Composite monthly single-day milk samples from the Florida Agricultural Experiment Station dairy herd 1959 to 1974 were analyzed for composition. Data were 22, 972 observations on five dairy breeds, but major statistical analyses were limited to Jerseys and Holsteins. Minimum relative humidity and maximum and minimum temperatures on day of evening sample were associated with 1.6 to 5.6% of variability within lactation (range for two breeds) of milk and milk constituent yields and 1.1 to 16.5% of constituent percentages. Yields of milk and constituents of the Holsteins seemed more sensitive to climatic variation than did Jersey, but Jersey constituent percentages were more sensitive. Yields were affected only slightly by increasing maximum daily temperatures from 8 to 29 degrees C but declined rapidly at greater than 29 degrees C; fat and protein percentages declined from 8 to 37 degrees C, whereas chloride content increased above 21 degrees C. Stage of lactation and pregnancy effects accounted for about 50% of the variability of yields and 3 to 23% of percentages. Effects were detected also for chloride and acidity percentages, specific gravity, and ratios solids-not-fat to fat and protein to fat.
Results confirm most other research on milk composition and yield. All responses were affected by climate, some considerably more than others, if percent of error variance is the criterion. Jersey yields were less sensitive to climate than were Holstein, but Jersey milk composition appeared more sensitive. Somatic cell count (REF), a measure of mastitis, was affected by climate but less than all other variables except protein/fat and LM%. Needed are estimates of interactions between climatic effects and response surface models to quantify possible improvement in performance following environmental modification. Genetic correlations between milk yield and REF and chloride % suggest that single trait selection for milk yield might increase incidence of mastitis although phenotypic correlations indicate that high yields and absence of mastitis are correlated.
Background. Bovine rotavirus (BRV) and bovine coronavirus (BCoV) are the most common viral agents in neonatal calf diarrhea and result in serious economic consequences. The aim of the study was to determine the epidemiology of those viruses in randomly selected dairy farms of Addis Ababa. Methods. A cross-sectional study was conducted from November 2018 to April 2019 using a probability proportional to size (PPS) sampling technique. A total of 110 calves, less than 30 days of age, from 57 dairy herds were involved in the study. Associated factors of herds and calves were collected using semistructured interviews from farm owners and through physical observation of selected calves. Fecal samples were collected and analyzed using the sandwich ELISA method. Data generated from both semistructured interviews and laboratory investigation were analyzed using STATA_MP version 15. Results. From the total 110 calves, 42 (38.18%) had diarrhea during the survey. The prevalence of bovine rotavirus and coronavirus was 3.64% (4/110) and 0.91% (1/110), respectively. Diarrhea, feeding colostrum timing, and sex of the neonatal calves had statistically significant association with bovine rotavirus infection (
p
<
0.05
). All rotavirus-positive neonatal calves were identified in small scale dairy farms and in dairy farms that reported mortality though they lack statistically significant association. Only one coronavirus case was detected among the neonatal calves. The case was identified among small scale herds and in a herd with diarrheal cases. The sex of the coronavirus calf was female, diarrheic, and among 11-20 days old. Conclusion. The prevalence of rotavirus and coronavirus infections in neonatal calves was seldom in dairy farms of the study area. Rotavirus was more common than coronavirus, and further studies should be initiated on other (infectious and noninfectious) causes of neonatal calf diarrhea in the area.
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