Pregnancy rates in mares following hysteroscopic or transrectally-guided insemination with low sperm numbers at the utero-tubal papilla

This study was conducted to evaluate two methods for insemination of a low number of sperm in the tip of the uterine horn, and to determine whether prebreeding intrauterine treatment with prostaglandin E2 would improve pregnancy rates. Estrus was synchronized in 36 fertile Quarter Horse and Thoroughbred broodmares. When a dominant follicle greater than or equal to 33 mm diameter was present, mares were treated with 2500 units hCG intravenously and were assigned to one of four treatment groups for insemination with five million total sperm in 200 microliters extender the next day as follows: (1) Group PGE-HYS (n=9): 0.25 mg PGE2 in 1 ml 0.9% NaCl solution infused into the tip of the uterine horn ipsilateral to the dominant follicle 2 h prior to hysteroscopic-guided inseminate placement onto the oviductal papilla; (2) Group SAL-HYS (n=9): 1 ml 0.9% NaCl solution infused into the tip of the uterine horn ipsilateral to the dominant follicle 2 h prior to hysteroscopic-guided inseminate placement onto the oviductal papilla; (3) Group PGE-PIP (n=9): 0.25 mg PGE2 in 1 ml 0.9% NaCl solution infused into the tip of the uterine horn ipsilateral to the dominant follicle 2 h prior to transrectally-guided pipette placement of the inseminate into the tip of the uterine horn; and (4) Group SAL-PIP (n=9): 1 ml 0.9% NaCl solution infused into the tip of the uterine horn ipsilateral to the dominant follicle 2 h prior to transrectally-guided pipette placement of inseminate into the tip of the uterine horn. Mares in estrus were evaluated daily by transrectal ultrasonography to monitor follicular status and confirm ovulation. If mares had not ovulated within 2 days of insemination, the assigned treatment was repeated. Pregnancy status was evaluated by transrectal ultrasonography 12-14 days postovulation, and pregnancy rates were compared. No interaction between prebreeding treatment (SAL:PGE) and insemination protocol (HYS:PIP) on pregnancy rates occurred (P>0.10). Pregnancy rates did not differ between mares inseminated by HYS (12/18; 67%) or PIP (10/18; 56%) (P>0.10). Pregnancy rates did not differ between mares treated prior to breeding with PGE (11/18; 61%) or SAL (11/18; 61%) (P=1.00). In summary, satisfactory pregnancy rates were obtained when a low number of sperm were either placed directly onto the oviductal papilla using hysteroscopy or placed in the tip of the uterine horn using a transrectally-guided uterine pipette. Infusion of 0.25 mg PGE2 in the tip of the uterine horn 2 h prior to insemination did not improve pregnancy rates.