Winter - Classical Mileend Alpacas

Jane Vaughan BVSc PhD MACVSc looks at the selection
of fertile male alpacas
20 Alpaca World Magazine Winter 2004/05
AND HOW
TO CHOOSE
THEM
Many alpaca breeders have a justifi ed
fi xation on body conformation and fi bre
characteristics of males during the
diffi cult process of selection of suitable stud sires.
Breeders should also include large testicular size
in the process to ensure males of high fertility are
selected. This will ensure males are more able to
pass on their genetics to more females, sooner and
thereby minimise generation intervals.
Male alpacas are usually born with descended
testes that are small, soft and diffi cult to
palpate (Sumar 1983, Bravo 1995, Fowler et al.
1998). Plasma testosterone levels are basal and
adhesions exist between the penis and prepuce
at birth. As males mature, the testes enlarge
and plasma testosterone levels increase (at
approximately 20 months of age in the majority
of alpacas; Bravo 1995). Rising concentrations
of testosterone allow the animal to grow and
put on body condition, develop secondary sexual
characteristics and apparently breakdown penopreputial
adhesions.
The onset of sexual maturity is often determined
by the age at which the penile adhesions disappear
and males become capable of a full erection, rather
than the time at which viable sperm are produced
(Smith 1999c). It has been observed in alpacas that
at one year of age 8–12% of males, at two years
of age 60–78% of males and at three years of
age 94–100 % of males have lost peno-preputial
adhesions ( Bravo et al. 2000). The variation in
age at which peno-preputial adhesions are lost
may be partially explained by plane of nutrition
as there is a correlation between body size and
mean testicular length and the wide variation
in testicular size at any one age or body size
suggests that other factors, probably genetic, are
also important (Galloway 2000). In South America,
alpacas are considered to have reached full sexual
development at fi ve years of age, at approximately
63kg body weight (Sumar 1983). This is a long time
to wait for access to genetics and breeders should
be selecting suitable males to decrease the age
of puberty in their stud sires and speed up genetic
gain.
SEASONALITY
Spermatogenesis occurs throughout the year in all
camelids and therefore mature males should be
fertile all year.
FERTILITY
Under conditions of natural mating, pregnancy and
subsequent parturition rates following a single