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Vital Statistics and Reasons for Disposal of United States and Canadian Artificial Insemination Dairy Sires1
Vital Statistics and Reasons for Disposal of United States and Canadian Artificial Insemination Dairy Sires 1 J. L. K R A T Z , 2 C. J. W I L C O X , 3 F. G. M A R T I N , 4 and R. B. BECKER 3 Dairy Science 3 and Statistics 4 Departments University of Florida institute of Food and Agricultural Sciences Gainesville 32611
ABSTRACT
MATERIALS AND METHODS
Vital statistics were evaluated for artificial insemination sires leaving service during 1939 through 1974. Data consisted of 11,704 sires of six breeds. The major cause for leaving service was reproductive failure at a frequency of 32.5%; next ranked was undesirable characteristics of offspring with a frequency of 20.7%. Overall culling rate for low yields of daughters was 14.8%, but after 1965 this cause accounted for about 30%. Mean life span was 3.4 yr with small differences among years. Breed differences were detected for service life and causes for leaving service. Modifications of classic life table techniques are needed to reflect entry of sires into service at various ages and evaluation of vital statistics subsequent to 1974.
Artificial insemination studs ( n = 1 4 6 ) f r o m the US and Canada and pure breed associations provided information on dates of birth and first and last successful semen collection, reason(s) for disposal, and fate. Complete records on 11,704 sires of six breeds were analyzed. Major statistical techniques involved were Chi-square goodness of fit and least squares analysis of variance; details of these analyses and development of life tables were described (2, 3). RESULTS AND DISCUSSION Reasons for Disposal
INTRODUCTION
Knowledge of the variation and mean artificiation insemination (AI) service life of bulls would help AI organizations develop realistic expectations for lifetime semen production. Results should be useful to project or model the service activity of individual bulls or a battery of bulls. Other studies on AI service life of beef bulls (2) and reasons why dairy bulls leave service (3) have been published. Objectives of the present study were to provide new information subsequent to (4) for dairy sires, including additional data (616 cases) for 1939 to 1964 and data for 1965 to 1974 (2201
CaSCS).
Received September 14, 1981. 1Florida Agricultural Experiment Station Journal Series No. 3223. 2Wisconsin Agricultural Reporting Service, Madison, Wl 53713. 1983 J Dairy Sci 66:642--646
Although 326 reasons for disposal have been listed, they were grouped into 21 subcategories and these in turn into 6 major categories (Table 1). Leading cause of disposal was reproductive failure (32.5%) followed by undesirable characteristics of offspring (20.7%). Overall culling rate of sires for low milk yield of daughters was 14.8%. Miscellaneous, which included over 250 reasons, accounted for 17.8%. Distribution of major categories differed (P<.01) among breeds. Major cause of heterogeneity was high frequency of culling of Holsteins for low milk yield of daughters with low frequency for Milking Shorthorns. Holsteins had high frequencies of loss for crampy (3.4%) and arthritis (2.6%) compared to other breeds, which averaged 1.1 and .6%. Holsteins and Ayrshires had fewer losses for reproductive failure. Problems in collection accounted for 10.9% of disposals. Increased selection pressure for milk yield of daughters has occurred, particularly after 1965 (Table 2), when over 30% of all sires left for this reason. Such increases should lead to even greater genetic improvement in the US dairy population. Further increases can be obtained by improved management practices that lead to
642
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m a i n d e r (7.9%) left t h e stud alive, usually for c o n t i n u e d use in service elsewhere. A f e w o f t h e l a t t e r ( < . 4 % ) w e r e r e t u r n e d to AI service at a later date; t h e y were c o n s i d e r e d as d i f f e r e n t animals in this s t u d y .
l o w e r i n v o l u n t a r y losses. F o r e x a m p l e , m a r k e d decreases o c c u r r e d in losses d u e t o r e p r o d u c t i v e failure, p o s s i b l y f r o m i m p r o v e d screening t e c h n i q u e s p r i o r to e n t r y into service and i m p r o v e d animal m a n a g e m e n t . Also, sires in r e c e n t years e n t e r e d service at earlier ages (Table 3), a l t h o u g h their service lives r e m a i n e d essentially t h e same a f t e r 1955. Losses due t o disease and injury (Table 2) increased t o 21.3% during 1955 to 1 9 5 9 b u t declined to 13.4% during 1970 t o 1974. Most sires were sold for slaughter (83.9%); an additional 8.2% died at t h e stud. The re-
Service Life
Least squares m e a n s are in Table 3. Age at e n t r y i n t o service d e c r e a s e d f r o m early years o f AI ( m a x i m u m o f 5.70 yr during 1 9 3 9 t o 1944) t o a b o u t 3.0 yr s u b s e q u e n t t o 1965. Sires w e r e c r e d i t e d with service time, even if n o s e m e n was collected, for t h e p e r i o d b e t w e e n their initial
TABLE 1. Reasons for disposal of AI dairy sires. Breed a Reason Characteristics of offspring Low milk yield Poor type Avoid inbreeding All others Total Disease and infection Crampy Hardware Arthritis All others Total Injuries Injured stifle Leg injury All others Total Reproductive failure Low conception rate Poor semen quality All others Total Problems in collection Refused to serve Old age All others Total Miscellaneous Leased out Unpopular Not needed All others Total
H
G
J
A
BS
MS
Overall
17.7 b 2.8 .4 4.0 24.9
11.8 2.3 1.1 .4 15.6
13.9 2.6 1.9 .9 19.3
16.4 3.2 2.3 .8 22.7
13.1 2.1 3.9 1.4 20.5
4.0 .4 4.8 .3 9.5
14.8 2.5 1.3 2.2 20.7
3.4 2.0 2.6 8.5 16.5
1.3 1.9 1.0 9.2 13.4
.4 1.6 .6 7.5 10.1
1.9 1.0 .4 9.9 13.2
.5 2.0 1.0 6.4 9.9
1.3 1.3 .2 7.4 10.2
2.1 1.8 1.6 8.5 13.9
.7 .6 3.9 5.2
.5 .2 2.4 3.1
1.2 .5 2.2 3.9
.0 .6 1.9 2.5
.2 .3 2,8 3,3
.4 .4 2.8 3.6
.7 .5 3.0 4.2
13.6 6.0 4.3 23,9
28.7 7.5 5.6 41.8
21.1 10.5 8.0 39.6
13.9 6.7 6.9 27.5
23.5 6.1 5.4 35.0
27.9 11.1 5.7 44.7
19.7 7.3 5.5 32.5
1.5 5.2 3.9 10.6
.7 4.2 5.6 10.5
3.7 3.6 4.1 11.4
1.7 4.4 4.2 10.3
3.1 5,6 3.8 12.5
2.9 5.3 4.8 13.0
2.2 4.7 4.0 10.9
3.4 1.3 1.2 13.0 18.9
.2 1.9 1.5 12.0 15.6
.3 1.5 1.3 12.5 15.6
.4 3.6 4.0 15.9 23.9
.3 1.1 2.0 15.5 18.9
.0 2.1 3.8 13.2 19.1
1.7 1.6 1.6 12.9 17.8
aH= Holstein; G = Guernsey; J = Jersey; A = Ayrshire; BS = Brown Swiss; MS = Milking Shorthorn. bpercentages. Journal of Dairy Science Vol. 66, No. 3, 1983
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KRATZ ET AL.
TABLE 2. Relative frequencies of reasons for disposal by time.
Period 1939--44 1945--49 1950--54 1955--59 1960--64 1965--69
1970--74
Low yield of daughters
Reproductive failure
Disease or injury
Remainder
1.8 8.4 10.8 10.9 13.9 29.4 35.8
32.6 35.1 29.8 29.4 27.6 14.8 16.5
14.5 15.7 18.2 21.5 19.3 15.4 13.4
51.1 40.8 41.2 38.4 39.2 40.4 34.3
sampling and their return to active service. Service life is the difference b e t w e e n age at disposal and age at entry into first service. Service lives were adjusted for age at e n t r y ; m a t h e m a t i c a l m o d e l also included stud, breed, and time. Service lives were greatest during 1960 to 1964 (actual, 4.19 yr; least squares mean, 4.14 yr) decreasing slightly to 3.81 and 3.99 yr (actual); least squares means were 3.54 and 3.73 yr during the last two periods. Relationship b e t w e e n ages at e n t r y and disposal were significant (P<.01), although age at e n t r y was n o t a good predictor of t e n u r e (R=.17). Overall age o f e n t r y of the entire sample o f 11,703 sires was 4.32 yr, age at disposal 7.73 yr, and tenure 3.41 yr. Breeds differed (P<.01) (Table 4). A l t h o u g h these are least squares means, w h e t h e r these differences were true breed differences or reflected o t h e r factors (e.g., semen demand,
breeder tradition, et al. ) is u n k n o w n . Brown Swiss had the longest adjusted service lives (3.77 yr) and Milking Shorthorns and Guernseys the shortest (3.11 and 3.24 yr). Variation associated with breed in service lives of less than 6 yr, when sire proofs for milk yield would be e x p e c t e d to be available, are in Table 5. Over 31% of all sires were n o t available at age 6 yr. F o r 1939 to 1961, Wilcox et al. (5) f o u n d that 45% of sires entering at < 2 yr and 38% entering at <3 yr still were available at 6 yr. The present study includes all previous data, new data for sires of t h a t age, and data f r o m sires entering service at 4 and 5 yr. Current estimates of service lives of y o u n g sires are needed. N u m b e r of sires leaving service at advanced ages (> 10 yr) was high, averaging over 27%. Ayrshire and Brown Swiss breeds particularly had high p r o p o r t i o n s ( ~ 3 4 % ) o f old sires.
TABLE 3. Average age at entry, age at disposal, and service period of dairy sires by time. Period
1939-1944 1945--1949 1950--1954 1955--1959 1960"--1964
1965--1969 1970--1974 Overall
Sires
Age of entry
Age at disposal
Mean service period a
(no.)
(yr)
(yr)
(yr)~
221 1,580 2,621 2,714 2,367 1,706 494 11,703
5.70
7.15 7.08 7.80 8.33 8.22 6.83 7.06 7.73
1.75 2.03 3.05 3.93 4.13 3.54 3.73 3.42
5.25 4.88 4.42 4.03 3.02 3.07 4.32
aLeast squares means from model which also included age at entry, breed, and stud. Arithmetic (raw) means can be obtained by difference between a~es at entry and disposal.
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TABLE 4, Average age at entry, age at disposal, and service period b y breed. Breed
Holstein Guernsey Jersey Ayrshire Brown Swiss Milking S h o r t h o r n Overall
Sires
Age at entry
Age at disposal
Mean service period a
(no) 5,245 2,877 1,929 524 609 476 11,660
(yr)
(yr)
(yr)
3.98 4.50 4.62 5.11 4.69 4.25 4.31
7.51 7.70 8.05 8.38 8.37 7.37 7.72
3.45 3.24 3.49 3.44 3.77 3.11 3.42
aLeast squares means from model which also included age at entry, time period, and stud. Arithmetic (raw) m e a n s can be obtained by difference between ages at entry and disposal.
TABLE 5. Sires with service periods o f less t h a n 6 and more t h a n 10 yr. Breed
< 6 yr
Holstein Guernsey Jersey Ayrshire Brown Swiss Milking Shorthorn Total or average
> 1 0 yr
(no.)
(%)
(no.)
(%)
1825 895 518 135 149 170 3,692
34.8 31.1 26.9 25.8 24.5 35.7 31.7
1463 716 538 178 210 103 3,207
27.9 24.9 27.9 34.0 34.5 21.6 27.5
TABLE 6. Life table for AI sires. Period of life
Holstein
Guernsey
Jersey
Ayrshire
Brown Swiss
Milking Shorthorn
Overall
<1 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5
7.531 6.59 6.24 5.58 4.87 4.22 3.73 3.23 2.78 2.36 1.99 1.63 1.44 1.31 1.16 1.04 .85
7.69 6.69 6.84 5.12 4.42 3.85 3.32 2.87 2.46 2.09 1.73 1.41 1.21 .97 .80 .58 .50
8.06 7.06 6.20 5.44 4.70 4.01 3.49 2.98 2.50 2.00 1.73 1.41 1.24 1.20 1.07 1.32 1.00
8.40 7.40 6.57 5.76 5.13 4.49 3.91 3.39 3.01 2.70 2.22 1.85 1.65 1.50 1.64 1.42 .83
8.38 7.38 6.49 5.73 4.99 4.32 3.75 3.31 2.95 2.47 1.97 1.60 1.14 .90 .79 .83 .50
7.39 6.38 5.43 4.68 4.16 3.58 3.14 2.69 2.38 2.14 1.68 1.48 1.32 1.75 1.17 1.00 .50
7.74 6.76 6.13 5.41 4.72 4.08 3.57 3.09 2.66 2.25 1.89 1.55 1.35 1.22 1.11 1.06 .83
1 Expected life span in years for sires entering service at period o f life indicated, for conditions during 1939 through 1974. Journal o f Dairy Science Vol. 66, No. 3, 1983
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KRATZ ET AL.
Life Tables
Table 6 is a population life table (1). Life for AI sires was considered completed at last successful semen collection. Sires were credited with being alive, however, prior to entry into service. Hence, estimates of expected lifespan are biased upward slightly by entry of sires into service at advanced ages. Magnitude of this bias can be seen by comparing estimates with Table 3. Average age at entry into service was 4.32 yr with subsequent tenure 3.41 yr. Linear interpolation between 3.5 and 4.5 yr (Table 6) suggested a predicted lifespan of 4.84 yr rather than 3.41 yr observed. Possible use of a cohort life table (1) was examined. The table created (not shown) included 3839 sires alive on Jan. 1, 1971. Although tenure appeared to increase during 1939 to 1964, there were no subsequent increases. Hence, 1971 seemed appropriate. This approach to estimating tenure suffered from the same weakness as Table 6, however, because of sires entering the population at ages >1 yr. Expected tenure, thus, would be overestimated, particularly for young sires. Without appropriate adjustment, therefore, it appears that neither approach gives realistic estimates of tenure. Objectives of future research concerning
Journal of Dairy Science Vol. 66, No. 3, 1983
vital statistics of AI sires should address this problem. ACKNOWLEDGMENT
Financial support of the National Association of Animal Breeders is gratefully acknowledged. Artificial insemination studs in the United States and Canada continue to supply data for this investigation as do the pure breed associations. REFERENCES
1 Gross, A. J., and V. A. Clark. 1975. Survival distributions: Reliability applications in the biomedical sciences. John Wiley and Sons, New York, NY. 2 Kratz, J. L., C. J. Wilcox, F. G. Martin, D. E. Franke, and R. B. Becket. 1977. Vital Statistics of US and Canadian beef sires. J. Anim. Sci. 45:43. 3 Kratz, J. L., C. J. Wilcox, F. G. Martin, and R. B. Becker. 1976. Culling rates of United States and Canadian artificial insemination dairy sires for type and production of daughters. J. Dairy Sci. 59:767. 4 Roman, J., C. J. Wilcox, R. B. Becker, and M. Koger. 1969. Tenure and reasons for disposal of artificial insemination dairy sires. J. Dairy Sci. 52:1063. 5 Wilcox, C. J., J. Roman, and R. B. Becker. 1967. Fate of young sires used for artificial insemination. J. Dairy Sci. 50:884.
ABSTRACT
MATERIALS AND METHODS
Vital statistics were evaluated for artificial insemination sires leaving service during 1939 through 1974. Data consisted of 11,704 sires of six breeds. The major cause for leaving service was reproductive failure at a frequency of 32.5%; next ranked was undesirable characteristics of offspring with a frequency of 20.7%. Overall culling rate for low yields of daughters was 14.8%, but after 1965 this cause accounted for about 30%. Mean life span was 3.4 yr with small differences among years. Breed differences were detected for service life and causes for leaving service. Modifications of classic life table techniques are needed to reflect entry of sires into service at various ages and evaluation of vital statistics subsequent to 1974.
Artificial insemination studs ( n = 1 4 6 ) f r o m the US and Canada and pure breed associations provided information on dates of birth and first and last successful semen collection, reason(s) for disposal, and fate. Complete records on 11,704 sires of six breeds were analyzed. Major statistical techniques involved were Chi-square goodness of fit and least squares analysis of variance; details of these analyses and development of life tables were described (2, 3). RESULTS AND DISCUSSION Reasons for Disposal
INTRODUCTION
Knowledge of the variation and mean artificiation insemination (AI) service life of bulls would help AI organizations develop realistic expectations for lifetime semen production. Results should be useful to project or model the service activity of individual bulls or a battery of bulls. Other studies on AI service life of beef bulls (2) and reasons why dairy bulls leave service (3) have been published. Objectives of the present study were to provide new information subsequent to (4) for dairy sires, including additional data (616 cases) for 1939 to 1964 and data for 1965 to 1974 (2201
CaSCS).
Received September 14, 1981. 1Florida Agricultural Experiment Station Journal Series No. 3223. 2Wisconsin Agricultural Reporting Service, Madison, Wl 53713. 1983 J Dairy Sci 66:642--646
Although 326 reasons for disposal have been listed, they were grouped into 21 subcategories and these in turn into 6 major categories (Table 1). Leading cause of disposal was reproductive failure (32.5%) followed by undesirable characteristics of offspring (20.7%). Overall culling rate of sires for low milk yield of daughters was 14.8%. Miscellaneous, which included over 250 reasons, accounted for 17.8%. Distribution of major categories differed (P<.01) among breeds. Major cause of heterogeneity was high frequency of culling of Holsteins for low milk yield of daughters with low frequency for Milking Shorthorns. Holsteins had high frequencies of loss for crampy (3.4%) and arthritis (2.6%) compared to other breeds, which averaged 1.1 and .6%. Holsteins and Ayrshires had fewer losses for reproductive failure. Problems in collection accounted for 10.9% of disposals. Increased selection pressure for milk yield of daughters has occurred, particularly after 1965 (Table 2), when over 30% of all sires left for this reason. Such increases should lead to even greater genetic improvement in the US dairy population. Further increases can be obtained by improved management practices that lead to
642
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m a i n d e r (7.9%) left t h e stud alive, usually for c o n t i n u e d use in service elsewhere. A f e w o f t h e l a t t e r ( < . 4 % ) w e r e r e t u r n e d to AI service at a later date; t h e y were c o n s i d e r e d as d i f f e r e n t animals in this s t u d y .
l o w e r i n v o l u n t a r y losses. F o r e x a m p l e , m a r k e d decreases o c c u r r e d in losses d u e t o r e p r o d u c t i v e failure, p o s s i b l y f r o m i m p r o v e d screening t e c h n i q u e s p r i o r to e n t r y into service and i m p r o v e d animal m a n a g e m e n t . Also, sires in r e c e n t years e n t e r e d service at earlier ages (Table 3), a l t h o u g h their service lives r e m a i n e d essentially t h e same a f t e r 1955. Losses due t o disease and injury (Table 2) increased t o 21.3% during 1955 to 1 9 5 9 b u t declined to 13.4% during 1970 t o 1974. Most sires were sold for slaughter (83.9%); an additional 8.2% died at t h e stud. The re-
Service Life
Least squares m e a n s are in Table 3. Age at e n t r y i n t o service d e c r e a s e d f r o m early years o f AI ( m a x i m u m o f 5.70 yr during 1 9 3 9 t o 1944) t o a b o u t 3.0 yr s u b s e q u e n t t o 1965. Sires w e r e c r e d i t e d with service time, even if n o s e m e n was collected, for t h e p e r i o d b e t w e e n their initial
TABLE 1. Reasons for disposal of AI dairy sires. Breed a Reason Characteristics of offspring Low milk yield Poor type Avoid inbreeding All others Total Disease and infection Crampy Hardware Arthritis All others Total Injuries Injured stifle Leg injury All others Total Reproductive failure Low conception rate Poor semen quality All others Total Problems in collection Refused to serve Old age All others Total Miscellaneous Leased out Unpopular Not needed All others Total
H
G
J
A
BS
MS
Overall
17.7 b 2.8 .4 4.0 24.9
11.8 2.3 1.1 .4 15.6
13.9 2.6 1.9 .9 19.3
16.4 3.2 2.3 .8 22.7
13.1 2.1 3.9 1.4 20.5
4.0 .4 4.8 .3 9.5
14.8 2.5 1.3 2.2 20.7
3.4 2.0 2.6 8.5 16.5
1.3 1.9 1.0 9.2 13.4
.4 1.6 .6 7.5 10.1
1.9 1.0 .4 9.9 13.2
.5 2.0 1.0 6.4 9.9
1.3 1.3 .2 7.4 10.2
2.1 1.8 1.6 8.5 13.9
.7 .6 3.9 5.2
.5 .2 2.4 3.1
1.2 .5 2.2 3.9
.0 .6 1.9 2.5
.2 .3 2,8 3,3
.4 .4 2.8 3.6
.7 .5 3.0 4.2
13.6 6.0 4.3 23,9
28.7 7.5 5.6 41.8
21.1 10.5 8.0 39.6
13.9 6.7 6.9 27.5
23.5 6.1 5.4 35.0
27.9 11.1 5.7 44.7
19.7 7.3 5.5 32.5
1.5 5.2 3.9 10.6
.7 4.2 5.6 10.5
3.7 3.6 4.1 11.4
1.7 4.4 4.2 10.3
3.1 5,6 3.8 12.5
2.9 5.3 4.8 13.0
2.2 4.7 4.0 10.9
3.4 1.3 1.2 13.0 18.9
.2 1.9 1.5 12.0 15.6
.3 1.5 1.3 12.5 15.6
.4 3.6 4.0 15.9 23.9
.3 1.1 2.0 15.5 18.9
.0 2.1 3.8 13.2 19.1
1.7 1.6 1.6 12.9 17.8
aH= Holstein; G = Guernsey; J = Jersey; A = Ayrshire; BS = Brown Swiss; MS = Milking Shorthorn. bpercentages. Journal of Dairy Science Vol. 66, No. 3, 1983
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KRATZ ET AL.
TABLE 2. Relative frequencies of reasons for disposal by time.
Period 1939--44 1945--49 1950--54 1955--59 1960--64 1965--69
1970--74
Low yield of daughters
Reproductive failure
Disease or injury
Remainder
1.8 8.4 10.8 10.9 13.9 29.4 35.8
32.6 35.1 29.8 29.4 27.6 14.8 16.5
14.5 15.7 18.2 21.5 19.3 15.4 13.4
51.1 40.8 41.2 38.4 39.2 40.4 34.3
sampling and their return to active service. Service life is the difference b e t w e e n age at disposal and age at entry into first service. Service lives were adjusted for age at e n t r y ; m a t h e m a t i c a l m o d e l also included stud, breed, and time. Service lives were greatest during 1960 to 1964 (actual, 4.19 yr; least squares mean, 4.14 yr) decreasing slightly to 3.81 and 3.99 yr (actual); least squares means were 3.54 and 3.73 yr during the last two periods. Relationship b e t w e e n ages at e n t r y and disposal were significant (P<.01), although age at e n t r y was n o t a good predictor of t e n u r e (R=.17). Overall age o f e n t r y of the entire sample o f 11,703 sires was 4.32 yr, age at disposal 7.73 yr, and tenure 3.41 yr. Breeds differed (P<.01) (Table 4). A l t h o u g h these are least squares means, w h e t h e r these differences were true breed differences or reflected o t h e r factors (e.g., semen demand,
breeder tradition, et al. ) is u n k n o w n . Brown Swiss had the longest adjusted service lives (3.77 yr) and Milking Shorthorns and Guernseys the shortest (3.11 and 3.24 yr). Variation associated with breed in service lives of less than 6 yr, when sire proofs for milk yield would be e x p e c t e d to be available, are in Table 5. Over 31% of all sires were n o t available at age 6 yr. F o r 1939 to 1961, Wilcox et al. (5) f o u n d that 45% of sires entering at < 2 yr and 38% entering at <3 yr still were available at 6 yr. The present study includes all previous data, new data for sires of t h a t age, and data f r o m sires entering service at 4 and 5 yr. Current estimates of service lives of y o u n g sires are needed. N u m b e r of sires leaving service at advanced ages (> 10 yr) was high, averaging over 27%. Ayrshire and Brown Swiss breeds particularly had high p r o p o r t i o n s ( ~ 3 4 % ) o f old sires.
TABLE 3. Average age at entry, age at disposal, and service period of dairy sires by time. Period
1939-1944 1945--1949 1950--1954 1955--1959 1960"--1964
1965--1969 1970--1974 Overall
Sires
Age of entry
Age at disposal
Mean service period a
(no.)
(yr)
(yr)
(yr)~
221 1,580 2,621 2,714 2,367 1,706 494 11,703
5.70
7.15 7.08 7.80 8.33 8.22 6.83 7.06 7.73
1.75 2.03 3.05 3.93 4.13 3.54 3.73 3.42
5.25 4.88 4.42 4.03 3.02 3.07 4.32
aLeast squares means from model which also included age at entry, breed, and stud. Arithmetic (raw) means can be obtained by difference between a~es at entry and disposal.
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TABLE 4, Average age at entry, age at disposal, and service period b y breed. Breed
Holstein Guernsey Jersey Ayrshire Brown Swiss Milking S h o r t h o r n Overall
Sires
Age at entry
Age at disposal
Mean service period a
(no) 5,245 2,877 1,929 524 609 476 11,660
(yr)
(yr)
(yr)
3.98 4.50 4.62 5.11 4.69 4.25 4.31
7.51 7.70 8.05 8.38 8.37 7.37 7.72
3.45 3.24 3.49 3.44 3.77 3.11 3.42
aLeast squares means from model which also included age at entry, time period, and stud. Arithmetic (raw) m e a n s can be obtained by difference between ages at entry and disposal.
TABLE 5. Sires with service periods o f less t h a n 6 and more t h a n 10 yr. Breed
< 6 yr
Holstein Guernsey Jersey Ayrshire Brown Swiss Milking Shorthorn Total or average
> 1 0 yr
(no.)
(%)
(no.)
(%)
1825 895 518 135 149 170 3,692
34.8 31.1 26.9 25.8 24.5 35.7 31.7
1463 716 538 178 210 103 3,207
27.9 24.9 27.9 34.0 34.5 21.6 27.5
TABLE 6. Life table for AI sires. Period of life
Holstein
Guernsey
Jersey
Ayrshire
Brown Swiss
Milking Shorthorn
Overall
<1 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5
7.531 6.59 6.24 5.58 4.87 4.22 3.73 3.23 2.78 2.36 1.99 1.63 1.44 1.31 1.16 1.04 .85
7.69 6.69 6.84 5.12 4.42 3.85 3.32 2.87 2.46 2.09 1.73 1.41 1.21 .97 .80 .58 .50
8.06 7.06 6.20 5.44 4.70 4.01 3.49 2.98 2.50 2.00 1.73 1.41 1.24 1.20 1.07 1.32 1.00
8.40 7.40 6.57 5.76 5.13 4.49 3.91 3.39 3.01 2.70 2.22 1.85 1.65 1.50 1.64 1.42 .83
8.38 7.38 6.49 5.73 4.99 4.32 3.75 3.31 2.95 2.47 1.97 1.60 1.14 .90 .79 .83 .50
7.39 6.38 5.43 4.68 4.16 3.58 3.14 2.69 2.38 2.14 1.68 1.48 1.32 1.75 1.17 1.00 .50
7.74 6.76 6.13 5.41 4.72 4.08 3.57 3.09 2.66 2.25 1.89 1.55 1.35 1.22 1.11 1.06 .83
1 Expected life span in years for sires entering service at period o f life indicated, for conditions during 1939 through 1974. Journal o f Dairy Science Vol. 66, No. 3, 1983
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KRATZ ET AL.
Life Tables
Table 6 is a population life table (1). Life for AI sires was considered completed at last successful semen collection. Sires were credited with being alive, however, prior to entry into service. Hence, estimates of expected lifespan are biased upward slightly by entry of sires into service at advanced ages. Magnitude of this bias can be seen by comparing estimates with Table 3. Average age at entry into service was 4.32 yr with subsequent tenure 3.41 yr. Linear interpolation between 3.5 and 4.5 yr (Table 6) suggested a predicted lifespan of 4.84 yr rather than 3.41 yr observed. Possible use of a cohort life table (1) was examined. The table created (not shown) included 3839 sires alive on Jan. 1, 1971. Although tenure appeared to increase during 1939 to 1964, there were no subsequent increases. Hence, 1971 seemed appropriate. This approach to estimating tenure suffered from the same weakness as Table 6, however, because of sires entering the population at ages >1 yr. Expected tenure, thus, would be overestimated, particularly for young sires. Without appropriate adjustment, therefore, it appears that neither approach gives realistic estimates of tenure. Objectives of future research concerning
Journal of Dairy Science Vol. 66, No. 3, 1983
vital statistics of AI sires should address this problem. ACKNOWLEDGMENT
Financial support of the National Association of Animal Breeders is gratefully acknowledged. Artificial insemination studs in the United States and Canada continue to supply data for this investigation as do the pure breed associations. REFERENCES
1 Gross, A. J., and V. A. Clark. 1975. Survival distributions: Reliability applications in the biomedical sciences. John Wiley and Sons, New York, NY. 2 Kratz, J. L., C. J. Wilcox, F. G. Martin, D. E. Franke, and R. B. Becket. 1977. Vital Statistics of US and Canadian beef sires. J. Anim. Sci. 45:43. 3 Kratz, J. L., C. J. Wilcox, F. G. Martin, and R. B. Becker. 1976. Culling rates of United States and Canadian artificial insemination dairy sires for type and production of daughters. J. Dairy Sci. 59:767. 4 Roman, J., C. J. Wilcox, R. B. Becker, and M. Koger. 1969. Tenure and reasons for disposal of artificial insemination dairy sires. J. Dairy Sci. 52:1063. 5 Wilcox, C. J., J. Roman, and R. B. Becker. 1967. Fate of young sires used for artificial insemination. J. Dairy Sci. 50:884.