In the Netherlands, separate activities of FSH and ICSH in the pituitary, morphological changes in ovaries and vaginal smears were examined in Texel ewes during the oestrus cycle. Both FSH and ICSH content of the pituitary decreased very sharply in late dioestrus. Immediately after ovulation, FSH content increased again but ICSH not before the end of luteinisation. Times of oestrus in Dorper sheep, (a non-wool mutton breed) and in the Merino (with good quality wool) were determined during grazing on mixed Karroo veld in South Africa. The relation between age or Reece type and oestrus was studied in the Dorper. Maiden ewes had a limited breeding season. Mature ewes, especially those of intermediate fleece type, exhibited oestrus throughout the year. Merino sheep had a limited breeding season as judged by oestrus and by ovarian morphology. The difference in length of breeding season between Dorper and Merino sheep seemed to be of great practical importance.
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