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.
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.
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