Studies on sub-clinical coccidiosis with a zootechnical approach

This project aimed at investigations (six studies) on whether sub-clinic coccidiosis impairs growth performance of naturally infected Saanen and Boer goat kids, and to determine whether the infection can be managed by certain management practices, e.g., host nutrition, weaning.In the first two studies, coccidial oocyst outputs of naturally infected dairy goat kids were followed during defined growth periods, and repeatability of oocyst excretion was estimated, respectively. Results showed that weaning method employed in the research farm resulted in a weaning shock, as indicated by the impaired growth traits of the kids, and the kids were not fully able to use growth potential, which was determined by the environmental conditions provided in the farm. Differences between faecal coccidial oocyst counts (oocysts per gram of faeces, OpG) of heavy and light kids, as well as between fast and slow growing kids during the growing periods, indirectly indicated that sub-clinical coccidiosis may to some extent contribute to the impaired growth of light or slow growing kids. A large variation was observed in OpG counts of the kids. Accordingly, low/moderate repeatabilities, ranging from r= 0.14 to r=0.43, were estimated for OpG throughout the growth period.Results from two experiments designed to determine whether and how efficiently kefir, a traditional probiotic source, would reduce OpG counts of dairy goat kids following weaning showed that sub-clinical coccidiosis did not have a significant overall effect on growth performance of the kids. Although kefir reduced oocyst excretion of the kids roughly by one-third, this effect was not associated with the performance of the kids. Thus it was concluded that kefir does not have an overall impact on sub-clinical coccidiosis, which was harmless to performance of the kids.Effects of weaning age (six or twelve weeks) on sub-clinical coccidiosis in Boer goat kids were investigated in another experiment. It was shown that early weaning resulted in a weaning stress, as indicated by increased vocalization as well as impaired performance. Early weaned kids had higher OpG counts at later ages, indicating that early weaning may increase susceptibility of the kids to infection at later ages.Effects of increased level of protein in host animal diet (23% vs 17% CP) on sub-clinical coccidiosis were investigated in the last experiment. Half of the kids were prophylactically treated with toltrazuril (20 mg/ kg BW) against coccidiosis at regular intervals, whereas the remaining kids, receiving either of the diets, were left untreated. Results showed that growth performance of the kids was enhanced by the increased level of protein whereas prophylactic treatment had no effect, indicating that the sub-clinical coccidiosis did not have an adverse effect on the performance. Overall oocyst output of kids fed different diets followed a quite similar pattern and did not differ significantly.It was concluded that the level of sub-clinical coccidiosis observed in different experiments was in general low, and did not have an overall adverse impacts on growth performance of naturally infected kids. However, level of the infection was influenced by the weaning methods and this may indicate that the management can play an important role in controlling sub-clinical infection. Given the low level of infection, kefir and increased level of protein did not influence sub-clinic infection although they reduced oocyst excretion of the kids by one-third. This may indicate a potential role of host-nutrition in controlling infection, particularly in case of higher levels of the infection.