Biomedical subjects

D D Lunstra

Publications and source records attributed to D D Lunstra.

At least 37 records · Page 2Linked to original sources

PubMed1997

Negative relationship between blood concentrations of follicle-stimulating hormone and testicular size in mature boars.

Relationships between blood concentration of FSH and testicular size and daily sperm production were evaluated with data obtained from five studies originally designed to investigate regulation of FSH secretion in Meishan (MS), White composite (WC), and crossbreds of these. A minimum of three blood samples/boar were obtained at greater than 4-d intervals for determination of FSH, and testes were obtained at castration or slaughter. In a random sample of boars, FSH was fivefold greater (P < .01) in MS than in WC boars (n = 22/group). Daily sperm production (DSP)/gram of testis (estimated by counting elongated spermatid nuclei in testicular homogenates) was similar in the groups, but testicular weight (TWT), adjusted for body weight, was less (P < .01) in MS than in WC, yielding lower total daily sperm production (TDSP; P < .05) in MS boars. In four populations (one with MS, one with WC, and two with crossbreds; n = 34 males), boars were selected for extremes in FSH concentrations from larger groups. Across all populations, a threefold greater plasma FSH concentration was associated with a 32% smaller TWT (P < .01). Coincident with increased FSH, TDSP was 33% less (P < .05). In 48 MS x WC boars that were selected for divergence in plasma FSH during pubertal development (4 to 6 mo of age), this divergence was retained at 1 yr (P < .01). Retrospectively, the divergence in FSH was also apparent at 2 and 8 wk of age (P < .05), and the boars with elevated FSH had smaller testicles, lower DSP, and lower TDSP (P < .01). These studies document a negative relationship in mature boars between FSH secretion and testicular size accompanied with decreased TDSP.

Aging↗

PubMed1997

Physiology of the Meishan boar.

Onset of puberty (sperm production) occurs at a much younger age (56-84 days) in Meishans than in conventional boars (120-180 days). Throughout postnatal development, Meishans exhibit markedly higher (two- to ten-fold) concentrations of serum FSH, LH and androgens compared with conventional boars, and these high hormone concentrations are maintained at maturity. Increased gonadotrophin concentrations occur only in Meishan males, since concentrations in female Meishans and conventional females do not differ. In the Meishan boar, FSH increases steadily during establishment of sperm production and LH increases markedly after tubule diameter stabilizes, while FSH and LH concentrations are low and change little during this period of rapid testicular growth in conventional boars. The proportion of the testis occupied by Leydig cells is two-fold greater and average Leydig cell size is two- to four-fold larger in Meishans than in conventional boars during the onset of spermatogenesis and into maturity. Testis size in Meishans is only half that of conventional boars at maturity, and the number of Sertoli cells is markedly reduced in Meishans. However, Meishan testes exhibit reduced degeneration of germ cells and spermatids during spermatogenesis, and spermatogenic efficiency per Sertoli cell in Meishans is double that in conventional boars. At maturity, Meishan pituitaries have greater mass, larger gonadotrophs, higher content of FSH, and greater expression of genes for FSH and LH subunits than found in conventional boars. The high concentrations of serum gonadotrophins in the mature Meishan exhibit a typical postcastration rise, respond to GnRH stimulation and are suppressed by gonadal steroids, indicating that the hypothalamo-pituitary-gonadal axis functions normally but with much higher set points in Meishan boars. These unusual endocrine and physiological attributes in boars of the highly prolific Meishan breed offer a unique model for further investigation of factors influencing early onset of puberty and efficiency of male reproductive function.

Animals↗

PubMed1996

Differential pituitary and gonadal function of Chinese Meishan and European white composite boars: effects of gonadotropin-releasing hormone stimulation, castration, and steroidal feedback.

Considerable breed differences exist in concentrations of gonadotropins between Chinese Meishan boars and meat-type crossbred boars of European origin. To define mechanisms that might be responsible, sensitivity to GnRH stimulation, hormonal clearance, and gonadal pituitary feedback effects were monitored in two experiments. In the first trial, jugular catheters were placed into mature Meishan (n = 7) and white composite boars (n = 8). Boars were repetitively sampled after administration of two doses of GnRH (150 and 1500 ng/kg BW) a week apart. Before administration of GnRH, FSH was greater in Meishan boars (554 +/- 50 vs. 102 +/- 8 ng/ml, p < 0.01). Both breeds responded with increases in FSH, LH, and testosterone; but concentrations of gonadotropins in Meishan boars were increased for a greater duration than in white composite boars. By 160 min after GnRH administration, gonadotropins were declining in white composite boars. Maximal plasma concentrations of FSH after GnRH stimulation were greater with the higher GnRH dosage than with the lower (1058 +/- 113 vs. 730 +/- 70 in Meishan and 184 +/- 40 vs. 141 +/- 14 ng/ml in white composite boars). In the second trial, boars were assigned to three groups related to their circulating FSH concentrations: European white composite boars (FSH = 100 ng/ml), Meishan boars with low FSH (FSH = < 500 ng/ml), and Meishan boars with high FSH (FSH > 750 ng/ml; n = 5 per breed group). Boars were cannulated and repetitively sampled during three protocols: 1) low GnRH stimulation (15 ng/kg BW), 2) pre- and postcastration, and 3) steroidal treatment (0.5 mg testosterone propionate and 20 micrograms estradiol cypionate/kg BW; then 24 days later, a 20-strength low-dosage steroid treatment). At the low GnRH stimulation, LH and testosterone concentrations were increased but FSH concentrations were not altered. Rate of increase of FSH and decline of testosterone concentrations were not different between the three treatment groups after castration. Castration levels of FSH were maintained and further increased with time. Rates of reduction in FSH concentration after gonadal steroidal stimulation were not different between breed groups, but Meishan boars escaped the exogenous steroid suppression earlier than white composite boars (p < 0.01). Differences in concentrations of gonadotropins in Meishan and white composite boars of European origin seem to be at the pituitary level of control and not related to gonadal factors.

Animals↗

PubMed1996

Number and function of Sertoli cells, number and yield of spermatogonia, and daily sperm production in three breeds of boar.

The objective of this study was to determine the number of Sertoli cells per boar, daily sperm production, and germ cell yield per type A spermatogonium in mature Whitecross, Meishan, and West African boars. The paired parenchymal mass was greatest in the Whitecross boars and greater in Meishan than in West African boars. Daily sperm production per boar (x 10(9)) differed significantly (P < 0.05) among breeds (Whitecross: 12.5 +/- 1.5; Meishan: 6.0 +/- 0.5; West African: 2.9 +/- 0.3). Daily sperm production per boar was positively (P < 0.01) correlated with parenchymal mass (r = 0.97), number of A spermatogonia per testis (r = 0.88), and Sertoli cells per testis (r = 0.87). Daily sperm production per gram of testis was similar among breeds. Number of Sertoli cells and number of type A spermatogonia per boar were greater for the Whitecross but similar in the Meishan and West African boars. The number of Stage VII germ cells per Sertoli cell was greater (P < 0.05) in the Meishan (39.08 +/- 5.07), but similar in the Whitecross (19.91 +/- 1.62) and West African boars (15.81 +/- 2.43). The number of type A spermatogonia per testis was highly and positively (P < 0.01) correlated with number of Sertoli cells per testis (r = 0.95), and parenchymal mass (r = 0.88). There was a trend for the spermatid yield per type A spermatogonium to be greater in the Meishan boars, and this ratio was positively correlated with spermatid:Sertoli cell ratio (r = 0.62) but not with daily sperm production per boar or Sertoli cells per testis. No significant germ cell degeneration occurred during the long meiotic prophase, but the loss of progeny during postprophase of meiosis averaged 32.62% across all breeds. Germ cell degeneration was similar (P > 0.05) across breeds during spermiogenesis, and on average amounted to 8.6%. The increased number of type A spermatogonia and of Sertoli cells associated with larger testes for the Whitecross over West African or Meishan boars is sufficient to explain the higher sperm production in the Whitecross. However, the lower index of degeneration and more efficient Sertoli cell function in Meishan boars results in the daily sperm production being intermediate between that of the Whitecross and West African boars.

Africa↗

PubMed1996

Prediction of breeding values for tenderness of market animals from measurements on bulls.

Data were tenderness measures on steaks from 237 bulls (Group II) slaughtered after producing freezable semen and on 1,431 related steers and heifers (market animals, Group I) from Angus, Hereford, Pinzgauer, Brahman, and Sahiwal crosses from the Germ Plasm Evaluation project at the U.S. Meat Animal Research Center. Tenderness was assessed through Warner-Bratzler Shear Force (SF), taste panel tenderness (TPT), marbling score (MS), and myofibrillar fragmentation index (MFI). For all traits, as fraction Bos indicus inheritance increased, implied tenderness decreased. Heritability estimates were generally not significantly different from zero. Genetic correlations generally indicated favorable associations among the traits. The range in predicted breeding values of bulls for market animal tenderness was small and from -.34 to .32 kg for market animal shear force. Because of low estimates of heritability for SF or TPT, results from this experiment indicate that selection based on tenderness of steaks sampled from intact or late castrate males slaughtered following collection of freezable quality semen would not be very effective in improving average tenderness of steaks from steers of heifer progeny. If a mean of heritability estimates reported in the literature of .27 for shear value was assumed for market steer and heifer progeny instead of .02 as found in the present study, then selection based on estimates of shear force in young bulls would be relatively more effective in improving shear force of market progeny.

Animals↗

PubMed1996

Thymic, gonadal, and endocrine relationships in gilts and boars administered porcine somatotropin.

We hypothesized that much of the positive effect of porcine somatotropin (pST) on the immune system would be offset by the pST/IGF stimulation of gonadal function and that there would be negative effects on thymic weight and function from increased androgens in males. Male and female hogs (78 boars, 90 gilts) representing three genetic lines (lean, obese, and crossbred meat type) received 0, 2, or 4 mg of recombinant pST/d via implant for 42 d. Blood samples were collected on 0, 7, 14, 28, and 42 d of the trial for changes in pST, IGF-I, IGF-II, thymosin beta 4, dehydroepiandrosterone/dehydroepiandrosterone sulfate (DHEA/DHEASO4), and testosterone concentrations. Thymic, splenic, gonadal, and adrenal weights were collected at slaughter (d 42). Thymic weights increased with dose of pST in both sexes (P < .01), but splenic weights were unaltered. Adrenal weights increased with dose of pST (P < .01), but gonadal weights showed no response to pST in either sex or any line. Overall, concentrations of pST, IGF, and thymosin beta 4 increased with dose of pST. Serum testosterone concentrations in boars declined with dose of pST in lean and obese lines, and DHEA/ DHEASO4 declined in all lines with pST treatment. Testicular testosterone concentrations were not different among lines or doses of pST, indicating no stimulatory effect of increased pST/IGF-I on Leydig cell function. Although pST and its effects through increased circulating IGF are thought to be overall stimulants of growth and protein accretion, the actions on the tissues of the immune system (thymus/spleen) and steroidogenic tissues (adrenal/gonadal) can be selective. Increases in thymic weights and thymosin beta 4 concentrations from pST treatment in boars were partially due to the pST-induced decline in circulatory androgens, and the responses found in this in vivo model do not support pST/IGF effects documented in in vitro systems on Leydig cell function.

Animals↗

PubMed1995

Sperm production in boars after nine generations of selection for increased weight of testis.

Body, testis, and epididymis weights were recorded and homogenization-resistant sperm nuclei were counted to determine daily sperm production and the number of sperm stored within the cauda epididymis (CAUDASP) in 145 boars of a control line (C) and 128 boars of a line selected for increased predicted weight of testis (TS) at 150 d of age. Random samples of boars were evaluated at five ages between 70 and 450 d in Generation 8 and 15 ages between 70 and 296 d in Generation 9. Data were analyzed using an animal model that included the fixed effect of line and the linear, quadratic, and cubic effects of age. Variance components were estimated using a DFREML algorithm. Boars of the TS and C line did not differ in body weight (P > .05) in Generation 8. In Generation 9, boars of line TS were heavier between 118 and 198 d of age (P < .001); thereafter, body weights of the lines were similar (P > .05). The increase in organ weights for the testes and epididymides between 70 and 160 d of age were greater (P < .01) for boars of line TS in each generation, and differences between the lines in testis weights established around puberty were maintained at 450 d of age. Daily sperm production and CAUDASP increased more rapidly at younger ages and plateaued at greater values (P < .05) in boars of line TS. At ages less than 200 d, boars of line TS produced more sperm per gram of parenchyma than control boars.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1995

Growth of testes and testicular morphology after eight generations of selection for increased predicted weight of testes at 150 days of age in boars.

Weights of testes and epididymides, body weight, and morphometric measurements of testicular tissue of 75 boars of a line selected for eight generations for predicted weight of testes at 150 d of age and 75 boars of a randomly selected control line were used to evaluate the effects of selection on testicular development at 70, 100, 130, 160, and 450 d of age (n = 15 boars per line per age). Body weights for boars of the select and control line did not differ (P < .05) and the shape of the body growth curve was similar for both lines. Boars of the select line had larger testes than control boars at each age (P < .05), but there was a significant line x age interaction. The percentage increase of the select line mean over the control mean for weight of testes was 37% at 70 d, a maximum of 120% at 100 d, and 25% at 450 d. The percentage of the testes made up of seminiferous tubules differed between lines (P < .01). Lines had similar means of approximately 28% at 70 d and 71% at 450 d, but the mean for the select line was larger between 100 and 160 d of age; the greatest difference was 11.6% (control = 43.7, select = 55.3%) at 100 d. After 70 d of age, select-line boars had a greater percentage of seminiferous tubules with lumens that contained elongated spermatids (P < .10).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1993

Semen characteristics, testicular size, and reproductive hormone concentrations in mature duroc, meishan, fengjing, and minzhu boars.

Chinese breeds of swine are known for their reproductive prolificacy and are noted for large litter size. The current investigation evaluated reproductive components of three breeds of Chinese boars in comparison to a contemporary site breed common in the U.S. Semen from postpubertal Duroc, Meishan, Fengjing, and Minzhu boars was collected during four seasons of the year. After each semen collection and evaluation period, boars were weighted and placed in a restraining chute for testicular measurements and blood sampling for measurement of FSH, testosterone, and inhibin. Although Duroc boars were 2 mo younger than Chinese boars, initial and final body weight and paired testis volume in Durocs were greater (p < 0.05) than in Chinese boars. Total spermatozoa per ejaculate was similar for Duroc and Minzhu boars, but was lower (p < 0.05) in Fengjing and Meishan boars. Progressive motility and sperm morphological characteristics were not affected by breed of boar. Serum FSH concentrations were markedly higher (p < 0.01) in Meishan and Fengjing boars than in other breeds, and concentrations were nearly 8-fold higher in Meishan than in Duroc boars. Breed differences in serum inhibin were essentially the inverse of those observed for FSH, with Durocs exhibiting the highest inhibin concentrations and Meishans exhibiting the lowest. Testosterone values were not different between breeds. However, testosterone concentrations fluctuated with season, and serum testosterone was highest during the fall of the year in all breeds. These results indicated that some reproductive characteristics differ dramatically between Duroc and Chinese breeds of boars. Breed differences existed in body size, testis size, sperm per ejaculate, ejaculate volume, and serum FSH and inhibin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Association between low birth weight and increased adrenocortical function in neonatal pigs.

This study examined differences in adrenocortical function between low- and high-birth-weight female neonatal pigs. Pigs born to unilaterally hysterectomized, ovariectomized sows were grouped by birth weight; "small" were < or = 1.2 kg and "large" were > 1.2 kg. Pigs were cross-fostered such that each sow had six to eight pigs that were either small or large. At 3 or 7 d of age a blood sample was obtained by venipuncture, pigs were killed, and adrenocortical cells were isolated. Adrenal weights (milligrams/kilogram BW) in small pigs were 46% greater (P = .001) than those in large pigs at both ages. Compared with those in large pigs, plasma cortisol concentrations were 70% greater (P = .006) in small pigs at 3 d and 199% greater at 7 d of age. Sensitivity of adrenocortical cell response to ACTH was enhanced at both ages in small pigs (P = .001). Corticosteroid binding globulin (CBG) binding capacity in small pigs was 75% greater (P = .03) than that in large pigs at 3 d and 26% greater at 7 d of age. Significant negative correlations existed between birth weight and relative adrenal weight, plasma cortisol, slopes of in vitro adrenocortical cell response curves to ACTH, and CBG binding capacity, irrespective of birth weight group classification. Such data indicate an association between adrenal function during early neonatal life and birth weight in female pigs. The current study does not indicate whether increased adrenal function causes or merely reflects conditions associated with low birth weight. However, we hypothesize that increased adrenal function is initiated prenatally and causes some instances of low birth weight.

Adrenal Cortex↗

PubMed1992

Effects of sexual experience, season, and mating stimuli on endocrine concentrations in the adult ram.

Two behavioral trials were conducted to determine the endocrine response of cortisol (C), luteinizing hormone (LH), testosterone (T), prolactin (PRL), and growth hormone (GH) in adult rams during exposure to estrous ewes during the breeding and nonbreeding seasons. One-half of the rams in each season were sexually experienced (SE) and the remainder were sexually inexperienced (SI). All SE rams (100%) achieved at least one ejaculation, but only 33% (summer) and 67% (fall) SI rams achieved ejaculation. In the fall, mean C, T, and GH concentrations were elevated (P less than .001) compared to values measured in the summer, whereas LH and PRL levels were higher (P less than .01) in the summer. Overall levels of C, LH, T, and PRL were higher (P less than .05) in SE rams than in SI rams. Mean GH concentration was higher (P less than .10) in SI than in SE rams during restricted and complete access to estrous ewes. In general, LH, PRL, and GH responses were similar during restricted and complete access to females for both SE and SI rams. Cortisol levels were higher (P less than .06) during periods of mating and T levels were higher (P less than .001) during periods where activity was limited to courtship behavior (nasogenital investigation). Correlations of hormones to reproductive behaviors indicated that mounting and intromission were associated with elevations in C and PRL, whereas elevated LH and T tended to be associated with courtship behaviors. Correlations between GH and behaviors were inconsistent. However, there was an increased coincidence between time of female exposure and hormonal response that occurred in the fall; brief exposure to estrous ewes resulted in increases in concentrations of all hormones examined. The most consistent response was observed in sexually experienced rams during restricted access to females during the breeding season. These results provide new information on the effects of season and level of sexual experience upon hormonal and behavioral characteristics of the ram during mating activity.

Animals↗

PubMed1992

Cortisol and prolactin concentrations during three different seasons in relocated Brahman and Hereford bulls.

The objective of this study was to evaluate seasonal changes of cortisol and prolactin (PRL) concentrations in Brahman and Hereford bulls moved to locations that differ in geographical and environmental conditions. Postpubertal Hereford bulls from Montana (n = 15) and Nebraska (n = 15) and Brahman bulls from Texas (n = 18) were located in or relocated to Montana, Nebraska or Texas so that each location had 5 Montana Herefords, 5 Nebraska Herefords and 6 Texas Brahman bulls. Blood samples were collected at 20-minute intervals for 8 hours in November (Fall 1), April (Spring) and November (Fall 2) of the next year. These dates corresponded to 6, 12 and 18 months, respectively, after relocation in May of the first year. Cortisol concentrations were higher (P<0.05) in Fall 1 than in Fall 2 and were higher (P<0.05) for bulls in Montana than for bulls in Texas. The decrease in cortisol concentrations from Fall 1 to Fall 2 was negatively related (P<0.05) to age and weight. There was a three-way interaction (P<0.05) of breed-type origin, location and season for PRL concentrations. Seasonal patterns of PRL concentrations differed between relocated Texas Brahman and Hereford bulls, and patterns for relocated bulls differed from those of the nonrelocated bulls. Seasonal patterns of PRL were influenced to a greater extent by relocation in Texas Brahman bulls than in Hereford bulls.

Journal Article↗

PubMed1992

Effect of implanting bull calves with testosterone propionate, dihydrotestosterone propionate or oestradiol-17 beta prepubertally on the pituitary-testicular axis and on postpubertal social and sexual behaviour.

Twelve non-implanted crossbred bull calves served as controls and 30 crossbred bull calves (10/treatment) were implanted for 82 days, beginning at 34 days of age, to determine the influence of testosterone propionate (TP), dihydrotestosterone propionate (DHTP) and oestradiol-17 beta (E2) on prepubertal and pubertal pituitary-testicular function and on postpubertal social and sexual behaviour. Compared with control bulls, concentrations of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and inhibin concentrations were suppressed (P less than 0.01) in all implanted bulls. Testosterone (T) concentration increased (P less than 0.001) in TP-implanted, but decreased (P less than 0.01) in DHTP and E2 bulls during the implant period. LH response to gonadotrophin-releasing hormone (GnRH) challenge during the implant period (2.5 months of age) was less (P less than 0.01) in TP, E2 and DHTP bulls than in controls. A small but significant T response to GnRH occurred in control bulls at 2.5 months of age. LH and T responses to GnRH challenge at 7 months of age (100 days after implant removal) was similar (P greater than 0.20) in control and implanted bulls. Steroid implants administered prepubertally had no effect (P greater than 0.10) on postpubertal social and sexual behaviours, including number of flehmen responses, abortive mounts, services and competitive order score. Body weight did not differ (P greater than 0.10) between treatment groups, but testis size was reduced (P less than 0.01) during the implant period and up to 10 months of age in treated bulls compared with controls. Testes remained smaller in E2-treated bulls up to the end of the study (23 months of age), but daily sperm production and epididymal weight did not differ (P greater than 0.10) between treatment groups at slaughter. Control bulls reached puberty earlier (P less than 0.01; 270 +/- 11 days of age) than did TP (302 +/- 11 days), DHTP (309 +/- 11 days) or E2 (327 +/- 11 days) bulls. Although puberty was delayed in all implant groups, there was no difference in scrotal circumference at puberty (average 28.4 +/- 0.4 cm) between treatment groups. Our findings indicate that TP, DHTP and E2 implants administered prepubertally result in acute suppression of serum LH, FSH and inhibin during the implant period and in post-implant suppression of testis size and delayed puberty in bulls. The lack of treatment effect on behaviour suggests that steroidal programming of sexual behaviour occurs before 1 month of age in bulls.

Animals↗

PubMed1991

Immunoneutralization of inhibin modifies hormone secretion and sperm production in bulls.

The objective of this study was to examine the role of endogenous inhibin in the regulation of FSH, LH, and testosterone secretion and sperm production in bulls. Bulls were actively immunized against bovine inhibin alpha 1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG) or HAG alone (controls) and emulsified in Freund's complete adjuvant. Primary immunization was at 14 wk of age, followed by booster immunizations in Freund's incomplete adjuvant at 28, 30, and 34 wk of age. Ten days after each booster immunization, scrotal circumferences and body weights were measured, and blood was sampled for determination of bINH antibody titer. Ten days after the third booster, blood was sampled at 1-h intervals for 8 h to quantify serum concentrations of FSH, LH, and testosterone. After this blood sampling period, bulls were castrated and testicular sperm production was determined. Serum diluted 1:4,000 from bINH-immunized bulls bound 36%, 52%, and 53% of radioiodinated bINH after the first, second, and third boosters, respectively. Serum from controls bound less than 1% radioiodinated bINH. After the third booster, serum concentrations of FSH and testosterone were increased (p less than 0.05) and LH concentrations were decreased (p less than 0.001) in bINH-immunized bulls compared with controls. After the third booster, daily sperm production per gram of testicular parenchyma was increased (p less than 0.05) in bINH-immunized bulls compared with controls. Scrotal circumferences and body weights were similar between treatment groups throughout the experiment. We concluded that inhibin has a role in regulation of secretion of gonadotrophins and testosterone and testicular sperm production, but not testicular growth, in bulls.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-Globulins↗

PubMed1991

Breed effects and heterosis in advanced generations of composite populations for puberty and scrotal traits of beef cattle.

Heterosis effects were evaluated in F1, F2, and F3 generations of females and in the F1, F2, and combined F3 and F4 generations of males in three composite populations of beef cattle. Traits included weight, height, and condition scores at different ages, percentage of females reaching puberty at 368, 410, and 452 d, adjusted age, and adjusted weight of females at puberty and scrotal circumference and paired testicular volume of males. Breed effects were evaluated for the nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 C, 1/4 B, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, 1/4 A). Breed effects were significant for all traits evaluated. Heterosis was significant for weight, height, and condition score at all ages and for most measures of puberty in each generation of each composite and for the mean of the three composite populations. Heterosis for age at puberty was largely independent of heterosis effects on 368-d weight. Heterosis was significant for scrotal circumference and paired testicular volume in each generation of each composite and for the mean of the three composite populations. Heterosis effects on scrotal measurements are mediated both through heterosis effects on growth rate and through factors that are independent of growth rate. Correlation coefficients among breed group means and correlations of breed rank for scrotal measurements with puberty traits of females were greater than or equal to .88 (P less than .01) for all puberty traits except weight at puberty, which was not associated with scrotal measurements. There was close agreement in heterosis observed for most traits and expectation based on retained heterozygosity. These results support the hypothesis that heterosis in cattle for size, puberty, and scrotal measurement traits is due to dominance effects of genes.

Analysis of Variance↗

PubMed1990

Effect of season and location on semen quality and serum concentrations of luteinizing hormone and testosterone in Brahman and Hereford bulls.

Hereford bulls from Montana (MH; n = 15) and Nebraska (NH; n = 15) and Brahman bulls from Texas (BB; n = 18) were relocated to one of three locations (LOC): Montana (MT), Nebraska (NE) or Texas (TX). All bulls were pubertal at the time of relocation in late May 1984. Semen was collected by electroejaculation within 1 wk after relocation and at 90-d intervals beginning in November 1984 through early February 1986. Bulls were given a GnRH challenge (200 micrograms i.m.) during the same week of semen collections. Bulls also were bled for 8 h at 20-min intervals in the fall of 1984 and the spring and fall of 1985 to determine endogenous concentrations of LH and testosterone. Season affected sperm concentration in all breeds (P less than .05) with decreases during the winter in BB and during the summer in NH and MH bulls. Brahman bulls had lower percentage of live cells (LIVE) than NH and MH bulls did (P less than .0001). Brahman bulls decreased in LIVE during the winter (P less than .001). Area under the LH curve after GnRH was lower (P less than .005) in BB than in MH and NH. Brahman bulls in MT had greater (P less than .02) area under the LH curve and lower (P less than .06) area under the testosterone curve than did BB in TX or NE during the winter. There was no seasonal fluctuation in LH or testosterone response to GnRH in NH or MH bulls at any LOC. Area under the endogenous LH curve was lowest (P less than .04) in BB. Basal endogenous testosterone concentration was greater (P less than .03) in NH than in MH or BB. Area under the endogenous testosterone curve was lower (P less than .03) in MH than in NH or BB. These results indicate that BB exhibit seasonal fluctuations in semen quality. This was not so apparent in semen quality traits of Hereford bulls. There also was a seasonal influence in BB on both endogenous testosterone and GnRH-stimulated LH and testosterone concentrations. Compared with Hereford bulls, Brahman bulls had lower endogenous and GnRH-stimulated concentrations of LH.

Animals↗

PubMed1990

Effect of location and season on body and testicular growth in Brahman and Hereford bulls.

To determine the effects of location and season on growth of bulls, Hereford bulls from Montana (MH; n = 15) and Nebraska (NH; n = 15) and Brahman bulls from Texas and Louisiana (BB; n = 18) were moved to three locations: Montana (MT), Nebraska (NE) or Texas (TX). Each location received 5 NH, 5 MH and 6 BB. Control bulls (not relocated) were maintained at each location. All bulls were pubertal at the time of relocation in May 1984. At 28-d intervals, body weight, hip height, testis length and scrotal circumference were recorded for each bull for 22 mo after relocation. Paired testes volume (PTV) was calculated. Among Hereford bulls, body weights were similar (P greater than .10) in all control and relocated bulls by the end of the study, except that MH bulls moved to TX had lower body weights (P less than .01). Brahman bulls moved to northern locations had dramatically reduced body weights, compared to control Brahmans kept in TX; body weight of Brahman bulls in MT remained lower (P less than .01) at the end of the study. Brahman bulls in NE and MT had smaller scrotal circumference and PTV (P less than .01) than did control Brahmans in TX during the 1st yr after relocation. Relocated BB exhibited marked seasonal fluctuations in testis size, with increases during the summer and decreases during the winter (P less than .01); seasonal changes were not apparent in control Brahmans in TX. These results indicate that moving Brahman bulls to northern environments reduced body weight gain and caused dramatic seasonal changes in testis size; these effects were more pronounced in Brahman bulls moved to the most northern location.

Animals↗

PubMed1989

The influence of the BoLA-A locus on reproductive traits in cattle.

Associations between the major histocompatibility complex (MHC) and reproductive performance have been reported in humans, mice, rats, pigs and chickens. Only the A locus of the bovine major histocompatibility complex (BoLA-A) has been well characterized, and 42 alleles of this locus have been identified in American cattle. Four studies were conducted to examine the association between alleles of the BoLA-A locus and reproductive performance. Testis size, which is an indicator of early puberty and increased fertility in young bulls, was examined in 440 yearling bulls from nine breeds with a gene substitution model that included the effects of breed, sire, age of dam and age or weight of the bull. Estimated breeding value for twinning was examined with a gene substitution model with 204 cattle from a herd with a high frequency of twinning. Fertility of potential partners having BoLA-A locus alleles in common was examined in a prospective study involving 101 pure-bred Hereford cows mated by artificial insemination to four pure-bred Hereford bulls. The effect of homozygosity on birth weight, preweaning weight gain and post-weaning weight gain was estimated in a sample of 683 calves from nine breeds; 22% of the calves were apparently homozygous and 78% were heterozygous at the BoLA-A locus. There were significant and large effects of some BoLA-A locus alleles on paired testicular volume, but the analyses on the other traits did not show significant associations. Substitution of the W6.1 allele for the W9A allele reduced paired testicular volume by 150 +/- 44 cm3. The W6.1 allele has now been shown to influence a reproductive trait, a production trait and susceptibility to an economically important disease. Selection for these traits may influence the frequency of the large number of alleles at the BoLA-A locus.

Alleles↗