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THE INCIDENCE OF OESTRUS DURING LACTATION IN FINNISH LANDRACE, DORSET HORN AND FINN-DORSET SHEEP

Summary.: The incidence of oestrus was observed in thirteen Finnish Landrace, twenty-five Dorset Horn and 123 Finn-Dorset females between 0 and 56 days after lambing in the spring of 1968, and in 133 Finn-Dorset females between 10 and 56 days after lambing in the spring of 1969.

In 1968, 100% of the Finnish Landrace, 68% of the Dorset Horn and 59% of the crossbred ewes showed an oestrus and of those mated, 77%, 29% and 40%, respectively, conceived. In 1969, 23% of the females showed an oestrus, of which 71% were fertile. Within the Finn-Dorsets, the mean incidence of oestrus was found to be positively correlated with the age of the females (r = 0·97).

In addition to the normal 17-day oestrous cycles, many of the sheep displayed oestrus around 7 days after the preceding oestrus.

The hypothesis is advanced that a high level of gonadotrophic stimulation is an important common factor underlying the various aspects of increased reproductive activity in Finnish Landrace sheep.