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Contents

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

The objective of this study was to determine the seasonal ovarian activity of domestic queens under the tropical conditions of southern Mexico (19° 30′ and 21° 35′ N latitude). A total of 250 reproductive tracts were evaluated, and the frequencies of queens with ovarian activity (oestrus, dioestrus or pregnant), anoestrus, pregnancies and ovulation rate by season of the year (spring, summer, autumn and winter) were calculated. Ovarian activity was observed throughout the year, but a significant reduction occurred during the winter; conversely, anoestrous cases were lower during spring and showed an increase during summer, autumn and winter. Pregnancies were most common during spring and decreased during summer, autumn and winter. Ovulation rate varied from 2.5 to 2.8 during the four seasons. Cystic endometrial hyperplasia, pyometra and ovarian follicular cysts were the most common lesions found. The results demonstrate that domestic queens are not seasonal in tropical conditions, but a clear effect of the season of the year reducing ovarian activity is present.


Introduction

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

The domestic queen (felis catus) is considered a seasonally polyoestrous species with induced ovulation, unless the cycle is interrupted by pregnancy, pseudopregnancy or disease. Extended daylights (>12 h/day) after a period of short days induces oestrus (Hurni 1981). Plasma concentration of melatonin plays the pivotal role, modifying the hypothalamus-hypophyseal-gonadal axis (Leyva et al. 1984). A short photoperiod is associated with high melatonin concentration produced by the pineal gland that reduces the ovarian activity (Little 2001). In the northern hemisphere, the peak season of oestrus is February to June, which shifts to July to August in temperate climates (Feldman and Nelson 1996). An anoestrous season occurs at the end of autumn because of short daylights, and ovarian cycles being re-established at the end of winter or beginning of spring. Very scarce information exists about the reproductive seasonality of the female domestic cat in the tropics. This study will generate information on the reproductive characteristics of queens and will provide information needed to develop reliable estimates of sexual activity under tropical conditions.

The objective of this study was to characterize the reproductive activity, during 1 year, of female domestic cats in southern Mexico.

Materials and Methods

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

Study area

The study was carried out in Merida, capital city of Yucatan, Mexico (19°30′ and 21°35′N latitude, 87°30′ and 90°24′W longitude), at 6 m above sea level. The climate in the region is warm sub-humid with rain during the summer. A difference of 2.5 h daylength is observed between summer and winter in the region. The seasons of the year were spring (22 March–21 June), summer (22 June–21 September), autumn (22 September–21 December) and winter (22 December–21 March). The average day length for each season of the year was 12.1, 13.1, 12.2 and 11.6 h for spring, summer, autumn and winter, respectively.

Animals

A total of 250 reproductive tracts were evaluated during 2010–2011. Tracts were collected from adult queens (≥1 year old) after elective standard ovariohysterectomy. Most of the cats, presented for surgery (97%), where domestic short hair (DSH). Age was determined based on clinical history (collected from owners) and by dental development. At least 50 reproductive tracts were collected for each season.

Collection of samples and evaluation

Vaginal smears were taken from each queen and stained with Diff-Quik and examined for the percentage or large intermediate epithelial cells. Recovered ovaries were macroscopically inspected for the presence of follicles or corpora luteal, and the number of each was recorded. Any ovarian abnormalities were noted. The uterus was carefully inspected and palpated for tone; uterine abnormalities and pregnancies were recorded.

A queen was considered to be in oestrus when at least one follicle ≥0.3 mm was present in an ovary, the vaginal cytology showed a high percentage (>50%) of superficial cells and the uterus was turgid at palpation. Ovulation rate was calculated as the mean number of corpora lutea observed in the ovaries in each season.

Statistical analysis

Frequency of queens with ovarian activity (oestrus, dioestrus or pregnant), anoestrus, pregnancies and ovulation rate by season of the year (spring, summer, autumn and winter) were obtained to determine the effect of season of the year for the binomial variables, and chi squared tests were used. Significance was stated at p < 0.05.

Results

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

Oestrous, anoestrous and pregnant queens were observed throughout the year. However, during the autumn and winter, a significant reduction in the ovarian activity was observed. Pregnancy showed a seasonal pattern, with more pregnancies seen during spring and summer (Table 1). Ovulation rate varied from 2.5% to 2.8% during the four seasons. Cystic endometrial hyperplasia (1.7%), pyometra (1.4%) and ovarian follicular cysts (0.9%) were the most common lesions found.

Table 1. Frequency by season of the year of the ovarian activity, anoestrus, pregnancy and ovulation rate for 250 female cats in a tropical area of Mexico
 Spring (%)Summer (%)Autumn (%)Winter (%)
  1. Within a row, means without a common superscript letter (a-b) differed (P <0.05).

Ovarian activity90.9a90.2a74.5a47.5b
Anoestrus9.1a9.8a25.5b52.5b
Pregnancy33.3a32.8a8.5b10.0b
Ovulation rate2.7a2.5a2.5a2.8a

Discussion

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

Although the domestic cat is considered a seasonal polyoestrous species with a peak of reproductive activity starting after the winter solstice (as daylight hours increases in the North hemisphere), results from the present study indicate that at 29° north latitude female cats can cycle and breed throughout the year. Similarly, a report from Da Silva et al. (2006) indicated that domestic cats in equatorial regions may cycle throughout the year. In a recent study in Argentina (31° south latitude), domestic cats were found to cycle throughout the year but most of them during periods of time when the day length was increased (Faya et al. 2011). Despite the fact that cats are non-seasonal in equatorial regions, the time of the year, in particular light hours, may exert a significant influence on ovarian activity. The cat is highly sensitive to photoperiod so that ovarian activity reduces because of a high serum concentration of circulating melatonin (Leyva et al. 1984). The controlled experiments of Hurni (1981) showed that at least 14 h of light were required to induce oestrus in female cats, interestingly under tropical conditions at 20° latitude north or along the Tropic of Cancer, the slight difference of hours light (2.5–3 h) throughout the year did not appear sufficient to reduce the reproductive cyclicity. In another study, 14 h of light stimuli preceded by 12 h light/day for 1 month were shown to be necessary to induce oestrus (Chantal 1993). Results from the present study indicate that even in the tropics, daylight hours have a significant effect on the ovarian activity of queens. However, other factors may also be involved including reproductive and social stimulation of other cats in heat or the presence of an entire male, both of which may encourage other females have ovarian activity (Chantal 1993).

In relation to the distribution of pregnant females, the seasonal pattern observed in the present study is similar to that obtained by Scott et al. (2002) in a study in Florida, at 29.7° N latitude. On the other hand, a 10-year study on a colony of cats shows that cats can give birth throughout the year but with a peak during spring and summer (Robinson and Cox 1971). This again indicates an environmental effect, probably as a result of increased ovarian activity observed in those months.

The ovulation rate in cats has been poorly described. It was noted that during the onset of oestrus, there is an average recruitment of 4.8 ± 0.2 follicles (range, 2–7) of which at least one reaches 3 mm of diameter (Malandin et al. 2011). In other study, the number of follicles present in ovulatory or non-ovulatory oestrus was 5.0 ± 0.5 and 5.5 ± 1.0 follicles, respectively (Wildt et al. 1981). Litter size depends in part on the number of follicles released. It has been reported that litters born in summer are larger than those born in winter (Robinson and Cox 1971). In Florida, a litter size of 3.6 ± 0.2 (range, 1–8 kittens) was observed, but the authors did not indicate the distribution of their data (Scott et al. 2002). However, litter size is not a good indicator of ovulation rate because of the probability of early embryonic death. In addition, 86–88% of mature follicles form corpora lutea and only about 67% of them represent a foetus (Schmidt 1986). In contrast, the ovulation rate found in the present study seems to be lower than previous reports. It is possible that breed, size and other factors may have been involved in the recruitment of follicles.

It is concluded that within the Tropics of Cancer, the 2–3 h day length difference throughout the year may induce seasonal variation of ovarian activity and pregnancies of domestic female cats, but do not totally stop breeding activity.

Acknowledgements

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

Authors would like to thank Dr Antonio Rios and Dr Nelson Miss from Planned Pethood Mexico and Dr Jeff Young from Planned Pethood International for their kind donation of the reproductive tracts during the spaying campaigns.

Authors contributions

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References

Dr Ortega-Pacheco and Concha-Guillermo designed the study and performed the collection and evaluation of genital tracts and vaginal cytology. Dr. Segura-Correa and Jimenez-Coello helped in the analysis of data and in the study design and draft of the manuscript.

References

  1. Top of page
  2. Contents
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Authors contributions
  10. References
  • Chantal M, 1993: Induction of oestrus in cats by photoperiodic manipulations and social stimuli. Lab Anim 27, 278280.
  • Da Silva TF, Silva LD, Uchoa DC, Monteiro CL, de Aguilar TL, 2006: Sexual characteristics of domestic queens kept in a natural photoperiod. Theriogenology 66, 14761481.
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