Studies on heterosis in the domestic fowl

IV. Hatchability of F₁ hybrids and their parental purebred chick embryos

Abstract

Within and between-beeed matings were performed among 11 sires and 84 dams of White Leghorns (WL) and 11 sires and 58 dams of Barred Plymouth Rocks (BPR). The averagecoefficients of inbreeding of parental purebreds were 2.3, 4.6, 5.1, and 3.9 per cent in WL sires, WL dams, BPR sires, and BPR dams, respectively. The mating systems were such that these purebreds and F1 hybrids were materenal half-sibs. Accordingly, comparison as possible between groups of pure and crossbred types. Data were collected from 1, 934 purebred and 2, 316 crossbred fertile eggs. The average hatchability and embryonic mortality at different incubation periods, which were determined with significance tests based on chi-square, are given in Tables 1 and 2. Abnormal embryos observed after various matings are shown in Table 3. The results of statistical analysis of the data obtained are summarized as follows:
1) The average hatchability of fertile eggs was 7.47% higher among F₁ hybrid embryos than purebreds (WL=88.16%, BPR=81.47%, WL_??_×BPR_??_=92.59%, and BPR_??_×WL_??_=91.97%). It was 6.69% higher in WL than in BPR. These differences were statistically significant at the 1% level. The hatchability of fertile eggs was 0.62% higher in WL_??_×BPR_??_ than its reciprocal, but this difference was not statistically significant.
2) The mortality rate of embryos after the 19th day of incubation was lower in F1 hybrids than purebreds (WL=7.04% and BPR=8.68% vs. WL_??_×BPR_??_=2.62% and BPR_??_×WL_??_=2.47%), and these differences were statistcally significant at the 1% level. It is obvious that the main cause of difference in average hatchability between the purebreds and F₁ hybrids was the presence of embryos found dead in the later period of incubation. The percentages of embryos found dead at various periods of incubation were remarkably higher in BPR than in any other group.
3) The non-genetic abnormalities observed were classified according to defect types. The percentages of abnormalities found in various groups are given in Table 3. The percentage of abnormalities was higher among BPR-maternal embryos than WL-maternal ones (BPR-maternal groups=0.52% vs. WL-maternal groups=0.160) and this difference was close to the significance level (x²=3.34, .10>P>.05). The difference of 0.27% in occurrence of abnormalities between the purebreds and F1 hybrids (purebreds=0.15% vs. crossbreds=0.42%) was not statistically significant.