GENETIC PARAMETERS FOR TESTOSTERONE PRODUCTION IN BOARS'

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1 GENETIC PARAMETERS FOR TESTOSTERONE PRODUCTION IN BOARS' D. Lubritz, B. Johnson and 0. W. Robison North Carolina State University, Raleigh ABSTRACT Data were collected in 1982 through 1989 from 66 sires and 358 Duroc boars. Testosterone production was measured from peripheral blood samples before (PRE) and after (POST) GnRH challenge. Additionally, data were collected on testes length at 168 d (TL168), testes width at 168 d (TW168), testes volume at 168 d (TVOL), birth weight (BWT), average daily gain (ADG), days to 104 kg (DAYSlW), and backfat adjusted to 104 kg (FAT). Overall means for these traits were 24.6 ng-ml-l.h-l, 75.7 ngmi?-h-', 12.3 cm, 11.6 cm, cm3, 1.5 kg,.5 kg, d, and 18.5 mm, respectively. Son-sire regressions were used to calculate genetic parameters. Heritabilities for F'RE, POST, TL168, TW168, TVOL, BWT, ADG, DAYS104, and FAT were.37,.26,.33,.34,.33,.21,.42,.35, and 0, respectively. Moderately favorable genetic correlations were obtained for PRE and POST with growth measurements. Large positive genetic correlations were present for both PRE and POST with TL168, TW168, and TVOL, and testes masmmmts had large positive genetic correlations with growth traits. Selection for testes size or testosterone production should be equally effective. However, it seems that selection for testes size would result in larger changes in measures of growth than selection for testosterone. This study suggests that testes measurements are good predictors of both basal and challenge testosterone levels. Selection for increased testis size or increased testosterone levels would be expected to enhance growth. Key Words: Testosterone, Boars, Testes, ~rowth, Fat Introduction One factor largely overlooked in swine production is the potential impact of intense selection for male traits on reproductive and(or) production efficiency of swine units. Genetic parameter estimates associated with testosterone levels, testicular traits, and correlated growth traits of boars are sparse. High heritabilities have been recorded for testicular traits (Coulter et al., 1976; Neely et al., 1982; Toelle et al., 1984). Effects of exogenous testosterone in promoting deposition of muscle protein and establishing a positive nitrogen balance in castrated animals have been well 'The technical assistance of Bruce Collins and Zola Turner is gratefully acknowledged. Rtceived October 15, Accepted March 15, J. Anim. Sci : documented (Lund-Larsen et al., 1977). The higher rate of gain seen in intact males compared with castrates of the same species is related to differences in endogenous testosterone levels (Gotsema et al., 1974). If a positive correlation exists between growth and defined biochemical characteristics, such as blood concentrations of certain hormones, the early determination of these hormone levels in addition to other criteria may represent a valuable tool for the identification of superior breeding animals. Coulter et al. (1976) and Neely et al. (1982), working with cattle, have shown that testicular measures are highly heritable and useful, phenotypically and genetically, for predicting sperm production. Neely et al. (1982) reported genetic correlations of weights and gains of cattle with scrotal circumference and testes characteristics to be moderately to

2 GENETIC PARAMETERS FOR "OSTERONFl IN BOARS 3221 highly favorable. These researchers suggested that selection for testes size should not adversely affect growth performance traits except through the reduction in selection intensity. The objectives of this study were to estimate phenotypic and genetic parameters of basal and GnRH-stimulated testosterone in the blood of young boars and to evaluate the genetic associations of testosterone production with growth and testicular traits. Materials and Methods Data were obtained from 66 sires and 358 purebred Duroc boars over the period 1982 to 1989 at North Carolina State University, Raleigh, NC. The animals were part of two lines in a study of divergent selection for high and low testosterone response to GnRH challenge. Boars were reared under conditions of total confinement. Pigs were weaned at 42 d of age, with creep feed available after 21 d. Boars were maintained (five or six per pen) fiom weaning through maturity in pens with slotted concrete floors. Measures for testes length (TL168), testes width (TW168), and testes volume (TVOL) were taken at 168 d of age. These measurements were obtained using a restraining crate. Boars were placed in the crate and restrained by adjustable squeeze panels. The crate was rotated on the horizontal axis so that boars were resting on their backs. Testes length and width measurements were then taken with calipers. Testes volume was estimated as TVOL = (TW168/2)2. TL168. Growth data were collected for birth weight (BWT), ADG, and days to 104 kg (DAYS104). Backfat depth was measured by ultrasound behind the shoulder at the 7th rib and at the middle of the loin approximately 3.8 cm off the midline. Backfat measures were adjusted to 104 kg BW (FAT) using the following formula: adj%fat = actbfat + (230 - wt168d) (actbfavwtl68d - 25). (Robison, 1981). To obtain blood samples, boars were restrained by a snout snare, and an indwelling catheter was inserted into the jugular vein and secured to the back with elasticon tape. Blood samples (10 ml each) were drawn from the jugular vein via the catheter over an 8-h period the next morning. Between 0700 and O900, one blood sample was drawn every 30 min from each boar. These were the five pre-gnrh testosterone measures (PRE). A GnRH challenge was given after the 0900 bleeding. Subsequently, boars were bled every 15 min from O900 to These constitute eight of the 12 post-gnrh testosterone samples (POST). The remainder of the post-gnrh samples were taken every 30 min from 1100 to The PRE value was the area under the curve for basal levels, and POST was the area under the curve for 4 h after the GnRH challenge. Area under the curve was measured in nanogrmmilliliter'.hourl. Blood samples were allowed to clot for 24 h and then centrifuged at 1,500 x g for 45 min. Serum was decanted and stored at -5'C until it was assayed for testosterone. Concentrations of testosterone were determined in duplicate loo-pl aliquots of serum by a previously validated RIA procedure (Juniewicz et al., 1984). Serum samples were not chromatographed, because only dihydrotestosterone cross-reacted significantly (50%) with the antiserum (MSU #74, rabbit antitestosterone- 3-0xime bovine serum albumin). Testosterone was extracted fiom serum using anhydrous ethyl ether, with an average recovery of > 95%. Testosterone was measured against standard curves of recrystallized 17p-hydroxy- 4-anhsten-3-0ne, which ranged from 0 to 4 ng. Son-sire regressions for all traits were obtained using the GLM procedure (SAS, 1982) with the following modek Yij = + Gi + b(xj - X) + qj, where Yij = observed value of a given dependent variable on the boar, p = overall mean, Gi = fixed effect of i~ line-generation, b = regression coefficient, x, = independent value of the sire, and eij = random error. Heritability estimates were obtained by doubling these regression coefficients. phenotypic correlations were generated by the correlation procedure of SAS (1982). Genetic correlations were calculated using covariances obtained through regressing all dependent traits of the boar on each independent trait of the sire. The following equation was used to calculate rg: Covpl ol.covp2 02'

3 ~ 3222 LUBRITZ ET AL. TABLE 1. MEANS AND STANDARD DEVIATIONS OF GROWTH W S, TESTICULAR TRUTS, AND TESTOSTERONF! LEVELS TAP N Meau SD ~~ PREb POSTb TW168, cm TL168, cm TVOL, cm ADG, kg 358 SO.M DAYS 104, d BWT, kg FAT, mm = basal testosterone, POST = testosterone levels after GnRH, TW168 = testes width at 168 d, TL168 = testes length at 168 d, TVOL = testes volume at 168 d, ADG = avexage daily gain, DAYS 104 = days to 104 kg, BWT = birth weight, and FAT = backfat adjusted to 104 kg. %easured as ng6l.h-l. where Covpl 02 is the covariance between Trait 1 of the parent and Trait 2 of the offspring, C0vp2 ol is the covariance between Trait 2 of the parent and Trait 1 of the offspring, Cov 1 ol is the covariance between Trait 1 of $e parent and Trait 1 of the offspring, and Cov 2 02 is the covariance between Trait 2 of $e parent and Trait 2 of the offspring. In instances in which the covariances between the two traits had different signs, the following altemative formula was used: n Results and Dlscussion Means and SD for the nine traits are shown in Table 1. The means tend to be slightly higher than those reported by Neely et al. (1980) but are in close agreement with those reported by Toelle et al. (1984). Heritability estimates are presented in Table 2. Pre- and post-gnrh testosterone production was moderately heritable, and measures of basal testosterone production were slightly more heritable than testosterone production after GnRH challenge (.37 vs.26). Heritability estimates of testes measurements (Table 2) suggest that all testicular traits at 168 d were moderately heritable. These results agree closely with the estimates of Eden et al. (1978), who reported heritabilities for testicular measures of to SO, and agree exactly with estimates reported by Toelle et al. (1984). TABLE 2. HERITABILITY ESTIMATES AND STANDARD FiRRORS Traits h2 SE PRE POST PAT TVOL TL168 TW168 DAYS 104 BWT ADG oo I4.I2 = basal testosterone, POST = testosterone levels after GnRFi, FAT = backfat adjusted to 104 kg, TVOL = testes volume at 168 d, TL168 = Wtes Ieugtl~ at 168 d, TW168 =testes width at 168 d, DAYS104 days to 104 kg, BWT = birth weight, and ADG = average daily gain. Heritabilities of growth traits ranged from.21 for BWT to.42 for ADG. These estimates are considered of moderate magnitude and agree with estimates reported in the literature. Backfat adjusted to 104 kg had a negative sonsire regression coefficient. Thus, the heritability was assumed to be zero. One possible explanation for this is that the ultrasound techniques used in this study may not have been effective in estimating backfat of boars. Table 3 contains son-sire regression coefficients. Each dependent trait of the boar was regressed on each independent trait of the sire. These regressions can be viewed as realized responses to selection. They provide an evaluation of the expected change m the boars testosterone, testicular size, or performance trait when sires are selected. These regressions suggest that selection for PRE would result in simcant increases in testes size and growth rate. However, the regressions of growth and testes size on POST were nonsignificant. Because PRE measures basal production of testosterone, it may be more closely associated with levels that affect growth, whereas POST is a response to GnRH challenge and measures what could be produced and not what is present. Thus, it may be expected that PRE would be more closely related to growth. Selection for any measure of testes size is expected to increase the other testes measures and growth, but regressions of testosterone level on testes size were nonsignificant. Phenotypic correlations among testicular traits, testosterone levels, and performance traits are given in Table 4. phenotypic correlations of testosterone levels with growth

4 GENEnC PARAMETERS FOR TESTOSTERONE IN BOARS 3223 traits and backfat were small and nonsignificant but were of favorable sign. Phenotypic correlations between testosterone levels and testicular traits were all positive and highly significant. phenotypic correlations of testicular traits were significant and favorable with all growth traits but nonsignificant with backfat. Genetic correlations (Table 4) between basal levels of and testes measures were large and positive. Correlations of PRE with measures of growth were moderate and favorable. The POST values had correlations of similar sign but slightly lower magnitude than PRE. Measures of testes size had large favorable correlations with measures of growth. Similar results have been reported in mice (Islam et al., 1975) and cattle (Neely et al., 1982). Because of negative son-sire regression for FAT, none of the genetic correlations with FAT could be estimated. The intense selection for testosterone levels may have biased the absolute value of genetic correlations involving POST downward (Van Vleck, 1968). Selection for testosterone or any measure of testes size should be effective. These results agree with those reported in cattle by Coulter et al. (1976) and Neely et al. (1982) and with those reported in boars (Toelle et al., 1974; Eden et al., 1978). From the son-sire regressions, it is expected that such selection would not be antagonistic to growth and might result in small increases in growth rate. However, some slight increases in FAT might be expected from selection for testosterone, whereas small decreases might accrue from selection for testes size. Testicular traits are intriguing with respect to their quantitative inheritance patterns (Toelle et al., 1984). Important heterosis effects have been reported (Wilson et al., 1977; Neely et al., 1980; Fent et al., 1983); however, the moderate to high heritabilities for testicular traits reported by Toelle et al. (1984) agree with the present study. It is unusual to find a trait with both large heterosis effects and relatively high heritabilities. The results herein lead to the conclusions that selection for increased testosterone levels TABLE 3. SON-SIRE REGRESSION COEPFICIENTS Son's traita Sire's DAYS trait PRE FAT TVOL TL168 TW BWT ADG POST m * NSb **e NS *** * NS * NS * FAT OW NS NS NS NS NS NS NS NS TVOL all od OOO.OOO.025 NS NS ** t ** * NS * NS TL I t NS *** * *** * NS ** NS TW lo NS NS * t ** * NS * NS DAYS104 -.m W , NS t t NS t *** NS *** NS BWT lo NS * NS NS NS NS * NS NS ADG , NS * t t *** NS *** NS POST.062.OD2 343.OD2.OD OOO.ooO.13 NS NS NS NS t NS NS NS NS = basal testosterone, FAT = backfat adjusted to 104 kg, TVOL = testes vohme at 168 d, TL168 = testes length at 168 d, TW168 = testes width at 168 d, DAYS104 = days to 104 kg, BWT = birth weigh4 ADG = average daily gain, and POST = testosterone levels after GnRH. 'WS = not significant. +P <.lo. *P <.05. **P <.01. ***P <.001.

5 ~ ~~ ~~ ~~~ ~ 3224 LUBRllZ ET AL. TABLE 4. PHENOTYPIC AND GENETIC CORRELATIONS DAYS Trait PRE POST TW168 TL168 TVOL ADG 104 BWT FAT PRE M -.lo *** *** *** *** NSd t NS NS POST m -.06 *** *** *** NS NS NS NS *** *** *** *** * NS TW %, M TL m *** *** *** *** NS *** *** *** NS TVOL ADG l8.05 *** *** NS DAYS *** NS *** BWT aphenotypic correlations above the diagonal. kenetic correlations below the diagonal. PRE = basal testosterone, POST = testosterone levels after GnRH, TW168 = testes width at 168 d, TL168 = testes length at 168 d, TVOL = testes volume at 168 d, ADG = average daily gain, DAYS104 days to 104 kg, BWT = birth weight, and FAT = backfat adjusted to 104 kg. %IS = not significant. tp <.lo. *P <.05. **P <.01. ***P <.001. should lead to favorable responses in testis size and perhaps in growth. implications Selection for either testosterone or testes size in boars would be effective and would be expected to have a favorable impact on growth. These measures could be used as adjuncts to conventional measures for selection of superior breeding stock Llterature Cited Coulter, G. H., T. R. RounsaviUe and R H. Foote Heritability of testicular size and coasistency in Holstein bulls. 1. Anim. Sci Eden, C. W., B. H. Johnson and 0. W. Robison Prenatal and postnatal influences on testicular grow and development in boars. J. Anim. Sci. 47:375. Fent.R. W., R. P. WettcmanandR K. Johnson Breed and heterosis effects on testicular development and endocrine fanction of puberal boars. J. Anim. Sci. 57: 425. Gortsema, S. R, J. A. Jacobs, R G. Sasser, T. L. Gregory and R C. Bnll Eflects of eedogenons testosterone on production and carcass traits in bed cattle. J. Anim. Sci Islam, A.B.M.M., W. G. Hil and R. B. Land Ovnlation rate of lines of mice selected for testes weight. Genet. Res. 27:23. Jdewicz, P. E., V. D. Toelle, 0. W. Robison and B. H. Johnson Variation in testosterone production among boan and its relationship to sexual interest and breeding performance. Theriogenology 22:259. Lmd-Larsen, T. R, A. Sundby, V. Kruse and W. Velle Relation between growth rate, serum somatomedin and plasma testosterone in young bulls. J. Anim. Sci Neely, J. D., B. H. Johnson. E. U. Dillard and 0. W. Robison Gemtic parameters for testes size and sperm mber in Herefmd bulls. J. Anim. Sci Neely J. D., B. H. Jolmson, and 0. W. Robison Heterosis estimates for measnre8 of reproductive traits in crossbred boars. 3. Anim. Sci. 51:lWO. Robison. 0. W Guide- for uniform swine improvement programs. Natl. Swine Improvancnt Fed. aod USDA Rogram Aid SAS SAS User s Guide: Statistics. SAS Inst., Cary, NC. Toelle. V. D., B. H. Johnson and 0. W. Robison Genetic parameters for testes haits in swine. J. Anim. Sci Van Vleck, L. D Selection bias in estimation of the genetic correlation. Biometrics. 24:951. Wilson, E. R. R K. Johnson and R. P. Wettanan Reproduction and testicular characteristics of purebred and crossbred boars. J. Anim. Sci