Relationship between LH and testicular development in progesterone-implanted prepubertal ram lambs

The relationship between systemic luteinizing hormone (LH) and testicular development was investigated in Finn and Suffolk ram lambs treated at 2 wk of age with sc progesterone implants for 0, 4, 8 or 12 wk. Serial samples of blood (30-min intervals for 3 h) were collected from five rams X breed-1 X treatment-1 at 6, 8, 10, 12, 14, 18 and 22 wk of age plus 1 and 2 wk after implant removal. Scrotal circumference was measured at 10, 14, 18 and 22 wk of age. A testicular biopsy was obtained at 14, 18 and 22 wk for microscopic evaluation of testicular development and spermatogenesis. Pulsatile LH releases occurred 60 to 180 min apart in control lambs between 6 and 22 wk of age; LH secretion was not affected by age except for a decrease (P less than .01) in mean LH at 22 wk. Transient increases in testosterone were found subsequent to LH pulses. Systemic testosterone increased (P less than .01) progressively with age, was higher (P less than .05) in Finn than in Suffolk rams at 18 and 22 wk and was correlated positively (P less than .01) within breeds with seminiferous tubule diameter at 14 wk and with scrotal circumference at 10 and 14 wk. Tubule diameter was larger (P less than .01) but testes size and weight were smaller (P less than .01) in Finn than in Suffolk rams. Progesterone implants decreased (P less than .01) LH secretion at 4, 6, 8, 10 and 12, but not at 14 wk of age; decreased systemic testosterone between 4 and 14 wk; decreased (P less than .01) seminiferous tubule diameter at 14 wk, which was related inversely to duration of progesterone treatment; and delayed puberty from 18 to 22 or more wk in rams implanted from 2 to 10 or 14 wk of age. Both control and treated rams with elongated spermatids at 18 vs 22 or more wk had increased LH secretion, higher systemic testosterone and larger tubule diameter and testes size at a younger age. These results suggest that rate of sexual maturation in ram lambs is related to level of postnatal LH stimulation and to the prepubertal age when increased LH stimulation occurs.     

Breed group differences in testicular growth patterns in spring-born ram lambs

Three groups of spring-born ram lambs were used to assess breed group differences in testicular growth patterns through 5 mo of age. Group 1 included 20 3/4-Finnish Landrace (Finn), 1/4-Rambouillet rams and 31 1/8-Finn, 7/8-Rambouillet rams. Group 2 included 23 3/4-Finn, 1/4-Dorset rams and 19 1/8-Finn, 7/8-Dorset rams. Group 3 included 21 black-faced (BF) rams (six Hampshire and 15 Suffolk) and 46 whitefaced (WF) rams (nine Dorset, 20 Barbados Blackbelly X Dorset, 10 Finn X Dorset and six Dorset X Finn). Scrotal circumference (C) was measured at 19, 43, 72, 100, 128 and 153 d in Group 1; at 20, 48, 76, 93 and 153 d in Group 2 and at 40, 60, 81, 103, 124 and 158 d in Group 3. Breed group X age interaction was tested to assess breed group differences in testicular growth patterns, and logistic curves were used to describe increases in scrotal circumference with age. In Group 1, 3/4-Finn and 1/8-Finn rams were similar in estimated final scrotal circumference at 150 d of age (260 and 259 mm, respectively), but rapid testicular growth began earlier in 3/4-Finn rams. The estimated age at which the growth rate in scrotal circumference was maximum was 81 d for 3/4-Finn rams and 93 d for 1/8-Finn rams. No differences were observed in testicular growth in Group 2 rams. However, in Group 3, smaller WF rams matured more rapidly than larger BF rams. Growth in scrotal circumference was most rapid at 99 d in BF rams and 88 d in WF rams. Within WF rams, Barbados Blackbelly X Dorset and Finn X Dorset rams matured earlier than Dorsets. In all groups, the primary breed difference was associated with age differences during the period of rapid testicular growth.     

Endocrine profiles, testicular gonadotropin receptors and sperm production in hemi-castrated ram lambs

The effects of hemi-castration upon compensatory hypertrophy, serum gonadotropin and testosterone concentrations, testicular gonadotropin receptors and daily sperm production (DSP) were studied in 10 crossbred ram lambs. At 4 mo of age lambs were either hemi-castrated (HC; n = 5) or left intact (INT; n = 5). Blood samples were collected every 2 h for the first 24 h post-surgery, every 6 h for the next 24 h and then three times weekly for the following 14 wk. Serial blood samples (15-min intervals for 8 h) were collected during the 4th, 8th and 12th week following hemi-castration. Individual mean testicular and epididymal weights increased (P less than .05) 48 and 33% in HC compared with INT rams, respectively. Serum follicle stimulating hormone (FSH) increased (P less than .05) within 8 h after HC, reached peak concentrations within 1 wk and remained elevated for 4 wk before returning to concentrations of INT rams. Neither mean serum luteinizing hormone (LH) nor pulse patterns of LH or FSH were different (P greater than .05) between these two groups at any period examined. Serum testosterone (T) concentrations were lower (P less than .05) during the first 48 h post-surgery in HC rams, but by 1 wk concentrations were similar (P greater than .05) to those in INT rams. Remaining testes from HC and INT rams were removed at 7 mo of age, 3 mo after initial gonadal manipulation. On a per-testis basis there were more (P less than .05) LH and FSH receptors in HC than INT rams, respectively; however, concentrations of receptors were not different (P greater than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Puberty and early sexual development in Libyan fat-tailed ram lambs

Puberty and early sexual development were studied in 143 Libyan fat-tailed ram lambs, equally representing Brownhead and Blackhead strains of this breed. The two strains did not differ in any of the measured parameters in a consistent way, yet the Brownhead lambs tended to be slightly heavier and to have a slightly larger testis diameter than Blackheads. At the commencement of the observations when the lambs were 69 days old, 25.2% had fully descended testes at a significantly higher (P less than 0.01) mean (SD) body weight (24.1 +/- 4.1 kg) than those with partly descended (69.2%, 15.7 +/- 6.3 kg) or with non-descended testes (5.6%, 19.5 +/- 3.2 kg). Testes development followed a triphasic pattern with an initial and a final phase of slow growth and a middle phase of fast growth, commencing at a weight of 24.5 kg and an age of 85 days and lasting until the weight of 36-43 kg and age of 180-200 days in both strains. The separation of penile adhesions commenced at a mean body weight and age of 33.6 +/- 3.7 kg and 125.5 +/- 27.4 days respectively and was completed at a mean weight and age of 38.3 +/- 4.2 kg and 153.4 +/- 29.9 days. Only four lambs failed to show complete penile separation. Age had little influence on testis descent or on penile development. Puberty was assessed in 71 lambs using sperm recovery following electroejaculation as an end point. Most of these lambs (92.9%) reached puberty at a mean (SD) age of 171.5 (39.9) days, mean body weight of 39.9 (9.3) kg, mean testis diameter of 4.1 (0.4) cm and mean horn length of 21.4 (3.7) cm. Puberal lambs were significantly superior to non-puberal lambs (P less than 0.01) in all these counts except for age which was similar in both categories. Direct testicular observation showed a strong correlation between testis diameter, testis weight, body weight, sperm concentration/g testis weight and to testis histology. Age was poorly correlated to testis weight, histology or sperm concentration. It is concluded that the body weight is a major determinant of puberty in this breed. It is also considered that the two strains of the breed are remarkably similar in the studied aspects of puberty and sexual development.     

Copper toxicity in confinement-housed ram lambs.

Fourteen Suffolk rams (6 mo) were diagnosed with chronic copper poisoning. Preliminary results indicated that a combination of serum aspartate aminotransferase, gamma glutamyltransferase, and copper could be used as a test so that high risk lambs could be treated more aggressively.     

Technical note: recombinant LHRH fusion protein suppresses estrus in heifers

A recombinant luteinizing hormone-releasing hormone (LHRH) fusion protein was evaluated for its effectiveness in suppression of estrus in heifers. Eight heifers were randomly assigned to two equal treatment groups. Treatments consisted of recombinant ovalbumin-LHRH-7 or recombinant ovalbumin (control). This recombinant chimeric fusion protein consisted of ovalbumin with seven LHRH peptides (ovalbumin-LHRH-7). The plasmid for this protein was expressed in E. coli and was collected and purified as an insoluble protein. One milligram of the respective proteins was suspended in 2 mL of Z-Max adjuvant and administered by intramammary injection three times at 7-wk intervals. Luteinizing hormone-releasing hormone antibody binding was elevated in heifers treated with ovalbumin-LHRH-7 compared to ovalbumin-treated heifers (P < .05). Serum progesterone concentrations (< 1 ng/mL) indicate that the estrous cycle of the four heifers treated with ovalbumin-LHRH-7 was suppressed for a time period ranging from 60 to 238 d, which was different from control heifers (P < .01). Serum progesterone for the control heifers continued to exhibit cyclic profiles over the experimental period. This preliminary study in heifers demonstrated that a chimeric LHRH fusion protein induced elevated concentrations of circulating LHRH antibodies that suppressed estrus for an average of 122 +/- 41 d.     

The physiological effects of natural variation in growth hormone gene copy number in ram lambs

The effects of natural variation in the number of copies of the growth hormone (GH) gene on growth parameters, plasma GH profiles, and the response to GHRH challenge were compared in Coopworth ram lambs from selection lines differing in body composition and GH levels. Different genotypes at the GH locus carried two, three, or four copies of the GH gene and GH secretion was studied under ad libitum feeding conditions and in the fasted state. There were no significant effects of GH genotype on any parameters of growth or body composition. Basal serum GH concentration, GH pulse frequency, and GH pulse amplitude differed significantly with selection line and fasting, but did not differ significantly between the GH genotypes. Significant differences of subtle nature were found between the GH genotypes in their responsiveness to GHRH. For the ad libitum-fed Lean selection line animals, the first GHRH challenge resulted in a higher mean maximum response for GH1/GH1 than GH2/GH2 (P < 0.05). Between the first and the second challenges there was a decrease in maximum response for the GH1/GH1 genotype and an increase for the GH2/GH2 genotype (P < 0.05 for GH genotype main effect). The differences between GH genotypes in response to GHRH challenge suggest that polymorphism in the number of GH gene copies in sheep may have physiological implications for the function of the GH axis, which may be manifested in growing lambs only under specific genotype-environment combinations.     

The effects of androgens and gonadotropins on testicular development in the prepubertal rat.

Treatment of male rat pups from five to 34 days of age with dihydrotestosterone or 5 alpha-androstane-3 alpha, 17 beta-diol, resulted in reduced testicular size at 35 days of age. This appeared to be due to decreased tubular diameters and reduced spermatocyte numbers, especially late pachytene cells in stages X to XIII. In rat pups treated with dihydrotestosterone or 5 alpha-androstane-3 alpha, 17 beta-diol, treatment with luteinizing hormone resulted in some restoration of tubular diameter and spermatocyte numbers. In 5 alpha-androstane-3 alpha, 17 beta-diol treated rat pups partial restoration of testes size resulted from follicle-stimulating hormone treatment, but tubular diameter and spermatocyte numbers were depressed. Single serum samples collected at 35 days of age were analysed for luteinizing and follicle-stimulating hormone concentrations. These data indicated that the effects of administered androgens were due primarily to depression of circulating gonadotropin concentrations but a direct inhibition at the level of the testis could not be ruled out.     

Genetic correlations for daily gain between ram and ewe lambs fed in feedlot conditions and ram lambs fed in Pinpointer units

When performance is recorded in automated facilities that measure feed intake of individual lambs that are penned in a group, such as Pinpointer units, a legitimate question is the degree to which daily gain is genetically correlated with daily gain achieved under feedlot conditions. Lambs were from a composite population (1/2 Columbia, 1/4 Suffolk, and 1/4 Hampshire germplasm) and of the F2 or more advanced generations. Data were daily gains of 1,101 rams (PR) fed in Pinpointer units (11 to 17 wk of age) and 2,021 rams (FR) and 3,513 ewes (FE) fed under feedlot conditions (9- or 10-wk period starting at 9 wk of age). The FR and FE lambs were born from 1983 through 1995, whereas the PR lambs were born from 1986 through 1995. Measurements of daily gain in PR, FR, and FE lambs were considered to represent three correlated traits. Unadjusted means were .411, .406, and .326 kg/d for PR, FR, and FE, respectively. Random effects in the model were animal direct genetic, maternal genetic, and maternal permanent environmental. Fixed effects were associated with age of dam (1 to 6 yr), type of rearing (1 to 4), and contemporary group (test date). Variances due to maternal genetic effects with single-trait analyses were near zero, so those effects were eliminated from the three-trait analysis although a random uncorrelated effect due to dam was included in the model. Estimates of heritability were .22, .14, and .23 for PR, FR, and FE, respectively, with fractions of variance due to dam effects ranging from .02 to .05. Estimates of genetic correlations were .86 for PR with FR, .83 for PR with FE, and 1.00 for FR with FE. Estimated phenotypic variances were similar for PR and FR, but one-third less for FE. The similarity of heritability estimates and estimates of genetic correlations all exceeding .83 suggest that daily gain of rams fed in Pinpointer units will reflect genetic expression for daily gain in both ram and ewe lambs fed under feedlot conditions.     

Effects of breed and intake level on growth and feed efficiency in ram lambs

Effects of breed and intake level on growth and feed efficiency in ram lambs were tested with 52 Rambouillet, 46 Dorset and 53 Finnish Landrace (Finn) rams. Rams were individually fed at 100, 85 or 70% of ad libitum or at maintenance. The experimental diet contained 79% digestible dry matter (DM), 3.28% N and 2.95 Mcal metabolizable energy/kg DM. Rams were serially slaughtered every 35 d for 175 d. The efficiency of deposition of body weight, protein, energy and trimmed cuts was determined by breed and intake level over constant time, weight, fat and maturity intervals. Ranking of the breeds for feed efficiency depended upon both the interval and the criterion of evaluation. Efficiency of protein and trimmed cut gain was positively related to mature size in the time and weight intervals, but all differences in efficiency were small in the fat or maturity intervals. Gross energetic efficiency did not differ greatly among breeds in any interval. Dorsets appeared to have a somewhat greater propensity to fatten than the other breeds and to be less able to retain N at a fixed N intake. In the constant time interval, maintenance requirements were estimated to be 115 kcal/kg.75, and the estimated partial efficiencies of energy deposition in fat and protein were .49 and .26, respectively.     

LHRH and beta-endorphin in the hypothalamus of the ram in relation to photoperiod and reproductive activity

The regional distribution and relative concentrations of LHRH and beta-endorphin immunoreactivity in the hypothalamus were compared in sexually active and sexually inactive Soay rams. LHRH was localized principally in the medial basal hypothalamus and median eminence with lower concentrations in the anterior hypothalamus and preoptic area. beta-endorphin immunoreactivity was also found in highest concentrations in these regions but was more widely distributed into the rostral, dorsal and lateral parts of the hypothalamus. LHRH content in the medial basal hypothalamus was significantly lower in the sexually active rams compared to inactive rams while there was no difference in beta-endorphin immunoreactivity content between the two groups. Gel filtration chromatography of hypothalamic extracts revealed that the beta-endorphin immunoreactivity was due to both beta-lipotropin and beta-endorphin; the ratio of beta-endorphin: beta-lipotropin tended to be less in the sexually active rams than in the sexually inactive rams. The results are consistent with the hypothesis that beta-endorphin is a physiologically important endogenous opioid involved in the modulation of LHRH secretion.     

Pubertal changes in the secretion of gonadotropic hormones, testicular gonadotropic receptors and testicular function in the ram

Developmental changes in pituitary content and secretory patterns of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL), testicular size and steroidogenic function, testicular LH- and FSH-binding activity, and growth of the accessory sex organs were examined for 24 Dorset X Leicester X Suffolk rams (born in March) every 30 days from 30 to 150 days of age, and again at 200 days. Pituitary LH and FSH contents increased between 30 and 60 days of age and remained constant until 150 days, when contents were somewhat greater than on either 120 or 200 days. LH-pulse amplitude and frequency, and mean FSH concentration, were highest at 60 and (or) 90 days of age. Testicular growth increased dramatically between 90 and 150 days of age in association with increases in the number of LH- (100-fold) and FSH- (33-fold) binding sites in the testis and a small increase in blood testosterone concentration (1 ng/ml). During the same period, pituitary content and blood concentration of PRL increased to maximal values, epididymal, vesicular gland and bulbourethral gland weights increased 6-fold, and body weight doubled. Between 150 and 200 days of age, testosterone concentration increased considerably (8 ng/ml), as did LH-pulse frequency and the amount of LH- and FSH- binding in the testis; the reproductive organs continued to grow at a rate faster than that of the body as a whole. Testicular development of ram lambs was accompanied by increases in the secretion of all three pituitary hormones with gonadotropic properties, and in the number of LH and FSH receptors.     

The effect of castration, estradiol and LHRH on LH secretion of lambs fed different levels of dietary energy

To examine the effect of diet on luteinizing hormone (LH) secretion, basal and luteinizing hormone releasing hormone (LHRH)-induced LH release was compared in intact or castrated-estradiol-17 beta implanted Finn-Dorset lambs. Ten to 12 wk old ram (n = 20) and ewe lambs (n = 20) were maintained under a 8L:16D photoperiod and fed for high (HG, 163 to 168 g/d) or low (LG, 76 to 103 g/d) rates of gain. Eight to 10 wk later, baseline LH concentrations were determined in blood samples collected at 20 min intervals for 7 h. The following day, lambs were given an iv injection of 5 micrograms of estradiol-17 beta followed within 4 h by LHRH (.5 or 2.5 micrograms). Baseline concentrations of LH for HG ewes were threefold greater than for LG ewes (4.2 vs 1.4 ng/ml), respectively. Time to peak response was inversely related to dietary energy level (P less than .025). Basal LH levels were similar across diets in rams. Total LH release following LHRH was dose-dependent (P less than .005). Effects of gonadal feedback were tested in a second group (n = 24) of castrated lambs. Changes in LH secretion were not different between diets within 3 to 4 wk after castration. A subcutaneous silastic implant (22 mm) of estradiol-17 beta inhibited (P less than .01) LH concentrations across diets in both ewes and rams. No differences in estradiol feedback on LH secretion (at the dose of steroid tested) were detected between HG and LG lambs. Within 8 d, however, basal LH concentrations were 60% lower (P less than .01) in HG vs LG ewes. Furthermore, peak LHRH-induced LH release was greater (P less than .025) in LG vs HG lambs of both sexes. Estradiol inhibited basal LH secretion in ewes and rams but facilitated LH release in lambs with a reduced rate of gain.     

Effects of implanting ram and wether lambs with zeranol at birth and weaning on palatability and muscle collagen characteristics.

Thirty-five zeranol-implanted (I) and nonimplanted (NI) ram and wether lambs representing four treatments (implanted rams [IR], nonimplanted rams [NIR], implanted wethers [IW], and nonimplanted wethers [NIW]) were evaluated for meat palatability and muscle collagen characteristics. Rib (longissimus muscle, LM) chops from I lambs were juicier (P less than .05) than rib chops from NI lambs. Chops from IR lambs had more (P less than .05) detectable connective tissue and lower myofibrillar and overall tenderness scores than chops from NIR, IW, or NIW lambs. Warner-Bratzler shear (WBS) values tended to be higher (P = .06) for LM chops from rams than for those from wethers, but WBS values for Biceps femoris (BF) chops were similar (P greater than .05) for rams and wethers. Implanting did not affect (P greater than .05) WBS values. Rams had more (P less than .05) LM heat-labile (soluble, SC), nonheat-labile (insoluble, IC), and total collagen (TC) and a higher (P less than .05) percentage of SC (SC/TC) than did wethers. Soluble collagen, TC, and percentage of SC for the BF were higher (P less than .05) and IC tended (P = .09) to be higher in chops from rams than in those from wethers. Implanting did not affect (P greater than .05) collagen amount or solubility. Serum nonprotein hydroxyproline (NPHP) was higher (P less than .05) in rams than in wethers throughout the feeding period and tended (P = .05) to be higher at slaughter. Implanting did not affect (P greater than .05) serum NPHP.(ABSTRACT TRUNCATED AT 250 WORDS)