The livestock industry provides significant benefits to Ontario’s economy; however, the odorous emissions from livestock facilities have caused concern among their non-farming rural neighbours. Measurement and reduction of odour is necessary to maintain a clean environment and to achieve high standards in the production of livestock. Efforts to remediate odour from livestock production facilities have been impeded by the limited understanding of the odour itself and lack of odour evaluation techniques. Livestock odour results from over 165 compounds and their interactions with each other. A variety of factors contribute to their generation, such as relative humidity, wind speed, air temperature, etc. (Zahn et al., 2001). Over the past few decades, research has been conducted to adequately model livestock farm odours, but with little success. These studies have provided evidence that the contributing factors such as environmental conditions should be incorporated into an odour analysis model. However, previous models have only analysed the influence of single factors on odour level and did not investigate their combined effect. Moreover, the relative significance of these contributing factors to odour strength has not been investigated. The aims of this study are to identify the factors that may impact people’s perception of livestock farm odour intensity, and to analyse the effects of the factors on the strength of downwind odour. Odour emissions from livestock operations in Ontario have raised significant public concerns. In this study, downwind odour measurements were conducted during a 7-week period in July and August in 2004. The study involved taking measurements at two poultry farms, six dairy farms, and six pig farms in southern Ontario using both human assessor observed Nasal Ranger field olfactometers and an electronic nose developed in our research laboratory. By analyzing the data collected, it was shown that livestock odour strength is affected by various factors, such as distance to the source and air temperature. Therefore, components-only or single-factor analysis method cannot provide a satisfactory assessment, and a more thorough multi-component and multi-factor analysis is required. However, the results of this research show the promise of using human assessors and Nasal Rangers for downwind odour evaluation but there are a number of disadvantages. For instance, Nasal Ranger field Olfactometer has limited levels of dilution, and is therefore less accurate. Moreover, Nasal Rangers are difficult to overcome the assessors’ personal bias in odour measurement and evaluation, regarding the influences of many factors, such as age and health, and an individual’s background and experience, on the human sense of smell. Therefore, unbiased automatic odour evaluating technologies are desirable. Experimental results showed that the predicted odour strengths by the electronic nose yields high accuracy in comparison to the perceived data by human panel, and proved its capability of producing a qualitative output, its automation, lower operation cost, and greater consistency in odour measurement. However, further research and development are still needed in order to improve the electronic nose techniques for use in livestock farm odour measurements.