Reproduction in Farm Animals by E. S. E. Hafez B. Hafez & E.S.E. Hafez

Author:E. S. E. Hafez,B. Hafez & E.S.E. Hafez
Language: eng
Format: epub
Publisher: John Wiley & Sons, Inc.
Published: 2013-05-09T16:00:00+00:00

FOLLICULAR DEVELOPMENT AND GAMETOGENESIS. Ovarian weight increases at the onset of sexual maturity. Of the thousands of oocytes present, many enlarge in size to about 6 to 8 mm in diameter. Once a yellow follicle exceeds 8 mm in diameter, it will normally continue to grow and ovulate. The majority of the follicles in this size range, however, fail to develop or become atretic (Fig. 16-10F) (59). In a high-producing chicken, one of the 8 mm follicles will enlarge and enter the follicular hierarchy every 25 to 27 hours. This follicle will continue to grow and will ovulate 5 to 7 days later. This successive maturation of follicles results in the follicular hierarchy that is characteristic of the bird ovary (Fig. 16-9). However, selection of chickens for rapid growth has resulted in an increase in ovarian weight and in the number of developing follicles on the ovary of the meat-type chicken. In contrast to egg-type chickens, the ovaries of the broiler breeder hen contain about twice as many yellow follicles. This increase in the number of developing follicles paradoxically results in a decline in egg production because two or more ova may be ovulated in one day and result in soft-shelled or double-yolked eggs. Some ova are ovulated into the body cavity and reabsorbed without entering the reproductive tract (60). This poor reproduction is typically improved by limiting the body weight of broiler breeders through feed restriction. Turkey hens lay at a lower rate than either egg-type or meat-type chickens (Table 16-3), due in part to a slower rate of follicular growth (9 to 10 days from 8 mm in diameter to ovulation) (61).

The liver, not the ovary, is the major source of yolk proteins and phospholipids (62). The production of yolk precursors in the liver is regulated by estrogen. A chicken that lays each day produces about 19 grams of yolk precursors daily that are transported to the ovary and deposited in growing follicles by receptor-mediated mechanisms. This transport of large quantities of phospholipids results in the extremely lipemic serum that is characteristic of laying hens.

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