The effect of the gene for polledness on conception rate and litter size in the Damascus goat

Abstract

Data on 1 709 matings and 1 247 parturitions were used to study the effect of the gene for polledness on conception rate and litter size in the Damascus breed of goat in Cyprus. With one exception all polled sires used in the study proved to be heterozygous Pp for the polled factor P. There was consistent excess of males in the offspring of all mating types with an overall proportion of males (53.1 p: 100) significantly different from the 50:50 ratio. Intersexes (6.0 p. 100) were found only when both parents were polled (Pp X Pp matings). The percentage of intersexes corresponds to an expressivity γ2 = .48 of the P genes for that trait in the PP females. Among alpine breeds y, was between .44 and .57. The percentage of males in excess corresponds to an expressivity of γ1= .16 of the P gene for that trait in the PP females (γ1= .43 to .56 in alpine breeds). Theoretically this excess must not been found in horned X polled and horned X horned crossings where no PP genotypes are produced. This discrepancy, as well as the low value of γ1 in the Pp polled X Pp polled matings has not been explained. Conception rate for polled (Pp) females was 74.7 p. 100, non significantly different from that of pp ones (76.4 p. 100). Litter size at birth for resp. all born and born live kids was 1.88 and 1.82 in polled goats (Pp) while it was resp. 1.75 and 1.71 in horned ones. This gives coefficients of surprolificacy of 1.074 and 1.066 in the Pp females compared to the pp ones for a value of 1.06 reported in alpine breeds. There is a light but significant fertility disadvantage of the Pp (polled) males compared to the pp (horned) ones which gives a r, coefficient of compared fertility of .91 instead of 1.007 observed in alpine stocks. Such a disadvantage is also found at the conception stage. These slight discreapancies indicate one needs more precise analysis of the behaviour of 1 gene in the goat.