Testicular morphology and sperm content relative to age, antler status and season in axis deer stags ( Axis axis)

Abstract

Testes were collected from 192 axis deer stags ( Axis axis) in south Texas to quantify changes in testicular morphology and sperm content relative to age (juvenile: 1–2 years of age; mature: >2 years of age), antler status (hard antler; velvet/no antler) and season. Following harvest, morphological measurements of each testis were recorded, and the left testis and epididymis (caput, corpus and caudal regions) were homogenized individually for the determination of sperm content. In summer and autumn, 96.2% (102/106) of the stags harvested were in hard antler; in contrast to 23.3% (20/86) in the winter and spring. Testis weight and epididymal weight were positively correlated ( r=0.75; P<0.0001), as were testis weight and total testis sperm content ( r=0.63; P<0.0001), testis volume and total testis sperm content ( r=0.60; P<0.0001), and epididymal weight and epididymal sperm content ( r=0.72; P<0.0001). Sperm content per gram of parenchyma for juvenile stags was similar ( P>0.10) during spring, summer and winter, while total testis sperm content in spring and summer were greater ( P<0.05) than in autumn or winter. Juvenile stags tended to have greater ( P<0.08) testis sperm content per gram of parenchyma and greater ( P<0.05) total testis sperm content in velvet/no antlered than in hard antlered stags. For mature stags, total testis sperm content and total epididymal sperm content were greater ( P<0.05) in summer than during all other seasons. Irrespective of seasonal fluctuations in testicular and epididymal sperm content, at no time were stags found to be azoospermic. Testis weight, total epididymal weight, total testis sperm content and total epididymal sperm content were greater ( P<0.05) in mature hard antlered than in velvet/no antlered stags. These data indicate that while seasonal changes in testis sperm content and morphology do occur and pattern antler cycles in the axis stag, these changes are less pronounced than in more temperate species of cervids. These results support previous field-based observations regarding the capability of axis stags in Texas to maintain testicular function throughout the year regardless of antler status. Nevertheless, additional investigations are needed to further assess the breeding potential (i.e. fertility) and libido of axis stags relative to antler status and season.