Appropriate Stocking Density And Group Size Of Caged Pullets

In previous studies,the effects of stocking density and group size are not only mixed up but also confounded by feeder or drinker space.Under the premise of ensuring the consistency of feeder space and watering density,we studied the separate and combined effects of these two factors on growth performance and stress sensitivity of pullets,tracking the follow-up effect of group environment during grower period on the production performance of laying hens,which laid a foundation for the scientific grouping of caged pullets.Trial 1 was conducted to establish the suitable stocking density of caged pullets.A total of 432 pullets were randomly divided into 3 groups at 10 wk of age,each with 12 replicates of12 birds.Pullets were respectively reared in a whole cage(1.48 m×0.68 m)(12 birds/m~2),3/4cage(16 birds/m~2)and 1/2 cage(24 birds/m~2)for group 1,2 and 3.In order to ensure the same feeder space and watering density for each pullet,we controlled the length of feed trough and number of nipple drinkers in each replicates.At the age of 13 wks,we selected 6replicates randomly from each group.Two pullets were chosen from each replicate to collect samples of blood and tissues.At the age of 16 wks,the remaining 6 repeats were sampled as described above.After that,pullets(the last 6 replicates)were transferred into the laying house and reared under the same environmental conditions(3 birds/cage,3 cages/replicate)throughout the production cycle.Results showed that carcass compostion of pullets(16 wk of age)was affected by stocking density.High stocking density increased the proportion of thigh muscle,ileum,femur and ovary(P<0.05).Since the feed intake wasn't changed,it seemed to be related to the reduced activities.Although stocking density had no effect on laying rate,egg mass and feed to egg ratio(P>0.05),high stocking density significantly increased mortality rate during the whole laying period(P<0.05).Therefore,we suggested the suitable stocking density of caged pullets at the age of 10 to 16 wks was 12-16 birds/m~2.Trial 2 was conducted to establish the suitable group size of caged pullets.A total of 324pullets were randomly divided into 3 groups at 10 wk of age,each with 12 replicates.In group1,12 pullets were reared in a whole cage(1.48 m×0.68 m)(12 birds/m~2);in group 2,9 pullets were reared in 3/4 cage(12 birds/m~2);in group 3,6 pullets were reared in 1/2 cage(12birds/m~2).In order to ensure that all pullets have the same feeder space and watering density,we controlled the length of feed trough and number of nipple drinkers in each replicate.At the age of 13 wks,6 replicates were randomly selected from each group and 2 pullets from each replicate were chosen to collect blood and tissue samples.At the age of 16 wks,the remaining6 replicates were sampled as described above.After that,pullets(the last 6 replicates)were transferred into the laying house and reared under the same environmental conditions(2birds/cage,4 cages/replicate)throughout the production cycle.Results showed that group size had little effect on growth performance of pullets and production performance of laying hens(P>0.05).There were some sporadic and irregular differences in blood biochemical parameters or liver index among treatment groups.However,the mortality showed an increasing trend for laying hens with large group size during the growing period.Therefore,we suggested the suitable group size of caged pullets at the age of 10 to 16 wks was 6-9birds/group.Trial 3 was conducted to investigate the combined effects of stocking density and group size during grower period on healthy production on caged layers.A total of 216 pullets were randomly divided into 4 groups at the age of 8 wks,each with 6 replicates.In group 1,6pullets were reared in 1/2 cage(12 birds/m~2);in group 2,12 pullets were reared in 1/2 cage(24 birds/m~2);in group 3,6 pullets were reared in 1/4 cage(24 birds/m~2);in group 4,12pullets were fed in a whole cage(1.48 m×0.68 m)(12 birds/m~2).In order to ensure that all pullets have the same feeder space and watering density,we controlled the length of feed trough and number of nipple drinkers in each replicate.At the age of 18 wks,we chose 2pullets from each replicate and collect blood and tissue samples.Results showed that there was an interaction of stocking density and group size on the growth and development of pullets.Birds with low stocking density and small group size(12 birds/m~2,6 birds/group)had significantly higher body weight and percentage of reproductive organ(ovary,oviduct)(P<0.05),which suggested that it is suitable for caged pullets to be reared with a greater space allowance and smaller group size.