Puberty and Estrus in Goats

Also see Breeding Soundness Examination of Bucks.

Goats are spontaneously ovulating, seasonally polyestrous animals with peak breeding activity occurring in the autumn, driven by photoperiod. As day length decreases, melatonin secretion from the pineal gland increases, which activates pulsatile GnRH release from the hypothalamus. Hypothalamic GnRH secretion stimulates release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary, which then acts on the ovary to promote the growth of follicles, stimulating the onset of the hypothalamic-pituitary-gonadal axis in short-day breeders.

Factors that affect onset and length of the breeding season include geographic location (ie, latitude and climate), breed, herd social structure, and photoperiod.

In temperate regions, the natural breeding season is mostly restricted to the autumn and winter to allow for kidding in the spring and summer, when nutritional resources are adequate. Under tropical and subtropical conditions, where temperature and photoperiod are less variable, an extended breeding period occurs in certain breeds if appropriate resources are available to allow for kidding year-round.

The onset of puberty in goats typically occurs at 6–8 months old in does and 4–6 months old in bucks. Age at onset can vary between breeds and is influenced by environmental factors, such as the season of birth, breed, and nutritional status. In temperate regions, spring-born animals will undergo puberty at a younger age, simply because physiologic maturity coincides with periods of decreased day length.

Though some breeds, such as Pygmy goats, may reach puberty as early as 3 months old, breeding should be delayed until the animal has reached at least 60% of its mature body weight to achieve higher conception rates and minimize the risk of dystocia.

Larger goat breeds (eg, Nubian, LaMancha, Boer, and Saanen) can be safely bred when approximately 70 lb (32 kg). Angora kids should weigh a minimum of 27 kg and are frequently not bred until they are 1½–2½ years old. Owners should be aware of the potential for earlier puberty to prevent unintentional breeding within the herd.

The estrous cycle in goats is 21 days, on average, but it can vary with different breeds or environmental conditions. A relatively high frequency of short cycles is characteristic of goats and tends to occur in young does and earlier in the breeding season. Longer cycles may be observed later in the season when does are transitioning into seasonal anestrus.

The mean duration of standing estrus has been reported to be 36 hours in does, although it can range from 24 to 48 hours depending on age, breed, season, and presence of a male (1). Breed-specific mean estrus duration has been reported for Mossi (20 hours), Angora (22 hours), Creole (27 hours), French Alpine (31 hours), Boer (37 hours), Nubian (42 hours) and Matou (58 hours) goats (1).

Estrus detection is based on behavioral signs, bleating, flagging of the tail, reddened vulva, vaginal discharge (which causes the tail hairs to stick together), and occasional “riding” by other does (see behavioral signs of estrus image). These behaviors are more pronounced in the presence of an intact male.

Behavioral signs of estrus, goat

Image

Does in estrus may ride or allow themselves to be ridden by a buck.

Courtesy of Dr. Jamie Stewart.

Ovulation can occur anywhere from 9 to 72 hours after the onset of estrus, typically toward the end of standing estrus. The ovulation rate varies based on breed, season, and nutritional status.

Angora goats typically experience a single ovulation period; however, they may have two if sufficient nutrition is available. The mean ovulation rate has been reported to be 1.7 eggs per doe in Boer goats and 1.5 in Maure goats (1).

"Flushing," or "focused feeding," is a strategy in which a nutritional boost is supplied in a short period of time to enhance reproductive efficiency in ruminants without affecting body condition. This practice leads to a positive energy balance, which increases leptin and insulin concentrations, enhances glucose uptake, and is associated with increased folliculogenesis and ovulation rate.

Dietary supplementation with beta carotene, a vitamin A and retinoid precursor, at 50 mg/goat/day has reportedly produced flushing in does (2, 3).

Another flushing strategy involves supplementing the diet of does with up to 0.45 kg/head/day of a 10–12% crude protein grain for approximately 2 weeks before and after breeding. In general, this technique works more effectively when the doe enters the breeding season in a marginal body condition score (2–3 out of 5) compared with those that enter the breeding season overconditioned (4 or 5 out of 5).