Reproductive and Maternal Behavior of Livestock - Genetics and the Behavior of Domestic Animals - page 166

Another important cause of Bos indicus calf losses is the neonatal weak-
ness syndrome (also known as “weak calf” and “dummy calf” syndrome)
which is associated with high morbidity and mortality in young Bos indicus
calves ( DeRouen et al., 1967; Franke et al., 1975; Landaeta-Hern´ndez
et al., 2004c; Radostits et al., 1994 ). Affected calves show clinical signs
which include poor cognitive and sensory responses, poor or absent suckling
ability, difficulty in standing and movement and marked intolerance to cold
weather (see review by Landaeta-Hern´ndez et al., 2002b ). Although similar
symptoms occur in Bos taurus calves, the relatively high occurrence of this
syndrome in Bos indicus cattle in general, as well as its association with
certain sires and breed types, suggests a genetic association ( Landaeta-
Hern ´ ndez et al., 2004b; Rowan, 1992 ). More recently, a congenital myas-
thenic syndrome caused by homozigosity for 20 base pair deletion in the
CHRNE gene (CHRNE 470del20) was identified in Brahman cattle in South
Africa. The CHRNE 470del20 leads to a non-functional acetylcholine recep-
tor causing progressive muscle weakness and mortality in young calves
( Thompson et al., 2003, 2007 ). Rapid progress in defining cattle genetic
traits can be expected in association with the complete sequencing of the
bovine genome ( Elsick et al., 2009 ) which should ultimately permit genetic
modification and enhanced selection for desired traits, such as improved
maternal ability, while ensuring other favorable traits are not compromised.
Biostimulation in Cattle
The effect of the male, or male-like factors, on the physiological and
reproductive status of exposed females is part of a phenomenon termed
biostimulation ( Chenoweth, 1983; Chenoweth and Landaeta-Hern´ndez,
1998 ). Although biostimulatory effects do occur in cattle ( Chenoweth and
Spitzer, 1995 ), they tend to be less evident than in other livestock species
such as sheep or swine ( Rekwot et al., 2001 ). Biostimulatory effects can be
induced via a number of mechanisms including pheromonal, visual, audi-
tory, and mechanical as well as others which are as yet unknown. Genetic
influences are suggested by observations that individuals, breeds, and lines
differ in their ability to either cause or respond to biostimulation.
Early speculation on possible biostimulatory effects in cattle came from
breeding programs where natural breeding showed advantages over artificial
insemination. Subsequently, a number of studies confirmed a positive effect
on the resumption of ovarian activity in both Bos taurus and Bos indicus
beef breeds ( Chenoweth and Spitzer, 1995; Landaeta-Hern ´ ndez et al.,
2004a, 2008; P ´ rez-Hern ´ ndez et al., 2002; Rekwot et al., 2000; Soto-
Belloso et al., 1997 ). Positive effects of biostimulation on other reproductive
parameters such as estrous expression and length of first postpartum estrous
cycle have also been reported ( Berardinelli and Joshi, 2005 ; Landaeta-
Hern´ndez et al., 2004a, 2006 ). Here it is relevant that a number of studies