The aim of this experiment was to evaluate the pregnancy rates for equine embryo recipients with different degrees of uterine tone (absent, fair moderate, intense), treated with phenylbutazone (PBZ). Thirty-two Paint Horse breed donors and 96 Mangalarga recipients were used during the 2001/2002 breeding season (October to January). The embryos were collected 8 days after ovulation, classified and then transferr...