RISK-FACTORS FOR RESPIRATORY-DISEASE MORTALITY IN LAMBS

A retrospective cohort study used records from a large flock of sheep in Illinois, USA in logistic regression models to identify risk factor s for respiratory disease mortality (RM) in lambs born from 1986 to 19 91 (n=6806). The flock of several purebred and crossbred lines was int ensively managed in open-front barns from birth to weaning (56 days) a nd fattened in slotted-floor barns. Annual postnatal mortality ranged from 12% to 19% of lambs born. Potential risk factors examined were ge nder, lamb breed, birth weight, lambing location, number of siblings a t birth and rearing, birth vigor, and the dam's parity, milk supply an d udder condition. RM occurred in 4.3% of lambs that survived the firs t 24h after birth, and this rate was fairly stable over all years of t he study (3.3-5.0%). One model compared RM cases with all lambs surviv ing the first day of age and a second model compared RM cases with all lambs surviving to weaning (56 days of age). In the first model, ther e was increased risk for RM in ram lambs (OR=1.9), purebred Suffolks ( OR=2.0), lambs from first parity dams (OR = 1.9), and lambs from dams with poor milk production (OR = 2.2). Lambs with average birth weight were at slightly lower risk for RM than light or heavy weight lambs (O R = 0.8). The second model identified similar factors, with ram lambs, Suffolks, and lambs from dams at first parity or with poor milk suppl y at increased RM risk (OR = 2.0, 2.3, 2.0, and 2.3, respectively) and average weight lambs at lower risk for RM (OR = 0.7). A strong birth vigor reduced risk for RM (OR = 0.7). Variables not included in final models included lambing location, number of siblings at birth/rearing, and the dam's udder condition. Although factors such as breed and gen der may not generally be manipulated to decrease RM, other factors suc h as birth weight and the dam's milking ability can be improved to red uce respiratory disease mortality. Awareness of variations in RM risk within a population can enhance early response to potential outbreaks, reducing losses. (C) 1997 Elsevier Science B.V.