Effects of confinement on attainment of puberty in gilts.

The present work is a review of experiments realized in order to determine the effects of confinement conditions on attainment of puberty in gilts. Few authors have compared age at first estrus or first ovulation of gilts bred in total confinement, in open front buildings and in outdoor dirt lots. Results are not always significant but lead to conclude to a detrimental effect of confinement on attainment of puberty (5 to 17 day delay). Interactions with other factors such as genotype, season of birth, age at treatment explain the differences between results. Large variations are also observed in the response of confined gilts housed in different conditions of intensity and duration of light, temperature and social environment. However, high temperature and individual penning induce a delay in age at puberty (4 to 10 days). Although the sexual development is known to depend on hormonal control, studies regarding the influence of environmental conditions on hormonal secretions are recent, rather scarce and incomplete. Significant variations in the pineal gland activity, the plasma levels of prolactin, LH and estrogens have not yet been associated with confinement, intensity and duration of light. A disruption of the corticosteroid rythm has been observed in individual compared to group penned animals. Estrus response to gonadotropin hormones is not modified but ovarian response to estrogen is reduced by confinement. Further experiments taking into account the existence of interactions between genotype, light and temperature conditions, season of birth and social relations are required in order to investigate more precisely the influence of the different types of environment on the hormonal secretions and consequently the sexual development of gilts.