- Email: [email protected]
Semen Production and Fertility of Dairy Bulls Ejaculated Either Once or Twice at Intervals of Either Four or Eight Days
SEMEN PRODUCTION AND FERTILITY
OF D A I R Y B U L L S
E J A C U L A T ] ~ ' D E I T H E R ONCE OR T W I C E A T I N T E R V A L S OF E I T H E R F O U R OR E I G H T D A Y S R. W. B R A T T O N A~D R. H. F O O T E
Dcpartme~t of AMmal H~sbandry, Corncll UMversily, Ithaca, N. Y.
The increased usefulness of d a i r y sires through artificial breeding has come about p r i m a r i l y f r o m increased extension rates of semen and improved extenders and processing procedures. Although there is still room for substantial improvement in each of these areas, it seems that f u r t h e r increases f r o m these sources are likely to be r a t h e r small and costly to obtain. I n contrast to the above situation, little is known about the m a x i m u m n u m b e r of spermatozoa that can be obtained f r o m bulls, p a r t i c u l a r l y over long periods of time, or what effects frequent ejaculation m a y have on fertility and subsequeut spermatozoa production (4, 9, 10, 11, 14, 15). W o r k b y Collins et al. (5) and more recently by B r a n t o n et al. (1) and Hale et al. (8) suggests that m a n y more spermatozoa m a y be obtained from bulls t h a n has generally been thought to be possible. Following the early work reported by ~Iereier et al. (11) a series of long-time experiments were u n d e r t a k e n by this laboratory in cooperation with the New York Artificial B r e e d e r s ' Cooperative, Inc., to obtain information on the relationship of frequency of ejaculation to spermatozoa production and fertility. The results reported here are from a year-long experiment in which d a i r y bulls were ejaculated once at either 4- or 8-day intervals or twice at 8-day intervals. EXPERIMENTAL PROCEDURE
Two groups of bulls eaeh eonsisting of eight Holsteins, four Guernseys, three Jerseys, and two Ayrshires were selected f r o m the active stud of the New York Artifieial B r e e d e r s ' Cooperative, Ine. One group was ejaeulated once at 4-day intervals for 360 days and the other group was ejaeulated onee at 8-day intervals for 272 days and then twice at 8-day intervals for the remaining 88 days of the 360-day experimental period. At the time these experiments were begun (August, 1948), the studies on sexual excitement of bulls had not been made (1, 5, 8); consequently, the bulls in this experiment were not restrained at the time semen was eolleeted. Feeding and other m a n a g e m e n t praetiees of the bulls were those common to the stud at that time. The volume of each ejaculate, the n u m b e r of spermatozoa per milliliter of semen, and the per cent of motile spermatozoa in the ejaculates were determined b y the routine procedures of this laboratory (12, 16). Only the semen ejaculates containing 900 × 102 or more spermatozoa p e r milliliter of semen and 70% or more motile spermatozoa and having a methylene blue reduction time of 7 minutes or less were extended for breeding purposes. The semen was p a r t i a l l y exReceived f o r publieation J u n e 24, 1954. 1439
1440
R. ~V. B R A T T O X
AND
R. I I . FOOTE
tended and cooled to 5 ° C. (7) and then made up to final volmne with either 2.9~c eitrate-sulfanilamide yolk (3. 13) or experimental whole egg extenders (6). The latter extenders were used for only tile Holstein and Guernsey semen on a splitejaculate basis to avoid confounding of these superimposed t r e a t m e n t s with the collection regimes. The extenders contained no penicillin or streptomycin. The semen extension rates varied, depending upon the day-to-day and seasonal demands for semen and the amount of semen produced by the individual bulls. D u r i n g the last 88 days of the experiment the two ejaculates obtained f r o m the 8-day interval bulls were mixed for processing and subsequent use in inseminating cows. Breedings were made b y the technicians affiliated with the New York Artificial B r e e d e r s ' Cooperative, Inc.. with semen which, on the average, was about 33 hours old. The extended semen of a p a r t i c u l a r ejaculate was shipped to as m a n y field technicians as the available volume would permit. The next time this bull was ejaculated his semen was shipped to technicians not receiving it the time before. B y rotating bulls among technicians in this m a n n e r all technicians received about equal opportunities to use each bull. The average 60- to 90-day per cent n o n r e t u r n s to first services for t r e a t m e n t s were calculated on the basis of the average per cent n o n r e t u r n s for the individual bulls, since the n u m b e r of services for a n y p a r t i c u l a r bull was not a random variable but was, to a large extent, dependent upon his breed, his popularity and whether or not he was a young bull being sampled and held in waiting for an AB proof. RESULTS AND DISCUSSION I n Table I are the group averages for the semen and fertility observations made d u r i n g the two periods of the experiment. Of p a r t i c u l a r interest and importance in this table are the numbers of motile spermatozoa per ejaculate and per 8-day period and the per cent n o n r e t n r n s to first services. D u r i n g the first 272 days of the experiment the 4-day interval bulls averaged 5.7 billion motile spermatozoa per ejaculate and 11.4 billion per 8-day period, whereas the 8-day interval bulls averaged 7.0 billion motile spermatozoa per ejaculate and per 8-day period. Thus, per 8-day period, 63% more motile s p e r m were obtained f r o m the 4-day t h a n f r o m the 8-day interval bulls. W h e n the 8-day interval bulls were changed f r o m one ejaculate to two ejaculates every eighth day their motile sperm output per 8-day period was 101.6% of that for the 4-day interval bulls. I t might be reasoned that the 4-day interval between ejaculations or the collecting of two ejaculates every eighth day would result in an increased percentage of unusable ejaculates. However, it is now known that the basis for discarding ejaculates at the time this experiment was in progress was not justified (2) and, consequently, the estimates of the percentages of discarded ejaculates shown in Table I were determined on the basis of criteria used in present day operations. T h a t is, an ejaculate was considered as unusable if it contained " m a n y morphologically abnormal s p e r m a t o z o a " or failed to meet a n y one of the following
~ERTILITY Ot~ BULLS EJACULATED AT DI]~ERENT INTERVALS
1441
TABLE 1 Semen and fertility data of bulls ejaculated either once or twice at either 4- or g-day intervals
Average values First 272 days ~
Criteria No. of bulls Ejae. discarded (%) Vol. of ejae. (ml.) Motile sperm (%) 109 total sperm/ml semen 10° motile sperm/ejac. 109 motile sperm/8 days Total 1st services 60- to 90-day nonreturns to 1st services (%)
Last 88 days ~
l e j a c , at 4-day interval
l e j a c , at 8-day interval
l e j a c , at 4-day interval
2ejac. at 8-day interval b
14 5.1 5.7 68 1.48 5.7 11.4 30,163 61.8
16 6.1 6.5 67 1.63 7.0 7.0 25,187 64.8
14 7.2 6.3 67 1.49 6.3 12.6 10,187 65.2
16 9.6 6.3 67 1.51 6.4 12.8 11,692 67.9
a Three bulls in the 4-day group and one in the 8-day group died for reasons not attributable to the experimental regimes. b Average of 1st plus 2nd ejaculates. m i n i m u m s t a n d a r d s : 50% m o t i l e s p e r m , 500 × 10" t o t a l s p e r m p e r m i l l i l i t e r of f r e s h u n e x t e n d e d semen, a m o t i l i t y r a t e of 2.0 ( 2 ) , 1,000 × l 0 G m o t i l e s p e r m p e r e j a c u l a t e . B e c a u s e t h e b u l l s in t h i s e x p e r i m e n t were n o t r e s t r a i n e d b e f o r e a l l o w i n g t h e m to e j a c u l a t e , t h e p e r c e n t a g e s of d i s c a r d e d e j a c u l a t e s do n o t a p p e a r excessive f o r a n y of the collection regimes. F u r t h e r m o r e , i n t e r m s of t h e p e r c e n t of m o t i l e s p e r m a t o z o a o u t p u t these d i s c a r d s a m o u n t to o n l y a f e w w a s t e d spermatozoa. A c o m p a r i s o n of t h e n o n r e t u r n r a t e s w h e n p o r t i o n s of e j a c u l a t e s w e r e ext e n d e d in e i t h e r y o l k - c i t r a t e or whole egg e x t e n d e r s i n d i c a t e d t h a t t h e p e r cent n o n r e t u r n a v e r a g e s f o r t h e t w o g r o u p s of b u l l s were n o t a l t e r e d . C o n s e q u e n t l y , i t was n o t n e c e s s a r y to delete t h e b r e e d i n g s m a d e w i t h s e m e n e x t e n d e d i n whole egg, a n d t h e f e r t i l i t y r e s u l t s r e p o r t e d h e r e r e p r e s e n t all b r e e d i n g s w i t h o u t r e g a r d to t h e k i n d of e x t e n d e r s used. T h e a v e r a g e 60- to 9 0 - d a y p e r cent n o n r e t u r n s were s l i g h t l y i n f a v o r of t h e 8 - d a y i n t e r v a l bulls. The differences of 3.0 a n d 2.7 p e r c e n t a g e u n i t s f o r t h e 2 7 2 - d a y a n d 8 8 - d a y e x p e r i m e n t a l p e r i o d s , r e s p e c t i v e l y , were n o t s t a t i s t i c a l l y significant, P < 0.05. The a m o n g - b u l l m e a n s q u a r e was u s e d as e x p e r i m e n t a l e r r o r , since b u l l d i f f e r e n c e d i d c o n t r i b u t e to t h e s a m p l i n g v a r i a n c e b e t w e e n t r e a t m e n t s . The t r e n d s in s p e r m o u t p u t a n d f e r t i l i t y a r e of some i n t e r e s t i n a n e x p e r i m e n t of 12 m o n t h s d u r a t i o n . F i g u r e 1 shows t h a t f o r a l l p r a c t i c a l p u r p o s e s t h e trends for both motile sperm output and fertility were essentially constant t h r o u g h o u t t h e 12 m o n t h s of t h e e x p e r i m e n t . The f a c t t h a t t h e 4 - d a y i n t e r v a l b u l l s d i d n o t d e c r e a s e in e i t h e r s p e r m o u t p u t or f e r t i l i t y d u r i n g t h e l a t t e r m o n t h s of t h e e x p e r i m e n t r a i s e s t h e q u e s t i o n of h o w l o n g t h i s p a r t i c u l a r f r e q u e n c y of e j a c u l a t i o n c o u l d be m a i n t a i n e d . A n a n s w e r m u s t a w a i t r e s u l t s f r o m s t u d i e s l a s t i n g s e v e r a l y e a r s . I t also r a i s e s t h e q u e s t i o n of w h a t is t h e s h o r t e s t i n t e r v a l b e t w e e n e j a c u l a t i o n s t h a t is c o m p a t i b l e w i t h a n o u t p u t of m a x i m u m n m n b e r s of h i g h l y f e r t i l e s p e r m a t o z o a d u r i n g a
R. W. BRATTON
1442
-J
A N D R. H . F O O T E
8-day interval bulls
80
•
~',,, i-
60 50 z
_=
+0o 30
oo
4-day interval bulls
i!
=
o6=
-
w
0
a. lO.O a • --
• i i, ,e-e-
6.0 =E %
,,, 0
i, ,,l i+
,l
,+,,,; 'o
p.... .+
i....
i
a "e I
". ...... " . ~ ~ 8-day interval bulls 40
80
I~0
160 2 0 0 2 4 0 ?-80 3 2 0 TIME IN DAYS
~60
Fzo. 1. T i m e t r e n d s i n s p e r m a t o z o a o u t p u t a n d f e r t i l i t y of d a i r y bulls e j a c u l a t e d e i t h e r once or t w i c e at i n t e r v a l s of either 4 or 8 days.
nmxinmm length of time. Here, again, f u r t h e r research is needed. I t is eoneeivable that an optimum relationship exists between these factors which, if known, would make possible the maximmn rate of genetic improvement by balancing slightly lower fertility against increased selection intensity. F r o m this experiment it is concluded that a 4-day interval between single ejaeulations or an 8 day interval between two ejaculations is not detrimental to semen production or fertility, and that approximately 60% more motile spermatozoa can be obtained per unit time by eollecting either one ejaculate at 4-day intervals or two ejaeulates at 8-day intervals instead of one ejaculate at 8-day intervals. SUM~,IARY
A group of 14 dairy bulls ejaculated once at 4-day intervals for 272 days averaged 5.7 billion motile spermatozoa per ejaculate. Another group of 16 bulls ejaculated once at 8-day intervals for 272 days averaged 7.0 billion motile spermatozoa per ejaculate. The average 60- to 90-day per cent nonreturns to more than 25,000 first services per group was 61.8 for the 4-day bulls and 64.8 for the 8-day bulls, a difference that was not statistically significant, P ~ 0.05. During an 88-day period immediately following the 272-day period the 8-day interval bulls were ejaculated twice every eighth day and averaged 5.7 billion motile spermatozoa per ejaculate and 12.8 billion per 8-day period. The 4-day interval bulls, continued on the original interval between ejaculates, averaged 12.6 billion motile spermatozoa on an 8-day basis during this same period. The 60- to 90-day per cent nonreturns to first services was 65.2 for the 4-day bulls and 67.9 for the 8-day bulls. Again, the difference was not statistically significant, P ~ 0.05.
FERTILITY OF BULLS EJACULATED AT DIFFERENT INTERVALS I t is c o n c l u d e d every eighth
that
one ejaculation
day for periods
every
fourth
as l o n g as 1 y e a r
day
1443
or two ejaculations
are not detrimental
to semen
production or fertility and that ejaculations at a rate of two per 8-day interval will yield about 60% more motile sperm than will ejaculations at the rate of one per 8-day interval. ACK~qOWLEDGMENTS The authors gratefully acknowledge the assistance of the management and the technicians of the New York Artificial Breeders' Cooperative, Inc., for furnishing the bulls; collecting, examining, and processing the semen; breeding the cows; and providing the fertility records for these studies. Acknowledgment is also due Mrs. Delma Muller and Mrs. Sully Shipman for summarizing many of the voluminous data collected during the course of the experiments and to C. R. Henderson for suggestions concerning statistical analysis of the data and preparation of the manuscript. REFERENCES (1) B~ANTON, C., D'ARENSBOURG, G., AN]) JOHNSTON, J. E. Semen Production, F r u c t o s e Content of Semen and Fertility of Dairy Bulls as Related to Sexual Excitement. J. Dairy Sci., 35: 801. 1952. (2) BRATTON, R. W., AN~) FOOT'E, R. tI. Unpublished data. Department of Animal Husbandry, Corne]l University, Ithaca, N. Y. (3) BRATTON~ R. W., FOOTE, R. H., MUSGRAVE,S. D., AND YANDEI~IAI~K, N. L. Livability and Fertility of Bovine Spernmtozoa in Different Diluents. J. Dairy Sci., 32: 604. 1949. (4) BUI~CH, G. E. Artificial Insemination in New ~-ork State Dairy Herds. Cornell Vet., 29: 395. 1939. (5) COLMNS, W . J . , BaaTTON, R. W., AND I-IEI'~DERSON, C. R. The Relationship of Semen Production to Sexual Excitement of Dairy Bulls. J. Dairy Sci., 34: 224. 1951. (6) DUNN, H. O., BRATTON, 1~. W., AND COLLINS, W. J. Fertility and Motility of Bovine Spermatozoa in Buffered Whole-Egg Extenders. J. Dairy Sei., 33: 434. 1950. (7) FOOTE, R. H., AND BaATTON, R. W. The Fertility of Bovine Semen Cooled with and without the Addition of Citrate-Sulfanilamlde-Yolk Extender. $. Dairy Sci., 32: 856. 1949. (8) ~tALt~, E. B., ALI~iQUIST, J. O., AND THACKER, D. L. Observations on the Sexual Behavior and Semen Production of Dairy Bulls. (Abs.) J. Dairy Sci., 36: 576. 1953. (9) KIRILLOV, V. S., AN]) MOROZOV, V. A. The Influence of Sexual Activity of Bulls on Their Reproductive Ability (Trans. title). Problemy Zhivotnovodst~'a, 5: 90. 1933. (Abs.) Animal ~reeding Abstr., 1: 237. 1934. (10) LASLE¥, J. F., AND BOaA~T, R. Some Factors Influencing Reproductive Efficiency of Range Cattle under Artificial and N a t u r a l Breeding Conditions. Mo. Agr. Expt. Sta., l~esearch B tdI. 375: 1943. (11) MERCIEa, E., BRATTON, R. W., AN]) SALISBURY, G. W. Semen Production and Fertility of Dairy Bulls as Related to Frequency of Ejaculation. Corneal Vet., 39: 32. 1949. (12) SALISBURY, G. W., BECK, G. H., ELLIOTT, I., AND WILLETT~ E. L. Rapid Methods for E s t i m a t i n g the Number of Spermatozoa in Bull Semen. J. Dairy Sci., 26: 69. 1943. (13) SALISBUaY, G. W., KNOI)T, C. B., A~D BRA~rON, R. W. The Freezing P o i n t Depression of Bull Semen and I t s Relation to the Diluter Problem. J. Animal Sci., 7: 283. 1948. (14) TRIMBEaGER, G. W. Present-Day Techniques of Artificial Insemination. J. Dairy ScL, 25: 671. 1942. (15) WEATHEaBY, E. T., REEC]~, R. P., AND BAKTL]~TT, J . W. The Ability of Dairy Bulls to W i t h s t a n d Regular Services for Artificial Insemination During One Year. Proc. A~n. Soc. An~wa~ Production, 33rd Ann. Meet. p. 224. 1940. (16) WILLETT~ E. L., AND SALISBURY, G. W. The Effect of Various Diluters, Cooling Rate, Temperature of Storage, and Some Other Factors on the Livability of Spermatozoa in Stored Samples of Bull Semen. Corne]l (N. Y.) Agr. Expt. Sta., Memoir 259. 1942.
OF D A I R Y B U L L S
E J A C U L A T ] ~ ' D E I T H E R ONCE OR T W I C E A T I N T E R V A L S OF E I T H E R F O U R OR E I G H T D A Y S R. W. B R A T T O N A~D R. H. F O O T E
Dcpartme~t of AMmal H~sbandry, Corncll UMversily, Ithaca, N. Y.
The increased usefulness of d a i r y sires through artificial breeding has come about p r i m a r i l y f r o m increased extension rates of semen and improved extenders and processing procedures. Although there is still room for substantial improvement in each of these areas, it seems that f u r t h e r increases f r o m these sources are likely to be r a t h e r small and costly to obtain. I n contrast to the above situation, little is known about the m a x i m u m n u m b e r of spermatozoa that can be obtained f r o m bulls, p a r t i c u l a r l y over long periods of time, or what effects frequent ejaculation m a y have on fertility and subsequeut spermatozoa production (4, 9, 10, 11, 14, 15). W o r k b y Collins et al. (5) and more recently by B r a n t o n et al. (1) and Hale et al. (8) suggests that m a n y more spermatozoa m a y be obtained from bulls t h a n has generally been thought to be possible. Following the early work reported by ~Iereier et al. (11) a series of long-time experiments were u n d e r t a k e n by this laboratory in cooperation with the New York Artificial B r e e d e r s ' Cooperative, Inc., to obtain information on the relationship of frequency of ejaculation to spermatozoa production and fertility. The results reported here are from a year-long experiment in which d a i r y bulls were ejaculated once at either 4- or 8-day intervals or twice at 8-day intervals. EXPERIMENTAL PROCEDURE
Two groups of bulls eaeh eonsisting of eight Holsteins, four Guernseys, three Jerseys, and two Ayrshires were selected f r o m the active stud of the New York Artifieial B r e e d e r s ' Cooperative, Ine. One group was ejaeulated once at 4-day intervals for 360 days and the other group was ejaeulated onee at 8-day intervals for 272 days and then twice at 8-day intervals for the remaining 88 days of the 360-day experimental period. At the time these experiments were begun (August, 1948), the studies on sexual excitement of bulls had not been made (1, 5, 8); consequently, the bulls in this experiment were not restrained at the time semen was eolleeted. Feeding and other m a n a g e m e n t praetiees of the bulls were those common to the stud at that time. The volume of each ejaculate, the n u m b e r of spermatozoa per milliliter of semen, and the per cent of motile spermatozoa in the ejaculates were determined b y the routine procedures of this laboratory (12, 16). Only the semen ejaculates containing 900 × 102 or more spermatozoa p e r milliliter of semen and 70% or more motile spermatozoa and having a methylene blue reduction time of 7 minutes or less were extended for breeding purposes. The semen was p a r t i a l l y exReceived f o r publieation J u n e 24, 1954. 1439
1440
R. ~V. B R A T T O X
AND
R. I I . FOOTE
tended and cooled to 5 ° C. (7) and then made up to final volmne with either 2.9~c eitrate-sulfanilamide yolk (3. 13) or experimental whole egg extenders (6). The latter extenders were used for only tile Holstein and Guernsey semen on a splitejaculate basis to avoid confounding of these superimposed t r e a t m e n t s with the collection regimes. The extenders contained no penicillin or streptomycin. The semen extension rates varied, depending upon the day-to-day and seasonal demands for semen and the amount of semen produced by the individual bulls. D u r i n g the last 88 days of the experiment the two ejaculates obtained f r o m the 8-day interval bulls were mixed for processing and subsequent use in inseminating cows. Breedings were made b y the technicians affiliated with the New York Artificial B r e e d e r s ' Cooperative, Inc.. with semen which, on the average, was about 33 hours old. The extended semen of a p a r t i c u l a r ejaculate was shipped to as m a n y field technicians as the available volume would permit. The next time this bull was ejaculated his semen was shipped to technicians not receiving it the time before. B y rotating bulls among technicians in this m a n n e r all technicians received about equal opportunities to use each bull. The average 60- to 90-day per cent n o n r e t u r n s to first services for t r e a t m e n t s were calculated on the basis of the average per cent n o n r e t u r n s for the individual bulls, since the n u m b e r of services for a n y p a r t i c u l a r bull was not a random variable but was, to a large extent, dependent upon his breed, his popularity and whether or not he was a young bull being sampled and held in waiting for an AB proof. RESULTS AND DISCUSSION I n Table I are the group averages for the semen and fertility observations made d u r i n g the two periods of the experiment. Of p a r t i c u l a r interest and importance in this table are the numbers of motile spermatozoa per ejaculate and per 8-day period and the per cent n o n r e t n r n s to first services. D u r i n g the first 272 days of the experiment the 4-day interval bulls averaged 5.7 billion motile spermatozoa per ejaculate and 11.4 billion per 8-day period, whereas the 8-day interval bulls averaged 7.0 billion motile spermatozoa per ejaculate and per 8-day period. Thus, per 8-day period, 63% more motile s p e r m were obtained f r o m the 4-day t h a n f r o m the 8-day interval bulls. W h e n the 8-day interval bulls were changed f r o m one ejaculate to two ejaculates every eighth day their motile sperm output per 8-day period was 101.6% of that for the 4-day interval bulls. I t might be reasoned that the 4-day interval between ejaculations or the collecting of two ejaculates every eighth day would result in an increased percentage of unusable ejaculates. However, it is now known that the basis for discarding ejaculates at the time this experiment was in progress was not justified (2) and, consequently, the estimates of the percentages of discarded ejaculates shown in Table I were determined on the basis of criteria used in present day operations. T h a t is, an ejaculate was considered as unusable if it contained " m a n y morphologically abnormal s p e r m a t o z o a " or failed to meet a n y one of the following
~ERTILITY Ot~ BULLS EJACULATED AT DI]~ERENT INTERVALS
1441
TABLE 1 Semen and fertility data of bulls ejaculated either once or twice at either 4- or g-day intervals
Average values First 272 days ~
Criteria No. of bulls Ejae. discarded (%) Vol. of ejae. (ml.) Motile sperm (%) 109 total sperm/ml semen 10° motile sperm/ejac. 109 motile sperm/8 days Total 1st services 60- to 90-day nonreturns to 1st services (%)
Last 88 days ~
l e j a c , at 4-day interval
l e j a c , at 8-day interval
l e j a c , at 4-day interval
2ejac. at 8-day interval b
14 5.1 5.7 68 1.48 5.7 11.4 30,163 61.8
16 6.1 6.5 67 1.63 7.0 7.0 25,187 64.8
14 7.2 6.3 67 1.49 6.3 12.6 10,187 65.2
16 9.6 6.3 67 1.51 6.4 12.8 11,692 67.9
a Three bulls in the 4-day group and one in the 8-day group died for reasons not attributable to the experimental regimes. b Average of 1st plus 2nd ejaculates. m i n i m u m s t a n d a r d s : 50% m o t i l e s p e r m , 500 × 10" t o t a l s p e r m p e r m i l l i l i t e r of f r e s h u n e x t e n d e d semen, a m o t i l i t y r a t e of 2.0 ( 2 ) , 1,000 × l 0 G m o t i l e s p e r m p e r e j a c u l a t e . B e c a u s e t h e b u l l s in t h i s e x p e r i m e n t were n o t r e s t r a i n e d b e f o r e a l l o w i n g t h e m to e j a c u l a t e , t h e p e r c e n t a g e s of d i s c a r d e d e j a c u l a t e s do n o t a p p e a r excessive f o r a n y of the collection regimes. F u r t h e r m o r e , i n t e r m s of t h e p e r c e n t of m o t i l e s p e r m a t o z o a o u t p u t these d i s c a r d s a m o u n t to o n l y a f e w w a s t e d spermatozoa. A c o m p a r i s o n of t h e n o n r e t u r n r a t e s w h e n p o r t i o n s of e j a c u l a t e s w e r e ext e n d e d in e i t h e r y o l k - c i t r a t e or whole egg e x t e n d e r s i n d i c a t e d t h a t t h e p e r cent n o n r e t u r n a v e r a g e s f o r t h e t w o g r o u p s of b u l l s were n o t a l t e r e d . C o n s e q u e n t l y , i t was n o t n e c e s s a r y to delete t h e b r e e d i n g s m a d e w i t h s e m e n e x t e n d e d i n whole egg, a n d t h e f e r t i l i t y r e s u l t s r e p o r t e d h e r e r e p r e s e n t all b r e e d i n g s w i t h o u t r e g a r d to t h e k i n d of e x t e n d e r s used. T h e a v e r a g e 60- to 9 0 - d a y p e r cent n o n r e t u r n s were s l i g h t l y i n f a v o r of t h e 8 - d a y i n t e r v a l bulls. The differences of 3.0 a n d 2.7 p e r c e n t a g e u n i t s f o r t h e 2 7 2 - d a y a n d 8 8 - d a y e x p e r i m e n t a l p e r i o d s , r e s p e c t i v e l y , were n o t s t a t i s t i c a l l y significant, P < 0.05. The a m o n g - b u l l m e a n s q u a r e was u s e d as e x p e r i m e n t a l e r r o r , since b u l l d i f f e r e n c e d i d c o n t r i b u t e to t h e s a m p l i n g v a r i a n c e b e t w e e n t r e a t m e n t s . The t r e n d s in s p e r m o u t p u t a n d f e r t i l i t y a r e of some i n t e r e s t i n a n e x p e r i m e n t of 12 m o n t h s d u r a t i o n . F i g u r e 1 shows t h a t f o r a l l p r a c t i c a l p u r p o s e s t h e trends for both motile sperm output and fertility were essentially constant t h r o u g h o u t t h e 12 m o n t h s of t h e e x p e r i m e n t . The f a c t t h a t t h e 4 - d a y i n t e r v a l b u l l s d i d n o t d e c r e a s e in e i t h e r s p e r m o u t p u t or f e r t i l i t y d u r i n g t h e l a t t e r m o n t h s of t h e e x p e r i m e n t r a i s e s t h e q u e s t i o n of h o w l o n g t h i s p a r t i c u l a r f r e q u e n c y of e j a c u l a t i o n c o u l d be m a i n t a i n e d . A n a n s w e r m u s t a w a i t r e s u l t s f r o m s t u d i e s l a s t i n g s e v e r a l y e a r s . I t also r a i s e s t h e q u e s t i o n of w h a t is t h e s h o r t e s t i n t e r v a l b e t w e e n e j a c u l a t i o n s t h a t is c o m p a t i b l e w i t h a n o u t p u t of m a x i m u m n m n b e r s of h i g h l y f e r t i l e s p e r m a t o z o a d u r i n g a
R. W. BRATTON
1442
-J
A N D R. H . F O O T E
8-day interval bulls
80
•
~',,, i-
60 50 z
_=
+0o 30
oo
4-day interval bulls
i!
=
o6=
-
w
0
a. lO.O a • --
• i i, ,e-e-
6.0 =E %
,,, 0
i, ,,l i+
,l
,+,,,; 'o
p.... .+
i....
i
a "e I
". ...... " . ~ ~ 8-day interval bulls 40
80
I~0
160 2 0 0 2 4 0 ?-80 3 2 0 TIME IN DAYS
~60
Fzo. 1. T i m e t r e n d s i n s p e r m a t o z o a o u t p u t a n d f e r t i l i t y of d a i r y bulls e j a c u l a t e d e i t h e r once or t w i c e at i n t e r v a l s of either 4 or 8 days.
nmxinmm length of time. Here, again, f u r t h e r research is needed. I t is eoneeivable that an optimum relationship exists between these factors which, if known, would make possible the maximmn rate of genetic improvement by balancing slightly lower fertility against increased selection intensity. F r o m this experiment it is concluded that a 4-day interval between single ejaeulations or an 8 day interval between two ejaculations is not detrimental to semen production or fertility, and that approximately 60% more motile spermatozoa can be obtained per unit time by eollecting either one ejaculate at 4-day intervals or two ejaeulates at 8-day intervals instead of one ejaculate at 8-day intervals. SUM~,IARY
A group of 14 dairy bulls ejaculated once at 4-day intervals for 272 days averaged 5.7 billion motile spermatozoa per ejaculate. Another group of 16 bulls ejaculated once at 8-day intervals for 272 days averaged 7.0 billion motile spermatozoa per ejaculate. The average 60- to 90-day per cent nonreturns to more than 25,000 first services per group was 61.8 for the 4-day bulls and 64.8 for the 8-day bulls, a difference that was not statistically significant, P ~ 0.05. During an 88-day period immediately following the 272-day period the 8-day interval bulls were ejaculated twice every eighth day and averaged 5.7 billion motile spermatozoa per ejaculate and 12.8 billion per 8-day period. The 4-day interval bulls, continued on the original interval between ejaculates, averaged 12.6 billion motile spermatozoa on an 8-day basis during this same period. The 60- to 90-day per cent nonreturns to first services was 65.2 for the 4-day bulls and 67.9 for the 8-day bulls. Again, the difference was not statistically significant, P ~ 0.05.
FERTILITY OF BULLS EJACULATED AT DIFFERENT INTERVALS I t is c o n c l u d e d every eighth
that
one ejaculation
day for periods
every
fourth
as l o n g as 1 y e a r
day
1443
or two ejaculations
are not detrimental
to semen
production or fertility and that ejaculations at a rate of two per 8-day interval will yield about 60% more motile sperm than will ejaculations at the rate of one per 8-day interval. ACK~qOWLEDGMENTS The authors gratefully acknowledge the assistance of the management and the technicians of the New York Artificial Breeders' Cooperative, Inc., for furnishing the bulls; collecting, examining, and processing the semen; breeding the cows; and providing the fertility records for these studies. Acknowledgment is also due Mrs. Delma Muller and Mrs. Sully Shipman for summarizing many of the voluminous data collected during the course of the experiments and to C. R. Henderson for suggestions concerning statistical analysis of the data and preparation of the manuscript. REFERENCES (1) B~ANTON, C., D'ARENSBOURG, G., AN]) JOHNSTON, J. E. Semen Production, F r u c t o s e Content of Semen and Fertility of Dairy Bulls as Related to Sexual Excitement. J. Dairy Sci., 35: 801. 1952. (2) BRATTON, R. W., AN~) FOOT'E, R. tI. Unpublished data. Department of Animal Husbandry, Corne]l University, Ithaca, N. Y. (3) BRATTON~ R. W., FOOTE, R. H., MUSGRAVE,S. D., AND YANDEI~IAI~K, N. L. Livability and Fertility of Bovine Spernmtozoa in Different Diluents. J. Dairy Sci., 32: 604. 1949. (4) BUI~CH, G. E. Artificial Insemination in New ~-ork State Dairy Herds. Cornell Vet., 29: 395. 1939. (5) COLMNS, W . J . , BaaTTON, R. W., AND I-IEI'~DERSON, C. R. The Relationship of Semen Production to Sexual Excitement of Dairy Bulls. J. Dairy Sci., 34: 224. 1951. (6) DUNN, H. O., BRATTON, 1~. W., AND COLLINS, W. J. Fertility and Motility of Bovine Spermatozoa in Buffered Whole-Egg Extenders. J. Dairy Sei., 33: 434. 1950. (7) FOOTE, R. H., AND BaATTON, R. W. The Fertility of Bovine Semen Cooled with and without the Addition of Citrate-Sulfanilamlde-Yolk Extender. $. Dairy Sci., 32: 856. 1949. (8) ~tALt~, E. B., ALI~iQUIST, J. O., AND THACKER, D. L. Observations on the Sexual Behavior and Semen Production of Dairy Bulls. (Abs.) J. Dairy Sci., 36: 576. 1953. (9) KIRILLOV, V. S., AN]) MOROZOV, V. A. The Influence of Sexual Activity of Bulls on Their Reproductive Ability (Trans. title). Problemy Zhivotnovodst~'a, 5: 90. 1933. (Abs.) Animal ~reeding Abstr., 1: 237. 1934. (10) LASLE¥, J. F., AND BOaA~T, R. Some Factors Influencing Reproductive Efficiency of Range Cattle under Artificial and N a t u r a l Breeding Conditions. Mo. Agr. Expt. Sta., l~esearch B tdI. 375: 1943. (11) MERCIEa, E., BRATTON, R. W., AN]) SALISBURY, G. W. Semen Production and Fertility of Dairy Bulls as Related to Frequency of Ejaculation. Corneal Vet., 39: 32. 1949. (12) SALISBURY, G. W., BECK, G. H., ELLIOTT, I., AND WILLETT~ E. L. Rapid Methods for E s t i m a t i n g the Number of Spermatozoa in Bull Semen. J. Dairy Sci., 26: 69. 1943. (13) SALISBUaY, G. W., KNOI)T, C. B., A~D BRA~rON, R. W. The Freezing P o i n t Depression of Bull Semen and I t s Relation to the Diluter Problem. J. Animal Sci., 7: 283. 1948. (14) TRIMBEaGER, G. W. Present-Day Techniques of Artificial Insemination. J. Dairy ScL, 25: 671. 1942. (15) WEATHEaBY, E. T., REEC]~, R. P., AND BAKTL]~TT, J . W. The Ability of Dairy Bulls to W i t h s t a n d Regular Services for Artificial Insemination During One Year. Proc. A~n. Soc. An~wa~ Production, 33rd Ann. Meet. p. 224. 1940. (16) WILLETT~ E. L., AND SALISBURY, G. W. The Effect of Various Diluters, Cooling Rate, Temperature of Storage, and Some Other Factors on the Livability of Spermatozoa in Stored Samples of Bull Semen. Corne]l (N. Y.) Agr. Expt. Sta., Memoir 259. 1942.