Circannual Variations in Intraovarian Oocyte but Not Epididymal Sperm Quality in the Domestic Cat1

Abstract

Ovaries and testes were collected throughout the year from domestic cats spayed and neutered at local veterinary clinics. Fresh oocytes recovered from minced ovaries were subjected to in vitro maturation and then stained to determine stage of maturation or were inseminated with conspecific sperm. The cauda and corpus regions of each epididymis were dissected into pieces and placed in medium; 30 min later, the epididymal tissue was removed, the medium centrifuged, and the sperm pellet resuspended. Samples were assessed for total sperm count and sperm motility traits, morphology, acrosomal integrity, 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 oocytes (p > 0.05). A high percentage of oocytes recovered from November–April completed 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 September 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 highest (p < 0.05) in May–August (33.8 ± 4.6%) compared to all other months. In contrast, the period of highest (p < 0.01) fertilization (i.e., ≥ 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 cleaved embryos was highest during February–April (44.3 ± 2.3%) and lowest during August–October (0.6 ± 0.1%; p < 0.01). Sperm recovered from the epididymides throughout the year did not differ (p > 0.05) in concentration or in any of the motility, structural, or functional variables evaluated. In summary, cat oocyte nuclear maturation in vitro is depressed during August–October, and the ability to form cleaved embryos remains low even when the capacity to achieve nuclear maturation is relatively high (November–January and May–July). In contrast, male cats are capable of consistently producing viable, progressively motile sperm throughout the year.