Dust Concentration and Mortality Distribution in an Enclosed Laying House

Dust concentration was monitored in a commercial enclosed laying unit that housed 56,000 laying hens. Thehens were confined in stair-step cages with five rows and four tiers. The unit measured 12 150 m and was ventilatedwith a negative pressure fan system. Dust concentration data were collected three times a day for three one-week periods(in April, May, and June). The data were collected in three different points of the laying house: (point A located in thelast aisle in front of the third group of fans; point B located in the third aisle at the end of the house; and point C located in the first aisle in the same transversal section of point A). All three sampling sites were fitted with two samplingstations. One station recorded the total dust (TD) and the other recorded the respirable fraction (RF); and one datalogger recorded temperature and relative humidity. In the same months mortality was recorded. The results show that dustconcentration was significantly higher during the period of feed distribution (TD = 1.94 mg/m3, RF = 0.31 mg/m3) andscraper cleaning (TD = 1.90 mg/m3, RF = 0.28 mg/m3), than during the night (TD = 0.74 mg/m3, RF = 0.22 mg/m3) andin point A (TD = 1.72 mg/m3, RF = 0.31 mg/m3). Moreover, the quantification of the effect of TD and RF on birdmortality showed that one point increase of TD and RF brings about, respectively, two and nine more dead birds.