Prolonged Duration of Fertility of Dog Ova

• Published in: Reproduction in domestic animals Vol. 44; no. s2; pp. 230 - 233
• Main Authors: Tsutsui, T, Takahashi, F, Hori, T, Kawakami, E, Concannon, PW
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.07.2009; Blackwell Publishing Ltd
• Subjects: Animal reproduction; Animals; Dogs; Dogs - physiology; Female; Fertility; Fertilization; Insemination, Artificial - veterinary; Ovum - physiology; Pregnancy; Pregnancy, Animal; Time; Time Factors; Veterinary medicine
• ISSN: 0936-6768; 1439-0531
• DOI: 10.1111/j.1439-0531.2009.01450.x

The fertile period for natural mating in dogs extends from before ovulation until day 5 post ovulation (PO) and involves a delay in oocyte maturation until 2-3 days PO and viability of secondary oocytes for 48-60 h or more. Spermatozoa do not enter the uterus after vaginal insemination in late oestrus. Cervical closure appears to occur on average 5 days PO, but conception may occur following intrauterine artificial insemination (IUAI) up to 8 days PO. Therefore, the present study was conducted to clarify the duration of fertility of canine ova. Using IUAI at 6, 7, 8 and 9 days PO (n = 5 bitches each) conception rates were 100%, 71.4%, 37.5% and 0%, respectively, with an average litter resorption rate of 30.8%, and with mean litter sizes and times to delivery PO being 4.3 ± 1.6 and 64.3 ± 0.3 days, 4.0 ± 1.4 and 66.3 ± 0.4 days, and 2.5 and 68 days for IUAI at 6, 7 and 8 days, respectively. The high pregnancy rates with IUAI at 6 and 7 days PO confirm that many canine oocytes are fertile at 4-5 days after maturation. The high rate of resorption was presumably because of aging of ova or asynchrony between embryonic development and the intrauterine environment.