SEARCH

SEARCH BY CITATION

Contents

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

There are limited data on feline sperm production. We exhausted epididymal spermatozoa (i.e. the number of ejaculated spermatozoa <5 × 106) by frequent semen collections using the artificial vagina method in five tomcats and determined the number of spermatozoa stored in the epididymis. We investigated the time (days) required for the number of epididymal spermatozoa to return to the pre-exhaustion level and determined the number of spermatozoa produced per day. After spermatozoa were exhausted by frequent semen collection, 6 or more days were required to return to the pre-exhaustion level. Based on the duration of resting (days) and total number of spermatozoa, the mean number of spermatozoa produced per day was 30 × 106.


Introduction

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

Three semen collection methods have been reported (Scott 1970; Tanaka et al. 2000a; Zambelli et al. 2007) for the evaluation of feline semen quality. It is rather difficult to frequently employ electro-ejaculation (EEM) and urethral catheterization after pharmacological induction (UrCaPIM), because these are performed under general anaesthesia. Moreover, urinary contamination of semen and an increase in seminal plasma have been recognized as additional problems of EEM. On the other hand, the artificial vagina method (AVM) requires training of the male cat in order to collect semen, and the presence of an oestrous female cat. The latter method is, however, the best to observe feline semen quality. For these reasons, there have been only a few reports on feline semen quality employing AVM. As cats copulate frequently, regular semen collections are necessary to assess feline semen quality and sperm productivity.

Only Tanaka et al. (2000a) and Oba et al. (2011) previously reported experiments on feline semen quality with the consideration that cats consecutively repeat copulation. Tanaka et al. (2000a) investigated the influence of ejaculation intervals on feline semen quality and observed that an every-other-day or longer interval of semen collection is necessary to obtain a stable semen quality. Oba et al. (2011) reported the quality of semen collected four times consecutively, in which the number of spermatozoa decreased as the frequency of semen collection increased, but no changes were noted in the semen volume or in the percentage of abnormal spermatozoa or immature spermatozoa. However, qualitative data on feline sperm production are not available. Therefore, we planned the preparation of a sperm-exhausted state by frequent semen collection employing AVM and determined the number of spermatozoa stored in the epididymis and that produced per day by observing the time (days) required for the number of spermatozoa to return to the pre-exhaustion level. Judgment of the state of sperm exhaustion caused by frequent ejaculation in male cats is important. In the study reported by Oba et al. (2011), the mean number of spermatozoa was approximately 15.0 × 106 at the 4th of four consecutive semen collections. Therefore, the state in which the number of spermatozoa decreased to <5 × 106 was regarded as exhaustion.

Materials and Methods

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

Five male cats (mix breed) from our colony aged 4.5–5.2years (mean: 4.8 ± 0.1 years) and weighing 3.9–5.1 kg (mean: 4.6 ± 0.2 kg) with a normal semen quality, copulation capability and fertility were used. Animals were maintained in an animal room in which the temperature was adjusted to 22 ± 2°C. Male cats were kept individually in cages measuring 60 × 90 × 120 (height) cm. The animal room was kept under a 12-h lighting cycle. Animals were supplied with dried food and water ad libitum. Female cats in our colony were used for semen collection during their oestrus. This study was conducted in conformity with the animal study guidelines of Nippon Veterinary and Life Science University.

Semen was collected using an artificial vagina (AV). The AV was replaced by a new one, and collection was repeated after approximately 10 min. While a male cat was mounting an oestrous female cat and thrusting, the penis was advanced into an AV held between the forefinger and middle finger, and ejaculation was induced.

The semen volume and number of spermatozoa were measured. The semen volume was measured using a sample tube with 10-μl graduations. The sperm concentration was assessed using a haemocytometer.

Semen collection was completed when the number of spermatozoa decreased below 5 × 106, which was considered that the tomcat was exhausted.

First semen was collected until reaching exhaustion. Subsequently, frequent semen collections were performed after 2, 5, 6, 8 or 10 days, and the semen volume and number of spermatozoa were compared among the groups. A 14-day resting period was set after each exhaustion experiment.

The data was analyzed by employing one-way anova and the Tukey–Kramer test. A p-value of < 0.05 was regarded as significant.

Results

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

Number of ejaculations to reach exhaustion: The frequencies of semen collection to reach exhaustion at various semen collection intervals in individual animals are shown in Table 1. Semen was collected frequently in all cats, but no decline of libido or copulation capability was observed. The mean number of ejaculations to reach exhaustion was 5.5 ± 0.3 in the control group, and those in the groups with a resting interval of 2–10 days were 3.8 ± 0.4, 4.6 ± 0.4, 4.8 ± 0.7, 5.4 ± 0.4 and 4.6 ± 0.4, respectively, showing that the frequencies in the groups with an interval of 2–10 days were not significantly different from that in the control group.

Table 1. Frequencies of ejaculation required to reach exhaustion after various resting periods in male cats
Tom no.Resting period (day)Control (14 day)
108642
T1354655.5 ± 1.0
T2545544.3 ± 0.3
T3565535.5 ± 0.3
T4563446.0 ± 0.5
T5567336.0 ± 0.5
Mean ± SE4.6 ± 0.45.4 ± 0.44.8 ± 0.74.6 ± 0.63.8 ± 0.45.5 ± 0.3

Semen quality until exhaustion: The total semen volumes collected until reaching exhaustion after various resting intervals in individual cats are shown in Table 2. The mean semen volume collected until exhaustion after the resting period was 277.7 ± 30.4 μl in the control group. The volume was 251.2 ± 37.1 μl in the 10-day interval group, similar to that in the 8- and 6-day interval groups, and 211.2 ± 27.8 and 197.1 ± 15.3 μl in the 4- and 2-day interval groups, respectively, showing that the volume decreased as the interval shortened, but no significant difference was noted among the groups. The total numbers of spermatozoa collected until reaching exhaustion after various resting intervals in individual cats are shown in Table 3. The mean total number of spermatozoa was 200 ± 12 × 106 in the control group, 179 ± 26 × 106 in the 10-day interval group, similar to that in the 8- and 6-day interval groups, and 116 ± 11 × 106 and 64 ± 5 × 106 in the 4- and 2-day interval groups, respectively. The total number of spermatozoa in the 2-day interval group was significantly different from those in the 6-day or longer interval groups. Significant differences were also noted between the 4- and 8-day interval groups and between the 2- and 4-day interval groups. No significant difference from the control group was noted in the 6- , 8- , and 10-day interval groups, showing that 6 days were necessary to recover to the number of spermatozoa before the exhaustion test. As 6 days were necessary to recover, the sperm productivity per day was calculated by dividing the total number of spermatozoa by the number of days between the exhaustion and experiment initiation in each animal in the 2–6-day interval groups, that is, the sperm productivity per day in the 2–6-day rest groups was 29–32 × 106 (mean ± SE: 30 ± 2 × 106).

Table 2. Total semen volumes (μl) of frequent semen collections after various resting periods in male cats
Tom no.Resting period (day)Control (14 day)
108642
T1120225175235200225 ± 48.7
T2300250440290240187.5 ± 30.8
T3290305300200165351.3 ± 45.4
T4265255145190170298.8 ± 27.1
T5280330430140210296.3 ± 44.9
Mean ± SE251.2 ± 37.1273.4 ± 21.5298.1 ± 68.9211.2 ± 27.8197.1 ± 15.3277.7 ± 30.4
Table 3. Total numbers of spermatozoa (× 106) of frequent semen collections after various resting periods in male cats
Tom no.Resting period (day)Control (14 day)
108642
  1. a

    Significant difference between control group (p < 0.01).

  2. b

    Significant difference between 6-day interval group (p < 0.01).

  3. c

    Significant difference between 8-day interval group (p < 0.01).

  4. d

    Significant difference between 10-day interval group (p < 0.01).

T116517619714361192 ± 37
T218814020112961218 ± 58
T326825217110569198 ± 09
T41391771328451195 ± 42
T513724719111981198 ± 12
Mean ± SE179 ± 26198 ± 24178 ± 14116 ± 11a,c64 ± 5a,b,c,d200 ± 12

Discussion

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

The total number of spermatozoa collected until exhaustion in individual animals after various resting intervals was approximately 200 × 106 after a 6-day rest in tomcats 1, 2, and 5, and approximately 250 × 106 and 180 × 106 after an 8-day rest in tomcats 3 and 4, respectively, showing that the number of spermatozoa ejaculated after a 6–8-day rest was similar to that in the control with a 14-day rest. Oba et al. (2011) reported that sperm in the first (55%) and second (20%) ejaculations accounted for approximately 75% of the total number when semen was collected 4 times consecutively. Cats are capable of multiple consecutive copulations, but most spermatozoa may be released in the first two ejaculations. This multiple copulation is considered to be a sexual behaviour necessary to induce ovulation. These experimental findings clarified that approximately 200 × 106 spermatozoa are stored in the epididymis and ejected by frequent ejaculations.

The number of spermatozoa necessary to achieve conception in cats through intravaginal insemination may be 80 × 106 or more based on a previous study (Tanaka et al. 2000b). Regarding the relationship between the frequency of copulation and conception, we experimentally clarified that the number of spermatozoa per copulation is insufficient to achieve conception (Tsutsui et al. 2009), showing that several copulations are necessary for conception in cats. For example, approximately 200 × 106 epididymal spermatozoa divided by the number necessary for conception (= 80 × 106) is 2.5, suggesting that spermatozoa stored in the epididymis are sufficient to fertilize at least two female cats. However, we did not investigate sperm motility, which is important for fertilization, or the percentages of abnormal spermatozoa and immature spermatozoa.

As the semen volume is influenced by the frequency of semen collection, the difference was small in all animals after a 2-day rest, but no apparent difference was noted in the semen volume per semen collection among all animals. The feline spermatogenic function was investigated by frequent semen collection using AVM. As cats consecutively copulate, frequent semen collections caused no problem. In addition, the accessory reproductive glands are highly functional and maintain the semen volume even after a short resting interval. Thus, there was no problem in counting spermatozoa, although their number decreased.

It was clarified that cats after a 6-day or longer interval ejaculated a number of spermatozoa similar to that ejaculated in the control group after a 14-day resting period, and the feline sperm productivity per day was 30 × 106 spermatozoa.

Conflicts of interest

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

None of the authors have any conflicts of interest to declare.

References

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