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PUBERTY AND FACTORS AFFECTING PUBERTY IN DOMESTIC ANIMALS

Puberty is manifested by the bulls through exhibition of libido and production of spermatozoa while the heifer exhibits reproductive cyclicity and occurrence of estrus at 21 days intervals. Heifer does not produce new oocyte while the bull produces spermatozoa continuously.  At birth heifers possess oocyte in maximum number. However, after the onset of puberty, the oocytes undergo development and maturation. It occurs in a wave pattern after commencement of puberty and continues for the rest of life.

Hormonal changes are seen with the onset of puberty. Before puberty, the required levels of LH and FSH are not available from the pituitary, for supporting for development and maturation of oocytes. The onset of puberty is manifested by release of LH and FSH coupled with and an increasing responsiveness of the ovary and oocytes to these hormones,
Factors that affect puberty may be classified into three categories: the breed, age and nutrition. These factors can enhance the onset of puberty by several months. Other factors may alter the age at puberty (AAP) up to a smaller extent of about a month.
The onset of puberty may be attributed to maturation of the central nervous system which is associated with initiation of release of LH and FSH. Age at puberty varies across the breeds and individuals within the same breed and herd. Breeding affects the age at puberty. The effect of breed on the age at puberty may vary from 6 to 20 months of age. Heifers may be made to clave at 24 months, if they are bred at the age of 14 or 15 months. If heifers gets into puberty and manifests 2 to 3 esrous cycles before the commencement of breeding season, the chances of getting pregnant to the first service increases. Age at puberty in crossbred heifers is smaller than purebred heifers. Heritability of reproductive traits is low; however, heterosis of reproductive traits is higher.
Nutritional status affects the onset of puberty in animals. For maintaining successful reproductive processes in replacement heifers, an optimum feeding regime is required. Optimum nutritional status accelerates the onset of puberty by few months by under nutrition results in retarded growth of the body system and impedes body weight gain leading to delayed puberty for a much longer time. The heifers must reach a critical weight during commencement of the breeding season, if they are to be bred successfully under nutrition prevents secretion of LH and FSH in a different way than age or genetics. An underweight heifer attaining sufficient age may show a rapid weigh gain through higher nutritional plan and will manifest onset of puberty.

Weight at puberty is more critical than age. After reaching a certain weight (about 70% of the adult body weight) the heifer will exhibit the symptoms of puberty. This critical weight may be brought about at an earlier stage of the life through appropriate feeding strategy. The feeding plain for replacement heifers should include good quality forage or grazing as well as ingredients’ of high energy contents. The scale of addition of supplements should range from 0.5 to 1% of body weight. In addition to energy, the availability of protein may also be ensured for earlier onset o puberty. In a research study 40% of heifers fed a low protein (9%) diet showed symptoms of puberty compared to 90% heifers fed adequate nutrition. The study further revealed that addition of extra energy in the heifer’s diet could not overcome the effect of protein deficiency.
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