72 Validation of an early open cow test based on lack of detection of interferon-tau: got OCT?

USA dairy cows have pregnancy rates of only 30 to 50% on the first service by AI following calving. Consequently, it can take 5 AI attempts to achieve pregnancy in high-producing dairy cows. This delay in time to pregnancy has the most detrimental impact on milk production/year in year 2 after these cows calve. Considering the 21-day oestrous cycle (time between ovulations), this delay in getting animals pregnant to produce milk after calving is costly. Interferon-tau (IFNT) is only produced by the ruminant conceptus trophectoderm and is not inducible by viral infection. Consequently, it is appropriate for use in identifying pregnant from nonpregnant (open) cows. It was hypothesised that a test designed to manage open cows (OCT) could be developed based on lack of detection of IFNT in bodily secretions within 15–21 days following AI. Glycosylated recombinant bovine IFNT was generated based on the bovine trophoblast protein-1 (IFNT) 509 cDNA coding sequence and was used to generate polyclonal goat and rabbit antibodies against IFNT. A 5-h ELISA was developed with a limit of detection 60–80 pg/mL. The IFNT was not detected in serum or milk from Day 17 to 18 pregnant cows that were retrospectively found to be pregnant at ultrasound on Day 32 (~200 cows tested). It was reasoned that IFNT concentrations would be greater in locations closer to the uterus. By using a commercially available equine transrectal-guided swab sampling device, IFNT could not reliably be detected in vulva or deep vaginal locations from Day 17 pregnant cows. However, IFNT was detected from external cervical opening (os) samples. The greatest IFNT concentrations were found on Days 17 to 19 following AI. When testing 350 cows on Day 17 on a conventional dairy using the equine swab device, there was a 21% false negative (FN; incorrectly calling a pregnant cow on Day 32 as open on Day 17), 18% false positive (FP incorrectly calling an open cow on Day 32 as pregnant based on OCT on Day 17) and 89% negative predictive value (NPV): true negative (TN)/(TN + FN). Testing 350 cows on an organic dairy on Day 17 revealed a 32% FN, 20% FP, and 87% NPV. After making a custom swab device and testing on Day 17 in 99 cows, there was a significant improvement in detection of IFNT. External os concentrations were 50-times greater by using the custom compared to the commercial equine swab device. Mid-cervical (passed the first ring) concentrations were 150-times greater in the custom swab device compared to the equine swab. Using the custom swab device at the external cervical os resulted in 5% FN, 71% FP, and 97% NPV. Likewise, using the custom swab device in the mid-cervical location revealed a 5% FN, 65% FP, and 97% NPV. The management of open cows on Day 17 is the primary focus for this diagnostic so that they can become pregnant earlier in the lactation curve. Any cow called pregnant on Day 17 would not be managed until subsequent tests for pregnancy on Day 32 or greater. Many of these cows called pregnant will certainly experience embryo mortality. In addition to managing open cows earlier following AI, detecting IFNT will provide a unique approach to studying early embryo mortality.

This research was funded by the USDA-NIFA W4112 Regional Project.