Laboratory Animals > Volume 25, Number 1 > Pp. 30-34

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Quantification and classification of pregnancy wastage in 5-day cyclic young through middle-aged rats

J. A. M. Mattheij and J. J. M. Swarts

Agricultural University, Department of Human and Animal Physiology, Haarweg 10, 6709 PJ, Wageningen, The Netherlands; Agricultural University, Department of Human and Animal Physiology, Haarweg 10, 6709 PJ, Wageningen, The Netherlands

Fecundity was quantified in 4 to 11-month old rats with regular 5-day cycles. On the day following mating, less than 5% luteinized unruptured follicles occurred in either 4-month old or 11-month old rats; ovulation rate and also fertilization rate were similar in these young and middle-aged rats. At day 19 of pregnancy embryonic and fetal mortalities were quantified. Pregnancy wastage increased gradually with age; it was already significant in 7-month old rats. In rats of 9 months old it was about 30% and in 11-month old rats it was greater than 65%. Pregnancy wastage was mainly due to preimplantation and early-postimplantation mortality. Pregnancy wastage did not decrease when the pre-ovulatory surge of luteinizing hormone (LH) was reinforced and timed, by injection of the LH-releasing hormone analogue Ovalyse at noon on the day of prooestrus. The results corroborate the idea that pregnancy wastage in middle-aged rats with regular cycles is caused by an age-related reduction of the viability of ovulating eggs.

Key Words: FECUNDITY • AGEING • OOCYTE VIABILITY • PREGNANCY WASTAGE • RAT

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