The effect of chronic non-progressive pneumonia on weight gain of pasturefed lambs

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Abstract
The liveweight gains and carcass weights of 40 lambs grazed under pastoral conditions were compared with those of a similar group with chronic non-progressive pneumonia which had been induced by intranasal inoculation of an aerosol of homogenised pneumonic lung at about 120 days of age. Half the lambs from each group were killed 30 days post-inoculation following rotational grazing on high quality pasture. At this time the pneumonic lambs had a mean liveweight gain of 1.74 kg less than the controls. The remainder were slaughtered at 60 days, when drier conditions prevailed, by which time the difference in mean liveweight had increased to 2.19 kg. During the second period, four of the severely affected lambs lost weight. A significant linear relationship was found between liveweight gain and the extent of the pneumonic lesions which indicated that a reduction of nearly 1 kg/month could be expected for every 10% of the lung surface area affected. Carcass weights were reduced by a mean of 1.5 kg over the 60-day period, 1.39 kg of which occurred in the first 30 days.