Tiago et al. Acta Veterinaria Scandinavica 2012, 54:20 http://www.actavetscand.com/content/54/1/20 Table 1 Pregnancy rates after AI with fresh extended and frozen thawed semen, and after natural service AI fresh extended AI frozen/thawed Natural Service N° of Mares 7 N° of Services 11 7 3 10 4 Pregnancy per cycle (%) 7/11 (64) 4/10 (40) 2/4 (50) Total pregnant mares (%) 7/7 (100) 4/7 (57) 2/3 (67) Page 4 of 5 IA/Pregnancy* 1.57 2.5 2.0 * Includes mares that did not get pregnant Table 2 summarizes the results obtained in relation to embryo recovery rates and embryo quality after NS or AI. Discussion The results of this study were based on a limited num- ber of observations and thus no solid inferences can be made about the fertilizing ability of inseminated semen vs. NS for this stallion. Notwithstanding that, conception rates and embryo recovery rates after AI with fresh and frozen semen were in the normal range obtained in our centre. Not all ejaculates were tested for the presence of P. aeruginosa, but the fact that the bacteria was not iso- lated from 8 fresh, undiluted ejaculates raises the possi- bility that it was not present in the semen or had a very low concentration. As no isolations were obtained in undiluted semen, none should be expected in extended semen even if without antibiotics (E-Z Mixin®) or even less when containing antimicrobials (Botu-crio®). The somewhat lower conception rate achieved with frozen semen may be attributed, at least in part [10], to degen- erative conditions of the endometrium of two older mares (18 years-old) which had a grade III Kenny’s endometrial classification. Pregnancy rates as well as embryo recovery rates obtained after NS with the infected stallion were acceptable despite having more than half of the NS resulting in uterine disease com- pared to only in 22% following insemination. These positive results may have been due, at least in part, to the intensive uterine treatments performed right after every natural service, up till day 4 post ovulation. Con- firmation of venereal transmission of P. aeruginosa and was obtained with 2 out of the 4 mares bred by natural service getting positive to P. aeruginosa and thus acquir- ing the potential to transmit the bacteria. The majority of recovered equine embryos were of good to excellent quality [8]. In the present case all embryos collected after AI were of excellent quality. However, and despite identical embryo recovery rates after AI or NS, embryo quality was decreased after the latter, compared to AI. In cattle, the use of P. aerugi- nosa - contaminated semen did not result in decreased embryo quality [11]. However, in cattle as opposed to in horses, P. aeruginosa it is not considered to be a poten- tially venereal transmitted disease. Taken together the data suggest that NS with a P. aeruginosa-carrier stallion resulted in acceptable fertilization rates, but despite aggressive post-insemination treatments originated a higher percentage of lower quality embryos. Conclusions With this carrier stallion, there was no evidence of low fertilization rates after AI or NS, but uterine disease was noted more often after NS than after AI. Venereal trans- mission of P. aeruginosa after NS did occur, and was associated with lower embryo quality after NS compared to AI. Overall, the data supports the indication for P. aeruginosa - carrier stallions to be bred by AI rather than by NS, both when used to impregnate mares or to breed embryo donors. Acknowledgements This work was partially financed by Projects PTDC/CVT/108456/2008 (FCT) and COMPETE:FCOMP-01-0124-FEDER-009565 (FEDER). The authors appreciatively acknowledge the revision of the final manuscript by Dr. John Edwards, College of Veterinary Medicine, Texas A&M University. Table 2 Embryo recovery attempts, embryo recovery rates and embryo quality after Artificial Insemination (fresh extended plus frozen/thawed semen) or Natural Service AI Natural Service N° of Mares N° of Services 4 2 6 9 Embryos/ Flushing (%) 4/6 (66.7) 6/9 (66.7) Grade 1 Embryos/Total Embryos (%) Grade 2 Embryos/Total Embryos (%) Grade 3-4 Embryos/Total Embryos (%) 4/4 (100) 2/6 (33.3) — 2/6 (33.3) — 2/6 (33.3)