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Breeding soundness examination of 1, 952 yearling beef bulls in North Carolina
BREEDING
SOUNDNESS EXAMINATION OF 1,952 YEARLING BEEF BULLS IN NORTH CAROLINA
K.A. Bruner,la R.L. McGraw,' M.D. Whitacre,' and S.D. Van Camp' 'Department of Food Animal and Equine Medicine, North Carolina State University College of Veterinary Medicine, Raleigh, NC 27606 'Department of Animal Science, North Carolina State University, Raleigh, NC 27606 Received
for publication: September 15, 1994 Accepted: January 13, 1995 ABSTRACT
During a 12-yr period, breeding soundness examinations (BSE) were performed on 1,952 yearling bulls of 4 different breeds: Angus (n=852); Charolais (n=520); and (n=205); Polled Hereford Simmental (n=375). The yearling bulls had satisfactorily completed a record of performance test at 1 of 4 North Carolina test stations. The 1976 BSE the Society guidelines of for Theriogenology were used; however, semen analysis was not always conducted as determined by test station policy, and thus fewer bulls had a satisfactory score while more bulls had a questionable score when semen analysis was also performed. No statistical difference was observed in bulls scoring unsatisfactory between years with and without semen analysis. Overall, 85.2% were classified as satisfactory, 9.0% as questionable and 5.7% as unsatisfactory. The mean BSE score was 77.0. Simmental bulls had the largest mean scrotal circumference (SC), followed by Angus, Charolais and Polled Hereford bulls. Final test weight had the greatest effect on SC. Mean sperm motility score was 12.8, and mean total sperm abnormalities 24.9%. Penile fibropapillomas were diagnosed in 2.8% of the yearling bulls. The incidence rate of persistent frenulums was 4.4%. Angus bulls had the highest incidence of penile fibropapillomas and persistent frenulums. The incidence of persistent frenulums was greater (PcO.01) in ll-mo-old bulls than in 12- to 15-mo-old bulls. Breeding soundness examinations of ll- to 15-mo-old bulls provide valuable information for selecting bulls for breeding programs. Key words:
breeding soundness examination, beef bulls, yearling, persistent frenulums, penile fibropapillomas
Acknowledgements Funding provided by,the NCSU-CVM Department of Food Animal and Equine Medicine Veterinary Faculty Practice Plan. The authors thank Ms. A. Brown for assistance in data analysis. "Reprint requests: Dr. K.A. Bruner, 3160 Francis Road, Alpharetta, GA 30201.
Theriogenology 44129-l 45, 1995 0 1995 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0093-691X/95/$1 0.00 SSDI 0093-691 X(95)001 54-Z
Theriogenology
130 INTRODUCTION
The breeding soundness examination (BSE) is an established method for evaluating potential fertility in the bull. Guidelines published by The Society for Theriogenology in 1976 incorporated semen evaluation, scrotal circumference and physical examination into a complete scoring system(4). Classification of bulls as satisfactory, questionable orunsatisfactorypotentialbreeders was determined by scores for scrotal circumference (SC) and semen Moreover, bulls were classified as motility and morphology. questionable or unsatisfactory for any physical or reproductive abnormality regardless of their BSE score. The new guidelines for BSE in bulls were presented by the Society for Theriogenology in 1992. soundness The examination of yearling bulls for breeding enables the selection of prospective herd sires at a younger age than would otherwise be possible. Early elimination of undesirable bulls is economically beneficial and contributes to increased record-ofefficiency. The combination of a reproductive performance test and breeding soundness examination provides broad indication of an individual bull's potential as a herd sire. Selection of breeding males for superior genetic and reproductive traits accelerates the improvement of offspring performance and productivity(l8). The North Carolina Beef Cattle Improvement Program annually conducts record-of-performance testing of yearling beef bulls. An average of 226 bulls has been tested for performance each year for the past 12 yr. A total of 2,720 bulls representing 23 different breeds has been tested since 1980, with Angus, Charolais, Polled Hereford and Simmental breeds representing 2,536 of the 2,720 bulls under study. Since 1980, BSE conducted at the completion of the performance tests have been used to evaluate potential fertility. Bulls which satisfactorily met performance, conformation, musculoskeletal, temperament and reproductive criteria were sold as prospective breeding bulls. The bulls which did not pass the performance test were not examined for breeding soundness (n=584). Thus this study is based on 1,952 of the original 2720 bulls from the North Carolina Cattle Improvement Program that were examined for breeding soundness, representing the 4 major breeds: Angus (n=852), Charolais (n=205), Polled Hereford (n=520), and Simmental (n=375). The objectives of this report are to summarize the findings of the 1,952 examinations and to demonstrate that the BSE provides valid information for the selection of yearling bulls for breeding programs.
131
Theriogenology MATERIALS
AND METHODS
Bull Test Stations The North Carolina Beef Cattle Improvement Program has record-of-performance tests at different conducted 3 annual Tests at the Piedmont Research Station, locations in the state. Salisbury, North Carolina (Location l), and the Mountain Research Station, Waynesville, North Carolina (Location 21, were completed each of the 12 yr (1980 to 1991). The third test was originally from 1980 to 1983 conducted at Rocky Mount, North Carolina (Location 3) and then at Butner, North Carolina from 1984 to 1991 (Location 4). Bulls were consigned to test stations by breeders enrolled in the Beef Cattle Improvement Program or in similar programs. More than 95% of the bulls tested were from farms located in North A 21-d adjustment period was allowed prior to the start Carolina. of a 140-d test (1980 to 1987) or a 112-d test (1988 to 1991). The age range of the bulls at the start of the test was 7 to 11 mo and 11 to 15 mo at the end. Bulls at Location 1 were fed a dry ration containing 12% crude protein and 68% total digestible nutrients (TDN). Mixed grass hay was provided ad libitum. Bulls at Locations 2, 3 and 4 received a corn silage based ration containing 12% crude protein and 70% TDN ad libitum. A salt-mineral mixture was also available ad libitum to all bulls at each station. Breeding
Soundness
Examination
examinations (BSE) were performed Breeding soundness by veterinarians from North Carolina State University College of Veterinary Medicine. The examinations were conducted at test stations immediately following the completion of performance tests. All examinations were performed during December, January and February. Only those bulls which satisfactorily completed the performance tests were evaluated for breeding soundness. Methods of evaluating breeding soundness varied over the 12 yr because of policy changes at the test stations. The BSE procedure described by the Society of Theriogenology(4) was used to evaluate bulls in 1980 to 1982 (all stations); 1986 (Location 4); 1987 (Locations 1,4) ; and 1988 to 1991 (all stations) _ A total of 1,236 bulls (Angus, n=533; Charolais, n=127; Polled Hereford, n=313; and Simmental, n=444) was evaluated using the BSE procedure. Semen evaluations were not conducted in 1983 to 1985 (all stations); 1986 (Locations 1, 2); and 1987 (Location 2) due to a policy adopted by the governing committee of the bull testing program. Instead, breeding soundness was determined by scrotal circumference (SC), examination of the internal and external genitalia, and physical examination. A minimum SC of 30 cm and normal physical and genital examinations were required for passing A total of 716 bulls (Angus, n=319; Charolais, n=78; the BSE. Polled Hereford, n=207; and Simmental, n=112) was evaluated.
132
Theriogenology
The facilities for semen evaluation were different between the From first 3 yr (1980 to 1982) and the last 6 yr (1986 to 1991). 1980 to 1982, modified on-farm facilities were used for semen evaluation. Control of environmental conditions in the field A heated mobile laboratory unit was laboratories was difficult. acquired and used from 1986 to 1991. Semen was evaluated at room temperature using microscope slides warmed to 37OC and a heated microscope stage. Statistical
Methods
Data were analyzed by regression analysis using general linear models of a statistical analysis program(33). Least squares means The BSE were used to make comparisons between groups of data. sperm motility total sperm classification, BSE score, and abnormalities were analyzed for 1986 to 1991 due to the differences facilities between 1980 and 1982. Scrotal in laboratory and persistent fibropapillomas frenulums were circumference, analyzed for all 12 yr. The model used to analyze the data included station, year, breed of bull, age, average daily test, final weight, and final hip height.
the effects of weight gain on
RESULTS Due to differences in evaluation over the 12-yr period, the Data in the first segment results are presented in 4 segments. include SC and physical examination findings for all 12 yr. The second segment contains information on semen analysis for those years in which it was evaluated. The parameters included sperm motility, total number of sperm abnormalities and BSE score. The third segment presents BSE classifications for all 12 yr regardless of whether semen analysis had been performed. The fourth segment describes performance test observations. All Years
(1980 to 1991)
The mean SC was 36.0 cm for all breeds Scrotal circumference. Final weight (PcO.Ol), breed (PcO.Ol), year and all years. (P~0.01) and age (PcO.05) were sources of SC variation. Final weight was the most significant of all factors in the model and breed was second. Least squares means for SC by breed and age of bull are The SC of Simmental bulls was larger presented in Tables 1. (PcO.01) than that for Angus, Charolais, and Polled Hereford bulls. Scrotal circumference was a1s.o larger (PeO.01) for Angus bulls than Charolais, or for Polled Hereford bulls. The SC of 13- and 14-moold bulls was larger (PcO.01) than that of ll- and 12-mo-old bulls. A decline in least squares means for 15-mo-old bulls was observed; however, no significant difference was found between means for the 14- and 15-mo-old bulls. A gradual trend towards a smaller SC was
Theriogenology
133
observed over the 12-yr period, although the trend was not affected (P>O.O5) by age in months.
Table 1.
Least squares means for scrotal circumference and breed (1980 to 1991)
Bull breed
(SC) by age
Bull age (months)
Angus (n=852) Charolais (n=205) Polled Hereford (n=520) Simmental (n=375)
11 12 13 14 15
36.3" 35.lb 34.9b 36.8'
"-"Valueswithin a column that have different significantly different (P
(n=201) (n=556) (n=617) (n=467) (n=lll)
35.3" 35.6" 36.1b 36.1b 35.9ab
superscripts
are
Penile fibrooapillomas. The mean incidence of penile fibropapillomas was 2.8% for the years 1980 to 1991. Year and breed affected (P
Least squares means for the incidence of penile fibropapillomas by breed (1980 to 1991) Fibropapillomas Bull breed
Incidence
Angus Charolais Polled Hereford Simmental ",bValues within a column with different significantly different (PcO.05).
(%)
3.5" 1.2"b 1.4b 0.7b superscripts
are
134
Theriogenology
Persistent frenulums. For years 1980 to 1991 the incidence rate for persistent frenulums in all 4 breeds was 4.4%. Age affected (PcO.01) the prevalence of persistent frenulums and ll-moold bulls had more (PcO.01) persistent frenulums than any other age group. Least squares means of the incidence of persistent frenulums by age and breed are shown in Table 3. Both year and breed affected the incidence of persistent frenulums (PcO.05). Simmental bulls were observed to have a lower incidence rate than Angus (PcO.01) and Polled Hereford (PcO.05) bulls. Table 3.
Least squares means for the incidence of persistent frenulums by bull age and breed (1980 to 1991)
Persistent Breed
frenulums Incidence
Angus Charolais Polled Herefords Simmental
Persistent (%)
Age
(months) 11 12 13 14 15
4.9' 2.0* 4.0' 1.2b
a "bValues within column significantly different
with different (PcO.01).
frenulums Incidence
($1
10.5" 4.4b 3.lb 1.7b 1.9b superscripts
are
The testing station did not significantly affect the incidence of persistent frenulums when age was included in the model. Age, however, did account (PcO.01) for much of the variation in the incidence of persistent frenulums. For example, at Location 2 the average incidence rate was 4.4 and the average age was 12.1 mo, whereas at Location 4 the incidence rate was 1.9 but the average age was 13.7 mo. Years of Semen Evaluation
(1986 to 1991)
Soerm motility. The simple mean for sperm motility score was 12.8 (scale: 1 to 20) for the years 1986 to 1991. Total number of abnormalities had the greatest influence (PcO.01) on motility. Scrotal circumference (PcO.Ol), year (PcO.01) and testing station (P
135
Theriogenology
The simple mean for the percentage Total soerm abnormalities. of total abnormalities was 24.9 for all BSE classifications (scale of 0 to 100). Sperm motility was the most significant source of variation of total abnormalities. Motility, average daily weight gain, SC, year, final weight and test station influenced the percentage of total sperm abnormalities (P
Least squares means for breeding soundness score by year and breed (1986 to 1991)
Year
BSE score
1986 1987 1988 1989 1990 1991
81.3" 77.ObC 77. Gabc 77.ObC 78.8ab 75.1C
Breed
BSE score
Angus Charolais Polled Hereford Simmental
"-Values within a column with different significantly different (PcO.05).
examination
superscripts
78.2" 79.3" 75.7h 78.0"
are
A graph of the BSE score least squares means by age is presented in Figure 1. The BSE scores at 11 and 12 mo were lower than those at 13, 14 and 15 mo of age (P
For The 2 Different
Year Groups
The final BSE classifications for all years, years with and without semen analysis are shown in Table 5. There was a significant difference between years with semen analysis and the years without semen analysis in the percentage of bulls classified
136
Theriogenology
and questionable breeders. No significant as satisfactory difference was found in the percentages of unsatisfactory breeders between these 2 groups of years. When semen analysis was not performed, more bulls were classified as satisfactory and fewer bulls were classified as questionable breeders.
2
80
8
fJJ75 ti m 70
60 12
Figure 1
Table
5.
13 Monthsof Age
14
15
Least souares means for breeding soundness examination %alues with different (BSE) score (1986 to 1991). superscripts are significantly different (PcO.01).
Breeding soundness years examined
(BSE) classification
examination
by
BSE classification Years examined
% Satisfactory
All years (n=1952) Years with semen analysis (n=1236) Years without semen analysis (rk716)
% Questionable
% Unsatisfactory
85.2
9.0
82.0'
12.7'
5.3'
90.ab
2.7b
6.6'
@Values within a column with different significantly different (PcO.05).
superscripts
5.7
are
According to the 1976 BSE classification guidlines of the Society for Theriogenology(4) a c30-cm SC is unsatisfactory in bulls older than 12 mo of age. To assess the effects of raising the acceptable minimum to 32 cm, an additional analysis was
137
Theriogenology
conducted. Thus for the years with and without a semen analysis, bulls with a <32-cm SC were regarded as unsatisfactory potential breeders. The percentage of bulls classified as satisfactory was With a 32-cm minimum SC, recalculated for both groups of years. 76.8% of the bulls were classified as satisfactory breeders during years of semen analysis, and 73.9% of the bulls for years without Compared with the original BSE classifications, semen analysis. raising the minimum SC to >32-cm eliminated 5.3% more bulls in years with semen evaluation and 16.9 % more bulls in the years without semen analysis. Classification of breeding soundness by breed for the years with semen analysis and those without semen analysis are shown in Tables 6 and 7. More Simmental bulls were determined to be satisfactory breeders than any other breed during both sets of percentage of years. Charolais bulls received the lowest satisfactory classifications. Angus bulls were found to be satisfactory breeders more often than Polled Hereford bulls when semen was evaluated; however, when semen was not analyzed more Polled Hereford bulls were satisfactory. Table
6.
Breeding soundness examination (BSE) classification by breed for years with semen evaluation (1980 to 1982, 1986 to 1991) BSE Classification
Breed
% Satisfactory
Angus Charolais Polled Hereford Simmental
Table
7.
% Questionable
%Unsatisfactory
12.4 17.3 14.4 9.1
4.5 7.9 6.4 4.2
83.1 74.8 79.2 86.7
Breeding soundness examination (BSE) classification by breed for years without semen evaluation (1983 to 1987) BSE classification
Breed
with semen evaluation
% Satisfactory
Angus Charolais Polled Hereford Simmental
89.3 84.6 92.3 96.4
without
semen evaluation
% Questionable 3.1 5.1 2.4 0.0
%Unsatisfactory 7.5 10.7 5.3 3.6
138
Theriogenology
Analysis of variance for BSE classification for 1986 to 1991, when semen evaluations were conducted, showed primary abnormalities to be the most important factor in determining BSE classification. There were no significant effects of year, station, breed or age. When classified as satisfactory or as questionable or unsatisfactory, age affected (PcO.05) the assessed classification. Breed, station and year were not significant factors affecting classification of bulls as satisfactory or questionable/unsatisfactory breeders. Performance
Data
(1980 to 1982, 1986 to 1991)
End of test aqe. At the start of the test, the bulls were 7 to 11 mo of age and at the end they were 11 to 15 mo of age. The mean age at the end of the test was 13.1 mo. Least squares means showed that Simmental bulls were younger (PcO.01) than the other 3 breeds. There was no significant difference in least squares means for age among the other breeds. End of test heiqht. The mean final height at the end of the test was 52.4 inches. A gradual trend was observed over the 12-yr period toward larger-framed bulls. A difference (PcO.01) was seen between least squares means for 1980 (height=51.5) and 1991 Final weight, year, (height=53.9). breed, and test station affected the final height of the bulls (PcO.01). Least squares means for final height by breed are presented in Table 8. Simmental and Charolais bulls were found to be taller than Angus and Polled Hereford bulls (PcO.01). No differences were detected in final height between Charolais and Simmental bulls. Similarly, no differences were observed between Angus and Polled Hereford bulls. Table
8.
Least squares means for final height breed (1980 to 1982, 1986 to 1991)
Final height
and
Final weight
Breed
Inches
Breed
AWPS
51.7" 54.0b 51.6" 54.lb
Angus Charolais Polled Hereford Simmental
Charolais Polled Hereford Simmental
weight
a%alues within a column with different significantly different (PcO.01).
superscripts
Pounds 1193.7" 1166.7b 1206.0" 1178.4b are
by
139
Theriogenology
End of test weight. The mean final weight at the end of the test period was 1191.6 pounds. A gradual trend was observed over the 12-yr period toward lighter-weight bulls. Least square means for final weight by year indicates a difference (P
squares means for final weight by breed are presented in Polled Hereford were the heaviest bulls weighing more (P
In our study the mean SC of the 1,952 bulls was 36.0 cm, and was within the previously reported range of means (32.3 to 36.4 cm) for yearling bulls(9,11,12,15,28,29,3O,35). Simmental bulls had the largest mean SC, followed by Angus, Charolais, and Polled Hereford breeds. Similar findings by breed have been previously reported(10,14,17,23,24,34). By contrast, Cassady et al reported that yearling Angus bulls have larger SC than Simmental, Charolais and Hereford hulls(8). The larger mean SC for Simmental bulls in our study is important since Simmental bulls were younger than the other bull breeds (PcO.Ol), and were taller than Angus or Hereford bulls (P
140
Theriogenology
allocating bulls to the test stations may have influenced the type of bulls evaluated each year. Participation or nonparticipation by the various breeders over different years and their individual criteria selection for yearling bulls may have affected the composition of annual test groups. Significance of the test year may also have reflected gradual changes in the population from which selections were made over the 12-yr period under review. A trend toward larger-framed, later-maturing bulls was observed in data. Between 1980 and 1991, a the analysis of performance difference (P
Theriogenology
141
Age was the most significant factor (P
A significant station effect was observed between Location 2 Environmental temperature and the the other locations.
142
Theriogenology
facilities may have affected spermmotility since Location 2 was in the mountains of North Carolina and the examinations were conducted in February. Moreover, younger bulls (PcO.01) were tested at Location 2 than at Location 1. The mean for the percentage of total sperm abnormalities was 24.9 in this study. Sperm abnormalities for yearling bulls have been reported to range widely: 18.2(15), 9.4(28), 12.5(30), This broad variation may 24.4(28), 26.8(26), and 30.6%(11). partially reflect differences in examination technique, handling of samples, and environmental conditions. The previously reported means for yearling BSE scores are in This range includes the the range of 70.4 to 80.4(11,26,30,35). Primary score observed in this study (77.0). mean BSE abnormalities were the most significant source of variation in BSE score. This is consistent with the findings of Godfrey et al(22) Of the 3 BSE score in Santa Gertrudis bulls >16 mo of age. components, sperm morphology was more highly correlated with the The importance of BSE score than SC or sperm motility(22). morphology may in part be attributed to its greater emphasis in the Society for Theriogenology scoring system(4). Both morphology and SC are assigned 40 points each in the final score; however, the lowest possible score is 10 points for morphology and 3 points for scrotal circumference. The difference in scoring for these traits may contribute to the significance of morphology in the BSE score. The effect of year (P
Theriogenology
143
significant for BSE score in our study, it had no effect on BSE classification. Spitzer, et al(36) reported similar findings in yearling bulls. Since a bull's status as a potential breeder is ultimately determined by BSE classification, the effect of age on BSE score appears to be accounted for in the final classification. However, when the data are analyzed as Vlpasstl (satisfactory breeder) or t'fail" (questionable or unsatisfactory breeder), age had an effect (PcO.05) on BSE score. Therefore, the adjustment for age in the final classification may not be adequate for determining a pass score on the BSE. The percentages of yearling bulls classified as satisfactory breeders have been reported as 26 to 36%(g), 80.1%(36) and 82%(25). Our results for the years of semen analysis were similar to the 2 latter reports (82.0%); however, they were much higher than the first study mentioned. When all ages of bulls were included, the percentages of satisfactory breeders has been reported to range from 79.2 to 88(7,12,19,20,25); thus, there appears to be no disadvantage to examining yearling bulls in the effort to identify satisfactory breeders. Primary sperm abnormalities had the most significant influence on BSE classification. Chenoweth et al(12) reported that primary, secondary and total abnormalities were responsible for differences in BSE classification in 92 beef bulls. Scrotal circumference and sperm motility did not influence final classification in their study. As previously noted, sperm morphology has been shown to be more highly correlated with BSE than SC or score sperm motility(22). Differences were observed between years for which semen was analyzed and for which it was not. A decrease in the percentage of satisfactory breeders increase in and an the percentage questionable breeders were seen when semen analysis was performed. Therefore, when semen analysis was taken into consideration for the final classification more bulls were designated as questionable breeders. This reflects the fact that primary abnormalities were the most significant factor in determining BSE classification. Further evidence that semen analysis caused more bulls to be classified as questionable was seen when the minimum scrotal circumference was raised to 32 cm. This change would have effectively eliminated 16.9% more bulls for the years without semen analysis compared with 5.3% when semen was evaluated. The lower rate of elimination of bulls (5.3%) from the status of satisfactory breeders with semen analysis indicates it removes many of the bulls with marginal SC. Since SC had a highly significant effect on both motility and total sperm abnormalities in this present study, bulls with smaller testicles would be expected to produce poorer quality semen. Breed, station and year had no influence in determining final BSE classification. It is apparent that the BSE can be applied equally to different subsets of bulls from the 4 breeds studied.
144
Theriogenology REFERENCES
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SOUNDNESS EXAMINATION OF 1,952 YEARLING BEEF BULLS IN NORTH CAROLINA
K.A. Bruner,la R.L. McGraw,' M.D. Whitacre,' and S.D. Van Camp' 'Department of Food Animal and Equine Medicine, North Carolina State University College of Veterinary Medicine, Raleigh, NC 27606 'Department of Animal Science, North Carolina State University, Raleigh, NC 27606 Received
for publication: September 15, 1994 Accepted: January 13, 1995 ABSTRACT
During a 12-yr period, breeding soundness examinations (BSE) were performed on 1,952 yearling bulls of 4 different breeds: Angus (n=852); Charolais (n=520); and (n=205); Polled Hereford Simmental (n=375). The yearling bulls had satisfactorily completed a record of performance test at 1 of 4 North Carolina test stations. The 1976 BSE the Society guidelines of for Theriogenology were used; however, semen analysis was not always conducted as determined by test station policy, and thus fewer bulls had a satisfactory score while more bulls had a questionable score when semen analysis was also performed. No statistical difference was observed in bulls scoring unsatisfactory between years with and without semen analysis. Overall, 85.2% were classified as satisfactory, 9.0% as questionable and 5.7% as unsatisfactory. The mean BSE score was 77.0. Simmental bulls had the largest mean scrotal circumference (SC), followed by Angus, Charolais and Polled Hereford bulls. Final test weight had the greatest effect on SC. Mean sperm motility score was 12.8, and mean total sperm abnormalities 24.9%. Penile fibropapillomas were diagnosed in 2.8% of the yearling bulls. The incidence rate of persistent frenulums was 4.4%. Angus bulls had the highest incidence of penile fibropapillomas and persistent frenulums. The incidence of persistent frenulums was greater (PcO.01) in ll-mo-old bulls than in 12- to 15-mo-old bulls. Breeding soundness examinations of ll- to 15-mo-old bulls provide valuable information for selecting bulls for breeding programs. Key words:
breeding soundness examination, beef bulls, yearling, persistent frenulums, penile fibropapillomas
Acknowledgements Funding provided by,the NCSU-CVM Department of Food Animal and Equine Medicine Veterinary Faculty Practice Plan. The authors thank Ms. A. Brown for assistance in data analysis. "Reprint requests: Dr. K.A. Bruner, 3160 Francis Road, Alpharetta, GA 30201.
Theriogenology 44129-l 45, 1995 0 1995 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0093-691X/95/$1 0.00 SSDI 0093-691 X(95)001 54-Z
Theriogenology
130 INTRODUCTION
The breeding soundness examination (BSE) is an established method for evaluating potential fertility in the bull. Guidelines published by The Society for Theriogenology in 1976 incorporated semen evaluation, scrotal circumference and physical examination into a complete scoring system(4). Classification of bulls as satisfactory, questionable orunsatisfactorypotentialbreeders was determined by scores for scrotal circumference (SC) and semen Moreover, bulls were classified as motility and morphology. questionable or unsatisfactory for any physical or reproductive abnormality regardless of their BSE score. The new guidelines for BSE in bulls were presented by the Society for Theriogenology in 1992. soundness The examination of yearling bulls for breeding enables the selection of prospective herd sires at a younger age than would otherwise be possible. Early elimination of undesirable bulls is economically beneficial and contributes to increased record-ofefficiency. The combination of a reproductive performance test and breeding soundness examination provides broad indication of an individual bull's potential as a herd sire. Selection of breeding males for superior genetic and reproductive traits accelerates the improvement of offspring performance and productivity(l8). The North Carolina Beef Cattle Improvement Program annually conducts record-of-performance testing of yearling beef bulls. An average of 226 bulls has been tested for performance each year for the past 12 yr. A total of 2,720 bulls representing 23 different breeds has been tested since 1980, with Angus, Charolais, Polled Hereford and Simmental breeds representing 2,536 of the 2,720 bulls under study. Since 1980, BSE conducted at the completion of the performance tests have been used to evaluate potential fertility. Bulls which satisfactorily met performance, conformation, musculoskeletal, temperament and reproductive criteria were sold as prospective breeding bulls. The bulls which did not pass the performance test were not examined for breeding soundness (n=584). Thus this study is based on 1,952 of the original 2720 bulls from the North Carolina Cattle Improvement Program that were examined for breeding soundness, representing the 4 major breeds: Angus (n=852), Charolais (n=205), Polled Hereford (n=520), and Simmental (n=375). The objectives of this report are to summarize the findings of the 1,952 examinations and to demonstrate that the BSE provides valid information for the selection of yearling bulls for breeding programs.
131
Theriogenology MATERIALS
AND METHODS
Bull Test Stations The North Carolina Beef Cattle Improvement Program has record-of-performance tests at different conducted 3 annual Tests at the Piedmont Research Station, locations in the state. Salisbury, North Carolina (Location l), and the Mountain Research Station, Waynesville, North Carolina (Location 21, were completed each of the 12 yr (1980 to 1991). The third test was originally from 1980 to 1983 conducted at Rocky Mount, North Carolina (Location 3) and then at Butner, North Carolina from 1984 to 1991 (Location 4). Bulls were consigned to test stations by breeders enrolled in the Beef Cattle Improvement Program or in similar programs. More than 95% of the bulls tested were from farms located in North A 21-d adjustment period was allowed prior to the start Carolina. of a 140-d test (1980 to 1987) or a 112-d test (1988 to 1991). The age range of the bulls at the start of the test was 7 to 11 mo and 11 to 15 mo at the end. Bulls at Location 1 were fed a dry ration containing 12% crude protein and 68% total digestible nutrients (TDN). Mixed grass hay was provided ad libitum. Bulls at Locations 2, 3 and 4 received a corn silage based ration containing 12% crude protein and 70% TDN ad libitum. A salt-mineral mixture was also available ad libitum to all bulls at each station. Breeding
Soundness
Examination
examinations (BSE) were performed Breeding soundness by veterinarians from North Carolina State University College of Veterinary Medicine. The examinations were conducted at test stations immediately following the completion of performance tests. All examinations were performed during December, January and February. Only those bulls which satisfactorily completed the performance tests were evaluated for breeding soundness. Methods of evaluating breeding soundness varied over the 12 yr because of policy changes at the test stations. The BSE procedure described by the Society of Theriogenology(4) was used to evaluate bulls in 1980 to 1982 (all stations); 1986 (Location 4); 1987 (Locations 1,4) ; and 1988 to 1991 (all stations) _ A total of 1,236 bulls (Angus, n=533; Charolais, n=127; Polled Hereford, n=313; and Simmental, n=444) was evaluated using the BSE procedure. Semen evaluations were not conducted in 1983 to 1985 (all stations); 1986 (Locations 1, 2); and 1987 (Location 2) due to a policy adopted by the governing committee of the bull testing program. Instead, breeding soundness was determined by scrotal circumference (SC), examination of the internal and external genitalia, and physical examination. A minimum SC of 30 cm and normal physical and genital examinations were required for passing A total of 716 bulls (Angus, n=319; Charolais, n=78; the BSE. Polled Hereford, n=207; and Simmental, n=112) was evaluated.
132
Theriogenology
The facilities for semen evaluation were different between the From first 3 yr (1980 to 1982) and the last 6 yr (1986 to 1991). 1980 to 1982, modified on-farm facilities were used for semen evaluation. Control of environmental conditions in the field A heated mobile laboratory unit was laboratories was difficult. acquired and used from 1986 to 1991. Semen was evaluated at room temperature using microscope slides warmed to 37OC and a heated microscope stage. Statistical
Methods
Data were analyzed by regression analysis using general linear models of a statistical analysis program(33). Least squares means The BSE were used to make comparisons between groups of data. sperm motility total sperm classification, BSE score, and abnormalities were analyzed for 1986 to 1991 due to the differences facilities between 1980 and 1982. Scrotal in laboratory and persistent fibropapillomas frenulums were circumference, analyzed for all 12 yr. The model used to analyze the data included station, year, breed of bull, age, average daily test, final weight, and final hip height.
the effects of weight gain on
RESULTS Due to differences in evaluation over the 12-yr period, the Data in the first segment results are presented in 4 segments. include SC and physical examination findings for all 12 yr. The second segment contains information on semen analysis for those years in which it was evaluated. The parameters included sperm motility, total number of sperm abnormalities and BSE score. The third segment presents BSE classifications for all 12 yr regardless of whether semen analysis had been performed. The fourth segment describes performance test observations. All Years
(1980 to 1991)
The mean SC was 36.0 cm for all breeds Scrotal circumference. Final weight (PcO.Ol), breed (PcO.Ol), year and all years. (P~0.01) and age (PcO.05) were sources of SC variation. Final weight was the most significant of all factors in the model and breed was second. Least squares means for SC by breed and age of bull are The SC of Simmental bulls was larger presented in Tables 1. (PcO.01) than that for Angus, Charolais, and Polled Hereford bulls. Scrotal circumference was a1s.o larger (PeO.01) for Angus bulls than Charolais, or for Polled Hereford bulls. The SC of 13- and 14-moold bulls was larger (PcO.01) than that of ll- and 12-mo-old bulls. A decline in least squares means for 15-mo-old bulls was observed; however, no significant difference was found between means for the 14- and 15-mo-old bulls. A gradual trend towards a smaller SC was
Theriogenology
133
observed over the 12-yr period, although the trend was not affected (P>O.O5) by age in months.
Table 1.
Least squares means for scrotal circumference and breed (1980 to 1991)
Bull breed
(SC) by age
Bull age (months)
Angus (n=852) Charolais (n=205) Polled Hereford (n=520) Simmental (n=375)
11 12 13 14 15
36.3" 35.lb 34.9b 36.8'
"-"Valueswithin a column that have different significantly different (P
(n=201) (n=556) (n=617) (n=467) (n=lll)
35.3" 35.6" 36.1b 36.1b 35.9ab
superscripts
are
Penile fibrooapillomas. The mean incidence of penile fibropapillomas was 2.8% for the years 1980 to 1991. Year and breed affected (P
Least squares means for the incidence of penile fibropapillomas by breed (1980 to 1991) Fibropapillomas Bull breed
Incidence
Angus Charolais Polled Hereford Simmental ",bValues within a column with different significantly different (PcO.05).
(%)
3.5" 1.2"b 1.4b 0.7b superscripts
are
134
Theriogenology
Persistent frenulums. For years 1980 to 1991 the incidence rate for persistent frenulums in all 4 breeds was 4.4%. Age affected (PcO.01) the prevalence of persistent frenulums and ll-moold bulls had more (PcO.01) persistent frenulums than any other age group. Least squares means of the incidence of persistent frenulums by age and breed are shown in Table 3. Both year and breed affected the incidence of persistent frenulums (PcO.05). Simmental bulls were observed to have a lower incidence rate than Angus (PcO.01) and Polled Hereford (PcO.05) bulls. Table 3.
Least squares means for the incidence of persistent frenulums by bull age and breed (1980 to 1991)
Persistent Breed
frenulums Incidence
Angus Charolais Polled Herefords Simmental
Persistent (%)
Age
(months) 11 12 13 14 15
4.9' 2.0* 4.0' 1.2b
a "bValues within column significantly different
with different (PcO.01).
frenulums Incidence
($1
10.5" 4.4b 3.lb 1.7b 1.9b superscripts
are
The testing station did not significantly affect the incidence of persistent frenulums when age was included in the model. Age, however, did account (PcO.01) for much of the variation in the incidence of persistent frenulums. For example, at Location 2 the average incidence rate was 4.4 and the average age was 12.1 mo, whereas at Location 4 the incidence rate was 1.9 but the average age was 13.7 mo. Years of Semen Evaluation
(1986 to 1991)
Soerm motility. The simple mean for sperm motility score was 12.8 (scale: 1 to 20) for the years 1986 to 1991. Total number of abnormalities had the greatest influence (PcO.01) on motility. Scrotal circumference (PcO.Ol), year (PcO.01) and testing station (P
135
Theriogenology
The simple mean for the percentage Total soerm abnormalities. of total abnormalities was 24.9 for all BSE classifications (scale of 0 to 100). Sperm motility was the most significant source of variation of total abnormalities. Motility, average daily weight gain, SC, year, final weight and test station influenced the percentage of total sperm abnormalities (P
Least squares means for breeding soundness score by year and breed (1986 to 1991)
Year
BSE score
1986 1987 1988 1989 1990 1991
81.3" 77.ObC 77. Gabc 77.ObC 78.8ab 75.1C
Breed
BSE score
Angus Charolais Polled Hereford Simmental
"-Values within a column with different significantly different (PcO.05).
examination
superscripts
78.2" 79.3" 75.7h 78.0"
are
A graph of the BSE score least squares means by age is presented in Figure 1. The BSE scores at 11 and 12 mo were lower than those at 13, 14 and 15 mo of age (P
For The 2 Different
Year Groups
The final BSE classifications for all years, years with and without semen analysis are shown in Table 5. There was a significant difference between years with semen analysis and the years without semen analysis in the percentage of bulls classified
136
Theriogenology
and questionable breeders. No significant as satisfactory difference was found in the percentages of unsatisfactory breeders between these 2 groups of years. When semen analysis was not performed, more bulls were classified as satisfactory and fewer bulls were classified as questionable breeders.
2
80
8
fJJ75 ti m 70
60 12
Figure 1
Table
5.
13 Monthsof Age
14
15
Least souares means for breeding soundness examination %alues with different (BSE) score (1986 to 1991). superscripts are significantly different (PcO.01).
Breeding soundness years examined
(BSE) classification
examination
by
BSE classification Years examined
% Satisfactory
All years (n=1952) Years with semen analysis (n=1236) Years without semen analysis (rk716)
% Questionable
% Unsatisfactory
85.2
9.0
82.0'
12.7'
5.3'
90.ab
2.7b
6.6'
@Values within a column with different significantly different (PcO.05).
superscripts
5.7
are
According to the 1976 BSE classification guidlines of the Society for Theriogenology(4) a c30-cm SC is unsatisfactory in bulls older than 12 mo of age. To assess the effects of raising the acceptable minimum to 32 cm, an additional analysis was
137
Theriogenology
conducted. Thus for the years with and without a semen analysis, bulls with a <32-cm SC were regarded as unsatisfactory potential breeders. The percentage of bulls classified as satisfactory was With a 32-cm minimum SC, recalculated for both groups of years. 76.8% of the bulls were classified as satisfactory breeders during years of semen analysis, and 73.9% of the bulls for years without Compared with the original BSE classifications, semen analysis. raising the minimum SC to >32-cm eliminated 5.3% more bulls in years with semen evaluation and 16.9 % more bulls in the years without semen analysis. Classification of breeding soundness by breed for the years with semen analysis and those without semen analysis are shown in Tables 6 and 7. More Simmental bulls were determined to be satisfactory breeders than any other breed during both sets of percentage of years. Charolais bulls received the lowest satisfactory classifications. Angus bulls were found to be satisfactory breeders more often than Polled Hereford bulls when semen was evaluated; however, when semen was not analyzed more Polled Hereford bulls were satisfactory. Table
6.
Breeding soundness examination (BSE) classification by breed for years with semen evaluation (1980 to 1982, 1986 to 1991) BSE Classification
Breed
% Satisfactory
Angus Charolais Polled Hereford Simmental
Table
7.
% Questionable
%Unsatisfactory
12.4 17.3 14.4 9.1
4.5 7.9 6.4 4.2
83.1 74.8 79.2 86.7
Breeding soundness examination (BSE) classification by breed for years without semen evaluation (1983 to 1987) BSE classification
Breed
with semen evaluation
% Satisfactory
Angus Charolais Polled Hereford Simmental
89.3 84.6 92.3 96.4
without
semen evaluation
% Questionable 3.1 5.1 2.4 0.0
%Unsatisfactory 7.5 10.7 5.3 3.6
138
Theriogenology
Analysis of variance for BSE classification for 1986 to 1991, when semen evaluations were conducted, showed primary abnormalities to be the most important factor in determining BSE classification. There were no significant effects of year, station, breed or age. When classified as satisfactory or as questionable or unsatisfactory, age affected (PcO.05) the assessed classification. Breed, station and year were not significant factors affecting classification of bulls as satisfactory or questionable/unsatisfactory breeders. Performance
Data
(1980 to 1982, 1986 to 1991)
End of test aqe. At the start of the test, the bulls were 7 to 11 mo of age and at the end they were 11 to 15 mo of age. The mean age at the end of the test was 13.1 mo. Least squares means showed that Simmental bulls were younger (PcO.01) than the other 3 breeds. There was no significant difference in least squares means for age among the other breeds. End of test heiqht. The mean final height at the end of the test was 52.4 inches. A gradual trend was observed over the 12-yr period toward larger-framed bulls. A difference (PcO.01) was seen between least squares means for 1980 (height=51.5) and 1991 Final weight, year, (height=53.9). breed, and test station affected the final height of the bulls (PcO.01). Least squares means for final height by breed are presented in Table 8. Simmental and Charolais bulls were found to be taller than Angus and Polled Hereford bulls (PcO.01). No differences were detected in final height between Charolais and Simmental bulls. Similarly, no differences were observed between Angus and Polled Hereford bulls. Table
8.
Least squares means for final height breed (1980 to 1982, 1986 to 1991)
Final height
and
Final weight
Breed
Inches
Breed
AWPS
51.7" 54.0b 51.6" 54.lb
Angus Charolais Polled Hereford Simmental
Charolais Polled Hereford Simmental
weight
a%alues within a column with different significantly different (PcO.01).
superscripts
Pounds 1193.7" 1166.7b 1206.0" 1178.4b are
by
139
Theriogenology
End of test weight. The mean final weight at the end of the test period was 1191.6 pounds. A gradual trend was observed over the 12-yr period toward lighter-weight bulls. Least square means for final weight by year indicates a difference (P
squares means for final weight by breed are presented in Polled Hereford were the heaviest bulls weighing more (P
In our study the mean SC of the 1,952 bulls was 36.0 cm, and was within the previously reported range of means (32.3 to 36.4 cm) for yearling bulls(9,11,12,15,28,29,3O,35). Simmental bulls had the largest mean SC, followed by Angus, Charolais, and Polled Hereford breeds. Similar findings by breed have been previously reported(10,14,17,23,24,34). By contrast, Cassady et al reported that yearling Angus bulls have larger SC than Simmental, Charolais and Hereford hulls(8). The larger mean SC for Simmental bulls in our study is important since Simmental bulls were younger than the other bull breeds (PcO.Ol), and were taller than Angus or Hereford bulls (P
140
Theriogenology
allocating bulls to the test stations may have influenced the type of bulls evaluated each year. Participation or nonparticipation by the various breeders over different years and their individual criteria selection for yearling bulls may have affected the composition of annual test groups. Significance of the test year may also have reflected gradual changes in the population from which selections were made over the 12-yr period under review. A trend toward larger-framed, later-maturing bulls was observed in data. Between 1980 and 1991, a the analysis of performance difference (P
Theriogenology
141
Age was the most significant factor (P
A significant station effect was observed between Location 2 Environmental temperature and the the other locations.
142
Theriogenology
facilities may have affected spermmotility since Location 2 was in the mountains of North Carolina and the examinations were conducted in February. Moreover, younger bulls (PcO.01) were tested at Location 2 than at Location 1. The mean for the percentage of total sperm abnormalities was 24.9 in this study. Sperm abnormalities for yearling bulls have been reported to range widely: 18.2(15), 9.4(28), 12.5(30), This broad variation may 24.4(28), 26.8(26), and 30.6%(11). partially reflect differences in examination technique, handling of samples, and environmental conditions. The previously reported means for yearling BSE scores are in This range includes the the range of 70.4 to 80.4(11,26,30,35). Primary score observed in this study (77.0). mean BSE abnormalities were the most significant source of variation in BSE score. This is consistent with the findings of Godfrey et al(22) Of the 3 BSE score in Santa Gertrudis bulls >16 mo of age. components, sperm morphology was more highly correlated with the The importance of BSE score than SC or sperm motility(22). morphology may in part be attributed to its greater emphasis in the Society for Theriogenology scoring system(4). Both morphology and SC are assigned 40 points each in the final score; however, the lowest possible score is 10 points for morphology and 3 points for scrotal circumference. The difference in scoring for these traits may contribute to the significance of morphology in the BSE score. The effect of year (P
Theriogenology
143
significant for BSE score in our study, it had no effect on BSE classification. Spitzer, et al(36) reported similar findings in yearling bulls. Since a bull's status as a potential breeder is ultimately determined by BSE classification, the effect of age on BSE score appears to be accounted for in the final classification. However, when the data are analyzed as Vlpasstl (satisfactory breeder) or t'fail" (questionable or unsatisfactory breeder), age had an effect (PcO.05) on BSE score. Therefore, the adjustment for age in the final classification may not be adequate for determining a pass score on the BSE. The percentages of yearling bulls classified as satisfactory breeders have been reported as 26 to 36%(g), 80.1%(36) and 82%(25). Our results for the years of semen analysis were similar to the 2 latter reports (82.0%); however, they were much higher than the first study mentioned. When all ages of bulls were included, the percentages of satisfactory breeders has been reported to range from 79.2 to 88(7,12,19,20,25); thus, there appears to be no disadvantage to examining yearling bulls in the effort to identify satisfactory breeders. Primary sperm abnormalities had the most significant influence on BSE classification. Chenoweth et al(12) reported that primary, secondary and total abnormalities were responsible for differences in BSE classification in 92 beef bulls. Scrotal circumference and sperm motility did not influence final classification in their study. As previously noted, sperm morphology has been shown to be more highly correlated with BSE than SC or score sperm motility(22). Differences were observed between years for which semen was analyzed and for which it was not. A decrease in the percentage of satisfactory breeders increase in and an the percentage questionable breeders were seen when semen analysis was performed. Therefore, when semen analysis was taken into consideration for the final classification more bulls were designated as questionable breeders. This reflects the fact that primary abnormalities were the most significant factor in determining BSE classification. Further evidence that semen analysis caused more bulls to be classified as questionable was seen when the minimum scrotal circumference was raised to 32 cm. This change would have effectively eliminated 16.9% more bulls for the years without semen analysis compared with 5.3% when semen was evaluated. The lower rate of elimination of bulls (5.3%) from the status of satisfactory breeders with semen analysis indicates it removes many of the bulls with marginal SC. Since SC had a highly significant effect on both motility and total sperm abnormalities in this present study, bulls with smaller testicles would be expected to produce poorer quality semen. Breed, station and year had no influence in determining final BSE classification. It is apparent that the BSE can be applied equally to different subsets of bulls from the 4 breeds studied.
144
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