Performance of Broiler Breeder Females from 1980 and 2000 under Different Feeding Regimes31 May 2014
Research from Israel shows that for broiler breeder females, threshold bodyweight for entry into lay is primarily a matter of lean body mass rather than body fat content. Overfeeding was confirmed to affect adversely reproductive performance.
During the 1990s, various disturbances arose affecting broiler breeder females at entry into lay. These disturbances were associated with even slight overfeeding during release of feed restriction in this critical maturation period, according to Y. Eitan from Kvutzat Yavne in Israel and co-authors at The Hebrew University of Jerusalem.
They set up an experiment - published in Poultry Science - to gain some insight into the causes of these disturbances by comparing the effect of fast (FF) and slow (SF) release from feed restriction at entry into lay in two broiler breeder populations: B1980, representing the genetic level of 1980, and B2000, the genetic level of 2000.
Under the FF treatment, B1980 entered lay 19.2 days earlier than B2000; this increased to 37.4 days earlier under SF. The B1980 population entered lay at virtually the same mean age for SF and FF, whereas B2000 entered lay 15.7 days earlier under the FF.
Bodyweight at first egg were 2,621g for the B1980 and 3,591g for B2000. Differences in bodyweight at first egg between feeding treatments within lines were minor.
As a percentage of bodyweight, ovary, oviduct and follicle weights were the same for B1980 and B2000; breast weight was 14.9 per cent for B1980 and 21.2 per cent for B2000; abdominal fat pad weight was 5.37 per cent for B1980 and 2.67 per cent for B2000. Follicle weight and absolute difference in weight between successive follicles was greater in B2000 than in B1980.
Eitan and co-authors concluded that body fat content does not limit entry into lay, and that threshold bodyweight for onset of sexual maturity of broiler breeder hens increased by about 1,000g between 1980 and 2000, indicating a tight association between juvenile growth rate and threshold bodyweight for onset of sexual maturity.
Disturbances at entry into lay due to overfeeding are not due to smaller differences between successive follicles in B2000 than in B1980, they added. There are hints, however, that overfeeding may contribute to these disturbances by decreasing differences between successive follicles.
In their conclusions, the researchers say that 20 years of selection for broiler performance traits have resulted in a marked increase in breast weight and an equally marked decrease in abdominal fat pad weight at entry into lay. This has been accompanied by a major increase in threshold weight for entry into lay. The results taken jointly indicate that threshold bodyweight for entry into lay is primarily a matter of lean body mass rather than body fat content. The increase in threshold weight apparently is a direct consequence of the increase in juvenile growth rate achieved in this period.
Their results also indicate that problems caused by overfeeding at entry to lay are not a matter of the effect of the overfeeding on body fat content because even with overfeeding, this remains well below that of the B1980. Furthermore, oviduct weight, ovary weight and weight of F1 through F7 follicles increased in direct proportion to the increase in bodyweight of the B2000. As a result, the absolute difference in weight between successive follicles was slightly more, and the relative weight the same, in the B2000 as in the B1980. Thus, the hierarchal structure of the follicle series was not disrupted by the 20 years of selection for broiler performance. Hence, this too is not the source of the problems at entry into lay.
Taken as a whole, Eitan and co-authors conclude, the results of the study confirm the deleterious effect of overfeeding on reproductive performance in the modern broiler, eliminate some potential explanations for this effect, and raise others. However, they added, the precise mechanism remains obscure.
Eitan Y., E. Lipkin and M. Soller. 2014. Body composition and reproductive performance at entry into lay of anno 1980 versus anno 2000 broiler breeder females under fast and slow release from feed restriction. Poultry Science. 93(5):1227-1235. doi: 10.3382/ps.2013-03239
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