Population Dynamics of Undifferentiated Neonatal Calf Diarrhea among Ranch Beef Calves

Abstract

We conducted a retrospective longitudinal study of a single population of calves from a grass-managed beef cattle system to determine which factors of time and subject explained the probability for calves to die from undifferentiated neonatal diarrhea. Data were collected from 402 beef calves at risk for undifferentiated neonatal calf diarrhea during a single calving season. Descriptive statistics from birth and mortality records were summarized, and factors of time and subject explaining the probability for calves to die of undifferentiated neonatal diarrhea were identified using a multivariable logistic regression model. Forty-eight of 402 calves (11.9%) died from undifferentiated neonatal diarrhea. Thirtynine of 47 calves with age-at-death information (83%) died between six and 15 days of age. The mean age at death did not change over the calving season, however, the weekly cumulative incidence of mortality increased as the calving season progressed. The probability of death was increasingly greater for calves born later in the calving season. The period of time a calf was born in the calving season (PcO.OOOl) and the age of the dam (P=0.006) explained the probability for a calf to die of neonatal diarrhea. Calves of two-year-old dams were more likely to die than calves of mature cows (OR= 5.79, P=0.003). The calves of three-year-old dams were intermediate in risk compared to calves of mature cows (OR=2.21), but not significantly different from calves from the other dam age-groups (P>0.10). The probability for calves to die was not explained by gender (P=0.68) or birth weight (P=0.43). Factors explaining mortality were age of the calf, age of the dam and point of time in the calving season the calf was born. Because the incidence of scours increased with the passage of time within the calving season, undifferentiated neonatal calf diarrhea might be prevented by designing beef calving systems which can maintain the more ideal conditions existing at the beginning of the calving season, which include low doses of pathogen exposure and fewer opportunities for older, highly-infective calves to transmit pathogens to younger, susceptible animals.