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Right testis length (cm)

9.4 ± 0.2

8.7 ± 0.2

9.6 ± 0.1

8.8 ± 0.2

Right testis width (cm)

5.7 ± 0.3

5.6 ± 0.1

6.0 ± 0.1

5.3 ± 0.2

Right testis volume (cm3)

163.9 ± 16.7

146.2 ± 7.6

184.3 ± 9.0

131.7 ± 11.0

Left testis length (cm)

9.5 ± 0.2

9.0 ± 0.1

9.4 ± 0.3

9.3 ± 0.1

Left testis width (cm)

6.0 ± 0.3

5.7 ± 0.2

6.3 ± 0.1

5.6 ± 0.2

Left testis volume (cm3)

183.5 ± 17.0

154.6 ± 14.3

199.7 ± 14.9

155.4 ± 13.4

Total testes volume (cm3)

347.4 ± 30.8

260.6 ± 15.3

363.4 ± 32.2

271.7 ± 18.8

a Values are means ± SEM in male giant pandas >6 years of age. The four young 5.5-year-old males were not included in analyses due to influence of age on seminal quality (as shown in Table 7.2).

high numbers of structurally normal, motile sperm which contained an intact acrosome with normal apical ridge. The most predominant sperm abnormality for both groups was a bent midpiece defect. Although sperm production was similar, there was an interesting trend (p = 0.06) for the breeding males to have larger testes than non-breeding males.

Testicular hypoplasia or atrophy

Testicular abnormalities and undescended testes were discovered in three males (SB 356, SB 323 and SB 345) and a closely related male SB 181 (already deceased; see below) (Table 7.4). SB 356 was a small (67 kg), emaciated, 8.5-year-old, captive-born male with a history of severe chronic illness. He was the progeny of a wild-born sire (SB 201) and captive-born dam (SB 278). This male, which met our criteria for Stunted Development Syndrome (see Chapter 4), also had a small penis and bilaterally retained inguinal testes with severe testicular hypoplasia. The testes were adequately positioned to allow a crude measurement but due to their small size no attempt was made to collect semen.

SB 323 was a robust 12.5-year-old male with one retained testis (near the inguinal canal; see Table 7.4) which adhered to the body wall. He was the offspring of a wild-born sire (SB 186) and captive-born dam (SB 148) who had wild-born parents. SB 323 was an active proven breeder with multiple living offspring. Similar to SB 356, the left retained testis adjacent to the inguinal canal could be measured. Zoo records revealed that this gonad had never developed normally or descended into the scrotum, indicating unilateral testicular hypoplasia. Even with only one normal-sized testis, excellent semen quality was measured (see Table 7.4). We speculated that testicular hypoplasia may be inherited because a related male (SB 181 and a sibling to SB 148, the dam of SB 323) also had only one testis. SB 181 was deceased at the time of the survey but his testicular anomaly was clearly evident in zoo records and historical photographs. In terms of the normality of SB 323's offspring, at least one son (SB 392) has two descended testes, but another (SB 469, born in 1998) has only one descended testis, suggesting that testicular hypopla-sia may have some paternal mode of inheritance.

In contrast to hypoplasia, SB 345 appeared to have experienced testicular atrophy. Historical records indicated that both testes had developed and increased in size during puberty, although the right

Table 7.4. Testicular abnormalities, morphometrics and seminal quality in giant pandas with a unilaterally or bilaterally retained testis

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