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Beef bulls mated to estrus synchronized heifers: Single- vs multi-sire breeding groups
THERIOCENOLOGY
BEEF BULLS MATED TO ESTRUS SYNCHRONIZED HEIFERS: SINGLE- VS MULTI-SIRE BREEDING GROUPS P. W. Farin, P. J. Chenowetha, E. R. Mateosb, and J. E. Pextonc,d,e Departments of Animal Sciences and Physiology and Biophysics Colorado State University, Fort Collins, Colorado 80523 Received for Publication: September 14, 1981 Accepted: February 4, 1982 ABSTRACT Beef bulls of approximately 15 months of age were placed with heifers at bull to female ratios (BFR) of 1:20 (n = 3) and 2:40 (n = 3) to compare the breeding efficiency of bulls used in either a single- or a multi-sire group. Prior to the breeding period, each bull was given a breeding soundness exam and two exposures to a libido/ synchronizing estrus, serving capacity test. For the purpose heifers received a nine-day Syncro-Mate- @ (G. D. Searle & Co.) treatment. Twenty-seven hr after removal of the implants, bulls were placed with heifers and sexual activity was observed continuously for the succeeding 30 hr. With the exception of number of services per heifer, the mating performance of bulls and pregnancy rates at both BFR's were not different (P>.O5). Heifers in single-sire groups were serviced more times (Pc.05) than those in multi-sire groups (4.1 ? 0.6 vs 2.6 * 0.2, respectively). Approximately 50% of heifers in multi-sire groups were serviced by both bulls. Due to the overlap in servicing heifers and the non-significant difference in pregnancy rates between the two BFR's. it was concluded that a single-sire mating program was more efficient.
(a)
Present address: Dept. of Animal Production, University of Queensland, St. Lucia, Queensland, Australia. 4067.
(b)
Present address:
(c)
Portions of these data were included in 70th Ann. Meeting, A.S.A.S., July 9-13, 1977. Abstr. No's. 359 and 404; and Colo. Exp. Sta. Bull., Gen. Series 970, p. 35.
(d)
The authors thank Mr. C. J. Streit for his assistance and use of cattle; C. E. Sheffel, D. Boyer, J. L. Sullins, D. W. Dowling, T. T. Olar, and Dr. L. Ball for assistance in data collection.
(e)
Supported in part by G. D. Searle & Co. and by the Colorado State University Exp. Sta. and published as Scientific Series Paper No. 2672.
Apartato 22, Badajo, Spain.
APRIL 1982 VOL. 17 NO. 4
365
THERIOGENOLBGY INTRODUCTION The maximum number of cows or heifers a bull can successfully service and impregnate during a restricted breeding period is affected by bull to female ratio (BFR) as well as a number of other factors (1). Under range conditions in the western United States, most ranchers use a BFR of approximately 1:25 (2). Recently, it was shown that BFR's of 1:25 were inefficient compared with breeding ratios of 1:44 and 1:60 (3). It was observed that all three breeding ratios resulted in similar rates of estrus detection by bulls and comparable pregnancy rates. In this same study, multi-sire breeding groups (BFR = 4:lOO and 2:89) appeared to be less efficient than single-sire groups, as pregnancy rates were similar for all groups (3). In a multi-sire situation, the social ranking of individual bulls influences their mating activity within the breeding group (3,4). In one study, it was found that more heifers were marked with chin-ball markers by dominant bulls than by subordinate bulls (3). Another investigator (4) observed that mating activity was greater in dominant bulls. Recent investigations have shown that beef bulls can be used effectively in programs where females have received a treatment to synchronize estrus. Those investigations used either a hand-mating (5) or a single-sire, group-mating (6) program. The purpose of this investigation was to determine if there were differences in breeding efficiency between single-sire and multi-sire breeding programs using females that have received a treatment to synchronize estrus. MATERIALS AND METHODS Anima 7-s and Location . Experimental animals consisted of nine yearling (15.2 to 16.0 month old) Hereford bulls, and 160 yearling cross-bred (Hereford x Angus) virgin heifers. All animals were in good physical condition at the time of this investigation. Trial was conducted on a ranch in the north-central part of Colorado near Walden. Each bull received a breeding Prior to breedin eriod. soundness exam (BSE) 477. Each bull was given two exposures to a modified libido/serving capacity test (8) as follows. Two non-estrus heifers were first p epared by administering an intramuscular injection (IM) of 20 mg Rompu#J (xylazine, 100 mg/ml; Haver-Lockhart Laboravagina and rectum of each heifer was tories, Shawnee, KS). T lubricated with K-Y JellP (Johnson & Johnson, New Brunswick, NJ). Each heifer was haltered and restrained in one of two service crates which were separated from each other by approximately 8 m. Bulls were subjected to prestimulation before being tested, This was accomplished by allowing them to observe the sexual activity of two bulls exposed to the restrained heifers in an adjacent pen for at least 10 min. Two of the bulls to be tested were then admitted into the pen with the restrained heifers and their sexual activity (sexual interest, mounts, and services) was recorded for 10 min.
366
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1982 VOL. 17 NO. 4
THERIOGENOUK;Y
After each of the two test periods, each bull received a libido score based on a 0 (no sexual interest) to 10 (two services followed by sexual interest, mounts, or further services) scoring system (9), and a serving capacity score (no. of services during the 10 min test period (10). Trial heifers received the Snycro-Mate-@) (G. D. Searle & co., Chicago, IL) treatment for the purpose of synchronizing estrus. This treatment consisted of an ear implant containing 6 mg norgestomet which was placed subcutaneously in the ear and remained in situ for 9 days. At the time of implantation, heifers received an injection (IM) containing 3 mg of norgestomet and 5 mg of estradiol valerate. Heifers were observed for standing estrus every 6 hr for the first 24 hr postimplant removal. DMing breeding period. Approximately 27 hr after removal of implants, bulls were placed with heifers in pens at BFR's of approximately 1:20 (n = 3) and 2:40 (n = 3) (Table I). Bulls and heifers for each breeding group were selected at random. Sexual activity for each group was observed continuously for the next 30 hr. Data were collected by one and two observers for single- and multi-sire groups, respectively. Care was taken not to interfere with mating activity. For each group, the following data were recorded: 1) time of first observed standing estrus for each heifer; 2) time of each mount and service by each bull and the number of the heifer that was mounted or serviced; 3) comments on mating behavior of the bulls. TABLE I.
PRE-BREEDING BSE, LIBIDO, AND SERVING CAPACITY SCORES OF BULLS AND BREEDING RATIOS USED DURING THE SYNCHRONIZED BREEDING PERIOD. ~ ---~ ~~~~._______
Group No.
Bull No.
1
1
44
9.0
1.5
1:20
2
2
44
6.0
0.0
1:20
3
3
76
9.5
2.5
1:19
4
4
58
10.0
2.5
5a
92
9.0
2.0
6
60
7.5
1.0
7a
68
6.0
0.0
Ba
68
10.0
3.5
9
44
6.5
0.5
5 6
BSE Score
Mean Libido Score
Mean Serving Capacity Score
Bull to Female Ratio
2:40 2:40 2:40
aBulls which were determined to be dominant during the observation period.
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367
After the 30 hr observation period, each bull remained with the group of heifers for an additional 24 hr. Following this synchronized breeding period, heifers were placed in pastures with other bulls (BFR = 1:50). Pregnancy diagnosis. Pregnancy and age of fetus were diagnosed by palpation per rectwn at least 60 but not more than 85 days following the initial introduction of bulls.
An unpaired t-test (11) was used to analyze the Andysis of data. effects of single- vs multi-sire breeding groups on bull performance during the synchronized breeding period. Simple correlation coefficients (11) were used to determine the relationships between BSE data and pregnancy rates. RESULTS AND DISCUSSION The percentage of heifers observed in estrus by the end of the 30 hr observation period were 98.2 + 1.8 and 95.1 + 2.8 for singleand multi-sire groups, respectively (Table II). These values are similar to those reported by other investigators (6,12) who used the same treatment for synchronization of estrus. The mean (*SE) response time to first observed estrus did not differ (P>.O5) between heifers in single-sire (26.0 ? 0.4 hr) and multi-sire (30.2 k 1.0 hr) breeding groups (Table II). TABLE II.
REPRODUCTIVE PERFORMANCE OF BULLS DURING THE 30 HR OBSERVATION PERIOD: SINGLE- VS MULTI-SIRE BREEDING GROUPS. Bull to Female Ratio 2:40
1:20 3
3
Percent females observed in estrus
98.2 +
1.8a
95.1 f
Response time from end of treatment to 1st female observed in estrus (hr)
26.9 t
0.4
30.2 it 1.0
237.7 k 12.9
169.3 f 24.1
No. groups
Total no. mountsb": Total no. servicesb
62.0 +
2.8
9.3
56.0 ?
7.2 0.4 0.2e
Mount to service ratiob
5.1 k
0.9
4.1 +
No. services per heifer
4.1 k
0.6d
2.6 +
Percent serviced/observed in estrus
77.9 +
5.6
78.0 ?r 5.1
Percent pregnant/observed serviced
34.5 +
4.7
41.1 +
1.8
Percent pregnant/observed in estrus
29.3 +
3.0
34.3 +
6.6
a
Mean + standard error. bPer bull. dCMgunts (not accompanied by a service). ’ Means significantly different (Pc.05).
368
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THERIOCENOLOGY Total number of mounts per bull in single-sire breeding groups (237.7 i 12.9) were higher than those by bulls in multi-sire groups (169.3 k 24.1). However, these differences in mount were not significant. Bulls used in single-sire groups did not differ (P>.O5) from those in multi-sire groups either in total number of services (62.0 f 9.3 and 56.0 f 7.2, respectively) or in mount to service ratio (5.1 f 0.9 and 4.1 + 0.4, respectively) (Table II). Overall, the proportion of estrus heifers serviced by bulls in single-sire breeding groups (77.9 -c 5.6%) was not different (Pb.05) from those in multi-sire groups (78.0 + 5.1%) (Table II). However, approximately 50% of the heifers serviced in multi-sire groups were serviced by both bulls (Figure 1). This overlap in heifers serviced by both bulls is indicative of lower efficiency of sire usage in multisire groups. Bull overlap in servicing heifers has also been reported by other investigators who placed groups of beef bulls with unsynchronized heifers (3).
Totol serviced Serviced
I:20
by both bulls
2~40
BULL TO FEMALE
FIGURE 1.
RATIO
PERCENTAGE (?SE) OF HEIFERS SERVICED BY BULLS DURING THE 30 HR OBSERVATION PERIOD.
The number of services per heifer ranged from 0 to 13 (R = 3.1 * 0.3). This measurement was significantly influenced by BFR. Heifers in the single-sire breeding groups were serviced more (Pc.05) times than those in multi-sire groups (4.1 c 0.6 vs 2.6 f 0.2, respectively) (Table II).
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1982 VOL. 17 NO. 4
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THERIOGENOLOGY
The relative dominance of bulls in multi-sire mating groups was determined during the observation period. The outcome of encounters when bull pairs competed for an estrus heifer was used to determine the dominant (successful) and subordinate (unsuccessful) bull. Competition for heifers was minimal since bulls spent more time mounting or servicing heifers than competing for individual heifers. This was most likely influenced by the large number of heifers in estrus. Other studies have shown that dominance in mixed-age bull groups is related to age of bull and seniority within the herd (4). Bulls used in this investigation were of approximately the same age (15.6 * 0.1 mo.) and were recently introduced into the herd. In two of three multi-sire groups, dominant bulls achieved more total services than subordinate bulls. The dominant bull in group 4 (No. 5) had more services than the subordinate bull (No. 4) (80 vs 63, respectively). This same trend was observed in group 6, in which the dominant bull (No. 8) had a total of 71 services versus 37 services by the subordinate bull (No. 9). However, number of services did not appear to be related to social hierarchy in group 5, since both bulls had a similar number of services (No. 6 = 43 and No. 7 = 42 services). In addition, there was no apparent relationship between a bull's social rank and the percentage of females that he serviced. Dominance has been shown to be related to mating activity in mixed-age bull groups (3,4) as well as in groups of bulls of the same age (3). Bulls with higher mean libido and mean serving capacity scores tended to have a higher number of services and serviced a higher percentage of estrus heifers. In a more extensive study that involved only single-sire BFR's, both mean libido and mean serving capacity scores of bull's were moderately correlated with mating activity (r = .39 to .58) and pregnancy rate (r = .48 to .54) (8). Similar results were reported by another investigator (10). Percentage of heifers that became pregnant was not different (P>.O5) between single- and multi-sire breeding groups (34.5 + 4.7 and However, in multi-sire groups, 44.1 + 1.8, respectively) (Table II). pregnancy rate was higher for heifers observed serviced by both bulls (48.7%) than for heifers observed serviced by only one bull (26.0%). These findings are not in agreement with other multi-sire, natural mating investigations (3), or with heterospermic insemination studies in cattle (13). Individual pregnancy rates of bulls were not Significantly (P>.O5) correlated with BSE score (r = .35) or with components of the BSE score. Correlations between pregnancy rate and components of the BSE score were: .15, .Ol, . 06, -.25, and -.43 for scrotal circumference, percentage of motile sperm cells, motility rate, percent age of primary and total abnormalities, respectively. Pregnancy rate, based on those heifers observed in estrus, was not affected (P>.O5) by BFR. Pregnancy rate for single-sire groups was 29.3 ? 3.0% while that of multi-sire groups was 34.3 * 6.6% (Table II).
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1982 VOL. 17 NO. 4
THERIOGENOLOCY It is concluded that single-sire groups were more efficient in sire usage than multi-sire groups. This is due to overlap in servicing in multi-sire groups, and non-significant difference in pregnancy rates for the two 5FR's. LITERATURE CITED 1.
Rupp, G. P. Bull behavior and management. Proc. The Range Beef cow: A Symp. on Prod. IV, Denver, Colorado, 1977, p. 25-29.
2.
Ensminger, M. E. Beef Cattle Science, 5th ed. Interstate Printers and Publishers, Danville, Illinois, 1976, p. 347.
3.
Rupp, G. P., Ball, L., Shoop, M. C., and Chenoweth, P. J. Reproductive efficiency of bulls in natural service: effects of male to female ratio and single- vs multiple-sire breeding groups. J. Am. Vet. Med. Assn. 171:639-642 (1977).
4.
Blockey, M. A. deB. Observations on group mating of bulls at pasture. Appl. Anim. Ethol. 5:15-34 (1979).
5.
Pexton, J. E., Denham, A. H., Mangus, W. L., Walck, J. D., and Brinks, J. S. Breeding by hand mating in synchronization of estrus program with beef heifers. Colorado Exp. Sta. Bull., Gen. Series 966:21-22 (1977).
6.
Pexton, J. E. and Chenoweth, P. J. Using bulls to breed beef heifers at a synchronized estrus. 69th Ann. Meeting, Am. Sot. Anim. Sci., Abstract No. 488, p. 195 (1977).
7.
Simons, J. C. (ed.) A compilation of current information on breeding soundness and evaluation and related subjects. The Sot. for Theriogenology J., Vol. VII, 2nd ed. pp. l-20 (1976).
8.
Farin, P. W. Sexual behavior and fertility in beef bulls. M. S. Thesis. Colorado State University, Ft. Collins, Colorado, 1980.
9.
Chenoweth, P. J. Consideration of behavioral aspects of the natural breeding bull. Proc. Ann. Meeting, Sot. for Theriogenology, Lexington, Kentucky, p. 109-122 (1976).
10.
Blockey, M. A. de5. The influence of serving capacity of bulls on herd fertility. J. Anim. Sci. -46:589-595 (1978).
11.
Snedecor, G. W. and Cochran, W. 6. Statistical Methods, 6th ed., Iowa State College Press, Ames, Iowa, 1967, Ch. 4 and 7.
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THERiOCENOLOCY 12.
Spitzer, J. C., Jones, D. L., Miksch, E. D., and Wiltbank, J. N. Synchronization of estrus in beef cattle: III. Field trials in heifers using norgestomet implant and injections of norgestomet and estradiol valerate. Theriogenology H:223-229 (1978).
13.
Nelson, L. D., Pickett, B. W., and Siedel, Jr., G. E. Effect of heterospermic insemination on fertility of cattle. J. Anim. Sci. 40:1124-1129 (1975).
372
APRIL 1982VOL. 17 NO. 4
BEEF BULLS MATED TO ESTRUS SYNCHRONIZED HEIFERS: SINGLE- VS MULTI-SIRE BREEDING GROUPS P. W. Farin, P. J. Chenowetha, E. R. Mateosb, and J. E. Pextonc,d,e Departments of Animal Sciences and Physiology and Biophysics Colorado State University, Fort Collins, Colorado 80523 Received for Publication: September 14, 1981 Accepted: February 4, 1982 ABSTRACT Beef bulls of approximately 15 months of age were placed with heifers at bull to female ratios (BFR) of 1:20 (n = 3) and 2:40 (n = 3) to compare the breeding efficiency of bulls used in either a single- or a multi-sire group. Prior to the breeding period, each bull was given a breeding soundness exam and two exposures to a libido/ synchronizing estrus, serving capacity test. For the purpose heifers received a nine-day Syncro-Mate- @ (G. D. Searle & Co.) treatment. Twenty-seven hr after removal of the implants, bulls were placed with heifers and sexual activity was observed continuously for the succeeding 30 hr. With the exception of number of services per heifer, the mating performance of bulls and pregnancy rates at both BFR's were not different (P>.O5). Heifers in single-sire groups were serviced more times (Pc.05) than those in multi-sire groups (4.1 ? 0.6 vs 2.6 * 0.2, respectively). Approximately 50% of heifers in multi-sire groups were serviced by both bulls. Due to the overlap in servicing heifers and the non-significant difference in pregnancy rates between the two BFR's. it was concluded that a single-sire mating program was more efficient.
(a)
Present address: Dept. of Animal Production, University of Queensland, St. Lucia, Queensland, Australia. 4067.
(b)
Present address:
(c)
Portions of these data were included in 70th Ann. Meeting, A.S.A.S., July 9-13, 1977. Abstr. No's. 359 and 404; and Colo. Exp. Sta. Bull., Gen. Series 970, p. 35.
(d)
The authors thank Mr. C. J. Streit for his assistance and use of cattle; C. E. Sheffel, D. Boyer, J. L. Sullins, D. W. Dowling, T. T. Olar, and Dr. L. Ball for assistance in data collection.
(e)
Supported in part by G. D. Searle & Co. and by the Colorado State University Exp. Sta. and published as Scientific Series Paper No. 2672.
Apartato 22, Badajo, Spain.
APRIL 1982 VOL. 17 NO. 4
365
THERIOGENOLBGY INTRODUCTION The maximum number of cows or heifers a bull can successfully service and impregnate during a restricted breeding period is affected by bull to female ratio (BFR) as well as a number of other factors (1). Under range conditions in the western United States, most ranchers use a BFR of approximately 1:25 (2). Recently, it was shown that BFR's of 1:25 were inefficient compared with breeding ratios of 1:44 and 1:60 (3). It was observed that all three breeding ratios resulted in similar rates of estrus detection by bulls and comparable pregnancy rates. In this same study, multi-sire breeding groups (BFR = 4:lOO and 2:89) appeared to be less efficient than single-sire groups, as pregnancy rates were similar for all groups (3). In a multi-sire situation, the social ranking of individual bulls influences their mating activity within the breeding group (3,4). In one study, it was found that more heifers were marked with chin-ball markers by dominant bulls than by subordinate bulls (3). Another investigator (4) observed that mating activity was greater in dominant bulls. Recent investigations have shown that beef bulls can be used effectively in programs where females have received a treatment to synchronize estrus. Those investigations used either a hand-mating (5) or a single-sire, group-mating (6) program. The purpose of this investigation was to determine if there were differences in breeding efficiency between single-sire and multi-sire breeding programs using females that have received a treatment to synchronize estrus. MATERIALS AND METHODS Anima 7-s and Location . Experimental animals consisted of nine yearling (15.2 to 16.0 month old) Hereford bulls, and 160 yearling cross-bred (Hereford x Angus) virgin heifers. All animals were in good physical condition at the time of this investigation. Trial was conducted on a ranch in the north-central part of Colorado near Walden. Each bull received a breeding Prior to breedin eriod. soundness exam (BSE) 477. Each bull was given two exposures to a modified libido/serving capacity test (8) as follows. Two non-estrus heifers were first p epared by administering an intramuscular injection (IM) of 20 mg Rompu#J (xylazine, 100 mg/ml; Haver-Lockhart Laboravagina and rectum of each heifer was tories, Shawnee, KS). T lubricated with K-Y JellP (Johnson & Johnson, New Brunswick, NJ). Each heifer was haltered and restrained in one of two service crates which were separated from each other by approximately 8 m. Bulls were subjected to prestimulation before being tested, This was accomplished by allowing them to observe the sexual activity of two bulls exposed to the restrained heifers in an adjacent pen for at least 10 min. Two of the bulls to be tested were then admitted into the pen with the restrained heifers and their sexual activity (sexual interest, mounts, and services) was recorded for 10 min.
366
APRIL
1982 VOL. 17 NO. 4
THERIOGENOUK;Y
After each of the two test periods, each bull received a libido score based on a 0 (no sexual interest) to 10 (two services followed by sexual interest, mounts, or further services) scoring system (9), and a serving capacity score (no. of services during the 10 min test period (10). Trial heifers received the Snycro-Mate-@) (G. D. Searle & co., Chicago, IL) treatment for the purpose of synchronizing estrus. This treatment consisted of an ear implant containing 6 mg norgestomet which was placed subcutaneously in the ear and remained in situ for 9 days. At the time of implantation, heifers received an injection (IM) containing 3 mg of norgestomet and 5 mg of estradiol valerate. Heifers were observed for standing estrus every 6 hr for the first 24 hr postimplant removal. DMing breeding period. Approximately 27 hr after removal of implants, bulls were placed with heifers in pens at BFR's of approximately 1:20 (n = 3) and 2:40 (n = 3) (Table I). Bulls and heifers for each breeding group were selected at random. Sexual activity for each group was observed continuously for the next 30 hr. Data were collected by one and two observers for single- and multi-sire groups, respectively. Care was taken not to interfere with mating activity. For each group, the following data were recorded: 1) time of first observed standing estrus for each heifer; 2) time of each mount and service by each bull and the number of the heifer that was mounted or serviced; 3) comments on mating behavior of the bulls. TABLE I.
PRE-BREEDING BSE, LIBIDO, AND SERVING CAPACITY SCORES OF BULLS AND BREEDING RATIOS USED DURING THE SYNCHRONIZED BREEDING PERIOD. ~ ---~ ~~~~._______
Group No.
Bull No.
1
1
44
9.0
1.5
1:20
2
2
44
6.0
0.0
1:20
3
3
76
9.5
2.5
1:19
4
4
58
10.0
2.5
5a
92
9.0
2.0
6
60
7.5
1.0
7a
68
6.0
0.0
Ba
68
10.0
3.5
9
44
6.5
0.5
5 6
BSE Score
Mean Libido Score
Mean Serving Capacity Score
Bull to Female Ratio
2:40 2:40 2:40
aBulls which were determined to be dominant during the observation period.
APRIL 1982 VOL. 17 NO. 4
367
After the 30 hr observation period, each bull remained with the group of heifers for an additional 24 hr. Following this synchronized breeding period, heifers were placed in pastures with other bulls (BFR = 1:50). Pregnancy diagnosis. Pregnancy and age of fetus were diagnosed by palpation per rectwn at least 60 but not more than 85 days following the initial introduction of bulls.
An unpaired t-test (11) was used to analyze the Andysis of data. effects of single- vs multi-sire breeding groups on bull performance during the synchronized breeding period. Simple correlation coefficients (11) were used to determine the relationships between BSE data and pregnancy rates. RESULTS AND DISCUSSION The percentage of heifers observed in estrus by the end of the 30 hr observation period were 98.2 + 1.8 and 95.1 + 2.8 for singleand multi-sire groups, respectively (Table II). These values are similar to those reported by other investigators (6,12) who used the same treatment for synchronization of estrus. The mean (*SE) response time to first observed estrus did not differ (P>.O5) between heifers in single-sire (26.0 ? 0.4 hr) and multi-sire (30.2 k 1.0 hr) breeding groups (Table II). TABLE II.
REPRODUCTIVE PERFORMANCE OF BULLS DURING THE 30 HR OBSERVATION PERIOD: SINGLE- VS MULTI-SIRE BREEDING GROUPS. Bull to Female Ratio 2:40
1:20 3
3
Percent females observed in estrus
98.2 +
1.8a
95.1 f
Response time from end of treatment to 1st female observed in estrus (hr)
26.9 t
0.4
30.2 it 1.0
237.7 k 12.9
169.3 f 24.1
No. groups
Total no. mountsb": Total no. servicesb
62.0 +
2.8
9.3
56.0 ?
7.2 0.4 0.2e
Mount to service ratiob
5.1 k
0.9
4.1 +
No. services per heifer
4.1 k
0.6d
2.6 +
Percent serviced/observed in estrus
77.9 +
5.6
78.0 ?r 5.1
Percent pregnant/observed serviced
34.5 +
4.7
41.1 +
1.8
Percent pregnant/observed in estrus
29.3 +
3.0
34.3 +
6.6
a
Mean + standard error. bPer bull. dCMgunts (not accompanied by a service). ’ Means significantly different (Pc.05).
368
APRIL 1982 VOL. 17 NO. 4
THERIOCENOLOGY Total number of mounts per bull in single-sire breeding groups (237.7 i 12.9) were higher than those by bulls in multi-sire groups (169.3 k 24.1). However, these differences in mount were not significant. Bulls used in single-sire groups did not differ (P>.O5) from those in multi-sire groups either in total number of services (62.0 f 9.3 and 56.0 f 7.2, respectively) or in mount to service ratio (5.1 f 0.9 and 4.1 + 0.4, respectively) (Table II). Overall, the proportion of estrus heifers serviced by bulls in single-sire breeding groups (77.9 -c 5.6%) was not different (Pb.05) from those in multi-sire groups (78.0 + 5.1%) (Table II). However, approximately 50% of the heifers serviced in multi-sire groups were serviced by both bulls (Figure 1). This overlap in heifers serviced by both bulls is indicative of lower efficiency of sire usage in multisire groups. Bull overlap in servicing heifers has also been reported by other investigators who placed groups of beef bulls with unsynchronized heifers (3).
Totol serviced Serviced
I:20
by both bulls
2~40
BULL TO FEMALE
FIGURE 1.
RATIO
PERCENTAGE (?SE) OF HEIFERS SERVICED BY BULLS DURING THE 30 HR OBSERVATION PERIOD.
The number of services per heifer ranged from 0 to 13 (R = 3.1 * 0.3). This measurement was significantly influenced by BFR. Heifers in the single-sire breeding groups were serviced more (Pc.05) times than those in multi-sire groups (4.1 c 0.6 vs 2.6 f 0.2, respectively) (Table II).
APRlL
1982 VOL. 17 NO. 4
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THERIOGENOLOGY
The relative dominance of bulls in multi-sire mating groups was determined during the observation period. The outcome of encounters when bull pairs competed for an estrus heifer was used to determine the dominant (successful) and subordinate (unsuccessful) bull. Competition for heifers was minimal since bulls spent more time mounting or servicing heifers than competing for individual heifers. This was most likely influenced by the large number of heifers in estrus. Other studies have shown that dominance in mixed-age bull groups is related to age of bull and seniority within the herd (4). Bulls used in this investigation were of approximately the same age (15.6 * 0.1 mo.) and were recently introduced into the herd. In two of three multi-sire groups, dominant bulls achieved more total services than subordinate bulls. The dominant bull in group 4 (No. 5) had more services than the subordinate bull (No. 4) (80 vs 63, respectively). This same trend was observed in group 6, in which the dominant bull (No. 8) had a total of 71 services versus 37 services by the subordinate bull (No. 9). However, number of services did not appear to be related to social hierarchy in group 5, since both bulls had a similar number of services (No. 6 = 43 and No. 7 = 42 services). In addition, there was no apparent relationship between a bull's social rank and the percentage of females that he serviced. Dominance has been shown to be related to mating activity in mixed-age bull groups (3,4) as well as in groups of bulls of the same age (3). Bulls with higher mean libido and mean serving capacity scores tended to have a higher number of services and serviced a higher percentage of estrus heifers. In a more extensive study that involved only single-sire BFR's, both mean libido and mean serving capacity scores of bull's were moderately correlated with mating activity (r = .39 to .58) and pregnancy rate (r = .48 to .54) (8). Similar results were reported by another investigator (10). Percentage of heifers that became pregnant was not different (P>.O5) between single- and multi-sire breeding groups (34.5 + 4.7 and However, in multi-sire groups, 44.1 + 1.8, respectively) (Table II). pregnancy rate was higher for heifers observed serviced by both bulls (48.7%) than for heifers observed serviced by only one bull (26.0%). These findings are not in agreement with other multi-sire, natural mating investigations (3), or with heterospermic insemination studies in cattle (13). Individual pregnancy rates of bulls were not Significantly (P>.O5) correlated with BSE score (r = .35) or with components of the BSE score. Correlations between pregnancy rate and components of the BSE score were: .15, .Ol, . 06, -.25, and -.43 for scrotal circumference, percentage of motile sperm cells, motility rate, percent age of primary and total abnormalities, respectively. Pregnancy rate, based on those heifers observed in estrus, was not affected (P>.O5) by BFR. Pregnancy rate for single-sire groups was 29.3 ? 3.0% while that of multi-sire groups was 34.3 * 6.6% (Table II).
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THERIOGENOLOCY It is concluded that single-sire groups were more efficient in sire usage than multi-sire groups. This is due to overlap in servicing in multi-sire groups, and non-significant difference in pregnancy rates for the two 5FR's. LITERATURE CITED 1.
Rupp, G. P. Bull behavior and management. Proc. The Range Beef cow: A Symp. on Prod. IV, Denver, Colorado, 1977, p. 25-29.
2.
Ensminger, M. E. Beef Cattle Science, 5th ed. Interstate Printers and Publishers, Danville, Illinois, 1976, p. 347.
3.
Rupp, G. P., Ball, L., Shoop, M. C., and Chenoweth, P. J. Reproductive efficiency of bulls in natural service: effects of male to female ratio and single- vs multiple-sire breeding groups. J. Am. Vet. Med. Assn. 171:639-642 (1977).
4.
Blockey, M. A. deB. Observations on group mating of bulls at pasture. Appl. Anim. Ethol. 5:15-34 (1979).
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Pexton, J. E., Denham, A. H., Mangus, W. L., Walck, J. D., and Brinks, J. S. Breeding by hand mating in synchronization of estrus program with beef heifers. Colorado Exp. Sta. Bull., Gen. Series 966:21-22 (1977).
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Pexton, J. E. and Chenoweth, P. J. Using bulls to breed beef heifers at a synchronized estrus. 69th Ann. Meeting, Am. Sot. Anim. Sci., Abstract No. 488, p. 195 (1977).
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Simons, J. C. (ed.) A compilation of current information on breeding soundness and evaluation and related subjects. The Sot. for Theriogenology J., Vol. VII, 2nd ed. pp. l-20 (1976).
8.
Farin, P. W. Sexual behavior and fertility in beef bulls. M. S. Thesis. Colorado State University, Ft. Collins, Colorado, 1980.
9.
Chenoweth, P. J. Consideration of behavioral aspects of the natural breeding bull. Proc. Ann. Meeting, Sot. for Theriogenology, Lexington, Kentucky, p. 109-122 (1976).
10.
Blockey, M. A. de5. The influence of serving capacity of bulls on herd fertility. J. Anim. Sci. -46:589-595 (1978).
11.
Snedecor, G. W. and Cochran, W. 6. Statistical Methods, 6th ed., Iowa State College Press, Ames, Iowa, 1967, Ch. 4 and 7.
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THERiOCENOLOCY 12.
Spitzer, J. C., Jones, D. L., Miksch, E. D., and Wiltbank, J. N. Synchronization of estrus in beef cattle: III. Field trials in heifers using norgestomet implant and injections of norgestomet and estradiol valerate. Theriogenology H:223-229 (1978).
13.
Nelson, L. D., Pickett, B. W., and Siedel, Jr., G. E. Effect of heterospermic insemination on fertility of cattle. J. Anim. Sci. 40:1124-1129 (1975).
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