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Analysis of Deferent Duct Morphology in Turkeys Characterized as Low or High Semen Volume Producers1
Analysis of Deferent Duct Morphology in Turkeys Characterized as Low or High Semen Volume Producers1 D. P. FROMAN2 and H. N. ENGEL, JR. Department of Animal Sciences and College of Veterinary Medicine, Oregon State University, Corvallis, Oregon 97331 (Received for publication February 19, 1991)
1991 Poultry Science 70:1981-1985 INTRODUCTION
Reproductive efficiency of breeder toms is of paramount importance to the turkey industry. In a practical sense, breeder torn reproductive efficiency is synonymous with semen yield. As outlined by Sexton (1983), semen yield is affected by factors such as genotype, photoperiod, and diet. However, semen yield is determined by the rate of daily sperm production, i.e., the number of spermatozoa produced by the testes per day, the volume of me extragonadal sperm reserve, and ejaculation frequency. As mentioned by Cecil and Bakst (1984), any given breeder torn tends to be characterized by reasonably consistent ejaculate volumes when the torn is ejaculated on a regular basis. Furthermore, ejaculate volume can vary appreciably among males within a breeder flock. Thus, when breeder toms are ranked by ejaculate volume, those at the extremes may be referred to as low and high semen volume producers (LSVP and HSVP, respectively). The disparity in semen yield between LSVP and HSVP is an enigma in that such toms are generally of similar genotype and have been
reared under identical conditions. As may be inferred from the work of Cecil and Bakst (1986, 1988b), differences in semen yield cannot be explained by differential responses of the pituitary-gonadal axis to environmental stimuli. Rather, Cecil and Bakst (1984) have observed that LSVP are characterized by a smaller extragonadal sperm reserve and a tendency to ejaculate a smaller proportion of diis reserve when compared with HSVP. To date, the distinction between LSVP and HSVP is limited to this knowledge. The Oregon Agricultural Experiment Station has maintained lines of LSVP and HSVP since 1975 when divergent selection began with the Wrolstad strain of Medium White turkeys. The HSVP have been characterized by ejaculate volumes that are approximately twice that of LSVP (Hales et al., 1989). Such birds appeared to be highly suitable for further elucidating determinants of semen yield. Therefore, the objective of the present work was to make the following comparisons between the Oregon State University lines: 1) testicular weight, 2) deferent duct semen volume, and 3) deferent duct morphology. MATERIALS AND METHODS
Oregon State University Technical Paper Number 9505. 2TO whom correspondence should be addressed.
After a week of sexual rest, nine males were selected randomly from each line of turkeys. Each male was killed with an overdose of barbiturate. The body was positioned in dorsal
1981
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
ABSTRACT The objective of the present research was to clarify the basis for the difference in performance of turkey toms characterized as low or high semen volume producers. Variables measured included testicular weight, deferent duct semen volume, and deferent duct morphology based upon plastic casts. Three organizational patterns emerged after viewing plastic casts of deferent ducts: helical, serpentine, and randomly folded coil. The randomly folded coil was the principal pattern in deferent ducts from low and high semen volume producers alike. No difference in patterns was observed between low and high semen volume producers. Differential semen yield was attributed to a greater testicular mass along with a greater storage capacity of the deferent duct in high semen volume producers. However, deferent duct storage capacity appeared to be the predominant factor affecting semen yield. (Key words: turkey, semen, reproductive efficiency, deferent duct, ductus deferens)
1982
FROMAN AND ENGEL, JR.
TJonegan Optical Co., Inc., Lenexa, KS 66215. Abbott Hospitals, Inc., North Chicago, IX. 60064. 5 Curtin Matheson Scientific, Inc., Houston, TX 77251. ^ a i n i n Instrument Co., Inc., Emeryville, CA 94608. 7 Polysciences, Inc., Warrington, PA 18976.
subsequent determination of sperm concentration. Excess Isoton was flushed through the duct and collected in the test tube along with seminal effluent. The total effluent was 1.5 to 1.8 mL in each case. Following perfusion of each duct with Batson's No. 17 Anatomical Corrosion Compound,7 the volume of semen that had been contained witfiin the deferent duct was estimated as follows. The volume of each effluent was brought to 2 mL in a volumetric flask by the addition of Isoton. Sperm concentration was determined with a hemacytometer. The unknown volume of undiluted semen was calculated with the following formula: (Initial milliliters) (Initial sperm + milliliters) = (Diluted milliliters) (Diluted sperm +• milliliters). Plastic replicas of deferent duct lumina were made as follows. Batson's No. 17 Anatomical Corrosion Compound, a mixture of monomer solution, polymerization promoter, reaction catalyst, and dye, was prepared according to instructions printed by Polysciences (Data Sheet Number 105). This medium was injected from a disposable 10-mL syringe through the cannula into the receptaculum. The deferent duct was filled by retrograde flow. Once filled, the free end of the duct was sealed with a hemostat. When both ducts were filled, the entire preparation was placed within a water bath at room temperature in order to prevent distortion of the cast due to constriction of surrounding tissue through desiccation. The casts were cured overnight after which each duct was cut free from the cloaca. Each duct was placed in a prelabeled 16- x 150-mm screw cap glass culture tube and then the tube was filled with 6 M KOH. Maceration was performed for approximately 24 h at 50 C. The KOH solution bathing each specimen was discarded periodically. The cast was rinsed with water and then was reimmersed in fresh 6 M KOH. Following removal of adherent tissue, each cast was dried and weighed. Luminal volume was calculated by multiplying cast weight by the density of the cast.
4
Deferent duct morphology was analyzed as follows. Each duct was sectioned with a razor blade into segments categorized as helical,
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
recumbency, and the reproductive tract was removed as follows. The colon was doubly ligated with string at its junction with the coprodeum and then transected. The caudal mesenteric vein was occluded with an angiotribe. The mesentery holding the caudal mesenteric vein along the colon was cut with scissors and then the vein was reflected laterally. A circumscribed incision was made around the cloaca with care taken to avoid transection of either deferent duct. With the aid of a 1.75x OptiVisor®,3 each deferent duct was dissected free along its entire length from the dorsal body wall. After each testis was freed similarly, the entire reproductive tract along with the cloaca was removed from the body cavity. Each deferent duct was transected at the caudal pole of the testis. The epididymis was removed from each testis and then the testis was weighed. The remainder of the reproductive tract was covered with a moist paper towel and the receptaculum of each deferent duct was exposed by dissection. Each receptaculum was nicked with a pair of iris scissors, and then the receptaculum was cannulated with a Butterfly® intermittent infusion set.4 Prior to cannulation, the 21-gauge needle had been cross-sectioned so that the needle was not beveled and was only 1 cm in length. Furthermore, the end of the needle had been blunted by sanding. While the needle was held in place manually, plastic flanges were secured with Size 0 cotton suture material so that the needle would not pull free from the receptaculum. Once both deferent ducts were cannulated, each duct was emptied by retrograde flushing with Isoton® H 5 Fine forceps were used to grasp tissue adhering to the free end of the deferent duct. The end of the duct was held so that when Isoton was injected from a 10-mL syringe through the cannula into tihe receptaculum, semen could be collected in a 12 x 75 mm test tube. Before me duct was completely flushed, a 10-uL sample of undiluted semen was removed from the test tube with an M-50 positive displacement piper5 for
1983
DEFERENT DUCT MORPHOLOGY
TABLE 1. Testicular weights, of turkeys characterized as low (LSVP) or high semen volume producers (HSVP) Group
Weight (g)
LSVP HSVP
22.3 ± 1.95b 28.0 ± 1.75"
A
B
C
FIGURE 1. Turkey deferent duct coil patterns: A) helical, B) serpentine, and C) randomly folded coil. Bar = 1 cm.
serpentine, or randomly folded coil (Figure 1). Sections from a duct were segregated and weighed by category. The percentage of each duct characterized by any given coil category was calculated as follows: Percentage = (category weight weight) x 100.
+
duct
The combined weight of left and right testes per male was compared between groups with a t test (Sokal and Rohlf, 1969). Deferent duct semen volume and luminal volume were also analyzed by t test on a per male basis. Morphological classes were analyzed by nested analysis of variance following arc sine transformation of percentages (Sokal and Rohlf, 1969).
deferent ducts of LSVP and HSVP were 8.3 x 109 and 9.5 x 109 per milliliter, respectively. These concentrations were not different (P>.05). According to Cecil and Bakst (1988a), the deferent duct of sexually rested toms holds 98% of the extragonadal sperm reserve. Assuming that daily sperm production was comparable between LSVP and HSVP, the difference in deferent duct semen volume (Table 2) would appear to be due to the difference in testicular size (Table 1). If this were the case, HSVP would produce approximately 1.25 times more semen than LSVP. However, when cumulative semen production was plotted as a function of time (Figure 2), the rate at which semen was produced by HSVP was 3.2 times greater than that observed for LSVP. Therefore, the difference in testicular weight alone cannot account for the difference in semen production. As shown in Table 2, when deferent duct luminal volume was estimated by plastic cast and semen content, only LSVP had comparable estimates. Luminal volume as estimated by plastic cast was 1.05 times greater than that estimated by semen content in the case of
RESULTS AND DISCUSSION
As shown in Table 1, testicular weight of LSVP was only 80% of that of HSVP (P<.05). This contrasts with the observation of Cecil and Bakst (1984), who reported no difference in testicular weight between Large White LSVP and HSVP. However, their birds were not a product of divergent selection for ejaculate volume. As shown in Table 2, the volume of semen obtained from deferent ducts of LSVP by retrograde flow was only 78% of that of HSVP (P<.05). Mean sperm concentrations of undiluted semen recovered from
TABLE 2. Deferent duct luminal volume1 of turkeys characterized as low (LSVP) or high semen volume producers (HSVP) Total volume (mL) of left and right ducts as estimated by Group
Semen content
Plastic cast
LSVP HSVP
.74 ± ,101 b .95 ± .OoP"
.78 ± .053 b 1.40 ± .084"
a, Tvfeans within a column having no common superscripts are significantly different at P<.05. Each value represents a x ± SEM from nine replicate males.
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
a, ^Ieans with no common superscripts are significantly different at P<.05. Each value represents a x ± SEM of the combined weight of left and right testes from nine replicate males.
1984
FROMAN AND ENGEL, JR.
FIGURE 2. Cumulative semen volume from toms categorized as high (HSVP) or low semen volume producers (LSVP). The solid lines represent the functions y(x) = -.9530 + 4.5664(x) and y(x) = .4024 + 1.4263(x). Weekly ejaculations began when males were 32 wk of age.
LSVP. In contrast, it was 1.47 times greater for HSVP. Therefore, the difference in semen production between LSVP and HSVP may be attributable, in part, to a greater compliance of the deferent duct and hence a greater storage capacity.
FIGURE 3. Representative plastic casts of turkey deferent ducts: A) cast from a low semen volume producer, B) cast from a high semen volume producer. Bar = 1 cm.
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
WEEKS
As shown by the representative casts in Figure 3, deferent ducts from LSVP did not appear to be as tightly coiled as those from HSVP and thus seemed to be less efficient for storage. However, in view of the distension induced by perfusion of HSVP deferent ducts with plastic, such a conclusion was questionable. An alternative explanation that might account for the difference in deferent duct storage capacity appeared to be the pattern in which ducts were coiled. It was hypothesized that a greater percentage of helical coil would confer a greater storage capacity per unit length. However, in view of Table 3, this hypothesis had to be rejected (P>.05). According to data tabulated by Cecil and Bakst (1984), Large White LSVP and HSVP ejaculated 34 and 52% of their extragonadal sperm reserve when semen was collected by abdominal massage. Based upon grand means of data sets used to estimate the functions shown in Figure 2, characteristic ejaculate volumes for LSVP and HSVP in the present study were .17 and .52 mL, respectively. Based upon estimates of deferent duct semen volume (Table 2), LSVP and HSVP obtained by divergent selection ejaculated 23 and 55% of their extragonadal sperm reserve. Therefore, the response of Medium White LSVP and HSVP to abdominal massage was comparable to that of the Large White LSVP and HSVP studied by Cecil and Bakst (1984). In either
1985
DEFERENT DUCT MORPHOLOGY
TABLE 3. Portions1 of deferent ducts categorized as helical, serpentine, or randomly folded coil from low (LSVP) and high semen volume producers (HSVP) Category Group
Duct
Helical coil
LSVP
Left Right Left Right
23 22 24 26
HSVP
± 3.8 ± 3.6 ±4.3 ± 5.1
Serpentine coil
Randomly folded coil
7 10 6 6
69 68 71 68
±2.4 ± 2.4 ± 2.4 ± 2.3
± ± ± ±
5.4 4.6 3.7 5.9
Each value represents a x ± SEM from nine replicate males.
case, the HSVP appear either to have been more responsive to stimuli used to induce ejaculation or were more proficient at ejaculation. In accordance with Cecil and Bakst (1984), the present work has shown that the extragonadal sperm reserve is a primary determinant of reproductive efficiency in breeder toms. It is suggested that future studies of semen yield take the following phenomena into account: 1) histological attributes of the deferent duct, especially the duct's muscular layer (Hess et al., 1976), and 2) neurological basis of ejaculation. Such knowledge, interpreted in terms of daily sperm production, would provide a comprehensive view of how the male reproductive tract affects reproductive efficiency in the breeder torn. ACKNOWLEDGMENT
The authors thank Tom Savage for the contribution of individual ejaculate volumes used to estimate the functions shown in Figure 2.
REFERENCES Cecil, H. C, and M. R. Bakst, 1984. Testicular weights, ductus deferens semen volumes, and sperm concentration of turkeys with high and low ejaculate volumes. Poultry Sci. 63:1432-1437. Cecil, H. C, and M. R. Bakst, 1986. Serum testosterone concentration during two breeding cycles of turkeys with low and high ejaculate volumes. Domest Anim. Endocrinol. 3:27-32. Cecil, H. C, and M. R. Bakst, 1988a. Daily output of spermatozoa and extragonadal spermatozoal reserves in turkeys. Poultry Sci. 67:327-332. Cecil, H. C , and M. R. Bakst, 1988b. Testosterone concentrations in blood and seminal plasma of turkeys classified as high or low semen volume producers. Poultry Sci. 67:1461-1464. Hales, L. A., T. F. Savage, and J. A. Harper, 1989. Heritability estimates of semen ejaculate volume in Medium White turkeys. Poultry Sci. 68:460-463. Hess, R. A., R. J. Thurston, and H. V. Biellier, 1976. Morphology of the epididymal region and ductus deferens of the turkey {Meleagris gallopavo). J. Anat 122:241-252. Sexton, T. I., 1983. Maximizing the utilization of the male breeder: A review. Poultry Sci. 62:1700-1710. Sokal, R. R., and F. J. Rohlf, 1969. Pages 204-298 in: Biometry. Freeman, San Francisco, CA.
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
1
1991 Poultry Science 70:1981-1985 INTRODUCTION
Reproductive efficiency of breeder toms is of paramount importance to the turkey industry. In a practical sense, breeder torn reproductive efficiency is synonymous with semen yield. As outlined by Sexton (1983), semen yield is affected by factors such as genotype, photoperiod, and diet. However, semen yield is determined by the rate of daily sperm production, i.e., the number of spermatozoa produced by the testes per day, the volume of me extragonadal sperm reserve, and ejaculation frequency. As mentioned by Cecil and Bakst (1984), any given breeder torn tends to be characterized by reasonably consistent ejaculate volumes when the torn is ejaculated on a regular basis. Furthermore, ejaculate volume can vary appreciably among males within a breeder flock. Thus, when breeder toms are ranked by ejaculate volume, those at the extremes may be referred to as low and high semen volume producers (LSVP and HSVP, respectively). The disparity in semen yield between LSVP and HSVP is an enigma in that such toms are generally of similar genotype and have been
reared under identical conditions. As may be inferred from the work of Cecil and Bakst (1986, 1988b), differences in semen yield cannot be explained by differential responses of the pituitary-gonadal axis to environmental stimuli. Rather, Cecil and Bakst (1984) have observed that LSVP are characterized by a smaller extragonadal sperm reserve and a tendency to ejaculate a smaller proportion of diis reserve when compared with HSVP. To date, the distinction between LSVP and HSVP is limited to this knowledge. The Oregon Agricultural Experiment Station has maintained lines of LSVP and HSVP since 1975 when divergent selection began with the Wrolstad strain of Medium White turkeys. The HSVP have been characterized by ejaculate volumes that are approximately twice that of LSVP (Hales et al., 1989). Such birds appeared to be highly suitable for further elucidating determinants of semen yield. Therefore, the objective of the present work was to make the following comparisons between the Oregon State University lines: 1) testicular weight, 2) deferent duct semen volume, and 3) deferent duct morphology. MATERIALS AND METHODS
Oregon State University Technical Paper Number 9505. 2TO whom correspondence should be addressed.
After a week of sexual rest, nine males were selected randomly from each line of turkeys. Each male was killed with an overdose of barbiturate. The body was positioned in dorsal
1981
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
ABSTRACT The objective of the present research was to clarify the basis for the difference in performance of turkey toms characterized as low or high semen volume producers. Variables measured included testicular weight, deferent duct semen volume, and deferent duct morphology based upon plastic casts. Three organizational patterns emerged after viewing plastic casts of deferent ducts: helical, serpentine, and randomly folded coil. The randomly folded coil was the principal pattern in deferent ducts from low and high semen volume producers alike. No difference in patterns was observed between low and high semen volume producers. Differential semen yield was attributed to a greater testicular mass along with a greater storage capacity of the deferent duct in high semen volume producers. However, deferent duct storage capacity appeared to be the predominant factor affecting semen yield. (Key words: turkey, semen, reproductive efficiency, deferent duct, ductus deferens)
1982
FROMAN AND ENGEL, JR.
TJonegan Optical Co., Inc., Lenexa, KS 66215. Abbott Hospitals, Inc., North Chicago, IX. 60064. 5 Curtin Matheson Scientific, Inc., Houston, TX 77251. ^ a i n i n Instrument Co., Inc., Emeryville, CA 94608. 7 Polysciences, Inc., Warrington, PA 18976.
subsequent determination of sperm concentration. Excess Isoton was flushed through the duct and collected in the test tube along with seminal effluent. The total effluent was 1.5 to 1.8 mL in each case. Following perfusion of each duct with Batson's No. 17 Anatomical Corrosion Compound,7 the volume of semen that had been contained witfiin the deferent duct was estimated as follows. The volume of each effluent was brought to 2 mL in a volumetric flask by the addition of Isoton. Sperm concentration was determined with a hemacytometer. The unknown volume of undiluted semen was calculated with the following formula: (Initial milliliters) (Initial sperm + milliliters) = (Diluted milliliters) (Diluted sperm +• milliliters). Plastic replicas of deferent duct lumina were made as follows. Batson's No. 17 Anatomical Corrosion Compound, a mixture of monomer solution, polymerization promoter, reaction catalyst, and dye, was prepared according to instructions printed by Polysciences (Data Sheet Number 105). This medium was injected from a disposable 10-mL syringe through the cannula into the receptaculum. The deferent duct was filled by retrograde flow. Once filled, the free end of the duct was sealed with a hemostat. When both ducts were filled, the entire preparation was placed within a water bath at room temperature in order to prevent distortion of the cast due to constriction of surrounding tissue through desiccation. The casts were cured overnight after which each duct was cut free from the cloaca. Each duct was placed in a prelabeled 16- x 150-mm screw cap glass culture tube and then the tube was filled with 6 M KOH. Maceration was performed for approximately 24 h at 50 C. The KOH solution bathing each specimen was discarded periodically. The cast was rinsed with water and then was reimmersed in fresh 6 M KOH. Following removal of adherent tissue, each cast was dried and weighed. Luminal volume was calculated by multiplying cast weight by the density of the cast.
4
Deferent duct morphology was analyzed as follows. Each duct was sectioned with a razor blade into segments categorized as helical,
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
recumbency, and the reproductive tract was removed as follows. The colon was doubly ligated with string at its junction with the coprodeum and then transected. The caudal mesenteric vein was occluded with an angiotribe. The mesentery holding the caudal mesenteric vein along the colon was cut with scissors and then the vein was reflected laterally. A circumscribed incision was made around the cloaca with care taken to avoid transection of either deferent duct. With the aid of a 1.75x OptiVisor®,3 each deferent duct was dissected free along its entire length from the dorsal body wall. After each testis was freed similarly, the entire reproductive tract along with the cloaca was removed from the body cavity. Each deferent duct was transected at the caudal pole of the testis. The epididymis was removed from each testis and then the testis was weighed. The remainder of the reproductive tract was covered with a moist paper towel and the receptaculum of each deferent duct was exposed by dissection. Each receptaculum was nicked with a pair of iris scissors, and then the receptaculum was cannulated with a Butterfly® intermittent infusion set.4 Prior to cannulation, the 21-gauge needle had been cross-sectioned so that the needle was not beveled and was only 1 cm in length. Furthermore, the end of the needle had been blunted by sanding. While the needle was held in place manually, plastic flanges were secured with Size 0 cotton suture material so that the needle would not pull free from the receptaculum. Once both deferent ducts were cannulated, each duct was emptied by retrograde flushing with Isoton® H 5 Fine forceps were used to grasp tissue adhering to the free end of the deferent duct. The end of the duct was held so that when Isoton was injected from a 10-mL syringe through the cannula into tihe receptaculum, semen could be collected in a 12 x 75 mm test tube. Before me duct was completely flushed, a 10-uL sample of undiluted semen was removed from the test tube with an M-50 positive displacement piper5 for
1983
DEFERENT DUCT MORPHOLOGY
TABLE 1. Testicular weights, of turkeys characterized as low (LSVP) or high semen volume producers (HSVP) Group
Weight (g)
LSVP HSVP
22.3 ± 1.95b 28.0 ± 1.75"
A
B
C
FIGURE 1. Turkey deferent duct coil patterns: A) helical, B) serpentine, and C) randomly folded coil. Bar = 1 cm.
serpentine, or randomly folded coil (Figure 1). Sections from a duct were segregated and weighed by category. The percentage of each duct characterized by any given coil category was calculated as follows: Percentage = (category weight weight) x 100.
+
duct
The combined weight of left and right testes per male was compared between groups with a t test (Sokal and Rohlf, 1969). Deferent duct semen volume and luminal volume were also analyzed by t test on a per male basis. Morphological classes were analyzed by nested analysis of variance following arc sine transformation of percentages (Sokal and Rohlf, 1969).
deferent ducts of LSVP and HSVP were 8.3 x 109 and 9.5 x 109 per milliliter, respectively. These concentrations were not different (P>.05). According to Cecil and Bakst (1988a), the deferent duct of sexually rested toms holds 98% of the extragonadal sperm reserve. Assuming that daily sperm production was comparable between LSVP and HSVP, the difference in deferent duct semen volume (Table 2) would appear to be due to the difference in testicular size (Table 1). If this were the case, HSVP would produce approximately 1.25 times more semen than LSVP. However, when cumulative semen production was plotted as a function of time (Figure 2), the rate at which semen was produced by HSVP was 3.2 times greater than that observed for LSVP. Therefore, the difference in testicular weight alone cannot account for the difference in semen production. As shown in Table 2, when deferent duct luminal volume was estimated by plastic cast and semen content, only LSVP had comparable estimates. Luminal volume as estimated by plastic cast was 1.05 times greater than that estimated by semen content in the case of
RESULTS AND DISCUSSION
As shown in Table 1, testicular weight of LSVP was only 80% of that of HSVP (P<.05). This contrasts with the observation of Cecil and Bakst (1984), who reported no difference in testicular weight between Large White LSVP and HSVP. However, their birds were not a product of divergent selection for ejaculate volume. As shown in Table 2, the volume of semen obtained from deferent ducts of LSVP by retrograde flow was only 78% of that of HSVP (P<.05). Mean sperm concentrations of undiluted semen recovered from
TABLE 2. Deferent duct luminal volume1 of turkeys characterized as low (LSVP) or high semen volume producers (HSVP) Total volume (mL) of left and right ducts as estimated by Group
Semen content
Plastic cast
LSVP HSVP
.74 ± ,101 b .95 ± .OoP"
.78 ± .053 b 1.40 ± .084"
a, Tvfeans within a column having no common superscripts are significantly different at P<.05. Each value represents a x ± SEM from nine replicate males.
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
a, ^Ieans with no common superscripts are significantly different at P<.05. Each value represents a x ± SEM of the combined weight of left and right testes from nine replicate males.
1984
FROMAN AND ENGEL, JR.
FIGURE 2. Cumulative semen volume from toms categorized as high (HSVP) or low semen volume producers (LSVP). The solid lines represent the functions y(x) = -.9530 + 4.5664(x) and y(x) = .4024 + 1.4263(x). Weekly ejaculations began when males were 32 wk of age.
LSVP. In contrast, it was 1.47 times greater for HSVP. Therefore, the difference in semen production between LSVP and HSVP may be attributable, in part, to a greater compliance of the deferent duct and hence a greater storage capacity.
FIGURE 3. Representative plastic casts of turkey deferent ducts: A) cast from a low semen volume producer, B) cast from a high semen volume producer. Bar = 1 cm.
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
WEEKS
As shown by the representative casts in Figure 3, deferent ducts from LSVP did not appear to be as tightly coiled as those from HSVP and thus seemed to be less efficient for storage. However, in view of the distension induced by perfusion of HSVP deferent ducts with plastic, such a conclusion was questionable. An alternative explanation that might account for the difference in deferent duct storage capacity appeared to be the pattern in which ducts were coiled. It was hypothesized that a greater percentage of helical coil would confer a greater storage capacity per unit length. However, in view of Table 3, this hypothesis had to be rejected (P>.05). According to data tabulated by Cecil and Bakst (1984), Large White LSVP and HSVP ejaculated 34 and 52% of their extragonadal sperm reserve when semen was collected by abdominal massage. Based upon grand means of data sets used to estimate the functions shown in Figure 2, characteristic ejaculate volumes for LSVP and HSVP in the present study were .17 and .52 mL, respectively. Based upon estimates of deferent duct semen volume (Table 2), LSVP and HSVP obtained by divergent selection ejaculated 23 and 55% of their extragonadal sperm reserve. Therefore, the response of Medium White LSVP and HSVP to abdominal massage was comparable to that of the Large White LSVP and HSVP studied by Cecil and Bakst (1984). In either
1985
DEFERENT DUCT MORPHOLOGY
TABLE 3. Portions1 of deferent ducts categorized as helical, serpentine, or randomly folded coil from low (LSVP) and high semen volume producers (HSVP) Category Group
Duct
Helical coil
LSVP
Left Right Left Right
23 22 24 26
HSVP
± 3.8 ± 3.6 ±4.3 ± 5.1
Serpentine coil
Randomly folded coil
7 10 6 6
69 68 71 68
±2.4 ± 2.4 ± 2.4 ± 2.3
± ± ± ±
5.4 4.6 3.7 5.9
Each value represents a x ± SEM from nine replicate males.
case, the HSVP appear either to have been more responsive to stimuli used to induce ejaculation or were more proficient at ejaculation. In accordance with Cecil and Bakst (1984), the present work has shown that the extragonadal sperm reserve is a primary determinant of reproductive efficiency in breeder toms. It is suggested that future studies of semen yield take the following phenomena into account: 1) histological attributes of the deferent duct, especially the duct's muscular layer (Hess et al., 1976), and 2) neurological basis of ejaculation. Such knowledge, interpreted in terms of daily sperm production, would provide a comprehensive view of how the male reproductive tract affects reproductive efficiency in the breeder torn. ACKNOWLEDGMENT
The authors thank Tom Savage for the contribution of individual ejaculate volumes used to estimate the functions shown in Figure 2.
REFERENCES Cecil, H. C, and M. R. Bakst, 1984. Testicular weights, ductus deferens semen volumes, and sperm concentration of turkeys with high and low ejaculate volumes. Poultry Sci. 63:1432-1437. Cecil, H. C, and M. R. Bakst, 1986. Serum testosterone concentration during two breeding cycles of turkeys with low and high ejaculate volumes. Domest Anim. Endocrinol. 3:27-32. Cecil, H. C, and M. R. Bakst, 1988a. Daily output of spermatozoa and extragonadal spermatozoal reserves in turkeys. Poultry Sci. 67:327-332. Cecil, H. C , and M. R. Bakst, 1988b. Testosterone concentrations in blood and seminal plasma of turkeys classified as high or low semen volume producers. Poultry Sci. 67:1461-1464. Hales, L. A., T. F. Savage, and J. A. Harper, 1989. Heritability estimates of semen ejaculate volume in Medium White turkeys. Poultry Sci. 68:460-463. Hess, R. A., R. J. Thurston, and H. V. Biellier, 1976. Morphology of the epididymal region and ductus deferens of the turkey {Meleagris gallopavo). J. Anat 122:241-252. Sexton, T. I., 1983. Maximizing the utilization of the male breeder: A review. Poultry Sci. 62:1700-1710. Sokal, R. R., and F. J. Rohlf, 1969. Pages 204-298 in: Biometry. Freeman, San Francisco, CA.
Downloaded from http://ps.oxfordjournals.org/ at West Virginia University, Health Science Libraryy on May 3, 2015
1