Annual Changes in Day-length, Temperature, and Circulating Reproductive Hormones in Thoroughbred Stallions and Geldings

Effects of an extended photoperiod on body composition of young Thoroughbreds in training

The effects of an extended photoperiod (EP) on body composition of Thoroughbreds colts and fillies from December at one year old to April at two years old were investigated. Seventy-three Thoroughbreds reared and trained in Hidaka Training and Research Center, Japan Racing Association, Hokkaido were used. Forty-one horses were under the EP conditions from December 20 to April 15, and the 32 horses were under natural light alone as the control group. Body weight (BW), rump fat thickness (RFT), fat free mass (FFM) and percentage of fat (%F) were used as parameters of body composition. The present study revealed that BW and FFM increased with age in the EP group in colts. In fillies, BW increased with age in both the EP and the control group, however FFM increased with age only in the EP group. From December to April, only colts had a higher rate of increase in both BW and FFM in the EP group than in the control group. However, according to the mean rates of increase in FFM from January to March, the EP group was significantly higher than the control group in both sexes. Furthermore, monthly increase rate of FFM in March was significantly higher in the EP group than in the control group in both sexes. These results suggests that EP treatment to young Thoroughbreds in training at Hokkaido, which is shorter daylength in winter, accelerate the increase of FFM, representing muscle mass.

Effects of different winter climates in Japan on body composition of young Thoroughbreds in training

Changes in the body composition of 50 Thoroughbreds colts and fillies, born between 2004 and 2010, were compared between those reared at the Hidaka Training and Research Center (Hidaka), Hokkaido, which is extremely cold in winter, and those reared at the Miyazaki Yearling Training Farm (Miyazaki), Kyushu, which is mildly cold in winter. The horses were divided into two sex groups and reared and trained in Hidaka or Miyazaki for 7 months from October of one year of age to April of two years of age. Body weight (BW), rump fat thickness (RFT), fat-free mass (FFM), and percentage of fat (%F) were used as parameters of body composition. This study revealed that BW and FFM were higher, and %F was lower in colts than in fillies at both training sites. Among colts, Miyazaki colts tended to have higher FFM values than Hidaka colts, and %F was significantly lower in Miyazaki colts than in Hidaka colts. Furthermore, from October to April, Miyazaki horses had a higher rate of increase in BW than Hidaka horses in both sexes and a higher rate of increase in FFM in colts. The higher rate of increase in FFM in Miyazaki colts suggests that training young Thoroughbreds in winter under mildly cold climate is more effective, than severely cold climate, particularly in colts.

Influence of exercise and emotional stresses on secretion of prolactin and growth hormone in Thoroughbred horses

The secretion of prolactin and growth hormone in response to exercise and emotional stresses was investigated in Thoroughbreds. Two experiments were performed: one with loading of only exercise stress and one with simultaneous loading of exercise and emotional stresses. Exercise stress was loaded in 4 steps using a treadmill for horses: pre-exercise period (5 min), walking period (6.5 min), galloping period (3 min), and cooling down period (10 min). Emotional stress was loaded by showing a loud video of an audience at a racetrack during the walking period. The results clearly demonstrated that exercise stress rapidly increased the secretion of prolactin and growth hormone and that secretion of them persisted for a specific period after the exercise. In addition, emotional stress promoted prolactin secretion.

Semen quality and freezability analysis during breeding and non-breeding seasons in heavy draft stallions in southern Chile

The aim of this study was to evaluate seasonal changes in basic parameters of sperm quality and freezability behaviour of ejaculates from 10 fertile heavy draft stallions. A total of 140 ejaculates were collected, processed and evaluated during both the breeding (September-November) and non-breeding seasons (April-June). Fresh semen was evaluated for volume, concentration, total spermatozoa per ejaculate, plasma membrane integrity and total sperm motility. Cryopreserved samples were evaluated for plasma membrane integrity and sperm motility by the CASA system, and for the freezability index (FI), which was defined as the decreased ratio of viability after freezing-thawing. In fresh ejaculates, only viability showed significantly higher values in the breeding than in the non-breeding season (64.0% ± 15.0% vs. 58.6% ± 12.0%, respectively; p < .05). The sperm post-thawing analysis of viability and total motility parameters showed no significant changes linked to the season. However, the FI analysis showed that the ejaculates collected in the non-breeding season had higher cryoresistance characteristics than those collected in the breeding season. Results suggest that the presence of some cryoprotective factor/s in heavy draft horse ejaculates could be modulated by seasonality, with higher protective effects in the non-breeding season.

The effects of extended photoperiod and warmth on hair growth in ponies and horses at different times of year

Photoperiod is considered the most dominant environmental cue allowing animals to anticipate and adapt to seasonal changes. In seasonally breeding mammals, changes in daylength alter pineal melatonin secretion and pituitary prolactin secretion. During the seasonal transition to shorter winter daylengths, increased production of melatonin and declining prolactin are associated with triggering winter coat growth in many animals. Similarly, studies have shown that artificial extension of photoperiod suppresses melatonin secretion and lifts prolactin inhibition to activate moulting. Four longitudinal cohort studies were conducted to determine if extended photoperiod and warmth, provided by mobile light masks and rugs (horse blankets), could reverse the onset of winter coat growth, maintain the summer coat and accelerate winter coat shedding in horses and in ponies. Studies began at dates corresponding to the autumnal equinox, one month post-summer solstice, one month pre-winter solstice and one month post-winter solstice, respectively. To extend photoperiod to approximately 15h of light, commercially available head-worn light masks provided low intensity blue light to one eye until 11pm daily. Coat condition and shedding rate were scored and hair samples collected, measured and weighed bi-weekly. Data from control and treatment groups were analysed by repeated measures ANOVA. Results revealed that extended photoperiod 1) did not reverse winter coat growth when initiated at the autumnal equinox, 2) effectively maintained the summer coat in stabled horses when initiated one month post-summer solstice, 3) accelerated shedding in outdoor living horses when initiated one month pre-winter solstice and 4) did not accelerate shedding in indoor or outdoor living ponies when initiated one month post-winter solstice. To successfully manage equine coat growth while also preserving optimal thermoregulation in both competition and breeding stock correct timing of light application is crucial and requires careful monitoring of environmental temperature. Further studies are needed where variations in breed and management are considered.

Luteinizing hormone concentrations in healthy horses and horses with trigeminal-mediated headshaking over an 8-hour period

Background

Trigeminal‐mediated headshaking results from a low threshold for firing of the trigeminal nerve. A seasonal component has been implicated in onset of clinical signs, which occur during the spring and summer months. Geldings are overrepresented in the affected population and hormonal differences as compared to a healthy control population of geldings might contribute to headshaking.

Objective/Hypothesis

To assess concentrations of luteinizing hormone (LH) over an 8‐hour period in gelded healthy controls and horses affected with headshaking. Our hypothesis was that geldings with seasonal headshaking would have higher concentrations of LH over an 8‐hour period compared to control horses during the summer when affected horses manifested headshaking.

Animals

Twelve geldings (6 controls and 6 affected).

Methods

Prospective controlled trial. Blood samples were drawn every 15 minutes over an 8‐hour time period during summer from all horses to measure circulating LH concentrations by using a radioimmunoassay for equine LH. All affected horses were actively affected by headshaking at the time of sample collection.

Results

No statistically significant differences in LH concentrations were found throughout the study period in headshakers as compared to control horses. Time had no significant effect, but a slight decrease in LH concentrations was observed for all horses. The main limitation of the study was the low number of horses.

Conclusions and Clinical Importance

Horses affected with headshaking did not have significant differences in circulating LH during the late summer as compared to control horses.

Reproductive seasonality of male dromedary camels

Reproductive seasonality has been reported in numerous species, including male dromedary camels, yet investigations into seasonal changes in camel semen quality have yet to be conducted. The aim of this study was to characterise the seasonal changes in camel semen quantity and quality as well as correlate these changes to testis and accessory sex gland morphology, sexual behaviour, libido and environmental factors such as day length and ambient temperature in Oman. Semen was collected twice a month for a year and testicular and accessory sex organ biometry recorded once a month via ultrasonography (n = 8 bulls). Blood samples were collected monthly to assess testosterone levels. Results indicated that testes and accessory sex glands size increased during October-April, peaking with testosterone concentrations during January (P<0.05). The sexual behaviour and libido of camels was also greater during the months of October-April (P<0.05). Attempts to collect semen were 100% successful during November-February. Semen volume, as well as sperm gross activity, concentration, motility, average path velocity and percentage with intact acrosomes were the greatest during January and decreased from May-September (P<0.05). Changes in values for semen variables, testosterone concentrations and sex organ anatomy were also highly correlated with seasonal changes in day length and ambient temperatures. In conclusion, a clearly defined reproductive season was observed in male camels in Oman ranging from December-March, with peak reproductive function occurring during December-January. To increase the success of breeding programs, matings or semen collections should be timed to occur when reproductive function is maximal.

Seasonal expressions of luteinising hormone receptor, follicle-stimulating hormone receptor and prolactin receptor in the epididymis of the male wild ground squirrel (Spermophilus dauricus)

Luteinising hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL) are pituitary-derived hormones and mediate their functions through LH receptor (LHR), FSH receptor (FSHR) and PRL receptor (PRLR) respectively. This study aimed to investigate the seasonal expression patterns of LHR, FSHR and PRLR in the epididymis of the male wild ground squirrel during the breeding and non-breeding seasons. Histologically, principal cells, basal cells, cilia and mature spermatozoa were found in the lumen of caput, corpus and cauda epididymidis in the breeding season, whereas in the non-breeding season, cilia and basal cells were rarely found and the epididymidal duct was devoid of spermatozoa. Immunohistochemical results showed that LHR, FSHR and PRLR were mainly present in the filamentous cytoplasm layer of epithelial cells of the caput, corpus and cauda epididymidis and FSHR and PRLR displayed stronger staining in the breeding season than in the non-breeding season. Furthermore, the mRNA and protein levels of FSHR and PRLR in all regions of epididymis as well as the levels of LHR in the caput and cauda epididymidis were higher during the breeding season. The protein levels of FSHR, LHR and PRLR were positively correlated with epididymal weight. Together, these results suggest that LHR, FSHR and PRLR may regulate epididymal functional changes in the male wild ground squirrel during its seasonal breeding cycle.

The effects of ergot alkaloids on the breeding stallion reproductive system

REASONS FOR PERFORMING STUDY

Ergot alkaloids cause a range of pathological conditions in mares. There is no evaluation of the effects of ergot alkaloids from endophyte-infected tall fescue on the stallion breeding soundness examination spermiogram.

OBJECTIVES

The objective of this study was to investigate the effect of ergot alkaloids from endophyte-infected tall fescue on the stallion's reproductive functions.

STUDY DESIGN

Crossover toxicology experiment.

METHODS

Six stallions were fed either toxic endophyte-infected tall fescue seed or a nontoxic endophyte tall fescue seed (Flecha AR-542, MaxQ). The fescue seed content was compounded at 45% of a grain diet and the stallions were fed the grain diet at 1% of their body weight. The stallions were fed the diet for 70 days, then rested for at least 70 days (no fescue seed) and then fed fescue seed for a second 70 days. At regular intervals blood sampling and a breeding soundness examination were performed.

RESULTS

The mean time to maximal systemic toxicity was 8.33 h after starting toxic seed ingestion with a mean toxicity level of 49.98 ng alkaloid/mg creatinine. After cessation of feeding toxic seed, the systemic alkaloid concentration fell to control levels within 48 h. There were no significant changes in sperm motility, sperm concentration, sperm cell morphology, total number of sperm cells, number of breeding doses, testicular volume, baseline and human chorionic gonadotropin stimulated testosterone levels. There were no changes in core body temperature and superficial scrotal temperature. The ejaculate from stallions consuming endophyte-infected tall fescue seed had significantly lower gel-free volume (47.5 ± 4.1 ml) than stallions consuming nontoxic endophyte tall fescue seed (62.8 + 4.3 ml, P<0.01).

CONCLUSION

Ergot alkaloids decreased the gel-free volume of stallions consuming high levels of ergot alkaloids but statistically significant effects on the spermiogram of adult breeding stallions were not found.

Promoting effects of an extended photoperiod treatment on the condition of hair coats and gonadal function in Thoroughbred weanlings

The effects of an extended photoperiod (EP) treatment (14.5 hr light, 9.5 hr dark) on Thoroughbred colts and fillies from December 25 at 7-9 months old to the following May at 12-14 months old on coat condition and gonadal functions were investigated. Coat condition was evaluated in April. The colts and fillies in the EP treatment group changed from winter to summer coats (molting of winter coats), whereas those in the control group did not. To determine the day of first ovulation, the plasma concentrations of progesterone were measured once a month in fillies. The day of first ovulation was advanced in the EP treatment fillies compared with the control fillies. The present study clearly demonstrated that the EP treatment advanced the molting of winter coats and advanced ovulation in fillies, even in weanlings.

Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions

One- to two-year-old Thoroughbred colts and fillies being reared in Miyazaki (warm climate) and Hidaka (cold climate), Japan, were administered extended photoperiod (EP) treatment between December 20 and the following April 10, and its effect on growth, endocrine changes, gonadal activation, and hair coat condition was investigated. In colts reared in Miyazaki, no effect of EP treatment was noted on the growth indices, including body weight (BW), height at withers (HW), girth, and cannon circumference (CC), whereas the BWs and CCs of fillies were significantly higher in the EP treatment group than the control. In Hidaka, the BWs and HWs of colts and HWs of fillies were significantly higher in the EP treatment group. Gonadal activation characterized by an increase in circulating hormone concentrations was earlier in the EP treatment group for fillies reared in Miyazaki [luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), and estradiol-17β (E2)] and in colts (LH, testosterone, and E2) and fillies (LH, FSH, P4, and E2) reared in Hidaka. Regardless of sex and climate, prolactin was significantly higher in the EP treatment group, whereas insulin-like growth factor (IGF-I) was not. Initial ovulation occurred before April in more of the EP treatment group than the control regardless of the climate. Molting of the hair coat, examined in March, was advanced in the EP treatment group regardless of sex and climate. These results suggest that EP treatment may promote growth and gonadal activation in fillies reared in Miyazaki and in colts and fillies reared in Hidaka and that the effect may be mediated by prolactin.

Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies

The effects of an extended photoperiod (EP) in Thoroughbreds colts and fillies from winter at one year old to spring at two years old on the gonadal functions, coat condition, and endocrine changes were investigated. Sixty-two Thoroughbreds (31 colts and 31 fillies) reared in the Hidaka Training and Research Center (Hidaka), Japan Racing Association were used. Thirty of them (15 colts and 15 fillies) were reared under EP conditions from December 20 to April 10, and the remaining 32 horses were reared under natural light alone as a control group. For EP, a 100-watt white bulb was set near the ceilings of stalls, and lighting conditions of 14.5-hr light and 9.5-hr dark periods were established. Blood was collected from the jugular vein once a month from October at one year old to February at two years old in both colts and fillies, and then twice a month in colts and weekly in fillies after March, and the coat condition was evaluated in January and April in 56 horses. To investigate endocrine changes, the plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), immunoreactive (ir-) inhibin, testosterone, estradiol-17β and progesterone were measured. No significant difference was noted in the coat condition between the two groups in January, but they changed from winter to summer coats (molting of winter coats) in April in the EP group compared with the control group. Regarding endocrine changes, the plasma concentrations of prolactin, FSH, ir-inhibin and testosterone were significantly higher in the EP colts than in the control group from January to April. The plasma concentrations of LH tended to rise in the EP colts from January to April compared with the control group. In the EP fillies, the plasma concentrations of prolactin, LH, ir-inhibin, estradiol-17β and progesterone were significantly higher during January and April, but a significantly high level of FSH was noted in the control than EP group in January. The ovulation day was advanced in the EP fillies compared with the control group. The present study clearly demonstrated that EP treatment during rearing advanced the molting of winter coats in both colts and fillies. These results suggested to be due to the action of prolactin being increased by EP treatment. In addition, EP treatment stimulated the hypothalamus-pituitary-gonadal axis even in yearlings, and advanced ovulation in fillies. Since EP treatment-induced changes in the yearlings were within the physiological range, and the method is safe and simple, EP treatment may be an effective technique in horse husbandry.

Comparison of growth and endocrine changes in Thoroughbred colts and fillies reared under different climate conditions

Development and endocrine changes in Thoroughbreds colts and fillies were compared between those reared at two facilities of the Japan Racing Association, the Hidaka Training and Research Center (Hidaka) and Miyazaki Yearling Training Farm (Miyazaki). Thoroughbred colts and fillies born in Japan between 2003 and 2010 were used. Each colt group and filly group was divided into 2 groups, respectively, and raised in Hidaka or Miyazaki for 7 months from September at 1 year old to April at 2 years old. For the growth parameters, the body weight, height at withers, and girth and cannon circumferences were measured once a month. For parameters of endocrine function, circulating prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), insulin-like growth factor-1 (IGF-1), testosterone, progesterone, and estradiol-17β levels were measured. Regarding growth, the rate of increase over the 7-month period was significantly higher in both colts and fillies raised in Miyazaki than in Hidaka in all 4 parameters: body weight, height at withers, and girth and cannon circumferences. The endocrine changes of the colts and fillies born in 2007 were as follows. In colts, although circulating prolactin tended to be higher in colts reared in Hidaka from October to April, circulating LH, FSH, testosterone, estradiol-17β and IGF-1 tended to be higher in colts reared in Miyazaki than in Hidaka, suggesting that the gonadotropin-releasing hormone-LH/FSH system and the growth hormone-IGF-1 system were more active in colts reared in Miyazaki as compared with those reared in Hidaka. In fillies, circulating prolactin tended to be higher in fillies reared in Hidaka in February and March, but no significant difference was noted in the serum LH, FSH, IGF-1, or progesterone level between the 2 groups. Circulating estradiol-17β tended to be higher in fillies reared in Miyazaki than in Hidaka in October and November. Regarding ovarian function, the initial ovulation occurred by the end of March in 2 (16.7%) of 12 fillies reared in Hidaka and 7 (38.9%) of 18 fillies reared in Miyazaki, suggesting that the ovarian function was more active in fillies reared in Miyazaki as compared with those reared in Hidaka. Based on these findings, it was clarified that development of the body and gonads was faster in Miyazaki compared with Hidaka in both colts and fillies.