Bovine Reproduction. Группа авторов

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Bovine Reproduction - Группа авторов


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scrotal circumference, testes weight, seminiferous tubules diameter, and number of germ and Sertoli cells in tubular cross‐sections at 12 months of age [29–31]. The LH secretion pattern during the prepubertal period is also associated with age at puberty in bulls raised in contemporary groups, suggesting that this is the physiological mechanism by which genetics affect sexual development. Studies have shown that LH pulse frequency was greater around 2.5–5 months of age and that mean LH concentrations increased earlier and reached greater maximum levels in early‐ than in late‐maturing Hereford bulls (age at puberty 9.5 and 11 months, respectively) [19, 21].

Schematic illustration of mean (± SEM) number of LH pulses and serum testosterone concentrations in Angus and Angus times Charolais bulls receiving low, medium (control), or high nutrition from 10 to 70 weeks of age. N, A, and N*A indicate nutrition, age, and nutrition-by-age interaction effects, respectively.

      Source: From [2], © 2007, Elsevier.

Schematic illustration of mean (± SEM) number of LH pulses and serum testosterone concentrations in Angus and Angus times Charolais bulls receiving medium (control) or high nutrition from 10 to 30 weeks of age and the same medium nutrition from 31 to 74 weeks. N, A, and N*A indicate nutrition, age, and nutrition-by-age interaction effects, respectively. Superscript a and b indicate differences (P = 0.09) between groups within age.

      Source: From [3], © 2007, Elsevier.

Schematic illustration of mean (± SEM) number of LH pulses and serum testosterone concentrations in Angus and Angus times Charolais bulls receiving medium (control) from 10 to 70 weeks of age or low nutrition from 10 to 26 weeks of age and either medium or high nutrition from 27 to 70 weeks of age.

      Source: From [4], © 2007, Society for Reproduction and Fertility.

      The pubertal period is characterized by reduced gonadotropin secretion, increased testosterone secretion, initiation of spermatogenesis, and the eventual appearance of sperm in the ejaculate. This period also coincides with the start of a phase of rapid testicular growth (see Chapter 6


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