EFFECT OF AGE ON TESTICULAR GROWTH AND CONSISTENCY OF HOLSTEIN AND ANGUS BULLS 1

Transcription

1 EFFECT OF AGE ON TESTCULAR GROWTH AND CONSSTENCY OF HOLSTEN AND ANGUS BULLS 1 G. H. Coulter 2, L. L. Larson 3 and R. H. Foote Cornell University 4, thaca, New York SUARY A total of 5,99 scrotal circumference and 5,373 tesricular consistency (tonometer) measurements were made on Holstein bulls in seven artificial insemination studs. Comparable measurements were made on 339Angus bulls. The multiple regression equation, Y = log X (log X)2), where ~f is scrotal circumference in cm and X is bull age in months, described the high rate of testicular growth in young Holstein bulls, limited growth in mature bulls, and a slight decrease in the oldest bulls. Angus tended to have larger testes than Holsteins up to 3 years of age, but they were surpassed after that age by Holstein bulls. Regression of testicular consistency on age of Holstein bulls resulted in the equation Y = log X (log X) 2, where CZ is the mean deflection averaged for weak and strong spring tonometers in mm and X is bull age in months. This equation describes the decrease in firmness of testes of bulls from 6 to 12 months of age up to 48 to 54 months of age. Then consistency became slightly firmer with age, but in the few oldest bulls measured there was a decline. Differences among bull studs existed for both traits. Differences in testis sie among bulls of the same age were large. Selection of bulls with large testes could decrease the number required to produce enough sperm to inseminate a specified population. 1 The authors gratefully acknowledge Richard Cole, ichael Simkin, Dr. J. Hahn, Dr. Gary B. Anderson, Dr. Peter J. H. Ball and s. Jacqueline Schiavo for their assistance, Eastern A.. Coop. nc., The National Association of Animal Breeders and the North Central Biological Research Committee for financial support and all the bull studs mentioned in the paper for their cooperation. Z Present Address: Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J-4B1. a Present Address: Department of Animal Science, University of Nebraska, Lincoln Department of Animal Science. (Key Words: Testis Growth, Bulls, Testis Consistency.) NTRODUCTON Previous studies by Boyd and VanDemark (1957), Willett and Ohms (1957), Almquist and Amann (1961), Amann and Almquist (1961; 1962a,b) and Hahn et al. (1969a) have demonstrated that a close relationship exists between testis weight at slaughter and scrotal circumference, and between testis sie and sperm output of growing bulls under frequent collection regimes. The use of scrotal circumference measurements made at 1 to 2 years of age may be valuable as a predictor of sperm output in the mature bull (G. H. Coulter and R. H. Foote, unpublished data, 1974). The tonometer (Hahn et al., 1969a; Foote et al., 197) was developed to provide a more objective measure of testicular consistency than the conventional palpation method. These authors demonstrated large significant positive correlations between testicular consistency and both semen quality and fertility as measured by percent 6- to 9-day nonreturns to service. The present study is an extension of previous work (Hahn et al., 1969a,b) to accumulate larger numbers of measurements from Holstein bulls to provide an accurate estimate of the relationship between age and both scrotal circumference and tonometer measurements. n addition, a limited number of corresponding testicular measurements are presented for Angus bulls. EXPERENTAL PROCEDURE easurements of scrotal circumference and testicular consistency of Holstein and Angus bulls were made with the cooperation of seven artificial insemination bull studs (Eastern Artificial nsemination Coop., thaca, N.Y.; American Breeders Service, DeForest, Wisconsin; innesota Valley Breeders Ass., New Prague, 1383 JOURNAL OF ANAL SCENCE, Voi. 41, No. 5, 1975

2 1384 COULTER, LARSON AND FOOTE innesota; idwest Breeders Coop., Shawano, Wisconsin and Stewartville, innesota; Tri- State Breeders Coop., Westby, Wisconsin; and East Central Breeders Ass. Coop., Waupun, Wisconsin). Scrotal circumference measurements of Holstein bulls were accumulated from 1967 through 1973 while tonometer measurements of Holstein bulls and all measurements of Angus bulls were made from 1969 through Testicular measurements were made on bulls from 6 to 18 months of age. All bulls in all studs, with the exception of Eastern A.. Coop., were measured at the same time each year during the last few days of August or the first days of September. n addition to these measurements, all bulls at American Breeders Service were measured in late arch or early April in 197 and At Eastern A.. Coop. all bulls were measured each year in late ay or early June, and bulls less than 48 months of age were again measured in December. Those less than 24 months of age were also measured in late February or early arch and in September to obtain more frequent measurements on rapidly growing young bulls. Bulls were restrained during measurement to the degree necessary to obtain an accurate measurement with relative safety for the tech- nicians. Scrotal circumference measurements were made using a flexible plasticied cloth tape at the largest diameter of the testis and scrotum (Foote, 1969). Testicular consistency measurements were obtained using the tonometers and techniques described by Foote et al., 197. Significance levels between multiple linear regression equations were tested using general linear hypotheses (Searle, 1971). RESULTS AND DSCUSSON Over the duration of this study 5,99 scrotal circumference measurements were made on Holstein bulls and 339 on Angus bulls. The mean values for scrotal circumference, hereafter usually referred to as testis sie, for Holstein and Angus bull groups at 6-month age intervals are presented in table 1. The observed mean testis sie of Holstein bulls of the different age groups in this study correspond well with the means for comparable age groups reported by Hahn et al. (1969b). The distribution of testis sie observations plotted against age is presented in figure 1. The best fitting regression equation describing this distribution was calculated to be Y log X (log X) 2, where ~/ is TABLE 1. CHANGES N TESTCULAR SZE N HOLSTEN AND ANGUS BULLS WTH AGE 9 Holstein Scrotal circumference Angus Age in No. of easurement No. of easurement months measurements (cm) measurements (cm) Total a +.. ean - standard devaatlon a a

3 TESTCULAR GROWTH AND CONSSTENCY N BULLS O.O 47.O C 9 - ::."..:.....: i 9 eooo it 9 H ":." ::. ::..... ==========================... :.::':::.;:;.".:'::: ":~... ":.:.. 9 l*ll~*~*lllmmlt~llll~ltt#t~lfllfglt!~ ~f 9 #~otlgt t ~! f ================================================== L. ;..:."2... ::.". " l l l l l l ~ l l t l l l l l i l i l t l l i l l l t l l l t l l l l l i i l l t!1 ii!t!11t~ tlt...,.o,oo.... s.s,,...c~s'~;'f.~'.=..~";.i'-'..~';. ~ "ooh'~h',wwa~hheilehohhhho elel~ut leh~.~..h~e H H oo cr..,p 38.C 35.C 9 ~ '~H 9!!111~111~!!~t~!!!!!11t~!1 ~!!111! U o ~ "iisi:i!': 9 ~. J...9 "lii li ~o9 l"!!. l ( t N = 599 = -~, ,26 LOG X q (LOG X) 2,, AGE N ONTHS Figure 1. Testicular sie in growing and aged Holstein bulls. scrotal circumference in centimeters and X is bull age in months. This regression equation is similar to that reported previoulsy by Hahn et al. (1969a), Y = log X (log X) 2. These curves have the appearance of a typical growth curve having a rapid growth rate initially followed by a plateau. The slight decrease in mean testis sie after approximately 144 months of age is likely due to testicular degeneration resulting from aging, as sperm output also declines with advanced age (Hahn et al., 1969b). The mean testis sie in Angus bulls until approximately 36 months (table 1) appears to be greater than Holstein bulls of a comparable age, as maximum testicutar sie for Angus is reached at a younger age than with Holstein bulls. After 36 months of age, the testis sie of Holstein bulls exceeds that of the Angus. Angus bulls at 6 to 12, 12 to 18 and 18 to 24 months of age have attained 84, 9 and 1% of the mean testicular sie for Angusbulls 6 to 72 months of age, respectively. n contrast, Holstein bulls at 6 to 12, 12 to 18, 18 to 24, 24 to 3, 3 to 36, 36 to 42, and 42 to 48 have reached only 71, 83, 89, 93, 95, 97 and 98% of the mean testicular sie of 6-to 72-month-old Holstein bulls, respectively. The variation about the mean testis sie, illustrated in figure 1, includes true bull differences, seasonal effects and year of measurement effects (Coulter and Foote, 1975). n addition, artificial insemination stud differences contribute to the variation about the mean as illustrated by the best fitting regression equations plotted in figure 2. Equations for bull studs 1 and 2 were calculated from 2,338 and 2,439 scrotal circumference measurements, respectively, while the third equation was based on 1,132 observations from five smaller bull studs each measured at the same time. A highly significant (P.1) improvement in the fit of multiple linear regression equations to the scrotal circumference data resulted when three individual equations were calculated, rather than using one equation. The greatest difference in the values for these equations occurs after approximately 72 months of age, which

4 1386 COULTER, LARSON AND FOOTE "g lull Stud No, Y = ^ 44,52 log g.1,74 (log X N = 2338 r =,76 Butl Stud No. 2 Bull Slud No~, 3 to 7 38 ^ A ~' =.7, log x Y =.5.1s ~" o= 48"57 xl ~~ X " 2 4 (~ xl2 3 2 ~ N 35 N =1132 r= 82 = 2439 r =.83 ~ AGE ;N ~ONT4S Figure 2. Scrotal circumference of Holstein bulls measured in different bull studs at various ages. tends to implicate differences due to selection following progeny testing; however, rearing system differences may be a contributing factor. Davies et al. (1957), Bratton et al. (1959), VanDemark and auger (1964) and VanDemark et al. (1964) have demonstrated an effect of nutrition on the weight and sie of dairy bulls' testes. Although no bull stud or seasonal comparisons were made within the Angus data, due to insufficient numbers of observations, work by Wilsey (1972) indicates an effect of nutritional regime on testis sie. The tonometer (Foote et al., 197) was used to make 5,373 and 339 measurements of testicular consistency, hereafter usually referred to as consistency, on Holstein and Angus bulls, respectively. Changes in consistency measured with either the weak or strong springs are relatively similar as bulls age (table 2). The multiple regression equation which best fits the distribution of the average of weak and strong spring tonometer values for Holstein bulls plotted in figure 3 is Y = log X (log X) 2. ~/is the mean deflection in mm resulting from the application of weak and strong spring tonometers to the testes and X represents bull age in months. The consistency of Holstein testes was firmest (highest deflection) in young bulls and decreased gradually until 42 to 54 months of age. Thereafter the firmness increased slightly and remained relatively constant until possible testicular degeneration was occurring in the oldest Holsteins. The Angus bulls had slightly 1g , E ~ ;L ;.: #... i: ~ l~.s : ~ ~ 9.5 ~ 8.~ 9 * * N = 2, LOS X + 2.q7 (LOG X) 2 5., AGE N ONTHS Figure 3. Testicular consistency in growing and aged Holstein bulls.

5 TESTCULAR GROWTH AND CONSSTENCY N BULLS 1387 u.'-.,. ~,,~..~-~ o o o,. o ~,.,-~,,d-,,.~ o~1 m oo r txl m '~,,~,,.~ m o~ N "d" m ~-"~ N , " ~ L }- "t"1,.1-1,~ e~ r~ ~ -r +i l +1 +l l +1 +l +1 Z e~ t i Z o [.-,.~ l ~1 Z,4 ~.~ +i +[ ~1 ~ l "5: +1 c~

6 1388 COULTER, LARSON AND FOOTE softer testes than the Holsteins at 12 to 24 months of age but, because they did not show a further decrease in tonometer values with age, their testes appeared to be firmer than Holsteins thereafter. The extent to which selection was practiced for high semen quality and thereby resulted in culling of bulls with less firm testes (Hahn et al., 1969a) cannot be determined from present data. Similar to testis sie there was a definite effect of season of measurement and year of measurement causing variations in tonometer deflections about the mean which exceed the variation attributable to bull differences alone (Coulter and Foote, 1975). Also, there were differences among A.. bull studs. Figure 4 presents graphically the best fitting multiple regression equations for two individual studs (2,338 and 1,94 observations for bull studs 1 and 2, respectively) and for 1,132 observations pooled from five bull studs (3 to 7). As with testis sie, a highly significant improvement in the fit of multiple linear regression equations to consistency values was obtained when three individual equations were calculated, rather than one quation. Causes of these A.. bull stud differences are unknown, but as with scrotal circumference, rearing and genetic selection would be expected to exert some influence. The "K ratio" values, which express the relationship between the forces applied to the testes by the two springs and the corresponding deflection observed (Hahn et al., 1969a), also is shown in table 2. This ratio has certain theoretical advantages, but, as in earlier studies (Hahn et al., 1969a), it did not prove to be anymore highly correlated with other measurements than were the deflections read directly from the tonometer. 16 i Butl stud NO. 15 ~ ~ = log X [log X) 2 o N = 2338 r =.36 ~ Y = log X \ 1.62 poox "rf2~ Bu. s,,,,4.., 3, 7 ~ 12 't = 19.3s - 7.6S o X ~ 2.7 (log Xl ~ N = 1132 r = 34 o oe i.,4 lao ~q ONHS AGe Figure 4. Testicular consistency of Holstein bulls measured in different bull studs at various ages. The cause of breed differences in testicular sie and consistency (tables 1 and 2) is unknown, but it is expected that they result from a combination of genetic and environmental components (Wilsey, 1972). With the marked differences inherent in the rearing and testing systems of beef and dairy bulls for artificial insemination, these results emphasie the need for research to partition the genetic and environmental contribution to variation in sperm output and semen quality. Previously it has been shown (Hahn et al., 1969b) that for Holstein bulls 17 to 42 months of age that 52 to 66% of the variation in total sperm output can be accounted for by differences in scrotal circumference. This relationship should be taken advantage of by measuring scrotal circumference. Young bulls with small testes should not be progeny tested as they are likely to have small testes when mature (G. H. Coulter and R. H. Foote, unpublished observations, 1974). By selecting bulls with larger testes more cows per superior sire could be inseminated, resulting also in a greater efficiency of production and processing of semen. This type of selection would be immediately advantageous to artificial breeding units involved in a semen banking and bull-slaughter program (Coulter and Foote, 1974). The tonometer should be used to predict and select those expected to have the highest semen quality and fertility. LTERATURE CTED Almquist, J. O. and R. P. Amann Reproductive capacity of dairy bulls.. Gonadal and extragonadal sperm reserves as determined by direct counts and depletion trials; dimensions and weight of genitalia. J. Dairy Sci. 44:1668. Amann, R. P. and J. O. Almquist Reproductive capacity of dairy bulls. V. Detection of testicular deficiencies and requirements for experimentally evaluating testis function from semen characteristics. J. Dairy Sci. 44:2283. Amann, R. P. and J. O. Almquist. 1962a. Reproductive capacity of dairy bulls. V. Direct and indirect measurement of testicular sperm production. J. Dairy Sci. 45:774. Amann, R. P. and J. O. Almquist. 1962b. Reproductive capacity of dairy bulls. V. Effect of unilateral vasectomy and ejaculation frequency on sperm reserves; aspects of epididymal physiology. J. Reprod. Fertil. 3:26. Boyd, L. J. and N. L. VanDemark Spermatogenic capacity of the male bovine.. A measurement technique. J. Dairy Sci. 4:689. Bratton, R. W., S. D. usgrave, H. O. Dunn and R. H. Foote Causes and prevention of reproduc-

7 TESTCULAR GROWTH AND CONSSTENCY N BULLS 1389 tive failures in dairy catde.. nfluence of underfeeding and overfeeding form birth to 8 weeks of age on growth, sexual development, and semen production of Holstein bulls. Comell Univ. Agr. Expt. Sta. Bull. 94. Coulter, G. H. and R. H. Foote The economics of selected systems of banking semen to maintaining bulls. Proc. 5th Tech. Conf. A.L and Reprod. NAAB. p. 67. Coulter, G. H. and R. H. Foote Effect of season and year of measurement on testicular growth and consistency of Holstein bulls. J. Anita. Sci. n press. Davies, D. V., T. ann, and L. E. A. Rowson Effect of nutrition on the onset of male sex hormone activity and sperm formation in monoygous bull-calves. Proc. Roy. Soc. (London) 147:332. Foote, R. H Research techniques to study reproductive physiology in the male. Techniques and Procedures in Animal Science Research. p. 8. American Society of Animal Science. Foote, R. H., J. Hahn and L. L. Larson Testicular measurements as predictors of sperm output and semen quality. Proc. 3rd. Tech. Conf. on A.. and Reprod. p. 31. Hahn, J., R. H. Foote and E. T. Cranch. 1969a. Tonometer for measuring testicular consistency of bulls to predict semen quality. J. Anim. Sci. 29:483. Hahn, J., R. H. Foote and G. E. Seidel, Jr. 1969b. Testicular growth and related sperm output in dairy bulls. J. Anita. Sci. 29:41. Searle, S. R Linear odels. John Wiley and Sons, nc. New Y~rk. VanDemark, N. L. arid R. E. ~auger Effect of energy intake on reproductive performance of dairy bulls.. Growth, reproductive organs, and puberty. J. Dairy Sci. 47:798. VanDemark, N. L., G. R. Frit and R. E. augar Effect of energy intake on reproductive performance of dairy bulls.. Semen production and replentishment. J. Dairy Sci. 47:898. Willett, E. L. and J.. Ohms easurement of tesdcular sie and its relation to production of spermatooa by bulls. J. Dairy Sci. 4:1559. Wiisey, C. O The effect of high levels of energy intake on growth and seminal quality of Angus bulls..sc. Thesis, Colorado State Univ., Ft. Collins.