Design of an artificial lighting system for estrus induction in gilts based on freeform optics

This study aims to design an advanced lighting system using freeform optical technology. The artificial lighting was also improved in the reproductive efficiency. An artificial lighting system was also developed to dynamically adjust the illuminance in response to the posture of gilts. Thereby, a stable and uniform lighting environment was created to promote the estrus expression for optimal hormonal regulation. The blue and green light were integrated to form a blue-green composite spectrum, in order to closely align with the spectral sensitivity of the pigs. The freeform optics were designed to realize the precise control over the light distribution. There was an average uniformity of 0.87 and a maximum illuminance of 311 lx. The experiment was conducted at the Guangxi Yangxiang Co., Ltd. Guigang Huanglian Pig Farm, China. The gilts were exposed to four lighting conditions: a control group with the conventional white LED lights, a blue light (B), a green light (G), and a blue-green composite light (B&G) group. The blue and green light was also combined in a ratio of 1:1. The lighting system was operated on a 12-hour daily cycle. The levels of the luteinizing hormone (LH) and estradiol (E2) were measured to evaluate their correlation with the estrus expression. The results revealed that the B&G group exhibited the most pronounced estrus behavior, with significantly higher levels of LH and E2 than the rest groups. The elevated hormonal levels were maintained consistently to result in a prolonged and more stable breeding window, which was essential to successful mating. These findings suggest that the combination of the blue and green light effectively stimulated the hormonal process with the estrus induction. In contrast, the green light group shared the less consistent estrus expression and the weaker hormonal responses, indicating that the green light alone was less effective inducing the estrus behavior. Although the blue light group shared the improvement over the control group, there was no same level of consistency or intensity in the hormonal variation as the B&G group. Furthermore, the stability and reliability of the lighting system were also assessed beyond behavioral observations. An ultrasonic distance sensor was incorporated to continuously monitor the posture of the gilts. The illuminance was dynamically adjusted using the distance between the gilt and the light source. The illuminance remained stable, with a ±5% variation whether the gilts were lying down or standing. Moreover, the lighting system also demonstrated impressive energy efficiency, with a 95% energy utilization rate. The energy loss was significantly reduced, compared with the conventional lighting systems. Therefore, freeform optical technology shared the promising potential to customize lighting systems, in order to enhance animal welfare and productivity in modern farming. The B&G lighting system effectively improved the reproductive environment for the gilts, thereby enhancing the reproductive efficiency in the pig industry. Furthermore, artificial lighting was emphasized to regulate animal behavior and physiology, particularly in the context of estrus induction. In conclusion, the freeform optical can be expected to offer a practical and efficient solution to the optimal lighting systems in the gilts, in order to improve both estrus expression and hormonal regulation. The insights were also gained for the valuable guidance of the lighting systems in pig farming or agricultural settings, where controlled lighting influences animal behavior. Future research should focus on refining the parameters of the blue-green light spectrum, such as the optimal light ratio, photoperiod duration, and illuminance, in order to further enhance estrus induction and reproductive performance. These efforts can greatly contribute to more effective, sustainable, and intelligent farming solutions for increasing productivity with animal welfare.