A Portable RGB Color-Sensor Platform for On-Farm Prediction of Sheep Pregnancy and Litter Size

Introduction: Early and accurate detection of sheep pregnancy and litter size (PLS) is important for flock management. The current ultrasonography-based systems are expensive and require trained operators. Our work is aimed to advance a handheld, real-time, pen-side blood analysis platform using red–green–blue (RGB) color sensor for rapid diagnosis of PLS in ewes.

Methods: Our team has successfully developed 6 in-house colorimetric assays to detect 6 biomarkers for PLS in ewes. These biomarkers include L-carnitine, glucose, lactate, creatinine, urea, and pyruvate. Among these, L-carnitine is the most crucial biomarker as it is detected in all three conditions of ewes - pregnancy, twin, and triplet. The assay system was integrated with an automated RGB color sensor platform and a smartphone/tablet application for data capture and interpretation. Each reaction output was expressed as a reaction-specific "colour number," a weighted combination of RGB channel values. Calibration curves were built using spiked pooled sheep serum, tested three times, and compared against benchtop plate reader/spectrophotometer.

Results: The portable sensor platform generated strong calibration performance, with linear or polynomial response curves showing R² values between 0.96 and 0.99 across assays, including glucose, pyruvate, and lactate. A custom-made heated reaction box improved assay performance under low-temperature field conditions, and the automated color sensor system successfully measured reaction color and reported results via onboard software.

Conclusions: Our work demonstrated the feasibility of an RGB-color sensor based handheld platform for on-farm real-time biochemical analysis in sheep. While further refinement is needed to reduce the assay number and shorten turnaround time, the current prototype establishes a strong foundation for practical pen-side PLS testing.