DIRECT AND INDIRECT EFFECTS OF THE FRIZZL E GENE (F) FOR THE PRODUCTIVE ADAPTABILITY OF LAYERS

The objective of the present investigation was to study the influence of the autosomal, incompletly dominant frizzle-gene ''F'' and the impo rtance of interactions between the three major genes i.e. naked neck g ene (Na), dwarf gene (dw) and the frizzle gene (F) on the productive a daptability of laying hens to a long-term constant hear stress. The da ta of 1534 laying hens were collected in two successive experiments. T he experimental hens were derived from crossing of a medium heavy sire line (Dahlem Red), heterozygous for the three genes (Nana Ff Dwdw) wi th a commercial dam line. Eight different genetic groups were obtained . The hens were kept for 13 laying-periods of 28 days each, half under temperature (18-20-degrees-C, 60-75% rel. H.) and half under constant high (32-degrees-C, 45% rel. H.) ambient temperature. During the test ing period egg performance traits (i.e. egg number, egg weight and fee d intake) and physical traits (i.e. body weight, body temperature and feather intensity) were measured. The most important results are as fo llows: 1. Independently of environmental temperatures, the F-gene caus ed a reduction of feather intensity of more than 40% (in respect to th e metabolic body weight) and body temperature increased slightly but s ignificantly. 2. Under heat stress the introduction of the F-gene lead s to a relative increase in feed-intake as well as improvement of layi ng performance and feed efficiency in comparison to the reductions in normal feathered birds. 3. The single effect of the F-gene under heat stress in inferior to that of the naked neck gene. 4. The results show ed a superiority of the combination type (Nana Ff) under the permanent longtermed heat stress (i.e. 48%) higher egg mass then the normally f eathered genotype nana ff). 5. The effect of the dwarf gene, also in c ombination with the two feathering major genes, resulted in a reduced performance. But reduction in feed intake was higher than reduction in the available energy supply for egg production. 6. Under high tempera ture, therefore, the dwarf naked neck combination types (Nana ff dw-; Nana Ff dw-) showed best performance for all biological and economical efficiency traits. The investigation documents that the frizzle gene increases the productive adaptability of high temperatures of laying h ens, although it is inferior to the naked neck gene in its single effe ct. Therefore research in the tropics is needed to clarify which combi nation of the three major genes is most efficient under the respective environmental conditions.