What Triggers A Seasonally Polyestrous Animal To Begin Having Estrous Cycles?
Estrous Bicycle
The estrous cycle is defined as the period from 1 ovulation to a subsequent ovulation, with each ovulation beingness accompanied past signs of heat and plasma progesterone concentrations less than 1 ng/ml.
From: Manual of Equine Reproduction (2d Edition) , 2003
Volume ane
Mark A. Crowe , in Encyclopedia of Dairy Sciences (Third Edition), 2022
Introduction
The estrous bike represents the cyclical pattern of ovarian activity that facilitates female animals to get from a menstruum of reproductive receptivity to non-receptivity ultimately allowing the establishment of pregnancy post-obit mating. The normal duration of an estrous wheel in cattle is 18–24 days. The cycle consists of two detached phases: the luteal phase (14–18 days; met-oestrus and di-estrus) and the follicular stage (4–six days; pro-oestrus and estrus). The luteal phase is the menstruation following ovulation when the corpus luteum (CL) is formed, while the follicular phase is the period following the demise of the corpus luteum (luteolysis) until ovulation. During the follicular phase final maturation and ovulation of the ovulatory follicle occurs which leads to the release of an oocyte (the female person gamete) into the oviduct assuasive the potential for fertilization.
Commencement of regular estrous cycles in cattle occurs at the time of puberty. Heifers achieve puberty between half dozen and 24 months of age typically at 50% of mature body weight. At the onset of puberty, the showtime estrous bike tends to be of a curt elapsing (three–12 days) and follows a silent ovulation (i.e., is not associated with expression of behavioral rut). Estrous cycles cease during pregnancy due to the prolonged presence of elevated progesterone from the CL, and placenta (in later pregnancy: ∼twenty% from approximately twenty-four hours 200). Post-obit parturition estrous cycles recommence afterward a variable period of anestrus and anovulation. Like to the transition from pre-puberty to puberty, the resumption of ovarian cycles post-partum is normally associated with a silent ovulation followed by a short bicycle.
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Reproductive management of sheep and goats
Reid Redden , Jacob Due west. Thorne , in Creature Agronomics, 2020
Length of flavour
The estrous wheel of ewes lasts 17 days and 21 days for the doe. It is common to leave the males in a minimum of 34–42 days to ensure that each female has had 2 periods of estrus. Two months is a common breeding menses, every bit ewes that accept not conceived inside 2 estrous cycles may exist genetically predisposed to lower fertility. Additionally, a gimmicky group that varies in age by greater than 60 days will be challenging to manage and market as there will be a meaning size differences for the first several months of the lamb's life. Yet, it is not uncommon for operations to leave males with the females until information technology is user-friendly to remove the males and separate them into some other pen or pasture, which could be 90 days or more than.
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Volume one
H. Wahid , Y. Rosnina , in Encyclopedia of Dairy Sciences (Third Edition), 2016
Estrous Cycle
The estrous cycle length is about 21 days with estrus lasting 12–30 h and ovulation occurring spontaneously afterward the cease of rut (Table two). However, factors such as climate, temperature, photoperiod, and diet have been shown to influence the length of estrous wheel and also the extent of estrus manifestation.
Table 2. Reproductive parameters of buffalo and cattle
| Parameter | River buffalo | Cattle |
|---|---|---|
| Sexual season | Polyestrus | Polyestrus |
| Age at puberty (months) | 15–36 | 10–24 |
| Estrous cycle | ||
| Length (days) | eighteen–22 | 14–29 |
| Estrus (h) | 12–xxx | 17–24 |
| Gestation length (days) | 305–320 | 278–293 |
| Age at beginning calving (months) | 36–56 | 24–36 |
| Calving intervals (months) | xv–21 | 12–fourteen |
| Ejaculate volume (ml) | three–6 | 4–10 |
| Sperm concentration (106ml−1) | 300–1500 | 800–2000 |
| First-service formulation rate (frozen semen) (%) | 10–50 | 45–75 |
Reproduced from Jainudeen, K.R., Hafez, E.S.E., 2000. Cattle and buffalo. In: Hafez, B., Hafez, E.S.East., (Eds.), Reproduction in Farm Animals, seventh ed. Lippincott Williams & Wilkins, Baltimore, pp. 159–171.
Different cattle, overt signs of estrus are not pronounced. In most smallholder farms, a male buffalo may not exist available for oestrus detection. Homosexual behavior or continuing to exist mounted by some other female person is observed only occasionally in the buffalo. As a result, nearly inseminations are based on less-reliable signs such equally articulate vulval discharge, restlessness, frequent urination, vocalism, and reduction in milk. Estrus commences toward late evening with peak sexual activity at night.
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The Endocrinology of the Mammalian Ovary
David O. Norris , Kristin H. Lopez , in Hormones and Reproduction of Vertebrates: Mammals, 2011
v.ii The Ewe
Sheep estrous cycles occur seasonally, and the elapsing of one complete ovarian wheel is sixteen–17 days ( Figure iv.7). A ewe may render to proestrus at to the lowest degree once if fertilization does not occur. During the follicular stage (= proestrus), in that location is a marked increase in estrogen and androgen levels. A surge of plasma LH occurs most 12 hours later the summit E2 level, although AND may be responsible for inducing estrous behavior, acting as a substrate for E2 synthesis in the encephalon. Ovulation of usually a unmarried follicle occurs well-nigh 24 hours subsequently the LH surge, and a corpus luteum soon forms under the influence of LH. Low levels of LH following ovulation and an E2-induced surge of PRL stimulate the corpus luteum to secrete P4. The uterine endometrium synthesizes a luteolytic prostaglandin (PGF2α) nether the influence of Pfour that causes degeneration of the corpus luteum and resumption of proestrus if fertilization does not occur.
Figure 4.7. Hormonal levels during the ovarian cycle of the ewe. LH, luteinizing hormone.
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Reproduction, Events and Management: Estrous Cycles: Characteristics
Mark A. Crowe , in Reference Module in Food Scientific discipline, 2016
Abstruse
The estrous bicycle in cattle lasts for xviii–24 days. It consists of a luteal phase (14–18 days) and a follicular phase (4–half-dozen days). During the cycle, there are more often than not ii (dairy cows) or three (heifers and beef cows) waves of ovarian follicle growth. Each wave of follicle growth consists of a period of emergence of a cohort of follicles, selection of a dominant follicle (DF), and either atresia or ovulation of the DF. These waves of follicle growth occur throughout the entire cycle, with only the DF of the final moving ridge coinciding with the follicular phase that undergoes final maturation and ovulation. Ovarian role (follicle growth, ovulation, luteinization, and luteolysis) are regulated by the endocrine hormones of the hypothalamus (gonadotropin-releasing hormone), anterior pituitary (follicle-stimulating hormone and luteinizing hormone), ovaries (progesterone, estradiol, and inhibins), and the uterus (prostaglandin F2α).
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Dystocia and the Mammary Gland
Natali Krekeler , ... Cathy Beck , in Comparative Veterinarian Anatomy, 2022
Canine estrous cycle
The canine estrous cycle is unique in that information technology lacks the luteolytic mechanism which, in other domestic animals and humans, allows the nonpregnant female person to undergo some other estrus or ovulation within 1–2 weeks after luteolysis.
Luteolysis is the procedure by which the corpus luteum (CL) is lysed ("declines" or wanes) at the stop of diestrus, assuasive the evolution of another ovarian follicle. The CL is the ovarian tissue that replaces the follicle after the release of the ovum during ovulation. The CL is responsible for progesterone product that hormonally defines diestrus or the interestrous phase of the estrous wheel.
Canids have an average interestrous interval of between vii (domestic dogs) and 12 months (wild canids such every bit wolves and coyotes). They are therefore divers as "monoestrous" animals, whereas cats are polyestrous animals (described afterward). Because the interestrous interval in domestic dogs is almost vii months, most bitches are normally in estrus approximately twice a yr, unless neutered.
The estrous cycle in both monoestrous and polyestrous animals includes 4 distinct phases: proestrus, estrus, diestrus, and anestrus.
For each of the phases of the estrous cycle, the noun (e.g., estrus) ends with -united states of america, whereas the adjective— east.g., estrous cycle—ends with -ous or with -ual, e.chiliad., estrual phase.
Proestrus in dogs is characterized externally by swelling of the vulva and sanguineous (L. sanguinolentus blood‑tinged) vulvar discharge. During this phase, ovarian follicles enlarge and serum estrogen levels ascent (produced by ovaries), reaching their peak in late proestrus. Proestrus lasts an average of 9 days, although information technology ranges from 3 days to 3 weeks.
Pseudopregnancy
Pseudopregnancy, also known as "pseudocyesis" (Gr. pseudēs- false + Gr. kyēsis pregnancy), is a physiologically normal stage for a nonpregnant bitch in diestrus. It is ordinarily "silent," although immature bitches in particular may show typical physiological and behavioral signs of the periparturient catamenia, such as mammary evolution, restlessness, nesting behavior, and caring for her "immature" in the class of stuffed toys, half dozen–eight weeks afterwards estrus. No treatment is necessary.
Pseudopregnancy occurs in queens following ovulation without fertilization. Pseudopregnant queens usually show no signs other than a longer-than-normal interestrous interval.
The beginning of oestrus is marked externally past the abeyance of the bloody vulvar belch seen during proestrus and transition to either clear or no belch and behaviorally by the bowwow'due south receptivity to mating (sometimes referred to every bit "standing estrus"). During estrus, the bowwow allows the male to mount, whereas during proestrus she is increasingly bonny to male dogs merely normally does not permit mating. The outset of oestrus is marked hormonally by a rapid increase in serum luteinizing hormone (LH) produced by the pituitary gland; ovulation follows this "LH surge" by a few days.
Oocytes are ovulated in a relatively immature state and demand to undergo further maturation in the uterine tube for 48–72
hours earlier fertilization is possible. Given the hormonal requirements for ovulation, the need for oocyte maturation, and the sequential release of multiple ova in this litter-bearing species, estrus in bitches typically lasts about 8
days.
The LH surge is defined as the twenty-four hours when serum progesterone levels significantly ascension (unremarkably
>
ii
ng/mL). Serum progesterone levels rise slowly during proestrus and then sharply increase at the time of the LH surge; they keep to increase well into diestrus.
Diestrus follows estrus and lasts for approximately 58 days in pregnant bitches, at which point parturition begins.
In nonpregnant bitches, diestrus lasts threescore–xc
days.
The precise mating dates are normally known by breeders, but because the point of conception is hard to make up one's mind accurately based solely on mating dates, the duration of pregnancy in bitches varies co-ordinate to the definition used. Published figures are 56–58
days from the kickoff day of diestrus (terminate of heat), 64–66
days from the LH surge (offset of estrus), and 58–72
days from the beginning mating.
Post-obit diestrus, all bitches—post-partum and nonpregnant—enter anestrus, a period of relative ovarian quiescence, earlier the next proestrus phase commences several months later.
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Volume 1
H.A. Garverick , One thousand.C. Lucy , in Encyclopedia of Dairy Sciences (Third Edition), 2011
Ovarian Follicular Dynamics during Estrous Cycles in Cattle
The characteristics of estrous cycles in cattle have been reviewed. However, a brief summary here is pertinent to the give-and-take of postpartum ovarian activity. The dynamic nature of ovarian follicular growth in cattle was unknown for a considerable menstruation of time. A typical estrous cycle in cattle has ii or three waves of follicular growth. The initiation of each follicular moving ridge (recruitment) is characterized past the growth of a cohort (usually ii–6) of small follicles from approximately 2–four to ≥five mm in bore. The initiation of each moving ridge of follicular growth is preceded past a transient increase in circulating follicle-stimulating hormone (FSH). The recruited follicles go along their growth to approximately 7–8 mm in diameter. At this time, 1 follicle is typically selected (selection) to keep to grow to ovulatory size (fourteen–18 mm in bore; ascendant follicle). The remaining subordinate follicles undergo atresia. If the cow is in the luteal phase of the estrous cycle, the ascendant follicle maintains its maximum size for 3–half dozen days, simply undergoes atresia and some other wave of follicular growth is initiated. The dominant follicle in the 2d or 3rd wave will ovulate if luteal regression occurs during the growing phase.
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Reproductive physiology of swine
Rodney D. Geisert , ... Ashley E. Meyer , in Animal Agriculture, 2020
Estrous cycle
The length of estrous cycles for gilts (females that accept never been pregnant) and sows (mature females that have given birth to at to the lowest degree i litter) is approximately 21 days (range eighteen–22 days). 18 Endocrine changes during the estrous bicycle are presented in Fig. 15.3. There are four stages of the estrous wheel: proestrus, oestrus, metestrus, and diestrus. Corpora lutea develop from the cells of the ovulated follicle and produce progesterone; a steroid hormone that maintains pregnancy. During proestrus, circulating concentrations of progesterone decline rapidly. The decrease in progesterone indicates regression of the CL (loss of function). Regression of the CL is acquired by the episodic release of prostaglandin F2α (PGF2α) from the uterine endometrium. 19 Following regression of the CL and concomitant pass up in circulating concentrations of progesterone in that location is an increase in the frequency of LH pulses that initiates a wave of ovarian follicular development. The development of large ovarian follicles increases the circulating concentrations of the steroid hormone estradiol and the protein hormone inhibin. The increases in both estradiol and inhibin crusade a decrease in circulating FSH when the pig approaches estrus and this decrease in FSH ends the process of follicular recruitment. High circulating concentrations of estradiol bring pigs into heat; the next phase of the estrous cycle. Ovarian follicles are fully mature at the initiation of estrus and are approximately 8 mm in diameter with ten–15 follicles on each ovary. 20 Pigs display lordosis behavior or "continuing heat" when they are in estrus significant that they will stand still with cock ears when mounted by the boar or following the awarding of back pressure level by a person. Boar exposure during estrus strengthens the lordosis response to the dorsum force per unit area test. 21 Other signs of estrus include swelling and reddening of the vulva, vocalization (estrual grunts), mounting other female pigs and boar-seeking beliefs. In response to estradiol, the neck becomes rigid and the uterine horns are tightly coiled.
Fig. 15.iii. Ovarian hormonal changes during the estrous bike of the pig.
Estrus tends to exist shorter in gilts (24–48 h) compared with mature sows (24–96 h). Circulating estradiol reaches elevation concentrations near the onset of rut and triggers the LH surge; a massive release of from the anterior pituitary and into the apportionment. eighteen The LH surge lasts for about 10 h and may occur before, during or after the initiation of estrus. Ovulation occurs during a ane–3 h period approximately 30–35 h after the LH surge and when the estrus period is lxx% complete.
Following ovulation, the granulosa cells and theca cells of the follicle wall become luteinized and course CL. Initially, claret fills the lumen of the ruptured follicle to class the corpus hemmorrhagicum (CH) and the CH is somewhen replaced by the CL. The metestrus phase of the estrous cycle follows as a vascular bed is established and luteal cells complete their differentiation and increase their capacity to synthesize progesterone. When fully mature, the CL are 8–11 mm in bore. The presence of multiple CL on each ovary results in a steady increase in circulating concentrations of progesterone. Diestrus, the period of maximal circulating progesterone follows metestrus and continues for approximately ii weeks during the estrous bicycle. Concentrations of progesterone greater than thirty–forty ng/mL are achieved during diestrus. The episodic release of PGF2α from the uterine endometrium and the regression of the CL defines the finish of diestrus and showtime of the proestrus phase which leads back into estrus.
Synchronization of estrus. A grouping of gilts will wheel at random and come into oestrus on any given day. Detection of estrus for breeding purposes, therefore, must be done daily. Synchronization of heat is washed to reduce the time and labor associated with estrous detection and to facilitate the apply of AI. 17 Rut in gilts tin can exist synchronized past feeding altrenogest (a progestin) marketed under the merchandise proper noun Matrix® at a dose of fifteen mg/day for 14 days. Feeding atrenogest suppresses follicular development in a grouping of gilts. A synchronous moving ridge of follicular growth occurs within the group later feeding is stopped. Gilts typically express estrus 4–9 days afterward the last day of altrenogest feeding.
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Physiology and pregnancy of beef cattle
Ky G. Pohler , ... Michael F. Smith , in Animal Agronomics, 2020
Regulation of the estrous cycle
In cattle, the estrous cycle normally ranges from 17 to 24 days and the duration of estrus is by and large 10–18 h; still, considerable variation exists amidst individual animals (range <8 to >30 h). 12 The preovulatory gonadotropin surge occurs around the onset of estrus and ovulation occurs approximately 28–thirty h afterwards. Unlike horses, pigs, and sheep, ovulation in cattle occurs a number of hours following the end of estrus. The primary sign of estrus in cattle is standing to be mounted and secondary signs of estrus include frequent mounting, watery mucus from the vulva, vocalization, and restlessness.
The estrous cycle is divided into three stages (follicular phase, oestrus, and luteal stage) and is regulated by hormones secreted by the hypothalamus (GnRH), anterior pituitary gland (follicle stimulating hormone [FSH] and LH), ovary (estradiol and progesterone), and uterus (prostaglandin F2α [PGF2α]). The preceding hormones serve as chemical messengers that circulate in the blood to effect change in specific target tissues that contain receptors that are hormone specific and regulate the preceding phases of the estrous cycle. The combination of hormone secretion and metabolism (e.g., liver, kidneys, and lungs) maintain an advisable endocrine balance during the follicular phase, estrus, and luteal phase of the estrous wheel. An agreement of the hormonal regulation of preovulatory follicular evolution and luteal lifespan resulted in the evolution of methods of synchronizing estrus and ovulation in cattle. 13 For a list of hormones, their biological functions, their role in estrous synchronization/superovulation, and product names see Table 3.i.
Tabular array 3.1. Reproductive hormones, the endocrine gland from which they originate, their functions during the estrous cycle, roles in estrous synchronization, product name, dosages, and road of administration.
| Hormone | Endocrine gland | Function of hormone | Biological action in estrous sync. | Product name | Dosage | Road of administration |
|---|---|---|---|---|---|---|
| Progesterone | Corpus luteum | Inhibit estrus | Inhibit heat | Melengestrol Acetate (MGA®) | 0.five mg/hd/solar day | Feed |
| Inhibit ovulation | Inhibit ovulation | |||||
| Prepares animal for pregnancy | Induce cyclicity | EAZI-Brood CIDR® | 1 CIDR per animate being (one.38 g) | Vaginal insert | ||
| Maintenance of pregnancy | Dominant follicle turnover | |||||
| Prostaglandin F2α | Uterus | Induce luteal regression | Induce premature luteal regression | Lutalyse® | 5 mL | im inject |
| Lutalyse Howdy-Con® | 2 mL | im or sq inject | ||||
| Estrumate® | 2 mL | im inject | ||||
| estroPLAN® | 2 mL | im inject | ||||
| Gonadotropin releasing hormone (GnRH) | Hypothalamus | Controls secretion of LH | Synchronize follicle wave | Cystorelin® | 2 mL | im inject |
| Factryl® | 2 mL | im inject | ||||
| Induces gonadotropin surge | Induce ovulation | Fertagyl® | 2 mL | im inject | ||
| GONAbreed | 1 mL | im inject | ||||
| Follicle Stimulating Hormone (FSH) | Anterior Pituitary Gland | Initiation of a follicular wave | Superovulation | Follitropin® | Depends on awarding | im inject |
| Luteinizing Hormone (LH) | Anterior Pituitary Gland | Stimulated by GnRH | Synchronize follicular moving ridge | Due north/A | N/A | N/A |
| Induction of ovulation | ||||||
| Oocyte maturation | Induction of ovulation | |||||
| Luteal tissue formation | ||||||
| Estradiol | Ovarian follicle | Estrous behavior | Ascendant follicle turnover | North/A | N/A | N/A |
| Induction of gonadotropin surge | ||||||
| Sperm transport | Estrous behavior |
N/A, not applicable.
A preovulatory follicle and the subsequently formed corpus luteum are the 2 primary ovarian structures that regulate the estrous bicycle through secretion of estradiol and progesterone, respectively. Changes in a preovulatory follicle and corpus luteum, patterns of secretion of LH, estradiol and progesterone, and changes in ovarian blood period during the ruminant estrous wheel are depicted in Fig. iii.i.
Fig. 3.i. Changes in ovarian structures (preovulatory follicle and corpus luteum), hormones (luteinizing hormone, estradiol, and progesterone) and ovarian blood flow (ovary containing [luteal ovary] or not containing [nonluteal ovary] a corpus luteum) during the three phases of the estrous bike (follicular, estrus, and luteal stage).
Modified from Garverick HA, Smith MF. Female reproductive physiology and endocrinology of cattle. In: Braun WF, Youngquist RS, eds. The Veterinary Clinics of North America, Food Fauna Practice. Philadelphia: W.B. Saunders Co; 1995:223–247.Follicular phase . The follicular phase (proestrus) begins with the initiation of corpus luteum regression (luteolysis) and ends with the onset of heat. Luteolysis is accompanied by a rapid decrease in circulating progesterone resulting in a decrease in the negative feedback on hypothalamic GnRH secretion and pituitary LH secretion. As circulating concentrations of progesterone subtract, LH pulse frequency increases followed by a rapid increase in follicular estradiol secretion. The production of follicular estradiol results from the coordinated actions of LH and FSH on theca and granulosa cells, respectively. 14,xv The follicle wall consists of 2 singled-out prison cell layers (granulosa and theca cells) that are separated by a basement membrane. Granulosa cells are located in the compartment with the oocyte; whereas, theca cells surroundings the granulosa cells and are in close association with a wreath of capillaries. Theca cells have membrane receptors that bind LH resulting in synthesis of androgens that subsequently diffuse through the basement membrane into granulosa cells. Following FSH bounden to its membrane receptors on granulosa cells the enzyme aromatase increases and converts androgens to estradiol.
Estrous phase. Increased circulating concentrations of estradiol following luteolysis initiate estrous behavior, increase uterine contractions (facilitate sperm transport), and induce the preovulatory gonadotropin surge. The preovulatory gonadotropin surge coordinates the post-obit events that are disquisitional for the establishment of pregnancy: resumption of meiosis within the oocyte, follicular rupture, and luteinization of follicular granulosa and theca cells. LH is considered to be the principal gonadotropin that controls the preceding events. The end of the estrous phase of the cycle is marked past follicular rupture, which is the culmination of a complex cascade of events leading to the activation of proteolytic enzymes that assimilate the follicular wall and allows the egg (oocyte) to be released for fertilization. In mammals, the cellular mechanisms culminating in follicular rupture are similar to inflammation. sixteen
Luteal stage . The luteal phase spans the fourth dimension of corpus luteum formation and maintenance, which begins with ovulation and ends with luteolysis (Fig. three.1). Progesterone is the primary secretory product of the corpus luteum and luteal lifespan is regulated past secretions of the anterior pituitary, uterus, ovary, and trophecoderm of the blastocyst. 17 The regulation of progesterone secretion is likely controlled by a residue of luteotropic (stimulate progesterone) and luteolytic (inhibit progesterone) stimuli, given that both types of stimuli are secreted concurrently during the estrous cycle. In ruminants, LH is considered to be the main luteotropic hormone and concentration of luteal LH receptors is positively correlated with changes in progesterone secretion and luteal growth. 18 Corpora lutea receive the majority of the ovarian blood flow and blood catamenia to the ovary containing the corpus luteum and progesterone secretion are highly correlated 17 (Fig. 3.ane). Progesterone has a primal role in female person reproductive physiology every bit it initiates cyclicity in anestrous females, determines estrous cycle length in cycling females, and is required for the maintenance of pregnancy.
In cattle, PGF2α is the uterine luteolysin and is commonly used to synchronize oestrus in cattle. In the absence of a developing blastocyst/conceptus (embryo and its actress-embryonic membranes), uterine release of PGF2α increases during the late luteal stage and PGF2α is secreted as pulses into the uterine veins on days 17–20 following estrus 19 (twenty-four hour period 0 = estrus). PGF2α is transported from the utero-ovarian vein into the ovarian artery via a counter-current transfer mechanism 20 and is transported to the corpus luteum. PGF2α may accept both a straight and an indirect effect on a ruminant corpus luteum to cause luteolysis. The mechanism past which the bovine blastocyst prevents luteolysis is discussed later.
Regulation of follicular waves. The bovine estrous cycle consists of two to three follicular waves and each wave begins with the recruitment of a cohort of antral follicles from a pool of growing small follicles. 21 Ane follicle is selected from this cohort for continued growth and becomes dominant. The remaining follicles in the accomplice die by a process called atresia. During a nonovulatory follicular wave, the dominant follicle eventually becomes atretic and a new follicular wave is initiated. A viable dominant follicle nowadays at luteolysis will generally become the ovulatory follicle. The estrous wheel length of cows that have iii follicular waves is generally longer (20–24 days) compared to cows with two follicular waves (17–20 days). In cattle, follicular waves can be detected during most reproductive states including the prepubertal period, estrous cycle, gestation, and postpartum anestrous period. 22 The merely exception to the continuous growth and evolution of follicular waves in cattle is during the last 21 days of gestation. During this time follicles greater than 6 mm in diameter have not been detected. 23 Following parturition, follicular waves resumed following a ascension in circulating concentrations of FSH, 24 and the first dominant follicle appears betwixt days 7 and 15 postpartum in both beef and dairy cows. 25,26 Inducing ovulation or atresia of a dominant follicle in a group of females will result in synchronization of the subsequent follicular wave. This approach has been used in the development of fixed-time artificial insemination protocols in cattle.
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Advances in Animal Biotechnology
L.B. Schook , ... K.Thousand. Schachtschneider , in Encyclopedia of Agriculture and Food Systems, 2014
Insemination procedure
The female person's estrous cycle must exist continuously monitored to detect when the animal reaches her rut phase and thus is ready for the insemination procedure. This estrus phase is also referred to as the 'heat stage' of the female person because she is sexually receptive to males. Many behavioral and physical signs indicate the animal is in heat. The most prominent sign is the standing position the animal assumes, which is referred to as 'standing heat.' This is a natural position the female person assumes to exist mounted by the male. Other physical indicators of estrus are swelling and reddening of the vulva, discharge of mucous from the vagina, and increased affectionate behavior toward other animals. Because ovulation occurs at the end of the estrus phase, the nigh efficient and effective time for sperm degradation is 12–26 h later the onset of estrus. This ensures that the sperm are viable in the uterus before ovulation occurs, which leads to a college conception charge per unit. To make breeding more efficient and simple, many cattle farmers practice estrus synchronization. Oestrus synchronization is the do of synching a female person population's estrus cycles through the injection of natural and artificially synthesized hormones. Once the animal is set up for insemination the sperm must exist properly thawed and loaded into the insemination catheter or gun. For most species, the sperm should be thawed to 36.7 °C for optimal results. Information technology is also crucial that the sperm not be thawed for more than 10 min, as exceeding this threshold leads to infertile sperm. In that location are a multifariousness of insemination techniques, and the ideal location for sperm deposition varies between species. Generally, depositions in the uterus lead to a higher conception rate versus deposition in the vagina and cervix (Dalton, 1999). Transcervical insemination is a common technique used among many animals and is preferred because information technology does not require surgery. Transcervical insemination utilizes an endoscope to locate the cervix then a catheter is passed through the cervix into the uterus for sperm degradation.
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