Reproductive Biology of the Broiler Breeder Male
In the poultry industry, there are numerous challenges facing individuals responsible for the reproduction of broiler breeders. Many of these problems stem from the knowledge that increasing body growth rate will generally result in a reduction in reproductive characteristics, and vice versa. This situation is likely to escalate due to increased consumer demands for more white meat and less dark meat, which are attained in the high yield faster growing birds. Therefore, the continued trend toward high-yielding, fast-growing broilers is evident. Consequently, it does not appear that the task of managing broiler breeders is going to get any easier in the near future.
Developing Fertile Males
The testes of young cockerel chicks contain cells that will form the structure of the testes (somatic cells) as well as cells that will later become sperm cells (germinal cells). Some somatic cells (called Sertoli or nurse cells) function to protect the developing sperm cells while other cells (called Leydig cells) are involved in testosterone production. Although the broiler breeder male can theoretically produce trillions of sperm, the number of Sertoli cells contained within the testes limits the actual number of mature sperm produced. Sertoli cell growth occurs sometime between 2 and 12 weeks of age (generally thought to be between eight and ten weeks) but not at anytime after this point (Kirby, 1998). Therefore, the maximum potential for sperm production is established in the first eight to ten weeks of age. Anything that may cause unnecessary stress to the developing male at this time may interfere with proper development of these very important testicular cells.
During this early period of development, portions of the brain (such as the hypothalamus) and the pituitary gland are also establishing a critical hormonal relationship with the testes. These portions of the brain must work together with the testes to maintain proper reproductive hormone levels so that testes functions (such as sperm production) can start and be sustained. During the early stages of maturation the testes help to establish a relationship called a “feed back loop” with the pituitary gland that will regulate pituitary function over the life of the male. Thus, appropriate levels of reproductive hormones (FSH, LH, etc.) are not only critical for the proper development and function of the testes, but also for the development of the relationship between the brain and the developing testes. These relationships can be established only at this time of male maturation.
Sexual Maturity in Males
As reproductive hormone secretions (primarily FSH) increase, there is a tremendous growth in testes mass that is associated with the onset of sperm production. This time period, also referred to as puberty, occurs between 16 and 24 weeks of age. Once the males attain peak semen production, testes weight and sperm production continue to decline thereafter.
The establishment of normal reproductive hormone secretion is at least partially completed within the first few weeks of a male´s life. Even mild stressors which cause either weight loss or reduced water intake can lead to complete shutdown of testes function when they occur during critical early stages of development (Kirby, 1998). These males may be those that are usually “grown back to the curve” due to problems during development. Additionally, it is possible to disrupt the normal pattern of testes development with too severe feed restriction between 6 to 8 weeks. This results in reduced testes size, sperm production, and the theoretical maximum number of sperm produced. Also, reduced reproductive performance has been demonstrated with severe feed restriction in males between 18-23 weeks of age (Kirby, 1998), suggesting that the resources and hormone secretion required for normal testes function can be negatively and permanently affected around the time of photostimulation.
Young cockerel chicks that are in stressful situations between 2 and 12 weeks of age may not develop the capacity to form sperm cells adequately. Testical development can also be disrupted by severe feed restrictions between 6 and 8 weeks. Normal testes function can also be negatively and permanently affected by sever feed restriction around the time of photostimulation.
Proper management of breeder males will reduces stress consideration these critical points in their development. Any unnecessary stress placed upon these birds at these critical points can have profound effects on the reproductive potential of the males. Many of these effects are either permanent or long lasting and can seriously affect the overall performance of the breeder males in the hen house. Once these biological systems are set firmly in place in the young breeder male, management to sustain these reproductive systems are less critical and more forgiving.
Kirby, John D., 1998. Broiler Breeder Male Reproductive Efficiency: Where Management and Biology Collide. Proceedings, North Carolina Breeder/Hatchery Management Symposium.
By R. Keith Bramwell • Extension Reproductive Physiologist
Center of Excellence for Poultry Science • University of Arkansas
Published in Avian Advice newsletter • Arkansas Cooperative Extension Service
Source: University of Arkansas Avian Advice