A path model of factors influencing morbidity and mortality in Ontario feedlot calves.

The principles of path analysis and causal modelling are discussed. Path analysis was applied to three data sets to assess the relationship between group characteristics (number per group and "mixing" subgroups of cattle, feeding-management of the group and processing factors (vaccination and prophylactic antimicrobials) and subsequent morbidity and mortality in feedlot cattle. The major findings agree with previously reported results but the timing and pathways of the effects are elaborated. In general, morbidity in week 1 was correlated with morbidity in week 2, which was correlated with morbidity in weeks 3-5. The same was generally true for mortality. In general, morbidity was not strongly correlated with mortality. Lots (unmixed groups) did not arrive in better condition, but experienced fewer subsequent health problems than mixed groups. (Silage-fed lots appeared to do poorly, however this was apparently due to the positive association between lots and vaccination, the latter being detrimental to mortality rates.) The more cattle per group, the greater the health problems in weeks 3-5 postarrival. Prophylactic antimicrobials in the water supply on arrival lead to increased health problems in the three to five week postarrival period. Antibiotic containing starter rations had a beneficial effect on health status in this period. This effect appeared to be partly due to delaying making silage the major ration component in silage-fed cattle receiving antimicrobial containing starter rations. Vaccination against respiratory disease in either of the first two weeks postarrival had detrimental direct and indirect effects on subsequent health status. Vaccination during weeks 3-5 postarrival was not significantly related to health status in that period.     

Schofield memorial lecture. Bull semen and muscle ATP: some evidence of the dawn of medical science in ancient Egypt.

The importance of animal experimentation to human and animal health is not well understood by an increasingly articulate segment of the public. This could have very unfortunate consequences for man and his domestic animals. Even veterinarians and physicians are not as conversant as they need be about the great extent to which advances in human health have depended upon animal observations and experiments. Some believe that resort to "animal models" of biomedical phenomena, including diseases--a comparative or analogical approach to medical studies--is a relatively recent event. Even medical historians often treat these subjects as occasionally recurring aberrations which began with the Greeks, thus largely overlooking the historical meaning and continuing importance of "one medicine" irrespective of species. In fact, comparative medicine has probably been basic to medical progress ever since the dawn of a medical science. Recent research indicates that this approach to biomedical mysteries began to evolve in the minds of Egypt's healer-priests long before Aristotle and the later Alexandrian Greeks made the whole process explicit. Here we examine the origins of what were possibly the first two biomedical theories profounded from inferences based upon dissections, confirmed in at least one instance by experiment, and then applied to medical practice.     

Recurring origins of allopolyploid species in asplenium

A large proportion of plant species has originated through allopolyploidy: interspecific hybridization followed by chromosome doubling. Heterozygosity remains fixed in allopolyploids because of nonsegregation of parental chromosomes. Two allotetraploid species of the fern genus Asplenium show allozyme polymorphisms at loci that are polymorphic in their diploid progenitors, indicating that each has originated more than once and implicating continued gene flow from diploids to tetraploids.