A study on puberty and oestrus in gilts.

The main purpose of this study was to investigate the oestrous symptoms at puberty and during the two subsequent oestrous periods in the gilt. The investigation comprised a total of 369 purebred Swedish Yorkshire gilts. The gilts were carefully checked for oestrous symptoms twice daily, from 160 to 260 days of age, and blood samples for progesterone determination were drawn from 170 days until puberty. The duration of prooestrus was longer (p less than or equal to 0.001) at the at the first oestrous period than at the two subsequent oestrous periods and decreased (p less than or equal to 0.05) with an increase in age at puberty. Most of the oestrous symptoms were significantly correlated within the first and between the first three oestrous periods. Twenty percent of the gilts did not show standing reflex and anovulatory oestrus was found in 2% of the gilts at puberty, as demonstrated by progesterone determinations. The frequency of gilts not showing standing reflex at the second and third oestrus was approximately the same as at the first oestrous period. The first oestrous cycle was longer (p less than or equal to 0.001) than the second cycle. Approximately 95% of the gilts had a cycle length within 18 to 24 days at the first and second oestrous cycle.