A. Yilmaz
M. E. Davis1
The Ohio State University
Department of Animal Sciences
R. C. M. Simmen2
Department of Animal Science
University of Florida
1 For more information contact at: The Ohio State University, 2027 Coffey Road, 221 Plumb Hall, Columbus, OH, 43210; 614-292-4984; fax: 614-292-2929; e-mail: davis.28@osu.edu.
2 For more information contact at: Department of Animal Science, University of Florida, Gainesville, FL 32611-0901.
The objectives of this study were to examine seasonal effects and differences in scrotal circumference, sperm motility, and percentage of normal sperm cells between two lines of Angus beef cattle selected for high vs. low blood serum IGF-I concentration. Data were obtained from an ongoing experiment involving 100 spring-calving (50 high- and 50 low-line) and 100 fall-calving (50 high and 50 low) purebred Angus cows. Scrotal circumference was significantly larger in spring-born bulls than in fall-born bulls, but did not differ between high and low IGF-I line bulls (P = 0.79). Percentage of motile sperm cells did not differ between high- and low-line bulls (P = 0.50). Fall-born bulls had higher sperm motility than spring-born bulls in every year in which motility was evaluated. Percentage of normal sperm cells did not differ between high- and low-line bulls (P = 0.56) however, fall-born bulls had a significantly higher percentage of normal sperm cells. Regression coefficients for the nonlinear relationship between scrotal circumference and IGF28, IGF42, and IGF56 were negative (P = 0.02, 0.07, and 0.08, respectively). The regression coefficient for the nonlinear relationship between percentage of normal sperm cells and IGF56 was negative and significant (P = 0.03). Regression coefficients for the nonlinear relationships of scrotal circumference, percent sperm motility, and percentage of normal sperm cells with mean IGF-I concentrations were negative, and were either significant or approached significance (P = 0.01, 0.16 and 0.04, respectively). Thus, scrotal circumference, percent sperm motility, and percentage of normal sperm cells are related to blood serum IGF-I concentration in Angus bulls.
Insulin like growth factor -I (IGF-I) is a polypeptide that increases cell proliferation (Svoboda and VanWyk, 1983) and sugar uptake (Poggi et al., 1979) by cells. Its effects on reproductive functions of animals have been extensively studied. However, there has been little research on relationships between IGF-I concentration and male reproductive traits in cattle.
IGF-I mRNAs have been detected in the testis in rats (Dombrowicz et al., 1992). IGF-I may play a role in differentiation of sperm cells in the epididymis (Leheup and Grignon, 1993). IGF-I increases testosterone production in the rat testis (Kasson and Hsueh, 1987). Season also influences scrotal circumference (Godfrey et al., 1990), which is related to sperm motility and percentage of normal sperm cells.
The objectives of this study were to examine seasonal effects and differences in scrotal circumference, sperm motility, and percentage of normal sperm cells between two lines of Angus beef cattle selected for high vs. low blood serum IGF-I concentration.
Selection for high vs. low blood serum IGF-I concentration was initiated in 1989 using 100 spring-calving (50 high-line and 50 low-line) and in 1990 using 100 fall-calving (50 high-line and 50 low-line) purebred Angus cows with unknown IGF-I levels located at the Eastern Ohio Resource Development Center (EORDC). The 1989 spring and 1990 spring and fall calf crops were produced using different sets of four bulls with unknown IGF-I concentrations. In subsequent years, the four bulls that had highest or lowest blood serum IGF-I concentrations, adjusted for age of calf and age of dam, were saved for breeding within the respective selection lines. Selection of bulls was done on a within-season basis.
Selection of bulls was based on serum IGF-I samples collected at days 28, 42, and 56, of the postweaning test. The IGF-I concentrations measured at days 28, 42, and 56, are abbreviated as IGF28, IGF42, and IGF56, respectively.
Spring-born calves were reared by their dams until weaning at approximately seven months of age. During an adjustment period of two weeks and a 140-day postweaning test period, bull calves were fed a corn-soybean meal based concentrate diet. Bulls were kept at EORDC for the postweaning test and were given ad libitum access to feed.
Fall-born calves were fed a growing diet that was designed to yield gains of 1.98 lbs./day during a 112-day growing period in drylot after weaning at approximately 140 days of age. Following the growing period, bulls remained at EORDC and were fed the same diet as spring-born bulls during a 140-day postweaning test period.
Approximately 25 milliliters (mL) of blood were collected in sterile glass tubes at days 28, 42, and 56, of the postweaning test, allowed to clot for 24 hours at 4 degrees C, and centrifuged. Serum was drawn off and frozen at -20 degrees C until it was assayed.
Procedures previously described by Bishop et al. (1989) were followed to determine IGF-I concentrations by radioimmunoassay.
Immediately following the postweaning test, breeding soundness exams (BSE) were performed by veterinarians at The Ohio State University's Ohio Agricultural Research and Development Center (OARDC). Breeding soundness exams were performed on all bulls born in 1995 and in 1996 and only on those bulls that were saved for breeding in previous years. The BSE exams were performed in the fall for fall-born bulls and in the spring for spring-born bulls at approximately 12 to 14 months of age. Semen was collected by electroejaculation. A flexible metal tape was used to measure scrotal circumference. The largest diameter of the scrotum was measured and scrotal circumference was recorded in centimeters.
All data were analyzed using PROC GLM procedures of SAS (SAS,1992). Year, line, and season were combined into one variable to obtain a unique identification for the nested effect of sire. Effects of age of dam, year-line-season, and sire nested within year-line-season, were included in all analyses. On-test age of calf was added to the models as a covariate. Orthogonal linear contrasts were used to compare IGF-I concentrations, scrotal circumference, and semen traits of spring- vs. fall-born calves and high vs. low IGF-I line calves. Sire nested within year-line-season was used as the error term to test year-line-season effects and to obtain significance levels for contrasts of high- vs. low-line and spring vs. fall means. In the regression analysis used to compute linear and nonlinear (i.e., quadratic) relationships of IGF28, IGF42, IGF56 and mean IGF-I with BSE traits, both linear and nonlinear terms for respective IGF-I measurements were included in the model as independent variables. A separate regression analysis was done for each IGF-I measurement. Data obtained from A.I. sires were included in the regression analyses, but not in the linear contrast analyses, because doing so would have reduced the divergence between the IGF-I lines.
IGF-I concentrations of bulls that had data for scrotal circumference, sperm motility, and percentage of normal sperm cells were significantly higher in high-line bulls than in low-line bulls. IGF-I concentrations did not differ between fall- and spring-born bulls, except that IGF42 was significantly higher in spring-born bulls.
| Table 1. Contrasts and Year-Line-Season and Age of Dam Means ± Standard Errors for Scrotal Circumference, Percent Sperm Motility, and Percentage of Normal Sperm Cells. | ||||||
|---|---|---|---|---|---|---|
| n | Scrotal circumference, cm | n | Percent sperm motility, % | n | Percentage of normal sperm cells, % | |
| Year line-season | P = 0.0001 | P = 0.005 | P = 0.0001 | |||
| 1990 high-fall | 11 | 35.7 ± 1.0 | 11 | 81.7 ± 5.3 | ||
| 1990 low-fall | 9 | 33.1 ± 0.8 | 8 | 81.9 ± 4.9 | ||
| 1991 high-spring | 13 | 34.3 ± 0.7 | 13 | 57.5 ± 3.7 | ||
| 1991 high-fall | 9 | 34.4 ± 1.0 | 6 | 67.4 ± 9.2 | 6 | 88.3 ± 6.2 |
| 1991 low-spring | 10 | 35.1 ± 0.8 | 10 | 61.4 ± 4.7 | ||
| 1991 low-fall | 7 | 34.8 ± 0.9 | 7 | 57.3 ± 7.7 | 7 | 85.0 ± 5.2 |
| 1992 high-spring | 13 | 36.0 ± 0.6 | 11 | 62.1 ± 6.1 | 11 | 86.2 ± 4.3 |
| 1992 high-fall | 16 | 33.4 ± 0.6 | 16 | 73.8 ± 5.3 | 15 | 68.3 ± 3.9 |
| 1992 low-spring | 13 | 36.2 ± 0.8 | 11 | 51.6 ± 7.7 | 11 | 81.5 ± 5.3 |
| 1992 low-fall | 11 | 32.5 ± 0.7 | 11 | 64.7 ± 6.8 | 11 | 68.5 ± 4.6 |
| 1993 high-spring | 16 | 32.5 ± 0.8 | 15 | 67.2 ± 5.5 | 15 | 58.7 ± 3.8 |
| 1993 high-fall | 11 | 32.6 ± 0.6 | 11 | 69.9 ± 6.3 | 11 | 85.6 ± 4.4 |
| 1993 low-spring | 16 | 33.6 ± 0.8 | 15 | 69.7 ± 5.5 | 16 | 57.5 ± 3.5 |
| 1993 low-fall | 10 | 33.4 ± 0.8 | 10 | 76.4 ± 6.5 | 10 | 88.5 ± 4.5 |
| 1994 high-spring | 17 | 37.5 ± 0.6 | 17 | 62.8 ± 5.2 | 17 | 78.9 ± 3.5 |
| 1994 high-fall | 20 | 33.9 ± 0.6 | 17 | 82.2 ± 4.3 | ||
| 1994 low-spring | 15 | 36.5 ± 0.6 | 13 | 72.4 ± 5.7 | 13 | 72.6 ± 3.9 |
| 1994 low-fall | 16 | 34.2 ± 0.8 | 13 | 81.7 ± 3.8 | ||
| 1995 high-spring | 22 | 35.6 ± 0.6 | 21 | 80.5 ± 4.7 | 20 | 81.0 ± 3.2 |
| 1995 high-fall | 18 | 36.1 ± 0.6 | 18 | 86.4 ± 5.0 | 17 | 91.1 ± 3.5 |
| 1995 low-spring | 20 | 36.1 ± 0.2 | 19 | 75.0 ± 4.7 | 18 | 87.0 ± 3.3 |
| 1995 low-fall | 18 | 36.2 ± 0.6 | 18 | 86.2 ± 5.2 | 18 | 90.5 ± 3.6 |
| 1996 high-spring | 15 | 37.8 ± 0.7 | 15 | 74.6 ± 5.5 | 14 | 86.5 ± 3.8 |
| 1996 high-fall | 21 | 32.5 ± 0.6 | 21 | 72.7 ± 3.2 | ||
| 1996 low-spring | 16 | 39.2 ± 0.8 | 15 | 74.7 ± 6.6 | 15 | 82.6 ± 4.5 |
| 1996 low-fall | 23 | 32.3 ± 0.5 | 24 | 67.7 ± 3.0 | ||
| Age of dam at calving | P = 0.12 | P = 0.29 | P = 0.97 | |||
| 2 | 50 | 34.6 ± 0.4 | 32 | 68.9 ± 3.9 | 48 | 78.5 ± 2.2 |
| 3 | 61 | 34.4 ± 0.3 | 43 | 70.9 ± 3.4 | 57 | 78.7 ± 2.0 |
| 4 | 52 | 35.0 ± 0.4 | 35 | 65.1 ± 3.7 | 50 | 77.9 ± 2.2 |
| 5a | 177 | 35.4 ± 0.2 | 109 | 70.2 ± 2.2 | 162 | 77.7 ± 1.2 |
| 10b | 46 | 34.8 ± 0.4 | 30 | 78.4 ± 4.3 | 45 | 76.7 ± 2.3 |
| Contrastsc | ||||||
| High minus low line | P = 0.79d | P = 0.50d | P = 0.56d | |||
| -0.07 ± 0.3 | 1.81 ± 1.8 | 0.9 ± 1.6 | ||||
| Spring minus fall | P = 0.0001e | P = 0.03e | P = 0.0008e | |||
| 2.0 ± 0.3 | -8.5 ± 3.4 | -6.5 ± 1.9 | ||||
| a Cows 5- to 9-year-old at calving. b Cows that were 10-years-old and older at calving. c Number of observations for scrotal circumference was 386, for percent sperm motility was 249, and for percentage of normal sperm cells was 362. d P is the level of statistical significance for the contrast of high- vs. low-line. e P is the level of statistical significance for the contrast of spring- vs. fall-calving. | ||||||
The overall mean for scrotal circumference was 35.1 cm. Means ± standard errors for scrotal circumference are shown in Table 1. Scrotal circumference was significantly larger in spring-born bulls than in fall-born bulls, but did not differ between high and low IGF-I line bulls (P = 0.79). Year-line-season effects on scrotal circumference were highly significant, reflecting yearly and seasonal variations. Age of dam effects on scrotal circumference were not significant (P = 0.12).
These results are consistent with previously reported results except that Curtis and Amann (1981) failed to detect a difference in testis weight and the establishment of spermatogenesis of fall-born vs. spring-born Holstein bulls. Godfrey et al. (1990) detected significant effects of season on scrotal circumference. They reported a significant decrease in the winter and an increase in the summer in scrotal circumference of Brahman bulls.
The overall mean for percent sperm motility was 72.0%. Means ± standard errors for sperm motility are presented in Table 1. Year-line-season effects on sperm motility were highly significant. Age of dam effects on sperm motility were not significant (P = 0.29). Percentage of motile sperm cells did not differ between high and low IGF-I line bulls (P = 0.50). Fall-born bulls had higher sperm motility than spring-born bulls in every year in which motility was evaluated (P = 0.03). Breier et al. (1996) reported that elevated IGF-I concentrations in seminal plasma were significantly associated with an increase in sperm motility, but not a change in the morphology of sperm cells, in GH-deficient dwarf rats during growth hormone treatment.
The overall mean for percentage of normal sperm cells was 77.3%. Means ± standard errors for percentage of normal sperm cells are presented in Table 1. Year-line-season effects on percentage of normal sperm cells were highly significant. Percentage of normal sperm cells did not differ between high and low IGF-I line bulls (P = 0.56). In contrast to our results, Glander et al. (1996) reported a correlation of 0.78 (P = 0.00001) between seminal IGF-I concentrations and percentage of morphologically normal sperm cells in humans. In this study, fall-born bulls had a higher (P = 0.0008) percentage of normal sperm cells than spring-born bulls.
Regression coefficients for these relationships are presented in Table 2. The regression coefficients for the nonlinear relationships between scrotal circumference and IGF28, IGF42, and IGF56 tended to be negative (P = 0.02, 0.07, and 0.08, respectively). The coefficient for the linear relationship between percentage of normal sperm cells and IGF28 tended to be positive (P = 0.06). The regression coefficients for the nonlinear relationship between percentage of normal sperm cells and IGF42 and IGF56 were important (P = 0.15 and 0.03, respectively).
Regression coefficients for the nonlinear relationships of scrotal circumference, percent sperm motility, and percentage of normal sperm cells with mean IGF-I concentrations were negative and were either significant or approached significance (P = 0.01, 0.16 and 0.04, respectively). The equation for the nonlinear relationships was Y = b0+ b1X-b2X2. b2 was negative in all analyses, indicating that all three variables increased as mean IGF-I concentration increased, but the rate of increase was less when mean IGF-I was large than when mean IGF-I was small.
Seasonal effects on scrotal circumference, percent sperm motility, and percentage of normal sperm cells were greater than IGF-I selection line effects in Angus bulls. However, IGF-I concentrations demonstrated some linear and nonlinear relationships with scrotal circumference, percent sperm motility, and percentage of normal sperm cells. Therefore, selection for IGF-I has implications for improvement of male reproductive efficiency in cattle.
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