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Sexuality and reproduction

Most bovids are polygynous. In a few species, individuals are monogamous, resulting in minimal male-male aggression and reduced selection for large body size in males. Thus, sexual dimorphism is almost absent. Females may be slightly larger than males, possibly due to competition among females for the acquisition of territories. This is the case in duikers and other small bovids. The time taken for the attainment of sexual maturity by either sex varies broadly among bovids. Sexual maturity may even precede or follow mating. For instance, the impala males, though sexually mature by a year, can mate only after four years of age. On the contrary barbary sheep females may give birth to offspring even before they have gained sexual maturity. The delay in male sexual maturation is more visible in sexually dimorphic species, particularly the reduncines, probably due to competition among males. For instance, the blue wildebeest females become capable of reproduction within a year or two of birth, while the males become mature only when four years old.

All bovids mate at least once a year, and smaller species may even mate twice. Mating seasons occur typically during the rainy months for most bovids. As such, breeding might peak twice in the equatorial regions. The sheep and goats exhibit remarkable seasonality of reproduction, in the determination of which the annual cycle of daily photoperiod plays a pivotal role. Other factors that have a significant influence on this cycle include the temperature of the surroundings, nutritional status, social interactions, the date of parturition and the lactation period. A study of this phenomenon concluded that goats and sheep are short-day breeders. Mating in most sheep breeds begins in summer or early autumn. Mating in sheep is also affected by melatonin, that advances the onset of the breeding season; and thyroxine, that terminates the breeding season. Estrus lasts for at most a day in bovids, with the exception of bovines and tragelaphines. Except for the hartebeest and the topi, all bovids can detect estrus in females by testing the urine using the vomeronasal organ. Once the male is assured that the female is in estrus, he begins courtship displays; these displays vary greatly from the elaborate marches among gregarious species to the fervent licking of female genitalia among solitary species. Females, initially not receptive, ultimately mates with the male which has achieved dominance over others. Receptiveness is expressed by permission for mounting by the male and setting aside the tail by the female. Copulation generally takes a few seconds.

Gestational period varies among bovids - while duiker gestation ranges from 120 to 150 days, gestation in African buffalo ranges from 300 to 330 days. Usually, a single offspring is born (twins are less frequent), and it is able to stand and run by itself within an hour of birth. In monogamous species, males assist in defending their young, but that is not the case in polygynous species. Most newborn calves remain hidden for a week to two months, regularly nursed by their mothers. In some bovid species, the neonates start following about their mothers immediately or within a few days, as in the impala. Different bovids have different strategies for the defence of juveniles. For instance, while wildebeest mothers solely defend their young, buffaloes exhibit collective defence. Weaning might occur as early as two months (as in royal antelope) or as late as a year (as in muskox).