Acute trichomoniasis and sub-optimal bull fertility in a cow/calf herd

An investigation and case management

Abstract

A beef cow/calf ranch contacted the veterinary teaching hospital concerning low pregnancy rates. The 600-cow herd consisted of three breeding groups of females, with each group being exposed to multiple-sire bull batteries for 90 days (April-June). Each breeding group was palpated for pregnancy approximately 60 days following bull removal from the cows. Pregnancy rates in the groups were 60, 25 and 41%. No abortions had been observed by management during or following the breeding season. Initial work-up found that each group of cows was in adequate body condition for reproduction. A high percentage of the ranch's bull population was positive for culture and polymerase chain reaction for Tritrichomonas foetus. In addition, a high percentage of the bull population failed to pass a breeding soundness examination. Treatment recommendations included culling the entire bull population and replacing it solely with virgin bulls that had passed a breeding soundness examination. Simultaneously, we recommended administration of a T. foetus vaccine to all females, followed by a vaccine booster dose 30 days later. All non-pregnant females were to be placed in separate breeding groups and exposed to the new bull population for 60 days (Dec-Jan). Palpation of non-pregnant females was to be performed 60 days following bull removal. The ranch followed these treatment recommendations. Following bull removal 60-day pregnancy rates were 95%. All replacement bulls passed a breeding soundness examination and were negative for T. foetus by polymerase chain reaction following exposure to the non-pregnant females. Ninety-eight percent of pregnant cows from the original bull exposure (April-June) delivered term calves.