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Bovine semen thermoresistance tests and their correlation with pregnancy rates after fixed-time artificial insemination  [Testes de termoresistência do sêmen bovino e sua correlação com taxas de prenhez após inseminação artificial em tempo fixo] ABSTRACTThe objective of the study was to determine whether or not there is a correlation between thermoresistance tests (TT) after semen thawing and pregnancy rate (PR) after fixed-time artificial insemination (FTAI). Four different TT were performed on ten samples used for AI; a rapid test (RTT) (30min / 46°C) and three slow tests (STT): STT1 (60min/38°C), STT2 (180min/38°C), and STT3 (300min/38°C). Two hundred and fifteen multiparous crossbred cows were submitted to FTAI under the following protocol: on day zero (d0) the animals received a P4 device +EB; on d7 PGF 2α ; on d8 P4 was removed and eCG+EC were administered; IATF was performed on d10. Three gestational diagnoses (G D) were performed on d40, d70 and d120. The mean sperm motility (%) in RTT and STTs were 19.84±6.13, 28.55±10.48, 17.62±5.87 and 8.63±3.46, respectively, and TP in the three DG 61.86%, 57.67%, and 55.81%, respectively. Through Person test a significant negative correlation (P< 0.05) was found between STT2 and PR at 60 days (r= -0.644) and between STT3 and all TPs (r= -0.774, -0.752, 0.748). It was concluded that TT parameters are not able to determine correlation between semen quality and TP.

This study aimed to determine the accuracy of assessing stallion sperm motility using a light microscope, a cell phone camera, and a free computer-assisted semen analysis (FCASA) package for ImageJ. The total motility of frozen (n=22) and cooled (n=48) equine semen was determined by FCASA and compared to the results of subjective visual analysis (SVA) by two technicians. Frozen samples were also evaluated by a commercial computer-assisted semen analysis (CCASA) system. The Friedman test revealed no significant differences (P>0.05) between cooled samples analyzed by FCASA (38.0) and SVA (technician 1, 40.0; technician 2, 40.0), nor between frozen samples analyzed by FCASA (23.36 ± 15.9), SVA (25.5 ± 18.8 and 25.8 ± 18.5), and CCASA (25.2 ± 18.3). However, mean FCASA results were underestimated by 7.2% compared with CCASA. The correlation between FCASA and CCASA was significant and strong (P<0.0001, r=0.95). Chi-squared tests indicated that FCASA provided similar results (P=0.14) to the reference method (CCASA), but SVA had lower accuracy (P=0.04). ImageJ analysis of cell phone videos captured under a light microscope can be used for estimation of stallion sperm motility with comparable accuracy to commercial systems.

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This study aimed to develop a spermdensimeter for evaluating stallion semen in a practical and efficient manner. This method is an alternative to the standard method that utilizes a Neubauer chamber under field conditions, which is typically employed because the Karras spermdensimeter ® model (for bovine and swine) is not suitable for determining equine semen concentrations. Two spermdensimeter models were developed. The appliances were made out of acrylic material, and each one had different angulations, with 8° for Model A and 10° for Model B. We tested 123 semen samples from stallions to evaluate and calibrate the two spermdensimeter prototypes based on the Neubauer chamber. Samples were analyzed by two evaluators. These results were compared to those obtained using the Neubauer chamber. Linear regression was used to establish the scale of concentrations for each model. Additionally, the correlation between the scales and the values found using the Neubauer chamber was calculated. Linear regression demonstrated a precise adjustment for the concentration curves, resulting in r² = 0.9395 for Model A and r² = 0.9418 for Model B. The correlations for the concentrations were significant (p < 0.0001). They were high and negatively correlated, measuring-0.83 for Model A and-0.8 for Model B. We concluded that the spermdensimeters we developed were effective for evaluating stallion sperm concentrations. These models can be used in routine practices associated with equine reproduction, achieving the main purpose of this work.