168 The relationship between age, ossicone volume, and testosterone concentration for prediction of sexual maturity in wild South African giraffes

Wildlife species are disappearing at an accelerated rate due to human activities and climate change. Recently, there has been breakthroughs in reproduction biology that can help in sustainable conservation of wildlife. Knowledge generated from several studies and species indicates that there is a positive relationship between plasma testosterone concentrations with semen volume, sperm motility, and sperm concentration. Testosterone is also associated with secondary sex characteristics of the male, such as heavy weight, which in turn positively correlates with early attainment of puberty. There is limited scientific literature on studies examining potential connections among sex steroids, morphology, and reproductive state in wild giraffes. This research was aimed at investigating the relationship between ossicone volume, age, and testosterone production in wild South African giraffes. This study was conducted at Rooipoort Nature Reserve, a 44,000-ha private nature reserve in South Africa, on a population of South African giraffes (Giraffa camelopardalis giraffe). A total of seven adult giraffe bulls were immobilized, and blood samples, morphological measurements and age were obtained. Age estimates were based upon dental wear (by 6 years of age, giraffes have their complete set of adult dentition). Blood was collected from the jugular vein of the giraffes, using a 18-gauge blood collection needle attached to a red cap tube. Blood was allowed to sit and clot at 5°C over 24 h. Samples were centrifuged at 2500g for 10 minutes for complete separation and extraction of the serum. Serum samples were stored at −20°C until analysis. Testosterone concentration was analysed using ultra high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS). Sliding callipers were used to measure ossicones and testicles. Statistical tests were conducted using IBM SPSS Statistics (version 20), and comparisons among subjects were achieved with the Kruskal-Wallis analysis of variance test. Bivariate relationships were determined using the Spearman’s rank order correlation coefficient. The average testes volume among the seven male subjects was 163.17 to 647.96 cc. The 4-year-old giraffe bull had the smallest testes volume, compared with the 10-year-old giraffe bull. For the ossicone volume the 4-year-old bull recorded the smallest ossicone volume (249.38 ± 065) compared with the older bull (698.31 ± 124.9). Additionally, male age was significantly correlated with ossicone size (rs = 0.815, n = 7; P = 0.025). Testes volume was independent of circulating testosterone concentrations (rs = 0.607; P = 0.148), and testes size was not associated with ossicone volume (rs = 0.536; P = 0.215). However, a statistically significant correlation characterised the relationship between testosterone concentrations and ossicone volume (rs = 0.964; P = 0.001). It was concluded that testes and ossicone volume increased with age in giraffes and higher ossicone volume were positively associated with high circulating testosterone concentrations. For future studies, it is recommended that an increase in sample size and expansion of the study to other giraffe subspecies would assist greatly in setting up an ossicone and testes volume standards with age for an appropriate conclusion on puberty attainment in giraffes.