Influence of Eqvalan (R) (ivermectin) on quality and freezability of stallion semen

The objective of this study was to evaluate the effect of Eqvalan(R) (iverm ectin) on stallion semen quality and freezability. Experiments were perform ed using 22 Freiberger stallions, randomly divided into a control and test group. Semen was collected once a week for 17 weeks from October 1997 to Fe bruary 1998. Eqvalan(R) was given orally to all stallions of the test group at a therapeutic dose of 0.2 mg ivermectin/kg. Besides measuring the scrot al width, ejaculates were collected to determine the volume, concentration, and the motility and morphology (normal sperm, major defects, vacuoles and acrosome defects). In addition, the motility and viability (fluorescence s taining with propidium iodide/SYBR-14) were tested in all frozen-thawed sem en samples. During the experimental period, stallions treated with Eqvalan(R) had signi ficantly better concentration (P < 0.0001) and motility (P < 0.0001) in fre sh semen compared to control animals. After freezing-thawing, the motility (P < 0.0001) and viability (P = 0.0003) of semen also increased significant ly for treated stallions. Regarding morphology, normal sperm (P < 0.0001), major defects (P = 0.0027) and vacuoles (P = 0.0236) were significantly bet ter in the Eqvalan(R) group. In addition to group differences we also obser ved a time effect on morphological parameters as shown by a decrease of nor mal sperm and an increase of major defects in both groups during the experi ment. Our results demonstrate that a single oral application of Eqvalan(R) did no t negatively influence the quality and freezability of stallion semen in th e nonbreeding season. Rather, it seems that Eqvalan(R) has a favorable effe ct on stallion fertility as most sperm parameters examined were significant ly improved in treated animals compared to control. (C) 2001 by Elsevier Sc ience Inc.