Description of fecal shedding of Cryptosporidium parvum oocysts in experimentally challenged dairy calves.

The objective was to describe the probability of Cryptosporidium parvum fecal oocyst shedding at different magnitudes of exposure, the pattern of fecal shedding over time, and factors affecting fecal shedding in dairy calves. Within the first 24 h of life, 36 calves were experimentally challenged with C. parvum oocysts at one of four possible magnitudes of oral exposure (1 × 10(3), 1 × 10(4), 1 × 10(5), and 1 × 10(6) oocysts), and 7 control calves were sham dosed. Fecal shedding occurred in 33 (91.7 %) experimentally challenged calves and in none of the control calves. There was a difference in the log-total number of oocysts counted per gram of feces dry weight among the four exposure groups; calves with the lowest magnitude of exposure (1 × 10(3) oocysts) shed less than the other three groups. At higher magnitudes of exposure, there was more variability in the range of fecal oocyst shedding. There was an inverse relationship between the log-total amount of oocysts counted per gram of feces dry weight and the number of days to the onset of fecal shedding per calf, i.e., the more time that elapsed to the onset of fecal shedding, the fewer oocysts that were shed. The pattern of fecal shedding over time for all calves shedding oocysts was curvilinear; the number of oocysts increased with time, reached a peak, and declined. Therefore, the dynamics of oocyst shedding can be influenced in part by limiting exposure among calves and delaying the onset of fecal oocyst shedding.

Effect of nutritional plane on health and performance in dairy calves after experimental infection with Cryptosporidium parvum.

OBJECTIVE: To evaluate the effect of nutritional plane on health and performance of dairy calves after infection with Cryptosporidium parvum. DESIGN: Randomized, controlled trial. ANIMALS: 20 Holstein bull calves. PROCEDURES: Calves were assigned to a higher plane of nutrition (HPN; 0.30 Mcal intake energy/kg of metabolic body weight using a 28% protein-20% fat milk replacer) or conventional nutrition (CN; 0.13 Mcal intake energy/kg of metabolic body weight using a 20% protein-20% fat milk replacer). Calves were inoculated with C parvum oocysts at 3 days old. Fecal and health scores, oocyst counts, weight gain, dry matter intake, and hematologic variables were measured for 21 days. Data were analyzed with nonparametric and regression methods. Results-Body weight (day 1), serum total protein concentration (day 3), and PCV (day 3) were not different between groups. Oocyst shedding was not different between groups. The PCV was higher in the CN group (40%), compared with the HPN group (32%) at the end of the study. Fecal scores (FS) improved faster in the HPN group (median, -0.1 FS/feeding), compared with the CN group (median, -0.06 FS/feeding). The HPN calves had better average daily gain (ADG) than did CN calves (median, 433 g/d vs -48 g/d, respectively). Feed efficiency (ADG:dry matter intake ratio) was better for HPN calves than CN calves (median, 131.9 g/kg vs -31.4 g/kg). CONCLUSIONS AND CLINICAL RELEVANCE: After a pathogen challenge, calves maintained hydration, had faster resolution of diarrhea, grew faster, and converted feed with greater efficiency when fed a higher plane of nutrition.

A comparison of fecal percent dry matter and number of Cryptosporidium parvum oocysts shed to observational fecal consistency scoring in dairy calves.

Evaluation of dairy calf feces is often used in research and for clinical decision making to assess severity of diarrhea. However, this has not been validated for agreement between dry matter content and observed fecal consistency. Therefore, a comparison of observed fecal consistency score to fecal percent dry matter and Cryptosporidium parvum oocyst shedding was performed to assess the accuracy of observational scoring as a measure of diarrhea and its association with number of oocysts shed. Fecal samples from 20 dairy calves experimentally infected with C. parvum oocysts were collected daily post-infection and scored on a scale from 1 to 4, with 1 being normal feces to 4 being severe diarrhea. An aliquot of each sample was analyzed for percent dry matter and Cryptosporidium oocyst counts by using immunofluorescent microscopy. Fecal consistency scores of 1, 2, 3, and 4 had median percent dry matter of 20.9, 16.3, 9.6, and 5.8, respectively. Using percent dry matter assessed by fecal consistency scoring were significantly different from each other (P < 0.001). A higher fecal consistency score also was associated with a greater number of Cryptosporidium oocysts shed (P < 0 .0001). Scores of 1, 2, 3, and 4 had median oocyst counts of 0, 0, 1.3 × 106, and 2.8 × 106, respectively. These results suggest that observational scoring is a useful proxy to assess diarrhea in dairy calves.