Questions and Answers
What induces luteal regression in ruminants?
How often is PGF2α released to facilitate luteal regression in ruminants?
What factor influences the sensitivity of the uterus to oxytocin during luteal regression?
What is the effect of exogenous oestradiol on oxytocin receptors?
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At what age do fillies typically begin to show signs of oestrus?
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What seasonal pattern do mares typically follow in terms of breeding?
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Which of the following factors can enhance a mare’s ability to cycle throughout the year?
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What is the classification of foals based on their birth date in thoroughbred racing in the northern hemisphere?
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What characterizes the regular periodic surges of FSH?
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What change occurs during the selection of a dominant follicle?
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Which statement about the corpus luteum (CL) is accurate?
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What does the duration of the interwave interval correlate with?
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Which of the following is NOT a cell type found in a fully formed corpus luteum?
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In which species are early signs of luteinisation observed before ovulation occurs?
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What is one of the primary functions of the hormones prolactin and LH regarding the corpus luteum?
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Which statement accurately describes follicular waves in relation to the oestrous cycle and species?
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What is the average length of the equine reproductive cycle?
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During which phase of the equine cycle does ovulation typically occur?
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What is a characteristic of the mare's reproductive status during the transitional phase before the first ovulation?
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On which day after foaling does heat usually commence?
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What is the typical duration of oestrus in mares?
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Which ovary is more likely to produce ovulations in mares?
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What is the effect of manual rupture of a ripe follicle on oestrus?
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What is a significant challenge in assessing a mare's reproductive status during the transitional phase?
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What characterizes the cervix during dioestrus in mares?
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Which behavior indicates a mare is in oestrus?
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How does the secretion of FSH behave during the oestrous cycle in mares?
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What is the primary reason for teasing mares at stud?
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What is indicated by the gradual increase in LH secretion in mares?
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What occurs in the vulva when a mare is in oestrus?
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What effect does domestication have on cattle regarding their reproductive cycle?
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What happens to oestrogen levels during oestrus in mares?
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What is the approximate size of the smaller ovary mentioned?
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During the interoestrus phase, how does the size of the ovaries vary?
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What change occurs to the corpus luteum (CL) by the middle of dioestrus?
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What is a distinguishing feature of the ovary containing the corpus luteum?
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Why do the ovaries of multiparous cows tend to be larger?
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What characterizes old scarred CLs from previous pregnancies?
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What structure changes to red or scarlet as it ages?
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What happens to small red remnants of corpora lutea?
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Study Notes
Follicular Dynamics in Ruminants
- Follicles in ruminants develop in a wave-like pattern, emerging due to periodic surges of FSH.
- Dominant follicles are determined by a decrease in FSH and an increase in LH responsiveness.
- Anovulatory follicular waves persist until an LH surge occurs; the duration of the estrous cycle correlates positively with the number of follicular waves.
- Progesterone suppresses LH secretion and influences the growth of dominant follicles, while the interwave interval is inversely linked to FSH levels.
- Follicular dominance is most pronounced during the initial and final waves of the estrous cycle.
- Conditions such as pregnancy and seasonal anestrus lead to regular FSH surges and the emergence of non-ovulatory follicular waves.
Corpus Luteum (CL) Formation and Function
- The CL, formed from the Graafian follicle post-ovulation, demonstrates significant mass increase, particularly in ewes, where it grows 20-fold in 12 days.
- Cell types in the mature CL include large and small luteal cells, fibroblasts, and endothelial cells—making it highly vascularized.
- Luteinization can be observed before ovulation in certain species, like the bitch.
- Hormone regulation of the CL formation involves prolactin and LH, with an important role of FSH in maintenance.
- Luteal regression occurs due to PGF2α, released episodically from the uterus, with oxytocin stimulating both PGF2α release and further oxytocin secretion.
- As the CL ages, sensitivity to luteolytic PGF2α increases, while its early stage remains unresponsive.
Mare Reproductive Cycle
- Fillies commonly enter estrus in their first spring but typically do not foal until over 3 years old.
- The mare exhibits seasonal breeding, with regular cycles occurring from spring through autumn, while some breeds cycle year-round under optimal conditions.
- Thoroughbred racing influences breeding schedules, with foaling dates standardized from January, causing many mares to breed when fertility is low.
- Transitional phases in estrus can show irregular cycles, with a lack of correlation between sexual behavior and ovarian activity.
Equine Estrous Cycle Characteristics
- The average equine cycle lasts 20-23 days, with oestrus typically lasting 6 days and dioestrus lasting 15 days.
- Ovulation often coincides with the end of estrous, while the presence of large follicles indicates imminent ovulation.
- First post-partum estrus occurs 5-10 days after foaling, often shorter in duration.
- Left ovary has a slight predominance for ovulation, with historical data reflecting 52.2% of ovulations occurring from this side.
Signs of Estrus in Mares
- Mares display restlessness, frequent urination, and raising of the tail in the presence of a stallion during estrus.
- The vulva may appear swollen with mucoid discharge, and non-receptive mares actively resist stallion advances.
- Professional management involves teasing mares approximately 15-16 days after the end of the last oestrus.
Endocrine Changes During the Estrous Cycle
- FSH secretion exhibits a biphasic pattern with surges at roughly 10-12 day intervals; the second surge occurs just before the subsequent ovulation.
- Unique to mares, LH shows a gradual increase without sudden surges, maintaining elevated levels around ovulation.
- Estrogens peak during estrus, while progesterone levels coincide with the physical changes of the CL.
Ovarian Structure in Cows
- Cows maintain polyoestrous cycles throughout the year under domestic conditions.
- The size of the ovaries remains relatively stable initially in the interestrus phase but may slightly enlarge due to the presence of both the mature and regressing CLs.
- Old scarred corpora lutea from previous pregnancies appear as whitish projections, typically around 0.5 cm in size, and may persist for several months.
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Description
Explore the intricate processes of follicular dynamics and CL formation in ruminants. This quiz covers the development of follicles, hormonal influences, and the implications of various physiological states on reproductive cycles. Test your understanding of these critical biological concepts.
