Administration of a gonadotropin-releasing hormone antagonist to mares at different times during the luteal phase of the estrous cycle

Evans, Margaret J.; Alexander, Susan; Irvine, C. H. G.; Kitson, N. E.; Taylor, T B

doi:10.1016/j.anireprosci.2011.07.020

Cited by 3 publications

(2 citation statements)

References 27 publications

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“…On the theca cells, LH is involved in oocyte maturation, ovulation, establishment and maintenance of corpus luteum (CL) as well as development and in the synthesis of P4. Both ovarian steroids control the Hypothalamus-Hypophysis axis (HHA) by feedback mechanisms that determine the estrous cycle in the mare [5][6][7].…”

Section: Reproductive Seasonality In the Marementioning

confidence: 99%

A Review of the Estrous Cycle and the Neuroendocrine Mechanisms in the Mare

2013

J Steroids Horm Sci

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With an understanding of basic reproductive science, veterinarians and breeders can be better positioned to achieve their goals. It is important to understand the heat or estrus cycle in order to maximize the chances of success when breeding the mare. Reproductive activity in horses is seasonally dependent, as it is primarily affected by the length of daylight. Therefore the mare has a seasonally polyestrous type of estrous cycle. This means they have breeding season in which they have multiple heat cycles, is receptive to the stallion and ovulates; and a period where they will not go into heat or anestrus. During the anestrus period, most mares show no behavioral signs of sexual receptivity and fail to develop follicles that ovulate. There are exceptions in that a small percentage of mares that do not express a seasonal pattern in that they stay both behaviorally and physiologically receptive to stallions throughout the year. During the ovulatory season, the mare is cycling, thereby exhibiting sexual receptivity to the stallion on a regular basis and is producing follicles that ovulate. The equine estrous cycle is commonly described as a combination of a follicular phase, or estrus, and a luteal phase, or diestrus. The endocrinology of the estrous cycle involves a balance between hormones produced by the pineal gland, hypothalamus, pituitary gland, ovaries, and endometrium. Growth of antral follicles in the ovary occurs in wave-like patterns, and is influenced by several factors such as stage of the estrous cycle, season, pregnancy, age, breed and the individual. In this article will describe the neuroendocrine mechanisms related to breeding seasonality, the hormonal changes that occur during the estrus cycle as well as the variations among mares in regards to the understanding the physiological mechanisms related with the estrous cycle in the mare.

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Section: Reproductive Seasonality In the Marementioning

confidence: 99%

A Review of the Estrous Cycle and the Neuroendocrine Mechanisms in the Mare

2013

J Steroids Horm Sci

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“…In addition, in vitro studies demonstrated that either eLH or hCG increased the P 4 production by equine luteal cells [14,24]. Moreover, treatment of mares with an antiserum against equine gonadotropins during diestrous decreased the luteal size [27,28], and treatment of mares with a GnRH antagonist during diestrous decreased the circulating P 4 concentrations [29,30]. These findings indicate that LH stimulates the production of P 4 by the CL and support luteal function in mares, as shown in other species [10,21,22].…”

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confidence: 99%

Seasonal Changes in Luteal Progesterone Concentration and mRNA Expressions of Progesterone Synthesis-related Proteins in the Corpus Luteum of Mares

Kozai

Hojo

Takahashi

et al. 2012

Journal of Reproduction and Development

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Abstract. Although circulating progesterone (P 4 ) levels tend to change with the season, little is known about the seasonal changes of P 4 synthesis-related proteins in the corpus luteum (CL) of mares. To examine these changes, seventy-four ovaries containing a CL were collected from Anglo-Norman mares at a local abattoir in Kumamoto, Japan (~N32°), five times during one year. The stages of the CLs were classified as early, mid and regressed by macroscopic observation of the CL and follicles. The mid CL, which had the highest P 4 concentration, was used to evaluate the seasonal changes in P 4 synthesis. The luteal P 4 concentration and mRNA expression of luteinizing hormone receptor (LHCGR) were lowest during early winter and highest during late winter. The mRNA expressions of steroidogenic acute regulatory protein (StAR), P450 cholesterol side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) were lowest during early winter and increased during late winter. These results suggest that P 4 synthesis in the CL is affected by the seasonal changes in the mRNA expressions of P 4 synthesis-related proteins in mares. Key words: Corpus luteum, Mares, Progesterone, Reproductive seasonality, Steroidogenesis (J. Reprod. Dev. 58: [393][394][395][396][397] 2012) M ares are seasonal breeders in which day length (DL) is one of the main environmental factors controlling reproductive seasonality [1][2][3]. The reproductive activity of mares reaches a peak during summer, then decreases during autumn and eventually stops through winter as DL decreases. January 1 in the Northern Hemisphere and August 1 in the Southern Hemisphere are used as the official birth dates for many breeds, especially for racing breeds [4]; therefore, the exposure of mares to artificial light has been used to hasten the reproductive season. Thus, studying reproductive seasonality in mares is relevant for the equine industry.In mammals, the corpus luteum (CL) is an endocrine organ producing progesterone (P 4 ), which is essential for the establishment and maintenance of pregnancy. Although several studies have examined seasonal changes in circulating P 4 concentration in mares, the reported results are not consistent, i.e., the circulating P 4 concentration has been reported to decrease [5][6][7], increase [8] or remain unchanged [9] from the breeding to non-breeding season. Therefore, the effects of season on P 4 synthesis in the CL of mares remain unclear.Luteal P 4 production is regulated by several P 4 synthesis-related proteins [10]. Luteinizing hormone (LH) secreted by the anterior pituitary is the main regulator of luteal function. LH acts through its specific cell surface receptor (LHCGR) and stimulates P 4 production by the CL in ewes [11], rats, sows [12], cows [13] and mares [14]. Steroidogenic acute regulatory protein (StAR) transfers cholesterol from the outer to inner mitochondrial membrane, allowing enzymatic cleavage of the side chain of cholesterol to pregnenolone by P450 cholesterol side-chain ...

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Superovulation in the Mare: A Work in Progress

Roser

Meyers-Brown

2012

Journal of Equine Veterinary Science

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Administration of a gonadotropin-releasing hormone antagonist to mares at different times during the luteal phase of the estrous cycle

Cited by 3 publications

References 27 publications

A Review of the Estrous Cycle and the Neuroendocrine Mechanisms in the Mare

A Review of the Estrous Cycle and the Neuroendocrine Mechanisms in the Mare

Seasonal Changes in Luteal Progesterone Concentration and mRNA Expressions of Progesterone Synthesis-related Proteins in the Corpus Luteum of Mares

Superovulation in the Mare: A Work in Progress

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