Jane Vaughan BVSc PhD MACVSc
Many alpaca breeders have a justified fixation on body conformation and fibre characteristics of males during the difficult 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 difficult 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 peno-preputial 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 1 year of age 8-12 % of males, at 2 years of age 60-78 % of males and at 3 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 5 years of age, at approximately 63 kg 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.
Spermatogenesis occurs throughout the year in all camelids and therefore mature males should be fertile all year.
Under conditions of natural mating, pregnancy and subsequent parturition rates following a single mating have been reported as low (Sumar 1985) and less efficient than other farm species (Wiepz et al. 1985). However, there have been reports of 21 out of 28 (75 %) female llamas pregnant after two matings 4-8 hours apart (Adams et al. 1990), a 46 % parturition rate in single-mated llamas (Condorena et al. 1988) and 34 out of 70 (49 %) females pregnant 60 days after a single random natural mating (Vaughan et al. 2002). These rates compare favourably with conception rates in other domestic livestock and suggest that unsuitable reproductive management, nutritional deficiencies and inbreeding contribute to low fertility (Parraguez et al. 1997). The sperm concentration required for successful fertilisation and pregnancy is not known, but intracornual semen deposition of semen during copulation may be an adaptation to overcome relatively low sperm concentrations in ejaculates (Brown 2000).
To maximise the number of sperm per ejaculate and matings per day, it has been recommended to select males with large testicular size on the assumption that the direct relationship between testis size and sperm production in other domestic livestock also occurs in camelids (Sumar 1983, Smith 1999c, Brown 2000, Galloway 2000). Mean testicular length (the average length of left and right testes) is correlated with testicular weight (Galloway 2000) and may be used as a simple means of assessing testicular size in alpacas. Mean testicular length may be used to estimate the likelihood of sperm production in alpacas
Differences in sperm output are largely due to testicular size in bulls. Testicular size is highly inherited in bulls. These two observations indicate that testicular size is important in selection and evaluation of sires. For example, Pugh (1999) observed male llamas with testes 3.5 x 2.9 cm achieved 21/30 (70 %) pregnancies, while males with smaller testes (2.5 x 2.2 cm) only achieved 12/30 (40 %) pregnancies. Body size has also been correlated with mean testicular length and suggests that nutrition is one important factor in determining testicular size. Precocious behaviour, mating ability (no penopreputial adhesions) and sperm production in yearlings and are also desirable traits in selection programmes (Sumar 1983, Galloway 2000).
The number of matings performed in one day by a male influences fertility. Bravo et al. (1997d) observed that male alpacas bred 2 or 4 times per day achieved a 77 % pregnancy rate, while those bred 6 times per day achieved a 59 % pregnancy rate. It was proposed that rates declined in response to exhaustion of sperm reserves and that the number of consecutive days that matings occur on also influences fertility (Bravo et al. 1997d). Copulation time decreased over consecutive breeding days and the percent pregnant decreased from 71 % on Day 1 of breeding, to 0 % on Day 9 and studies by Bravo (1995) indicate that three to 4 matings per day for 4 to 5 days may not compromise fertility in male alpacas.
WHAT CAN YOU DO ABOUT SELECTION OF FERTILE MALES?
When selecting males for breeding, breeders need to select early maturing males with large testicular size,
in conjunction with appropriate body conformation and fibre characteristics. Aim to select males with more sperm, sooner! Minimise generation intervals by minimising time at which puberty is reached through genetic selection of early maturing males and good nutrition of lactating females, crias and tuis. Breeders are encouraged to measure testicular length and body weight/body size index every 6 months from 12 to 36 months of age to assist with selection of potential stud sires. Record your findings and select males accordingly.