The objectives of this study were to induce ascites in three pure male line populations by subjecting them to cold stress, and to calculate heritability estimates for ascites (ASCITES) and the ratio of right to total ventricle weight (RATIO) in these populations under cold stress. Data were collected during the winter of 1993 to 1994 from 3,436 cockerels representing three commercial broiler breeder male lines. The male lines used in this study were characterized by: rapid growth rate and good feed efficiency (RG), moderate growth, good conformation, and excellent livability (MG), and maximum white meat yield and rapid growth (YD). Birds were cold stressed and euthanatized at 8 wk of age. Ratios of right to total ventricle weight and ascites (birds with fluid in the abdominal cavity) were recorded on every bird. Line means for the incidence of ascites were 17.5, 18.7, and 33.5% for RG, MG, and YD, respectively. Lines RG and MG did not differ from each other for ascites, but both were less than YD (P < .05). Means and standard deviations for the ratio of right to total ventricle weight (RATIO) were .299 +/- 0.9, .297 +/- .08, and .294 +/- .09 for RG, MG, and YD, respectively. Line means for RATIO did not differ. Heritability estimates of RATIO were .21 +/- .09, .21 +/- .09, and .27 +/- .08 for RG, MG, and YD, respectively; and heritabilities of ascites were .36 +/- .10, .11 +/- .08, and .44 +/- .09, respectively. Phenotypic correlations of ASCITES with RATIO were .54, .43, and .50 in RG, MG, and YD and genetic correlations of ASCITES with RATIO were .69 +/- .13, .46 +/- .33, and .78 +/- .10 in RG, MG, and YD, respectively.

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A series of experiments was conducted to estimate phenotypic correlations between incubation characteristics, and to evaluate the effects of cold stress and genotype during incubation on chick weight, egg weight loss, hatching time, and embryonic mortality. Eggs were cooled at 18 or 24 C, for 12, 24, 36, 48, or 72 h beginning on Day 8, 12, 14, 16, or 18 of incubation. Other eggs were cooled intermittently for 6 h every 48 h or 12 h every 96 h. A control group in each experiment was not cold stressed. Results indicated a low and negative correlation between hatching time and chick weight, and a low and positive correlation between hatching time and weight loss from transfer to hatching when variability due to egg weight was removed. Chick weights at hatching were lower in chicks from cooled eggs than those of chicks from eggs incubated under normal temperature. The chicks from cooled eggs were more susceptible to dehydration during holding in the hatcher. Incubation times were delayed approximately as long as the times of embryonic cooling. Embryonic mortality was significantly increased under continuous (single period) cold stress, but not under intermittent cooling (6 h every 48 h). Significant genotype by environment interactions were found in the response of embryos of various strains to cold stress. Exposure for 36 h or longer had detrimental effects on chick weight and embryo viability, but these effects were modified by interactions among the factors involved. The results indicated that embryos from cooled eggs lose more weight during incubation and that the neonatal chicks are more susceptible to dehydration during holding time, and have a longer incubation period, and a greater embryonic mortality.

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