| Popis: |
The effectiveness of selection for hen-days without beak-inflicted injuries was studied. The base population was known to have a high incidence of beak-inflicted injuries when pullets' beaks were intact. Data from the foundation stock yielded nonsignificant family heritability estimates ranging from .05 to .17, depending on length of the test period (varying from 16 to 28 to 16 to 40 wk of age) and number of six-hen cages per family (one to three). Selection was practiced on sire family groups of either 30 or 36 pullets. Birds used for selection were housed six birds per cage and had intact beaks. The criterion of selection was mean hen-days without beak-inflicted injuries from 16 to 40 wk of age. Three selected and three unselected strains were involved. After two generations, mean hen-days without beak-inflicted injuries from 16 to 40 wk of age were 164.8 and 155.3 for selected and unselected stocks, respectively, yielding a realized family heritability of .65 ± .13 (SE). Selection did not appear to alter the relative frequency of beak-inflicted injuries by body regions affected; about 30% of all injuries involved the vent-cloacal area. Egg production traits were measured also. No differences were detected in Generation 1, but selected pullets had higher hen-housed rates of lay and egg mass in Generation 2. It is tentatively concluded that stocks having high levels of cannibalism when kept with intact beaks can benefit from selection against beak-inflicted injuries when evaluated by techniques similar to those used in the present study. |
