Risk factors for colic in the Michigan (USA) equine population.

A population-based prospective epidemiological study was conducted to assess risk factors for equine colic. A stratified sample of 3925 equids in 138 randomly selected equine farms in the state of Michigan was monitored in two 12-month rounds of data collection. Incidence densities were used to describe the rate of development of colic in the study population. Mortality rates, case fatality rates and survival rates were used to describe the severity of colic on the study population. Multivariable logistic regressions with random effects (grouped according to farm) were used to identify risk factors associated with occurrence of colic. A total of 3175 equids from 132 farms from the starting population of 3925 equids in 138 farms was used in the multivariable analysis. There were 77 cases of colic reported during the study period in 62 animals. Of these animals, 54 (87%) had one case, 5 (8%) had two cases, 2 (3%) had three cases, and 1 (2%) had seven cases. Of the cases reported, 49 (64%) were non-specific diagnoses, 13 (17%) impaction/acute intestinal obstruction colics, 7 (9%) spasmodic colics, 4 (5%) sand colics, 2 (3%) gas colics, 1 (1%) verminous mesenteric arteritis, and 1 (1%) enteritis due to ingestion of moldy grain. The annual incidence density of colic in the study was 3.5 cases per 100 equid-years. The surgical treatment risk was 17% (13/77). The overall mortality risk due to colic was 0.5 deaths per 100 equids, and the case fatality risk was 13% (10/77). The case fatality risk for cases treated surgically was 31% (4/13), while the case fatality risk for non-surgical colics was 10% (7/69). Risk factors associated with significantly increased likelihood of developing colic were foaling during the study, deworming during the study, increased age, and participation in showing activities. Geldings and equids provided group drinking water from sources other than tanks, buckets and automatic waterers were significantly associated with reduced risk of colic.