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AI bull evaluation standards for dairy and dual purpose breeds
Livestock Production Science, 4 (1977) 115--128
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© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
AI BULL EVALUATION BREEDS
STANDARDS
FOR DAIRY AND DUAL PURPOSE
C. G A I L L A R D ~ (Reporter), J. DOMMERHOLT 2, E. FIMLAND 3, L. GJq)L-CHRISTENSEN J. L E D E R E R s, A.E. McCLINTOCK 6, J.C. MOCQUOT 7 and J. PHILIPSSON ~
Federation Suisse pour l'Insgmination Artificielle, Zollikofen (Switzerland) 2 Research Institute for Animal Husbandry "Sehoonoord", Zeist (The Netherlands) 3 Institute o f Animal Breeding and Genetics, Agricultural College o f Norway, ~ s (Norway) "National Institute for Animal Science, Copenhagen (Denmark) 5 Rechenzentrum zur Forderung der Landwirtschaft in Niedersachsen, Verden (Federal Republic o f Germany) 6 Milk Marketing Board, Thames Ditton, Surrey (Great Britain) 7 Institut Nationale de Recherche Agronomique, Dgpartement de Gdndtique Animale, Jouy-en-Josas (France) 8 Institute o f Animal Breeding and Genetics, Agricultural College o f Sweden, Uppsala (Sweden) (Received 21 February 1977)
ABSTRACT Gaillard, C., Dommerholt, J., Fimland, E., Gj61-Christensen, L., Lederer, J., McClintock, A.E., Mocquot, J.C. and Philipsson, J., 1977. AI bull evaluation standards for dairy and dual purpose breeds. Livest. Prod. Sci., 4: 115- -128. The purpose of this report is to recommend a code of practice to be followed by AI organisations and sire evaluation centres. The genetic merit of AI sires should be expressed as Breeding Values (BV) or as Relative Breeding Values (RBV). This value should be calculated for all traits which are considered for sire selection. The methods of estimation of the BV are discussed and it is suggested that where possible, methods based on the solution of properly constructed simultaneous equations (e.g. BLUP) should be used. For these new methods, a clearly defined reference base is required. It is recommended that where possible, this should be the average BV of the latest batch of bulls completing progeny test. If a fixed base is used, the average merit of bulls completing tests each year should be available. Besides good evaluation procedures and correction factors it is most important to ensure random use of the young bulls in many herds when they are doing their test inseminations in order to get unbiased progeny test figures. Only reliable figures should be published: the minimum requirements are suggested. A list of economically important traits is discussed. The traits are grouped under three headings: production traits, reproduction traits and management traits. Possible systematic environmental factors which have to be considered when estimating Breeding Values are listed in Appendix 1. The calculation of a selection index is recommended for use as a guide for proven bulls. The index can only be used in areas where the applied economic factors are appropriate, and so it is important to publish BV's for each trait separately.
116 It is important that all test results should also be published in official bulletins. It is suggested, however, that the BV of important traits should not be published if the repeatability (r 2 ) is less than 65%; for less important traits the repeatability of the estimated BV should be at least 35%. A scheme is suggested as to how the proofs can be presented. For international semen exchange the Relative Breeding Value is the recommended unit of evaluation. This value has the advantages that it is fairly independent of the mean levels and unit of measurement, and it is similar for all traits. A list of additional information which should be available is provided. Some important items are mentioned that should be taken into consideration when trials are planned, to compare different populations.
INTRODUCTION M o s t E u r o p e a n c a t t l e are b r e d b y artificial i n s e m i n a t i o n . T h e m a i n f a c t o r which determines the quality of the European cattle population for the future is t h e r e f o r e t h e m e r i t o f t h e bulls in AI. T h e s e bulls are b r e d a n d t e s t e d a n d s e l e c t e d in a g r e a t v a r i e t y o f w a y s b y m a n y o r g a n i s a t i o n s in d i f f e r e n t c o u n t r i e s . M o s t o f t h e s e s e l e c t i o n s c h e m e s h a v e n o w r e a c h e d t h e stage w h e r e it is w o r t h d e v e l o p i n g r e c o m m e n d e d s t a n d a r d s b y w h i c h t h e y can b e j u d g e d a n d c o m pared. T h e p u r p o s e o f this r e p o r t is t o r e c o m m e n d a c o d e o f p r a c t i c e t o be foll o w e d b y AI o r g a n i s a t i o n s a n d sire e v a l u a t i o n centres. I t is h o p e d t h a t t h e s e r e c o m m e n d a t i o n s will guide a n y decisions o n c h a n g e s o f existing t e s t i n g m e t h o d s or o n t h e i n t r o d u c t i o n o f n e w t e s t i n g p r o c e d u r e s . P r o b l e m s assoc i a t e d w i t h c o m p a r i n g bulls t e s t e d o n d i f f e r e n t p o p u l a t i o n s are c o n s i d e r e d briefly. A s u r v e y o f 16 o r g a n i s a t i o n s in n i n e E u r o p e a n c o u n t r i e s was a n a l y s e d . T h e results w e r e p r e s e n t e d t o t h e E.A.A.P. m e e t i n g in Ziirich in 1 9 7 6 . A s u r v e y o f m e t h o d s u s e d in 21 c o u n t r i e s was p r e s e n t e d b y t h e I n t e r n a t i o n a l D a i r y F e d e r a t i o n in Q u e b e c in 1976. T h e m a i n c o n c l u s i o n s w h i c h m a y be d r a w n f r o m t h e s e t w o surveys are as follows: (a) T h e q u a n t i t y o f i n f o r m a t i o n p r o v i d e d varies c o n s i d e r a b l y f r o m o n e organisation to another. (b) I t is n o t i c e a b l e t h a t , e x c e p t f o r l a c t a t i o n y i e l d i n f o r m a t i o n , t h e results are u s u a l l y e x p r e s s e d as averages r a t h e r t h a n as e s t i m a t e d G e n e t i c Merit. (c) A c o n s i d e r a b l e n u m b e r o f o r g a n i s a t i o n s are in t h e p r o c e s s o f i n t r o d u c i n g n e w m e t h o d s o f sire e v a l u a t i o n , such as B L U P , etc. EXPRESSION AND CALCULATION OF GENETIC MERIT
Expression T h e genetic m e r i t o f a bull can b e e x p r e s s e d in t h e f o l l o w i n g w a y s : (a)
B r e e d i n g V a l u e (BV). BV is d e f i n e d as t h e s u m o f t h e additive e f f e c t o f t h e bull's genes (additive genetic m e r i t ) .
117 (b)
Estimated Transmitting Ability (ETA) or Predicted Difference (PD). These values are defined as the genetic superiority of the progeny and are equal t o half of the BV. (c) Relative Breeding Value (RBV). RBV is the BV expressed as a percentage of the mean of the trait in a given year. This mean should be the same over a long period of time for the sake of retaining the linearity of the estimates. Examples. Let the BV of a bull be 500 kg milk above the average of the latest batch of bulls. The bull's BV = +500 kg and the average of the latest batch of bulls is 0. The RBV can then be expressed as: 100 RBV = 1 0 0 + 5 0 0 - 5 0 0 0 = 110% where 5000 kg is the mean for the breed. It is recommended t h a t the genetic merit should be defined as the breeding value (BV) or the relative breeding value (RBV) of a bull. If RBV is used, values above 100 should be "desirable".
Prediction of the breeding value It cannot be emphasised too much that the random use of the y o u n g bulls when their test inseminations are done is of great importance. Even the most sophisticated statistical techniques cannot completely correct the possible biases caused by a non-random use of the y o u n g bulls. Therefore AI organisations must ensure t h a t the test inseminations are done in a sensible way, i.e. not exclusively in high producing herds or only in one region, but in a random sample of milk recorded herds in different areas of the country. In order to avoid a non-random use within the herds, it is preferable to give the information in a way which minimises a discrimination between the y o u n g bulls. In order to estimate the breeding value, it is necessary to describe the structure of the data by an appropriate model which may differ from one population to another. Some known systematic environmental effects can be removed by using adjustment factors obtained from the population considered (e.g. age at calving). The remaining ones should be eliminated by the procedure used for evaluating the sires (e.g. herd). In m a n y cases the genetic structure has been changed due to efficient breeding schemes. These structural changes appear as genetic trend in the breeding population and different means of sub-population of daughters. In order to remove these effects a more sophisticated procedure for sire evaluation is needed (best linear unbiased prediction m e t h o d or similar method). The advantages of best linear unbiased prediction methods (BLUP) can be summarised as follows: (a) Takes into account the genetic trend of different batches of sires. (b) It is possible to eliminate most of the effects of differential selection of mates by taking into account the breeding value of the maternal grandsire simultaneously.
118 (c)
Takes into account most of the genetic differences between herds (regions). (d) Removes more completely the major sources of environmental variation (such as herd--year). (e) The additive relationship among sires can be used for the purpose of reducing error of prediction. (f) Limits the requirement for randomisation of matings (see (b)). It is believed that the BLUP procedure has the best obtainable properties of the existing sire evaluation methods suggested. Future research should therefore be focused on development of realistic models that describe the actual structure of the population considered. By using BLUP procedures it is necessary to define a base to which all breeding values are related. There seem to be t w o main types of alternatives which may be stated as follows: (a) Fixed base. The base is here defined as the average breeding value of one particular batch of bulls. In this case the breeding value of every new batch of bulls improves in accordance with the genetic trend. Bulls of older generations remain nearly the same throughout time. There are computational advantages if the breeding values of bulls from older generations stay almost unchanged through time. The steady change of the breeding value of every new batch of bulls might, however, reduce the actual selection intensity. Genetic improvement should lead to more and more bulls with positive proofs which do n o t improve the present population. The level of the breeding value needed to improve the present population (updated population) must also be calculated for each year (and herd). In order to avoid this deficiency, the mean breeding values of the latest batch of bulls tested should be given. (b) Rolling base. The base is here defined as the average breeding value of the most recent batch of bulls completing progeny tests. This means that the breeding value of a sire will fall with time if there is genetic improvement even if there are no additional daughter records available. This has the computational consequences that the breeding values of previous batches of bulls are changed every year depending on the average genetic level of the latest batch of bulls. On the other hand, these figures can be used directly to predict the expected breeding value of any relatives. Thus the breeding value of a particular bull indicates his genetic merit in the present population. This t y p e of base would therefore encourage selection by both farmer and breeding organisations, and so the farmer's use of a rolling base is strongly recommended. Repeatability o f a breeding value and its standard error
It is well known that the reliability of the progeny test results is greater with an increase in the number of progeny. The standard error of the estimated breeding value may be calculated as follows:
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aBV ~ X/o2e/n *
(1)
where o 2e is the error variance of individual records which is n o t explained by the model or correction factors and n* is the n u m b e r of effective progeny which is defined as number of progeny corrected for contemporaries and n u m b e r of related progeny within herds (i.e. the diagonal element in the BLUP equations). Alternatively: °BY _~ x / ( 1 0 0 - r 2) og2 /100
(2)
where Og2 is the additive genetic variance in the population and r 2 is the percentage repeatability of the proof; r 2 may be calculated as follows: r 2 = 100 × [ n * / ( n * + ( 4 - h 2 ) / h 2 ) ]
(3)
h 2 is the heritability of the trait considered. It is realised t h a t grouping of bulls into stud/year cohorts has an effect on the repeatability, but the approximate formulae shown above should be adequate for most purposes. The repeatability value should be provided with each BV or RBV; it has the advantage of being on the same scale as h 2 and is independent of the unit of measurement. However, oBV may also be given in addition to r 2 . TRAITS TO BE CONSIDERED Traits t h a t are of economic importance for dairy or dual purpose cattle populations are listed below. These traits generally show a genetic variation between and within breeds which underlines the importance of testing bulls and publishing breeding values for these traits. However, the economic importance of the characters m a y vary between populations according to different p a y m e n t systems, level of expression and structure of farming. The traits will be grouped under the three headings; production traits, reproduction traits and management traits. As has been pointed out in the previous section, systematic environmental factors have to be considered when estimating breeding values. In Appendix 1 the more important environmental factors are listed for each separate trait. P r o d u c t i o n traits M i l k p r o d u c t i o n . According to different p a y m e n t systems, information is
needed for a m o u n t of milk as well as for milk composition. There are three possible sets of information, one of which should represent the m i n i m u m a m o u n t of information on a bull. The three sets are: -- milk yield, fat yield and protein yield -milk yield, fat per cent, protein per cent -- fat-corrected milk yield, fat per cent, protein per cent
120 The genetic merit should preferably be estimated from 305-day lactations of first calvers. If second and further lactations are included, appropriate estimation techniques should be applied in order to eliminate effects of culling. Records from cows culled during the first lactation should be included. Since milk production traits are likely to be the main basis for selection, it is r e c o m m e n d e d that optimal methods of calculation of BV for these traits (e.g. BLUP) should be used.
Beef production. In dual-purpose cattle populations beef production traits are of great economic value. Traits to be considered are -- daily weight gain -- carcase quality -- feed conversion These characters may either be measured on the bull himself in performance tests, or on his progeny. The performance tests should have a constant length and start at a fixed age. Special attention has to be paid to the comparison group; if this consists of many related animals the BLUP procedure including the relationship matrix is suggested for assessing breeding values. Daily weight gain and feed conversion may be measured accurately enough during a performance test while carcase quality will b e measured most accurately by using a progeny test. However, scanning techniques used for performance testing may give sufficient information on carcase quality for breeding purposes (Bech Andersen, 1975). Detailed information a b o u t procedures for performance and progeny testing including feeding regime, feed consumption etc, are given by Kr~usslich et al. (1974).
Reproduction traits Reproduction traits generally show low heritability b u t in spite o f this a big variation maY be noted b o t h between and within breeds. A high reproductive rate is of fundamental importance in breeding stock, and consequently results for these traits should be given for the bulls.
Male fertility. Usually male fertility is measured as non-return-rate within a certain number o f days after first insemination. This figure depends both on the semen quality {trait of the sire) and on the early abortion rate (trait of the foetus). Furthermore, some prior selection of semen is usual and so it is not correct to calculate a breeding value. However, as a guide to farmers, it is r e c o m m e n d e d that non-return-rate of bulls should be published.
Female fertility. This may be measured either as non-return rate or as number of inseminations per 'service period' (starting at the first insemination and ending a given number of days after the last insemination). According to Janson (1976) the latter measurement should be preferred. Data from maiden (nulliparous) heifers have the advantage of being non-selected and less influ'
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enced by environmental factors. Results from first calvers may also be used; the progeny tests can still be ready before the proofs for milk production are available.
Dystocia. Dystocia can be considered as a trait of either the calf or the dam. The former expresses the direct influence of the sire of the calf. The latter expresses the calving results of the daughters of the bull. As the genetic correlation between the direct and maternal characters is close to zero (Philipsson, 1976), information on the bulls should be given for both. Direct dystocia results should be published for all bulls, b u t daughter dystocia may be optional, depending on whether it is a serious problem in the population. The traits that should be measured are stillbirth rate and calving difficulty. Stillbirths should include calves born dead, those that die within 24 hours after birth and those delivered b y caesarian section. Calving difficulty is measured subjectively, usually in 3--4 classes. Despite the subjectivity, this m e t h o d of scoring generally has a higher heritability than stillbirth rate. If possible, results from b o t h traits should be given as these characters are only partly related. It is especially r e c o m m e n d e d that heifer calvings be considered because the genetic variability of these traits in cows is very low and poorly related to heifer results. Only single births after normal gestation periods (mean +3a) should be considered.
Management traits The c o m m o n feature for the traits given below is that they influence the a m o u n t of labour, survival rates and other production costs.
Ease of milking. The importance of this character depends very much on the milking system and the overall level of the population in question; this character has an o p t i m u m value. However, it is of sufficient general importance that production of test results for all widely used AI bulls should be regarded as a valuable requirement. For this proof, only a random sample of first lactation daughters should be considered. Different measures of ease of milking generally show large genetic variation. The most convenient ways of measuring milk flow rate or milking time may be used. Per cent milk in the fore udder has t o o small a genetic variation to be considered important. For this trait, extreme results may be mentioned under "remarks".
Type traits. The number of t y p e traits should be restricted to those that are relevant for management purposes. Those listed below all characterise b o d y size or ease of handling the cows. The characters can be divided into measurable or subjectively scored traits:
122 Measurable traits
Subjectively scored traits
Udder--floor distance Length of teats Placement o f front teats Height at withers Heart girth
Udder shape Udder attachment Teat shape Feet and legs (separately) Temperament
The subjectively scored traits should be classified into well defined descriptive codes based on illustrations or photographs of each code-class. A random sample of first lactation daughters only should be used. For calculations of breeding values, comparisons should preferably be made with rolling, regional breed averages, as measuring and scoring techniques may vary between areas and AI studs. Disease resistance. This is a new and growing field in relation to development of measuring techniques and assessing breeding values. Several of these traits are of great economic importance. Especially important to consider is resistance to mastitis, which is, to some extent, determined genetically, and which is n o w measured routinely in several countries. Selection index
When the n u m b e r of traits increases there is a need for weighting the information into an index according to the economic value of each trait. This index should be used as a guide for choice of proven bulls. The selection index should only be used within the area where the economic values are appropriate. Each local organisation decides which traits should be involved in the index and determines the economic values for the different traits' units. Indexes for AI bulls should be calculated on a "per insemination" basis. This will require inclusion of factors to allow for the differential expression of a bull's genotypes for different traits (McClintock and Cunningham, 1974). For some traits the economic evaluation is difficult. However, the bulls must be ranked before deciding which proven bulls should be used. A value given subjectively will be better than leaving the trait out. Some examples of indexes in use at present are shown in Table I. Miscellaneous
It is obvious that carriers of clearly defined genetic defects, such as chromosome aberrations, achondroplasia in Friesians, etc., should be mentioned if they are known. A system of surveillance to detect such carriers should be part of the routine of bull evaluation. Information on the genetic background for colour may be important in some populations, e.g. red factor in Friesians.
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TABLE I Selection indexes Netherlands
Norway
Sweden
Index expressed as breeding points
Index expressed as breeding score (milk units)
Index expressed in breeding value units for milk yield (M-tal)
Butterfat yield Protein yield Ease of milking Conformation traits: strength and balance -- development -- type -- mammary system legs musculature
Milk yield (FCM) Protein % Ease of milking Type: body and legs udder and teats Daily weight gain Fertility of bulls Fertility of daughters
Milk yield (FCM) Daily weight gain Fertility of daughters Stillbirth rate (sire of the calves) Stillbirth rate (daughters of the bull Ease of milking Udder shape and attachment Udder--floor distance Teat length Teat placement Extra teats Legs Temperament
-
-
-
-
-
-
PUBLICATION
OF RESULTS
Test results should be published in an official Journal or Bulletin for all bulls with sufficiently accurate results. Promotional catalogues will n o t normally contain bulls which have been culled. The minimum level of accuracy before a p r o o f is published should be decided by each organisation for TABLE II Number of effective progeny (n*) required to give a repeatability of 35% or 65% at different levels of heritability Heritability
Repeatability (35%)
Repeatability (65%)
2% 5% 10% 15% 20% 25% 30%
108 46 21 14 Ii 9 7
370 147 73 48 36 28 23
40% 50%
5 4
17 13
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each breed and trait. The following scheme of publication of the results is suggested as a guide. The m i n i m u m numbers of effective progeny records (n*) to achieve a repeatability of 35% or 65% are shown in Table II; formula (3) was used. For very important traits (e.g. milk and fat yields) the repeatability (r 2 ) should be at least 65%. The results can be expressed as follows: Year of evaluation
Number of progeny
Estimated genetic value (BV or RBV)
Repeatability or SE of BV
For less important traits (e.g. milking flow rate) the accuracy should be at least 35%. The results could be expressed as above or using the following more simplified method: Year of evaluation
Number of progeny
"Appreciation" of the estimated genetic value
The term "appreciation" is defined in Table III. It will be n o t e d that irrespective of the accuracy of the test or of the trait being expressed, there will be approximately the same percentages of bulls in each of the five classes. The appreciation could also be used for the more important traits but should in these cases be in addition to the RBV or BV and the standard error or repeatability of the proof. COMPARISONS BETWEEN POPULATIONS
It has been well recognised t h a t comparisons between populations, using average milk production for example, can be grossly misleading; management systems and climate vary from one area to another. Since semen sales between countries are likely to increase, it is necessary to establish the real differences between sires independent of their c o u n t r y of origin. In order to make good comparisons between sires from different populations for different traits, well planned experiments are needed. In all types of comparisons the following items should be taken into consideration: (a) nonrandom mating of sires and cows; (b) non-random choice of bulls used to represent a strain; and (c) special treatment which might be given to the daughters of famous bulls.
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TABLE III Definition of appreciation Appreciation
Definition
++
B V more than B V more than but less than B V plus or minus B V less than but more than BV less than
+
"average"
Approximate % of bulls in each class +2oBV +lOBv + 2aBV IaBV --lOBv --2aBV --2oBv
2.5 13.5 68.0 13.5
2.5
aBV is the standard deviation of the estimated breeding values of bulls that have been tested with a repeatability of at least 35%.
Availability o f accounts o f methods used when semen is exported (1)
Each country should have available an account of the m e t h o d of measuring traits and of calculating genetic values for bulls. This should include methods for correcting environmental factors. (2) The following population parameters should be available: mean and standard deviation of single observations for each trait, its heritability, and the standard deviation of the estimated BV's. In countries where the genetic merit is estimated using a fixed base, the mean of the latest batch of bulls should be given. (3) It is suggested that the Relative Breeding Value (in %) is adopted as the international unit of evaluation. This figure should be adjusted to the mean of the most recent batch of tested bulls. The base used to calculate the RBV should also be known. The main reasons for using this m e t h o d of expression are that it is: (i) independent of the mean levels (ii) independent of the unit of measurement (iii) similar for all traits. Although the traits in the different populations are expressed in the same manner, (RBV) comparison between populations cannot be done unless the populations are linked by means of c o m m o n breeding animals. If the linkage is not recent, the genetic trend in both populations has to be known also. ACKNOWLEDGEMENTS
The authors would like to thank Spermex, Federal Republic of Germany, and VEEPRO, The Netherlands, for their financial support.
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REFERENCES Bech Andersen, B., 1975. Recent experimental development in ultrasonic measurement of cattle. Livest. Prod. Sci., 2: 137--146. Janson, L., 1976. Effects in cattle of non-genetic factors and estimation of genetic parameters of female fertility. 27th Ann. Meeting E.A.A.P., Zurich, 10 pp., mimeographed. Kr~usslich, H., 1974. General recommendations on procedures for performance and progeny testing for beef characteristics. Livest. Prod. Sci., 1: 33--45. McClintock, A.E. and Cunningham, E.P., 1974. Selection in dual purpose cattle populations: defining the breeding objective. Anita. Prod., 18: 237--247. Philipsson, J., 1976. Studies on calving difficulty, stillbirth and associated factors in Swedish cattle breeds. III. Genetic parameters. Acta Agric. Scand., 26: 211--220. RI~SUMI~ Gaillard, C., Dommerholt, J., Fimland, E., Gj~bl-Christensen, L., Lederer, J., McClintock, A.E., Mocquot, J.C. et Philipsson, J., 1977. Directives pour l'~valuation des taureaux d'ins~mination des races laiti~res et ~ deux fins. Livest. Prod. Sci., 4 : 1 1 5 - - 1 2 8 (en anglais). Ce rapport a pour but de faire quelques recommandations aux organisations d'ins~mination et centres d'interpr~tation des r~sultats de testage des taureaux. La valeur h~r~ditaire des taureaux d'ins~mination devrait ~tre exprim~e c o m m e "valeur g~n~tique additive" ou "valeur g~n~tique additive relative". Cette valeur dolt ~tre calcul~e pour t o u s l e s caract~res qui sont pris en consideration dans la s~lection des taureaux. Les m~thodes d'estimation de la valeur g~n~tique sont discut~es et il est sugg~r~ d'utiliser si possible des m~thodes se basant sur la r~solution simultan~e d'~quations convenablement ~tablies (p. ex. BLUP). Pour ces m~thodes, une base de r~f~rence doit ~tre clairement d~finie. I1 est recommand~, quand cela est possible, d'utiliser la valeur g~n~tique moyenne du dernier groupe de taureaux dont le contr61e de descendance est termin~. Si l'on a recours ~ une base fixe, il faut -- lors de l'estimation de la valeur g~n~tique -- tenir compte du progr~s g~n~tic_ue. Outre l'utilisation de proc~d~s d'estimation et de facteurs de correction appropri~s, il est tr~s important d'assurer une r~partition au hasard, dans un grand hombre d'~tables, des inseminations de testage des jeunes taureaux mis a l'~preuve, afin d'obtenir des estim~es sur descendance non biais~es. Seules des valeurs sfires peuvent ~tre publi~es: les exigences minimales sont mentionn~es. Une liste des caract~res ~conomiques les plus importants est discut~e. Us sont divis~s en trois groupes: caract~res de production, caract~res de reproduction et caract~res li~s la conduite des animaux. Les facteurs syst~matiques de milieu, qui sont ~ prendre en consideration lors du calcul de la valeur g~n~tique, sont mentionn~s dans l'appendice 1. Le calcul d'un indice de s~lection est recommand~ pour guider le choix des taureaux test~s. Un tel indice peut seulement ~tre utilis~ darts les r~gions of~ les pond~rations ~conomiques appliqu~es sont appropri~es. Il est important que tous les r~sultats de testage soient publi4s dans des bulletins officials. Les valeurs g~n~tiques pour des caract~res importants ne devraient pas ~tre publi~es si leur precision (r 2 ) n'atteint pas 65% et, pour les caract~res moins importants, cette precision devrait atteindre au moins 35%. Une proposition est faite sur la mani~re de presenter les r~sultats. Pour l'~change de semence sur le plan international, il est recommand~ d'utiliser la valeur g~n~tique relative c o m m e unit~ d'estimation. Cette valeur a l'avantage d'etre ind~pendante du niveau moyen, de l'unit~ de mesure et elle est semblable pour t o u sl es caract~res. I1 est dress~ une liste des informations suppl~mentaires qui devraient ~galement ~tre fournies. On mentionne ~galement quelques points importants dont il faut tenir compte lors de la planification d'un essai ayant pour but de comparer diff~rentes populations.
127
KURZFASSUNG
Gaillard, C., Dommerholt, J., Fimland, E., Gj~bl-Christensen, L., Lederer, J., McClintock, A.E., Mocquot, J.C. und Philipsson, J., 1977. Richtlinien fiir die Zuchtwertsch~tzung yon KB-Bullen der Milch- und Zweinutzungsrassen. Livest. Prod. Sci., 4 : 1 1 5 - - 1 2 8 (in Englisch). Der Zweck dieses Berichtes ist,Richtlinien fiirdie Besamungsstationen und DatenAuswertungszentralen zu geben. Der genetische Wert yon KB-Bullen sollte als Zuchtwert oder als relativer Zuchtwert angegeben werden. Dieser Wert ist nach MSglichkeit fiiralle Merkmale zu ermitteln, die in der Bullenselektion zu beriicksichtigen sind. Methoden der Zuchtwertsch~tzung werden diskutiert. Es wird empfohlen Verfahren anzuwenden, die auf einer simultanen LSsung yon korrekt aufgestellten Gleichungen beruhen (z.B. BLUP-Verfahren). Fiir diese neuen Methoden muss die Bezugsbasis klar definiert werden. Es wird vorgeschlagen, den Mittelwert der Zuchtwerte des letzten Priifbullenjahrganges, der die Nachkommenpriifung beendet hat, als Bezugsbasis zu w~hlen. Wird eine fixe Basis benutzt, so muss der genetische Trend in der Zuchtwertsch~tzung mitberiicksichtigt werden. Neben guten Sch~/tzverfahren und Korrekturfaktoren ist es sehr wichtig, dass die Priifbullen bei ihrem Testeinsatz zuf~/lligund in vielen Betrieben eingesetzt werden, u m unverf~Ischte Nachzuchtergebnisse zu erhalten. Nur zuverl~ssige Resultate diirfen verSffentlicht werden, minimale Anforderungen werden angegeben. Eine Liste mit den wirtschaftlich wichtigen Merkmalen wird diskutiert. Sie sind in drei Gruppen eingeteilt;Leistungsmerkmale, Fortpflanzungsmerkmale und arbeitstechnische Merkmale. Im Anhang 1 werden mSgliche systematische Umwelteinfliisse angegeben, die bei der Zuchtwertsch~tzung beriicksichtigt werden sollten. Die Berechnung eines Selektionsindexes wird als Hilfsmittel fiirdie Auswahl yon geprtiften Bullen empfohlen. Der Index kann nut in Gebieten angewendet werden, fiirdie die wirtschaftlichen Faktoren zutreffend bestimmt wurden.
Es ist wichtig, dass alle Priifresultate in offiziellen Mitteilungsbl~ttern publiziert werden. Die Zuchtwerte der wichtigen Eigenschaften diirfen nicht publiziert werden, wenn die Zuverl~ssigkeit (r 2 ) kleiner als 65% ist. Bei weniger wichtigen Eigenschaften sollte fiir die Ver5ffentlichung die Zuverl~/ssigkeit mindestens 35% betragen. Es wird ein Schema vorgeschlagen, wie die Ergebnisse dargestellt werden kSnnen. Fiir den internationalen Samenaustausch wird der relative Zuchtwert als Bewertungsgrundlage empfohlen. Dieser Weft hat den Vorteil, dass er sowohl yore Niveau des Mittelwertes wie auch yon der Masseinheit unabh~ngig ist. Ferner ist er fiir alle Merkmale gleichwertig. Eine Liste mit zus~tzlichen Informationen, welche ebenfalls zur Verfiigung stehen sollten, ist angegeben. Einige wichtige Punkte, die bei der Planung yon Populationsvergleichsversuchen beriicksichtigt werden sollten, sind aufgefiihrt.
Management traits
Reproduction traits
Production traits
daily weight gain
Beef
Type traits
milk flow rate milking time measurable traits subjectively scored traits
stillbirth rate calving difficulty
Dystocia
Ease o f m i l k i n g
male fertility female fertility
Fertility
carcass quality feed conversion
milk yield fat, y i e l d or p e r c e n t protein, yield or per cent
Milk
F a c t o r s t o b e t a k e n i n t o c o n s i d e r a t i o n in b r e e d i n g v a l u e e s t i m a t i o n
APPENDIX 1
x x
x
x x x
Herd
x x
x x
x x x
Year/ season
x x
x x
x x x
Age
x x x
Open days
x x x x
Stage of lactation
x x x x
x x
x
x x x
Only first lactations
smilk yield tmilking equipment
sex of the calf
technician h e i f e r s a n d fLrstcalves
correction for weight
constant length of period
~part lactations ~ o f cull d a u g h t e r s jgenetic standard of contemporaries
In addition:
t~ o0
115
© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
AI BULL EVALUATION BREEDS
STANDARDS
FOR DAIRY AND DUAL PURPOSE
C. G A I L L A R D ~ (Reporter), J. DOMMERHOLT 2, E. FIMLAND 3, L. GJq)L-CHRISTENSEN J. L E D E R E R s, A.E. McCLINTOCK 6, J.C. MOCQUOT 7 and J. PHILIPSSON ~
Federation Suisse pour l'Insgmination Artificielle, Zollikofen (Switzerland) 2 Research Institute for Animal Husbandry "Sehoonoord", Zeist (The Netherlands) 3 Institute o f Animal Breeding and Genetics, Agricultural College o f Norway, ~ s (Norway) "National Institute for Animal Science, Copenhagen (Denmark) 5 Rechenzentrum zur Forderung der Landwirtschaft in Niedersachsen, Verden (Federal Republic o f Germany) 6 Milk Marketing Board, Thames Ditton, Surrey (Great Britain) 7 Institut Nationale de Recherche Agronomique, Dgpartement de Gdndtique Animale, Jouy-en-Josas (France) 8 Institute o f Animal Breeding and Genetics, Agricultural College o f Sweden, Uppsala (Sweden) (Received 21 February 1977)
ABSTRACT Gaillard, C., Dommerholt, J., Fimland, E., Gj61-Christensen, L., Lederer, J., McClintock, A.E., Mocquot, J.C. and Philipsson, J., 1977. AI bull evaluation standards for dairy and dual purpose breeds. Livest. Prod. Sci., 4: 115- -128. The purpose of this report is to recommend a code of practice to be followed by AI organisations and sire evaluation centres. The genetic merit of AI sires should be expressed as Breeding Values (BV) or as Relative Breeding Values (RBV). This value should be calculated for all traits which are considered for sire selection. The methods of estimation of the BV are discussed and it is suggested that where possible, methods based on the solution of properly constructed simultaneous equations (e.g. BLUP) should be used. For these new methods, a clearly defined reference base is required. It is recommended that where possible, this should be the average BV of the latest batch of bulls completing progeny test. If a fixed base is used, the average merit of bulls completing tests each year should be available. Besides good evaluation procedures and correction factors it is most important to ensure random use of the young bulls in many herds when they are doing their test inseminations in order to get unbiased progeny test figures. Only reliable figures should be published: the minimum requirements are suggested. A list of economically important traits is discussed. The traits are grouped under three headings: production traits, reproduction traits and management traits. Possible systematic environmental factors which have to be considered when estimating Breeding Values are listed in Appendix 1. The calculation of a selection index is recommended for use as a guide for proven bulls. The index can only be used in areas where the applied economic factors are appropriate, and so it is important to publish BV's for each trait separately.
116 It is important that all test results should also be published in official bulletins. It is suggested, however, that the BV of important traits should not be published if the repeatability (r 2 ) is less than 65%; for less important traits the repeatability of the estimated BV should be at least 35%. A scheme is suggested as to how the proofs can be presented. For international semen exchange the Relative Breeding Value is the recommended unit of evaluation. This value has the advantages that it is fairly independent of the mean levels and unit of measurement, and it is similar for all traits. A list of additional information which should be available is provided. Some important items are mentioned that should be taken into consideration when trials are planned, to compare different populations.
INTRODUCTION M o s t E u r o p e a n c a t t l e are b r e d b y artificial i n s e m i n a t i o n . T h e m a i n f a c t o r which determines the quality of the European cattle population for the future is t h e r e f o r e t h e m e r i t o f t h e bulls in AI. T h e s e bulls are b r e d a n d t e s t e d a n d s e l e c t e d in a g r e a t v a r i e t y o f w a y s b y m a n y o r g a n i s a t i o n s in d i f f e r e n t c o u n t r i e s . M o s t o f t h e s e s e l e c t i o n s c h e m e s h a v e n o w r e a c h e d t h e stage w h e r e it is w o r t h d e v e l o p i n g r e c o m m e n d e d s t a n d a r d s b y w h i c h t h e y can b e j u d g e d a n d c o m pared. T h e p u r p o s e o f this r e p o r t is t o r e c o m m e n d a c o d e o f p r a c t i c e t o be foll o w e d b y AI o r g a n i s a t i o n s a n d sire e v a l u a t i o n centres. I t is h o p e d t h a t t h e s e r e c o m m e n d a t i o n s will guide a n y decisions o n c h a n g e s o f existing t e s t i n g m e t h o d s or o n t h e i n t r o d u c t i o n o f n e w t e s t i n g p r o c e d u r e s . P r o b l e m s assoc i a t e d w i t h c o m p a r i n g bulls t e s t e d o n d i f f e r e n t p o p u l a t i o n s are c o n s i d e r e d briefly. A s u r v e y o f 16 o r g a n i s a t i o n s in n i n e E u r o p e a n c o u n t r i e s was a n a l y s e d . T h e results w e r e p r e s e n t e d t o t h e E.A.A.P. m e e t i n g in Ziirich in 1 9 7 6 . A s u r v e y o f m e t h o d s u s e d in 21 c o u n t r i e s was p r e s e n t e d b y t h e I n t e r n a t i o n a l D a i r y F e d e r a t i o n in Q u e b e c in 1976. T h e m a i n c o n c l u s i o n s w h i c h m a y be d r a w n f r o m t h e s e t w o surveys are as follows: (a) T h e q u a n t i t y o f i n f o r m a t i o n p r o v i d e d varies c o n s i d e r a b l y f r o m o n e organisation to another. (b) I t is n o t i c e a b l e t h a t , e x c e p t f o r l a c t a t i o n y i e l d i n f o r m a t i o n , t h e results are u s u a l l y e x p r e s s e d as averages r a t h e r t h a n as e s t i m a t e d G e n e t i c Merit. (c) A c o n s i d e r a b l e n u m b e r o f o r g a n i s a t i o n s are in t h e p r o c e s s o f i n t r o d u c i n g n e w m e t h o d s o f sire e v a l u a t i o n , such as B L U P , etc. EXPRESSION AND CALCULATION OF GENETIC MERIT
Expression T h e genetic m e r i t o f a bull can b e e x p r e s s e d in t h e f o l l o w i n g w a y s : (a)
B r e e d i n g V a l u e (BV). BV is d e f i n e d as t h e s u m o f t h e additive e f f e c t o f t h e bull's genes (additive genetic m e r i t ) .
117 (b)
Estimated Transmitting Ability (ETA) or Predicted Difference (PD). These values are defined as the genetic superiority of the progeny and are equal t o half of the BV. (c) Relative Breeding Value (RBV). RBV is the BV expressed as a percentage of the mean of the trait in a given year. This mean should be the same over a long period of time for the sake of retaining the linearity of the estimates. Examples. Let the BV of a bull be 500 kg milk above the average of the latest batch of bulls. The bull's BV = +500 kg and the average of the latest batch of bulls is 0. The RBV can then be expressed as: 100 RBV = 1 0 0 + 5 0 0 - 5 0 0 0 = 110% where 5000 kg is the mean for the breed. It is recommended t h a t the genetic merit should be defined as the breeding value (BV) or the relative breeding value (RBV) of a bull. If RBV is used, values above 100 should be "desirable".
Prediction of the breeding value It cannot be emphasised too much that the random use of the y o u n g bulls when their test inseminations are done is of great importance. Even the most sophisticated statistical techniques cannot completely correct the possible biases caused by a non-random use of the y o u n g bulls. Therefore AI organisations must ensure t h a t the test inseminations are done in a sensible way, i.e. not exclusively in high producing herds or only in one region, but in a random sample of milk recorded herds in different areas of the country. In order to avoid a non-random use within the herds, it is preferable to give the information in a way which minimises a discrimination between the y o u n g bulls. In order to estimate the breeding value, it is necessary to describe the structure of the data by an appropriate model which may differ from one population to another. Some known systematic environmental effects can be removed by using adjustment factors obtained from the population considered (e.g. age at calving). The remaining ones should be eliminated by the procedure used for evaluating the sires (e.g. herd). In m a n y cases the genetic structure has been changed due to efficient breeding schemes. These structural changes appear as genetic trend in the breeding population and different means of sub-population of daughters. In order to remove these effects a more sophisticated procedure for sire evaluation is needed (best linear unbiased prediction m e t h o d or similar method). The advantages of best linear unbiased prediction methods (BLUP) can be summarised as follows: (a) Takes into account the genetic trend of different batches of sires. (b) It is possible to eliminate most of the effects of differential selection of mates by taking into account the breeding value of the maternal grandsire simultaneously.
118 (c)
Takes into account most of the genetic differences between herds (regions). (d) Removes more completely the major sources of environmental variation (such as herd--year). (e) The additive relationship among sires can be used for the purpose of reducing error of prediction. (f) Limits the requirement for randomisation of matings (see (b)). It is believed that the BLUP procedure has the best obtainable properties of the existing sire evaluation methods suggested. Future research should therefore be focused on development of realistic models that describe the actual structure of the population considered. By using BLUP procedures it is necessary to define a base to which all breeding values are related. There seem to be t w o main types of alternatives which may be stated as follows: (a) Fixed base. The base is here defined as the average breeding value of one particular batch of bulls. In this case the breeding value of every new batch of bulls improves in accordance with the genetic trend. Bulls of older generations remain nearly the same throughout time. There are computational advantages if the breeding values of bulls from older generations stay almost unchanged through time. The steady change of the breeding value of every new batch of bulls might, however, reduce the actual selection intensity. Genetic improvement should lead to more and more bulls with positive proofs which do n o t improve the present population. The level of the breeding value needed to improve the present population (updated population) must also be calculated for each year (and herd). In order to avoid this deficiency, the mean breeding values of the latest batch of bulls tested should be given. (b) Rolling base. The base is here defined as the average breeding value of the most recent batch of bulls completing progeny tests. This means that the breeding value of a sire will fall with time if there is genetic improvement even if there are no additional daughter records available. This has the computational consequences that the breeding values of previous batches of bulls are changed every year depending on the average genetic level of the latest batch of bulls. On the other hand, these figures can be used directly to predict the expected breeding value of any relatives. Thus the breeding value of a particular bull indicates his genetic merit in the present population. This t y p e of base would therefore encourage selection by both farmer and breeding organisations, and so the farmer's use of a rolling base is strongly recommended. Repeatability o f a breeding value and its standard error
It is well known that the reliability of the progeny test results is greater with an increase in the number of progeny. The standard error of the estimated breeding value may be calculated as follows:
119
aBV ~ X/o2e/n *
(1)
where o 2e is the error variance of individual records which is n o t explained by the model or correction factors and n* is the n u m b e r of effective progeny which is defined as number of progeny corrected for contemporaries and n u m b e r of related progeny within herds (i.e. the diagonal element in the BLUP equations). Alternatively: °BY _~ x / ( 1 0 0 - r 2) og2 /100
(2)
where Og2 is the additive genetic variance in the population and r 2 is the percentage repeatability of the proof; r 2 may be calculated as follows: r 2 = 100 × [ n * / ( n * + ( 4 - h 2 ) / h 2 ) ]
(3)
h 2 is the heritability of the trait considered. It is realised t h a t grouping of bulls into stud/year cohorts has an effect on the repeatability, but the approximate formulae shown above should be adequate for most purposes. The repeatability value should be provided with each BV or RBV; it has the advantage of being on the same scale as h 2 and is independent of the unit of measurement. However, oBV may also be given in addition to r 2 . TRAITS TO BE CONSIDERED Traits t h a t are of economic importance for dairy or dual purpose cattle populations are listed below. These traits generally show a genetic variation between and within breeds which underlines the importance of testing bulls and publishing breeding values for these traits. However, the economic importance of the characters m a y vary between populations according to different p a y m e n t systems, level of expression and structure of farming. The traits will be grouped under the three headings; production traits, reproduction traits and management traits. As has been pointed out in the previous section, systematic environmental factors have to be considered when estimating breeding values. In Appendix 1 the more important environmental factors are listed for each separate trait. P r o d u c t i o n traits M i l k p r o d u c t i o n . According to different p a y m e n t systems, information is
needed for a m o u n t of milk as well as for milk composition. There are three possible sets of information, one of which should represent the m i n i m u m a m o u n t of information on a bull. The three sets are: -- milk yield, fat yield and protein yield -milk yield, fat per cent, protein per cent -- fat-corrected milk yield, fat per cent, protein per cent
120 The genetic merit should preferably be estimated from 305-day lactations of first calvers. If second and further lactations are included, appropriate estimation techniques should be applied in order to eliminate effects of culling. Records from cows culled during the first lactation should be included. Since milk production traits are likely to be the main basis for selection, it is r e c o m m e n d e d that optimal methods of calculation of BV for these traits (e.g. BLUP) should be used.
Beef production. In dual-purpose cattle populations beef production traits are of great economic value. Traits to be considered are -- daily weight gain -- carcase quality -- feed conversion These characters may either be measured on the bull himself in performance tests, or on his progeny. The performance tests should have a constant length and start at a fixed age. Special attention has to be paid to the comparison group; if this consists of many related animals the BLUP procedure including the relationship matrix is suggested for assessing breeding values. Daily weight gain and feed conversion may be measured accurately enough during a performance test while carcase quality will b e measured most accurately by using a progeny test. However, scanning techniques used for performance testing may give sufficient information on carcase quality for breeding purposes (Bech Andersen, 1975). Detailed information a b o u t procedures for performance and progeny testing including feeding regime, feed consumption etc, are given by Kr~usslich et al. (1974).
Reproduction traits Reproduction traits generally show low heritability b u t in spite o f this a big variation maY be noted b o t h between and within breeds. A high reproductive rate is of fundamental importance in breeding stock, and consequently results for these traits should be given for the bulls.
Male fertility. Usually male fertility is measured as non-return-rate within a certain number o f days after first insemination. This figure depends both on the semen quality {trait of the sire) and on the early abortion rate (trait of the foetus). Furthermore, some prior selection of semen is usual and so it is not correct to calculate a breeding value. However, as a guide to farmers, it is r e c o m m e n d e d that non-return-rate of bulls should be published.
Female fertility. This may be measured either as non-return rate or as number of inseminations per 'service period' (starting at the first insemination and ending a given number of days after the last insemination). According to Janson (1976) the latter measurement should be preferred. Data from maiden (nulliparous) heifers have the advantage of being non-selected and less influ'
121
enced by environmental factors. Results from first calvers may also be used; the progeny tests can still be ready before the proofs for milk production are available.
Dystocia. Dystocia can be considered as a trait of either the calf or the dam. The former expresses the direct influence of the sire of the calf. The latter expresses the calving results of the daughters of the bull. As the genetic correlation between the direct and maternal characters is close to zero (Philipsson, 1976), information on the bulls should be given for both. Direct dystocia results should be published for all bulls, b u t daughter dystocia may be optional, depending on whether it is a serious problem in the population. The traits that should be measured are stillbirth rate and calving difficulty. Stillbirths should include calves born dead, those that die within 24 hours after birth and those delivered b y caesarian section. Calving difficulty is measured subjectively, usually in 3--4 classes. Despite the subjectivity, this m e t h o d of scoring generally has a higher heritability than stillbirth rate. If possible, results from b o t h traits should be given as these characters are only partly related. It is especially r e c o m m e n d e d that heifer calvings be considered because the genetic variability of these traits in cows is very low and poorly related to heifer results. Only single births after normal gestation periods (mean +3a) should be considered.
Management traits The c o m m o n feature for the traits given below is that they influence the a m o u n t of labour, survival rates and other production costs.
Ease of milking. The importance of this character depends very much on the milking system and the overall level of the population in question; this character has an o p t i m u m value. However, it is of sufficient general importance that production of test results for all widely used AI bulls should be regarded as a valuable requirement. For this proof, only a random sample of first lactation daughters should be considered. Different measures of ease of milking generally show large genetic variation. The most convenient ways of measuring milk flow rate or milking time may be used. Per cent milk in the fore udder has t o o small a genetic variation to be considered important. For this trait, extreme results may be mentioned under "remarks".
Type traits. The number of t y p e traits should be restricted to those that are relevant for management purposes. Those listed below all characterise b o d y size or ease of handling the cows. The characters can be divided into measurable or subjectively scored traits:
122 Measurable traits
Subjectively scored traits
Udder--floor distance Length of teats Placement o f front teats Height at withers Heart girth
Udder shape Udder attachment Teat shape Feet and legs (separately) Temperament
The subjectively scored traits should be classified into well defined descriptive codes based on illustrations or photographs of each code-class. A random sample of first lactation daughters only should be used. For calculations of breeding values, comparisons should preferably be made with rolling, regional breed averages, as measuring and scoring techniques may vary between areas and AI studs. Disease resistance. This is a new and growing field in relation to development of measuring techniques and assessing breeding values. Several of these traits are of great economic importance. Especially important to consider is resistance to mastitis, which is, to some extent, determined genetically, and which is n o w measured routinely in several countries. Selection index
When the n u m b e r of traits increases there is a need for weighting the information into an index according to the economic value of each trait. This index should be used as a guide for choice of proven bulls. The selection index should only be used within the area where the economic values are appropriate. Each local organisation decides which traits should be involved in the index and determines the economic values for the different traits' units. Indexes for AI bulls should be calculated on a "per insemination" basis. This will require inclusion of factors to allow for the differential expression of a bull's genotypes for different traits (McClintock and Cunningham, 1974). For some traits the economic evaluation is difficult. However, the bulls must be ranked before deciding which proven bulls should be used. A value given subjectively will be better than leaving the trait out. Some examples of indexes in use at present are shown in Table I. Miscellaneous
It is obvious that carriers of clearly defined genetic defects, such as chromosome aberrations, achondroplasia in Friesians, etc., should be mentioned if they are known. A system of surveillance to detect such carriers should be part of the routine of bull evaluation. Information on the genetic background for colour may be important in some populations, e.g. red factor in Friesians.
123
TABLE I Selection indexes Netherlands
Norway
Sweden
Index expressed as breeding points
Index expressed as breeding score (milk units)
Index expressed in breeding value units for milk yield (M-tal)
Butterfat yield Protein yield Ease of milking Conformation traits: strength and balance -- development -- type -- mammary system legs musculature
Milk yield (FCM) Protein % Ease of milking Type: body and legs udder and teats Daily weight gain Fertility of bulls Fertility of daughters
Milk yield (FCM) Daily weight gain Fertility of daughters Stillbirth rate (sire of the calves) Stillbirth rate (daughters of the bull Ease of milking Udder shape and attachment Udder--floor distance Teat length Teat placement Extra teats Legs Temperament
-
-
-
-
-
-
PUBLICATION
OF RESULTS
Test results should be published in an official Journal or Bulletin for all bulls with sufficiently accurate results. Promotional catalogues will n o t normally contain bulls which have been culled. The minimum level of accuracy before a p r o o f is published should be decided by each organisation for TABLE II Number of effective progeny (n*) required to give a repeatability of 35% or 65% at different levels of heritability Heritability
Repeatability (35%)
Repeatability (65%)
2% 5% 10% 15% 20% 25% 30%
108 46 21 14 Ii 9 7
370 147 73 48 36 28 23
40% 50%
5 4
17 13
124
each breed and trait. The following scheme of publication of the results is suggested as a guide. The m i n i m u m numbers of effective progeny records (n*) to achieve a repeatability of 35% or 65% are shown in Table II; formula (3) was used. For very important traits (e.g. milk and fat yields) the repeatability (r 2 ) should be at least 65%. The results can be expressed as follows: Year of evaluation
Number of progeny
Estimated genetic value (BV or RBV)
Repeatability or SE of BV
For less important traits (e.g. milking flow rate) the accuracy should be at least 35%. The results could be expressed as above or using the following more simplified method: Year of evaluation
Number of progeny
"Appreciation" of the estimated genetic value
The term "appreciation" is defined in Table III. It will be n o t e d that irrespective of the accuracy of the test or of the trait being expressed, there will be approximately the same percentages of bulls in each of the five classes. The appreciation could also be used for the more important traits but should in these cases be in addition to the RBV or BV and the standard error or repeatability of the proof. COMPARISONS BETWEEN POPULATIONS
It has been well recognised t h a t comparisons between populations, using average milk production for example, can be grossly misleading; management systems and climate vary from one area to another. Since semen sales between countries are likely to increase, it is necessary to establish the real differences between sires independent of their c o u n t r y of origin. In order to make good comparisons between sires from different populations for different traits, well planned experiments are needed. In all types of comparisons the following items should be taken into consideration: (a) nonrandom mating of sires and cows; (b) non-random choice of bulls used to represent a strain; and (c) special treatment which might be given to the daughters of famous bulls.
125
TABLE III Definition of appreciation Appreciation
Definition
++
B V more than B V more than but less than B V plus or minus B V less than but more than BV less than
+
"average"
Approximate % of bulls in each class +2oBV +lOBv + 2aBV IaBV --lOBv --2aBV --2oBv
2.5 13.5 68.0 13.5
2.5
aBV is the standard deviation of the estimated breeding values of bulls that have been tested with a repeatability of at least 35%.
Availability o f accounts o f methods used when semen is exported (1)
Each country should have available an account of the m e t h o d of measuring traits and of calculating genetic values for bulls. This should include methods for correcting environmental factors. (2) The following population parameters should be available: mean and standard deviation of single observations for each trait, its heritability, and the standard deviation of the estimated BV's. In countries where the genetic merit is estimated using a fixed base, the mean of the latest batch of bulls should be given. (3) It is suggested that the Relative Breeding Value (in %) is adopted as the international unit of evaluation. This figure should be adjusted to the mean of the most recent batch of tested bulls. The base used to calculate the RBV should also be known. The main reasons for using this m e t h o d of expression are that it is: (i) independent of the mean levels (ii) independent of the unit of measurement (iii) similar for all traits. Although the traits in the different populations are expressed in the same manner, (RBV) comparison between populations cannot be done unless the populations are linked by means of c o m m o n breeding animals. If the linkage is not recent, the genetic trend in both populations has to be known also. ACKNOWLEDGEMENTS
The authors would like to thank Spermex, Federal Republic of Germany, and VEEPRO, The Netherlands, for their financial support.
126
REFERENCES Bech Andersen, B., 1975. Recent experimental development in ultrasonic measurement of cattle. Livest. Prod. Sci., 2: 137--146. Janson, L., 1976. Effects in cattle of non-genetic factors and estimation of genetic parameters of female fertility. 27th Ann. Meeting E.A.A.P., Zurich, 10 pp., mimeographed. Kr~usslich, H., 1974. General recommendations on procedures for performance and progeny testing for beef characteristics. Livest. Prod. Sci., 1: 33--45. McClintock, A.E. and Cunningham, E.P., 1974. Selection in dual purpose cattle populations: defining the breeding objective. Anita. Prod., 18: 237--247. Philipsson, J., 1976. Studies on calving difficulty, stillbirth and associated factors in Swedish cattle breeds. III. Genetic parameters. Acta Agric. Scand., 26: 211--220. RI~SUMI~ Gaillard, C., Dommerholt, J., Fimland, E., Gj~bl-Christensen, L., Lederer, J., McClintock, A.E., Mocquot, J.C. et Philipsson, J., 1977. Directives pour l'~valuation des taureaux d'ins~mination des races laiti~res et ~ deux fins. Livest. Prod. Sci., 4 : 1 1 5 - - 1 2 8 (en anglais). Ce rapport a pour but de faire quelques recommandations aux organisations d'ins~mination et centres d'interpr~tation des r~sultats de testage des taureaux. La valeur h~r~ditaire des taureaux d'ins~mination devrait ~tre exprim~e c o m m e "valeur g~n~tique additive" ou "valeur g~n~tique additive relative". Cette valeur dolt ~tre calcul~e pour t o u s l e s caract~res qui sont pris en consideration dans la s~lection des taureaux. Les m~thodes d'estimation de la valeur g~n~tique sont discut~es et il est sugg~r~ d'utiliser si possible des m~thodes se basant sur la r~solution simultan~e d'~quations convenablement ~tablies (p. ex. BLUP). Pour ces m~thodes, une base de r~f~rence doit ~tre clairement d~finie. I1 est recommand~, quand cela est possible, d'utiliser la valeur g~n~tique moyenne du dernier groupe de taureaux dont le contr61e de descendance est termin~. Si l'on a recours ~ une base fixe, il faut -- lors de l'estimation de la valeur g~n~tique -- tenir compte du progr~s g~n~tic_ue. Outre l'utilisation de proc~d~s d'estimation et de facteurs de correction appropri~s, il est tr~s important d'assurer une r~partition au hasard, dans un grand hombre d'~tables, des inseminations de testage des jeunes taureaux mis a l'~preuve, afin d'obtenir des estim~es sur descendance non biais~es. Seules des valeurs sfires peuvent ~tre publi~es: les exigences minimales sont mentionn~es. Une liste des caract~res ~conomiques les plus importants est discut~e. Us sont divis~s en trois groupes: caract~res de production, caract~res de reproduction et caract~res li~s la conduite des animaux. Les facteurs syst~matiques de milieu, qui sont ~ prendre en consideration lors du calcul de la valeur g~n~tique, sont mentionn~s dans l'appendice 1. Le calcul d'un indice de s~lection est recommand~ pour guider le choix des taureaux test~s. Un tel indice peut seulement ~tre utilis~ darts les r~gions of~ les pond~rations ~conomiques appliqu~es sont appropri~es. Il est important que tous les r~sultats de testage soient publi4s dans des bulletins officials. Les valeurs g~n~tiques pour des caract~res importants ne devraient pas ~tre publi~es si leur precision (r 2 ) n'atteint pas 65% et, pour les caract~res moins importants, cette precision devrait atteindre au moins 35%. Une proposition est faite sur la mani~re de presenter les r~sultats. Pour l'~change de semence sur le plan international, il est recommand~ d'utiliser la valeur g~n~tique relative c o m m e unit~ d'estimation. Cette valeur a l'avantage d'etre ind~pendante du niveau moyen, de l'unit~ de mesure et elle est semblable pour t o u sl es caract~res. I1 est dress~ une liste des informations suppl~mentaires qui devraient ~galement ~tre fournies. On mentionne ~galement quelques points importants dont il faut tenir compte lors de la planification d'un essai ayant pour but de comparer diff~rentes populations.
127
KURZFASSUNG
Gaillard, C., Dommerholt, J., Fimland, E., Gj~bl-Christensen, L., Lederer, J., McClintock, A.E., Mocquot, J.C. und Philipsson, J., 1977. Richtlinien fiir die Zuchtwertsch~tzung yon KB-Bullen der Milch- und Zweinutzungsrassen. Livest. Prod. Sci., 4 : 1 1 5 - - 1 2 8 (in Englisch). Der Zweck dieses Berichtes ist,Richtlinien fiirdie Besamungsstationen und DatenAuswertungszentralen zu geben. Der genetische Wert yon KB-Bullen sollte als Zuchtwert oder als relativer Zuchtwert angegeben werden. Dieser Wert ist nach MSglichkeit fiiralle Merkmale zu ermitteln, die in der Bullenselektion zu beriicksichtigen sind. Methoden der Zuchtwertsch~tzung werden diskutiert. Es wird empfohlen Verfahren anzuwenden, die auf einer simultanen LSsung yon korrekt aufgestellten Gleichungen beruhen (z.B. BLUP-Verfahren). Fiir diese neuen Methoden muss die Bezugsbasis klar definiert werden. Es wird vorgeschlagen, den Mittelwert der Zuchtwerte des letzten Priifbullenjahrganges, der die Nachkommenpriifung beendet hat, als Bezugsbasis zu w~hlen. Wird eine fixe Basis benutzt, so muss der genetische Trend in der Zuchtwertsch~tzung mitberiicksichtigt werden. Neben guten Sch~/tzverfahren und Korrekturfaktoren ist es sehr wichtig, dass die Priifbullen bei ihrem Testeinsatz zuf~/lligund in vielen Betrieben eingesetzt werden, u m unverf~Ischte Nachzuchtergebnisse zu erhalten. Nur zuverl~ssige Resultate diirfen verSffentlicht werden, minimale Anforderungen werden angegeben. Eine Liste mit den wirtschaftlich wichtigen Merkmalen wird diskutiert. Sie sind in drei Gruppen eingeteilt;Leistungsmerkmale, Fortpflanzungsmerkmale und arbeitstechnische Merkmale. Im Anhang 1 werden mSgliche systematische Umwelteinfliisse angegeben, die bei der Zuchtwertsch~tzung beriicksichtigt werden sollten. Die Berechnung eines Selektionsindexes wird als Hilfsmittel fiirdie Auswahl yon geprtiften Bullen empfohlen. Der Index kann nut in Gebieten angewendet werden, fiirdie die wirtschaftlichen Faktoren zutreffend bestimmt wurden.
Es ist wichtig, dass alle Priifresultate in offiziellen Mitteilungsbl~ttern publiziert werden. Die Zuchtwerte der wichtigen Eigenschaften diirfen nicht publiziert werden, wenn die Zuverl~ssigkeit (r 2 ) kleiner als 65% ist. Bei weniger wichtigen Eigenschaften sollte fiir die Ver5ffentlichung die Zuverl~/ssigkeit mindestens 35% betragen. Es wird ein Schema vorgeschlagen, wie die Ergebnisse dargestellt werden kSnnen. Fiir den internationalen Samenaustausch wird der relative Zuchtwert als Bewertungsgrundlage empfohlen. Dieser Weft hat den Vorteil, dass er sowohl yore Niveau des Mittelwertes wie auch yon der Masseinheit unabh~ngig ist. Ferner ist er fiir alle Merkmale gleichwertig. Eine Liste mit zus~tzlichen Informationen, welche ebenfalls zur Verfiigung stehen sollten, ist angegeben. Einige wichtige Punkte, die bei der Planung yon Populationsvergleichsversuchen beriicksichtigt werden sollten, sind aufgefiihrt.
Management traits
Reproduction traits
Production traits
daily weight gain
Beef
Type traits
milk flow rate milking time measurable traits subjectively scored traits
stillbirth rate calving difficulty
Dystocia
Ease o f m i l k i n g
male fertility female fertility
Fertility
carcass quality feed conversion
milk yield fat, y i e l d or p e r c e n t protein, yield or per cent
Milk
F a c t o r s t o b e t a k e n i n t o c o n s i d e r a t i o n in b r e e d i n g v a l u e e s t i m a t i o n
APPENDIX 1
x x
x
x x x
Herd
x x
x x
x x x
Year/ season
x x
x x
x x x
Age
x x x
Open days
x x x x
Stage of lactation
x x x x
x x
x
x x x
Only first lactations
smilk yield tmilking equipment
sex of the calf
technician h e i f e r s a n d fLrstcalves
correction for weight
constant length of period
~part lactations ~ o f cull d a u g h t e r s jgenetic standard of contemporaries
In addition:
t~ o0