Evaluation of pig behavior changes related to temperature, relative humidity, volatile organic compounds, and illuminance

Review: The influence of light on pig welfare

While several countries impose minimum light requirements for pig housing, it remains unknown whether these requirements are beneficial for pig welfare. Therefore, we aim to review the current knowledge on the effects of light on pig welfare. In this paper, we explain concepts defining light, discuss the relevance of vision for pigs and systematically review the effects of light on pig welfare. Systematic literature searches were performed in two databases to find studies about light and welfare-related topics, including behaviour, health, hormonal secretions and productivity. After screening, 63 studies were reviewed. According to literature, light is relevant in pigs' lives as they are diurnal animals and use vision in combination with other senses to, for example, locate food and interact with conspecifics. Throughout this paper, the investigated light parameters are photoperiod, intensity and spectrum. Pigs seem to have p for a certain light intensity and spectrum, but these preferences vary over production phases. Photoperiod influences feed intake and growth, especially in piglets, but no conclusion can be drawn because of contradictory results. Furthermore, pigs' activity patterns adapt to the provided light schedule and show a diurnal rhythm with higher activity during lit hours. Photoperiod also plays a role in the diurnal secretion of hormones. Cortisol secretion increases shortly before the moment of light onset, and melatonin secretion is influenced by the light and dark contrast with a nocturnal rise after light offset. Some behaviours are impacted by light intensity; for instance, dim conditions are associated with resting and bright conditions with elimination behaviour. Moreover, a few studies showed that in dimmer conditions, more negative social interactions occur, while brighter conditions lead to more positive interactions. Lastly, even though light spectrum is the least explored light parameter, several studies showed that UV B light can activate the cutaneous synthesis of vitamin D3. A limitation in the current literature is that several studies tested light treatments differing in more than one light parameter, making the interpretation of each light parameter difficult. Moreover, most studies do not provide information on other light parameters not targeted by the study, particularly on light spectrum. Some clear knowledge gaps that emerged from this review are on light spectrum and on affective states of pigs in relation to light.

Effect of light intensity on behaviour, health and growth of growing-finishing pigs

The effect of light intensity has been explored in relation to endocrine functions and reproduction in pigs, but effects on health and behaviour are scarcely documented. The objective of this study was to evaluate the effects of different light intensities on behaviour, health and growth of growing-finishing pigs. An experiment was conducted on a commercial farm equipped with light-emitting diode-based luminaires creating four light intensity treatments: low (45 lux), medium (198 lux), high (968 lux) and spatial gradient of intensity (from 71 lux to 330 lux). Per treatment, 112 pigs were studied in two batches of eight pens. Once every two weeks behaviours such as exploration, positive and negative social interactions, play and abnormal behaviours were observed. Health issues were assessed weekly and included biting lesions, skin lesions, leg and respiratory disorders. The average daily gain over the experiment was calculated and after slaughter carcasses were inspected. Generalised linear mixed models were used for the analysis of behaviours, binary health scores, carcass abnormalities, ordinal logistic regression for multilevel health scores, and linear mixed models for average daily gain. Interactions between intensity and week were found for some behaviours (i.e., exploration, negative social interactions and abnormal behaviour) and health issues (i.e., tear stains, conjunctivitis, body lesions, bursitis and tail lesions). However, none of the treatments consistently outperformed another one. Light treatments did not affect pig growth and carcass abnormalities. These variable results support studies suggesting that pigs are adaptable to light intensities, and inconsistencies over weeks might have been caused by environmental factors that could not be controlled in a commercial farm setting. To conclude, tested light intensities had no clear effects on pig behaviour, health and growth.

Modelling of Animal Activity, Illuminance, and Noise on a Weaned Piglet Farm

Measuring animal activity and its evolution in real time is useful for animal welfare assessment. In addition, illuminance and noise level are two factors that can improve our understanding of animal activity. This study aims to establish relationships between animal activity as measured by passive infrared sensors, and both illuminance and noise level on a conventional weaned piglet farm. First, regression models were applied, and then cosine models with three harmonics were developed using least squares with a Generalized Reduced Gradient Nonlinear method. Finally, all the models were validated. Linear models showed positive correlations, with values between 0.40 and 0.56. Cosine models drew clear patterns of daily animal activity, illuminance and noise level with two peaks, one in the morning and one in the afternoon, coinciding with human activity inside the building, with a preference for inactivity at night-time and around midday. Cosine model fitting revealed strong correlations, both in the measurement and validation periods, for animal activity (R = 0.97 and 0.92), illuminance (R = 0.95 and 0.91) and noise level (R = 0.99 and 0.92). The developed models could be easily implemented in animal welfare monitoring systems and could provide useful information about animal activity through continuous monitoring of illuminance or noise levels.