Related sexual interest and behaviors are expressed and accepted only during this period. At other times of the year, they will be an estrus, or have a dearth of their sexual cycle.
Unlike reproductive publicity, seasonality is described in both males and females. Male seasonal breeders may exhibit changes in testosterone levels, testes weight, and fertility depending on the time of year.
A primary influence on the timing of reproduction is food availability. Organisms generally time especially stressing events of reproduction to occur in sync with increases in food availability.
For example, species that are preyed upon frequently may time reproduction to occur out of sync with the peak in density of predators. The hypothalamus is considered to be the central control for reproduction due to its role in hormone regulation.
Hence, factors that determine when a seasonal breeder will be ready for mating affect this tissue. GRH in turn transits to the pituitary where it promotes the secretion of the gonadotropin and FSH, both pituitary hormones critical for reproductive function and behavior, into the bloodstream.
Changes in gonadotropin secretion initiate the end of an estrus in females. Photo period likely affects the seasonal breeder through changes in melatonin secretion by the pineal gland that ultimately alter GRH release by the hypothalamus.
Hence, seasonal breeders can be divided into groups based on fertility period. “ Long day breeders cycle when days get longer (spring) and are in an estrus in fall and winter.
Some animals that are longdaybreeders include; ring-tailed lemurs, horses, hamsters, groundhogs, and mink. “Short day breeders cycle when the length of daylight shortens (fall) and are in an estrus in spring and summer.
“The GRH System of Seasonal Breeders : Anatomy and Plasticity”. Williams, Cory T.; Lassen, Marcel; Barnes, Brian M.; Buck, C. Loren; Arnold, Walter; Giraud, Sylvain; Better, Sebastian G.; RUF, Thomas (2017).
“Seasonal reproductive tactics: annual timing and the capital-to-income breeder continuum”. “After consultation with our vets Cambridge Equine Hospital and, in particular, Dr. Robert Hitchcock, we decided to install Equine lighting in our new stallion barn, built during 2019.
We were very pleased with the returns from all stallions, but particularly our French shuttle stallion Manor and first season sire Embellish, both of whom covered books in excess of 140 mares and achieved pregnancy rates in the low 90s after all testing was complete.” Henry Plumper, CEO, Cambridge Stud, NZ. This biannual (yearly) rhythm ensures that after an 11-month gestation period, environmental conditions such as temperature and grass growth are optimal for foals to thrive.
While stallions, unlike mares, are capable of breeding all year round, there are significant improvements in reproductive performance associated with the spring and summer months. Nature conveys the signal for the breeding season to start through the gradual increases in day length in spring.
As day length shortens in the autumn and the duration of melatonin production increases, reproductive activity in both stallions and mares is suppressed, and they enter the non-breeding season. A study evaluating the effect of optimum lighting on testosterone levels in 24 Sport Horse stallions was conducted over a six-month period at a stud in Germany.
In addition, blue-enriched light boosts activity, metabolism, alertness and appetite and acts as a natural air sanitizer by reducing growth of microbes. Health Strengthening their immune system Enhancing alertness and mood Accelerating wound healing Performance Increases in muscle mass Advancing and extending the season of peak performance Improving appetite Improving top-line Coat Condition Accelerating winter shedding Maintaining coat condition Reducing or eliminates clipping For more information about Equine lighting solutions check out the Equine Stable Light and the Equine Light Mask.
It is important that horse owners and breeders understand and recognize the basics of equine reproductive behavior for management purposes. Research has noted that both stallions and, to a lesser degree, fillies may exhibit sexual display before their reproductive tracts are physiologically mature.
Pregnancy cannot occur until the respective reproductive tract matures at the time of puberty. Estrus, or heat, is the period of the reproductive cycle when the mare ovulates and, if bred, is likely to conceive.
Mares are also “seasonally poly estrous,” meaning they have multiple estrous cycling throughout the spring and summer. The natural breeding season for horses in the Northern Hemisphere is the spring or summer.
Light is the controlling factor in causing mares to come into heat in early spring. A mare in heat may actively seek out and attempt to stay in the vicinity of a stallion.
The classic behavioral display of the stallion when it “checks” a mare is to lift its nose into the air and curl his upper lip. The stallion will frequently nudge the mare, apparently to signal readiness and to assess her “firm stance” response.
Dominance patterns are not as easily seen on most modern stud farms, where stallions are not allowed to run in groups with bands of mares. A stallion with a high libido will exhibit an eagerness to mount and attempt to breed a mare.
In natural situations, stallions exhibit a wide range of libido levels, from zero activity to extreme aggressiveness. Some stallions will have such a strong libido that they will sacrifice all other pursuits in favor of searching for and breeding mares in heat.
Young stallions with extremely low libido are hard to breed and require patience from those handling them. Young horses with very high libido require extreme caution by the handler and those working the breeding shed.
During the day, light levels are detected by the retina which sends impulses to the suprachiasmatic nucleus of the hypothalamus and then to the superior cervical ganglion. These fibers cause inhibition of the pinealocyte cells of the pineal gland preventing synthesis of the hormone melatonin.
High frequency, low amplitude LH pulses lead to breeding activity. Whereas low frequency, high amplitude LH pulses lead to ancestors and inactive gonads.
Ewe, Doe, Goat Their breeding season is at the end of summer and beginning of autumn. Apart from pharmacological manipulation of the estrous cycle, photo period, nutrition and temperature may also play a part in the controlling entry into the breeding season in some species.
In order to synchronize a group of mares so that they may all be mated at the same time or to make Embryo Transfer possible. Control of entry into the breeding season is particularly important in producing foals for the racing industry.
If you decide that breeding your horse is something you are prepared to do, it is important to recognize the behaviors associated with a mare in heat, a mare that is receptive to a stallion, mating, signs of foaling and normal behavior after foaling as well as the estrous cycle and how it can vary. During this breeding soundness examination the veterinarian will do a visual inspection of the vulva and vagina of the mare and a palpation of the cervix, uterus and ovaries.
Mares are “seasonally poly estrous” because they have multiple estrous cycles throughout the spring and summer. Mares have light receptors in the back of the eyes that send signals to the brain to release hormones that initiate the estrous cycle.
With advances in science and technology, horse breeders can use synthetic hormones to control the estrous cycle and better manage breeding. Progesterone can be given to prevent a mare from coming into estrus and prolonging the distrust stage of the cycle.
Typically, during the breeding season a mare will have a 21-day estrous cycle which is the interval from one ovulation to the next. Accurate estrus detection is often done by using different “teasing” methods along with a scoring system that can be applied to individual mares.
The goal in teasing is to identify changes associated with estrus that are typical for that mare when she is most receptive and capable of being bred. The person doing the teasing needs to be an excellent observer of mare behavior and a good record keeper since the individual behaviors that a particular mare exhibits during estrus will be fairly consistent from one cycle to the next and during subsequent cycles.
General receptivity to the stallion Tail raising Frequent urination Winking of the vulva Assuming a breeding/squatting stance These systems keep handlers and horses safe and provide opportunities for close observation of the mare's behavior.
Teasing over a paddock fence assumes that a mare in estrus will move toward the stallion and show interest. This means producing semen containing adequate quality and numbers of spermatozoa to fertilize the mare's ovum.
When a veterinarian conducts a breeding soundness exam, measurement of scrotal circumference is one of the procedures used. Production then increases in March, then peaks in May and June and begins to decline in July and August.
As with mares, use of artificial lighting programs will increase or maintain spermatozoa production during the shorter daylight months. Libido is the term used to denote the degree of sexual urge or drive in animals.
A stallion with a high libido will exhibit eagerness to mount and attempt to breed a mare. The classic behavioral display of a stallion when it “checks' a mare is to lift its nose into the air and curl its upper lip.
The response appears to help the stallion trap the pheromone scents, or chemical signals, emanating from the mare. As the stallion draws in the odor, he curls his lip to temporarily close the nasal passages and hold the particles inside.
The upward head tilt helps the airborne molecules linger in the vomeronasal organs that are located under the floor of the horse's nasal cavity. The estrous cycle or estrous cycle (derived from Latin estrus “frenzy”, originally from Greek bistros “gadfly”) is the set of recurring physiological changes that are induced by reproductive hormones in most mammaliantherianfemales.
Estrous cycles start after sexual maturity in females and are interrupted by an estrous phases or by pregnancies. Some animals may display bloody vaginal discharge, often mistaken for menstruation.
There are, however, subtle signs to which heterosexual human males may favorably respond, including changes in a woman's scent and facial appearance. Animals with estrous cycles often have unmistakable outward displays of receptivity, ranging from engorged and colorful genitals to behavioral changes like mating calls.
Estrus is derived via Latin estrus (' frenzy ', gadfly '), from Greek bistros (literally 'gadfly', more figuratively 'frenzy', 'madness', among other meanings like 'breeze'). Specifically, this refers to the gadfly in Ancient Greek mythology that Hera sent to torment Io, who had been won in her heifer form by Zeus.
Plato also used it to refer to an irrational drive and to describe the soul “driven and drawn by the gadfly of desire”. Somewhat more closely aligned to current meaning and usage of estrus, Herodotus (Histories, ch.
Typically, this phase can last as little as one day or as long as three weeks, depending on the species. Under the influence of estrogen, the lining of the uterus (endometrium) starts to develop.
The female is not yet sexually receptive; the old corpus lute um degenerates; the uterus and the vagina distend and fill with fluid, become contractile and secrete a sanguinary fluid; the vaginal epithelium proliferates and the vaginal cytology shows many non-cornified nucleated epithelial cells. Estrus or estrus refers to the phase when the female is sexually receptive (“ in heat “).
Under regulation by gonadotropin hormones, ovarian follicles mature and estrogen secretions exert their biggest influence. The female then exhibits sexually receptive behavior, a situation that may be signaled by visible physiologic changes.
Especially among quadrupeds, a signal trait of estrus is the Lords reflex, in which the animal spontaneously elevates her hindquarters. This phase is characterized by the activity of the corpus lute um, which produces progesterone.
The signs of estrogen stimulation subside and the corpus lute um starts to form. In the absence of pregnancy the distrust phase (also termed pseudo-pregnancy) terminates with the regression of the corpus lute um.
Other spellings include metoestrus, mete strum, sequestrum, disastrous, die strum, and rostrum. An estrus refers to the phase when the sexual cycle rests.
This is typically a seasonal event and controlled by light exposure through the pineal gland that releases melatonin. Melatonin is thought to act by regulating the hypothalami pulse activity of the gonadotropin-releasing hormone.
An estrus is induced by time of year, pregnancy, lactation, significant illness, chronic energy deficit, and possibly age. Chronic exposure to anabolic steroids may also induce a persistent an estrus due to negative feedback on the hypothalamus/pituitary/gonadal axis.
After completion (or abortion) of a pregnancy, some species have postpartum estrus, which is ovulation and corpus lute um production that occurs immediately following the birth of the young. For example, the mouse has a fertile postpartum estrus that occurs 14 to 24 hours following parturition.
Even within species significant variability can be observed, thus cats may undergo an estrous cycle of 3 to 7 weeks. Domestication can affect estrous cycles due to changes in the environment.
Some species, such as cats, cows and domestic pigs, are poly estrous, meaning that they can go into heat several times per year. Short- day breeders, such as sheep, goats, deer and elk are sexually active in fall or winter.
A few mammalian species, such as rabbits and cats, do not have an estrous cycle, instead being induced to ovulate by the act of mating and are able to conceive at almost any arbitrary moment. Generally speaking, the timing of estrus is coordinated with seasonal availability of food and other circumstances such as migration, predation etc., the goal being to maximize the offspring's chances of survival.
Some species are able to modify their astral timing in response to external conditions. However, various incidents of spontaneous ovulation have been documented in the domestic cat and various non-domestic species.
Without ovulation, she may enter interestrus, which is the combined stages of distrust and an estrus, before reentering estrus. With the induction of ovulation, the female becomes pregnant or undergoes a non-pregnant luteal phase, also known as pseudo pregnancy.
Cats are poly estrous but experience a seasonal an estrus in autumn and late winter. Pro estrus bleeding in dogs is common and is believed to be caused by diaeresis of red blood cells from the blood vessels due to the increase of the estradiol-17 hormone.
Horses mate in spring and summer; autumn is a transition time, and an estrus occurs during winter. A feature of the fertility cycle of horses and other large herd animals is that it is usually affected by the seasons.
The number of hours daily that light enters the eye of the animal affects the brain, which governs the release of certain precursors and hormones. As it happens, this benefits these animals in that, given a gestation period of about eleven months, it prevents them from having young when the cold of winter would make their survival risky.
Although they ovulate spontaneously, they do not develop a fully functioning corpus lute um unless they receive coital stimulation. A set of follicles starts to develop near the end of pro estrus and grows at a nearly constant rate until the beginning of the subsequent estrus when the growth rates accelerate eightfold.
During this day, the corpora lute grow to a maximal volume, achieved within 24 hours of ovulation. The plasma progesterone concentration was 1.68±0.37, 4.29±0.22, 3.89±0.33, and 0.34±0.14 NG/ml while mean vascular density (mean number of vessels/10 microscopic fields at 400x) in corpus lute um was 6.33±0.99, 18.00±0.86, 11.50±0.76, and 2.83±0.60 during the met estrus, early distrust, late distrust and pro estrus/estrus, respectively.
^ Kuukasjärvi, Tempo; Eriksson, C. J. Peter; Korea, ESA; Mapped, Tapir; Mission, Kari; Rental, Markus J. “Attractiveness of women's body odors over the menstrual cycle: the role of oral contraceptives and receiver sex”.
^ Roberts, S. C.; Alice, J.; Fleur, J.; Hruskova, M.; Little, A. C.; Jones, B. C.; Percent, D. I.; Metric, M. (7 August 2004). “Female facial attractiveness increases during the fertile phase of the menstrual cycle”.
Copyright 2006 ^ Pelican et al., 2006 ^ Spindler and Wild, 1999 ^ Walter, I.; Alabama, G.; Simon, D.; Heinrich, M. (February 2011). “Gonadotrophin-induced hormone secretion and structural changes in the ovary during the nonpregnant reproductive cycle”.
“Morphometric and anxiogenic changes in the corpus lute um of nili-ravi buffalo (Bubbles bubbles) during estrous cycle”. In the Southern Hemisphere, spring begins in October and fall arrives in February.
Researchers from Massey University in New Zealand used this separation in time of birth to design a study to examine the effects of season, age, and body weight on the onset of puberty in Thoroughbred horses raised in the Southern Hemisphere. Foals were examined daily, and body weight and blood samples were taken every two weeks.
An increase in testosterone greater than two times the standard deviation above baseline was diagnostic for puberty. This suggests there is a weight threshold of about 617 pounds (280 kilograms) for the onset of puberty to occur.
Therefore, the researchers concluded that both season of the year and body weight are critical for foals to achieve puberty. Autumn-born foals in the Southern Hemisphere, therefore, reach puberty at a younger age and a lighter body weight.
Created By: Chelsea Rorschach, Dana John, Kayla Pick, and Darcy O'Brien. Numbering a little over 1 billion, domestic sheep are the most numerous species in their genus (Athenian).
Sheep are most likely descendants from the wild mouflon of Europe and Asia and where one of the earliest animals to be domesticated for agricultural purposes. The domestic sheep is a multi-purpose animal, and the more than 200 breeds to serve these diverse purposes (Athenian).
Wild species have a breeding season that is initiated at a time when the environment will allow for the best survival of the young. Domestication has stopped seasonal breeding in some species: Cattle & Swine.
The time when a ewe will reach puberty depends on many factors including, the breed, body size, nutrition, season of birth etc. Due to their genetics and biological clock ewes will usually show puberty their first fall (Athenian).
This can have a large effect on the age variation of when they have their first estrus, since ewe lambs born in January instead of April would be three months older. Estrous cycles are commonly affected by the seasons in different species, vine is one of those which are very receptive.
It is due to the number of hours daily that light enters the eye of the animal. The cycles of estrous will continue every 16 to 17 days until the ewe is bred or returns to an estrus (Athenian).
Estrus lasts approximately 24 to 36 hours, and is where the ewe will stand to be mounted by the male. Animals that are seasonally an estrus is believed to have come from preventing the ewes from conceiving during a time when the survival rate of the embryo would not be high.
The embryo survival rate is reduced a lot by the temperature and the humidity in the environment (Pathways to Pregnancy and Parturition). In the mid and high latitudes of temperate regions, breeding begins in autumn, when the daylight becomes shorter.
(Go´mez-Brunet et al., 2008) The effects of photo period are caused by the stimulation of the retina by the amount of light present. The Mechanism behind the effects of photo period involves the secretion of melatonin, which stimulates GRH release.
When light is abundant, an excitatory pathway is active inhibiting melatonin release. Melatonin is a modified amino acid secreted by the pineal gland that communicates information about environmental lighting to various parts of the body.
Light that is exposed to the retina is first relayed to the suprachiasmatic nucleus of the hypothalamus, an area of the brain well known for coordinating biological clock signals Fibers from the hypothalamus descend to the spinal cord and project back to the pineal gland. Seasonal changes in day length have profound effects on reproduction in sheep, and melatonin is a key player in controlling such events.
Photo period is the most important cue to allow animals to determine what season it is. The pineal gland is able to measure day length and adjust secretion of melatonin accordingly.
In species with longer gestation times, such as sheep, the anticipation of spring must occur much earlier, and seasonal changes in the fall act as a stimulus. Conversely, after the winter solstice, the photo period increases and the duration of the melatonin signal falls(Essential Reproduction, 2007).
One practical application of melatonin’s role in controlling seasonal reproduction is found in its use to artificially manipulate cycles in sheep that normally breed only once per year, but can be induced to have two breeding seasons by treatment with melatonin(Bowen). Potential genetic improvements are possible by selection to reduce seasonal breeding.
These breeds will increase fertility but will reduce lamb growth rates and carcass value (Potter). Potter, D. R, “Opportunities to Reduce Seasonality of Breeding in Sheep by Selection”.
Utilization of artificial light to advance the breeding season is common practice within the Thoroughbred industry. The artificially extended day length acts to inhibit the hormone melatonin and fools the mare’s reproductive system into activating earlier in the year.
In 2011, we investigated the threshold level of blue light required to inhibit circulating concentrations of melatonin in the horse and found it to be within the range of 10-50 lux (the standard international unit of illuminance). Of greater significance was that the level of melatonin inhibition achieved did not differ when light was administered to one or both eyes.
At two-week intervals until mid-February, all mares received rectal ultrasound examinations and blood was collected for progesterone hormone analysis. Studies are underway to investigate additional applications of mobile blue light therapy in horses for the purposes of increasing foal birth weights in early foals and mitigating the effects of jet lag in performance horses.
This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. There are approximately 42 ponds on the Maryland portion of Assateague Island, and during a rainy period there are countless ephemeral pools.
During the summer, well-meaning visitors often turn on a spigot to give the horses water. The coat starts to grow long before the cold days of winter.
As the days began to shorten and the retinas receive fewer hours of sunlight each day, the brain is stimulated to release extra melatonin, a hormone that prompts the hair follicles to produce more hair. Even more incredible…the long outer hairs form channels that help repel water.
Whenever severe weather threatens Assateague Island National Seashore, we inevitably get asked “how will the horses survive the storm?”. Generally, the Assateague horses retreat from the developed areas of the park to spend the cooler months in the Bayside marshes where their preferred forage, Starting alterniflora (Salt marsh Cord grass), grows abundantly.
During extreme weather conditions they find shelter from high winds and storms by temporarily retreating from the marshes to forested or densely vegetated areas and turning their tails to the wind. People often ask if there is something wrong with the foals when they have mostly black hair around their eyes, wondering if they have a skin condition based on their appearance.
Maternal lineage is just one thing you can discover by looking closely at the horses alphanumeric code. A harem band consists of a dominant stallion and his mares and immature offspring.
At that point the alphabet was started over with a dash in front of the letter, resulting in -A for foals born in 2002. N6 was present in the herd during the initial 1975 survey and so does not have a birth year letter.
Psychosis thrives in stagnant pools of fresh water and is a naturally occurring pathogen. Of note is that many of the freshwater ponds in MD often get surrounded by salt water, thereby potentially minimizing the overall risk of psychosis.
There are approximately 42 ponds on the Maryland portion of Assateague Island, and during a rainy period there are countless ephemeral pools. That plus the smaller size of the MD herd both attribute to a much less hospitable environment for swamp cancer.
The Chincoteague ponies are kept in grazing compartments on the Virginia portion of Assateague and there is a physical fence at the state line to prevent the two herds from coming in contact. If you have questions about this or other items, we encourage you to reach out directly to the Assateague Island National Seashore team.
Light is the controlling factor in causing mares to come into season in the early spring. Mares carry their young (called foals) for approximately 11 months from conception to birth (average range is 320 – 370 days).
Horses will curl their upper lip and press it to the back of their nose, which is called the Lehman response (almost as if they are laughing). A stallion will make this face when he examines a mares' urine to find out if she is in heat or season.
The Lehman response increases the flow of air through the nostrils, which brings the scent openings behind the incisors on the upper palette to the vomeronasal organ. There is even some signage at the State Park that says “ponies.” That being said, the National Seashore refers to them as horses.
Many breeds of horses and ponies have been turned out on the island for hundreds of years, and over time, many were left to go feral. The smaller type we see now is what has adapted best to the conditions on the island and to the available forage, surviving and thriving over the years.
If you see someone breaking the law or doing things that prevent these horses from remaining wild, please contact the ranger station at 410.641.1441. Keep in mind that these numbers are staffed intermittently throughout the day ; there is no guarantee that a call will be answered due to a variety of factors.
Each November, Assateague Island National Seashore biologists conduct pregnancy tests on the mares among the population of wild horses on the barrier island in an attempt to predict how many, if any, new foals are expected to join the herd in the coming year. Samples are collected, frozen and sent to a lab to be analyzed to determine if any of the mares will be expecting next spring.
For example, in 2019, SCSI Sole (N2BHS-M) gave birth to N2BHS-MR (Senses Bay Breeze or “Breezy”) in January and it was a complete surprise (albeit, her tummy was very, very round).