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Analysis of the Young Sire Service1
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JOURNAL OF DAIRY SCIENCE
lb of milk, which is identical with the maximum stud superiority value. The difference between the proved stud superiority at maxinmm net returns and that of the sampling stud is 760 lb of milk, or about 380 Ib per cow per year or $9.50 a cow per year, which indicates a dairyman using young bull semen should receive either free artificial insemination, be paid for D H I A testing the daughters, or both.
rate of genetic improvement and net returus to dairymen. Consolidation with across-the-board use of young bulls is less effective financially than with no consolidation and young bull services in testing herds only. The results indicate clearIy that for maximum net returns the same number of bulls need be sampled as for maximum genetic improvement. Another set of cost and profit values might, however, exhibit a completely different picture.
SUMMARY
REFERENCES
Factors which determine the daughter superiority of a selected group of young sires over all those sampled have been discussed. Fornmlae have been developed for predicting the daughter superiority of the permanent stud and the sampling stud. The assignment of profit and cost values associated with genetic improvement for various combinations of fraction of services to the permanent stud and number of daughters for evaluating young sires revealed that the programs for maximum genetic improvement and maximum net returns were the same for the example discussed. In general, to maximize genetic improvement many young bulls should be sampled and with 20-50 daughters per bull. Consolidation of studs with 50,000 first services and using young bulls in testing herds can substantially increase the ANALYSIS
OF THE
(1) HARTZR, H. L. Expected Values of Normal Order Statistics. ARL Tech. Rept. 60-292. July, 1960. (2) HENDERSOn, C. :R. Selecting the Young Sire to Sample in Artificial Insemination. Symposium: Young Sire Selection for Commercial Artificial Insemination. A.D.S.A. Annual Meeting, June 18, 1963. (3) SEARLE, S. R. Bull S a m p l i n g P r o g r a m m e s in
the Artificial Breeding of Dairy Cattle. Proc. New Zealand Soc. Animal Production, °2: 54. 1962. (4) SPECH% L. W., AND MeGILLIARI),L. D. Rates of Improvement hy Progeny Testing in Dairy Herds of Various Sizes. J. Dairy Sci., 43: 63. 1960. (5) VANVLEeK,L. D. Genetic Progress from Artificial Insemination. Paper presented New York Artificial Breeders Cooperative Sire Conference. January 3, 1962. (Mimeo.)
YOUNG SIRE
SERVICE 1
J. E. LEGATES Department of Animal Science, North Carolina State, Raleigh Most sire-sampling programs are devised with the aim of maximizing improvement in production, although information on other traits is drawn upon in making decisions regarding the re-entry of a sire to the active stud. Since the expected genetic progress per year for production will decline as additional traits are considered, it is most important that we use our opportunity to select as wisely as our knowledge and judgment will permit. Of necessity, more than one trait nmst enter into the evaluation of the sire, but how should these qualities be meshed with the emphasis on production? A practical and complete working answer is not yet available, but there are certain principles which can be of assistance in helping to make proper judgments. On the basis of registration reports, over 90% of artificial insemination services are to grade animals. It logically follows that primary emphasis in sire analysis should be given to those qualities which will make the largest Published with the approval of the Director of l~esearch, North Carolina Agricultural Experiment Station, :Raleigh, as Paper No. 1716 of the Journal Series.
economic contribution through the performance of the daughters of selected sires. I n considering the numerous qualities that appear desirable, we nmst first ask if the trait contributes to the net returns for the dairy enterprise. The actual dollar income on the daily farm arises from three sources: milk, beef or veal, and breeding stock sales. A large volume of milk of desirable composition is the most important key to economic success. Beef and veal sales may be considered as offsetting replacement costs, but they generally are not a major source of returns. The sale of breeding stock or surplus heifers contributes in only a limited fashion to the returns for most commercial herds. Other traits can contribute to net returns only as they influence milk yield and composition, or as they reduce production costs for the marketable items mentioned above. In addition to economic considerations, the genetic variability (heritability) of tile traits is also important. The opportunity to select among sires should not be dissipated on traits which give little promise of being responsive to selection. Information on the inter-relationships among other traits and production is
447
sY~POSlU~
meager, largely because satisfactory objective measures for these traits are not yet available. Nevertheless, these inter-relationships are important to project long-time selection goals. BASIS FOR EVALUA~IO~ The principle of the herd-mate comparison has now received general acceptance as the basis of evaluating a sire's transmitting ability for production. While the details of its application vary depending on the genetic and the between and within herd variances, it eventually should be useful in the analysis of other traits. In view of the extensive coverage which the herd-mate comparison and the various adjusted daughter averages have received in previous months, it does not seem appropriate to review these details. However~ there are a few points which a p p e a r worthy of mention. In regular sire analysis procedures, production records are corrected f o r / o r comparisons are made so as to account for age, herd, year, and seasonal influences. Days dl~ prior to calving do not a p p e a r to contribute an appreciable amount of variability to lactation records (15, 30). Under improving future managemental regimes, it will likely create less confusion in sire appraisals. On the contrary, the influence of gestation, expressed as days open, has an important influence on lactation production. I t accounts for from 4 to 7% of the variance (30, 31), which is approximately twice the nmgnitude of the variance generally associated with month of freshening within a given herd and a given year (3). Even in extremely well-managed herds, the degree of control over the time of conception will not likely be as great as that which can be exercised over the dry period. Hence, variation in production due to days open should be taken into account as soon as an operational approach can be developed to obtain the information. The analysis of a sire based on the daughters from his initial sampling is by f a r the most important one. At this time a major portion of the bull's productive life is before him, and he should be placed into heavy service without waiting for additional daughters. The time and expense involved in progeny testing also reqmre that nmst of the decisions be based on the first lactations of the daughters of a sire. A n unselected sample of the daughters of the young sire must be sought for his appraisal. When the first lactations of the young sire's daughters are compared with herd-mates of all ages, biases may arise in these comparisons. Selection among older animals, which will be expected to vary in intensity i r m a herd to herd, could result in a bias against the bulls being evaluated on only the first lactations of their daughters. Possible inadequacies in the age-conversion factors also could produce a systematic bias when young animals are being compared with the cross-section of the herd
(32). The differences between first and al] lactations vary from herd to herd (33). As a consequence, an adjustment based on the average effect of selection in a population would not be appropriate. Herd size continues to increase and there appears to be nmch to justify further study of comparing daughters' first lactations with firstlactation herd-mates. Such a procedure would minimize both the effects of differential selection and discrepancies in age factors for l~rstlactation appraisals. Information on second and later lactation can be utilized by making comparisons with second and later-lactation herd-mates. /~EED FOR E A R L Y SELECTIObT
Concern is frequently expressed that many mistakes may be made by choosing bulls on the basis of their daughters' first lactation or partial lactation records. Most of this concern has been phrased, in terms of production, but the same questions arise in the consideration of other traits. Even with the sire himself, evidence is desired to establish the relationship between his fertility during sampling and again at maturity or re-entry into the stud. More recently, partial records have been advocated to reduce the time required to test a young bull. This shortening of the testing interval must be balanced against the possible reduction in accuracy of evaluation and the costs involved in waiting for the complete lactation records. The key question here concerns the genetic relationship between partial and 305-day lactation yields. Differences in persistency among the daughters of bulls could reduce the genetic relationship between p a r t and 305-day records. Most investigations (21, 27, 28, 34) have shown a high genetic relationship between p a r t lactations of 150 to 180 days and 305-day records, and the heritabilities for these partial records have been almost equal to those for 305-day records. Thus, there is justification for making earlier decisions on sires than has been the practice in the past. Concern has been expressed that selection of sires on first-lactation performance of their daughters fosters the development of animals with short productive lives. Perhaps individual circumstances, where the udders of heavy-milking daughters have not stood the strain of year-after-year production, have clouded the interpretation of the general picture. Actually, the evidence indicates that higher producers during the first lactation remain in the herd longer and continue to produce at a higher level than the lower-producing first-lactation animals (24). An excellent inquiry into the economic value of longevity hs.s been presented by Rendel and Robertson (25). When all factors are considered, an increase in average productive life of one additional lactation would represent only a snlall increase in average herd yield or
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J O U R N A L OF D A I R Y S C I E N C E
in economy of costs of production. Moreover, the evidence suggests that the heritability of length of productive life is so low that managemental factors must be utilized to enhance productive life (24). While additional inquiry is warranted, current evidence suggests that selection of sires whose daughters have .high first lactations should not reduce productive life. CONSIDERATION OF INDIVIDUAL TRAITS
Fertility. The young sire must first pass the health and fertility test to gain re-entry into the stud. While little evidence has been reported which relates early fertility of a hull to his later fertility, enough information should now be available from the various studs to provide an indication of the relationship. Preventative and therapeutic measures are nmin]y relied upon to maintain health and high fertility. Yet, Shannon and Searle (29) reported evidence that there is a genetic influence on the fertilizing power of a sire's semen. Heritability of conception rate based on nonreturns to first service by 38 days was estinmted to be 0.55 ~ 0.26. The volume of semen produced and the freezability of the semen is also an important consideration in most breeding organizations. Dunn and Young (10) have reported significant bull differences based on laboratory motility evaluation of frozen semen. Reports of bulls whose semen exhibits satisfactory fertility in liquid use but whose semen doe~s not maintain fertility after freezing and thawing are reasonably numerous, although not fully documented. Several workers (6, 9, 12) have studied the conception rates of daughters of sires used in artificial breeding. Dunbar and Henderson (9) found the heritabilitv~ for 180-day nonreturns to be zero. Wisconsin workers (6, 12) found the heritability of obtaining a live calf from first service to range from 0.02 to 0.10. Consideration was given to the selection of sires whose daughters had higher conception rates as a means of improving the conception rate. However, in order to make substantial progress at least half of the sires would be discarded on the basis of fertility alone. Such a heavy culling at this point would leave little opportunity to cull for other items, including production. Type. The conformation of the bull often enters into the decision regarding his acceptability. Apart from the popularity consideration, just what does conformation mean to the serviceable life of the bull? Feet and leg conditions have contributed to the removal of ninny bulls from service (1, 2). Some emphasis may be given to beef confornmtion in the future. Other than these items, it is difficult to justify emphasis on conformation of a sire for use in commercial artificial insemination. Next, how important is the conformation of the cows in our commercial herds? I t is reported that cows which look like we say they
should look, even though they are grades, bring more money when sold for dairy purposes. But the commercial producer has little market for special conformational details which are not associated with the utility of the cow. An objective consideration of conformation should emphasize those qualities related to serviceability and productivity. Feet and legs are often referred to, and recent reports indicate that about 1% of the cows in herds leave because of reported feet and leg troubles (23). Such an evaluation may not fully reflect the practical importance of good feet and legs, since foot trimming can be an important chore, especially with loose-housing arrangements. Udders are needed that will be useful for a long time, but they do not necessarily need to be fancy. While lower udders are more prone to mastitis (36), there is some evidence suggesting that animals with deeper udders are higher producers (4). Swedish workers (13, 14) found wide variations in yield between the fore and rear quarters of the udder, but ve~" little difference between the yields of the left and right sides of the udder. The heritability of differences between the front and rear halves of the udder were about 0.75; whereas, the differences between the left and right halves of the udder were largely developmental and environmentally caused. Selection for more fully developed fore quarters might be expected to yield good results when decisions are based on actual measurements of yield for the front and rear quarters. External judging of the udder permitted identification of the most extreme types, but special investigations have shown that there is a rather poor agreement between udder scores and actual measurements of yields (13). Johansson (13) also reported a high heritability for length, diameter, and placement of teats, as has been noted in less precise observations. Size can be considered as a component of type, and the general practice has been to give preference to the larger cow, all other things being equal. Nonetheless, the increase in lactation milk yield per 100 lb of body weight for cows of the same age have been shown to be only about 200 lb (5, 19). Furthermore, the genotype for larger size and the genotype for production do not appear to be closely associated. Thus, when feed costs for maintenance and the additional milk produced are accounted for, there should be a negative emphasis on size. Current evidence indicates that dairymen should give little attention to weight or size, except where the cows depart markedly from the breed average. Mastitis. This disease continues as the most costly in dairy cattle, in spite of major efforts to control it. Its impact is felt through the direct reduction of milk flow and loss of milk during infection, through increases in replacement costs, and by added expense for treatment. The economic importance of this prob-
sYm~OSllJM lem varies with the severity and length of the infection; thus, a direct dollars-and-cents appraisal is difficult to provide. Certain aspects of udder conformation appear to be associated with mastitis. The low and pendulous udders are more subject to inj u r y and prone to attacks of clinical mastitis (36). Workers have also stressed the importance of the teat sphineter as a barrier to udder infection (22). MeEwan and Cooper (20) reported a higher incidence of mastitis among fast-milking than among slow-n~ilking cows. Dodd and Neave (8) also found this association when using peak flow for measuring milking rate. They did not deem it advisable to breed for slow milkers, since the more rapid-milking animals also had the higher milk yields. Evidence is consistent that there is a hereditary basis for mastitis resistance (11, 16, 17, 36). Mastitis incidence is highest early in lactation, when daily production is high, but there is no substantial evidence that genetically links high lactation production and mastitis incidence. One of the major deterrents to effective selection against mastitis is that the incidence of the disease is low during first lactations. This delays obtaining the phenotypic evaluation of a bull's daughters. Most daughters would have to complete two lactations before an effective appraisal of the sire's transmitting ability for resist,~nce would be available. Thus, until an early method for detecting mastitis susceptibility is available, there will be little opportunity to select against it among young sampled bulls. Milk composition. High milk volume of satisfactory composition is most important in insuring high economic returns. Interest in milk composition is now growing, and certain markets are beginning to give some attention to the S N F and protein content as well as fat percentage. This change is extremely slow. Current evidence suggest that the heritability of fat, SNF, and protein per cent are about 0.50 to 0.60. The genetic associations among the percentage composition of these components are positive and each of the components is apparently negatively correlated with milk volume. Low wxiability, especially for S N F and protein, a p p e a r to be limiting factors to rapid genetic change (26). As each of the major constituents are positively correlated both genetically and phenotypically, the influence of these inter-relationships on other constituents are of interest. I f selection is practiced for either S N F or protein some increase ii~ fat percentage is expected. While the evidence is limited, the genetic correlation between protein and S N F appears high enough to permit selection for protein to be reasonably effective in changing SNF, and vice versa. F a t percentage is not nearly as effective a basis on which to select for S N F or protein. Little market incentive is now available for either S N F or protein. Hence, it appears wise
449
to discriminate only against those bulls whose daughters produce below-desired standards. As f a r as total yield of S N F or protein is concerned, it can be enhanced more rapidly by increasing milk yield than by seeking to raise the percentage composition. Milking qualities. As dairying continues its move toward larger mechanized operations, the importance of milking qualities in our cows is being forcefully brought to our attention. Peak flow, measuring the maximum rate per minute, has been widely used as a measure of milking rate. Machine time expressed as the milking time up to the start of machine stripping has also been used. I n evaluating peak flow, the daily milk yield also must be considered, since peak flow increases with increasing daily yield. Dodd and Foot (7) found evidence of appreciable genetic variance in peak flow. Johansson (13) has also reported that peak flow and milking time have heritabilities of about 0.35. The importance of rapid nlilking can be seen more vividly by noting that a difference of 7 as compared to 5 rain to milk a cow would entail just over 20 additional hours to nlilk the slowernfilking tow twice daily during a 305-day lactation. Peak flow appears to be the best field measure for milking rate. Most workers agree that it is less influenced by the skill and care of the milker than is the average rate of flow. Possibly four measurements during the second to the fifth month in lactation could be useful in field appraisals of sires (18). Abnormalities. There are a number of defective traits in cattle identified as having a genetic origin. Certain of these have lethal effects on the fetus prior to birth; others may reduce the viability of the new-born calf. This problem has and will continue to be with us in varying degrees. W i t h artificial insemination and the reduction in the effective number of sires, the problem is now seen in a new light. The individual dairyman using artificial insemination, which provides the services of several sires, is usually better protected now than when he used his own sires. Sires used in artificial insemination are mated to a large number of cattle of various genetic backgrounds, increasing the likelihood of matings with females wilich are carriers. As a consequence, there is a greater chance that a defective calf wilt be reported. I f the suspected carrier is a mediocre individual, the decision regarding its disposal is not difficult. However, if the suspect is an individual with much promise, a satisfactory testing procedure must be devised. Some have advocated that all bulls should be tested for deleterious genes by mating them back to about 20 of their own daughters. Such a testing plan places a burden on the population. A more logical approach would be first to practice careful pedigree selection for freedom from these defects. Known carriers should be removed from service. I f the genetic merit for
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JOUI~NAL OF DAIRY SCIENCE
production of a carrier bull warrants keeping the sire as a contributor to the gene pool, then sons of this bull should be tested prior to sampling. All suspected carriers should be tested prior to being placed in service. Such testing could be carried out with (a) homozygous carriers where they are viable and fertile, or to (b) heterozygous carriers where the defect is lethal. I f such testers are not available the bull could be mated to daughters of other bulls which are known to be carriers, or as a last resort the sire may be mated to his own daughters (c). Mating to the sire's own daughters would not only be expected to detect the specific defect, but any other recessives the bull may be carrying. It has the disadvantage that the offspring have an average inbreeding coefficient of 0.25, and the test is not available until the bull is about 41/2 years old. Under procedures (a), (b), and (e) approximately 5, 10, and 23 offspring, respectively, are required to reach a probability of I in 20 that the suspected bull is not a carrier. DISCUSSION
Our infornmtion has not progressed to the point where the various traits can be combined in a conventionalselection index. A summary of some of the needed information has been attempted in Table 1, although it is recognized that there are many gaps. The question marks indicate this lack of solid infornmtion. Milk yield, milk composition,and type scores have sufficient genetic variability to suggest that selection for them would result in genetic change. Mastitis resistance, milking qualities, and body size probably have a reasonable degree of genetic variability, but infornmtion regarding them is inadequate. Longevity and fenmle reproductive efficiency have little genetic variability. Managemental factors rather than sire selection should be relied upon to gain higher levels of expression for these traits. Various inter-relationships are of interest, although many are not known with much certainty. Fat, protein, and S N F percentages are
positively correlated with each other, but they are probably negatively correlated with milk volume. Certain milking qualities appear to be positively correlated with milk yield, and there is some evidence to suggest that rapid milking may be related to a higher mastitis incidence. Over-all type score has a slight positive association with milk production. Except for relationships among the milk constituents and yield, negative associations between important traits are not suggested by current information. Nevertheless, the fact that there are no decisive antagonisms does not insure against competition in selection for traits which may be of major economic significance. We must continually guard against excessive attention to qualities which our dairymen have no reasonable chance to market. In most situations this would point toward primmT emphasis on more milk of desired composition. Each additional trait tht~t is selected for uses a portion of the selection potential which a herd or population possesses. This is not to argue that selection should be directed to a single trait, but merely to emphasize that our choices nmst be wise ones. Assume that a stud can maintain a battery of A.I.-proved sires whose composite adjusted daughter average is 800 lb of milk above their herd-mates, when production is the sole criterion for choosing the bulls. Then assmne that additional independent traits are given equal consideration in sire choices. Table 2 shows how the superiority for production would be expected to decline when TABLE 2 Expected decline in mean production superiority over herd-mates for a battery of sires as additional independent traits enter into sire choices Mean superiority (lb)
No. of traits 1 2 3 4 5
800 570 460 400 360
TABLE 1 Summary of information on individual traits and their relationship with milk yield Correlation with milk yield
Range of heritability
Phenotypic
Genetic
Milk Fat (%) SNF (%) Protein (%) 'Type scores Mastitis
.15 to .30 .45 to .55 .45 to .55 .45 to .55 .15 to .30 .10 to .30
--.15 to --.35 --.20? --.25% .05 to .20 ?
--.20 to --.50 ? ? .05 to .20 ?
Milking qualities Mature size Productive life l~eproductive eft.
.30 to .30 to 0 to 0 to
Trait
.40 .50 .10 .10
.05 to .15 to .15 to .10 to
.20 .30 .20 .25
? --.20 to +.10 ? 07
Economic importance Direct sales Price diff. Price diff.? Price diff.? Breeding sales? Yield--treatment costs Labor costs Feed costs Repl. costs Yield and rep].
sYMPOSIUM
additional traits are considered. I t does not require many additional items to decrease the potential superiority by one-half. Broadly speaking, the young sire sampliug programs can provide bulls which can be used and recommended with confidence. Daughters of young bulls perform contemporaneously with daughters of proved A.I. sire% and direct evidence is available to determine whether these sires are capable of genetically improving the population. A young sire program cannot guarantee an outstanding bull at all times, but it can eliminate h'om extensive service sires that would be responsible for genetic deterioration of the population. By limiting the initial use of these bulls to what is required to provide sufficient daughters for an accurate appraisal, herds participating in sampling are not burdened with an excessive number of daughters of undesirable sires.
451
(3)
(4)
(5)
(6)
(7)
(8)
CONCLUSIOI~S Since over 90% of the services from artificial insemination are to grade animals, emphasis in sire analysis and evaluation should be given to those qualities which provide the greatest econonlic return. Long generation interval and high costs of sampling require that sire choices be made as soon as practicable. Selections based on the first lactations of the daughters should not have an adverse effect on length of productive life. The high genetic relationship between part lactations and 305-day records suggests that increased use of partial records is justified. The principle of herd-nlate comparisons has gained acceptance and it is the most accurate practical procedure for sire appraisal. Continued improvements should be sought in operational procedures which would renmve environnlental variance and account for the influence of selection. Suspected carriers of genes for abnormalities should pass a negative test for the suspected abnormality prior to their use in the general population. Complete reporting of abnornlalities should be encouraged to enhance the accuracy of pedigree selection against such genes. Most of the traits which should enter into sire analyses have a reasonable degree of genetic variation. However, unjustified emphasis on a u x i l i a ~ traits detracts from the selection pressure that can be applied to milk yield. We must continue to guard against giving excessive attention to traits not likely to contribute to econonlie returns. REFERENCES (1) ]~ECKEa, R. B. Life Span of Sires in A.L Prec. Natl Assco. Artificial Breeders. p. 77. 1960. (2) BECI~ER, R. B., WILCOX, C. J., AND PI~ITCIt.~aD, W. R. Crampy or Progressive Poste-
(9) (10) (11) (]2)
(]3) (]4)
(15)
(16)
(17) (18)
(19)
(20) (21)
(22)
tier Paralysis in Mature Cattle. J. Dairy Sci., 44: 543. 1961. BEaESKIN, B., AND FREEMAN, A. E. Effect of Month of Calving in Herds at Three Levels of Production. J. Dairy Sci., 44: ]196. ]961. BURNSIDE, E. B., MCDANIEL, B. T., AND LEGATES, J. E. The Relatimlships Among Udder Height, Age, and Milk Production. J. Dairy ScL, 46: 157. 1963. CLARK, R. D., AND TOUCttBERRY, R. W. Effect of Body Weight and Age at Calving on Milk Production in Holstein Cattle. J. Dairy Sci., 45: 1500. 1962. COLLINS, W- ]~., INSKEEF, E. K., TYLER, W. J., AND CASIDA, L. E. Variation in Conception Rates of Guernsey Cattle. J. Dairy Sci., 45: 1234. 1962. DODD, I~. H., AND FOOT, A. 8. The Importance of Machine Milking Rate in Dairy Cow Management. J. Dairy l%search, 20: 138. 1953. DODD, ~. H., AND I~E&VE, F. K. Machine Milking Rates and Mastltis. J. Dairy Research, 18: 240. 1951. DUNBAI~,R. S., AND HENDERSON,C. R. Heritability of Fertility in Dairy Cattle. J. Dairy Sci., 36: 1063. 2953. DUNN, H. O., AND YOUNG, G. F. Laboratory and ~'ield Studies with Frozen Semen. J. Animal Sei., 12: 893. 1953. GAUNYA,W. S-, AND MATHEI~, R. E. I~Ieritability of Resistance to Bovine Mastitis. J. Dairy Sci., 45: 1577. 1962. INSKEEP, E. K., TYLER, W. J., AND CASIDA, L. E. Hereditary Variation in Conception Rate of Holstein Cattle. J. Dairy Sci., 44: 1857. 1961. JOHANSSON, I. Genetle Aspects of Dairy Cattle Breeding. 259 pp. University of Illinois Press, Urbana. 1961. JOHANSSON, I., AND KORKI~AN7 N. Heritability of Udder Proportions in Dairy Cows. Itereditas, 38: 131. 1952. LEE, J. E., FOSGATE, O. T., AND CAI~I~AN, J. L. Some Effects of Certain Environmental Influences on Milk and Fat Production in Dairy Cattle. J. Dairy Sci., 44: 296. ]961. LEGATES, J. E., AND GaINNELLS, C. D. Genetic Relationships in Resistance to Mastitis in Dai~T Cattle. J. Dairy Sci., 35: 829. 1952. LUSH, J. L. Inheritance of Susceptibility to Mastitis. J. Dairy ScL, 33: 121. 1950. McDANIEL, B. T., BUI~NSIDE, E. B., AND LEGATES, J. E. Reliability of an Estimate of Maximum Milking Rate and Its Relationship with Production. J. Dairy Sci., 45: 677. ]962. MCDANIEL, B. T., AND LEGATES, ~-. E. Relationship Between Body Weight and Production Traits in Holstein Cows. J. Dairy SoL, 46: 620. 1963. MeEwAN, A. D., AND COOPER, M. E. Bovine Mastitis. Vet. Record, 59: 655. ~1947. MADDEN, D. E., LUSH, J. L., AND MCGILLIAI~D, L. D. Relations of Parts of Lactations and Producing Ability of Holstein Cows. J. Dairy Sci., 38:1264. 1955. MURPHY, J. M. The Relationship of Teat Patency to Udder Infection. Cornell Vet., 34: 64. 1944.
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(27) (28) (29)
(30)
AND VANVLECK, L. D. Reasons for Disposal of Dairy Cows from New York Herds. J. Dairy Sci., 45: 1087. 1962. PARKER, J. B., BAYLEY, N. D., FOHB,MAN, M. H., AND PLOWMAN, R. D. Factors Influencing Dairy Cattle Longevity. J. Dairy Sci., 43: 401. 1960. RENDEL, J. M., AND ROBERTSON, A. Some Aspects of Longevity in Dairy Cows. Empire J. Exptl. Agr., 18:49. 1950. ROBERTSON, A., WAITE, R., AND WHITE, J. C. D. Variations in the Chemical Composition of Milk with Particular Reference to Solids-not-fat. II. The Effect of Heredity. J. Dairy Research, 23: 82. 1956. SEARLE, S. R. P a r t Lactations. II. Genetic and Phenotypic Studies of Monthly Milk F a t Yield. J. Dairy Sci., 44: 282. 1961. SEARLE, S. R. P a r t Lactations. III. Progeny Testing with P a r t Lactation Records. J. Dairy Sci., 44: 921. 1961. SHANNON,P~, AND SEARLE, S. ~. Heritability and Repeatability of Conception Rate of Bulls in Artificial Breeding. J. Dairy Sci., 45: 86. 1962. SMnrH, J. W., AND LEGATES, J. E. Factors Affecting Persistency and I t s Importance
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(33) (34)
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(36)
in 305-Day Lactation Production. J. Dairy Sci., 45: 676. 1962. SPALDING, R. W. Some Effects of Service Period and Dry Period on Milk and Butterf a t Production. Dissertation Abstr., 22: 3794. 1962. TUCKER, W. L., LEGATES, g. E., AND FARTtIING, B. R. Genetic Improvement in Production Attributable to Sires Used in Artificial Insemination in North Carolina. J. Dairy Sci., 43: 982. 1960. TUCKER, W. L., AND LEGATES, J. E. Effective Use of Herdmates in Sire Evaluation. J. Animal Sci., 21: 976. 1962. VANVLECK, L. D., AND HENDERSON, C. R. Estimates of Genetic Parameters of Some Functions of P a r t Lactation Milk Record. J. Dairy Sci., 44: 7073. 1961. VANVLECK, L. D., AND HENDERSON, C. R. Utilizing Both P a r t and Complete Daughter Records in Sire Evaluation. J. Dairy Sci., 44: 2068. 1961. YOUNG, C. W., LEGATES, J. E., AND LECCE, J . G . Genetic and Phenotypic Relationships Between Clinical Mastitis, Laboratory Criteria, and Udder Height. J. Dairy Sci., 43: 54. ]960.
EVALUATING A R T I F I C I A L INSEMINATION RESULTS ~ED D. BAYLEY A n i m a l H u s b a n d r y R e s e a r c h Division, U S D A , Beltsville, M a r y l a n d The definition of evaluation can be dichotomized into rhetorical a n d n m t h e m a t i c a l m e a n ings. The three s p e a k e r s p r e c e d i n g me are well k n o w n to be f a r more a r t i c u l a t e in m a t h e m a t i c a l e v a l u a t i o n s t h a n I am. Therefore, it is quite possible t h a t the committee o r g a n i z i n g this s y m p o s i u m was c o g n i z a n t of these relative talents a n d hoped t h a t I, f e a r i n g the c o n t r a s t of exposure, would avoid m a t h e m a t i c a l discussions in my p r e s e n t a t i o n . I accept the implications of t h e i r a s s i g n m e n t . Therefore, in k e e p i n g with the n a t u r e of m y a s s i g n m e n t , I shall sumlnarize the artificial ins e m i n a t i o n ( A . I . ) results related to g r o w t h by s a y i n g t h a t there are some A.I. o r g a n i z a t i o n s b i g g e r t h a n others, a n d the big ones are differe n t t h a n the little ones. I n a more serious vein, Table 1 shows some of the r e l a t i o n s h i p s between A.I. o r g a n i z a t i o n s of different size t h a t
exist today. Sixty p e r cent of the o r g a n i z a t i o n s p r o v i d e d less t h a n 100,000 first services each i n 1962. These studs owned 3 3 % of the bulls in A.I. However, t h e i r services a m o u n t e d to only ] 5 % of the cows inseminated. On the o t h e r h a n d , only ten studs h a d more t h a n 200,000 first services, owned 4 6 % of the bulls, a n d i n s e m i n a t e d 6 9 % o f the cows. I t is obvious t h a t the genetic i m p a c t o f the large studs on the i n d u s t r y is g r e a t l y out of p r o p o r tion to the n u m b e r of such studs. F u r t h e r m o r e , as shown by the n u m b e r of cows i n s e m i n a t e d p e r bull, the efficiency in utilization of bulls is m u c h g r e a t e r in the large studs t h a n in the smaller ones. These c h a r a c t e r i s t i c s a r e extremely imp o r t a n t to the c a p a b i l i t y o f c a m T i n g on sire selection a n d testing, as described b y others in this symposium.
TABLE 1 Characteristics of A.I. organizations stratified by number of cows inseminated during 1962 (2)
No. cows inseminated Less than 100,000 100,000 but less than 200,000 200,000 or more
No. bulls total
Per cent of all bulls
Per cent of all cows inseminated
Cows inseminated per bull
60
858
33
15
1,322
20 20
545 1,156
21 46
16 69
2,317 4,629
No. studs
Per cent of all studs
31 10 10
JOURNAL OF DAIRY SCIENCE
lb of milk, which is identical with the maximum stud superiority value. The difference between the proved stud superiority at maxinmm net returns and that of the sampling stud is 760 lb of milk, or about 380 Ib per cow per year or $9.50 a cow per year, which indicates a dairyman using young bull semen should receive either free artificial insemination, be paid for D H I A testing the daughters, or both.
rate of genetic improvement and net returus to dairymen. Consolidation with across-the-board use of young bulls is less effective financially than with no consolidation and young bull services in testing herds only. The results indicate clearIy that for maximum net returns the same number of bulls need be sampled as for maximum genetic improvement. Another set of cost and profit values might, however, exhibit a completely different picture.
SUMMARY
REFERENCES
Factors which determine the daughter superiority of a selected group of young sires over all those sampled have been discussed. Fornmlae have been developed for predicting the daughter superiority of the permanent stud and the sampling stud. The assignment of profit and cost values associated with genetic improvement for various combinations of fraction of services to the permanent stud and number of daughters for evaluating young sires revealed that the programs for maximum genetic improvement and maximum net returns were the same for the example discussed. In general, to maximize genetic improvement many young bulls should be sampled and with 20-50 daughters per bull. Consolidation of studs with 50,000 first services and using young bulls in testing herds can substantially increase the ANALYSIS
OF THE
(1) HARTZR, H. L. Expected Values of Normal Order Statistics. ARL Tech. Rept. 60-292. July, 1960. (2) HENDERSOn, C. :R. Selecting the Young Sire to Sample in Artificial Insemination. Symposium: Young Sire Selection for Commercial Artificial Insemination. A.D.S.A. Annual Meeting, June 18, 1963. (3) SEARLE, S. R. Bull S a m p l i n g P r o g r a m m e s in
the Artificial Breeding of Dairy Cattle. Proc. New Zealand Soc. Animal Production, °2: 54. 1962. (4) SPECH% L. W., AND MeGILLIARI),L. D. Rates of Improvement hy Progeny Testing in Dairy Herds of Various Sizes. J. Dairy Sci., 43: 63. 1960. (5) VANVLEeK,L. D. Genetic Progress from Artificial Insemination. Paper presented New York Artificial Breeders Cooperative Sire Conference. January 3, 1962. (Mimeo.)
YOUNG SIRE
SERVICE 1
J. E. LEGATES Department of Animal Science, North Carolina State, Raleigh Most sire-sampling programs are devised with the aim of maximizing improvement in production, although information on other traits is drawn upon in making decisions regarding the re-entry of a sire to the active stud. Since the expected genetic progress per year for production will decline as additional traits are considered, it is most important that we use our opportunity to select as wisely as our knowledge and judgment will permit. Of necessity, more than one trait nmst enter into the evaluation of the sire, but how should these qualities be meshed with the emphasis on production? A practical and complete working answer is not yet available, but there are certain principles which can be of assistance in helping to make proper judgments. On the basis of registration reports, over 90% of artificial insemination services are to grade animals. It logically follows that primary emphasis in sire analysis should be given to those qualities which will make the largest Published with the approval of the Director of l~esearch, North Carolina Agricultural Experiment Station, :Raleigh, as Paper No. 1716 of the Journal Series.
economic contribution through the performance of the daughters of selected sires. I n considering the numerous qualities that appear desirable, we nmst first ask if the trait contributes to the net returns for the dairy enterprise. The actual dollar income on the daily farm arises from three sources: milk, beef or veal, and breeding stock sales. A large volume of milk of desirable composition is the most important key to economic success. Beef and veal sales may be considered as offsetting replacement costs, but they generally are not a major source of returns. The sale of breeding stock or surplus heifers contributes in only a limited fashion to the returns for most commercial herds. Other traits can contribute to net returns only as they influence milk yield and composition, or as they reduce production costs for the marketable items mentioned above. In addition to economic considerations, the genetic variability (heritability) of tile traits is also important. The opportunity to select among sires should not be dissipated on traits which give little promise of being responsive to selection. Information on the inter-relationships among other traits and production is
447
sY~POSlU~
meager, largely because satisfactory objective measures for these traits are not yet available. Nevertheless, these inter-relationships are important to project long-time selection goals. BASIS FOR EVALUA~IO~ The principle of the herd-mate comparison has now received general acceptance as the basis of evaluating a sire's transmitting ability for production. While the details of its application vary depending on the genetic and the between and within herd variances, it eventually should be useful in the analysis of other traits. In view of the extensive coverage which the herd-mate comparison and the various adjusted daughter averages have received in previous months, it does not seem appropriate to review these details. However~ there are a few points which a p p e a r worthy of mention. In regular sire analysis procedures, production records are corrected f o r / o r comparisons are made so as to account for age, herd, year, and seasonal influences. Days dl~ prior to calving do not a p p e a r to contribute an appreciable amount of variability to lactation records (15, 30). Under improving future managemental regimes, it will likely create less confusion in sire appraisals. On the contrary, the influence of gestation, expressed as days open, has an important influence on lactation production. I t accounts for from 4 to 7% of the variance (30, 31), which is approximately twice the nmgnitude of the variance generally associated with month of freshening within a given herd and a given year (3). Even in extremely well-managed herds, the degree of control over the time of conception will not likely be as great as that which can be exercised over the dry period. Hence, variation in production due to days open should be taken into account as soon as an operational approach can be developed to obtain the information. The analysis of a sire based on the daughters from his initial sampling is by f a r the most important one. At this time a major portion of the bull's productive life is before him, and he should be placed into heavy service without waiting for additional daughters. The time and expense involved in progeny testing also reqmre that nmst of the decisions be based on the first lactations of the daughters of a sire. A n unselected sample of the daughters of the young sire must be sought for his appraisal. When the first lactations of the young sire's daughters are compared with herd-mates of all ages, biases may arise in these comparisons. Selection among older animals, which will be expected to vary in intensity i r m a herd to herd, could result in a bias against the bulls being evaluated on only the first lactations of their daughters. Possible inadequacies in the age-conversion factors also could produce a systematic bias when young animals are being compared with the cross-section of the herd
(32). The differences between first and al] lactations vary from herd to herd (33). As a consequence, an adjustment based on the average effect of selection in a population would not be appropriate. Herd size continues to increase and there appears to be nmch to justify further study of comparing daughters' first lactations with firstlactation herd-mates. Such a procedure would minimize both the effects of differential selection and discrepancies in age factors for l~rstlactation appraisals. Information on second and later lactation can be utilized by making comparisons with second and later-lactation herd-mates. /~EED FOR E A R L Y SELECTIObT
Concern is frequently expressed that many mistakes may be made by choosing bulls on the basis of their daughters' first lactation or partial lactation records. Most of this concern has been phrased, in terms of production, but the same questions arise in the consideration of other traits. Even with the sire himself, evidence is desired to establish the relationship between his fertility during sampling and again at maturity or re-entry into the stud. More recently, partial records have been advocated to reduce the time required to test a young bull. This shortening of the testing interval must be balanced against the possible reduction in accuracy of evaluation and the costs involved in waiting for the complete lactation records. The key question here concerns the genetic relationship between partial and 305-day lactation yields. Differences in persistency among the daughters of bulls could reduce the genetic relationship between p a r t and 305-day records. Most investigations (21, 27, 28, 34) have shown a high genetic relationship between p a r t lactations of 150 to 180 days and 305-day records, and the heritabilities for these partial records have been almost equal to those for 305-day records. Thus, there is justification for making earlier decisions on sires than has been the practice in the past. Concern has been expressed that selection of sires on first-lactation performance of their daughters fosters the development of animals with short productive lives. Perhaps individual circumstances, where the udders of heavy-milking daughters have not stood the strain of year-after-year production, have clouded the interpretation of the general picture. Actually, the evidence indicates that higher producers during the first lactation remain in the herd longer and continue to produce at a higher level than the lower-producing first-lactation animals (24). An excellent inquiry into the economic value of longevity hs.s been presented by Rendel and Robertson (25). When all factors are considered, an increase in average productive life of one additional lactation would represent only a snlall increase in average herd yield or
448
J O U R N A L OF D A I R Y S C I E N C E
in economy of costs of production. Moreover, the evidence suggests that the heritability of length of productive life is so low that managemental factors must be utilized to enhance productive life (24). While additional inquiry is warranted, current evidence suggests that selection of sires whose daughters have .high first lactations should not reduce productive life. CONSIDERATION OF INDIVIDUAL TRAITS
Fertility. The young sire must first pass the health and fertility test to gain re-entry into the stud. While little evidence has been reported which relates early fertility of a hull to his later fertility, enough information should now be available from the various studs to provide an indication of the relationship. Preventative and therapeutic measures are nmin]y relied upon to maintain health and high fertility. Yet, Shannon and Searle (29) reported evidence that there is a genetic influence on the fertilizing power of a sire's semen. Heritability of conception rate based on nonreturns to first service by 38 days was estinmted to be 0.55 ~ 0.26. The volume of semen produced and the freezability of the semen is also an important consideration in most breeding organizations. Dunn and Young (10) have reported significant bull differences based on laboratory motility evaluation of frozen semen. Reports of bulls whose semen exhibits satisfactory fertility in liquid use but whose semen doe~s not maintain fertility after freezing and thawing are reasonably numerous, although not fully documented. Several workers (6, 9, 12) have studied the conception rates of daughters of sires used in artificial breeding. Dunbar and Henderson (9) found the heritabilitv~ for 180-day nonreturns to be zero. Wisconsin workers (6, 12) found the heritability of obtaining a live calf from first service to range from 0.02 to 0.10. Consideration was given to the selection of sires whose daughters had higher conception rates as a means of improving the conception rate. However, in order to make substantial progress at least half of the sires would be discarded on the basis of fertility alone. Such a heavy culling at this point would leave little opportunity to cull for other items, including production. Type. The conformation of the bull often enters into the decision regarding his acceptability. Apart from the popularity consideration, just what does conformation mean to the serviceable life of the bull? Feet and leg conditions have contributed to the removal of ninny bulls from service (1, 2). Some emphasis may be given to beef confornmtion in the future. Other than these items, it is difficult to justify emphasis on conformation of a sire for use in commercial artificial insemination. Next, how important is the conformation of the cows in our commercial herds? I t is reported that cows which look like we say they
should look, even though they are grades, bring more money when sold for dairy purposes. But the commercial producer has little market for special conformational details which are not associated with the utility of the cow. An objective consideration of conformation should emphasize those qualities related to serviceability and productivity. Feet and legs are often referred to, and recent reports indicate that about 1% of the cows in herds leave because of reported feet and leg troubles (23). Such an evaluation may not fully reflect the practical importance of good feet and legs, since foot trimming can be an important chore, especially with loose-housing arrangements. Udders are needed that will be useful for a long time, but they do not necessarily need to be fancy. While lower udders are more prone to mastitis (36), there is some evidence suggesting that animals with deeper udders are higher producers (4). Swedish workers (13, 14) found wide variations in yield between the fore and rear quarters of the udder, but ve~" little difference between the yields of the left and right sides of the udder. The heritability of differences between the front and rear halves of the udder were about 0.75; whereas, the differences between the left and right halves of the udder were largely developmental and environmentally caused. Selection for more fully developed fore quarters might be expected to yield good results when decisions are based on actual measurements of yield for the front and rear quarters. External judging of the udder permitted identification of the most extreme types, but special investigations have shown that there is a rather poor agreement between udder scores and actual measurements of yields (13). Johansson (13) also reported a high heritability for length, diameter, and placement of teats, as has been noted in less precise observations. Size can be considered as a component of type, and the general practice has been to give preference to the larger cow, all other things being equal. Nonetheless, the increase in lactation milk yield per 100 lb of body weight for cows of the same age have been shown to be only about 200 lb (5, 19). Furthermore, the genotype for larger size and the genotype for production do not appear to be closely associated. Thus, when feed costs for maintenance and the additional milk produced are accounted for, there should be a negative emphasis on size. Current evidence indicates that dairymen should give little attention to weight or size, except where the cows depart markedly from the breed average. Mastitis. This disease continues as the most costly in dairy cattle, in spite of major efforts to control it. Its impact is felt through the direct reduction of milk flow and loss of milk during infection, through increases in replacement costs, and by added expense for treatment. The economic importance of this prob-
sYm~OSllJM lem varies with the severity and length of the infection; thus, a direct dollars-and-cents appraisal is difficult to provide. Certain aspects of udder conformation appear to be associated with mastitis. The low and pendulous udders are more subject to inj u r y and prone to attacks of clinical mastitis (36). Workers have also stressed the importance of the teat sphineter as a barrier to udder infection (22). MeEwan and Cooper (20) reported a higher incidence of mastitis among fast-milking than among slow-n~ilking cows. Dodd and Neave (8) also found this association when using peak flow for measuring milking rate. They did not deem it advisable to breed for slow milkers, since the more rapid-milking animals also had the higher milk yields. Evidence is consistent that there is a hereditary basis for mastitis resistance (11, 16, 17, 36). Mastitis incidence is highest early in lactation, when daily production is high, but there is no substantial evidence that genetically links high lactation production and mastitis incidence. One of the major deterrents to effective selection against mastitis is that the incidence of the disease is low during first lactations. This delays obtaining the phenotypic evaluation of a bull's daughters. Most daughters would have to complete two lactations before an effective appraisal of the sire's transmitting ability for resist,~nce would be available. Thus, until an early method for detecting mastitis susceptibility is available, there will be little opportunity to select against it among young sampled bulls. Milk composition. High milk volume of satisfactory composition is most important in insuring high economic returns. Interest in milk composition is now growing, and certain markets are beginning to give some attention to the S N F and protein content as well as fat percentage. This change is extremely slow. Current evidence suggest that the heritability of fat, SNF, and protein per cent are about 0.50 to 0.60. The genetic associations among the percentage composition of these components are positive and each of the components is apparently negatively correlated with milk volume. Low wxiability, especially for S N F and protein, a p p e a r to be limiting factors to rapid genetic change (26). As each of the major constituents are positively correlated both genetically and phenotypically, the influence of these inter-relationships on other constituents are of interest. I f selection is practiced for either S N F or protein some increase ii~ fat percentage is expected. While the evidence is limited, the genetic correlation between protein and S N F appears high enough to permit selection for protein to be reasonably effective in changing SNF, and vice versa. F a t percentage is not nearly as effective a basis on which to select for S N F or protein. Little market incentive is now available for either S N F or protein. Hence, it appears wise
449
to discriminate only against those bulls whose daughters produce below-desired standards. As f a r as total yield of S N F or protein is concerned, it can be enhanced more rapidly by increasing milk yield than by seeking to raise the percentage composition. Milking qualities. As dairying continues its move toward larger mechanized operations, the importance of milking qualities in our cows is being forcefully brought to our attention. Peak flow, measuring the maximum rate per minute, has been widely used as a measure of milking rate. Machine time expressed as the milking time up to the start of machine stripping has also been used. I n evaluating peak flow, the daily milk yield also must be considered, since peak flow increases with increasing daily yield. Dodd and Foot (7) found evidence of appreciable genetic variance in peak flow. Johansson (13) has also reported that peak flow and milking time have heritabilities of about 0.35. The importance of rapid nlilking can be seen more vividly by noting that a difference of 7 as compared to 5 rain to milk a cow would entail just over 20 additional hours to nlilk the slowernfilking tow twice daily during a 305-day lactation. Peak flow appears to be the best field measure for milking rate. Most workers agree that it is less influenced by the skill and care of the milker than is the average rate of flow. Possibly four measurements during the second to the fifth month in lactation could be useful in field appraisals of sires (18). Abnormalities. There are a number of defective traits in cattle identified as having a genetic origin. Certain of these have lethal effects on the fetus prior to birth; others may reduce the viability of the new-born calf. This problem has and will continue to be with us in varying degrees. W i t h artificial insemination and the reduction in the effective number of sires, the problem is now seen in a new light. The individual dairyman using artificial insemination, which provides the services of several sires, is usually better protected now than when he used his own sires. Sires used in artificial insemination are mated to a large number of cattle of various genetic backgrounds, increasing the likelihood of matings with females wilich are carriers. As a consequence, there is a greater chance that a defective calf wilt be reported. I f the suspected carrier is a mediocre individual, the decision regarding its disposal is not difficult. However, if the suspect is an individual with much promise, a satisfactory testing procedure must be devised. Some have advocated that all bulls should be tested for deleterious genes by mating them back to about 20 of their own daughters. Such a testing plan places a burden on the population. A more logical approach would be first to practice careful pedigree selection for freedom from these defects. Known carriers should be removed from service. I f the genetic merit for
450
JOUI~NAL OF DAIRY SCIENCE
production of a carrier bull warrants keeping the sire as a contributor to the gene pool, then sons of this bull should be tested prior to sampling. All suspected carriers should be tested prior to being placed in service. Such testing could be carried out with (a) homozygous carriers where they are viable and fertile, or to (b) heterozygous carriers where the defect is lethal. I f such testers are not available the bull could be mated to daughters of other bulls which are known to be carriers, or as a last resort the sire may be mated to his own daughters (c). Mating to the sire's own daughters would not only be expected to detect the specific defect, but any other recessives the bull may be carrying. It has the disadvantage that the offspring have an average inbreeding coefficient of 0.25, and the test is not available until the bull is about 41/2 years old. Under procedures (a), (b), and (e) approximately 5, 10, and 23 offspring, respectively, are required to reach a probability of I in 20 that the suspected bull is not a carrier. DISCUSSION
Our infornmtion has not progressed to the point where the various traits can be combined in a conventionalselection index. A summary of some of the needed information has been attempted in Table 1, although it is recognized that there are many gaps. The question marks indicate this lack of solid infornmtion. Milk yield, milk composition,and type scores have sufficient genetic variability to suggest that selection for them would result in genetic change. Mastitis resistance, milking qualities, and body size probably have a reasonable degree of genetic variability, but infornmtion regarding them is inadequate. Longevity and fenmle reproductive efficiency have little genetic variability. Managemental factors rather than sire selection should be relied upon to gain higher levels of expression for these traits. Various inter-relationships are of interest, although many are not known with much certainty. Fat, protein, and S N F percentages are
positively correlated with each other, but they are probably negatively correlated with milk volume. Certain milking qualities appear to be positively correlated with milk yield, and there is some evidence to suggest that rapid milking may be related to a higher mastitis incidence. Over-all type score has a slight positive association with milk production. Except for relationships among the milk constituents and yield, negative associations between important traits are not suggested by current information. Nevertheless, the fact that there are no decisive antagonisms does not insure against competition in selection for traits which may be of major economic significance. We must continually guard against excessive attention to qualities which our dairymen have no reasonable chance to market. In most situations this would point toward primmT emphasis on more milk of desired composition. Each additional trait tht~t is selected for uses a portion of the selection potential which a herd or population possesses. This is not to argue that selection should be directed to a single trait, but merely to emphasize that our choices nmst be wise ones. Assume that a stud can maintain a battery of A.I.-proved sires whose composite adjusted daughter average is 800 lb of milk above their herd-mates, when production is the sole criterion for choosing the bulls. Then assmne that additional independent traits are given equal consideration in sire choices. Table 2 shows how the superiority for production would be expected to decline when TABLE 2 Expected decline in mean production superiority over herd-mates for a battery of sires as additional independent traits enter into sire choices Mean superiority (lb)
No. of traits 1 2 3 4 5
800 570 460 400 360
TABLE 1 Summary of information on individual traits and their relationship with milk yield Correlation with milk yield
Range of heritability
Phenotypic
Genetic
Milk Fat (%) SNF (%) Protein (%) 'Type scores Mastitis
.15 to .30 .45 to .55 .45 to .55 .45 to .55 .15 to .30 .10 to .30
--.15 to --.35 --.20? --.25% .05 to .20 ?
--.20 to --.50 ? ? .05 to .20 ?
Milking qualities Mature size Productive life l~eproductive eft.
.30 to .30 to 0 to 0 to
Trait
.40 .50 .10 .10
.05 to .15 to .15 to .10 to
.20 .30 .20 .25
? --.20 to +.10 ? 07
Economic importance Direct sales Price diff. Price diff.? Price diff.? Breeding sales? Yield--treatment costs Labor costs Feed costs Repl. costs Yield and rep].
sYMPOSIUM
additional traits are considered. I t does not require many additional items to decrease the potential superiority by one-half. Broadly speaking, the young sire sampliug programs can provide bulls which can be used and recommended with confidence. Daughters of young bulls perform contemporaneously with daughters of proved A.I. sire% and direct evidence is available to determine whether these sires are capable of genetically improving the population. A young sire program cannot guarantee an outstanding bull at all times, but it can eliminate h'om extensive service sires that would be responsible for genetic deterioration of the population. By limiting the initial use of these bulls to what is required to provide sufficient daughters for an accurate appraisal, herds participating in sampling are not burdened with an excessive number of daughters of undesirable sires.
451
(3)
(4)
(5)
(6)
(7)
(8)
CONCLUSIOI~S Since over 90% of the services from artificial insemination are to grade animals, emphasis in sire analysis and evaluation should be given to those qualities which provide the greatest econonlic return. Long generation interval and high costs of sampling require that sire choices be made as soon as practicable. Selections based on the first lactations of the daughters should not have an adverse effect on length of productive life. The high genetic relationship between part lactations and 305-day records suggests that increased use of partial records is justified. The principle of herd-nlate comparisons has gained acceptance and it is the most accurate practical procedure for sire appraisal. Continued improvements should be sought in operational procedures which would renmve environnlental variance and account for the influence of selection. Suspected carriers of genes for abnormalities should pass a negative test for the suspected abnormality prior to their use in the general population. Complete reporting of abnornlalities should be encouraged to enhance the accuracy of pedigree selection against such genes. Most of the traits which should enter into sire analyses have a reasonable degree of genetic variation. However, unjustified emphasis on a u x i l i a ~ traits detracts from the selection pressure that can be applied to milk yield. We must continue to guard against giving excessive attention to traits not likely to contribute to econonlie returns. REFERENCES (1) ]~ECKEa, R. B. Life Span of Sires in A.L Prec. Natl Assco. Artificial Breeders. p. 77. 1960. (2) BECI~ER, R. B., WILCOX, C. J., AND PI~ITCIt.~aD, W. R. Crampy or Progressive Poste-
(9) (10) (11) (]2)
(]3) (]4)
(15)
(16)
(17) (18)
(19)
(20) (21)
(22)
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EVALUATING A R T I F I C I A L INSEMINATION RESULTS ~ED D. BAYLEY A n i m a l H u s b a n d r y R e s e a r c h Division, U S D A , Beltsville, M a r y l a n d The definition of evaluation can be dichotomized into rhetorical a n d n m t h e m a t i c a l m e a n ings. The three s p e a k e r s p r e c e d i n g me are well k n o w n to be f a r more a r t i c u l a t e in m a t h e m a t i c a l e v a l u a t i o n s t h a n I am. Therefore, it is quite possible t h a t the committee o r g a n i z i n g this s y m p o s i u m was c o g n i z a n t of these relative talents a n d hoped t h a t I, f e a r i n g the c o n t r a s t of exposure, would avoid m a t h e m a t i c a l discussions in my p r e s e n t a t i o n . I accept the implications of t h e i r a s s i g n m e n t . Therefore, in k e e p i n g with the n a t u r e of m y a s s i g n m e n t , I shall sumlnarize the artificial ins e m i n a t i o n ( A . I . ) results related to g r o w t h by s a y i n g t h a t there are some A.I. o r g a n i z a t i o n s b i g g e r t h a n others, a n d the big ones are differe n t t h a n the little ones. I n a more serious vein, Table 1 shows some of the r e l a t i o n s h i p s between A.I. o r g a n i z a t i o n s of different size t h a t
exist today. Sixty p e r cent of the o r g a n i z a t i o n s p r o v i d e d less t h a n 100,000 first services each i n 1962. These studs owned 3 3 % of the bulls in A.I. However, t h e i r services a m o u n t e d to only ] 5 % of the cows inseminated. On the o t h e r h a n d , only ten studs h a d more t h a n 200,000 first services, owned 4 6 % of the bulls, a n d i n s e m i n a t e d 6 9 % o f the cows. I t is obvious t h a t the genetic i m p a c t o f the large studs on the i n d u s t r y is g r e a t l y out of p r o p o r tion to the n u m b e r of such studs. F u r t h e r m o r e , as shown by the n u m b e r of cows i n s e m i n a t e d p e r bull, the efficiency in utilization of bulls is m u c h g r e a t e r in the large studs t h a n in the smaller ones. These c h a r a c t e r i s t i c s a r e extremely imp o r t a n t to the c a p a b i l i t y o f c a m T i n g on sire selection a n d testing, as described b y others in this symposium.
TABLE 1 Characteristics of A.I. organizations stratified by number of cows inseminated during 1962 (2)
No. cows inseminated Less than 100,000 100,000 but less than 200,000 200,000 or more
No. bulls total
Per cent of all bulls
Per cent of all cows inseminated
Cows inseminated per bull
60
858
33
15
1,322
20 20
545 1,156
21 46
16 69
2,317 4,629
No. studs
Per cent of all studs
31 10 10