37 Use of Thermo-Resistance Test (Trt) to Evaluate Equine Cooled Semen Stored at 5°c

Abstract

Evaluation of seminal characteristics is an important step to predict the reproductive potential of equine semen in natural or AI programs. Thermo-resistance test (TRT) has wide acceptance among tests in the bovine species, mainly because of its high correlation with fertility field. However, the TRT for stallion semen has not been widely studied. The objective of this study was to evaluate the effective use of TRT for equine cooled semen diluted with different extenders. Three stallions of Mangalarga Marchador breed aged between 8 and 14 years were used. Five semen samples per stallion were obtained, collected 3 times a week, with the aid of an artificial vagina (adapted Hannover model) using mares in natural estrus as dummy. The semen was diluted in 2 extenders: skim dried milk-glucose (E1) and glycine-egg yolk (E2), packaged in samples containing 12 mL of diluted semen to reach a final concentration of 30 million viable spermatozoa mL-1 and then stored at 5°C in an Equitainer® for 24 h. The cooled semen was warmed at 37°C in a water-bath. Spermatozoal progressive motility and vigor of semen were evaluated at 0 (TRT0), 30 (TRT30), 60 (TRT60), and 90 (TRT90) min after the start of warming. Treatment differences for sperm parameters were determined using ANOVA. The average values of sperm motility during TRT0, TRT30, TRT60, and TRT90 in E1 and E2 were, respectively, (E1) 37.0, 31.3, 23.7, and 19.7 and (E2) 30.3, 23.7, 18.3, and 15.7. The average values of vigor during TRT0, TRT30, TRT60, and TRT90 in E1 and E2 were, respectively, (E1) 2.4, 2.03, 1.53, and 1.43 and (E2) 1.97, 1.53, 1.33, and 1.17. During the test, the progressive motility obtained with E1 was higher (P < 0.05) than that with E2, and is within the patterns of motility considered acceptable only at 0 and 30 min of TRT. The E2 extender gave the worst result of the test, which was below the standards recommended for cooled semen. The seminal characteristics decreased in a very short time of TRT (30 min). This test is for use in insemination program. Thus, this demonstrates that changes in interpretation of the test need to be made in equine semen evaluation. A marked reduction of progressive motility at 30 min of test can be caused by loss of intracellular components or lesions in sperm movement structures. Possibly, availability of cyclic nucleotides involved in oxidative phosphorylation and motility are insufficient, although the mitochondria have the ability to produce energy. The TTR time of 90 min is long for equine cooled semen, and a duration for TTR of 30 min may be more appropriate in this species. Supported by grants from CNPq and CAPES.