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. The hens were confined in stair-step cages with five rows and four tiers. The unit measured 12 x 150 m and was ventilated w ith 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 the last 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 i n the first aisle in the same transversal section of point A). All three sa mpling sites were fitted with two sampling stations. One station recorded t he total dust (TD) and the other recorded the respirable fraction (RF); and one data logger recorded temperature and relative humidity. In the same mo nths mortality was recorded. The results show that dust concentration was s ignificantly higher during the period of feed distribution (TD = 1.94 mg/m( 3), RF = 0.31 mg/m(3)) and scraper cleaning (TD = 1.90 mg/m(3), RF = 0.28 m g/m(3)), than during the night (TD = 0.74 mg/m(3), RF = 0.22 mg/m(3)) and i n point A (TD = 1.72 mg/m(3), RF = 0.31 mg/m(3)). Moreover the quantificati on of the effect of TD and RF on bird mortality showed that one point incre ase of TD and RF brings about, respectively, two and nine more dead birds.