Herding and snaking by the harem stallion in domestic herds

Four herds of pony mares, each consisting of a stallion and six mares, were used to characterize the nature of herding by the stallion and the factors that induced the herding behavior. Herding behaviors were compared among four successive treatments (six mares alone, stallion added, two new mares added, and entire herd moved to a new pasture). A new treatment was initiated every 7 days and behavior was studied for 5 consecutive days (Days 1-5) for each treatment. Observations were made every 10 min during a 2-h period for each day. The extent of herding was quantitated by the mean distances between mares. The extent of snaking (herding with the head and neck extended and ears held back) was scored 0, 1, 2, or 3 (nil, minimal, intermediate, and maximal, respectively). The mean distance among the original mares on Day 1 when the mares were alone was 5.0 mare lengths and was reduced (P < 0.05) to 1.9 mare lengths when the stallion was added. The mean distance among the original mares of an established stallion/mare herd (3.8 mare lengths) was reduced (P < 0.05) on the day the herd was moved to a new pasture (1.9 mare lengths), similar to the effect of the introduction of the stallion. Scores for the extent of snaking, as well as the extent of herding, were highest (P < 0.05) on Day 1 when the stallion was added or the stallion/mare herd was moved to a new pasture. The extent of herding and snaking decreased (P < 0.05) by Day 2 and was seen only occasionally on Days 3-5. The addition of new mares to the herd did not induce herding of the original mares. However, the new mares maintained mean distances of 8-12 mare lengths from the original mares, resulting primarily from chasing by the stallion. By Day 4, the distances between the new and original mares were not different (P > 0.05) from the distances among the original mares.     

Effects of a copper-bearing intrauterine device on the ovarian function, body weight gain and pregnancy rate of nulliparous heifers

A copper-bearing intrauterine device (IUD), designed to cause a slight distention of the uterus, was inserted through the cervix into each uterine horn of 230 heifers; an additional 230 heifers served as the control group. Blood was drawn at 0, 1, 2, 20 and 120 d for progesterone and testosterone assays. The heifers were checked twice daily for estrus and examined at 0, 60 and 120 d for weight gain. Thereafter they were bred over a 120-d period. The IUD caused anestrus in 98% of the heifers, with a daily weight gain 25.5 % higher than in the control heifers. Moreover, the device was 100% effective in preventing pregnancy. At 20 and 120 d after IUD insertion progesterone levels averaged 0.7 ng/ml, which was 4 to 5 times lower than in the control animals, suggesting a failure in ovulation or in corpus luteum (CL) formation due to the IUD. Simultaneously, testosterone values were increased up to 8 times in IUD-treated heifers, reaching a mean concentration of 163 pg/ml. Associated histological evaluations of the ovaries from UD-treated heifers revealed the presence of 2 or more cysts per ovary, with marked hyperthecosis in many antral follicles in which the granulosa cell layers were either thinned or lacking. The results suggest that the action of the copper-releasing IUD used in this study resulted in high contraceptive efficiency but also in disturbance of ovarian function. Our findings further raise the possibility of a cause and effect relationship between hyperandrogenism and the higher body weight gain observed in heifers treated with the IUD.     

Preliminary evaluation of porcine zona pellucida (PZP) immunocontraception for behavioral effects in feral horses (Equus caballus)

Successful management of captive populations of wild animals requires effective control of reproduction. Contraception is one tool for controlling reproduction of animals in zoos; however, the options available to the animal manager are limited. Contraceptives vary in efficacy, reversibility, and side effects, and thus may not be suitable for widespread use. One consideration when selecting a contraceptive is its potential for side effects on behavior, especially given the fact that reproduction plays such a prominent role in the biology of any species. To date, there have been few evaluations of contraceptives for behavioral effects, and those that have been conducted have focused on hormone-based contraceptives. This study sought to evaluate a novel method of population control, immunocontraception, for behavioral effects in a population of feral horses. Porcine zona pellucida (PZP) immunocontraception prevents fertilization of ova and does not alter normal hormone secretion patterns. It therefore should leave the animal behaviorally intact in terms of reproductive behavior. The study examined the behavior of 43 sexually mature mares on Assateague Island during the 1997 breeding season and, with help from Earthwatch volunteers, collected observations over a 3-month period. The study found no significant differences between treated and untreated mares in general activity budget, aggression given or received, and spatial relationships relative to the stallion. These preliminary findings indicate that PZP contraception seems to have no acute behavioral effects on the behavior of individuals. The study findings also suggest that PZP could be a desirable and effective management tool for captive species in which social behavior plays an integral role in group dynamics. Analyses of group level effects and population level effects are continuing.     

Mechanisms behind intrauterine device-induced luteal persistence in mares

Intrauterine glass balls are used to prevent oestrous signs in sports mares, but the mechanism of action is unknown. It has been suggested that the glass ball can mimic an embryo or act via an induced chronic uterine inflammation and absent or continuous low-grade prostaglandin (PG) release. The purpose of this study was to induce prolonged luteal function in mares using a small intrauterine device (IUD) and to study the mechanisms behind prolonged IUD-induced luteal function. A uterine swab and a biopsy specimen were obtained in early oestrus. A water-filled plastic ball, diameter 20mm and weight 3.6g, was inserted into the uterus 2-4 days after ovulation; the control mares underwent similar cervical manipulation without ball insertion. The mares were examined three times per week until day 23 and twice weekly thereafter until they returned to oestrus (transrectal palpation, ultrasonography and progesterone determination). The location of the IUD was recorded and ultrasound scans were video-recorded to assess the frequency of uterine contractions. When the mare returned to oestrus, a uterine swab and biopsy specimen were obtained and the bacteriological, cytological and histological (inflammation and glandular dilation) results compared with the samples obtained before the IUD insertion. The PG F(2alpha) metabolite levels were measured in the plasma of four control mares and eight IUD mares on days 11-16. The IUD induced a prolonged luteal phase in 75% of the mares (9/12; IUD-P); the mean dioestrous length was 57.0 days. The three mares that did not respond to the IUD (IUD-N) showed a mean dioestrous length of 15.7 days and the 12 control mares 16.1 days. The inflammation and glandular dilation scores were not significantly different in pre- and post-manipulation biopsy specimens. Although locational changes of the IUD were observed, they occurred over very small distances and were mostly limited within the body-bifurcation area. The IUD-N and control mares showed increased uterine contractility 11-16 days post-ovulation, whereas the IUD-P mares did not. The control mares (n=4) and IUD-N mares (n=2) showed increased PG levels from day 14 post-ovulation, while the IUD-P mares (n=6) showed basal levels only. We concluded that the IUD did not cause continuous PG release and suggest that close contact of the IUD with the endometrium may prevent the endometrial cells from releasing PGF(2alpha).     

Use of a semen extender containing antibiotic to improve the fertility of a stallion with seminal vesiculitis due to Pseudomonas aeruginosa

A breeding trial was conducted to determine if a semen extender containing polymixin-B sulfate would improve the fertility of a stallion with seminal vesiculitis due to Pseudomonas aeruginosa . Twenty-three mares were bred to the stallion by one of three methods: artificial insemination with raw semen (Group 1, n = 10), artificial insemination with semen mixed 1:1 with a nonfat dry skim milk/glucose extender containing 1000 units/ml polymixin-B sulfate (Group 2, n = 9), or natural service immediately following infusion of the uterus with 100 ml of the same extender (Group 3, n = 4). Artificial breedings contained a minimum insemination dose of 500 x 10(6) progressively motile spermatozoa. All mares were bred every other day while in estrus. Pregnancy status was determined by transrectal ultrasound examination 15 d after the last breeding. First-cycle pregnancy rate for Group 2 mares (78%) was greater (P < 0.01) than for Group 1 mares (10%). There was a tendency (P = 0.10) for the pregnancy rate of Group 3 mares (50%) to be greater than Group 1 mares. The use of a semen extender containing polymixin-B sulfate improved the fertility of this stallion.     

Sexual behavior following introduction of a stallion into a group of mares

A rested stallion was introduced daily for 30 days into each of three herds of 20 mares. Observations of sexual and mating behavior were made for one hour. The stallion remained with a herd until another stallion was introduced the following day. Other mares were isolated from stallions and were bred by artificial insemination. The diameter or growth rate of the preovulatory follicle for the six days preceding ovulation and the length of the interovulatory interval for mares which did not become pregnant were not affected significantly by the presence of a stallion. The number of breedings per hour of observation (2.4 ±0.2) and the length of the interval from introduction of a stallion into the herd of mares to first breeding (12 ±1 min) were significantly different among stallions, but the length of the interval between breedings (17 ±2 min) was not. The mean number of breedings per stallion per hour was not affected significantly by the number of posturing (estrous) mares. The number of times that the stallion rebred the same mare when more than one mare postured during the observation hour (49%) was greater (P<0.01) than what would be expected to occur by chance (30%). The hypothesis that breeding occurs preferentially in those estrous mares that are closest to ovulation was not supported, except for significantly lower breeding activity in posturing mares on days 8 and 7 before ovulation and on days 0 (day of ovulation) and ?1 (26% bred) than on days 6 to 1 (52%).     

Induction of male sex behavior in pony mares with testosterone propionate

Two pony mares were administered 150 mg of testosterone propionate every other day for 20 days (ten injections) and every ten days there-after. An additional two mares and one stallion were not treated and served as controls. Testosterone propionate was dissolved in absolute ethanol and administered subcutaneously. Sex behavior tests were conducted 26 and 40 days after the first injection. Control mares exhibited very little male sex behavior. Both testosterone propionatetreated mares, however, exhibited mounting, sniffing, flehmen, biting and vocalization behavior in the presence of an estrous mare. The testosterone propionate-treated mares mounted and bit estrous mares more frequently than the stallion but exhibited less sniffing, flehmen and vocalization behavior in the presence of an estrous mare than the stallion. Testosterone propionate-treated mares and the stallion mounted an estrous mare 23.3 +/- 9.7 seconds and 172.5 +/- 22.5 seconds, respectively, after being introduced into the pen. Mares in estrus were mounted by the testosterone propionate-treated mares and the stallion an average of 4.0 +/- 1.3 and 1.0 +/- 0 times, respectively, during a ten-minute test. None of the non-estrous mares was ever mounted by the testosterone propionate-treated mares. In summary, testosterone propionate induced male sex behavior in intact mares and the testosterone propionate-treated mares effectively detected estrous mares.     

Embryo recovery from mares exposed to a year-to-year artificially prolonged daylength

The aim of the experiment was to determine the effect of a year-to-year prolonged daylength on the patterns of equine reproductive activity and results of embryo recovery. Experiments using Konik Polski mares were conducted over four reproduction seasons. Five mares were exposed to a regimen of artificially prolonged daylength (APD) and another five mares in a control group were kept under conditions of natural daylight. Both the control and experimental groups were examined for appearance of estrus, ovulation and also for the state of their coats. A single stallion was used for breeding all of the mares. The embryos were recovered nonsurgically 6 to 9 days after ovulation. All of the mares exposed to APD showed increased ovarian activity, which commenced earlier than in the control group. About 19% more ovulations were detected in the experimental group. The average number of ovulations per lighted mare per year was 15.3, while in the control group it was 12.4 ovulations (P<0.05). However, the embryo recovery rate and total number of embryos obtained from the mares exposed to APD did not exceed the number of embryos collected from the control mares (P<0.05). Modification of daylength had a visible effect on the mares by producing a change in their coats.     

Efficacy of a Y-Design Silastic Elastomer Intrauterine Device as a Horse Contraceptive

To successfully manage population growth rates of free-roaming horses (Equus ferus caballus), an effective, long-acting contraceptive could be beneficial. We evaluated the efficacy and safety of an intrauterine device (IUD) in a breeding trial using seasonal pasture assemblages of 2 males individually pastured in large enclosures (~81 ha) each with 10 females per male. The study took place at a large animal research facility at Oklahoma State University in Stillwater, Oklahoma, USA. Specific objectives of the study were to evaluate the effectiveness of IUDs in preventing pregnancy over 20.5 months with return to fertility assessed over the subsequent 6 months and to evaluate potential effects of this IUD on ovarian function and uterine health (e.g., endometrial inflammation, infection, fibrosis). We developed a Y-design IUD, made of silastic elastomer, and set the desired retention rate at 75%. After procurement of endometrial biopsies, we inserted IUDs into the uteri of 20 females and examined them via transrectal ultrasound every 2 weeks for detection of the device and assessment of uterine health. After 20.5 months we removed the remaining 15 IUDs, obtained a second endometrial biopsy for comparision, and returned the females to their respective males for continued breeding in efforts to assess uterine return to health as indicated by pregnancy rates. The Y-design IUD met the 75% retention rate goal, with 100% contraception in females that retained the device; 12 of 20 treated females became pregnant (i.e. returned to fertility) after removal of the IUD. Based on these results, we conclude that the Y-design IUD is a safe and effective device to control fertility in free-roaming horses. © 2021 The Wildlife Society.     

The effect of x-radiation upon the quality and fertility of stallion semen

The exposure that stallion semen might receive during examination using an airport x-ray security screening system was found to be between 0.5 and 1.0 micro Sieverts (μSv). Ejaculates from 2 stallions were diluted 1:4 (volume:volume) using a nonfat dried milk-glucose extender. A total of 6 ejaculates from each stallion was collected, and each ejaculate was divided into 3 aliquots and these were then exposed to x-radiation at a dose of 0, 1.0, or 10.0 (μSv. Semen quamy was examined immediately post exposure, and the aliquots were then placed into a water bath at 37 °C, after which sample longevity was evaluated.In a second trial, 3 groups of 8 pony mares were inseminated with semen that had been exposed to x-radiation at doses of 0, 1.0, or 10.0 μSv. An entire ejaculate was irradiated and inseminated into each mare on one occasion during estrus, based upon ultrasonographic evaluation of the reproductive tract.After exposure to x-radiation there were no differences among the 3 treatment groups for spermatozoal motility, morphology, or longevity. The 14-d pregnancy rates for the 3 treatment groups were 0 μSv (7 mares), 1.0 μSv (8 mares), and 10.0 μSv (7 mares). One mare (0 (μSv) aborted at 65 d of pregnancy; 21 mares had a pregnancy of normal length, with each delivering a foal at term, although 1 foal died at parturition (1.0 μSv).These findings indicate that the exposure of stallion spermatozoa to x-radiation up to doses of 10 μSv does not have deleterious effects upon spermatozoal motility, morphology, longevity or fertility. The exposure received during examination using an x-ray security screening system is likely to be lower than this dose.     

Effect of intrauterine treatment with prostaglandin E2 prior to insemination of mares in the uterine horn or body

Two trials were conducted to investigate the effects of intrauterine infusion of PGE2 and uterine horn insemination on pregnancy rates in mares achieved by breeding with a suboptimal number of normal spermatozoa. Estrus was synchronized and mares were teased daily with a stallion to detect estrus. Mares in estrus were examined by transrectal palpation and ultrasonography to monitor follicular status. On the first day a 35-mm diameter follicle was present, hCG (1500 IU, iv) was administered and the mares were bred the next day. Mares (Trial 1, n = 34; Trial 2, n = 28) were inseminated with 25 million total spermatozoa from either a stallion with good semen quality (Trial 1) or poor semen quality (Trial 2). In each trial, mares were assigned to 1 of 4 treatment groups as follows: Group PGE-HI - infusion of 0.25 mg PGE2 into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the proximal end of the same uterine horn; Group PGE-BI - infusion of 0.25 mg PGE2 into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the uterine body; Group SAL-HI - infusion of 1 mL sterile saline into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the proximal end of the same uterine horn; or Group SAL-BI - infusion of 1 mL sterile saline into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the uterine body. After breeding, mares were examined daily by transrectal ultrasonography to confirm ovulation, and were re-examined 14 to 16 d after ovulation for pregnancy status. Data were analyzed by Chi-square. Overall pregnancy rates were 59% for stallion 1 and 29% for stallion 2. Group pregnancy rates did not differ for mares bred by either stallion (P > 0.10). Pregnancy rates were not altered by horn insemination for either stallion (P > 0.10). Intrauterine infusion of PGE2 improved pregnancy rate in mares bred by the stallion with good quality semen (P < 0.05), but did not alter pregnancy rate in mares bred by the stallion with poor quality semen (P > 0.10). Further research is warranted to determine if intrauterine infusion of PGE2 will enhance spermatozoal colonization of the oviduct and pregnancy rates in mares, and if PGE-treatment will improve pregnancy rates achieved by subfertile stallions.     

Stallion karyotype variability and lack of association with abortion: a case report

Karyotype analysis was done on a stallion that impregnated 23 mares during the 1991 breeding season, of which 14 aborted between 2 and 4 mo fo gestation. Lymphocytes examined contained a 64,XY complement of normal appearing sex chromosomes and autosomes, except for slight dimorphism of the centric heterochromatin of chromosome No. 1. A skin biopsy was procured form the stallion for karyotype analysis, and the stallion was bred to 11 mares. Three mares were detected pregnant 16, 35, 45 d after breeding. The fetuses were recovered transcervically using curved intestinal forceps 47 (n=2) and 49 (n=1) d after breeding. Fetal tissue was rinsed and packed in culture media, transported overnight in a chilled container, cultured by standard tissue culture techniques, and prepared for karyotype analysis. No abnormalities were found in standard karyotypes from those cultures. One fetal karyotype revealed slight dimorphism of the heterochromatin of chromosome No. 1. Chromosome spreads obtained from the stallion's skin biopsy revealed a normal karyotype with no difference in the amount of heterochromatin present in No. 1 chromosomes. During the 1992 breeding season, the stallion impregnated 23 of 25 mares bred. Only 1 mare aborted, at 8 mo of gestation. Apparently, the amount of heterochromatin of No. 1 horse chromosomes can vary, and caution should be used in diagnosing this as a cause of pregnancy failure.     

Effects of inbreeding and other systematic effects on fertility of Black Forest Draught horses in Germany

Background

The Black Forest Draught horse (BFDH) is an endangered German coldblood breed with its origin in the area of the Black Forest in South Germany. In this retrospective study, the influence of the inbreeding coefficient on foaling rates was investigated using records from ten breeding seasons. Due to the small population size of BFDH, the level of inbreeding is increasing and may have an effect on foaling rates.The data of the present study included all coverings reported for 1024 BFDH mares in the years 2001–2009. These mares were covered by 32 BFDH stallions from the State Stud Marbach. Data from 4534 estrus cycles was used to calculate per cycle foaling rate (CFR). Pedigree data contained all studbook data up to the foundation of the breed as early as 1836. The level of inbreeding of the mare, stallion and expected foal along with other systematic effects on CFR were analysed using a generalized linear mixed model approach. Stallion was employed as a random effect. Systematic fixed effects were month of mating, mating type, age of the mare and stallion, reproductive status of the mare and stallion line of the mare. Inbreeding coefficients of the stallion, mare and expected foal were modelled as linear covariates.

Results

The average CFR was 40.9%. The mean inbreeding coefficients of the mares, stallions and expected foals were 7.46, 7.70 and 9.66%. Mating type, age of the mare, reproductive status of the mare and stallion line of the mare had a significant effect.

Conclusions

The results showed that the mating type, stallion line of the mare, sire, age and reproductive status of the mare exerted the largest influences on CFR in BFDH. Inbreeding coefficients of the stallion, mare and expected foal were not significantly related with CFR.

     

A mare mule--dam or foster mother?

A female, horse-like foal was apparently born to a mare mule from mating to a Shetland stallion. The presence of three pregnant Shetland mares in the same pasture, however, raised some questions about parentage, even though all three mares apparently gave birth to single foals within 6 weeks after the birth of the propositus. The transferrin system indicated that the foal was not born to the mare mule but was the offspring of one of the Shetland mares. Apparently one Shetland mare gave birth to twins 3 to 6 weeks apart, and the mare mule came into lactation spontaneously and adopted the first twin. The offspring was determined to be a horse by appearance, karyotype, blood type, and voice.     

Pregnancy rates and sexual behavior under pasture breeding conditions in mares

Pony mares (n=480) and 16 stallions were assigned to four herds of 60 mares and one stallion (large herds) and to 12 herds of 20 mares and one stallion (small herds). The stallions remained with the herds continuously for all of the large herds and seven of the small herds. In the five remaining small herds the stallion was put into a herd for three hours every two days for 12 observation periods. Pregnancy rates and day of ovulation were estimated by size of embryonal enlargements. Mean pregnancy rates of 51% and 54% were obtained in the small herds and 42% in the large herds during a 48-day period (equivalent to two estrous cycles). Pregnancy rates for herds with the stallion present continuously were higher (P<0.01) for the small herds than for the large herds for days 1-24 (42% versus 19%). There was no effect of herd size on number of mares becoming pregnant per herd on days 1-24, but more mares (P<0.01) became pregnant during days 25-48 in the large herds (13.2 mares per herd versus 1.8). In the herds in which the stallion was present intermittently, the number of times that the stallion rebred the same mare when more than one mare was in estrus was greater (P<0.01) than what would be expected to occur by chance (observed, 21%; expected, 11%). Repeated breeding of the same mare seemed related to the availability or activity of the mare, since such mares more frequently followed and positioned themselves in the vicinity of the stallion. Most of the interferences by a mare which involved keeping the stallion and another mare apart were directed at the mare, whereas most of the interferences during mounting were directed at the stallion (P<0.01). Mares were more likely (P<0.01) to interfere when in estrus than when in nonestrus. When interfering mares were in nonestrus, their hostility was usually directed at the stallion (92%), whereas when in estrus their interference was more frequently directed at a mare (73%, P<0.01).     

Dexamethasone suppression of sexual behavior in the ovariectomized mare

The influence of steroids of adrenal cortical origin on estrous behavior in the ovariectomized mare was evaluated by adrenal suppression via dexamethasone (DEX) administration in two experiments. In Experiment I, 12 mares (six DEX, six control) were tested for sexual behavior in harem groups (two DEX and two control mares plus one stallion per group) for 9 consecutive days. In Experiment II, estradiol (E₂) was given to a group of DEX-treated mares as an additional control. Twelve mares (four DEX, four DEX + E₂, and four control) were tested in harem groups (one DEX, one DEX + E₂, and one control mare plus one stallion per group) for 10 days. All DEX mares showed a clear suppression of sexual response compared to control or DEX + E₂ mares, indicating that the estrous behavior seen in ovariectomized mares may be due to steroids from the adrenal cortex. The control and DEX + E₂ mares were similar in all measures of proceptivity. Despite being more receptive, as indicated by fewer negative responses, the DEX + E₂ mares received fewer intromissions and ejaculations than did the control animals. The ability of estradiol to induce estrous behavior in the dexamethasone-suppressed mare notwithstanding, other adrenal steroids, e.g., androgens, may be involved in estrous behavior in the untreated, ovariectomized mare.     

Ovarian function in captive feral mares

Ovarian function was monitored for 33 mo in captive feral mares (Equus caballus) by following serum progesterone (P) levels. A P level greater than 2.0 ng/ml was considered indicative of ovulation. Feral mares were seasonally polyestrus with the majority of animals ovulating between May and October. During the first year after capture, none of the mares ovulated during the anestrous season. However, in subsequent years, approximately 10% of mares ovulated during the months of November, January and February. P levels during the luteal phase of the cycle ranged from 2.0 to 21.0 ng/ml which were similar to levels in domestic breeds of mares. The pattern of P concentrations during pregnancy was also similar to the pattern in domestic mares. These data confirmed the seasonality of ovulation in feral mares but indicated that this seasonality was not as rigid as previously believed. Captive feral mares were similar to domestic breeds in the percentage of mares ovulating all year and in the P levels achieved during the estrous cycle and pregnancy.     

Social relationships in a herd of Sorraia horses Part II. Factors affecting affiliative relationships and sexual behaviours

The influence of age, dominance rank, kinship and aggressiveness over affiliative relationships and sexual behaviours were analysed in a herd of Sorraia horses, Equus caballus, kept under extensive management. Subjects were 10 adult mares 5-18 years old that had known each other since birth, and a stallion introduced into the group for breeding for the first time. Kinship coefficient and dominance rank were the most important factors affecting affiliative relationships. Bonds were reciprocal and stronger among mares with higher kinship. Mares spent more time in proximity to close-ranking and lower-ranking females. Mares with stronger affiliative relationships or higher relatedness were not less aggressive towards each other. Affiliative relationships between the stallion and the mares were not reciprocal: lower-ranking mares formed stronger bonds with the stallion but he preferred the less genetically related mares for proximity. However, the stallion was involved in sexual behaviours more frequently with the mares that were more genetically related to him. These results suggest that kinship beyond close relatives may affect affiliative relationships both among familiar and among unfamiliar horses. However, the influence of kinship does not imply that horses possess a kin recognition system and alternative explanations are discussed.     

Effects of hormone implants on estrus and ovulation in feral mares

Five groups of 30 captive feral mares each were implanted with silastic rods containing estradiol (E) and/or progesterone (P): E only with 8 g, P only with 24 g, P+HE with 8 g P + 8 g E, HP+E with 12 g P + 4 g E, HP+LE with 12 g P + 2 g E. Arbitrary group designations were differentiated by relative high (H) and low (L) amounts of steroid. Thirty mares received silastic rods containing no hormone (CI). Five mares from each group were bled every 2 wk for 4 mo and monthly for another 5 mo. All mares were tested for estrus by allowing them to stand in an alley between two pens of stallions and visually monitoring her response to the stallion. Serum P levels increased from 0.3 +/- 0.1 to 1.8 +/- 0.1 ng/ml in the P only group during the first 3 wk after implanting. Levels remained stable for the next 2 wk and then began a gradual decline. Serum P levels in the other groups were lower. Serum E levels were slightly increased in the groups receiving 8 g of E (E only and P+HE groups). Significantly fewer animals in the E only and P+HE groups exhibited estrus as compared with control animals (10 of 23 and 13 of 26 versus 22 of 25, respectively, P less than or equal to 0.003). However, animals receiving 24 g of P (P only) showed similar occurrences of estrus as controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Equine antisperm antibodies (EASA): Preliminary study of the clinical response following breeding in immunized mares

Maiden mares (n=6), previously injected with stallion sperm cells (SC group, N=2), stallion seminal plasma (SP group, N=2), or phosphate-buffered saline as a control (C group, N=2) were followed through 5 consecutive estrous cycles to evaluate their clinical response when exposed to stallion sperm cells via breeding. Management was similar to that expected on typical breeding farms. The mares were teased daily and bred by artificial insemination (AI) in all 5 cycles. Differences in serum and uterine flushing equine antisperm antibody (EASA) levels, endometrial culture and cytology results, endometrial biopsy score and fertility were evaluated between treatment groups. An enzyme-linked immunosorbant assay (ELISA) was used to determine serum and uterine IgG and IgA levels specific for sperm cell or seminal plasma antigens. Serum IgG specific for sperm cell antigen was higher in the SC group than in the SP and C groups following exposure to sperm cells via breeding (P<0.05). All other EASA levels were not different between groups (P>0.05); however, uterine IgA levels in one of the SC treated mares did rise over all 5 cycles. No differences were detected in culture, cytology, biopsy or fertility results between groups (P>0.05). Changes in EASA levels were detected after breeding mares previously immunized with stallion sperm cells, however an associated clinical response was not apparent.