Avian Infectious Bronchitis Virus: A Possible Cause of Reduced Fertility in the Rooster

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Abstract
The formation of epididymal stones in the rooster epididymis is a widespread problem that has detrimental effects on sperm production and fertility. The cause of epididymal stones is unknown, but an infectious agent, the avian infectious bronchitis virus (AIBV), has been implicated. The goal of this study was to determine if administering the live attenuated AIBV vaccine to male chicks increases the incidence of stones in the epididymal region of the adult rooster. Specific pathogen free (SPF) Leghorn roosters were divided into two groups: a vaccine-free group (n = 7) and a group vaccinated with AIBV (n = 12). The vaccine was administered orally at 2, 4, 10, and 14 wk of age. Blood was drawn weekly to monitor antibodies to AIBV. At 26 wk of age, blood was obtained to determine testosterone concentrations, and reproductive tracts were removed to analyze daily sperm production and to detect epididymal stones. Nine of 12 vaccinated roosters developed stones, whereas those not given the vaccine did not develop stones. Serum testosterone concentrations were significantly (P < 0.05) reduced in vaccinated roosters with epididymal stones (3.6 +/- 0.30 ng/ml) when compared with nonvaccinated roosters that did not have epididymal stones (7.0 +/- 1.63 ng/ml). Testis weight was significantly (P < 0.05) reduced in vaccinated roosters with epididymal stones (12.1 +/- 0.76 g), as compared with nonvaccinated roosters without epididymal stones (15.2 +/- 0.81 g). Daily sperm production was significantly (P < 0.05) decreased in vaccinated roosters with epididymal stones (5.03 +/- 0.31 x 10(8) sperm/testis/day) when compared with nonvaccinated roosters without epididymal stones (7.43 +/- 0.52 x 10(8) sperm/testis/day). Comparing daily sperm production on a per gram basis, vaccinated roosters with epididymal stones had 4.38 +/- 0.14 x 10(7) sperm/g of testis, which was significantly (P < 0.05) smaller than nonvaccinated roosters without epididymal stones, which had 5.17 +/- 0.17 x 10(7) sperm/g of testis. We conclude that the use of a live attenuated AIBV vaccine increases the incidence of epididymal stones in roosters, resulting in decreased sperm production and decreased serum testosterone concentrations.