Changes in the frequency of the poll gene and the effect of polledness on production were measured from 1970 to 1979 in four closed lines of crossbred cattle. The lines were Africander cross (AX), Braham cross (BX) and two Hereford × Shorthorn (HS lines, one selected for production (HSS) and one a control line (HSR).
Calves were classified as horned, polled or scurred. Except in the HSS line, horned males were more common than horned females. Horned HS bulls sired only horned calves when mated to horned cows but corresponding matings of AX and BX breeds produced some polled progeny. The incidence of scurs was highest in the AX line, lowest in the HS lines and higher in males than females. These observations are discussed in relation to existing models of inheritance of horn-type.
Prior to 1970 the frequencies of the poll gene declined from their initial values in the BX and HS lines and increased in the AX line. These changes were ascribed to random genetic drift. After 1970 the frequency of the poll gene remained stable in all lines.
No significant differences were observed between horned and polled cattle in live weight, fertility or mortality rates indicating that polledness had no detrimental effect on production in these lines.