OVARIAN ACTIVITY AT NATURALLY ATTAINED ESTRUS IN THE SOW - AN ULTRASONOGRAPHIC AND LH STUDY

In 6 multiparous crossbred sows (2nd to 4th parity, Swedish Landrace x Swedish Yorkshire), 15 proosestrous-oestrous periods during 2 oestrou s cycles were studied after weaning. The animals were controlled for o estrus, and the follicular growth and ovulation in their ovaries were followed by transrectal ultrasonography. Blood was sampled through ind welling catheters for analyses of LH and progesterone (P-4). The durat ion of oestrus (standing reflex) was 47 +/- 12.4 h, and the interval f rom onset of standing reflex until the end of ovulation was 39 +/- 12. 4 h (range 20-64 h). The LH peak concentration was 3.7 +/- 0.8 mu g/l, and the interval from LH peak level until ovulation was 23 +/- 8.4 h (range 8-32 h). The onset of standing reflex occurred in average 13 h before the LH peak level (range -4 - +36 h). The peripheral plasma con centration of P-4 showed a normal cyclic pattern in all animals. Low l evels (mean levels, 1.1-1.3 nmol/l) were seen during prooestrus and oe strus, high mean levels were found on days 10-16 (45-75 nmol/l) in the oestrous cycle. It was concluded that for an accurate determination o f ovulation, each animal has to be examined repeatedly. Ultrasonograph y is a most valuable tool for this purpose.