轻重型鸡生长性能比较

进行两次试验,比较轻(蛋鸡)、重(肉鸡)型鸡0—10周的生长发育及营养物质利用。试验1,白洛克和白来航公鸡喂以能量相同,高、中、低蛋白水平(0—4周,23%、21%、19%;5—10周,22%、19%、16%)的饲粮,以比较两类型鸡在不同蛋白水平下的反应。试验2,比较两类型鸡的生长和营养物质利用在性别间的差异,以及把采食量调整到同一水平后的生长性能。结果表明:在相同性别同一蛋白质水平条件下,肉鸡增重均为蛋鸡的两倍。肉鸡公鸡为母鸡的1.23倍;蛋鸡公鸡则为1.24倍。肉鸡在中、低蛋白水平生长较好;而蛋鸡在高、中水平为佳。两类型鸡采食同等料量,肉用公母鸡的体重仍分别为蛋鸡的1.25和1.62倍,即不同类型鸡生长快慢之别不能仅从采食量本身解释,而饲料转化效率的差异同样重要。两类型鸡组织器官随周龄的发育以及与空体重的异速生长模式相似。饲粮蛋白水平对内部组织器官发育没有明显影响,但限食明显影响其发育。10周龄时,肉用公、母鸡胴体能值比蛋鸡分别高13.92%和20.99%;粗脂肪含量分别高3.66%和4.14%;而胴体蛋白含量后者比前者高1.35%和2.14%,母鸡间差异较大。在供试蛋白水平下,随饲粮蛋白质增加,胴体能值、胴体脂肪、饲粮粗蛋白和代谢能利用率下降,肉鸡反应更为明显,而对胴体蛋白影响不大。两类型鸡饲粮粗蛋白和代谢能利用率随周龄增加近于直线降低,其幅度随蛋白水平增高而加大。肉鸡饲粮代谢能利用率在各蛋白水平均高于蛋鸡,而粗蛋白利用率除低蛋白饲粮外,其它水平肉鸡高于蛋鸡。公鸡粗蛋白质利用率高于母鸡,代谢能利用率母高于公,但限食后相反。根据代谢能进食量和沉积能推算的维持代谢能需要(MEm),品种间无明显差异(P>0.05),而饲粮代谢能用于沉积的效率肉鸡高于蛋鸡,但尚未达显著水平(P>0.05)。注:粗蛋白利用率=体沉积蛋白质/食入粗蛋白×100% 代谢能利用率=体沉积能/食入代谢能×100%

A COMPARISON OF THE GROWTH PERFORMANCE OF LIGHT-TYPE AND HEA VY-TYPE CHICKENS

Two experiments were performed to compare the growth and developmeat and nutrient utilization of light-type (layer) and heavy-type (broiler) chickens during ten weeks. Experiment I, day-old male White Rock and White Leghorn chicks were reared on diets with identical metabolizable energy (ME), but three crude protein(CP) levels(0-4weeks,23%、21%、19%,5-10weeks, 22%、19%、16%) to compare the response of two chicken types under different CP levels. Experiment II, a comparison of the difference between sexes of two chicken types in growth and nutrient utilization and growth performance after feed consumption was adjusted to the same level. Chickens in both experiments were reared in the wire floor battery and feeding and management were carried out normally. Body weight and feed consumption of each group were recorded weekly. The chickens were slaughtered biweekly to measure their internal organs and analyse their body chemical components. Results indicated that broiler chicks gained twice as much as layer chicks of the same sex and same protein level. Broiler males gained 23% more than females. Layer males gained 24% more weight. Broilers grew better on the medium or low protein diets, but layer type did better on the high or medium levels. When the two chicken types were fed equal feeds, the pody weight of the male and female broilers were still 25% and 62% more than layer-type males and females respectively, i. e. the faster growth rate of broilers can not be explained only by higher feed consumption alone, it was mainly due to difference in feed conversion ratio. Development of tissues and organs of the two types by week and the model of allometrie growth pattern were similar. Dietary CP levels did not significantly affect the development of tissues and organs of both strains. But feed restriction significantly affected their development. At the tenth week, carcass energy contents of the male and female broilers were 13.0% and 20.99% more than that of respective layers. And carcass fat was 3.6% and 4.I4% higher. For carcass protein the latter was 1.35% and 2.41% higher than the former respectively, the difference being larger for females of the two chicken types. The carcass energy, carcass fat and efficiency of dietary CP and ME utilization decreased with increase in dietary CP level, with carcass protein practically unaffected, response of broilers being more marked. Efficiency of dietary CP and ME utilization decreased almost linearly with increasing age, and discrepancy increased with increase in protein level. Efficiency of ME utilization of broilers was better than that of layers at all protein levels, and, likewise was the efficiency of CP utilization, except at the low protein diet. Males utilized dietary CP more efficiently than females. As for efficiency of ME utilization, the female was better than the male. However, when the broiler chicks were restricted in feed, opposite result was obtained. MEm estimated according to the regression of IME on RE was not significantly different between the two types (P>0.05). The efficiency of dietary ME for retention of broilers was slightly better than that of layers, difference did not approach significant level.