Sensitivity to overfeeding and the role of broiler breeder genetics on breeder chick quality
The reproductive efficiency of broiler parents is increasingly dependant on very specific feed restriction and lighting programmes to optimise reproduction.
Broiler breeders must have the genetic potential for efficient growth as well as the ability to effectively reproduce.
Excess body weight can result in reduced egg production, hatchability, livability, egg weight, feed efficiency and increased shell porosity while overfeeding can accelerate the sexual maturation process and elevate ovarian large yellow follicle (LYF) numbers in birds.
Four commercial strains were reared on a common body weight target, and fed one of three feeding programs from photostimulation (22 wk):Ad libitum; Fast-Feed (weekly feed adjustments based on a 5 g increase for every 5% increase in production); and Slow-Feed (daily adjustments of 1 g/d between 22 and 26 weeks of age, and 0.5 g/d until 31 weeks of age).
Ad-libitum feeding did not accelerate sexual maturation in two of the strains, suggesting these birds have a later maturation. This serves to show genetic differences in photo-sexual response among commercial stocks.
In these late-maturing strains, it would seem pointless to subject these birds to increasing day lengths and feed allocations as soon as you would more traditional early maturing strains.
In the strains responding to overfeeding, maturation was accelerated by 6 to 7 days.
The number of large yolky follicles varied among strains, with the two strains that reached sexual maturity first having the fewest large follicles. These data strongly suggest that it is essential to follow management recommendations specific to a breeder genotype.
Another study was designed to show the effects of yield traits on the ability to cope with a feeding challenge.
The strains were: Random-bred (unselected since 1977), Ross 308 (a high-yield bird suited for the whole-bird market), and Ross 508 (a very high-yield bird suited for the cut-up and further processing market).
Beginning at photostimulation (22 wk of age), pullets were fed 100% (control), 120%, and 140% of the feed needed to maintain the Ross 508 growth curve.
The timing of sexual maturity was affected by strain, with the RB20, Ross 508 and Ross 308 birds laying eggs after photostimulation.
At sexual maturity (onset of lay), the Ross 508 birds had the highest proportion of breast muscle. Conversely, the Random-bred hens were the fattest - reflecting the less efficient growth of their older genetics.
The 120 and 140% treatments only added an additional 5.3% and 9.7% to weight at sexual maturity, respectively.
Feeding regimen had a big impact on egg production, with 166, 159, and 137 settable eggs produced by the 100, 120, and 140% groups, respectively.
The modern, high breast-yield Ross 508 birds were the most sensitive to overfeeding, producing 177 eggs with the 100% feed allocation compared to only 123 eggs on the 140% feed allocation.
When coupled with decreased rates of fertility and hatchability in the 140% treatment, overfeeding had a devastating effect on chick numbers. The hatchability of the 140% Ross 508 hens near the end of the study ranged between 20 and 30%.
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Article made possible through the contribution of the Australian Poultry Science Symposium (APSS) 2006.