SHIC Funds Assessment of Stillborn Piglet Tongue Fluids as Risk-Based Sample

The Swine Health Information Center funded a study to evaluate tongue fluids (TF) samples from stillborn pigs as an indicator of PRRS detection in liveborn littermates. Led by Drs. Isadora Machado and Daniel Linhares of Iowa State University, the study investigated TF as a risk-based sample type in commercial breeding herds to predict PRRSV detection in the litter. Litters with stillborn piglets and small litter size had a higher probability of being PRRSV positive. Moreover, TF from stillborn piglets were shown to be a reliable indicator of PRRSV status for their liveborn littermates, indicating that TF can be an effective risk-based approach for PRRSV detection.

Find the study industry summary for project #23-076 on this page.

A risk-based approach to animal selection for sampling enhances PRRSV detection by increasing the probability of selecting an animal harboring the pathogen while requiring a smaller sample size. Aggregated TF from dead animals has emerged as a promising risk-based approach. It has a similar PRRSV RNA positivity rate as serum, processing fluids, and family oral fluids. Its composition is complex, especially in stillborns, consisting of blood, saliva, respiratory mucus, amniotic fluid, meconium, and environmental contaminants, which may reflect the litter’s PRRSV status upon laboratory testing.

Objectives of the study described herein had a goal to further knowledge on the use of TF from stillborns in commercial sow herds for PRRSV detection. Objectives included evaluating 1) the incidence of stillborn piglets on the probability of PRRSV RNA detection within the litter, 2) the stillborn TF PCR-results as an indicator of PRRSV in liveborn piglets, and 3) the litter size as a risk factor for PRRSV

To investigate these objectives, samples were collected from two PRRSV-positive breeding herds (Herd A: 2,500-sow farm with a three-week batch farrowing system; Herd B: 4,500-sow farm with a weekly batch farrowing system). A total of 130 litters were sampled within 12 hours after farrowing: 66 litters without stillborn piglets and 64 litters with stillborn piglets. This totaled 1,723 liveborn and 105 stillborn piglets sampled. Regarding the litters’ parity, in Herd A, 14 were parity 1 sows, seven were parity 2, four were parity 3, and one was parity 4. For Herd B, all 104 litters came from parity 1 sows.

TF and intracardiac blood samples were individually collected from stillborn piglets. Tail blood swabs were individually collected from all liveborn littermates. Samples were individually tested for PRRSV RNA detection by RT-qPCR at the Iowa State University Veterinary Diagnostic Laboratory. Litters with ≤ 11 liveborn piglets were defined as small litters, whereas litters with ≥ 12 were defined as large.

Across all sample types, the percentage of PRRSV-positive litters was 22.3% (29/130 litters), of which 15.4% (20/130 litters) were tail blood swab PCR positive, 10% (13/130 litters) were intracardiac blood PCR positive, and 16.9% (22/130 litters) were TF PCR positive. At an individual animal-level across both herds, 3.4% (59/1,723 liveborn piglets) were tail blood swab PCR positive, 16.2% (17/105 stillborn piglets) were intracardiac blood PCR positive, and 26.7% (28/105 stillborn piglets) were TF PCR positive. The mean positivity of liveborn piglets within the litter was 5% but varied between 0 – 85.7%, while the total born (stillborn and liveborn piglets combined) was 4.6% (0 – 76.4%).

Regarding sample type Ct values, tail blood swabs had a median of 35.5 (interquartile range, IQR: 29.2-37.7), intracardiac blood a median of 22.4 (IQR: 20.7-26.0), and TF a median of 29.2 (IQR: 25.2-35.7) (Figure 1). Intracardiac blood exhibited the lowest median Ct value, which was significantly different from the median Ct values of the other sample types (P < 0.05).