蛋呈椭圆形，指数超过1.35的蛋呈细长型，不足1.30的呈近似球形。放养组的蛋形指数大于笼养组，蛋形偏椭圆，笼养组蛋形偏球形，与顾荣等[114]以如皋黄鸡为试验对象得出的结论一致。蛋壳厚度也是一项重要指标，蛋壳厚度大，其抗压能力也较强。这一点对于鸡蛋的运输和保存上具有重要作用，可有效避免鸡蛋在长途运输中发生破碎，且能防止鸡蛋中水分的过度蒸发。黄山黑鸡笼养组鸡蛋蛋壳厚度显著高于放养组鸡蛋，与笼养组种鸡全价日粮钙磷营养供应相对平衡有关。王晓亮等[115]报道表明，放养下的绿壳蛋鸡的鸡蛋在蛋壳厚度方面与笼养的无明显差异。蛋壳颜色通常被消费者作为一种质量变量，颜色比较整齐一致的深褐色蛋在多数情况下会对消费者产生强烈的吸引力。笼养组与放养组鸡蛋的蛋壳颜色差异显著，放养鸡的蛋壳颜色比笼养鸡浅，与王晓亮的研究结果一致。
本研究放养鸡种蛋受精率和孵化率低于笼养鸡，胚胎死亡率高于笼养，与周淑亮等[116]以华北柴鸡作为研究对象得出的结论一致。放养鸡种蛋死胚率高的原因可能与放养鸡种蛋卫生条件差和种蛋收集不及时有关。Buhr等[117]研究发现种蛋的胚胎成活率与种蛋的干净程度有关，脏蛋的死胚率明显高于表面洁净的种蛋。放养鸡大多数是采用产蛋窝的方式收集鸡蛋，由于产蛋窝的垫料不经常更换，因此会受到粪便、泥土等污染，导致鸡蛋的污染，从而造成种蛋的受精率和孵化率下降。另外，由鸡白痢检测结果可知，放养组鸡白痢阳性率要高于笼养组，成年鸡感染鸡白痢后，种蛋的受精率和孵化率也会明显降低[85]。Fasenko等[118]的研究表明种蛋的收集频率影响鸡的孵化性能，放养鸡种蛋通常是一天收集一次，这就可能造成种蛋在产蛋窝中受到长时间的污染。
本次孵化试验还发现笼养鸡种蛋孵化出的雏鸡初生重明显高于放养，杨海明等
[119]
的研究发现蛋重大，雏鸡初生重就大，蛋重与雏鸡初生重呈强正相关。本次试验
中笼养鸡种蛋蛋重明显高于放养，蛋重大的种蛋中内容物及营养物质多，使得胚胎在发育过程中所吸收的营养物质就越多，在同一生长条件下增重就越大，雏鸡的初生重也就随之增大。
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4 结论
1. 笼养组泄殖腔棉拭子检测p27抗原阳性检出率为19.6%，高于放养组的7.8%。笼养组种蛋蛋清检测p27抗原阳性率为7.8%，高于放养组的3.3%。笼养组子代胎粪阳性率为3.4%，高于放养组的2.9%。
2. 笼养组各日龄鸡白痢阳性率分别为0%、1.01%、2.38%、1%和0%，放养组为7%、7.44%、3.13%、2%和1%，放养组231日龄、251日龄、274日龄、301日龄和327日龄的鸡白痢阳性率均高于笼养组。
3. 笼养组黄山黑鸡种蛋蛋重为48.1 g，高于放养组的45.0 g；笼养组种蛋蛋壳厚度为0.423 mm，高于放养组的0.416 mm；笼养组种蛋蛋壳颜色为41.3，放养组为46.6，笼养组蛋壳颜色深度高于放养组；而放养组黄山黑鸡种蛋蛋形指数为1.31，优于笼养组的1.29。
4. 笼养组黄山黑鸡种蛋的受精率为93.98%，受精蛋孵化率为96.94%，入孵蛋孵化率为91.10%，分别高于放养组的93.46%、95.52%、89.26%，笼养组黄山黑鸡种蛋的死胚率为3.06%，低于放养组的4.48%。
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