The seminiferous epithelium cycle and its duration in different breeds of dog (Canis familiaris)

Abstract

Testis structure and function in dogs are relatively poorly investigated. The aim of the present study was to carry out a comparative investigation of the stages of the seminiferous epithelium cycle and its duration in different breeds of dog. Fifty-six sexually mature dogs (mongrel, n = 12; pinscher, n = 12; beagle, n = 5; American pit bull, n = 9; poodle, n = 12; and Labrador retriever, n = 6) were analysed. Intratesticular injections of tritiated thymidine were given to determine the duration of spermatogenesis. Orchiectomy was performed at different time periods following injection (1 h, 2 and 4 weeks). Testis fragments were embedded in plastic and routinely prepared for histological and autoradiographic evaluations. Eight stages were characterized based on the acrosome system. Significant (P < 0.05) differences were found for the frequencies of the different stages characterized (except Stages V, VI and VIII), particularly for the mongrel. Stage IV (when spermiation occurs) was the most frequent in all six breeds (~25%), whereas Stages II and VIII were the least frequent (< 8%). Each spermatogenic cycle and the total duration of spermatogenesis lasted 13.73 +/- 0.03 and 61.9 +/- 0.14 days, respectively, for the mongrel, poodle, pinscher, beagle, and Labrador retriever. These values were approximately 10% lower (P < 0.03) for the American pit bull (12.55 +/- 0.26 and 56.5 +/- 1.17 days, respectively). To our knowledge, this is the first comprehensive study to perform a careful investigation of stage frequencies and seminiferous epithelium cycle duration in this very important domestic species.

Fig. 1

Different stages of the seminiferous epithelium cycle characterized according to the acrosome system in dogs. VIII stages were characterized and the following cell types are indicated: A, Type A spermatogonia; In, intermediate spermatogonia; B, Type B spermatogonia; Pl, pre-leptotene; L, leptotene; Z, zygotene; P, pachytene; D, diplotene; M, meiotic division; R, round spermatids; E, elongated spermatids; Rb, residual bodies; SC, Sertoli cell. In each figure, the inserts in the upper right and left corners show, respectively, a representative spermatid step and spermatogonial type characteristic/predominant of the particular stage illustrated. Bar = 10 µm.

Fig. 2

Frequency of the eight stages of the seminiferous epithelium cycle characterized according to the development of the acrosome in the spermatids of the six different breeds investigated. Different letters for the same stage indicate statistical significance (P < 0.05).

Fig. 3

The most advanced labelled germ cell types found after intratesticular thymidine injections in mongrel, beagle, pinscher, poodle and Labrador. At 1–2 h, 14 days and 27 days after injection, these cells were respectively pre-leptotene spermatocytes (Pl) in Stage V (A), pachytene spermatocytes (P) in Stage V (B) and round spermatids (R) in Stage V (C). Bar = 15 µm.

Fig. 4

In American pit bulls, the most advanced germ cell types labelled 1–2 h, 14 days and 26 days were pre-leptotene spermatocytes (Pl) in Stage V (A), pachytene spermatocytes (P) in Stage VI (B) and round spermatids in Stage V (C), respectively. Bar = 15 µm.

Fig. 5

Germ cell composition and the most advanced germ cell type labelled for the different dog breeds investigated in the eight cycle stages and at different time periods (1 h, 14, 26 and 27 days) following tritiated thymidine injections. Roman numerals indicate the stage and Arabic numerals indicate the spermatogenic cycle. The space given for each stage is a proportional representation of its frequency and duration. Letters within each column indicate the germ cell types present in each stage of the cycle. A, Type A spermatogonia; In, intermediate spermatogonia; B, Type B spermatogonia; Pl, pre-leptotene spermatocytes; L, leptotene; Z, zygotene; P, pachytene; D, diplotene; MI/MII, meiotic division; R, round spermatids; E, elongated spermatids.