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Genetic and phenotypic parameter estimates for scrotal circumference and semen traits in young beef bulls
THERIOGENOLOGY
GENETIC AND PHENOTYPIC PARAMETER ESTIMATES FOR SCROTAL CIRCUMFERENCE AND SEMEN TRAITS IN YOUNG BEEF BULLS T.A. Gipson,a D.W. Vogt,l M.R. Ellersieck2 and J.W. Massey1 lDepartment of Animal Sciences 2Agricultural Experiment Station University of Missouri Columbia, MO. 65211 Received for publication: June 123 1986 Accepted: September 8, 1987 ABSTRACT Estimated in this study were heritabilities and genetic and phenotypic correlations involving scrotal circumference (SC), percent live sperm, sperm number, sperm concentration, sperm motility, and an ov,erallmeasure of a bull's potential breeding efficiency. Potential breeding efficiency is a composite trait based on a consideration of sperm concentration, sperm motility, sperm morphology and scrotal circumference. Data used were from three sources. Records on 863 Angus, 753 Polled Hereford, and 302 Simmental bulls were made available through the Missouri Performance-Tested Bull Sale and records on 1169 Polled Hereford bulls came from the American Polled Hereford Association. Information from these first two data sets were used to estimate heritability of scrotal circumference. The third data set was provided by Nichols Farms of Bridgewater, Iowa, and included information from the records of 465 yearling Polled Hereford and 264 yearling Simmental bulls. This latter data set was used to estimate all of the above mentioned parameters. Each data set was kept separately for the Parameters were estimated using purpose of statistical analysis. ccmponents from paternal half-sib analysis of variance and covariance, Pooled estimates of heritability for SC, sperm concentration, sperm motility, percent live sperm, sperm number and potential breeding efficiency were 0.51 f 0.09, 0.20 f 0.13, 0.11 * 0.12, 0.00, 0.19 f Phenotypic correlations involving 0.14 and 0.13 f 0.12, respectively. the six traits were very consistent for the two breeds. Combined across breeds their values ranged from 0.47 for SC and percent live sperm to 0.96 for sperm concentration and potential breeding efficiency. Corresponding genetic correlatic.nswere generally positive and high and ranged from 0.65 fcr SC and sperm motility to 1.14 for sperm number and potential breeding efficiency. Key words:
beef bulls, scrotal circumference, heritab.i.lities, correlations
semen quality,
Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 10113. Supported in part by funds in Animal Sciences Project C-2-5032E,. The authors thank Mrs. Lillian Nichols of Nichols Farms in Bridgewater, IA, and Dr. J. Gibb, Director of Research and Education, American Polled Hereford Association, Kansas City, MO, for providing portions of these data for this study. aPresent address: 402 W. Springfield Ave., Urbana, IL.61801.
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INTRODUCTION In recent years, there has been considerable attention focused on scrotal development in the male as a means of improving bovine male fertility. Most studies involving associations of scrotal circumference with semen traits have been phenotypic (l-4). Much less information is available regarding genetic association of these same Additionally, only a few studies (6-8) have reported traits (5-7). heritabilities of semen traits. Knowledge of the heritabilities of scrotal circumference and semen traits and the genetic and phenotypic correlations between them facilitates selection for increased fertility in the bull. Furthermore, this knowledge is requisite to predictions of direct and indirect responses to selection for improvement in these reproduction-oriented traits. The objectives of this study are to estimate heritabilities and genetic and phenotypic correlations involving scrotal circumference with each of four semen traits and one composite trait representing an overall measure of a bull's potential breeding efficiency. MATERIALS AND METHODS The data for this study came from three sources. Each was kept separately for the purpose of statistical analysis.
data set
Missouri Tested Bull Sale (Data Set 1)~ Approximately 300 bulls are sold annually through University of Missouri performance-tested bull sales. These sales are held in April Scrotal circumference measurements are and November of each year. taken the day before the sale under the supervision of the faculty of the Theriogenology Department in the School of Veterinary Medicine. Measurements are taken in accordance with the technique recommended by Scrotal circumference measurement, the Society for Theriogenology. age at day of sale, weight at day of sale, and pedigree were collected on 863 Angus, 753 Polled Hereford, and 302 Simmental bulls from 1978 through 1983. These data were subdivided into 16 year-season subsets Data Set 1 was used to (eight years and two seasons per year). Angus, Polled estimate heritability of scrotal circumference in Hereford and Simmental bulls. Scrotal circumference measurements were adjusted for age and body weight differences as described previously (9). Adjusted data were analysed within breed and year-season subsets by paternal half-sib analysis of variance. Subset data were subsequently combined by summing (separately) degrees of freedom and sums of New variance squares obtained from appropriate subset analyses. components were determined from the combined data sets, and heritability was estimated as four times the sire component of variance divided by the sum of the sire and within sire components of variance. Standard errors of the heritability estimates were calculated using routine procedures (10).
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American Polled Hereford Association (Data set 2) Measurements on scrotal circumference and body weight as well as age and pedigree information on 1169 yearling Polled Hereford bulls were made available for this study by the American Polled Hereford Association. The American Polled Hereford Association requests that scrotal circumference measurements be taken according to the technique established by the Society for Theriogenology. Data were collected in the three-year period from 1981 through 1983, with most being collected in 1982. Data were subdivided into 129 year-location subsets (3 years and 97 locations). Not all locations are represented in all years. Information in this data set, as in data Set 1, was used to estimate heritability of scrotal circumference. As with data Set 1, SC measurements were adjusted for differences in age and body weight using adjustment factors and procedures given previously (9). The methods of statistical analysis were the same as outlined for data Set 1. In data Set 2, however, there was only one breed and data were subdivided into year-location subsets. Nichols Farms (Data -Set a ~Data in this subset were provided by Nichols Farms of Bridgewater, Iowa, and included information from the records of 465 yearling Polled Hereford bulls and 264 yearling Simmental bulls. Records were for the five-year period from 1978 through 1982. Data taken from the records included age, body weight, scrotal circumference, percent live sperm, sperm number, sperm concentration, sperm motility, and an overall measure of a bull's potential breeding efficiency. All measurements were made at the conclusion of a 140-day full-feed postweaning test period that was completed in the spring of each year. Measurements of scrotal circumference and semen quality were made by Hawkeye Breeders Service, Inc., Des Moines, IA. Scrotal circumference was measured in accordance with recommendations of the Society for Theriogenology. Semen evaluations were made using fresh, undiluted semen collected by electroejaculation. One to three ejaculates were collected and evaluated depending on the quality of the first semen sample. Bulls with poor quality in the first and/or second samples were subsequently collected again for reevaluation. Semen quality measurements were based on the best single sample. It is recognized that sperm production is not as accurately estimated in semen samples collected by electroejaculation as in samples collected by means of an artificial vagina. However, electroejaculation is a standard technique for semen collection in young beef bulls and provided the best practical collection method for the animals used in this study. Percent live sperm was estimated to the nearest 10% figure, with values ranging from 0 to 70%. Sperm number was based on a photometer reading and recorded in millions of cells per cc. Sperm concentration ratings were based on sperm number and assigned classifications of excellent, good +, good, good -, fair and unsatisfactory. Ranges in millions of cells per cc of raw semen for these six classifications, beginning with excellent, were >1500, 1350 to 1500, 1150 to 1350, 1000 to 1150, 500 to 1000 and (500, respectively. Sperm motility was evaluated from a thin smear of semen on slides warmed to 3i'OC and viewed at 100 magnifica-
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tion. Sperm motility was classified in the same six classifications as sperm concentration (i.e. excellent to unsatisfactory) and coded in like manner. Ranges in the percentage motility values corresponding to these six classifications, beginning with excellent, were >70, 65 to 69.9, 60 to 64.9, 55 to 59.9, 25 to 54.9 and <25, respectively. Classifications of excellent to unsatisfactory for both sperm concentration and sperm motility were coded 6 to 1, respectively. Potential breeding efficiency of bulls is a composite trait based by Hawkeye Breeders Service on sperm concentration, sperm motility, sperm morphology and scrotal circumference. These traits were given percent weights of 35, 15, 15 and 35, respectively, in assigning potential breeding efficiency scores. Evaluations of this composite trait are classified excellent, good +, good, good -, fair, questionable, or unsatisfactory. In the present data set there were no bulls in the questionable category. These classifications, thus, were the same as those for sperm concentration and sperm motility, and consequently, they were coded in the same manner as sperm concentration and sperm motility. Information in this data set was used to estimate heritabilities of scrotal circumference, percent live sperm, sperm number, sperm concentration, sperm motility, and potential breeding efficiency as well as the genetic and phenotypic correlations between these traits. Scrotal circumference measurements, as in data Sets 1 and 2, were adjusted for differences due to age and body weight (9). Paternal half-sib analyses of variance and covariance were conducted on a within-breed and year basis. Results of these subset analyses were combined in a manner analogous to that described for data Set 1. New variance and covariance components were determined from the combined data sets and were subsequently used to estimate heritabilities and genetic and phenotypic correlations. Heritability estimates and their standard errors were calculated using statistical methods employed with data Sets 1 and 2. Genetic correlations were computed as the ratio of the sire component of covariance to the square root of the product of the appropriate sire components of variance. Phenotypic correlations were calculated as the sum of the sire and within sire components of covariance divided by the square root of the product of the summed sire and within-sire components of variance of each trait. RESULTS AND DISCUSSION Heritability Estimates Table 1 shows estimates of heritability for SC, sperm concentration, sperm motility, percent live sperm, sperm number and the overall measure of a bull's potential breeding efficiency. Estimates are shown within breed and data source as well as combined across breeds and, for SC, across breeds and data source. Breed estimates of heritability for
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SC range from 0.48 * 0.24 to 0.55 f 0.24. Breed differences were not significant (P > 0.05). Previously reported estimates of the heritability of this trait in yearling beef bulls ranged from 0.21 * 0.15 Present estimates are similar to those (11) to 0.69 * 0.15 (12). previously reported. Table 1.
Estimates of heritability --m-e
Data source Missouri Bull Sale Amer. Polled Hereford Assoc. Nichols Farms Data sources combined Nichols Farms
Angus
Breed Polled Hereford
Simmental
SC
0.55 + 0.24
0.56 _+0.25
1.16 _+0.53
SC
---
0.83 t 0.18
SC
---
0.19 + 0.17
0.30 ? 0.27
0.51 0.28 0.19 0.02 0.16 0.20
0.48 _+0.24 0.09 + 0.20 0.02 t 0.18 o.ooc 0.25 + 0.25 0.05 f 0.18
Trais
SC 0.55 4 0.24 spc --SpM --PLSp --SpN --PBE ---
+ 0.11 _+ 0.17 _+0.16 _+ 0.14 _+ 0.16 ? 0.17
Combined Across breeds _
---
0.51 t O.Ogb 0.20 t 0.13 0.11 + 0.12 o.ooc 0.19 t 0.14 0.13 _+ 0.12
aSC = Scrotal circumference. SpC = Sperm concentration. SpM = Sperm motility. PLSp = Percent live sperm. SpN = Sperm number. PBE = Potential Breeding Efficiency. bcombined across breeds and data source. CSire component of variance was negative and heritability estimate assumed to be zero.
Heritability estimates for potential breeding efficiency and the Within breed estimates for four semen traits were consistently low. these traits ranged from 0.00 for percent live sperm to 0.28 * 0.17 for sperm concentration. Breed differences were not significant (P >0.05). Previous estimates (6-8, 13) of the heritability of semen component traits generally have been low. With one exception, these estimates ranged from 0.00 for percent live sperm (7) to 0.28 for sperm concentration (6). The exception (13) was a relatively high estimate of 0.44 for sperm concentration. Correlations Phenotypic and genetic correlations involving SC, percent live sperm; sperm-number,-sperm concentration; and sperm-motility, potential breeding efficiency are presented by breed and combined across breeds (Table 2). Breed estimates of phenotypic correlations were very
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consistent and, with one exception, differed in numerical value by onlv 0.00 to 0.05. Breed differences were not sienificant (P > 0.05). Estimates combined across breeds were medium to high, ranging from 0.47 for percent live sperm and SC to 0.96 for potential breeding efficiency and sperm concentration.
Table 2.
Estimates of phenotypic and genetic correlations
TraitZ
SC
SC Polled Hereford Simmental Combined
spc
SpM
PLSP
SpN
PBE
0.58 0.59 0.58
0.56 0.59 0.57
0.49 0.47 0.47
0.57 0.68 0.64
0.58 0.56 0.56
0.95 0.92 0.94
0.81 0.86 0.82
0.86 0.84 0.84
0.96 0.96 0.96
SPC Polled Hereford Simmental Combined
0.60 1.16 0.67
SPM Polled Hereford Simmental Combined
0.63 1.83 0.65
0.97 1.44 1.00
1.97
b b
2.13 b b
1.68 b b
SPN Polled Hereford Simmental Combined
0.78 0.85 0.69
1.07 1.40 1.06
1.11 1.80 1.02
2.57 b b
PBE Polled Hereford Simmental Combined
0.68 1.49 0.76
1.02 1.25 1.03
1.03 1.18 1.04 -
2.o!
PLSp Polled Hereford Simmental Combined
-----
552
0.82 0.86 0.83
0.87 0.87 0.87
0.96 0.93 0.95
0.80
0.86 0.91 0.87
0.80 0.80
b
0.87 0.84 0.85
1.18 1.67 1.14
aSC = Scrotal circumference. SpC = Sperm concentration. SpM = Sperm motility. PLSp = Percent live sperm. SpN = Sperm number. PBE = Potential breeding efficiency. bNot estimated because sire component of variance for PLSp was negative. Of the five inestimable within breed (Simmental) genetic correlations, three (SpC, PLSp; SpM, PLSp; FBE, PLSp) had negative genetic convariances and two (SC, PLSp; SpN, PLSp) had positive genetic convariances. Genetic convariances combined across breeds, however, were positive.
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A 1984 report (7) provides estimates of phenotypic and genetic Data upon which that correlations for these same pairs of traits. report was based, and part of the data upon which the present report is based, was provided by Nichols Farms in Bridgewater, IA. The 1984 report (7) used data on Angus bulls while the present study, as indicated previously, is based on data collected on Polled Hereford and Simmental bulls. Trait designation in these two studies also differs slightly. In the 1984 study (7), the semen score trait is a composite trait that considers sperm concentration, motility, morphology and scrotal circumference. the designated It corresponds, thus, to potential breeding efficiency trait in this study. A number of corresponding phenotypic correlations from these two studies are of opposite algebraic sign. This difference, however, was artificially produced by coding sperm concentration, sperm motility and potential breeding efficiency in reverse orders in the two studies. Recognizing this, estimates from the two studies are very similar. Differences in absolute.values between the 15 corresponding phenotypic correlations in these two studies ranged from 0.01 to 0.10 and averaged 0.03. Additional estimates of phenotypic correlation involving some of these same trait pairs in yearling beef bulls include 0.63 for SC with sperm number (5), 0.46 for SC with sperm concentration (6) and, for SC The -0.36 correlation with sperm motility, 0.25 (6) and -0.36 (14). for SC and sperm motility is in disagreement with other estimates and suggests an undesirable association between the two traits. Except for the 0.63 correlation between SC and sperm number, these additional estimates are slightly lower than corresponding correlations in this report. Genetic correlations combined across breeds were high and positive and ranged from 0.65 for SC with sperm motility to 1.14 for sperm number with potential breeding efficiency. Five of the 15 estimates using only Simmental data as well as data combined across breeds were inestimable because the sire component for percent live sperm was negative. This is also shown (Table 1) by the Simmental breed and combined across breeds estimates of zero heritability for percent live sperm. Considering Simmental data only, three of the five inestimable genetic correlations (sperm concentration, percent live sperm; sperm motility, percent live sperm; potential breeding efficiency, percent live sperm) had a negative genetic covariance and two (SC, percent live sperm; sperm number, percent live sperm) had a positive genetic covariance. Combined across breeds, however, all genetic covariances were positive. Estimated genetic correlations involving three of the four semen traits (sperm concentration, sperm motility, sperm number) and the composite trait (potential breeding efficiency) are consistently high and positive and range from 1.00 for sperm concentration with sperm motility to 1.14 for sperm number with potential breeding efficiency. All agree very well with those reported in the earlier-discussed 1984 report (7). In the 1984 report (7) and in this report, the five genetic correlations involving percent live sperm were inestimable because the percent live sperm sire component of variance was negative.
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Across breed estimates of genetic correlation involving SC with sperm concentration, sperm motility, sperm number and potential breeding efficiency were also consistently high and positive and ranged from 0.65 for SC with sperm number to 0.76 for SC with potential breeding efficiency. These values, in the sense of desirability of algebraic sign, agree with, but are consistantly higher than, those reported in the previously discussed 1984 study (7). Additional previous estimates of genetic correlation involving some of these same traits include 1.5 fcr SC with sperm number (5), 0.53 for sperm concentraticn and sperm motility (6), 0.26 for sperm concentration with percent live sperm (6) and 0.44 for sperm motility with percent live sperm (6). The high heritability for SC, low heritabilities for semen traits, and consistently high desirable genetic correlations between SC and those semen traits suggest that direct selection for increased SC size would be more effective in bringing about semen trait imprcvement than direct selection pressure on the semen traits themselves. Using parameters obtained in this study, and assuming equal selection intensities under direct and indirect selection schemes, rates of indirect change in semen traits from direct selection for increased SC would be 1.5 to 3.C times greater than those produced by direct selection pressure on the semen traits themselves.
REFERENCES 1.
killett, E.L. and Ohms, J.I. Measurement cf testicular size and its relation to production of spermatozoa by bulls. J. Dairy Sci. x:1559-1569 (1957).
2. Ruttle, J.L., Bartlett, D.C., Hallford, D.M., Southward, G.M. and circumference and semen Bolgiano, D. Relationship of scrotal characteristics in New Mexico range beef bulls, Proc. West. Sec. Amer. Sot. Anim. Sci. x:24&242 (1981). 3. Fields, M.J., Hentges, J.F., Jr. and Ccrnelisse, K.W. Aspects of the sexual development of Brahman versus Angus bulls in Flcrida. Theriogenology -18:17-31 (1982). 4. Gipson, T.A., Vogt, D.W., Massey, J.W. and Ellersieck, M.R. Associations of scrotal circumference with semen traits in young beef bulls. Theriogerology -24:217-225 (1985). 5. Neely, J.D., Johnson, E.H., Dillard, E.U. and Rchinson, C.W. Genetic parameters for testes size and sperrr number in Hereford bulls. J. Anim. Sci. 5:1033-1040 (1982). 6. Brinks, J.S. Genetic aspects of reproduction in beef cattle. 3'4th Annual Beef Cattle Improvement Report and Sale Data. Colorado State Univ. Expt. Sta., Special Series -25:18-22 (1983).
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7. Knights, S.A., Baker, R.L., Gianola, D. and Gibb, J.B. Estimates of heritabilities and of genetic and pbenotypic correlations among growth and reprcductive traits in yearling Angus bulls. J. Ania. Sci. -58:887-893 (1984). 8. Taylor, J.F., Bean, B., Marshall, C.E. and Sullivan, J.J. Genetic and environmental components of semen production traits of artificial inseminaticn Holstein bulls. J. Dairy Sci. -68~2703-2722 (1985). 9.
Gipson, T.A., Vogt, D.W., Mass,ey, J.W. and Ellersieck, M.R. Scrotal circumference adjustment factors fcr age and weight differences in beef bulls. JAVMA 186:580-582 (1985).
10. Dickerson,
genetics. Research. 11.
G.E. Iecbniques fcr research in quantitative animal In: Techniques and Prccedures in Animal Producticn A&. Sot. Anim. Prod., 1959, pp. 56-105.
Blockey, M.A. deB., Straw, W.M. and Jones, I.-P.Heritability of serving capacity and scrotal circumference in beef bulls. J. Anim. Sci. -47(Suppl. 1):253-254 (1978).
Scrotal circumference and its 12. Coulter. G.H. and Keller. D.G. heritability in yearling beef bulls. J. Anim. Sci. -49(Suppl. 1): 288-285 (1979). Genetic and Jasiorowski, T. and Czeczot, H. 13. Strezezek, J., biochemical indices used for an assessment of suitability of young bull semen for preservation in liquid nitrogen. 2nd Wld. Gong. Genetics Applied to Livestock Prod. 1:493-502 (1982). 14. Chenoweth, P.J., Abbitt, El.,McInerney, M.J. and Brinks, J.S. Libido, serving capacity and breeding soundness in beef bulls, Series No. -966:18-21 Univ. Expt. Sta. General State Colcrado (1977).
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GENETIC AND PHENOTYPIC PARAMETER ESTIMATES FOR SCROTAL CIRCUMFERENCE AND SEMEN TRAITS IN YOUNG BEEF BULLS T.A. Gipson,a D.W. Vogt,l M.R. Ellersieck2 and J.W. Massey1 lDepartment of Animal Sciences 2Agricultural Experiment Station University of Missouri Columbia, MO. 65211 Received for publication: June 123 1986 Accepted: September 8, 1987 ABSTRACT Estimated in this study were heritabilities and genetic and phenotypic correlations involving scrotal circumference (SC), percent live sperm, sperm number, sperm concentration, sperm motility, and an ov,erallmeasure of a bull's potential breeding efficiency. Potential breeding efficiency is a composite trait based on a consideration of sperm concentration, sperm motility, sperm morphology and scrotal circumference. Data used were from three sources. Records on 863 Angus, 753 Polled Hereford, and 302 Simmental bulls were made available through the Missouri Performance-Tested Bull Sale and records on 1169 Polled Hereford bulls came from the American Polled Hereford Association. Information from these first two data sets were used to estimate heritability of scrotal circumference. The third data set was provided by Nichols Farms of Bridgewater, Iowa, and included information from the records of 465 yearling Polled Hereford and 264 yearling Simmental bulls. This latter data set was used to estimate all of the above mentioned parameters. Each data set was kept separately for the Parameters were estimated using purpose of statistical analysis. ccmponents from paternal half-sib analysis of variance and covariance, Pooled estimates of heritability for SC, sperm concentration, sperm motility, percent live sperm, sperm number and potential breeding efficiency were 0.51 f 0.09, 0.20 f 0.13, 0.11 * 0.12, 0.00, 0.19 f Phenotypic correlations involving 0.14 and 0.13 f 0.12, respectively. the six traits were very consistent for the two breeds. Combined across breeds their values ranged from 0.47 for SC and percent live sperm to 0.96 for sperm concentration and potential breeding efficiency. Corresponding genetic correlatic.nswere generally positive and high and ranged from 0.65 fcr SC and sperm motility to 1.14 for sperm number and potential breeding efficiency. Key words:
beef bulls, scrotal circumference, heritab.i.lities, correlations
semen quality,
Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 10113. Supported in part by funds in Animal Sciences Project C-2-5032E,. The authors thank Mrs. Lillian Nichols of Nichols Farms in Bridgewater, IA, and Dr. J. Gibb, Director of Research and Education, American Polled Hereford Association, Kansas City, MO, for providing portions of these data for this study. aPresent address: 402 W. Springfield Ave., Urbana, IL.61801.
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1987 VOL. 28 NO. 5
THERIOGENOLOGY
INTRODUCTION In recent years, there has been considerable attention focused on scrotal development in the male as a means of improving bovine male fertility. Most studies involving associations of scrotal circumference with semen traits have been phenotypic (l-4). Much less information is available regarding genetic association of these same Additionally, only a few studies (6-8) have reported traits (5-7). heritabilities of semen traits. Knowledge of the heritabilities of scrotal circumference and semen traits and the genetic and phenotypic correlations between them facilitates selection for increased fertility in the bull. Furthermore, this knowledge is requisite to predictions of direct and indirect responses to selection for improvement in these reproduction-oriented traits. The objectives of this study are to estimate heritabilities and genetic and phenotypic correlations involving scrotal circumference with each of four semen traits and one composite trait representing an overall measure of a bull's potential breeding efficiency. MATERIALS AND METHODS The data for this study came from three sources. Each was kept separately for the purpose of statistical analysis.
data set
Missouri Tested Bull Sale (Data Set 1)~ Approximately 300 bulls are sold annually through University of Missouri performance-tested bull sales. These sales are held in April Scrotal circumference measurements are and November of each year. taken the day before the sale under the supervision of the faculty of the Theriogenology Department in the School of Veterinary Medicine. Measurements are taken in accordance with the technique recommended by Scrotal circumference measurement, the Society for Theriogenology. age at day of sale, weight at day of sale, and pedigree were collected on 863 Angus, 753 Polled Hereford, and 302 Simmental bulls from 1978 through 1983. These data were subdivided into 16 year-season subsets Data Set 1 was used to (eight years and two seasons per year). Angus, Polled estimate heritability of scrotal circumference in Hereford and Simmental bulls. Scrotal circumference measurements were adjusted for age and body weight differences as described previously (9). Adjusted data were analysed within breed and year-season subsets by paternal half-sib analysis of variance. Subset data were subsequently combined by summing (separately) degrees of freedom and sums of New variance squares obtained from appropriate subset analyses. components were determined from the combined data sets, and heritability was estimated as four times the sire component of variance divided by the sum of the sire and within sire components of variance. Standard errors of the heritability estimates were calculated using routine procedures (10).
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American Polled Hereford Association (Data set 2) Measurements on scrotal circumference and body weight as well as age and pedigree information on 1169 yearling Polled Hereford bulls were made available for this study by the American Polled Hereford Association. The American Polled Hereford Association requests that scrotal circumference measurements be taken according to the technique established by the Society for Theriogenology. Data were collected in the three-year period from 1981 through 1983, with most being collected in 1982. Data were subdivided into 129 year-location subsets (3 years and 97 locations). Not all locations are represented in all years. Information in this data set, as in data Set 1, was used to estimate heritability of scrotal circumference. As with data Set 1, SC measurements were adjusted for differences in age and body weight using adjustment factors and procedures given previously (9). The methods of statistical analysis were the same as outlined for data Set 1. In data Set 2, however, there was only one breed and data were subdivided into year-location subsets. Nichols Farms (Data -Set a ~Data in this subset were provided by Nichols Farms of Bridgewater, Iowa, and included information from the records of 465 yearling Polled Hereford bulls and 264 yearling Simmental bulls. Records were for the five-year period from 1978 through 1982. Data taken from the records included age, body weight, scrotal circumference, percent live sperm, sperm number, sperm concentration, sperm motility, and an overall measure of a bull's potential breeding efficiency. All measurements were made at the conclusion of a 140-day full-feed postweaning test period that was completed in the spring of each year. Measurements of scrotal circumference and semen quality were made by Hawkeye Breeders Service, Inc., Des Moines, IA. Scrotal circumference was measured in accordance with recommendations of the Society for Theriogenology. Semen evaluations were made using fresh, undiluted semen collected by electroejaculation. One to three ejaculates were collected and evaluated depending on the quality of the first semen sample. Bulls with poor quality in the first and/or second samples were subsequently collected again for reevaluation. Semen quality measurements were based on the best single sample. It is recognized that sperm production is not as accurately estimated in semen samples collected by electroejaculation as in samples collected by means of an artificial vagina. However, electroejaculation is a standard technique for semen collection in young beef bulls and provided the best practical collection method for the animals used in this study. Percent live sperm was estimated to the nearest 10% figure, with values ranging from 0 to 70%. Sperm number was based on a photometer reading and recorded in millions of cells per cc. Sperm concentration ratings were based on sperm number and assigned classifications of excellent, good +, good, good -, fair and unsatisfactory. Ranges in millions of cells per cc of raw semen for these six classifications, beginning with excellent, were >1500, 1350 to 1500, 1150 to 1350, 1000 to 1150, 500 to 1000 and (500, respectively. Sperm motility was evaluated from a thin smear of semen on slides warmed to 3i'OC and viewed at 100 magnifica-
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tion. Sperm motility was classified in the same six classifications as sperm concentration (i.e. excellent to unsatisfactory) and coded in like manner. Ranges in the percentage motility values corresponding to these six classifications, beginning with excellent, were >70, 65 to 69.9, 60 to 64.9, 55 to 59.9, 25 to 54.9 and <25, respectively. Classifications of excellent to unsatisfactory for both sperm concentration and sperm motility were coded 6 to 1, respectively. Potential breeding efficiency of bulls is a composite trait based by Hawkeye Breeders Service on sperm concentration, sperm motility, sperm morphology and scrotal circumference. These traits were given percent weights of 35, 15, 15 and 35, respectively, in assigning potential breeding efficiency scores. Evaluations of this composite trait are classified excellent, good +, good, good -, fair, questionable, or unsatisfactory. In the present data set there were no bulls in the questionable category. These classifications, thus, were the same as those for sperm concentration and sperm motility, and consequently, they were coded in the same manner as sperm concentration and sperm motility. Information in this data set was used to estimate heritabilities of scrotal circumference, percent live sperm, sperm number, sperm concentration, sperm motility, and potential breeding efficiency as well as the genetic and phenotypic correlations between these traits. Scrotal circumference measurements, as in data Sets 1 and 2, were adjusted for differences due to age and body weight (9). Paternal half-sib analyses of variance and covariance were conducted on a within-breed and year basis. Results of these subset analyses were combined in a manner analogous to that described for data Set 1. New variance and covariance components were determined from the combined data sets and were subsequently used to estimate heritabilities and genetic and phenotypic correlations. Heritability estimates and their standard errors were calculated using statistical methods employed with data Sets 1 and 2. Genetic correlations were computed as the ratio of the sire component of covariance to the square root of the product of the appropriate sire components of variance. Phenotypic correlations were calculated as the sum of the sire and within sire components of covariance divided by the square root of the product of the summed sire and within-sire components of variance of each trait. RESULTS AND DISCUSSION Heritability Estimates Table 1 shows estimates of heritability for SC, sperm concentration, sperm motility, percent live sperm, sperm number and the overall measure of a bull's potential breeding efficiency. Estimates are shown within breed and data source as well as combined across breeds and, for SC, across breeds and data source. Breed estimates of heritability for
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SC range from 0.48 * 0.24 to 0.55 f 0.24. Breed differences were not significant (P > 0.05). Previously reported estimates of the heritability of this trait in yearling beef bulls ranged from 0.21 * 0.15 Present estimates are similar to those (11) to 0.69 * 0.15 (12). previously reported. Table 1.
Estimates of heritability --m-e
Data source Missouri Bull Sale Amer. Polled Hereford Assoc. Nichols Farms Data sources combined Nichols Farms
Angus
Breed Polled Hereford
Simmental
SC
0.55 + 0.24
0.56 _+0.25
1.16 _+0.53
SC
---
0.83 t 0.18
SC
---
0.19 + 0.17
0.30 ? 0.27
0.51 0.28 0.19 0.02 0.16 0.20
0.48 _+0.24 0.09 + 0.20 0.02 t 0.18 o.ooc 0.25 + 0.25 0.05 f 0.18
Trais
SC 0.55 4 0.24 spc --SpM --PLSp --SpN --PBE ---
+ 0.11 _+ 0.17 _+0.16 _+ 0.14 _+ 0.16 ? 0.17
Combined Across breeds _
---
0.51 t O.Ogb 0.20 t 0.13 0.11 + 0.12 o.ooc 0.19 t 0.14 0.13 _+ 0.12
aSC = Scrotal circumference. SpC = Sperm concentration. SpM = Sperm motility. PLSp = Percent live sperm. SpN = Sperm number. PBE = Potential Breeding Efficiency. bcombined across breeds and data source. CSire component of variance was negative and heritability estimate assumed to be zero.
Heritability estimates for potential breeding efficiency and the Within breed estimates for four semen traits were consistently low. these traits ranged from 0.00 for percent live sperm to 0.28 * 0.17 for sperm concentration. Breed differences were not significant (P >0.05). Previous estimates (6-8, 13) of the heritability of semen component traits generally have been low. With one exception, these estimates ranged from 0.00 for percent live sperm (7) to 0.28 for sperm concentration (6). The exception (13) was a relatively high estimate of 0.44 for sperm concentration. Correlations Phenotypic and genetic correlations involving SC, percent live sperm; sperm-number,-sperm concentration; and sperm-motility, potential breeding efficiency are presented by breed and combined across breeds (Table 2). Breed estimates of phenotypic correlations were very
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consistent and, with one exception, differed in numerical value by onlv 0.00 to 0.05. Breed differences were not sienificant (P > 0.05). Estimates combined across breeds were medium to high, ranging from 0.47 for percent live sperm and SC to 0.96 for potential breeding efficiency and sperm concentration.
Table 2.
Estimates of phenotypic and genetic correlations
TraitZ
SC
SC Polled Hereford Simmental Combined
spc
SpM
PLSP
SpN
PBE
0.58 0.59 0.58
0.56 0.59 0.57
0.49 0.47 0.47
0.57 0.68 0.64
0.58 0.56 0.56
0.95 0.92 0.94
0.81 0.86 0.82
0.86 0.84 0.84
0.96 0.96 0.96
SPC Polled Hereford Simmental Combined
0.60 1.16 0.67
SPM Polled Hereford Simmental Combined
0.63 1.83 0.65
0.97 1.44 1.00
1.97
b b
2.13 b b
1.68 b b
SPN Polled Hereford Simmental Combined
0.78 0.85 0.69
1.07 1.40 1.06
1.11 1.80 1.02
2.57 b b
PBE Polled Hereford Simmental Combined
0.68 1.49 0.76
1.02 1.25 1.03
1.03 1.18 1.04 -
2.o!
PLSp Polled Hereford Simmental Combined
-----
552
0.82 0.86 0.83
0.87 0.87 0.87
0.96 0.93 0.95
0.80
0.86 0.91 0.87
0.80 0.80
b
0.87 0.84 0.85
1.18 1.67 1.14
aSC = Scrotal circumference. SpC = Sperm concentration. SpM = Sperm motility. PLSp = Percent live sperm. SpN = Sperm number. PBE = Potential breeding efficiency. bNot estimated because sire component of variance for PLSp was negative. Of the five inestimable within breed (Simmental) genetic correlations, three (SpC, PLSp; SpM, PLSp; FBE, PLSp) had negative genetic convariances and two (SC, PLSp; SpN, PLSp) had positive genetic convariances. Genetic convariances combined across breeds, however, were positive.
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A 1984 report (7) provides estimates of phenotypic and genetic Data upon which that correlations for these same pairs of traits. report was based, and part of the data upon which the present report is based, was provided by Nichols Farms in Bridgewater, IA. The 1984 report (7) used data on Angus bulls while the present study, as indicated previously, is based on data collected on Polled Hereford and Simmental bulls. Trait designation in these two studies also differs slightly. In the 1984 study (7), the semen score trait is a composite trait that considers sperm concentration, motility, morphology and scrotal circumference. the designated It corresponds, thus, to potential breeding efficiency trait in this study. A number of corresponding phenotypic correlations from these two studies are of opposite algebraic sign. This difference, however, was artificially produced by coding sperm concentration, sperm motility and potential breeding efficiency in reverse orders in the two studies. Recognizing this, estimates from the two studies are very similar. Differences in absolute.values between the 15 corresponding phenotypic correlations in these two studies ranged from 0.01 to 0.10 and averaged 0.03. Additional estimates of phenotypic correlation involving some of these same trait pairs in yearling beef bulls include 0.63 for SC with sperm number (5), 0.46 for SC with sperm concentration (6) and, for SC The -0.36 correlation with sperm motility, 0.25 (6) and -0.36 (14). for SC and sperm motility is in disagreement with other estimates and suggests an undesirable association between the two traits. Except for the 0.63 correlation between SC and sperm number, these additional estimates are slightly lower than corresponding correlations in this report. Genetic correlations combined across breeds were high and positive and ranged from 0.65 for SC with sperm motility to 1.14 for sperm number with potential breeding efficiency. Five of the 15 estimates using only Simmental data as well as data combined across breeds were inestimable because the sire component for percent live sperm was negative. This is also shown (Table 1) by the Simmental breed and combined across breeds estimates of zero heritability for percent live sperm. Considering Simmental data only, three of the five inestimable genetic correlations (sperm concentration, percent live sperm; sperm motility, percent live sperm; potential breeding efficiency, percent live sperm) had a negative genetic covariance and two (SC, percent live sperm; sperm number, percent live sperm) had a positive genetic covariance. Combined across breeds, however, all genetic covariances were positive. Estimated genetic correlations involving three of the four semen traits (sperm concentration, sperm motility, sperm number) and the composite trait (potential breeding efficiency) are consistently high and positive and range from 1.00 for sperm concentration with sperm motility to 1.14 for sperm number with potential breeding efficiency. All agree very well with those reported in the earlier-discussed 1984 report (7). In the 1984 report (7) and in this report, the five genetic correlations involving percent live sperm were inestimable because the percent live sperm sire component of variance was negative.
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Across breed estimates of genetic correlation involving SC with sperm concentration, sperm motility, sperm number and potential breeding efficiency were also consistently high and positive and ranged from 0.65 for SC with sperm number to 0.76 for SC with potential breeding efficiency. These values, in the sense of desirability of algebraic sign, agree with, but are consistantly higher than, those reported in the previously discussed 1984 study (7). Additional previous estimates of genetic correlation involving some of these same traits include 1.5 fcr SC with sperm number (5), 0.53 for sperm concentraticn and sperm motility (6), 0.26 for sperm concentration with percent live sperm (6) and 0.44 for sperm motility with percent live sperm (6). The high heritability for SC, low heritabilities for semen traits, and consistently high desirable genetic correlations between SC and those semen traits suggest that direct selection for increased SC size would be more effective in bringing about semen trait imprcvement than direct selection pressure on the semen traits themselves. Using parameters obtained in this study, and assuming equal selection intensities under direct and indirect selection schemes, rates of indirect change in semen traits from direct selection for increased SC would be 1.5 to 3.C times greater than those produced by direct selection pressure on the semen traits themselves.
REFERENCES 1.
killett, E.L. and Ohms, J.I. Measurement cf testicular size and its relation to production of spermatozoa by bulls. J. Dairy Sci. x:1559-1569 (1957).
2. Ruttle, J.L., Bartlett, D.C., Hallford, D.M., Southward, G.M. and circumference and semen Bolgiano, D. Relationship of scrotal characteristics in New Mexico range beef bulls, Proc. West. Sec. Amer. Sot. Anim. Sci. x:24&242 (1981). 3. Fields, M.J., Hentges, J.F., Jr. and Ccrnelisse, K.W. Aspects of the sexual development of Brahman versus Angus bulls in Flcrida. Theriogenology -18:17-31 (1982). 4. Gipson, T.A., Vogt, D.W., Massey, J.W. and Ellersieck, M.R. Associations of scrotal circumference with semen traits in young beef bulls. Theriogerology -24:217-225 (1985). 5. Neely, J.D., Johnson, E.H., Dillard, E.U. and Rchinson, C.W. Genetic parameters for testes size and sperrr number in Hereford bulls. J. Anim. Sci. 5:1033-1040 (1982). 6. Brinks, J.S. Genetic aspects of reproduction in beef cattle. 3'4th Annual Beef Cattle Improvement Report and Sale Data. Colorado State Univ. Expt. Sta., Special Series -25:18-22 (1983).
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7. Knights, S.A., Baker, R.L., Gianola, D. and Gibb, J.B. Estimates of heritabilities and of genetic and pbenotypic correlations among growth and reprcductive traits in yearling Angus bulls. J. Ania. Sci. -58:887-893 (1984). 8. Taylor, J.F., Bean, B., Marshall, C.E. and Sullivan, J.J. Genetic and environmental components of semen production traits of artificial inseminaticn Holstein bulls. J. Dairy Sci. -68~2703-2722 (1985). 9.
Gipson, T.A., Vogt, D.W., Mass,ey, J.W. and Ellersieck, M.R. Scrotal circumference adjustment factors fcr age and weight differences in beef bulls. JAVMA 186:580-582 (1985).
10. Dickerson,
genetics. Research. 11.
G.E. Iecbniques fcr research in quantitative animal In: Techniques and Prccedures in Animal Producticn A&. Sot. Anim. Prod., 1959, pp. 56-105.
Blockey, M.A. deB., Straw, W.M. and Jones, I.-P.Heritability of serving capacity and scrotal circumference in beef bulls. J. Anim. Sci. -47(Suppl. 1):253-254 (1978).
Scrotal circumference and its 12. Coulter. G.H. and Keller. D.G. heritability in yearling beef bulls. J. Anim. Sci. -49(Suppl. 1): 288-285 (1979). Genetic and Jasiorowski, T. and Czeczot, H. 13. Strezezek, J., biochemical indices used for an assessment of suitability of young bull semen for preservation in liquid nitrogen. 2nd Wld. Gong. Genetics Applied to Livestock Prod. 1:493-502 (1982). 14. Chenoweth, P.J., Abbitt, El.,McInerney, M.J. and Brinks, J.S. Libido, serving capacity and breeding soundness in beef bulls, Series No. -966:18-21 Univ. Expt. Sta. General State Colcrado (1977).
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