The effect of scrotal circumference, sperm motility and morphology in the ram on conception rates and lambing percentage in the ewe

Ten Suffolk and ten Lincoln yearling rams were examined for breeding soundness. Semen was evaluated, and the scrotal circumference measured. They were single-sire mated to ten to twelve, whiteface ewe lambs during a 45-day breeding season (October 15 - December 1). First-service conception rates, total conception rate, lambing percentage and lambing percentage per ewe exposed were calculated for each ram and breed. The mean scrotal circumference was 36.5 cm (range 31 - 41.5 cm). The breeding data was then compared for eleven rams with a scrotal circumference of less than 36.5 cm and nine rams greater than 36.5 cm. No direct relationship was demonstrated between scrotal circumference, sperm motility or morphology with fertility in the rams used in this experiment. However, there was a tendency for rams with a high first-service conception rate to have sired more lambs per ewe exposed. The mean first-service conception rate was 63.2% (range 44.4 - 80.0%). When rams with greater than 63.2% first-service conception rate were compared to those with less than 63.2%. the lambs born per ewe exposed were 1.04 and .89, respectively, a significant difference (P<.05). There were no significant differences (P<.05) in performance between the two groups when rams with a scrotal circumference less than 36.5 cm and greater than 36.5 cm were compared, nor were there any differences between scrotal circumference, sperm motility, and morphology when rams with total conception rates greater than 80% were compared to those with conception rates less than 80%.     

Associations of scrotal circumference with semen traits in young beef bulls

Associations of percent live sperm, sperm number, sperm concentration, sperm motility, and potential breeding efficiency score with scrotal circumference were studied using data from the records of 465 Polled Hereford and 264 Simmental bulls. Data were subdivided by breed and within breed into three groups according to scrotal circumference (SC) size. Group I bulls had SC measurements <32 cm. Group II included bulls with SC measurements between 32 cm and the mean measurement of the breed (i.e., 35 cm for Polled Hereford and 38 cm for Simmentals). Group III was comprised of bulls with SC values above their respective breed averages. Age and body weight differences were also evaluated in the three groups. Average age differences among bulls in the three groups differed by not more than nine days in the two breeds. Average body weight differences among the three groups were statistically significant (P<0.05) with the maximum difference between any two groups within breed being 80 pounds. Average differences in percent live sperm and sperm number were greater (P<0.05) in Groups II and III than in Group I. For sperm concentration ratings, sperm motility ratings and potential breeding efficiency score, and for both breeds, Group I had a significantly lower (P<0.05) number of bulls classified satisfactory and a significantly greater (P<0.05) number of bulls classified unsatisfactory than did groups II and III.     

Use of the point-score system for breeding soundness examination in yearling Dorset, Hampshire and Suffolk rams

Performance tests were conducted on 583 purebred Dorset, Hampshire and Suffolk yearling rams at the Virginia Ram Test Station from 1986 to 1989. Birth dates at entry and weights (lbs) at entry and end-of-test were recorded for each ram. Entry and exit scrotal circumference (SC; cm) data were recorded for each year of the study. Breeding soundness examination (BSE) data at entry were obtained for only the last two years (1988-1989). The BSE followed the basic format recommended by the Society for Theriogenology. The number of seminal white blood cells per (100x) microscope field (WBC/LPF) were also recorded for each ram's ejaculate. Classification of rams into breeding groups (satisfactory, questionable and unsatisfactory) were made using a point-scale system based upon values obtained from SC, sperm motility and morphology assessments. Between-breed differences were noted for age at entry to the test station, weight per day of age, final weight at the end of the test period and average daily gain. Suffolk rams were younger in age (P0.05). Overall the percentage of rams classified as unsatisfactory, questionable and satisfactory was 11.8, 16.5 and 71.7, respectively. Rams with more than 10 WBC/LPF had significantly smaller SC at entry (P<0.01) than rams with less than 10 WBC/LPF. Most of the differences (75%) in BSE scores in this study were contributed by differences in semen quality (spermatozoal motility and morphology) not by differences in SC.     

The determination and correlation of reproductive parameters of performance-tested Hereford and Simmental bulls

Purebred Hereford and Simmental bulls (n = 120), managed similarly to bulls in the Ontario Bull Evaluation Program, were evaluated for reproductive parameters. Four diets, equivalent except for the form of dietary fiber, were fed in a growth performance trial. Diet had no direct effect (P > 0.10) on any of the reproductive variables examined. Of the 117 bulls that had complete breeding soundness evaluations, 75% were classified as satisfactory potential breeders, 24% as questionable potential breeders and 1% as unsatisfactory potential breeders. The 2 breeds were significantly different (P < 0.05) for several end of test parameters. When controlling for age and weight differences, Herefords had a higher backfat thickness, smaller scrotal circumference, lower paired testicular weight and lower epididymal weight. Semen morphology and motility did not differ (P > 0.10) between the breeds. When examining simple correlations, scrotal circumference was highly correlated with paired testicular weight, moderately correlated with epididymal weight, daily sperm production and extragonadal sperm reserves, and negatively correlated with backfat thickness. Scrotal circumference was not related to backfat thickness when controlling for breed effects. The degree of germinal epithelium loss was moderately and negatively correlated with the percentage of spermatozoa with normal morphology and progressive motility, epididymal sperm reserves and epididymal weight, but was not correlated with scrotal circumference.     

Relationship of testicular growth and size to age, body weight and onset of puberty in Menz ram lambs

Scrotal circumference as an index of testes size, along with body weight, wither height, heart girth and body condition score were measured fortnightly for 114 Menz ram lambs from weaning (91+/-7 SD days) until puberty, which was defined as age at first collection of an ejaculate with 50 x 10(6) spermatozoa and 10% motility. The animals were maintained on poor (n=28), low (n=29), medium (n=29) or high (n=28) levels of nutrition through grazing and supplementation. Further, half the lambs in each group were drenched for endoparasites. Daily gains in live weight, wither height, heart girth and scrotal circumference were 48.5+/-1.6 g, 0.05+/-0.01 cm, 0.07+/-0.01 cm and 0.07+/-0.03 cm, respectively for the period from weaning to puberty and varied with level of nutrition (P<0.05 to 0.001) but not with drenching or its interaction with nutrition level (P>0.10). Scrotal circumference increased linearly and was strongly correlated with age, body weight, wither height, and heart girth (r = 0.83 to 0.85, P<0.001), and lamb weight could be predicted by the equation: 6.35 + 0.53 scrotal circumference (R(2) = 0.73). Mean age, body weight and condition score at puberty were 288+/-6 days, 19.3+/-0.4 kg and 2.6+/-0.06, respectively, and varied due to season of birth, level of nutrition and weaning weight (P<0.01 to 0.001). The nutrition level also influenced (P<0.001) scrotal circumference at puberty, averaging 21.5+/-0.3 cm. It was concluded that postweaning nutrition management had a strong influence on lamb weight gain, which in turn was related to testicular growth and puberty onset in Menz ram lambs. The suitability of scrotal size measurement as a criterion for early selection of tropical ram lambs is emphasised.     

Scrotal dimensions and ejaculate characteristics of three breeds of sheep in tropical Nigeria

Scrotal circumference and semen characteristics of three breeds of sheep (Udda, Balami and Yankasa) indigenous to Nigeria and Southern Guinea Savannah zones of Africa were compared. The age, body weight, scrotal circumference and spermiogram of the rams were studied by standard techniques. The mean age, body weight, and scrotal circumference of the three breeds were not comparable with significant interbreed, but were with significant intrabreed differences. The mean ejaculate concentration of sperm cells (x 10 /ml) were: Udda, 3.8 +/- 0.050, Balami, 4.1 +/- 0.32, Yankasa, 4.5 +/- 0.11. The mean morphological sperm cell abnormalities for the Udda, Balami and Yankasa were; 7.5 +/- 2.1%, 4.5 +/- 0.58% and 6.0 +/- 0.87%, respectively, with significant inter- and intrabreed differences. There were significant intrabreed differences in the other semen traits, i.e., percent of live cells, percent of motility, mean volume and mean concentration. In all the breeds of sheep studied, the scrotal circumference and spermiogram were comparable to, and within the range reported for the exotic breed of rams.     

Testicular development, body weight changes, puberty and semen traits of growing guzerat and Nellore bulls

One hundred fifty-nine purebred Guzerat (8 to 110 months of age) and sixty Nellore bulls (8-30 months of age) were used in two trials to examine testicular development and consistency, body weight changes, puberty and semen traits. Scrotal circumference measurements and semen collections by electroejaculation were made every 28 d. At both trial locations, bulls were maintained under grazing conditions and fed commercial protein supplements (2 kg/head/day) during the dry season. Age and body weight affected (P<0.01) scrotal circumference in both breeds. Scrotal circumference increased (P<0.01) linearly with age and body weight. However, scrotal circumference tended to reach mature size more rapidly than did body weight in both Guzerat and Nellore bulls. Correlation coefficients between scrotal circumference and semen traits were positive (P<0.01) ranging from 0.49 to 0.73 in the two breeds, but were not significant for testicular consistency in either breed. Scrotal circumference and age at puberty of Guzerat and Nellore bulls averaged 25.6 +/- 2.2 cm at 18.0 +/- 2.0 mo and 23.6 +/- 0.2 cm at 18.5 +/- 2.7 mo, respectively. Nellore bulls were 42 kg lighter than Guzerat at puberty. Testicular consistency was not affected by either age of body weight (P>0.10) in these young bulls. The percentages of abnormal spermatozoa were higher (P<0.01) at 13 to 15 mo of age in Guzerat (11.1%) and Nellore (14.4%) bulls than at 22 to 24 mo (6.7 and 8.0%, respectively). These data indicate that scrotal circumference measurements can be a useful tool for selecting and improving semen traits of young Guzerat and Nellore bulls under tropical grazing conditions.     

Seasonal thyroidal activity and reproductive characteristics of Iranian fat-tailed rams

An experiment was conducted to study seasonal variations of thyroidal activity, serum testosterone concentration and seminal characteristics of two breeds of Iranian fat-tailed sheep. Eight 3 to 4-year-old rams of Ghezel and Mehraban breeds (4 rams/breed) were randomly selected from a flock of fertile rams. Semen was collected by using an artificial vagina, and blood samples were obtained via jugular vein. Seminal characteristics, scrotal length, width, and circumference, and blood parameters were measured at 3-week intervals. Time of the year significantly (P < 0.05) affected the volume of semen, sperm concentration, percent live sperm, percent normal sperm, total sperm number, seminal pH, seminal lactate dehydrogenase (LDH) concentration, scrotal circumference, scrotal width, and serum levels of testosterone, cholesterol, triiodothyronine (T(3)), tetraiodothyronine (T(4)), free T(4) index (FT(4)I), and TSH. Scrotal length was not affected by the time of sampling (P > 0.05). The effect of breed on the serum concentrations of hormones and cholesterol was not significant. Volume of semen, percent normal sperm, and total number of normal sperm were significantly (P < 0.05) higher in Mehraban but scrotal circumference, scrotal width and scrotal length were greater in Ghezel rams. Breedxtime interaction effect was significant for T(4), FT(4)I, sperm concentration, and total sperm number. The largest values for TSH, T(4), FT(4)I, testosterone, total sperm number, percent normal sperm, percent live sperm, sperm concentration, volume of semen and scrotal circumference were found from early summer to winter and the lowest values were recorded at the end of spring and in early summer. In both breeds, high and negative correlations (r = -0.7 to -0.8) were found between LDH levels in semen and percent live sperm, percent normal sperm and total sperm number (P < 0.01). It is unlikely that such variations in seminal quality would affect the fertility under natural mating.     

Genetic parameters of libido in Brazilian Nellore bulls

Genetic, environmental and phenotypic correlations between libido, testicular measurements, body weight and semen traits were estimated by multiple-trait-restricted maximum likelihood (MTDFREML) under animal models. Reproductive records, collected from 1992 to 1997, of 288 Nellore bulls were used. Estimates of heritability for libido unadjusted, adjusted for scrotal circumference and adjusted for body weight, were 0.34 +/- 0.10, 0.31 +/- 0.10, and 0.19 +/- 0.11, respectively. Genetic correlations between libido and body weight, scrotal circumference, testis length, testis width, testis volume and testis consistency were, respectively, 0.69, -0.43, -0.31, -0.16, 0.10, 0.87, and between libido and semen volume, sperm motility, vigor, gross motility, major, minor and total defects were, respectively, 0.71, 0.51, 0.12, 0.16, 0.31, 0.26 and 0.43. Results suggested that selection for libido would be effective and that it would lead to desirable correlated response for scrotal circumference, physical and morphological semen traits and undesirable correlated response in body weight.     

Seasonal variations in testicular consistency,scrotal circumference and spermiogramme parameters of extensively reared Brahman (Bos indicus) bulls in the tropics

Twenty-five mature Brahman (Bos indicus) extensively reared breeding bulls were clinically examined and electroejaculated at monthly intervals for 13 months to study if testicular consistency (TC), scrotal circumference (SC), sperm motility and morphology show seasonal variation under tropical conditions. Changes in SC were positively related to body condition (BC) (beta = 0.7 cm, P < 0.001) and age (P < 0.01). These changes were, however, not associated with deviations in TC, sperm motility or morphology (P > 0.05). Sperm motility was higher in samples collected during the breeding season than in samples collected at other times (62 versus 52%, LSM, P < 0.01). The frequency of bent tails with cytoplasmic droplet entrapped fluctuated between monthly ejaculates, (LSM range 3-21%, P < 0.05). However, there was no relationship between these fluctuations and environmental temperature, rainfall or changes in BC, TC or SC of the bulls (P > 0.05). Other sperm abnormalities did not change significantly during the study period. The absence of a relationship between any of the climatic variables studied and SC, TC and sperm motility or morphology, respectively, indicates that temperature is not a main factor influencing reproductive performance in Brahman bulls in the tropics. On the contrary, the changes found in BC followed by variations in SC suggest that nutrition may be a major factor affecting seasonal variations in male reproductive parameters, especially testicular size, in these sires.     

Spermatozoa output, testicular sperm reserve and epididymal storage capacity of the Red Sokoto goats indigenous to northern Nigeria

Fifteen Red Sokoto goats (bucks) aged 2 to 2 1 2 years with a mean body weight of 17.80+/-1.24 kg were used for studying daily spermatozea output, testicular and epididymal sperm reserves. Semen ejaculates were obtained from each buck and evaluated daily for six weeks. Semen characteristics were as follows: volume, 0.72+/-0.91ml; colour, milky/creamy; sperm concentration/ml, 0.61+/-0.05 x 10(9); mass motility, 3.80+/-0.33; individual metility, 77.50+/-5.60; and normal sperm morphology, 80.00+/-10.50. Mean scretal circumference was 21.80+/-0.29. Mean testicular and spididymal (capita, corpora and caudas) weights (gm) were 83.74+/-5.33, 7.27+/-0.63, 2.22+/-0.23 and 6.13+/-0.73 respectively. Corresponding sperm reserves were 44.32+/-5.79, 8.82+/-1.95, 4.99+/-0.86 and 45.64+/-7.87 x 10(9). Scrotal circumference was positively correlated to testicular weight (r = 0.86), testicular spermatids (r = 0.77), and caudas spermatozoa (r = 0.83).     

Reproductive patterns of stray male dogs in the tropics

Two studies were performed to determine annual reproductive patterns in stray male dogs in the tropics. In Study 1, four dogs housed individually outdoors were monitored once monthly for 12 months, including collection and assessment of semen, measurements of scrotal width, and determination of serum testosterone and prolactin concentrations. In Study 2 (conducted concurrently), a single blood sample (for serum testosterone concentration) was collected from 220 clinically healthy dogs, and after euthanasia, scrotal width and morphology of epididymal sperm were determined. The year was divided into three seasons: warm-dry (March to June); warm-humid (July to October) and fresh-humid (November to February). In Study 1, scrotal width, ejaculate volume, sperm count and motility were significantly lower during the fresh-humid season and sperm midpiece abnormalities were significantly more common during the warm-humid and fresh-humid seasons. Serum testosterone concentrations remained constant during the year. Prolactin concentrations did not differ significantly among seasons, but had a well-defined increase from the beginning of March to the end of August. In Study 2, sperm morphology was similar to in Study 1 and serum testosterone concentrations varied nonsignificantly during the year. Environmental factors, e.g. daylength may have influenced circannual changes in prolactin secretion. Seasonal variations in some reproductive tract and seminal traits were significant but of small magnitude and the percentage of morphologically normal sperm did not vary significantly among seasons. In conclusion, healthy male dogs constantly produced sperm and were apparently fertile throughout the year.     

Scrotal circumference does not accurately predict degree of germinal epithelial loss or semen quality in yearling Hereford and Simmental bulls

The accuracy of scrotal circumference as a predictor of specific pathologic changes within testicular parenchyma was assessed by scoring 121 Hereford and Simmental bulls for scrotal circumference, degree of germinal epithelial loss and semen quality. Scrotal circumference was not linearly related to the degree of germinal epithelial loss or to the percentage of tubules (Grade 4+ or higher, no germinal epithelium) for either breed (P > 0.1). Thirty-two centimeters was the minimal acceptable scrotal circumference to ensure both a low prevalence of tubules with irreversible loss of germinal epithelium and acceptable semen quality. Scrotal circumference had a positive predictive value (the proportion of test-positive animals truly diseased) of 0.07 (95% confidence interval [CI] of 0 to 0.29) and a specificity (the proportion of test postive individuals that are diseased) of 0.89 (95% CI of 0.83 to 0.95) for 25% Grade 4 + tubules. For acceptable semen morphology (>/= 75% morphologically normal spermatozoa), scrotal circumference had a positive predictive value of 0.08 (95% CI of 0 to 0.34), a sensitivity (the proportion of diseased individuals testing positively) of 0.06 (95% CI of 0 to 0.24), and a specificity of 0.88 (95% CI of 0.80 to 0.95). For acceptable sperm motility (>/= 30% progressively motile spermatozoa) scrotal circumference had a positive predictive value of 0.0 (95% CI of 0 to 0.22), a sensitivity of 0.0 (95% CI of 0 to 0.15), and a specificity of 0.87 (95% CI of 0.80 to 0.94). Although scrotal circumference is widely accepted as a useful test, its accuracy should be recognized as low when 32 cm is used as the minimal acceptable scrotal circumference in predicting unacceptable testicular histology or unacceptable semen quality in a healthy population of yearling bulls.     

Peripubertal traits of Brahman bulls in Yucatan

In order to investigate elements of puberty in Brahman (Bos indicus) bulls, 12 animals were studied from 10 mo of age until puberty, which was defined as the moment of production of the first ejaculate with at least 50 x 10(6) sperm with 10% progressive motility. Body weight and scrotal circumference were recorded every 2 weeks. From 14 mo of age onwards, the bulls were electroejaculated at the same intervals and ejaculates were evaluated. Blood samples were taken from 6 of the bulls every 30 min for 6 h at 12, 14, 17 and 20 mo of age to study serum concentrations of testosterone, which were determined by RIA. Mean age (+/- SEM) at puberty was 17 +/- 0.4 mo, body weight was 374.6 +/- 22.5 kg and scrotal circumference was 28.6 +/- 0.6 cm. Serum testosterone increased from 12 to 17 mo and then decreased slightly, mean (+/- SEM) concentration being 0.4 +/- 0.1, 1.4 +/- 0.4, 2.9 +/- 0.5 and 2.7 +/- 0.3 at 12, 14, 17 and 20 mo of age, respectively. It was concluded that Brahman bulls, under the conditions studied, attain puberty between 16 and 17 mo of age, with considerable variation, and that serum concentrations of testosterone prior to puberty seem to form a pattern similar to that shown by Bos taurus bulls, however the pattern occurs at a later age.     

Correlation of in vivo testicle and seminal vesicle size with post mortem dimensions in bulls

This study was conducted to quantify the relationships between in vivo measurements of testicular and seminal vesicle size and post mortem size of these organs in 30 Santa Gertrudis bulls. The in vivo measurements of testicles were obtained by transrectal ultrasonography and palpation per rectum, while scrotal circumference was measured by scrotal tape. Linear post mortem dimensions were obtained by direct measurements of the excised organs. Volume was assessed by water displacement while the testicles were weighed. Seminal vesicle length, determined by palpation, had the highest correlation with post mortem measurements (r = 0.70; P = 0.0001). Accurate estimation of the thickness of the vesicles (1.47 vs 1.55 cm for in vivo and post mortem, respectively) was performed by ultrasonograph. Of all seminal vesicle linear measurements, width had the highest correlations with volume measured by water displacement (r = 0.67; P = 0.0001 and r = 0.38; P = 0.04 for post mortem and in vivo, respectively). Testicular diameter was accurately measured by ultrasonography (5.54 vs 4.58 cm in vivo and post mortem, respectively) and was highly correlated (range r = 0.84 to 0.89; P = 0.0001) with post mortem measurements of testicular volume, weight and circumference. The correlation between scrotal circumference and diameter of the testicle was 0.75 (P = 0.0001). The correlations of testicular diameter measured by ultrasound with the post mortem measurements of testicular weight and circumference were similar to the correlations between scrotal circumference and those 2 post mortem measurements. We conclude that palpation of vesicle length is highly correlated with volume of the seminal vesicle in situ. Individual linear measurements do not seem to be an accurate predictor of the relativ size of the seminal vesicle. Furthermore, ultrasonography does not seem to be a more accurate measure of testicular size than scrotal circumference for evaluation of breeding soundness.     

Effects of ultrasonography on the bovine testis and semen quality

Ten yearling beef bulls were assigned to control (n = 5) or ultrasound treatment (n = 5) groups. Treatment consisted of a single 3-min exposure per testis to ultrasonic radiation at a frequency of 5 MHz and at low acoustical intensity (spatial peak temporal averages at 10 and 18 mm, focal points of 0.14 and 0.59 mW/cm(2) and spatial peak pulse averages of 1.1 and 3.4 W/cm(2) at corresponding focal points). Ultrasonic treatment had no effect (P > 0.05) on the percentage of progressively motile spermatozoa, primary sperm defects, secondary sperm defects or normal acrosomes over a 10-wk posttreatment evaluation period. Similarly, scrotal circumference, testicular consistency, paired testes weight, paired epididymal weight, daily sperm production per gram of testicular parenchuma, and epididymal sperm reserves were not affected (P > 0.05) at 69 d following ultrasound treatment. Ultrasonography of bovine scrotal contents did not affect reproductive capacity over the interval studied.     

Effect of growth rate from 6 to 16 months of age on sexual development and reproductive function in beef bulls

Sexual development and reproductive function were studied in 22 Angus × Charolais and 17 Angus bulls from 6 to 16 mo of age. Associations of average daily gain (ADG) and body weight with ages at puberty and at maturity (satisfactory semen quality), scrotal circumference, paired-testes volume and weight, testicular vascular cone diameter and fat thickness, scrotal temperature, sperm production and morphology, and testicular histology, were determined. There were no significant correlations between cumulative average daily gain and any of the end points investigated. Body weight at various ages was negatively correlated with ages at puberty and maturity in Angus × Charolais bulls, positively correlated with paired-testes weight in Angus × Charolais and Angus bulls, and positively correlated with seminiferous tubule volume in Angus bulls (P < 0.05). Semen quality improved gradually with age and the interval between puberty and maturity (mean ± SD; 309.4 ± 29.7 and 357 ± 42 days of age) was approximately 50 days. Age, weight, scrotal circumference, and paired-testes volume were all good predictors of pubertal and mature status, with moderate to high sensitivity and specificity (71.6% to 92.4%). In summary, growth rate between 6 and 16 mo of age did not affect sexual development and reproductive function in beef bulls. However, greater body weight at various ages was associated with reduced age at puberty and maturity, and with larger testes at 16 mo of age, indicating that improved nutrition might be beneficial, but only when offered before 6 mo of age. Average daily gains of approximately 1 to 1.6 kg/day did not result in excessive fat accumulation in the scrotum, increased scrotal temperature, or reduction in sperm production and semen quality, and could be considered “safe” targets for growing beef bulls.     

Gonadal and extragonadal sperm reserves in Boran and Boran x Friesian bulls raised on two planes of nutrition in the Highlands of Ethiopia

Gonadal and extragonadal sperm reserves were determined in testicular and epididymal tissues obtained from Boran (n=10) and Boran x Friesian (n=12) bulls fed either a high or low plane nutrition diet for a 1-year period. The bulls were 32 months of age at castration. Mean (+/-SEM) daily body weight gains over a 1-year period were 776+/-34 and 264+/-34 g/day (P<0.001) for bulls on high and low nutrition, and their respective body weights at castration were 458+/-17 and 276+/-17 kg (P<0.01). Mean body weights did not differ between Boran and Boran x Friesian bulls. Mean scrotal circumference measurements were 32.1+/-0.6 and 28.8+/-0.6 cm for the high and low planes of nutrition (P<0.01) and 31.8+/-0.7 and 29.2+/-0.6 cm for the Boran and the Boran x Friesian bulls (P<0.05). Paired testes and epididymal weights averaged 432+/-22 and 313+/-22 g (P<0.01) and 46.3+/-2.0 and 32.5+/-2.0 g (P<0.001) for bulls on the high and low planes of nutrition, respectively. Boran x Friesian bulls had significantly heavier (P<0.05) testes, but epididymal weithts did not differ between breeds. Although daily sperm production per gram was not influenced by either plane of nutrition or breed, daily sperm production differed between high (5.3 x 10(9)) and low nutrition (2.9 x 10(9)) bulls (P<0.001) and between Boran (4.6 x 10(9)) and Boran x Friesian (3.5 x 10(9)) bulls (P<0.01). Extragonadal sperm reserves were significantly higher in high than in low nutrition bulls (13.1 x 10(9) vs 6.9 x 10(9); P<0.001) and in Boran than Boran x Friesian bulls (12.9 x 10(9) vs 7.1 x 10(9); P<0.01). The cauda epididymis contributed 50 to 54% to the total epididymal sperm reserves. It was concluded that the plane of nutrition influenced growth rates and testes and epididymal weights, and it improved gonadal and extragonadal sperm reserves in young Boran and Boran x Friesian bulls.     

Effects of dietary gossypol on aspects of semen quality, sperm morphology and sperm production in young Brahman bulls

Eight young reproductively normal Brahman bulls (average age and bodyweight 20 months and 500 kg, respectively) received either cottonseed meal delivering 8.2 g free gossypol/bull/d (treatment group, n=4) or soybean meal (control group, n=4) for 12 wk. After adjustment (1 wk), weekly procedures (11 wk) included blood collection, scrotal circumference measurement and electroejaculation. Semen assessments included sperm motility, percentage of live spermatozoa, general sperm morphology (using brightfield microscopy), and midpiece morphology (using DIC microscopy). After sacrifice (Week 12), sperm production rates (daily and per gram testicular parenchyma) were determined. Treated bulls did not differ from controls in scrotal circumference or the percentage of live spermatozoa. Sperm motility differed at Weeks 9 (P<0.05), 10 and 11 (both P=0.06). Treated bulls had fewer normal spermatozoa at Weeks 5 (P<0.05), 6 (P<0.01) and 7 thru 11 (P<0.001). Beginning from Week 3, treated bulls showed an increased proportion of sperm midpiece abnormalities (P<0.05) which stabilized at 52 to 62.5% between Weeks 5 and 11 (P<0.01 or P<0.001). Treated bulls also had lower sperm production than untreated bulls, both on a daily (P<0.01) and per gram testicular parenchyma (P<0.001) basis. A cottonseed supplement providing 8.2 g of free gossypol per bull per day had adverse effects upon both sperm morphology and spermatogenesis in young Brahman bulls, with the former being first evident within 3 to 4 weeks of feeding of cottonseed meal.     

Reversibility of the reproductive toxicity of gossypol in peripubertal bulls

Gossypol has been shown to impair sperm production in male ruminants. The purpose of this study was to determine if the adverse effects of gossypol on spermatogenesis in peripubertal bulls were reversible. Twenty-eight crossbred Angus bulls were allocated into treated and control groups at 11 months of age. For 8 weeks, treated bulls were fed a ration containing 8 mg of free gossypol per kilogram of body weight per day while control bulls were fed a soybean meal ration free of gossypol. At 28-days intervals, scrotal circumference was measured and semen collected to assess sperm motility and morphology. Seven control and seven treated animals were castrated 56 days after the start of the experiment and the testes were examined histologically. The remaining bulls were fed a gossypol-free diet for 210 days prior to castration. There were significant increases in primary and secondary sperm abnormalities in treated bulls 28 and 56 days after gossypol feeding. The number of sperm with proximal droplets was significantly higher in gossypol-treated bulls, suggesting testicular degeneration. There was no significant effect on the sperm motility, scrotal circumference, or histopathological characteristics of the testes. Four weeks after the end of gossypol feeding, primary and secondary abnormalities were still increased in gossypol-treated bulls, however in subsequent collection periods the percentage of abnormalities were similar between groups. At 210 days, there was no treatment effect on scrotal circumference, and histological characteristics of the testes were not different between groups. The deleterious effects of gossypol on the morphological characteristics of spermatozoa were reversible. Gossypol (8 mg/kg per day for 56 days) increased sperm abnormalities but the effects were reversible.