The effect of high air temperature on pregnancy and birth weight in Merino sheep

Abstract

During the winter of 1954, 21 pregnant Peppin strain Merino ewes were subjected daily, 7 hours a day, 7 days a week, to an air temperature of 105°F dry-bulb, 92°F wet-bulb, in a psychrometric room. Nine of the ewes were heated from the date mating started and the other 12 from the 38th day of pregnancy. Birth weights of the lambs of the two groups showed no significant difference from those of 10 unheated control ewes pregnant during the same period. However, when subjected the following year, for the same period daily throughout the whole of pregnancy, to a higher temperature, namely, 112°F dry-bulb, 98°F wet-bulb, 10 experimental ewes produced lambs having a mean birth weight 1 lb 13 oz less than that of the lambs of eight unheated control ewes. The difference is highly significant statistically. It is concluded that pregnancy in Merinos is adversely affected by extremely high atmospheric temperature; and that this could well explain the low birth weight of lambs born following a summer gestation in tropical Queensland and in certain other parts of Australia when an unusually hot summer occurs.