Public health implications related to spread of pathogens in manure from livestock and poultry operations.

During the 20th century, food animal agriculture grew from small operations, where livestock (cattle, sheep, and swine) and poultry (chickens and turkeys) had access to free range, to large operations where animals and poultry were concentrated and confined to feed lots or buildings. The quantity of manure produced by confinement animals in the United States has been estimated to be in excess of 61 million tons of dry matter per year, and another report states that 1.2 billion tons of manure are produced by cattle annually in the United States (US Senate Agricultural Committee, 1998). As urban developments have come closer to livestock operations, there has been increasing public concern for the impact of the latter on public health and the environment. Although management practices for livestock production have increased in efficiency, insufficient attention has been given to managing and utilizing wastes so that they benefit rather than pollute the environment. Animal manure includes urine and various bodily secretions such as those from the nose, vagina, and mammary glands. Dust from animals and manure may be blown from buildings by powerful fans, and manure is often piled near the animal quarters or is spread on land in solid or liquid form. Public concerns associated with disposal of animal manure include objectionable odors, flies, excessive levels of phosphorous and nitrogen, and the potential for spread of human pathogens. It has been observed that despite linkages between outbreaks of gastroenteritis in humans and livestock operations, the importance of animal manure in the spread of infectious agents tends to be underestimated.