ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 82 Number 4
Factors affecting serum testosterone levels in growing Syrian Awassi ram lambs. (344)
Fifteen Syrian Awassi ram lambs (nine single and six twin births), born between 20 December 2000 and 14 February 2001 were used in the experiment starting at an age of one week. Jugular blood samples were collected from the ram lambs at weekly intervals during the whole study which lasted for a period of 10 months. Serum concentration of testosterone was determined in the aforementioned blood samples using a radioimmunoassay technique. Lambs were also weighed at birth and once a week throughout the study period. Results showed that testosterone was detectable in the blood of ram lambs as early as the first month of age (0.23 ± 0.12 nmol L-1), with no significant difference (P > 0.05) between single and twin births (0.24 ± 0.09 vs 0.21 ± 0.15 nmol L-1). A sharp increase in testosterone concentration was recorded at the age of eight months in single (7.26 ± 3.29 nmol L-1) and twin (5.32 ± 2.99 nmol L-1) births. The mean serum concentration of testosterone during the study period was 3.29 ± 2.73 and 2.54 ± 2.15 nmol L-1 for the single and twin births, respectively (the overall mean being 3.00 ± 2.49 nmol L-1). Results also indicated increases in body weight with advancing age and that the body weight in single births was not significantly (P > 0.05) higher than that in twin ones throughout the study period. In addition, clear increases in the mean body weight were also recorded at the age of eight months in single (48.5 ± 9.3 kg) and twin (44.1 ± 10.8 kg) births (the overall mean body weight being 34.5 ± 15.2 kg). A highly positive correlation (r = 0.95. P < 0.0001) was found between serum concentration of testosterone and lamb body weight during the first 10 months of age. It could be concluded that the concentration of serum testosterone in Syrian Awassi ram lambs can be detected at an early age of one month, that such lambs reach puberty at an age of around eight months with a mean body weight of around 47 kg and that the type of birth, weight of birth, or weaning weight had no significant effect on the concentration of their serum testosterone.
Keywords: Testosterone; Radioimmunoassay; Ram lambs; Syrian Awassi; Single births; Twin births; Birth weight; Weaning weight; Body weight; Puberty