Seasonal and Other Changes in The gestation duration of Sheep

Data from 266 pregnancies of 144 Finn x German Mutton Merino and Finn x Awassi ewes were used to determine the effects of season of mating, dam and sire breeds, litter size and sex of the offspring, and age of the ewe on the duration of gestation. June, September–October and January matings resulted in significantly different durations of gestation of 143·3, 145·3 and 146·1 days, respectively. Suffolk rams’ matings resulted in a significantly shorter gestation than matings with German Mutton Merino, Schwarzkopf or cross-bred rams. A highly significant linear regression ( b = –0·80) of the duration of gestation on the number of lambs was found. Male lambs were carried longer than female lambs. The intraclass correlation between the gestation periods for lambs which were maternal half-sibs was highly significant.