Control and prevention of complicated Mycoplasma Hyopneumoniae among pigs reared in an age segregated production system

This thesis discusses two problems of increasing economical importance in modem pig production which are excess death loss and excess numbers of substandard pigs, that is, pigs which do not reach the minimal weight to assure optimal revenue. In one farm system studied, the proportion of weaned pigs sold at full value was 21.4 percentage points below a target value of 94.0%. A review of the literature proposes many potential causes for increased mortality, but relatively little published literature on substandard pigs is available. In a retrospective analysis of farm production data, the interaction quarter*year was associated with mortality rate and substandard rate (p < 0. 01), and sex was significantly related to mortality rate (p<0.01). In a prospective trial of 12 cohorts, the administration of an antibiotic with a bacteriostatic effect on M hyopneumoniae was associated with a 12.7% substandard rate, compared with at 26.4% substandard rate for cohorts offered feeds with antibiotics not labeled for respiratory diseases (p