The effects of recessive white and dominant white genotypes on early growth rate.

The purpose of the studies reported herein was to determine whether the depressing effects on growth rate of dominant white (I) and recessive white (c/c) are additive or possibly interact with each other. A synthetic stock was used that was segregating for both dominant white and recessive white. Using phenotypic observations of down color and juvenile plumage color; it was possible to identify the genotypes at the I and C+ loci and to utilize a factorial experiment that provided for an evaluation of interaction effects between the loci. Five replications of this design were conducted with the following results: 1) the main effect of dominant white on 6 and 8 week body weight was not statistically significant; 2) recessive white consistently depresses early growth rate and the difference (congruent to 4%) between C+/- vs. c/c was highly significant (P less than .01); 3) there was a significant interaction (P less than .05) between I and c indicating that depressing effects of these loci are not additive. It does not appear to be necessary to eliminate (I) from recessive white broiler stocks, but it would be economically advantageous to remove hypostatic (c) from dominant white lines.