Number Of Mares Research Articles

The relationship of increased susceptibility of sperm DNA to denaturation and fertility in the stallion

The relationship between fertility and susceptibility of sperm DNA to denaturation was determined in a group of 84 actively breeding, clinically fertile stallions. Susceptibility of DNA to denaturation was determined using the sperm chromatin structure assay (SCSA). The SCSA measures, mean of alpha-t (meanα t), standard deviation of alpha-t (SDα t), and the COMP of alpha-t (cells outside the main population)] were significantly correlated with the percentage seasonal pregnancy rate (SPR; meanα t, r = −0.24, P ≤ 0.05; % COMPα t, r = −0.27, P≤ 0.05); percentage pregnant per first cycle (FCP; SDα t, r = −0.30, P ≤ 0.01; % COMPα t, r = −0.42, P≤ 0.0001); and the percentage pregnant per cycle (PC; meanα t, r = −0.31, P≤ 0.01; SDα t, r = −0.32, P≤ 0.01; % COMPα t, r = −0.41, P≤0.0001). This study describes detectable intrinsic variation in sperm chromatin structure among fertile stallions (SPR, mean = 83%; FCP, mean = 58%; PC, mean = 57%) in an active breeding population (number of mares bred/stallion/year, mean = 37), in the absence of overt reproductive abnormalities and apparent diseases such that an increase in the susceptibility of sperm DNA to denaturation is associated with reduced fertility, both in terms of efficiency of reproduction (FCP and PC) and seasonal pregnancy rate (SPR). Both COMPα t and meanα t were useful indicators of fertility, with COMPα t being the only SCSA value able to identify mean differences between fertility groupings for SPR and FCP, and overall it was the most reliable indicator of fertility in this group of stallions. The SCSA is able to evaluate a compartment of the spermatozoa which is different from that of traditional tests for sperm quality such as motility and morphology.

Fertility of Shetland pony stallions used in different breeding systems: A retrospective study

Summary In horses reproductive performance is usually expressed as the foaling rate. This rate ranges from 40% to 80%. Three major factors contribute to this variation namely, the stallion, the mare and management. In this study, the performance of Shetland ponies kept in three different breeding systems was investigated retrospectively. In one breeding system, the stud farmer travelled with his stallion (n = 9) to the mare (system 1) while in another system, the stallion (n = 3) stayed at the studfarm and the mares came to the stallion (system 2). The last system was pasture breeding (system 3; n = 9). Each stallion participated in only one system. The average number of cycles per mare used for breeding did not differ significantly between systems 1 and 2. However, the number of matings per cycle was higher in system 2 than in system 1. The average number of mares serviced per stallion was 91, 50, and 17 for systems 1, 2 and 3, respectively. Mares mated in pasture had a 2.8‐fold higher chance (p < 0.05) of having a foal the next season than the mares mated under systems 1 and 2. The foaling rate per season was 58%, 48%, and 80% for systems 1, 2 and 3, respectively. Management aspects play an important role in the relatively low foaling percentages of systems 1 and 2.

Comparison of two dosage regimens of the GNRH agonist deslorelin acetate on inducing ovulation in seasonally anestrous mares

This study investigated the efficacy of two dosage regimens of a potent GnRH analogue (GnRHa), deslorelin acetate, in inducing ovulation in seasonally anestrous mares. Forty-five seasonally anestrous mares were randomly assigned according to follicular size to one of three treatment groups: control, increasing GnRHa dose, and constant GnRHa dose. Treatment began on February 28 and continued until ovulation or for a maximum of seven treatments. Mares were palpated every other day until a 35 mm follicle was detected, then every day until ovulation or regression of the follicle occurred. Blood samples were taken from five randomly chosen mares in each treatment group and analyzed for LH levels. Twenty percent of mares in both deslorelin treatment groups ovulated, while no control mares ovulated during the treatment period. There was no difference in the number of mares that ovulated between treatment groups. Four of the six mares that ovulated were in transitional anestrus at the initiation of treatment, while only two were in deep anestrus. Concentrations of LH were greater (p=0.0008) in both GnRH-treated groups than in the control mares. Concentrations of LH did not differ between the two GnRH-treated groups until day 12 of treatment, when mares treated with a constant dosage had higher (p=0.0358) levels of LH than those treated with an increasing dosage. It is possible that administration of larger amounts of the GnRH agonist lowered the sensitivity of the pituitary to stimulation by GnRH. Deslorelin acetate did stimulate follicular growth and ovulation in a limited number of anestrous mares. Further investigation into the potential of this short-term implant to shorten the onsent of the breeding season is recommended.

Follicular activity and concentrations of FSH and LH associated with senescence in mares

The nature of reproductive senescence was studied during the expected ovulatory season in pony mares by transrectal ultrasonic monitoring of the ovaries and assay of circulating concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Old mares (⩾20 years) were less likely ( P<0.005) to ovulate at regular intervals than younger mares as indicated by the number of mares with two consecutive interovulatory intervals (IOI; 5–7 years, 9/9; 15–19 years, 10/10; ⩾20 years, 8/16). In addition, a central area of nonechogenic fluid (unknown source) was detected at the ovulatory site in more ( P<0.005) ovulations in old mares than in younger mares (5–7 years, 1/91; 15–19 years, 4/78; ⩾20 years, 10/68). Old mares were grouped as follows: (1) normal length of the follicular phase (interval from luteolysis to ovulation) of the IOI ( n=9); (2) elongated follicular phase (>2 SD from the mean of all mares with an IOI) ( n=2); (3) one ovulation in 80 days ( n=2); and (4) no ovulations or follicles ⩾5 mm in 60 days ( n=3). Mares with an IOI but with an elongated, compared with a normal length of the follicular phase, had fewer follicles per ovulatory wave (1.5 ± 0.5, 3.1 ± 0.3, P< 0.05), a longer IOI (30.0 ± 1.0, 25.8 ± 0.6 days, P < 0.01), a longer interval from administration of a luteolytic dose of PGF 2α to ovulation (29.5 ±8.5, 15.8 ± 0.9 days, P < 0.02), and higher mean concentrations of FSH (13.0 ± 3.4, 3.3 ± 0.6 ng ml −1, P < 0.001) and LH (18.5 ± 5.3, 7.6 ± 1.5 ng ml −1, P < 0.02) during the follicular phase. Mean concentrations of FSH, LH and progesterone during the luteal phase were not different among ovulating mares; however, during the follicular phase, concentrations of FSH and LH were significantly different among groups with the lowest mean concentrations occurring in mares with a follicular phase of normal length. Mean concentrations of FSH for mares that did not ovulate were higher ( P<0.05) than for the 3 days encompassing ovulation in the mares with an IOI and tended to be higher ( P<0.08) than during the 3 days prior to luteolysis (period of maximal FSH concentrations). Results indicated that ovarian senescence in these mares involved the following progression: lengthening of the follicular phase, sporadically occurring ovulations, and a final state of persistent follicular inactivity (follicles ≤5 mm). Ovarian senescence was accompanied by elevated circulating concentrations of gonadotropins.

Regulation of estrus and ovulation in mares with progesterone or progesterone and estradiol biodegradable microspheres with or without PGF 2α

A single injection of a microsphere preparation, designed to deliver 1.25 gm progesterone and 100 mg estradiol-17β at a controlled rate, for a duration of 12 to 14 days, produces accurate control of estrus and fertile ovulations in mares. Theatment is followed by PGF 2α injection 14 days after steroid injection. The objectives of the present study were to determine whether estradiol added to the progesterone treatment or PGF 2α administered at the end of the steroid treatment regimen, would improve synchronization of estrus and ovulation. A total of 45 cyclic horse mares was randomly assigned to 1 of 5 treatment groups as follows: Group 1 (control, n=9) sterile microsphere vehicle + sterile PGF 2α vehicle 14 days after treatment with microsphere vehicle; Group 2 (n=9) progesterone and estradiol microspheres + PGF 2α 14 days after treatment with microspheres; Group 3 (n=9) progesterone and estradiol microspheres + PGF 2α vehicle 14 days after treatment with microspheres; Group 4 (n=9) progesterone + PGF 2α 14 days after treatment with microspheres; and Group 5 (n=9) progesterone + PGF 2α vehicle 14 days after treatment with microspheres. Addition of estradiol (P<0.05) or PGF 2α (P<0.05) to the treatment regimen increased synchronization efficary by reducing variation in days to ovulation. All treatments significantly reduced variation in days to estrus compared with that of the controls; however, mares in the progesterone groups had an increased incidence of silent or shortened estrous behavior (<- 2 days) following treatment. Estradiol added to the treatment regimen increased (P<0.05) the number of mares with post treatment estrus > 2 days in duration compared with mares treated with progesterone (78 vs 33%, respectively). Therefore, estradiol and PGF 2α each appear to reduce variation in days to ovulation while estradiol seems to promote better expression of posttreatment estrous behavior.

Dominance, aggression frequencies and modes of aggressive competition in feral pony mares

Feral pony mares, Equus caballus, at Assateague Island, Maryland, formed linear dominance hierarchies within bands. Generally, older mares dominated younger mares, and larger mares dominated smaller mares. Large mares initiated aggression more often than small mares when age was controlled for but, surprisingly, older mares initiated aggression less often than younger mares when size was controlled for. Thus, mares peak in aggressiveness fairly soon after achieving full size and then, while maintaining or improving their rank in the domainance hierarchy, progressively reduce their involvement in aggression as they grow older, Involvement in aggression per mare increased as number of mares in the group increased; this effect was independent of nearest-mare distances. Frequency of involvement in aggression did not differ between mares that had changed bands within the year and mares whose band association had continued for a year or more. Aggression was directed more frequently than expected at subordinate mares who were nursing, and also occurred more frequently than expected at water holes. The proportion of aggressive encounters during grazing closely matched the total proportion of time spent grazing. Subordinate mares with foals received aggression more often than subordinate mares without foals. The high frequency of aggression associated with foals and nursing suggests that interference with reproduction of subordiantes is an important mode of competition between mares. Such interference may be common in animals that feed on dispersed resources and live in small, cohesive groups.

Use of gonadotropin-releasing hormone for hastening ovulation in transitional mares.

Natural GnRH and its analog have potential for hastening ovulation in mares. A study was conducted to evaluate the efficacy of a GnRH agonist given either as an injectable or s.c. implant for induction of ovulation in mares. Forty-five seasonally anestrous mares (March) were assigned to one of three groups (n = 15/group): 1) untreated controls; 2) i.m. injection of the GnRH agonist buserelin at 12-h intervals (40 micrograms/injection for 28 d or until ovulation) and 3) GnRH agonist administered as a s.c. implant (approximately 100 micrograms/24 h for 28 d). Six mares per group were bled on d 0, 7, 14 and 21 after injection or insertion of implant. Samples were taken at -1, -.5 and 0 h and at .5, 1, 1.5, 2, 4, 6 and 8 h after GnRH. Additional daily samples were drawn for 28 d after injection or until ovulation. Samples were assayed for concentration of LH and FSH. Progesterone concentrations were determined in samples collected on d 4, 6 and 10 after ovulation. Number and size of follicles and detection of ovulation were determined by ultrasonography. Number of mares induced to ovulate within 30 d was 0 of 15, 7 of 15 and 9 of 15 for groups 1, 2 and 3, respectively. During treatment, follicle sizes were smaller for mares in group 3 (implant). The LH response to GnRH agonist (area under curve) was similar among groups at d 0 but was greater (P less than .05) for mares in group 3 on d 7 and 14 and groups 2 and 3 on d 21 than for controls. A similar pattern was detected for peak concentrations of LH after GnRH on d 0, 7, 14 and 21. Daily concentrations of LH remained low in untreated control mares compared with GnRH-treated mares throughout the sampling period. Concentrations of LH for mares in group 3 that ovulated were elevated greatly above those for group 2 mares, whereas concentrations of FSH were similar in both treatment groups prior to ovulation.

Effects of postparturient uterine lavage on uterine involution in the mare

Eighteen postparturient mares were used to evaluate effects of uterine lavage on uterine involution. Mares were randomly assigned to one of three treatment groups: Group 1 (seven mares), no lavage; Group 2 (five mares), lavage on Day 3 post partum; and Group 3 (six mares), lavage on Days 3, 4, and 5 post partum. Five liters sterile physiologic saline, prewarmed to 42°C, were used for each lavage. Transrectal ultrasound examination of the reproductive tract was performed on Day 11 post partum to detect the presence of free fluid in the uterine lumen, to estimate the cross-sectional diameter of the uterine horns and body, and to determine if ovulation had occurred. Endometrial biopsies were also taken on Day 11 post partum to evaluate endometrial histologic characteristics. Lavage had no effect (P>0.05) on diameter of the uterine body or previously gravid uterine horn, presence of fluid in the uterine lumen, or number of mares which had ovulated by Day 11 post partum. Histologic characteristics of the endometrium (height of luminal epithelium, gland depth, relative gland vclume, and inflammatory-cell score) were not affected by treatment (P>0.05). Postpartum uterine lavage did not significantly affect uterine involution by the parameters measured in normal-foaling mares at Day 11 post partum.

Use of serial progesterone measurements to assess cycle length, time of ovulation and timing of uterine flushes in order to recover equine morulae

SummaryIn 1987, as part of an embryo transfer programme to produce monozygotic twin foals, mares were flushed during the morning (09:30 to 13:30 h) of Day 6. Of 100 flushes, 48 embryos were recovered half of which were morulae. In 1988, in an attempt to increase the proportion of morulae, various flushing times between 17.00 h on Day 5 and the afternoon of Day 6 were used. For flushes carried out during the morning of Day 6, recovery rates were similar to those of the previous year. However, although the proportion of flushes resulting in the recovery of morulae was not significantly different for times between 23:00 h on Day 5 and 13:00 h on Day 6, the overall recovery rates for flushes on Day 6 were higher than those on Day 5. In addition, a number of mares that did not produce an embryo when flushed before 09:00 h on Day 6, were subsequently found to be pregnant when scanned at Day 18 suggesting that flushing had been carried out before arrival of the embryo in the uterus. To determine whether valid predictions could be made as to when to flush a mare to maximise recovery of morulae, a review of embryo recovery rates and plasma progesterone profiles of a large herd of mares over two breeding seasons was carried out. Mean plasma progesterone levels on the first three days after ovulation were higher for mares that produced embryos when flushed on Day 5 than for all other groups. Comparison of the results of previous flushes with the corresponding plasma progesterone profiles suggested that the characteristics of the post ovulation progesterone rise may have some value in deciding when a mare should be flushed. A review of the effects of uterine flushing, PGF2α and hCG on cycle length and ovulation time was also carried out in order to devise more efficient methods of herd management and ensure a supply of suitably synchronised recipient and donor mares at convenient times for embryo transfer experiments.

Postpartum reproductive performance in the multiparous mare fed to obesity

Twenty multiparous Quarter Horse mares were assigned to one of two treatment groups at 40 to 75 d of pregnancy. Group 1 was the control group and the mares were fed to maintain a moderate degree of body fat (condition score 5.5 to 7). Group 2 was the obese group and the mares were fed to achieve (prepartum) and then maintain (post partum) an extremely high degree of body fat (condition score 9). Estrous intensity was evaluated using subjective teasing scores ranging from 0 (rejection) to 4 (maximum receptivity). Mares were artificially inseminated beginning with the second postpartum ovulatory cycle; the study was terminated after 63 d of pregnancy. Duration of estrus, maximum teasing score and the number of mares exhibiting overt estrus (teasing score > 2) did not differ between treatment groups during the first and second postpartum ovulatory cycles. The intervals from foaling to first cycle ovulation, foaling to second cycle ovulation, and first to second cycle ovulation were also similar between treatment groups. All mares in both treatment groups conceived and maintained pregnancy. The first cycle conception rate and the number of cycles per conception did not differ between treatment groups. A high degree of body fat produced by overfeeding during gestation did not adversely affect postpartum reproductive performance in the multiparous mare.

Ovariectomized steroid-treated mares as embryo transfer recipients and as a model to study the role of progestins in pregnancy maintenance

Embryo transfer into ovariectomized steroid-treated mares was used as a model to evaluate various progestin/estradiol treatments and to determine the level of progesterone necessary for the maintenance of pregnancy in mares. Once a donor mare was in estrus and had a ≥35 mm follicle, an ovariectomized recipient was selected and assigned to one of three groups: 1) 1 mg estradiol (E 2) was injected subcutaneously daily until the donor mare ovulated; on the day of the donor mare's ovulation, daily intramuscular injections of 300 mg progesterone (P4) were commenced and continued until the end of the experiment (Day 35); 2) E 2 and P4 treatments were identical except E 2 was continued daily until Day 20; and 3) The same E 2 treatment as Group 1, 0.044 mg altrenogest per kilogram body weight were administered daily until Day 35. Embryos were recovered 7 d after the donor mare's ovulation and were transferred via surgical flank incision. Twenty additional embryos (controls) were transferred into intact recipients that ovulated 1 d before to 3 d after the donor. Pregnancy rates did not differ (P>0.05) among groups at Days 14 or 35. Pregnancy rates at Day 35 for mares administered injectable P4 (70%) were identical to those given altrenogest. Overall, pregnancy rates for ovariectomized-progestin treated recipients (28 of 40, 70%) were similar (>0.05) to that of intact mares (16 of 20, 80%). Dose of P4 was decreased in Groups 1 and 2 to 200 mg (Days 35 to 39), 100 mg (Days 40 to 44), 50 mg (Days 45 to 49) and 0 mg (≥Day 50). Blood samples were collected once on Days 34, 35, 39, 40, 44, 45, 49 and 50 and assayed for P4. Dose of altrenogest was decreased to 0.022, 0.011, 0.0055 and 0 mg per kilogram body weight at Days 35 to 39, 40 to 44, 45 to 49 and ≥50. Number of mares in Groups 1 and 2 that lost their pregnancy while given 200, 100, 50 or 0 mg P4 was 0, 2, 8 and 4, respectively. Doses of 0.022, 0.011, 0.0055 and 0 mg altrenogest per kilogram body weight resulted in 0, 6, 4 and 3 mares aborting. Fetal death did not occur until concentrations of P4 decreased below 2.56 ng/ml 24 h after injection.

Ultrasonic anatomy and pathology of the equine uterus

The morphological and pathological status of the uterus in mares was evaluated using a linear-array ultrasound scanner, and the ultrasonic properties of the uterus were characterized. The uterus was examined each day in 16 mares, beginning at mid-diestrus. The uterus was recorded as having an ultrasonic morphology characteristic of diestrus (endometrial folds not distinguishable), estrus (prominent endometrial folds) or an intermediate stage (folds only moderately distinguishable). The number of mares with an intermediate or estrous image increased gradually between day −7 ( 2 14 mares; ovulation = day 0) and days −3 ( 11 16 ) and −2 ( 10 16 ) and then declined between days −2 and +1 ( 0 12 ). In another study, a large nonechogenic area (ejaculate) was visible in the uterine lumen immediately after mating in all of six mares. During the course of pregnancy diagnoses and hand-breeding, several pathological conditions of the uterus were first observed by ultrasound examination and confirmed by digital exploration of the uterus or at slaughter. Cysts contained nonechogenic material (fluid) and were usually compartmentalized. The purulent material associated with pyometria was relatively nonechogenic but contained echogenic spots. Mummified fetuses and remnants of fetal bones showed echogenic properties consistent with high tissue density. The results demonstrated that ultrasound technology provides a noninvasive form of visual access to the uterus to evaluate normal, morphological changes and to detect and study certain pathological processes.

Effects of placement of intravaginal sponges on LH, FSH, estrus and ovarian activity in mares during the nonbreeding season.

Eight seasonally anestrous mares were administered intravaginal polyurethane sponges on December 15 and then weekly thereafter until February 1. Control mares received no sponges or genital contact. Sponge insertion caused an immediate surge in follicle-stimulating hormone (FSH) concentrations in jugular plasma in 50% of treated mares whereas no control mares had surges in FSH (P less than .05). The effect of treatment on luteinizing hormone (LH) concentrations was much less dramatic and only three treated mares appeared to have positive responses. Sponge-treated mares exhibited positive responses in FSH concentrations 11 times out of 32 mare-days and control mares zero out of 28 (P less than .05). The magnitude of the FSH response decreased rapidly with successive responses. Sponge insertion induced estrus in four of eight treated mares; no control mares exhibited estrus (P less than .05). Sponge insertion also increased ovarian size and the incidence of large follicles. When all mares were fed altrenogest for 14 d beginning February 1, there was no beneficial effect of sponge treatment on number of mares exhibiting estrus or on pregnancy rate. These data confirm earlier speculations that sponge treatment causes surges in gonadotropins and increased ovarian size in approximately 50% of anestrous mares. However, sponge treatment does not appear to provide a practical means of preparing mares for progestogen synchronization during the nonbreeding season.

Intrauterine embryo reduction in the mare

The site of a hypothesized embryo reduction mechanism was studied. The number of normal-sized embryos and undersized embryos (>2 standard deviations below the mean embryo diameter in control mares) was determined at day 7 and 11 post-ovulation in single-ovulating control mares and in multiple-ovulating pituitary extract-treated mares in which all ovulations occurred on a single day. In two additional groups (control and treated), the embryonal enlargement was monitored by rectal palpation until day 49. An average of 0.7 normal-sized embryos per control mare at day 7 and at day 11 and 0.6 vesicles per control mare at day 49 was found. More normal-sized embryos (P<0.05) were recovered per extract-treated mare at day 7 (2.9 embryos/mare) than at day 11 (0.7), and fewer undersized embryos per extract-treated mare (P<0.05) were recovered at day 7 (0.1) than at day 11 (1.1). The total number of embryos (normal-sized plus undersized) per treated mare was greater (P<0.05) at day 7 and at day 11 than the number of palpated vesicles per treated mare at day 49. The number of mares with more than one normal-sized embryo in the day 7 treated group ( 10 14 ) was greater (P<0.05) than in the day 11 treated group ( 1 14 ) and was greater than the number of mares with more than one palpated vesicle in the day 49 treated group ( 2 14 ). Intrauterine reduction was therefore manifested between days 7 and 11 in multiple-ovulating mares, as demonstrated by the number of multiple normal-sized blastocysts recovered at day 7 and by the reduced number of normal-sized and the increased number of undersized blastocysts recovered at day 11.

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).

Ethogram of agonistic behaviour for thoroughbred horses

Social interactions between individual horses were observed in two herds each comprising a stallion and a number of mares. In one herd, the animals were observed whilst grazing and resting; in the other, nearest neighbours were recorded when the animals were grazing, and social interactions were noted when the animals were feeding on hay. In both herds, the horses showed marked preferences for the company of specific individuals when they were grazing. In one herd, the associations were mainly between individuals that had been associated prior to being put in the herd. In the other herd, this was not the case. A new statistic was produced for testing for specific company preference. In both herds, the stallion was dominant over all mares and never received any aggression. The complete social hierarchy could not be determined for the herd which was observed only when grazing because social contact was restricted to that within groups or pairs that associated together. In the herd to which hay was fed, a non-linear hierarchy existed. Statistics were produced to quantify both the general level of dominance of a horse and its specific dominance or subordination to every other horse. It is suggested that these statistics, and one for quantifying the general aggressiveness of a horse, could be widely used. A principal component analysis allowed the horses to be characterised socially according to aggressiveness, their attitude to other horses and their attractiveness to other horses.

Preliminary investigation on the fecundity of premium stallions

A Recent statistical survey of the records of premium stallions by Sanders (1) draws attention to the fact that the breeding efficiency of the horse is much below that of the other domesticated animals and that it has apparently declined within recent years. For example, between 1887 and 1889 the average number of mares served by Light Horse stallions and which produced foals was about 59 per cent, of the total mares served. Between 1904 and 1910 this figure had fallen to about 56 per cent, and at the present time is not much above 50 per cent. While this decline may in part be due to the record of infertile services being kept more strictly now than formerly, and perhaps also to the more rigorous conditions to which travelling stallions are subjected, the figures are sufficient to indicate that much loss is actually occasioned by low breeding efficiency and also that there might be considerable improvement on the present standard.