Reproductive and Maternal Behavior of Livestock - Genetics and the Behavior of Domestic Animals - page 163

The role that genetic influences play on the expression of bull sex-drive
has been confirmed in a number of studies. An early classic study was that
of Bane (1954) who, despite raising six pairs of monozygous twin bulls on
differing regimes, observed greater similarity within than among pairs in
mating behavior and temperament. Subsequent studies have established that
sires and lines are significant sources of bull sex-drive variation (see review
by Chenoweth, 1981 ). A heritability estimate of 0.59

0.16 was obtained
for serving capacity in a study of 157 paternal half-sib bull groups in
Australia ( Blockey et al., 1978 ). In addition, high sex-drive in bulls is not
necessarily in those with either superior production traits (average daily gain
or final test weight) or high social ranking ( Ologun et al., 1981 ). It is appar-
ent that conventional breeding soundness criteria, such as scrotal circumfer-
ence and semen traits, are not predictive of bull sex-drive ( Chenoweth,
2000 ) indicating that these are separate traits. This raises the possibility that
bulls of high sex-drive may not be either dominant or fertile, which has
important implications for the management of cattle breeding programs.

6

Female Reproductive Behavior
The duration of observable estrus in Bos indicus females is usually shorter and
its external signs less intense than in Bos taurus cattle ( Chenoweth, 1994b;
Galina et al., 1996 ). Part of this difference may be due to difficulties encoun-
tered with estrus detection in Bos indicus females, especially as they tend to
display behavioral estrus during the evening hours ( Chenoweth, 1994b ). In
Bos taurus cattle, the mounted female is more likely to be in estrus than the
mountee, particularly if she exhibits immobility ( Baker and Seidel, 1985 ),
whereas social status of Bos indicus females can influence an individual's
chances of being ridden by another female ( Mukasa-Mugerwa, 1989; Orihuela
et al., 1988 ). Also, some high-ranking Bos indicus females appear to not par-
ticipate in mounting behavior at all, either actively or passively. If so, this dif-
fers from Bos taurus cattle in which cows higher in the social order are usually
those which initiate mounting activity ( Mylrae and Beilharz, 1964 ).
Females of dairy breeds reputedly exhibit more mounting behavior than
those of beef breeds ( Baker and Seidel, 1985 ), possibly because of greater
selection for this trait in systems where males are largely or completely
absent. In this respect, the widespread use of artificial insemination in dairy
cattle has probably encouraged selection for overt estrous behavior as
females showing weak estrus signs would tend not be inseminated
( Hohenboken, 1987 ). Despite this, intense genetic selection towards highly
efficient dairy cows has occurred over the past 50 years with probable
adverse effects on reproductive efficiency and fertility ( Lucy, 2001 ). This
reinforces observations that high milk production in dairy cows may be asso-
ciated with weak or irregular estrus ( Morrow, 1966; Walsh et al., 2011 ),
with poor estrus expression being a major contributor to reduced fertility