 days) and late (60 days) diestrus. The UM was monitored in unanesthetized bitches for 2 days after the estrous-cycle stage had been determined by vaginal cytologic findings. Natural UM, expressed as Alexandria units (pressure X frequency X duration of contractions), was greatest during estrus, moderate during proestrus, and appreciably decreased or lacking during early and late diestrus. During proestrus and estrus, prostaglandin F2 alpha (5 micrograms/kg of body weight, IV) induced intrauterine pressures of 107 and 115 mm of Hg, respectively, and oxytocin (0.05 USP units/kg, IV) induced pressures of 106 and 116 mm of Hg, respectively. In contrast, the intrauterine pressure values induced by prostaglandin F2 alpha given IV during early and late diestrus were 61 and 58 mm of Hg, respectively, and for oxytocin, were 61 and 51 mm of Hg, respectively. Prostaglandin F2 alpha given IM (50 micrograms/kg) also induced a greater intrauterine pressure during proestrus and estrus than during diestrus. We concluded that in the bitch, natural and drug-induced UM are decreased during early and late diestrus.     

Control of the bovine estrous cycle with melengestrol acetate (MGA): a review

Expanded use of artificial insemination in the beef cattle industry depends on successful application of treatments designed to synchronize estrus. Regulation of estrous cycles is associated with control of the corpus luteum (CL), whose life span and secretory activity are subject to trophic and lytic mechanisms. The advantages of melengestrol acetate (MGA) in estrous synchronization incorporate ease of administration, lower cost relative to other estrous synchronization products, and potential for use to induce estrus in prepubertal heifers. Treatments first designed to synchronize estrous cycles of normally cycling heifers by feeding MGA were imposed daily for 14 to 18 d at levels of .5 to 1 mg. The minimal daily effective dose required to inhibit ovulation was .42 mg. Longer feeding periods of MGA were associated with low fertility at the first synchronized estrus, but at the second estrus, conception was normal. Low fertility at the synchronized estrus resulted in development of alternative treatment practices, which combined feeding of MGA with injections or implants of estradiol-17 beta, estradiol cypionate, luteinizing hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, or oxytocin. Estrus was synchronized after MGA and estradiol-17 beta or estradiol cypionate treatments, but fertility was low. Short-term feeding of MGA (5 to 7 d) combined with prostaglandin F2 alpha or its analogs (PGF) on the last day of MGA reduced fertility at the synchronized estrus. The reduced conception at first service occurred in animals that began treatment after d 12 of the estrous cycle. However, feeding MGA for 14 d and then injecting PGF 17 d later avoided problems with reduced conception. Fertility of animals after this treatment was similar to that of contemporaries synchronized with Syncro-Mate-B. However, the length of the treatment period creates a need for increased management and may extend management beyond practical limits. Further research is warranted to address problems associated with reduced fertility after short-term treatment with MGA.     

Oxidative state in the estrus cycle of the buffaloes: a preliminary study

Tropical Animal Health and Production - The oxidative status, the relationship between oxidizing agents (free radicals) and antioxidant system, is able to influence the correct performance of the...     

Influence of uterine inflammation on the estrous cycle in rats

To investigate how uterine inflammation affects ovarian activity in rats, endometritis was induced and changes in the length of estrous cycle and serum concentrations of estradiol-17beta (E(2)) and progesterone (P(4)) were examined. A suspension of Staphylococcus aureus (bacterial solution) or iodine solution was infused into the uterine lumen at various estrous phases. When the bacterial solution was infused at estrus, metestrus, or the first day of diestrus, the following diestrus continued for 5 to 12 days. In the case of the iodine solution, regardless of the estrous phase of the infusion, the following diestrus continued for approximately 6 days. E(2) concentration after infusion of each solution did not fluctuate largely and remained at a low concentration (around 5 pg/ml). P(4) concentration was high (35-45 ng/ml) on the day following infusion, but decreased rapidly to base line values within a few days and remained thereafter at a low level (around 5 ng/ml). It is assumed that the endometritis caused by biological or chemical stimulation raises the concentration of P(4) to depress gonadotrophic hormone secretion, and hence this high P(4) concentration might inhibit the growth of ovarian follicles.     

绵羊发情周期中VEGF在卵巢中的表达

应用免疫组化方法结合计算机图像分析技术,分析同期发情后0、5、9、12、15d的绵羊卵巢中血管内皮生长因子（Vascular endothelial growth factor,VEGF）表达强度变化,以期了解VEGF在绵羊卵巢发情周期不同时期的表达规律。结果显示：VEGF阳性目标主要出现于卵泡膜与颗粒细胞。原始卵泡、初级卵泡、次级卵泡VEGF表达依次增强（P〈0．05）。发情周期0～5d,大窦腔卵泡（颗粒细胞4～8层）VEGF表达量骤然上升（P〈0．05）,而9d开始显著下降,与5d比较差异显著（P〈0．05）。12d继续下降（P〈0．05）且为最低值,15d又明显上升（P〈0．05）。VEGF在卵巢间质呈弱表达,各个时期之间差异不显著（P〉0．05）。结果表明,绵羊卵巢存在着血管周期性新生的变化特点,而VEGF在这种周期性血管新生过程中起着重要的调控作用。     

Temporal sequence of events in the estrous cycle of the bitch.

Serum concentrations of luteinizing hormone (LH), estradiol-17 beta, and progesteron were compared with the onset of diestrus in Beagle bitches. The LH peak occurred 8.0 (standard error (SE), 0.3) days before the onset of diestrus. Vaginal cytologic characteristics during proestrus were studied, and vaginal cornification was complete 12.1 (SE,0.2) days before the onset of diestrus. A time sequence of hormonal, vaginal cytologic, and developmental events was outlined during proestrus, estrus, and early diestrus.