Natural mating in broiler breeders: present and future concerns

Intensive selection based on growth traits in meat-type breeder flocks has resulted in new breeds expressing early sexual precocity but limited persistence of gonad development. This can be in part circumvented by adequate use of specific light regimes. However, these breeds require environmentally controlled housing in which light, temperature and ventilation can be properly balanced, a situation which to date is technically feasible only under relatively mild climatic conditions. In recent years there has been a progressive shift in chicken production to warm geographic regions. As a consequence, increasing numbers of breeder flocks are now raised in open houses in which light regimes are only partly controlled. In most instances, reproductive performance in standard meat-type breeds remains satisfactory if sexual precocity can be delayed until 23-25wks of age. However, the early maturation of flocks stimulated by external photoperiods may result in small eggs during the early parts of the season. Early sexual precocity in breeder males is generally followed by a rapid decline in reproductive performance, resulting in their partial or even total replacement to maintain acceptable fertility rates throughout the season. Such changes, which are currently performed on a large scale, are costly, pose health risks and are only partly effective in maintaining adequate fertility rates. In addition to photoperiod, another common practice to for controlling sexual precocity and reproductive performance in meat-type chickens is based on strict control of feed allowance for each sex. In countries where housing and feed equipment are accessible, techniques such as sex-separate feeding combined with quantitative feed restriction have been of practical value to limit body growth. However, such equipment is costly and requires strict management practices. Severe feed restriction in maturing breeder flocks may be stressful and, which induces heterogeneity in body growth. Another concern is the moderate but constant decline in fertilising potential. A Furthermore a negative correlation between reproductive and growth traits may be responsible for such the decline in fertilising potential of birds selected for rapid growth. This may ultimately favour the emergence of breeds with less intensive growth rates and/or the extension of artificial insemination.