Alzenbarakji, Nada
(2011)
Influence of age and strain on reproductive performance of the broiler breeder female.
PhD thesis, University of Nottingham.
Abstract
Chicken meat is an important source of high quality protein in the diet of most people in the world. Consequently, the increasing demand for this meat has made chicken meat production the most important growth sector among other meat species. This has been achieved by a half century of intensive genetic selection for growth traits; however, this was coupled with poor reproductive performance of broiler breeders.
Ross 708 represents a broiler breeder strain that has been developed for breast-meat yield, and has been reported to exhibit poor reproductive performance in comparison to Ross 308, a typical broiler breeder strain. Accordingly, the current study investigated key points involved in the reproductive process that might influence variation in reproductive performance. Ovarian follicles number was the first point to investigate, as they are the main material of the egg. Liver fatty acid profiles were also investigated in order to identify lipid metabolism and the efficiency of dietary fat utilisation, as the liver is the main site that supplies different body tissues with fatty acids. Carcass fat content was also examined as its negative relationship with reproduction is well documented. Finally, the content of calcium in the tibia bone was examined to identify whether variation in egg production was associated with differences in the metabolism of this element. Accordingly, broiler breeder females from Ross 308 and 708 strains, reared under the standard production system on two different commercial farms of PD Hook, were collected throughout the reproductive cycle; starting at 25-week-old and in five weeks interval until 55-weeks of age.
Findings showed no difference in the number of both the large yellow follicles (P=0.332), and the small yellow follicles (P=0.134); whereas the number of large white follicles was higher in the 708 ovaries (P=0.005).
Differences in lipid metabolism were identified with a strong tendency for the 708s towards having lower content of linoleic acid (P=0.056) in addition to significantly lower a-linolenic acid (P=0.005). Of particular importance is the latter fatty acid as it is the precursor to (n-3) fatty acids, some of which were found to be less (P<0.001) in the 708s including docosapentaenoic (DPA) and docosahexaenoic (DHA). The importance of these fatty acids in follicular maturation is well documented in addition to the importance of the linoleic acid; these findings indicate that the 708s were not receiving adequate levels of the essential fatty acids which might have contributed to their poor reproductive performance. The 708s also laid down significantly more fat (P<0.001) in comparison to the 308s which could be another factor that has impaired their reproduction performance. This could indicate different levels of metabolic hormones which, in turn, have been found to act in concert with the reproductive hormones. 708s also exhibited a trend towards lower content of calcium in their tibiae, with an age by strain interaction and thus suggesting a difference in the metabolism of this element at some ages.
The current study has addressed changes of the investigated parameters with age, but the effect of genetic selection on reproductive performance was difficult to address. Rather, some physiological differences have been identified; 708s were found to be receiving inadequate amounts of essential fatty acids, calcium content was found to be less at some ages and they exhibited a higher content of carcass fat. All these factors have the potential to contribute to poor reproductive performance, and once they are taken into consideration better assessment for the effect of the continued genetic selection for more growth traits can investigated.
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