Abstract This study aims to investigate the gene expression of sperm-borne phospholipase C zeta (PLCζ), WW domain-binding protein 2N-Terminal Like (WBP2NL), and Tumor necrosis factor (TNF-α), as a negative control, in spermatozoa and their relationship with fertility and seminal quality in stallions. Ejaculates from 40 Criollo stallions were used, whose fertility was assessed on the basis of their pregnancy rate per cycle in at least two breeding seasons. Pregnancy rates ranged from 20% to 90% and were used to divide the stallions into two groups: High rates (≥ 50%) (n = 25), and Low rates (< 50%) (n = 15). A computer-assisted sperm analysis system - (CASA) analyzed semen after collection. Also were evaluated the physical and functional integrity of the plasmatic membrane and sperm morphology alterations. All stallions expressed PLCζ, WBP2NL, and TNF-α. PLCζ positively correlates with conception rate, total motility (TM), progressive motility (PM), plasmatic membrane functionality, and integrity. A simple linear regression was detected between pregnancy rate and PLCζ expression (P = 0.003), TM (P < 0.001) and PM (P < 0.001). PLCζ gene expression was higher (P = 0,012) in the High rates group than in the Low group. WBP2NL and TNF-α did not correlate with seminal quality and stallion’s fertility. It was concluded that PLCζ gene expression in the spermatozoa might be used as a biomarker of fertility and seminal quality in stallions. Parameters of sperm kinetics also showed, positive correlation between TM, PM and pregnancy rate. spermborne borne , (PLCζ) domainbinding domain binding 2NTerminal NTerminal 2N Terminal N WBPNL WBP NL (WBP2NL) TNFα, TNFα TNF α (TNF-α) control 4 seasons 20 90 groups ≥ ( 50% 50 n 25, 25 25) 15. 15 . 15) computerassisted computer assisted CASA (CASA collection alterations TNFα. α. (TM) PM, (PM) functionality P 0.003, 0003 0.003 0 003 0.003) 0.001 0001 001 0.001. 0,012 0012 012 stallion s showed (PLCζ (WBP2NL (TNF-α 2 9 5 1 (TM (PM 000 0.00 00 0,01 01 0.0 0,0 0. 0,

Abstract Reproductive biotechniques in the equine species have advanced in the last decade and horse breeders have started to question the possibilities of interfering in the determination of foal sex. The aim of the present study was to verify whether the variables mares and stallion’s age, side of the ovary containing the preovulatory follicle, preovulatory follicle diameter, time between breeding and ovulation, and ovulation inducing hormones influence the sex of the foal. A total of 259 reproductive cycles of 160 mares and 22 Thoroughbred stallions were used. Statistical analysis was performed using R software, including Pearson's chi-square test and logistic regression. Of the total foals born, 136 were males (52.51%) and 123 were females (47.49%). In mares that ovulated with -24h after ovulation induction, 104 foals (54.74%) were males and 86 (45.26%) were females, while in mares that ovulated with +24h, 32 foals (46.38%) were males and 37 (53.62%) were females. Stallions up to 15 years old had 44.14% (n=49) females and those over 15 years had 49.66% (n=73) females. The simple logistic regression model showed that mares and stallions under 15 years old, mares with ovulation time less than 24 hours and treated with Deslorelin had a higher probability of having male foals, but the Pearson's chi-square test showed that foals gender were not influenced by the variables studied. stallion s age diameter 25 16 2 used software Pearsons Pearson chisquare chi square born 13 52.51% 5251 52 51 (52.51% 12 47.49%. 4749 47.49% . 47 49 (47.49%) 24h h induction 10 54.74% 5474 54 74 (54.74% 8 45.26% 4526 45 26 (45.26% +24h 3 46.38% 4638 46 38 (46.38% 53.62% 5362 53 62 (53.62% 1 4414 44 14 44.14 n=49 n49 n (n=49 4966 66 49.66 n=73 n73 73 (n=73 studied 52.51 525 5 (52.51 474 47.49 4 (47.49% 54.74 547 7 (54.74 45.26 452 (45.26 46.38 463 (46.38 53.62 536 6 (53.62 441 44.1 n=4 n4 (n=4 496 49.6 n=7 n7 (n=7 52.5 (52.5 47.4 (47.49 54.7 (54.7 45.2 (45.2 46.3 (46.3 53.6 (53.6 44. n= (n= 49. 52. (52. 47. (47.4 54. (54. 45. (45. 46. (46. 53. (53. (n (52 (47. (54 (45 (46 (53 (5 (47 (4 (