Our primary goal was to generate an accurate estimate of the daily environmental loading rate of Cryptosporidium parvum oocysts for adult beef cattle, using immunomagnetic separation coupled with direct immunofluorescence microscopy for a highly sensitive diagnostic assay. An additional goal was to measure the prevalence and intensity of fecal shedding of C. parvum oocysts in pre-and postparturient cows as an indicator of their potential to infect young calves. This diagnostic method could detect with a >90% probability oocyst concentrations as low as 3.2 oocysts g of feces ؊1 , with a 54% probability of detecting just one oocyst g of feces ؊1 . Using this diagnostic method, the overall apparent prevalence of adult beef cattle testing positive for C. parvum was 7.1% (17 of 240), with 8.3 and 5.8% of cattle shedding oocysts during the pre-and postcalving periods, respectively. The mean intensity of oocyst shedding for test-positive cattle was 3.38 oocysts g of feces ؊1 . The estimated environmental loading rate of C. parvum ranged from 3,900 to 9,200 oocysts cow ؊1 day ؊1 , which is substantially less than a previous estimate of 1. . Use of this highly sensitive assay functioned to detect a greater proportion of low-intensity shedders in our population of cattle, which reduced the estimated mean intensity of shedding and thereby reduced the associated environmental loading rate compared to those of previous studies.Cryptosporidium parvum has emerged as a ubiquitous waterborne microbial pathogen, with specific genotypes readily transmitted ambidirectionally between livestock and humans (7,9,12,25,28,36). One of the first steps in designing watershed management programs for minimizing the occurrence of C. parvum in drinking water supplies is to identify significant quantitative sources of this parasite. Adult cattle are often considered potential nonpoint sources of environmental contamination for C. parvum, but there is some disagreement over the relative importance that adult cattle have in loading watersheds with significant amounts of C. parvum oocysts. In particular, there is a wide range of reported prevalences of fecal shedding of C. parvum for adult beef and dairy cattle. Numerous investigators have reported mean prevalences of fecal shedding from ϳ20 to ϳ70% in groups of clinically healthy adult cattle (23,31,34), yet several large cross-sectional epidemiologic surveys have observed prevalences of only 2% or less in asymptomatic adult cattle populations (4, 20, 41). Some of this variation in the observed prevalence of fecal shedding can be explained by different investigators using diagnostic assays of differing sensitivity and specificity (11,13,15), but much of the variation is the result of studying different populations of cattle (e.g., beef versus dairy), different age distributions within those populations, and groups of cattle under different management practices, especially when only a single farm or a small sample is examined. For example, we found in two different studies that calving duration fo...

Shedding of G. duodenalis was primarily limited to crias 1 to 4 months old. Llamas from properties with large numbers of crias born in the previous year, resulting in large numbers of yearlings in the current year, were at greater risk of infection. In addition, housing llamas in smaller pens or pastures and managing llamas and crias in large groups also increased the risk of G. duodenalis shedding.

The effect of venipuncture on blood serum catecholamine concentrations was studied in five yearling Red Angus bulls. Treatments consisted of sampling jugular vein blood via indwelling cannulas in a squeeze chute every 10 min for 1 h; sampling jugular vein blood from an indwelling catheter before, during and after venipuncture simulation; sampling jugular vein blood by venipuncture in a chute after shipment of 320 km to a slaughter plant; and sampling pooled blood from the neck during exsanguination at slaughter. Plasma epinephrine (E) and norepinephrine (NE) concentrations were determined by high performance liquid chromatography (HPLC) with electrochemical detection (ECD). Prevenipuncture NE and E in blood sampled from an indwelling catheter extended through a solid wall were 1.0 and .5 pmol/ml plasma, respectively. Plasma NE and E during venipuncture (1.6 and 1.1 pmol/ml, respectively) and immediately after cannulation in a squeeze chute (1.8 and 1.2 pmol/ml, respectively) were higher than prevenipuncture concentrations. Plasma NE and E, 1.9 and 1.2 pmol/ml plasma after shipment of 320 km, increased during exsanguination to 135.8 and 81.3 pmol/ml plasma, respectively. The NE and E in blood samples collected by venipuncture in a chute or box stall do not represent resting concentrations of these catecholamines.

Waterborne transmission of the pathogenic protozoa Cryptosporidium parvum has emerged as an important public health concern. To develop focused strategies to minimize the risk of waterborne transmission of this parasite to humans or animals, a standardized methodology is needed for comparing environmental loading rates for different populations of vertebrate hosts for C. parvum. A reasonable approximation for an estimate of the environmental loading rate is to measure the prevalence of infection and the intensity of shedding using cross-sectional surveys of the mammalian population, and then multiplying by an estimate of fecal production. We applied this concept to a variety of livestock and wildlife species found throughout California. In general we found that regardless of age, striped skunks, coyotes, California ground squirrels, and yellow-bellied marmots were substantial sources of C. parvum oocysts. In contrast, only the young stock of beef and dairy cattle were substantial sources of oocysts; adult cattle appear to excrete only limited numbers oocysts relative to either calves or wildlife. Watershed management plans that endeavor to minimize contamination of drinking water with C. parvum need to focus on appropriate management of wildlife reservoirs of C. parvum in addition to the traditional concern of animal agriculture.