Circannual variations in intraovarian oocyte but not epididymal sperm quality in the domestic cat

Ovaries and testes were collected throughout the year from domestic cats sp ayed and neutered at local veterinary clinics. Fresh oocytes recovered from minced ovaries were subjected to in vitro maturation and then stained to d etermine stage of maturation or were inseminated with conspecific sperm. Th e cauda and corpus regions of each epididymis were dissected into pieces an d placed in medium; 30 min later, the epididymal tissue was removed, the me dium centrifuged, and the sperm pellet resuspended. Samples were assessed f or total sperm count and sperm motility traits, morphology, acrosomal integ rity, and ability to penetrate cat oocytes in vitro. Fewer excellent (grade I) oocytes were recovered per ovarian pair during September-November (mean +/- SEM, 19.2 +/- 2.1%) than during January-July (36.8 +/- 3.6%, p < 0.05) , while the remaining months had intermediate percentages of grade I oocyte s (p > 0.05). A high percentage of oocytes recovered from November-April co mpleted nuclear maturation (64.3 +/- 6.8%), which was different (p < 0.05) from the values for May-July (32.2 +/- 3.8%) and August-October (10.4 +/- 2 .9%). Percentage of oocytes with bound sperm was lowest (p < 0.01) in Septe mber and October (32.0 +/- 3.1%) compared to February and March (91.4 +/- 1 .7%). Percentage of oocytes with sperm within the perivitelline space was h ighest (p < 0.05) in May-August (33.8 +/- 4.6%) compared to all other month s, In contrast, the period of highest (p < 0.01) fertilization (i.e., great er than or equal to 4-cell embryo formation) was March-April (51.7 +/- 3.1% ) as compared to May-July (17.2 +/- 1.8%) or November-January (12.4 +/- 2.6 %). Negligible numbers of oocytes recovered during August-October developed beyond the 2-cell stage (1.1 +/- 0.3%). Blastocyst development from cleave d embryos was highest during February-April (44.3 +/- 2.3%) and lowest duri ng August-October (0.6 +/- 0.1%; p < 0.01). Sperm recovered from the epidid ymides throughout the year did not differ (p > 0.05) in concentration or in any of the motility, structural, or functional variables evaluated. In sum mary, cat oocyte nuclear maturation in vitro is depressed during August-Oct ober, and the ability to form cleaved embryos remains low even when the cap acity to achieve nuclear maturation is relatively high (November-January an d May-July). In contrast, male cats are capable of consistently producing v iable, progressively motile sperm throughout the year.