Bohrer, E. (2016). Determining the Onset of Reproductive Capacity in Free-Roaming, Unowned Cats (Doctoral dissertation).Oregon State University. University Honors College
The purpose of this thesis was to determine if an underlying biological cause exists for the exuberant reproductive success in free-roaming unowned (FRU) cats. The hypothesis for this thesis was that FRU tom and queen cats have reproductively adapted to man-made sterilization efforts by lowering the age at which they enter puberty. For domestic cats, puberty is reported to occur around 8 months of age. Cats were presented for surgical sterilization at either a feral cat clinic or at a local Humane Society during August-October 2014 and 2015. Age was determined by records provided from feral cat colony managers and confirmed with dental eruption patterns. The age groups for tom cats were: 2-2.5 months (weanling; n=6), 3-4 months (juvenile; n=6), 5-6 months (pubertal; n=6), and 12-24 months (adult; n=6). Queens were grouped by age (<4 months (pet n=5, FRU n=10) and 4-6 months (pet n=2, FRU n=7)).
For tom cats, the penis was evaluated to determine if spines were present and the contents from both vasa deferentes were milked onto a microscope slide, mixed with eosin-nigrosin stain, spread with a spreader slide, allowed to air dry and evaluated at 1000X. The percentage of sperm with normal morphology was determined after evaluating 100 sperm/slide. Testicles were hemi-sectioned, formalin-fixed, paraffinembedded, cut into sections (6 µm), stained with hematoxylin and eosin (H&E), and evaluated at 200X for evidence of spermatogenesis and measurement of seminiferous tubule diameter. For queens, the total ovarian uterine weights from FRU queens were also recorded. Ovaries were hemi-sectioned, formalin-fixed, paraffin-embedded, cut into sections (6 μm), stained with H&E, and evaluated at 200X. Follicles were counted and classified as primary, secondary, or tertiary. More adult toms (16/16) than juvenile toms (4/13) had penile spines (p<0.05). Mean±SD morphologically normal sperm for the juvenile and adult tom cats was not significantly different (77±11% and 81±13%, respectively). Evidence of spermatogenesis in weanling, juvenile, pubertal, and adult toms was 0%, 17%, 67%, and 100%, respectively (p<0.05 between successive age groups). The seminiferous tubular diameter was significantly larger in each successive age group (weanlings 88.10±10.88 µm; juveniles 109.8±8.89 µm; pubertal 142.2±16.89 µm; adult 237.90±52.45 µm). FRU queen cats under 4 months old had more tertiary follicles compared to owned cats under 4 months of age (33% and 17%, respectively; p<0.05). Total ovarian uterine weights were significantly higher in 4-6 month old FRU queens compared to under 4 months (1.18±0.31 g vs 0.93±0.28 g, respectively).
These observations provide an explanation for why TNR efforts to reduce FRU cat populations have not successful. Selective pressures and a significantly shortened life span may be factors contributing to this finding.