Relative Efficiency of Selection for Performance of Birds Housed in Colony Cages Based on Production in Single Bird Cages

Relative efficiency of selection based on sire families housed in individual versus colony cages was determined from the genetic correlation of production traits observed in the two cage environments. Two separate experiments, using a sample from the North Central Randombred White Leghorn Population, were conducted simultaneously to compare production in single cages with that in 4-bird and 9-bird colony cages, while initially holding density constant in the colony cages (413 cm2/bird). In each experiment, sire families were split between single and colony cages in a replicated manner. Records were obtained from 20 to 72 weeks of age on eggs per hen-day (EHD), egg weight (EW), days survival (DS), egg mass (EM), and eggs per hen housed (EHH). The mechanisms operating to reduce production in colony cages were shown to be cumulative in nature. Reductions of EHH and EM in 4-bird cages were due to a decline in EHD per bird. Further reductions of EHH and EM in 9-bird cages were due to increased mortality (DS). The only genetic correlation significantly (P<.05) less than unity was for DS between single and 9-bird colony cages. Evidence was presented that showed that EHD increased in 9-bird cages in which one or two birds had died, while production in single cages was maximum when no deaths had occurred. The implication is that selection in colony cages for increased production may result in increased mortality because optimal production occurs after one or two deaths. Furthermore, selection for improved performance in single cages may not improve survival in colony cages because competition is eliminated in single cages. Due to the conflict between production of the individual hen and that of the colony as a whole, current selection procedures are not appropriate for maximizing performance in large colony cages. The optimal method is not clear as present selection theory is inadequate.