Reproductive and Maternal Behavior of Livestock - Genetics and the Behavior of Domestic Animals - page 167

comparing estrus detection effectiveness between bulls and human sourced
systems have not ruled out the possibility that biostimulation could influence
female sexual activity ( Rekwot et al., 2001 ).
A positive effect of biostimulation on age of puberty in females, has been
reported in Bos taurus ( Chenoweth and Landaeta-Hern´ndez, 1998 ) and Bos
indicus heifers ( Oliveira et al., 2009; Rekwot et al., 2000 ) although other
studies could not demonstrate such an effect ( Berardinelli et al., 1979;
Roberson et al., 1987; Wehrman et al., 1996 ). It is possible that confounding
factors include social, managerial, and nutritional effects as well as genetic
influences.
A number of factors can influence the effectiveness of biostimulation in
different species and we could assume that this is also true of cattle. These
include social effects, stress, novelty of male introduction, and effectiveness
of the stimulating male. The latter can embrace age, dominance, experience,
sex-drive, and relative size. An example is illustrated by ongoing work in
Venezuela (Landaeta-Hern ´ ndez, unpublished data) in which differences
occurred in the responses of Bos indicus cross females served by bulls of dif-
fering relative size and experience. Here, the number of served and/or preg-
nant cows after 90 days of exposure to males above 400 kg was higher
(P

0.005) than in cows exposed to young males below 400 kg. (Landaeta-
Hern´ndez, unpublished data) and Bos indicus females appeared to be more
receptive to males of Bos indicus type than were Bos taurus females.
Biostimulatory influences are not limited to the direct presence of the
male, as both the presence of estrous females as well as those which have
been testosterone-primed may also affect the resumption of ovarian activity
after calving, the intensity of estrus expression, ovulation rates, and fertility
under conditions of natural mating to a synchronized estrus ( Burns and
Spitzer, 1992; Chenoweth and Lennon, 1984 ).
In contrast with the relatively large amount of evidence supporting the
effects of biostimulation in beef cattle, corresponding studies in dairy cattle
are relatively scarce and biostimulatory effects on either the resumption of
ovarian activity postpartum and estrus expression have not been conclusively
demonstrated ( Roelofs et al., 2008; Shipka and Ellis, 1998, 1999 ). For exam-
ple, in a study with Brown Swiss cows in Mexico ( Izaguirre-Flores et al.,
2007 ), biostimulation was reported to reduce the interval from calving to
conception, although this finding may have been compromised by factors
such as low milk production, nutrition and study design as suggested by an
earlier New Zealand study (Macmillan et al., 1979).

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REPRODUCTIVE BEHAVIOR IN SHEEP AND GOATS
Sheep and goats are seasonally polyestrus, with breeding season length being
influenced by both genotype and environment ( Hulet et al., 1975 ). For exam-
ple, female Alpine and Saanen dairy goats cease ovulating for much of the