Longitudinale Untersuchung zum Einfluß distinktiver Kälbermerkmale und verschiedener Umwelt- und Managementparameter auf die Morbidität und Mortalität von Kälbern im Rukungiri Distrikt, Uganda

Abstract

A prospective field study was carried out on 656 calves over a study period of one year (September 94 to September 95) on 38 randomly selected smallholder farms in the Rukungiri District, South-West Uganda. The overall objectives of this longitudinal study were to describe morbidity and mortality patterns of dairy calves from birth to 1 year of age and to examine calf and herd management practices as risk factors for calf morbidity and mortality. The study farms were visited every 4 to 6 weeks and standardized questionnaires recording calf management, herd- and farm parameters were used, all calves were examined clinically and newborn calves were blood sampled and their birth weight taken. From newborn calves up to 7 days blood samples were taken for colostral immunoglobulin transfer determination.

A total of 170 calves less than 7 days old from all study herds were tested for the adequacy of passive immunoglobulin transfer. The zinc sulphate turbidity test in each case showed levels higher than 800 mg/dl. There was no obvious seasonality in calving. Birth weight increased with an increase of exotic blood. Calves of exotic breeds at birth weighed on average 36.7 kg, pure indigenous calves 27.7 kg.

The most common suspected diseases were East Coast Fever (ECF) with a morbidity density rate of 1.0 cases per 1000 calf days at risk. Eye problems and diarrhoea were diagnosed each in 0.5 cases, lung affections in 0.3 cases per 1000 calf days at risk and 14 cases of navel infections were recorded. Lung affections and navel infections occurred most commonly in the first week of life and morbidity rates for suspected ECF and diarrhoea were highest in the first month of life. The highest density rate for eye problems was found between month 3 and weaning age. All diseases were spread between most herds but inter-herd rates varied considerably. No association between morbidity and calf-herd-size was established.

The annual crude calf mortality rate in Rukungiri District of 8.23% is comparably low, it corresponds to a crude calf mortality of 0.34 cases per 1000 calf days at risk. Suspected tick borne diseases accounted for the largest proportion of all deaths (40%) during the monitoring period. Death due to diarrhoea (19%), unknown causes (15%), accidents (15%) and sudden death (11%) further contributed to the proportional mortality on the study farms.

The inter-herd variability of calf mortality rates was remarkable. 36% of the study herds did not show any mortality while 12.8% had a calf mortality rate over 1 case per 1000 calf days. In one locality (Kambuga) of the project area, calf mortality was particularly low. Death occurred in all calf-herd-sizes and did not show associations to seasons and climate.

No statistical significant association between distinctive calf parameters and calf mortality could be established. The highest density of mortality was found in the first month of age. A trend of a higher calf mortality rate for bull calves is suggested. Losses were highest in low grade crosses (0.42 cases per 1000 calf days at risk) while no pure Friesian calf died. In regards to parity calf mortality was higher in heifer calvings than in multiparous cow calvings (0.41 and 0.27 per 1000 calf days at risk, respectively).

The univariate analysis of calf- and herd mangement factors (location of farm, herd size, breed, composition of the herd, management at birth, feeding, calf housing and calf care) did not establish significant associations to the observed calf mortality.

A logistic regression and a classification tree were used as multivariate models to estimate the relationship between explanatory variables and death of calves. The predictive ability of both models failed to explain the outcome variable "death yes".

The wide-meshed usually dichotomous variables used failed to explain mortality. It is concluded that these variables in fact sub-summarize a multitude of levels, rather than being truly dichotomous. The factors in the analysis in consequence did not delineate satisfactory standardized routine management practices. It is concluded that calf management in Rukungiri District still follows traditional, haphazard procedures, rather than accommodating needs of modern dairy herds.