PHYSIOLOGY AND REPRODUCTION. Annual Variation in Semen Characteristics of Pigeons (Columba livia)

PHYSIOLOGY AND REPRODUCTION Annual Variation in Semen Characteristics of Pigeons (Columba livia) F. P. Cheng,*,1 T. J. Guo,* J. T. Wu,* T. E. Lin,* P. J. F. Ursem, B. Colenbrander, and H. P. Fung* *Graduate Institute of Veterinary Medicine, College of Veterinary Medicine, National Chung-Hsing University, Taichung City, Taiwan 402, ROC; and Department of Farm Animal Health, Utrecht University, Yalelaan 7 3584 CL, De Uithof, Utrecht, The Netherlands ABSTRACT The purpose of this study was to evaluate minimum was 3.8 ± 0.2 10 9 sperm/ml observed in annual semen characteristics of pigeons (Columba livia). Ten selected male pigeons, aged 2 to 5 yr were housed under natural environmental conditions, and semen collection was conducted via a digital massage twice weekly October. Donors generally exhibited susceptible (54%) or dull submission (43%), whereas resistance to handling was rarely observed (3%). During collections, a red (47%) or pink (44%) cloacal membrane was often observed, throughout the year. The success rate of semen collection whereas during only 9% of the collections, the cloacal in a total of 920 attempts was 40% (371/920) over the membrane was pale. When the ambient temperature decreased below 15 C, semen could not be obtained (0/80). whole year. The highest success rate was 69% (55/80) in A high amount of semen (>10 µl) was obtained when March followed by 66% (53/80) in November, whereas the temperature ranged between 19 and 24 C. Optimal the lowest rates were in August (13%, 10/80) and September (13%, 8/60) (P < 0.01). Volume of the ejaculate aver- sperm motility (approximately 80%) and viability (>85%) was observed when the temperature was between 18 and aged 11.0 ± 0.9 µl (mean ± SEM). The greatest volume 24 C. At temperatures greater than 28 C, sperm motility was obtained in November (13.5 ± 1.0 µl), whereas the and viability decreased. Sperm concentration was not significantly influenced by temperature fluctuations. In sum- least was obtained in August (7.0 ± 1.0 µl). The average sperm motility was 72 ± 2% of all ejaculates, of which the mary, annual variation in semen characteristics exhibited highest motility (82 ± 2%) was observed in March, two peaks per year with mean motility and viability whereas the least motility (48 ± 3%) was in August. Sperm reaching peak annual values in March and November. viability and sperm motility were positively correlated (r = 0.91; P < 0.01). Maximum sperm concentration was 4.9 ± 0.4 10 9 sperm/ml noted in March, whereas the Both of these months had mean ambient temperatures between 19 and 24 C, a range associated with maximal ejaculatory volumes. (Key words: pigeon, semen characteristic, semen quality, season) 2002 Poultry Science 81:1050 1056 INTRODUCTION The merits of semen evaluation in poultry breeding, for selecting breeding males or for routinely monitoring their reproductive performance, are well recognized. The diagnosis of subfertility in pigeons based on semen evaluation has not been possible due to the lack of knowledge of semen characteristics. Avian semen has been collected and evaluated in several species including drakes (Setioko and Hetzel, 1984), cocks (Saeid and Al-Soudi, 1975; Lake and Stewart, 1978), ganders (Pawluczuk and Grunder, 1989), turkeys (Burrows and Quinn, 1937; Noirault and Brillard, 1999), and pheasants (Mantovani et al., 1993) and has been widely used in the breeding industry 2002 Poultry Science Association, Inc. Received for publication August 9, 2001. Accepted for publication January 31, 2002. 1 To whom correspondence should be addressed: fpcheng@dragon. nchu.edu.tw. (Sexton, 1977; Lake and Stewart, 1978; Setioko and Hetzel, 1984). For domestic fowls and turkey, the earliest and the most frequently used method of collection semen is manual massage (Burrows and Quinn, 1937). Later-developed collection methods use the artificial vagina in ganders (Pawluczuk and Grunder, 1989) or electro ejaculation in drakes (Setioko and Hetzel, 1984). Although great skill is required from the operator, the manual massage method is safe, harmless, and not stressful to the donor. The first paper regarding the yield of pigeon semen by manual massage was documented as early as 1941 (Owen). Nevertheless, no direct description of semen characteristics has been made, nor has evaluation of pigeon breeding potentials been made. Avian semen quality has a significant effect on fertility (Sexton, 1983), which is affected by environmental conditions (McDaniel et al., 1995, 1996). Study of seasonal variation in semen quality of domestic fowls has shown that semen characteristics are influenced by seasons (Saeid 1050

ANNUAL PIGEON SEMEN CHARACTERISTICS 1051 and Al-Soudi, 1975). Ambient temperature greater than 31 C significantly affects rooster sperm motility, viability, and fertilizing potential (McDaniel et al., 1996). Other studies indicate that changes in environmental temperature at ejaculation are one of the important exogenous physiological factors influencing avian sperm motility (Ashizawa and Sano, 1990; Wishart and Wilson, 1999). Although the negligible effect of a high ambient air temperature (between 50 to 60 C) on the breeding potential of rock pigeons (Columba livia) has been demonstrated (Arieli et al., 1988), the general ejaculation performance in response to ambient temperature remains unclear. We describe semen collection from pigeons (Columba livia) via a modified manual massage and discuss the seasonal variation of ejaculation performance as well as of semen characteristics. In addition, the degree of submission of semen donors and the variation in color of the cloacal mucosa in relation to successful ejaculation were investigated. Birds MATERIALS AND METHODS Twenty, spotted grey-white, mixed-breed, racing male pigeons that were sexually mature, healthy, and fertile (at least four squabs/yr), from 2 to 5 yr of age and weighing 250 to 350 g, were used. Pigeons were housed individually in separate metal cages (40 cm 30 cm 50 cm). All cages were in a roofed and open-sided shelter equipped with a wind insulation to the north under native environmental conditions (24 07 N, 120 40 E), where birds received a natural light:dark photoperiod (12L:12D to 15L:9D) throughout the experiment. 2 During the experiment, 10 g of complete feed was provided twice daily and water was available ad libitum. Pigeons were allowed 2 wk to adjust and become accustomed to the operator. Training was conducted over a 2-wk period. Pigeons that did not produce semen by the end of the training period were excluded from the experiment. Finally, 10 pigeons with optimal ejaculation performance were used throughout the study. Attempts were made to collect semen from each pigeon twice weekly (Monday and Thursday) between 0800 and 1000 h. The arbitrary scoring of submission of donor and the color of the cloacal mucosa was recorded. To evaluate the influence of ambient temperature on the ejaculation performance, the temperature in the shelter was recorded twice weekly. Semen Collection To avoid variation, one operator performed semen collection throughout the study. The technique described by Owen (1941) was slightly modified by applying a brief caudally directed abdominal massage combined with pressure exerted caudally to the cloacal area. When the 2 Central Weather Bureau, Taichung, Taiwan. pigeon was caught, it was held with its chest positioned against the collector s belly. Prior to massage, the donors wings were stretched and then closed to relax the birds while fixing the main feathers in order. Subsequently, massage was exerted by placing applying pressure with thumbs and index fingers, up and down the surface of the pygostyle. Thumbs were rhythmically pressed on the rump region, while the index fingers massaged the opposite abdominal region in the vicinity of cloaca for a few rounds. Simultaneously, the middle finger of the right hand pressed the os pubis, just below the vent. If the positions of the fingers were correct, the cloaca opened wide showing two fleshy folds. Subsequently, for the right-handed collector, the little finger on the left hand was hooked under the right wing while the other fingers were extended along the donor s back. The donor was then turned onto its back and lay on the left palm. The tail of the pigeon was free to move and spread. Thereafter, the thumb and index finger of the left hand were rhythmically pressed against the opposite sides of the caudal bone. A milking action by thumb and index finger of the right hand was exerted on the base of the cloacal projection while the middle finger was pressed deeply between the pubis bones. The required strength for massage varies and depends on the donor. The massage can be conducted directly after the bird is caught. After 2 s of massage, a small drop of white semen showed on the opening surface of the cloaca. Often the quantity could be increased when the massage was continued for a few seconds after the first drop of semen was observed. When the massage was stopped, the thumb and index finger of the left hand were moved from the rump region to the vicinity of cloaca. The pressure of these fingers kept the cloaca open. The semen was then aspirated, and the quantity measured with a micropipette equipped with a tip. The whole procedure was completed within 30 s. If no ejaculate was obtained within 30 s, the donor was returned to his cage, and a second attempt was made after 15 min. Feathers around the cloaca were clipped 1 or 2 d before semen collection to prevent contamination of the ejaculate. Moreover, this enabled a better view of the cloacal opening. Submission and Cloacal Mucosa Color Evaluation Semen collection sessions were subjectively classified as submissive, tolerant, or resistant, according to donor response. Pigeons usually respond to massage by waving the tail and showing the cloacal opening. If the pigeon was calm and submissive to operator s handling, it was subjectively classified as submissive. Those that responded slightly by struggling but allowed collection were classified as tolerant. If the bird vigorously responded to the handling by struggling or flapping and attempted to escape, it was classified as resistant. In the process of the second massage, the everted membrane

1052 CHENG ET AL. folds exhibited various degrees of redness, subjectively classified as red, pink, or pale. Semen Quality Evaluation Semen was microscopically examined for contamination with blood, feces, and uric acid. Volume of semen was measured when aspirated from the cloacal vent by using a micropipette. The sperm motility was estimated by microscopic observation (250 magnification) on a warm (30 C) stage with semen samples that were diluted 20-fold in Beltsville poultry semen extender (Sexton, 1977). Ten microliters of diluted semen was covered by a cover glass (18 18 mm) and at least 10 microscopic fields were examined. Motility was expressed as the percentage of motile spermatozoa with moderate to rapid progressive movement. Sperm concentration was calculated with a hemocytometer after dilution of the semen (1:200) with a weak eosin solution (Brillard and McDaniel, 1985). Sperm morphology was examined microscopically (500 ) in smears stained with nigrosin and eosin (Blom, 1950). The proportions of live (eosin-impermeable) and dead (eosin-permeable) spermatozoa in a sample were assessed on the basis of 200 spermatozoa. Statistics Data were subjected to analysis of variance to study the effect of months on semen characteristics. Significant differences between means were determined by Duncan s multiple-range tests. RESULTS The success rate of semen collection by manual massage in a total of 920 attempts was 40% (371/920) over the year. A dual climax and seasonal pattern in success rate was observed. The highest success rate was 68% (55/80) in March followed by 66% (53/80) in November, whereas significantly lower rates were obtained in August (13%, 10/80) and in September (13%, 8/60) (Table 1). The semen volume averaged 11.0 ± 0.9 µl (mean ± SEM) over the whole period. The highest volume (13.5 ± 1.0 µl) was obtained in November, whereas the lowest (7.0 ± 1.0 µl) was obtained in August (P < 0.01). The average sperm motility was 72 ± 2% of all ejaculates, the highest motility (82 ± 2%) being observed in March and the lowest (48 ± 3%) in August (P < 0.01). Sperm viability and sperm motility were positively correlated (r = 0.91; P < 0.01). Maximum sperm concentration was 4.9 ± 0.4 10 9 sperm/ml noted in March, whereas the minimum was 3.8 ± 0.2 10 9 sperm/ml observed in October (P < 0.05) (Table 1). In total, the ejaculation performances in March and November were superior to those in the other months for all semen characteristics (Table 1). The instances of semen contamination, i.e., feces or uric acid, were low. Occasionally, struggling donors may produce feces-contaminated semen. Blood contamination was rarely observed. The percentage of abnormal sperma- TABLE 1. Annual semen characteristics of pigeons (Columba livia) 1 Average Relative Average Sperm Sperm temperature humidity photoperiod Collection Ejaculates Collection Volume motility viability Concentration Month (Min.-max., C) (Min.-max., %) (Min.-max., h) attempts (n) rate (%) (µl) (%) (%) (10 9 /ml) January 17.5 (9.7 28.6) (37 75) 12.5 (12.4 12.7) 80 18 23 10.5 ± 1.3 bc 77 ± 2 bc 80 ± 2 bc 4.2 ± 0.2 bcd February 16.8 (11.2 26.3) (47 79) 13.0 (12.7 13.3) 70 19 27 9.8 ± 0.8 cd 75 ± 2 c 80 ± 1 bc 4.7 ± 0.3 ab March 19.5 (13.8 29.7) (34 74) 13.7 (13.3 14.0) 80 55 69 11.1 ± 0.9 bc 82 ± 2 a 84 ± 1 a 4.9 ± 0.4 a April 23.2 (15.1 31.1) (39 80) 14.3 (14.0 14.8) 80 43 54 10.9 ± 0.9 bc 76 ± 2 bc 82 ± 2 abc 4.7 ± 0.2 ab May 26.2 (19.8 34.4) (41 76) 15.1 (14.9 15.5) 80 34 43 8.5 ± 1.1 de 75 ± 1 c 79 ± 2 bcd 4.4 ± 0.2 bc June 27.8 (18.4 34.9) (50 78) 15.6 (15.5 15.6) 70 33 47 11.5 ± 1.4 bc 68 ± 3 d 75 ± 2 d 3.9 ± 0.3 d July 28.6 (22.6 35.5) (49 77) 15.4 (15.1 15.6) 80 22 28 12.6 ± 1.0 ab 65 ± 2 de 71 ± 2 e 3.8 ± 0.2 d August 27.6 (22.9 34.2) (54 81) 14.7 (14.4 15.1) 80 10 13 7.0 ± 1.0 e 48 ± 3 f 58 ± 3 f 4.5 ± 0.1 abc September 27.4 (22.0 34.1) (36 72) 14.0 (13.6 14.3) 60 8 13 7.0 ± 1.2 e 51 ± 3 f 59 ± 4 f 4.6 ± 0.1 abc October 26.5 (20.7 34.0) (42 74) 13.2 (12.9 13.6) 80 39 49 11.8 ± 0.7 abc 63 ± 2 e 70 ± 2 e 3.8 ± 0.2 d November 22.5 (15.3 30.2) (41 71) 12.3 (12.5 12.9) 80 53 66 13.5 ± 1.0 a 79 ± 1 ab 86 ± 1 a 4.4 ± 0.3 bc December 17.6 (4.7 27.7) (33 72) 12.4 (12.4 12.5) 80 37 46 10.3 ± 0.8 bcd 74 ± 1 c 79 ± 1 bcd 4.2 ± 0.3 bcd Total/mean ± SEM 920 371 40 ± 5 11.0 ± 0.9 72 ± 2 79 ± 3 4.4 ± 0.3 a-c Values with different superscripts differ significantly (P < 0.01) between months. 1 Data source: local temperature (24 07 N, 120 40 E), relative humidity, and photoperiod using nautical twilight of each month were quoted from Central Weather Bureau, Taiwan. The molt period of pigeons is during August and September. Semen characteristics were recorded from 10 adult fertile pigeons and are expressed as mean ± SEM.

ANNUAL PIGEON SEMEN CHARACTERISTICS 1053 trast, sperm concentration was not affected by temperature changes (Table 2). DISCUSSION FIGURE 1. Semen collection attempts (n = 920) from pigeons (Columba livia) subjectively classified according to donor response. Three hundred seventy-five ejaculates were successfully obtained. tozoa, i.e., coiled, hooked, or ruptured heads or coiled, broken, or absent tails, was low (<10%) in all ejaculates obtained, regardless of cell viability. When the 371 ejaculates were obtained, donors were generally rated as submissive (54%; 15.5 ± 1.6 µl) or tolerant (43%; 10.7 ± 0.9 µl). In only 3% (5.5 ± 1.5 µl) of the cases were semen donors resistant to handling (Figure 1). The degree of submission increased as the donors gained experience. The cloacal membrane was red during 47% (16.1 ± 1.3 µl; motility 73 ± 6%; viability 80 ± 8%; 4.4 ± 0.3 10 9 sperm/ml) of the collections, pink in 44% (12.4 ± 1.1 µl; 71 ± 7%; 77 ± 8%; 4.3 ± 0.3 10 9 sperm/ ml), and pale in 9% (5.5 ± 0.9 µl; 54 ± 8%; 66 ± 10%; 3.7 ± 0.5 10 9 sperm/ml) of the instances (Figure 2). When the ambient temperature declined below 15 C, semen could not be obtained (0/80). A high amount of semen (>10 µl) was collected when the temperature varied between 19 and 24 C. The highest sperm motility (approximately 80%) and viability (>85%) was observed when the temperature was between 18 and 24 C. At temperatures greater than 28 C, sperm motility and viability decreased, and less semen output was observed. In con- FIGURE 2. Semen collection attempts (n = 920) from pigeons (Columba livia) subjectively classified according to donor cloacal mucosa color during ejaculation. Three hundred seventy-five ejaculates were successfully obtained. In this study, pigeons exhibited a high variation in semen quality and quantity. In general, a high concentration of spermatozoa is accompanied by a low volume per ejaculate. The volume of ejaculate varied from 7 µl to twice that volume and sperm motility, from approximately 50 to 80%. Owen (1941) observed an average semen quantity in domestic pigeons from 10 to 20 µl per ejaculate, containing approximately five to six million spermatozoa. In this study, the total number of spermatozoa per ejaculate was seven times higher. In domestic pigeons, the quantity of semen produced does not appear to be related to the size of birds (Owen, 1941). Among species, apart from larger sizes of internal and external reproductive organs, larger species consistently produce larger quantities of semen per ejaculate (chicken and turkey: Lake and Stewart 1978; cockerel: de Reviers and Williams, 1984). This difference is due to the number of Sertoli cells in testis, because the capacity of semen production is closely related to the number of these cells (de Reviers and Williams, 1984). For breeding purposes, the challenge is to maximize the production of viable or functional spermatozoa per ejaculate (Sexton, 1983). Semen characteristics of pigeons were significantly affected by season, although pigeons (Columba livia) are apparently not typically seasonal breeders (Arieli et al., 1988). During winter, Mallards become photosensitive and subsequently respond to the increasing photoperiod in the spring with gonadal growth and increasing plasma testosterone levels (Hasse, 1983). Unlike most domestic chickens that produce high quality semen only in the spring (Saeid and Al-Soudi, 1975), semen quality of pigeons is superior in dual seasons, i.e., spring and autumn. Accordingly, the major reproductive periods are during these two seasons, even though pigeons will breed throughout the year. This timing results in a high breeding efficiency of pigeon males. The lowest sperm concentration was produced during summer, being in line with an earlier report in domestic fowls (Saeid and Al-Soudi, 1975). Seasonal collection rates, sperm motility, and viability exhibit a trough plateau during August and September. These months correspond to the stage of the natural molt that begins from July to October for pigeons raised in Taiwan. When the molt begins, major metabolic energy is shifted toward the release and regrowth of remiges (Decuypere and Verheyen, 1986; Brake, 1993). Similarly to pigeons, a marked decrease in semen volume and sperm concentration has been noted in ganders as the annual molt begins (Zeman et al., 1990) and has been attributed to the decline of plasma testosterone after molt (Zeman et al., 1990). The postnuptial molt in Mallard ducks also resulted in a decrease of circulating testosterone (Stunden et al., 1998). Subsequently, the decline of testosterone adversely affects the semen quality and reproductive activities (Zeman et al., 1990; Stunden et al., 1998). In the male

1054 CHENG ET AL. TABLE 2. Pigeon (Columba livia) semen characteristics and corresponding ambient temperatures at the time of semen collection 1 Ambient Collection Ejaculates Collection Volume Sperm motility Sperm viability Concentration temperature attempts (n) rates(%) (µl) (%) (%) (10 9 /ml) 10 C 20 0 0 0 11 C 10 0 0 0 13 C 10 0 0 0 14 C 20 0 0 0 15 C 20 0 0 0 18 C 50 23 46 9.4 ± 1.1 82 ± 6 89 ± 1 4.3 ± 0.3 19 C 30 15 50 11.6 ± 1.7 82 ± 3 87 ± 2 4.3 ± 0.2 20 C 30 20 67 10.5 ± 1.1 79 ± 2 87 ± 2 4.5 ± 0.4 21 C 30 22 60 14.4 ± 1.9 84 ± 1 89 ± 2 4.7 ± 0.5 22 C 70 41 54 12.1 ± 1.0 78 ± 2 86 ± 1 4.6 ± 0.3 23 C 20 16 80 10.8 ± 1.6 82 ± 2 88 ± 1 4.2 ± 0.1 24 C 30 18 60 13.8 ± 1.9 79 ± 3 86 ± 2 4.7 ± 0.3 25 C 20 10 50 8.5 ± 1.2 77 ± 3 83 ± 3 4.2 ± 0.1 26 C 20 7 35 10.3 ± 2.8 69 ± 7 76 ± 7 3.9 ± 0.2 27 C 20 9 45 10.7 ± 2.1 76 ± 4 81 ± 2 4.9 ± 0.3 28 C 20 10 50 9.1 ± 1.4 73 ± 4 82 ± 3 4.8 ± 0.1 29 C 20 9 45 7.0 ± 1.2 65 ± 5 70 ± 5 5.0 ± 0.3 30 C 20 9 45 9.0 ± 1.2 60 ± 6 71 ± 5 4.3 ± 0.3 32 C 20 5 25 5.8 ± 0.9 53 ± 2 60 ± 5 4.8 ± 0.1 1 Data were obtained from 480 collection attempts and sorted according to the recorded temperature. Semen characteristics were recorded from 10 adult fertile pigeons and are expressed as mean ± SEM. ring dove (Streptopelia risoria), sexual activity has been shown to depend upon the presence of androgen (Cheng, 1979). Physiologically, a successful molt process is influenced by, e.g., health status of the birds, photoperiod, and endocrine factors, i.e., decreased plasma thyroxine and increased triiodothyronine (Decuypere and Verheyen, 1986; Zeman et al., 1990; Brake, 1993). Some birds may experience physiological disturbances, resulting in unsuccessful remex molt. In this study, certain pigeons (3/10) experienced a February molt. These data explain in part the suboptimal ejaculation performance in pigeon males at this time. Irrespective of the month, current data show that low ambient temperature (<15 C) affects ejaculation. This cold stress resulted in a lack of sex drive. In a relatively cold environment, birds are forced to reserve energy for maintenance of body temperature. Similarly, heat stress (>30 C) compromises semen output. The decreased sperm viability and motility were evident as ambient temperature increased to 32 C. Heat-induced subfertility was reported in roosters housed at 27 C for 1 wk, and the degree of subfertility increased as the temperature rose to 32 C (McDaniel et al., 1996). Heat affected the semen quality and particularly caused an increase in the percentage of nonviable sperm. Interestingly, these impairments quickly waned once the temperature returned to 21 C (McDaniel et al., 1996). This rapid response of the domestic fowl to elevated ambient temperatures is not related to impaired sperm formation (McDaniel et al., 1996) because spermatogenesis takes 10 to 12 d followed by 1 to 5dfor sperm to pass through the excurrent ducts (Lake, 1984). However, the decrease in rooster sperm motility and concentration at ambient temperatures above 23 C was attributed to two secondary effects caused by the heat stress, namely testicular rest and reduced food intake (Saeid and Al-Soudi, 1975). The later effect was also observed in this study as evidenced by increased remaining feed. Nevertheless, the ambient temperature has only a minor effect on the pigeon sperm concentration as recorded in current study. Thus, thermal stress disturbs semen output rather than production. Moreover, temperatures between 19 and 24 C are critical for optimal ejaculation performance. In agreement with our observation, optimal semen quality was observed in rooster males exposed to 21 C in comparison to those that experienced heat stress (32 C) (McDaniel et al., 1996). Ejaculated spermatozoa of several avian species showed decreased in vitro motility at 40 C, but motility was restored at 30 C (Ashizawa and Sano, 1990; Wishart and Wilson, 1999). Pigeon spermatozoa diluted with Beltsville poultry semen extender exhibited vigorous motility at 30 C, similar to that of other species. Poultry ejaculation is initiated by sexual arousal, starting with the ejection of semen from the muscular end of vas deferens into the urodeum. The erection of the fleshy cloacal folds is characteristic of a sexually aroused male. After reaching the urodeum, semen is then transported into proctodeum where, during collection, the edematous phallic folds are visible and the mucosal folds are engorged with lymphatic fluid (Lake, 1981; Knight et al., 1984). The filling of the sinus network under the phallic folds resulted in varying degress of redness of the cloacal mucosa surface, indicating the level of sexual arousal. In the present study, ejaculation rarely occurred when the mucosal membranes were pale, and less semen was ejaculated. A pale membrane indicated that sexual arousal was not sufficiently initiated in these males. Frequently, these were the males that were resistant to handling by the operator. This phenomenon became more obvious during the molt stages. Some resistant pigeons became submissive during the second collection attempt; however, the nervous temperament of certain pigeons impaired the sexual arousal, and no ejaculate could be obtained. Improper manipulation or extra handling could impair sexual arousal on some occasions (Lee et al., 1999).

ANNUAL PIGEON SEMEN CHARACTERISTICS 1055 In this study, pigeons that were resistant to handling produced less semen. These pigeons commonly exhibited signs of fear, and fearful poultry have poor reproductive performance (Craig et al., 1983; Shabalina, 1984; Lee et al., 1999). The association between resistance and poor semen production in roosters is possibly caused by common stress factors such as pain or injury (Lee et al., 1999). The resistant response to handling could be an indication of the nervous temperament of the pigeons. In ducks, stress also inhibited the reflex response to massage (Tan, 1980). Occasional contamination of the pigeon semen with urine or feces might be expected, particularly with untrained males. Ciliates, products of the rete testis (de Reviers and Williams, 1984) that can be observed under the microscope in the clean ejaculate of cockerel, were commonly observed. However, these ciliates do not seem to affect pigeon fertility (Owen, 1941). Blood cells, probably the result of rupture of capillaries in the mucosal wall of the cloaca, can be found upon microscopical examination but was rarely seen in the ejaculates. Those pigeons that responded submissive to massage produced semen that generally was not contaminated in contrast to that from resistant birds. Contaminated semen can hamper the fertility in ducks (Tan, 1980). To avoid contamination by uric acid or feces, the collection frequency of poultry should be at least twice weekly (Sexton, 1983; Noirault and Brillard, 1999). Pigeons perform copulation several times daily, once nest-building behavior is established (personal observation). Likewise, most male pigeons can be collected more than once a day. In a preliminary study, semen could be obtained hours after first successful ejaculation on the same day. But the quantity and sperm count decrease remarkably to be oligospermia. In some cases, pigeons failed to ejaculate and often became aspermic after first success. Besides, sperm count seems to be restored after at least 2 d of rest from sex. On the other hand, turkey breeder males have an optimal reproductive capacity when semen is collected as frequent as seven times per week (Noirault and Brillard, 1999). Whether the higher frequency of collection, i.e., daily, could affect the reproductive performance of male pigeon remains to be answered. In summary, annual variation in semen characteristics exhibited two peaks per year with mean motility and viability reaching peak annual values in March and November. Both of these months had mean ambient temperatures of between 19 and 24 C, a range associated with maximal ejaculatory volumes. In the future, the effects of frequency of semen collection on quantitative and qualitative semen characteristics should be investigated to maximize the breeding potential of pigeon males. 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