314.0 ± 22.4

(Liu, 1981; Platz et al., 1983; Moore et al., 1984; Masui et al., 1989). Semen collection by electroejaculation is used widely in China and is considered safe when conducted by trained staff using appropriate equipment. The major breeding facilities (i.e. in Chengdu, Beijing and Wolong) commonly use this approach to evaluate male fertility and to collect sperm for AI. Because electroejaculation is used extensively, there are substantial data on basic semen and sperm characteristics, especially on semen volume, sperm motility and number of motile sperm per ejaculate (Platz et al., 1983; Moore et al., 1984; Howard, 1993). Individual sperm appearance and size have also been described. The giant panda spermatozoon has a rounded head (mean ± SEM, i.e. standard error of the mean; length 5.0 ± 0.1 mm, width 4.2 ± 0.1 mm), narrow midpiece (length 7.2 ± 0.1 mm, width 0.8 ± 0.04 mm), flagellum (length 39.0 ± 1.3 mm) and an average total length of 51.2 ± 0.4 mm (Platz et al, 1983). Overall spermatozoon shape is generally similar to other bears although the total length is shorter than that reported for the sloth bear (72.5 mm), Kodiak bear (69.4 mm) and spectacled bear (73.1 mm) (Platz et al., 1983). Other than a few reports discussing ultrastructure (Chen et al., 1984; Moore et al., 1984; Sun et al., 1996), there is little published information on giant panda sperm morphology and membrane integrity.

Of the 16 electroejaculated males in our survey, all produced spermic ejaculates (see Table 7.1). The semen of the giant panda (average volume, 3.9 ± 0.6 ml) contained prodigious numbers of sperm (mean 1182.4 ± 220.6 x 106 sperm ml"1) that were highly motile (~69%; see Table 7.1). Thus, an average ejaculate can contain almost three billion motile sperm, which is slightly higher than other bear species (Ishikawa et al, 1998) but much greater than what has been reported for other carnivores such as felids (Howard, 1993; Wildt & Swanson, 1998) and canids (Amann, 1986).

Most giant panda ejaculates contained high proportions of structurally normal sperm (>65%), including a high proportion (>85%) of sperm with an abaxial attachment of the neck. The observed defects included acrosomal anomalies, a coiled flagellum, bent midpiece, bent flagellum or cytoplasmic droplet (see Table 7.1 and Fig. 7.2). Similarly, other bear species produce high numbers of morphologically normal sperm (Ishikawa et al., 1998). Most giant panda spermatozoa had an intact acrosome with normal apical ridge (>90%) with a low incidence of a damaged apical ridge (<2%), a missing apical ridge (<5%) or loose acrosomal cap (<2%) (see Table 7.1 and Fig. 7.3).

Influence of age on reproductive traits

Seminal traits, including sperm morphology, were influenced by age (see Table 7.2) but only near the onset of puberty. Ejaculate quality in adult males 6.5 to 16.5 years old was consistently similar (regardless of age) and superior to the four 5.5-year-old pubertal counterparts (see Table 7.2). Semen from the latter group had the greatest variability in sperm concentration (range 3-3664 x106 sperm ml-1), motility (range 0-95%) and forward progression scores (range 0-3.5). The 5.5-year-old males also produced fewer structurally normal sperm (mean 30.5 ± 15.2%; range 4-68%) than older giant pandas (see Table 7.2). Even so, in general, acrosomal integrity in these younger males was similar to the older group, with the exception of male SB 400, which ejaculated sperm with only 26% normal acrosomes (see Table 7.2). This individual had a subadult-sized penis and produced an extremely low sperm concentration (3 x 106 sperm ml-1) compared to all other males (see Table 7.2). All spermatozoa in SB 400's ejaculate lacked motility with the ejaculate containing many spermatids (immature cells). Combined with his smaller testes and many body metrics, we concluded that SB 400 probably was experiencing delayed development and/or puberty. And, although having a history of chronic gastrointestinal disease, SB 400 was not classified as having Stunted Development Syndrome, largely because of his overall normal body length.

Reproductive traits in wild- versus captive-born, and breeding versus non-breeding males

One of the most important findings from our contribution to the Biomedical Survey was that male physiological function was not compromised. Of the 12 giant pandas of more than six years of age, reproductive traits and body measures were the same for the seven wild-born versus the five captive-born males (Table 7.3). Despite many captive-born males failing to reproduce, there were no differences (p > 0.05) in ejaculate traits, sperm morphology, acrosomal integrity, body measurements and testicular size compared to pandas of a wild origin. However, there was a trend (p = 0.06) for the wild-born males to have larger testes (see Table 7.3). Ejaculate and morphometric traits of the five males that had sired offspring were also the same as the seven non-breeding counterparts (see Table 7.3). Both groups produced similarly (p > 0.05)

Table 7.3. Ejaculate and morphometric traits in wild-born versus captive-born, and breeding versus nonbreeding male giant pandasa

Wild-born males Captive-born males Breeding males Non-breeding males

Ejaculate volume (ml)

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