Breed-type effects on fertility traits of young bulls

Measures of fertility in young beef bulls (N=76) representative of divergent breeds and F₁ crosses were evaluated. Breed-types were straightbred Hereford and Red Poll, Hereford × Red Poll reciprocal crosses, Angus × Hereford, Angus × Charolais, Brahman × Hereford and Brahman × Angus.There was evidence of significant breed-type variation in scrotal circumference and total testicle weight, although differences were less pronounced when animal weight was taken into account. Scrotal circumference in Brahman × Hereford bulls was less (P<.05) than straightbred Hereford, Red Poll × Hereford and Angus × Hereford crosses at 8 months of age. However, at 13 months there was no difference in scrotal circumference measurements of Brahman × Hereford, Red Poll × Hereford and Angus × Hereford crosses, and all three crosses exceeded (P<.05) straightbred Herefords. Breed-type differences in semen score and presence of normal, mature sperm in the seminiferous tubules at 13 months of age approached significance at the .10 probability level. Heterosis effects on bull fertility characteristics were insignificant when body weight was included as a covariate in the analyses.     

The seasonal fertility of North American bison (Bison bison) bulls

The objective of this study was to determine the presence and magnitude of seasonal fluctuations in semen quality and other reproductive indices in bison bulls. Testicles from 288 commercially slaughtered bison bulls were collected monthly over a 1-year period. Carcass and testicle weight were determined and measurements of seminiferous tubule lumen, diameter, and epithelial thickness were made. Sperm cell morphology and defects were described and quantified using epididymal semen from each testicle. Twenty-one Plains (Bison bison bison) and Wood bison (Bison bison athabascae) breeding bulls, averaging 6.0 years of age (range 2.5-8.0), from three farms were selected for semen collection and evaluation on the basis of producer co-operation. Semen was collected by electro-ejaculation on four seasonal occasions during a 12-month period. Ejaculate quality was judged on the basis of volume, density, gross and individual motility, morphology, live/dead ratio, and concentration. Sperm cell morphologies were evaluated microscopically and classified according to criteria used for bovine semen. Fecal testosterone was measured at each semen collection using a commercial competitive binding radioimmunoassay. There was an increase in carcass weights over the study period and testis weights were moderately correlated (r=0.44) with carcass weights. However, mean testes weights were heavier (P<0.05) in the summer than in winter, spring, or fall periods. There were no differences in the proportion of normal and abnormal epididymal sperm between seasons but there were seasonal changes in the testicular parenchyma. Seminiferous tubule and lumen diameter, and epithelial thickness were greatest (P<0.05) in summer. Live bulls gained weight between April and November, but lost weight over the winter. Normal sperm cell percentages as well as individual sperm cell motility in electro-ejaculated sperm samples were higher (P<0.05) at the pre-breeding collection relative to other collections, but no change in sperm cell concentrations occurred over the study period. Fecal testosterone concentrations were highest at the pre-breeding period (June) but decreased (P<0.05) in each subsequent collection to reach their lowest levels in the April. While many changes in seen characteristics were not significant, overall results indicate the presence of some reproductive seasonality and increased testicular capacity in the summer breeding season. Bulls showing marginal semen quality in the winter but otherwise carrying desirable genetic traits may warrant another evaluation in late spring prior to being culled from a breeding program.     

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.     

Nutritional influences on growth and onset of puberty in Boran and Boran x Friesian bulls in Ethiopia

Twenty-seven Boran and 37 Boran x Friesian crossbred bulls were weaned at 6 months of age and randomly assigned to either a dry season supplementary feed containing 16% crude protein or control groups. Data were collected on body weight, wither height and scrotal circumference (SC) at monthly intervals. Bulls were also challenged with 100 mug of gonadotropin releasing hormone (GnRH) at 2-month intervals and plasma testosterone responses were determined. Semen was collected at monthly intervals by electroejaculation. Post weaning average daily weight gain was significantly (P<0.001) higher in supplemented than in control groups (302 vs 208 g/day). Scrotal circumference growth rates were also significantly (P<0.001) higher in supplemented than in control bulls (0.38 vs 0.31 mm/day). Bulls fed supplemented diets were younger (430 vs 473 days; P<0.001) and heavier (217 vs 203 kg; P<0.05) and had better semen quality at puberty than the control bulls. There was a trend for larger SC at puberty in supplemented than in control bulls (P=0.06). There were no significant differences in wither height or in testosterone response to GnRH at puberty between supplemented and control bulls. Body and SC growth rates to puberty for Boran and Boran x Friesian bulls were 189 and 321 g/day (P<0.001) and 0.27 and 0.42 mm/day (P<0.01), respectively. Boran bulls were older (513 vs 406 days; P<0.01) and lighter (201 vs 215 kg; P<0.05), and had smaller SC (23.9 vs 26 cm; P<0.01) at puberty than Boran x Friesian bulls. Testosterone responses to GnRH increased (P<0.001) with age and were significantly higher (P<0.05) in supplemented and in Boran x Friesian bulls than in control and Boran bulls. Wither height, testosterone response to GnRH and semen quality at puberty did not differ between breeds. Dry season supplementation improved growth rate and enhanced sexual development and maturity in both Boran and Boran x Friesian bulls, and would be a useful management strategy for enhancing fertility in bulls in the tropics.     

The relationship between scrotal circumference and quantitative testicular traits in yearling beef bulls

A study was designed to investigate relationships between testicle size and histological, sperm production and endocrinological traits in yearling beef bulls at the end of performance test. Twenty-five beef bulls, (Hereford, n=16; Angus, n=4; and Charolais, n=5), with scrotal circumference (SC) measurements ranging from 28.5 to 36.0 cm, were used. Just prior to slaughter at 15 mo of age, SC measurements were taken, semen was collected, and a GnRH response test was conducted. Testicles were processed for daily sperm production (DSP), epididymal sperm reserves (ESR), seminiferous epithelial area (SEA), and degree of germinal epithelial loss (DGEL). There were significant positive correlations between SC and testicular weight (P<0.05), DSP/g (P<0.02), and DSP/bull (P<0.01) and ESR (P<0.01); however, the correlation between SC and SEA was not significant (P=0.4). Scrotal circumference was negatively correlated with DGEL (P<0.05). Degree of germinal epithelial loss was also negatively correlated with DSP/g, DSP/bull and ESR (P<0.01). Morphological characteristics of spermatozoa were diversely related to sperm production traits, and the percentage of normal spermatozoa was positively related to SC (P<0.02) and negatively related to DGEL (P<0.001). Gonadotropin releasing hormone stimulation did not reveal evidence of gonadotropin deficiency in any of the bulls. However, peak testosterone levels were lower in bulls with SC below 31 cm (P<0.05) than those with SC measurements above 31 cm.     

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.     

Ultrasonographic examination and measurement of ram testicles

Ten adult rams were used in a study to compare ultrasonographic and physical measurements of testicles. Scrotal circumference measurements were correlated with both physical and ultrasonographic measurements and with semen analysis results. Scrotal circumference correlated well with most of the physical and ultrasonographic measurements and with semen motility and percent abnormalities. Ultrasonographic measurements correlated with scrotal circumferences but not with the semen analysis. There were significant differences in physical and ultrasonographic measurements of testicle circumference and diameter, especially when the ultrasonographic measurements were made through the intact scrotal wall. There appear to be problems in the accuracy of ultrasonographic measurements of testicle size in rams.     

Thermoresistance sperm tests are not predictive of potential fertility for cryopreserved bull semen

Different studies demonstrate positive correlations between seminal variables determined in the laboratory and subsequent fertility after artificial insemination. It is clear, however, that there is still a deficiency in predicting in vivo fertility results of semen samples. The present study intended to verify the efficiency of rapid and slow thermoresistance tests in predicting fertility of frozen semen of bulls. Sperm from 64 ejaculates of 39 Nelore bulls (Bos indicus), aged 2-10 years, were cryopreserved in 0.5 mL straws. Thawed straws containing 30 x 10(6) sperm were analyzed for seminal variables in the laboratory and used to inseminate 4920 cows to evaluate fertility in the field. The ejaculates were frozen in a Tris-based extender and samples were evaluated for total motility after rapid (46 degrees C/30 min) and slow (38 degrees C/5h) thermoresistance tests by conventional and computerized (CASA) methods. Sperm samples were grouped according to their ability to retain motility after thermoresistance testing: group 0 (0% motility), group 1 (1-20% total motility), group 2 (21-40% total motility) and group 3 (>40% total motility). Correlation and association between these groups and fertility diagnosed by rectal palpation at 90 days were verified. Chi-square test demonstrated no association between motility groups and fertility (P>0.25) and both rapid and slow thermoresistance tests had a lesser correlation to fertility (r=0.11 and 0.14, respectively). These results demonstrated that these tests are not reliable in predicting in vivo behavior of bull frozen semen and are not effective to estimate fertility.     

Inoculation of bulls with bovine virus diarrhea virus: Excretion of virus in semen and effects on semen quality

Bovine virus diarrhea (BVD) virus was inoculated into 9 bulls. Semen samples were collected to determine if BVD virus could be isolated from semen and to determine if the virus affected semen quality. The reproductive tracts of 6 bulls were recovered following slaughter and subjected to virus isolation procedures and histologic examination.BVD virus was detected in 4 of 98 semen samples following inoculation. The virus was also recovered from the testicle of one bull following slaughter. Inoculation of BVD virus into bulls did not affect semen quality and did not cause gross or microscopic lesions in the reproductive tract. This experiment indicates that following inoculation of BVD virus into bulls, the virus may be shed in the semen. However, the probability of this occurring is low.     

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.     

Assessment of the fertilizing potential of frozen bovine spermatozoa by in vitro induction of acrosome reactions with calcium ionophore (A23187)

The relationship between nonreturn rates of bulls in a commercial artificial insemination program and in vitro induction of acrosome reactions in frozen-thawed spermatozoa by the calcium ionophore, A23187, was investigated. Washed spermatozoa from 3 to 5 ejaculates, collected from each of 23 Holstein bulls, were incubated for 1 h with 1 microM A23187. Acrosome reactions were determined by fluorescence microscopy. The percentage of increase in acrosome reaction in the ionophore-treated compared with control samples was significantly correlated to the 90-d nonreturn rate of the bulls (r = 0.86; P < 0.001). In a second experiment, a significant correlation was obtained between the fertility of bulls predicted on the basis of induced acrosome reaction and achieved 90-d nonreturn rate (r = 0.84; P < 0.005). No other assessments of semen quality (post-freezing motility, percentage of morphologically normal spermatozoa) was significantly correlated with fertility. Finally, the regression between acrosome reaction induction obtained from young bulls was used to predict the fertility of mature bulls whose semen was in widespread use (actual versus predicted nonreturn rate, r = 0.88; P < 0.0001).     

Effect of reducing sperm concentration during IVF on the ability to distinguish between bulls of high and low field fertility: work in progress

The objectives of this study were to evaluate the effect of sperm dose and sire on the fertilization rate, cleavage rate and blastocyst yield following insemination in vitro, to examine the relationship between these parameters and field fertility in cattle, and to examine the relationship between blastocyst quality and sire used in IVF. Frozen semen from four bulls with 150-day nonreturn rates ranging from 57 to 78% was used. In Experiment 1, oocytes were inseminated with sperm from one of the four bulls at concentrations ranging from 0.016 to 0.5 x 10(6)sperm/ml. A proportion of presumptive zygotes were fixed at 17 h post-insemination (hpi), while the remainder was transferred to in vitro culture (IVC) in droplets of synthetic oviduct fluid (SOF). Cleavage at 48 hpi and the percentage of oocytes reaching the blastocyst stage by Day 8 were recorded. In Experiment 2, to assess blastocyst quality, after insemination with semen from one of the four bulls, presumptive zygotes were cultured in SOF until Day 7. Blastocysts for each bull were removed and vitrified/warmed and survival was recorded at 24, 48 and 72 h after warming. Regardless of bull used, a concentration of 0.125 x 10(6)sperm/ml or above resulted in higher blastocyst yields than any lower concentration used. Fertilization and cleavage rates were also higher at higher sperm concentrations. The best predictor of field fertility was fertilization rate at a concentration of 0.5 x 10(6)sperm/ml (r=0.94, P<0.0001). There was also a significant correlation between cleavage rate at a concentration of 0.5 x 10(6)sperm/ml and nonreturn rate (r=0.90, P<0.0001). In Experiment 2, blastocysts derived from one bull, HTA, were of superior quality as measured by survival 24h after thawing, although these differences were less significant at the subsequent time points measured. In conclusion, these data show that differences between the field fertility of bulls can be determined at sperm concentrations routinely used in IVF. Lowering the sperm concentration does not increase the likelihood of optimizing the differences in fertility or cleavage rate between bulls of different field fertility. We have also demonstrated that the bull can have a significant effect on the quality of blastocysts produced using IVF techniques.     

Effects of the anabolic steroid, boldenone undecylenate, on certain reproductive parameters in bulls

A total of 17 bulls was used to study the effects of boldenone undecylenate on growth and semen characteristics in beef bulls. In trial 1 nine mature mixed-breed beef bulls with satisfactory semen quality were divided into two groups. Group I (n = 5) received boldenone undecylenate (1.1 mg/kg) at 21 d intervals for a total of seven treatments (147 d). Group II (n = 4) served as untreated controls. Semen was collected from each group by electroejaculation on each treatment day and evaluated according to the standards of the Society for Theriogenology. Although neither the percentage of spermatozoa with primary or secondary morphological abnormalities was different, the ejaculates of Group I bulls contained a higher percentage of abnormal spermatozoa than those in Group II. In trial 2, eight mixed-breed bull calves, average weight 140.4 kg, were maintained under drylot conditions in a single paddock. The bulls were divided into two equal groups. Group I (n = 4) received boldenone undecylenate as in Trial 1. Group II (n = 4) served as untreated controls. The bulls were weighed and the scrotal circumference (SC) was measured every 21 d until it reached 30 cm, at which time semen was collected and evaluated as in Trial 1. Group I bulls had a higher percentage of spermatozoa with primary morphological abnormalities than bulls in Group II. Group I bulls had a higher average daily gain (ADG) than Group II bulls and required 21 d longer for the SC to reach 30 cm. Semen quality for all bulls was satisfactory at each sampling day.     

Effect of different levels and sources of zinc supplementation on quantitative and qualitative semen attributes and serum testosterone level in crossbred cattle (Bos indicus x Bos taurus) bulls

An experiment was conducted on 16 crossbred bulls (about 2 years of age, 316.2+/-0.77 kg average body weight), divided into groups I, II, III and IV to study the effect of different levels of Zn supplementation from inorganic and organic sources on semen quality. The animals in the first 3 groups were supplemented with 0, 35 and 70 ppm Zn from Zn sulfate, respectively and the animals in-group IV were supplemented with 35 ppm Zn as Zn propionate. Semen collection and evaluation was done in the first month (to assess semen quality at the start of the experiment) and 7th, 8th and 9th month of experimental feeding to evaluate the effect of supplemental Zn on semen attributes. We gave 6 months for Zn feeding, so that 3 sperm cycles of spermatogenesis had passed and the collected semen reflected the complete effect of Zn supplementation. Six ejaculates from each bull were collected and evaluated for semen quantitative (ejaculate volume, sperm concentration and sperm number per ejaculate) and qualitative characteristics (semen pH, mass motility, individual motility, sperm livability percent and abnormal sperm percent, percent intact acrosome, bovine cervical mucus penetration test, hypo-osmotic sperm swelling test) and activity of seminal plasma enzymes i.e., alkaline phosphatase, acid phosphatase, GOT and GPT. Testosterone level in the blood serum of crossbred bulls was also estimated. Mean values of semen quantitative and qualitative characteristics at the start of the experiment were statistically non significant (P > 0.05) in all the crossbred cattle bulls, however, there were statistically significant differences among the bulls of different groups after 6 months of zinc supplementation. Mean ejaculate volume (mL) was 2.37, 4.70, 5.86 and 6.38, respectively in groups I to IV, indicating a statistically significant (P < 0.05) higher semen volume in Zn-supplemented groups as compared to the control group of bulls. Similarly, sperm concentration (million.mL(-1)), live sperm (%) and motility (%) were significantly (P < 0.01) higher in Zn-supplemented groups as compared to the control group. The results of BCMPT and HOSST revealed a significant improvement in sperm functional ability in all the groups supplemented with Zn as compared to the control group. The activity of alkaline and acid phosphatase in seminal plasma was significantly (P < 0.05) higher in the Zn-supplemented groups, whereas GOT and GPT activities in seminal plasma were significantly (P < 0.05) lower in the Zn propionate supplemented group as compared to the control group. Testosterone concentration (ng.mL(-1)) in blood serum was significantly higher in animals of groups III and IV, as compared to control group. It may be concluded that Zn supplementation either in the inorganic or organic form in the diet of crossbred bulls improved the qualitative and quantitative attributes of semen; however, the number of sperm per ejaculate, mass motility and semen fertility test like bovine cervical mucus penetration was significantly higher in bulls given Zn in an organic form (Zn propionate) as compared to an inorganic form (Zn sulfate).     

Effects of severe chronic scrotal Dermatophilus congolensis (kirchi) infection on semen characteristics in Zebu/Friesian crossbred bulls and effect of long-acting terramycin chemotherapy

The semen characteristics of 12 Zebu/Friesian crossbred bulls, aged 2 to 3 years, were studied during a 21-month period. At the 12th month of the study, the commencement of the rainy season, the bulls were infected naturally with Dermatophilus congolensis . Lesions were scattered over the body and limbs, but were particularly pronounced on the scrotum. Monthly treatments with injection of terramycin were begun as soon as lesions were detected and continued until the end of the study. The lesions worsened and became pronounced particularly on the scrotum of all the bulls. Scrotal scab formation caused by infection became prominent at the 14th month of the study. Until that period, the bulls had normal semen characteristics. From the 15th month until the end of the study, there was progressive deterioration of semen characteristics in all the bulls; this was manifested by some or all of the following effects: decreased volume, increased percentage of dead spermatozoa, increased percentage of total sperm morphological abnormalities, decreased percentage of progressively motile spermatozoa, oligospermia and terminal azoospermia. Therefore, severe chronic scrotal dermatophilosis may be a significant cause of infertility or sterility in bulls.     

Effect of dialysis or centrifugation on post-thaw motility and fertility of Santa Gertrudis bull semen collected by electroejaculation

Electroejaculated semen from Santa Gertrudis bulls was used to study the effect of centrifugation (600 x g for 5 min) or dialysis [molecular weight cutoff <14,000 Daltons (Da)] on post-thaw motility and on fertility in beef cattle. Analysis of post-thaw motility showed that the main effects (bulls and semen treatment) were significant (P<0.05). Dialysis significantly improved post-thaw motility in four of seven bulls. Initial volume of seminal plasma in the ejaculate was negatively correlated to post-thaw motility (r = -0.73). No significant improvement in post-thaw motility was observed for bulls with high volumes of ejaculate. In a fertility trial, calving rates of heifers synchronized with PGF(2)alpha and inseminated at 72 and 96 h after the second PGF(2)alpha injection with dialyzed or commercial semen were not statistically different (P>0.05; 54.4% vs 55.4%). These results show that dialysis could be used to improve post-thaw motility of electroejaculated bull semen without altering its fertilizing capacity. However, a high initial volume of seminal plasma seems to have a deleterious effect on sperm freezability that cannot be reversed by dialysis.     

Phenotypic relationships between hair whorl characteristics and spermatozoal attributes in Holstein bulls

The objective of this study was to characterize facial whorl characteristics in Holstein stud bulls (n = 485) and to investigate their association with measures of semen quantity and quality. Bulls had 1 (n = 454), 2 (n = 21) or no facial hair whorls (n = 5). Some 39% of bulls had whorls in the middle of their forehead, whereas 43% had whorls very low down on their forehead. Spiral whorls were present on 77% of bulls while 22% had elongated whorls. Abnormally shaped whorls were found more often on bulls with low whorls (27% versus 17%, P = 0.01) than on bulls with high or middle whorls. Semen production data were obtained from the AI center database to provide a representative sample of each sires most recent semen production characteristics. The number of semen collections per bull averaged 38 with a range of 1 (n = 9) to 272 (n = 1). The average number of days between collections was 5 but varied from 1 to 425 days. Average age of bulls at first recorded collection was 679 days and ranged from 307 to 4555 days. There were no significant differences between black and white bulls in semen quality or quantity. Semen quality over the summer months was reduced in comparison to the winter months. Age of the bull at time of collection had no effect on any of the semen quality traits. Older bulls had larger scrotal circumference and produced more semen (P > 0.01). Bulls with whorls located in the center of the forehead were not significantly different in semen quality or quantity for the 10 traits considered when compared to bulls with whorls located outside the center. In contrast to previous research findings with Angus cattle, semen attributes were not significantly different between bulls characterized with round (or spiral) epicenters and those with abnormally shaped whorls. The difference between the two studies may be due to the fact that Angus bulls have a higher percentage of abnormal elongated whorls compared to Holsteins.     

Pregnancy rate in cows and heifers bred to bulls selected for semen quality

A two-year study was conducted to compare fertility in cows or heifers bred to either an unselected group of bulls or bulls selected for semen quality. An improvement of 5% in pregnancy rate was found the first year in 591 cows bred to bulls having 80% or more normal sperm, compared to the 656 cows bred to a group of bulls representative of the original population (original group). A similar difference in pregnancy rate was noted the second year between 1179 heifers bred to the original group of bulls and the 522 heifers bred to bulls having 80% or more normal sperm and the 769 heifers bred to bulls with 70% or more normal sperm.