ESTROUS BEHAVIOR AND OVARIAN ACTIVITY IN PREPUBERAL AND POSTPUBERAL DAIRY HEIFERS

The reproductive tracts of 53 Holstein heifers were examined per rectum twice weekly beginning at least 30 days before the first ovulation and continuing until ten days after the third ovulation, to determine pre- and postpuberal ovarian activity. The heifers were observed twice daily for estrus. The mean interval from birth to first ovulation was 42.3 weeks and from first to second ovulation and second to third, 20 days. The first ovulation was accompanied by silent estrus in 74% of the heifers. The occurrence of silent estrus declined to 43% at the second ovulation and to 21% at third ovulation. These differences were highly significant (P < 0.005). Estrous behavior did not affect subsequent ovarian conditions. Normal corpora lutea occurred during 79.9% of the cycles, cystic corpora lutea during 12.6%, cystic follicles during 2.5%, and anovulation during 5%. The occurrence of anovulation was significantly greater at first estrus than at subsequent estrous periods (P < 0.005). © 1969, American Dairy Science Association. All rights reserved.