In conclusion, we found no evidence that broiler breeder females inherently discriminate against broiler breeder males. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Broiler breeder; Mate choice; Genetics; Sexual behaviour; Chickens
1. Introduction
In this study, we were interested in investigating if broiler breeder females display an inherent male-strain preference and how this preference might be affected by sexual
experience. The commercial broiler breeder industry has reported problems of male aggression
Ž .
towards females in recent years Mench, 1993 . Outbreaks of severe male aggression occur sporadically and causal factors remain elusive. Producers report that aggression is
particularly common when males are mixed with sexually underdeveloped females Ž
. Millman, 1999 . When males are extremely aggressive, broiler breeder females remain
on raised slatted areas in the barn and are therefore less accessible to males. Since females often have lacerations on the back of the head or along the torso, it is likely that
they learn to remain on the slats to avoid injury. However, it is also possible that avoidance by females precedes injury and male aggression results from frustration. It
may even be that problems of male aggression arise in response to low sexual receptivity of broiler breeder females.
Our previous research suggests that broiler breeder females display sufficient levels of sexual motivation to allow full sexual intercourse, particularly when housed with
Ž .
laying strain males Millman et al., 1996 . Broiler breeder females housed with laying strain males had significantly higher fertility than females housed with broiler breeder
males, and females responded to displaying laying strain males by approaching them more frequently than broiler breeder males. Broiler breeder males displayed less
courtship behaviour and performed more forced copulations than did commercial laying
Ž .
strain males. For further discussion of this point, see Millman 1999 . It is not clear if differences in females approaching males resulted from the effectiveness of courtship
displays by laying strain males, or because females found laying strain males inherently Ž
. more attractive. Kruijt 1964 found that junglefowl males could learn to change their
courtship displays. Frequency of one courtship element, such as waltzing, could be increased by reinforcement with access to a female. When a different element, such as
cornering, was reinforced, males decreased frequency of waltzing and increased corner- ing. If females in our study found laying strain males more attractive, they may have
been more attentive to the courtship displays of these males. Consequently, courtship displays by laying strain males may have been reinforced more frequently than displays
by broiler breeder males.
The preference by females for males of one strain over another could result from differences in the physical conformation andror the behaviour of males. Previous
research indicates that female domestic fowl prefer same-strain males based on differ- Ž
ences in morphology rather than courtship behaviour Lill, 1968b; Lill and Wood-Gush, .
1965 . However, this research involved Leghorn and crossbred strains and the results may not be applicable to modern broiler breeder males, which have been dramatically
altered through selection for meat traits, with massive muscle development particularly in the breast.
Although some studies found male displays to be important in mate choice by Ž
females Zuk et al., 1992, 1995; Collins, 1994; Chappell et al., 1997; Leonard and .
Ž Zanette, 1998 , others did not Lill and Wood-Gush, 1965; Zuk et al, 1990c; Ligon and
. Zwartjes, 1995; van Kampen, 1994 . In our previous study, broiler breeder strain males
Ž .
performed less courtship behaviour than laying strain males Millman et al., 1996 . It is also possible that limitations of conformation may make courtship displays by broiler
breeder males less effective in releasing female sexual motivation than displays by laying strain males.
The objectives of this study were to tease apart mechanisms of female mate Ž .
Ž . preference involving 1 male physical characteristics and 2 male behaviour. We also
wanted to determine if sexual experience would affect mate preferences by females. Our hypothesis was that females would discriminate against broiler breeder males.
2. Materials and methods
