Diagnosing american bison pregnancy during its two last trimesters: Comparison between rectal palpation associated with ultrasonography and hormonal assays in serum or in feces.

The study aimed to propose sensitive, specific and easy pregnancy diagnosis for American Bison. Trans-rectal Palpation and Ultrasonography (TRPUS), concentration of Pregnancy Associated Glycoproteins (PAG), Progesterone (P4), Estrone (E1), Estrone-Sulfate (E1S) in serum and P4 and E1S in feces were compared. Immunoassay was used for PAG, whereas steroids were assayed using Liquid Chromatography coupled to Mass Spectrometry. Pregnancy and its period were retrospectively assessed after calving. Animals included were distributed as follows: 40 were non-pregnant, 27 were in their second and 15 in their third trimester of gestation. Fisher's test was used to determine sensitivity and specificity of TRPUS. Thresholds leading to best sensitivities and specificities for hormonal assays were determined using Receiver Operating Characteristic Curves. Although TRPUS requires contention, palpation skills, it was conclusive in 70.63 % of cases and good sensitivity (97.50 %) and decent specificity (83.33 %) were observed. Concentrations of PAG, P4, E1S and E1 in serum were higher in Pregnant animals (P), with thresholds giving decent specificity and sensitivity (lower sensitivity for E1 and E1S: 92.11 %; lower specificity for P4: 93.48 %). In feces, P4 and E1S were higher in P: pregnancy diagnosis using E1S assay in feces showed 100 % of sensitivity and specificity. In conclusion, assaying E1S in feces during the two last trimesters of American Bisons pregnancy is a sensitive and specific gestation diagnosis. Pregnancy diagnosis using TRPUS can be useful in ranches but requires contention and skill adaptation. Serum hormonal assays can help evaluating the pregnancy period but also require contention.