CHAPTER 70 Clinical Examination of the Female Reproductive Tract
Goats are usually seasonal breeders. With respect to reproduction, the single most important regulating factor is the day length, or photoperiod. This influence is more pronounced the further north or south of the Equator the animal is located.
The underlying influence of photoperiod affecting cyclicity is mediated through the secretion of luteinizing hormone (LH) from the anterior pituitary. In making the transition from anestrus to cyclicity, serum concentration of LH begins to increase.1–9 The reason for this increase has been attributed to an increase in the frequency and magnitude of the LH pulses.8 Final maturation and ovulation of ovarian follicles depend on sufficient LH release.8–10
A currently accepted hypothesis referred to as the “gonadostat hypothesis,” maintains that in prepubertal and seasonally anestrus does, estrogen secretion from the follicles strongly inhibit the release of LH.9,10 As the animal matures or is exposed to decrease in day length (late summer and fall), this inhibitory effect is lost, and there is increased LH release leading to ovulation and cyclicity.8–10
This change in sensitivity or alternating inhibitory influence of estrogen remains unclear. It may be due to changes in melatonin production from the pineal gland, mediated through the light perceived by the eye.9–15
European goat breeds (Saanen, Toggenburg, and French Alpine), Spanish, Angoras, and Kikos have a more restricted breeding season (September to February). Whereas Nubian, Nubian crosses, Boer, pygmy, and Tennessee stiff-legged goats have a longer or extended breeding season.16 There is not only great variation among breeds regarding the length of the breeding season, but there are significant variations within a breed. Selection for long breeding season should be utilized as a management tool.
Nutrition and body size play an important role when doelings reach puberty. In general, doelings born in late winter or early spring will reach puberty that fall. Breeding should be delayed till animals reach 65% of their mature weight, approximately 70 lb in meat goats and 70 to 90 lb in dairy goats.16
Reproductive problems in goats are usually management problems associated with confinement, attempts to breed them outside their natural breeding season, improper heat detection, poor breeding management, or improper artificial insemination.17
A complete history should be an important part of the breeding soundness examination (BSE) because of the inaccessibility to the majority of the reproductive tract to palpation or visual inspection.16,17 Information regarding the intention of the owner in utilization of these goats for production (meat, milk, and fiber), brush control, or as a companion animal should be gathered.