Risk factors for mortality associated with respiratory disease among Menz and Horro sheep in Ethiopia.

A retrospective case-control study was conducted on 6718 sheep of two breeds (2772 Horro and 3946 Menz) on risk factors for mortality associated with respiratory disease (MARD) in Ethiopia, based on data collected between October 1993 and December 1997. Potential risk factors examined were breed, gender, age, month, and air temperatures.Fifty-four per cent of total deaths in the flock could be attributed to respiratory disease and the annual MARD rate ranged between 6.3 and 19.0%. There was significant breed (P<0.0001) and gender (P<0.0001) difference in MARD. The Horro breed had a higher (P<0.0001) annual MARD than the Menz breed (16.5+/-0.18 vs. 12.4+/-0.15%). A higher (P<0.0001) proportion of males suffered than females (15.1+/-0.23% vs. 13.8+/-0.13%). Age was also an important risk factor for MARD: there was a strong polynomial relationship (R(2)=0.91, P<0.0001) between MARD and age; the risk of being young if a sheep was a MARD case was high. MARD was high between October and March but relatively low between the months of April and September. There was a significant (P<0.05) negative cubic relationship (R(2)=0.49) between monthly MARD and monthly average minimum air temperatures. There was also a significant (P<0.01) positive exponential relationship (R(2)=0.61) between monthly MARD and average monthly daily deviation between maximum and minimum air temperatures. Timely health and management interventions focusing on these factors are necessary to alleviate losses from MARD. Understanding variations in MARD risk within a population can enhance early response to potential outbreaks, reducing losses.