Efficacy of a chute-side pregnancy test on early pregnancy determination in small ruminants

Ultrasonography and hormone quantification are established pregnancy detection methods but require specialized equipment and training. Two experiments evaluated a commercial bovine on-farm pregnancy test in sheep and goats using different blood constituents and assessed postpartum pregnancy-associated glycoprotein (PAG) persistence. In experiment 1, 30 Rambouillet ewes (60.9 ± 1.1 kg; age 2 to 8 yr) were synchronized and exposed to a fertile ram. Whole blood (WB), serum (SE), and plasma (PL) collected on d 20, 35, and 70 post-breeding were analyzed using the IDEXX Alertys OnFarm bovine pregnancy test. Ultrasonography was performed on d 35 and 70; pregnancy was classified using d 100 SE progesterone (P4; ≥ 4 ng/mL). On d 20 of gestation, IDEXX pregnancy detection in WB, SE, and PL was 32.1, 56.6, and 56.6%, respectively, compared with 93.1% by P4 (χ2 < 0.0001). Detection increased to 62, 63.3, and 63.3% of WB, SE, and PL samples classified pregnant on d 35 (χ² = 0.02) and 90, 93.3, and 93.3% of WB, SE, and PL samples on d 70, similar to P4 classification (χ² = 0.95). In experiment 2, 19 Boer does were synchronized and exposed to two fertile bucks. Whole blood, SE and PL were collected on d 20, 28, and 70 post-breeding, with pregnancy classified using d 70 P4. In does, IDEXX detection of pregnancy was 56 to 58% in SE and PL across sampling days. Postpartum PAG persistence was evaluated in ewes and does using WB, SE, PL, and milk collected on d 0, 20, 40, 60, and 80 after parturition. In ewes, 100% of WB, SE, and PL samples tested positive on d 0 and 20, declining to 8, 31, and 8%, respectively, by d 80 (P < 0.05). In does, positivity declined from 100% in all blood constituents on d 0 to 15, 5, and 10%, respectively, by d 80. With the IDEXX chute-side assay, 85 to 92% of ewe milk samples remained positive from d 0 to 40, declining to 12% by d 80. Milk positivity in does declined progressively from 85% at parturition to 7% by d 80. These results support use of the bovine on-farm pregnancy test in ewes by d 70 after breeding. In does, the proportion testing positive more closely approximated ultrasound-based pregnancy detection than P4-based classification. Testing within 80 d postpartum may yield false-positive results due to residual PAGs.