Evaluation of Breeding Value of Bulls Used in Two Herds in India

E V A L U A T I O N OF B R E E D I N G V A L U E OF B U L L S U S E D IN T W O H E R D S I N I N D I A

D. SUNDARESAN, ~ M. GURNANI, A~D S. P. SIDItU National Dairy Research Institute, Karnal, India

ABSTRACT

Sire indices on milk production and maturity on 30 Tharparkar and 18 Sahiwal bulls used in the two respective herds were calculated by five methods: two involving daughter-dam comparisons, one with daughter's production only, and two using contemporary averages.

A sire index to be valuable is expected to be accurate. Accuracy was measured by repeatability of the test, i.e., whether a bull evaluated by a sample of daughters maintained a similar index or ranking when he was further evaluated by information from more daughters, thus approximating the magnitude of the correlation between the sire index and the true breeding value of the bull. The

fifth method used, U q--~-~ (D-C.A): k = 12 or 6. was found to be more

accurate in estimating the breeding value of a bull under Indian conditions.

In dairy cattle breeding, genetic gain from generation to generation is obtained by the culling of poor milk-producing cows from the herd and by the extensive use of bulls with transmitting capacity for high milk produe- tion. Since very few 'bulls are needed, compared to the female population, and if bulls of high transmitting capacity could he chosen with accuracy, there would be greater oppor- tunity for a higher intensity of selection. How- ever, an estimate of the milk-transmitting capacity of a bull can be obtained only from relevant information on relatives.

Robertson (8) discusses the problem of optimum number of sires to be tested. For optimum results he recommends an intensity of selection of one for every four tested sires. Robertson (7), in another paper, discusses still another complication of progeny testing. The rational use of progeny testing involves the continued building up of good genes in a unit into which new genes are introduced. This creates the main problem of balancing the use of existing proven sires and the neees- sity of testing new ones ±'or future use.

A scheme of progeny-testing for selection of herd sires was initiated recently at the National Dairy Research Institute (N.D.R.I.). The need for evaluating a few of the important methods of progeny testing with available data from the two herds, to compare their efficiency and also to rank bulls recently used for the purpose

Received for publication September 16, 1963.

Present address: Dean, Pos~Graduate Studies, Punjab Agricultural University, Ludhiana, India.

of choosing sons for future progeny tests, is apparent.

DATA

The data used belonged to the Tharparkar and Sahiwal herds of the Institute. In the Tharparker herd, the 30 bulls used during the period 1925-60 had five or more daughters complete a lactation at the N.D.R.I. in Karnal and in the Sahiwal herd; the 18 bulls used during the period 1945-60 had five or more daughters complete a lactation either in the Indian Agricultural Research Institute at New Delhi or at the Institute at Karnal. (The Sahiwal herd which used to be in the Indian Agricultural Research Institute in New Delhi was transferred to Karnal in 1951.) The production of each cow completing its first lactation was collected. For the investigation the first 305 days' production was taken as the lactation production. Those cows which gave milk for less than 100 days, or those which died or were sold in milk before completing 305 days' production, were removed from the investigation. Where cows gave milk for more than 100 but less than 305 days in a complete lactation the yield of this period was taken as 305 days' production. The age at first calving of every cow starting a first lactation was also collected. The records were grouped on their sire, for both first-lactation production and age at first calving.

Evaluation of sires' breeding values for milk production was planned, using only first-lactation production, since suitable age-correction factors are not available. Even if such factors

1498

B R E E D I N G VALUE OF B U L L S 1 4 9 9

could be designed, it is best to work with first- lactation records only, to avoid confounding selection effects on sire indices. Evaluation of the breeding value of sires for sexual maturity, as evidenced by age at first calving of the daughters, was also included in the investigation, because under our f'arm conditions age at first calving is not controlled by management practices. Heifers are invariably bred at first heat and there is considerable evidence that heritability for the character is high, though it is quite clear that environmental factors do cause serious differences in this characteristic, as evidenced by early maturity of well-fed young stock. For milk production information on the 30 'bulls with 5-60 daughters each in the Tharparkar herd and 18 bulls with 5-35 daughters in the Sahiwal herd was used. Simi- larly, for age at first calving information on these 30 Tharparkar bulls with 5-80 daughters each and on these 18 Sahiwal bulls with 5-38 daughters was used.

:MET:ttODS OF EVALUATIO:N

Hofmeyer (4) has given a historic review of the major indices designed and used. These can be classed into two major groups: first, those methods using information on the daughters and mates of bulls, and secondly, those methods using information on the daughters only. One of the methods used from the earliest days is the Equal Parent Index: I : 2 D - M (where I is the index, D is daughters' average production, and M is mates' average production).

Lush (6), in his chapter on Sire Indexes, discusses the theoretical basis of the index and its limitations. Several workers have attempted to modify the index to correct for its limitations. Krishnan (5) developed a modification which brought into the formula the herd average and intrasire regression of daughter's performance on the dam's, to remove the bias introduced by ( D - M ) in the Equal Parent Index. The index is given by the formula, S : D-b (M-H)~ where S is sire index, D is daughter's average production, b is intrasire regression of daughter's record on dam's, and H is herd average. As indices were refined by correcting for the exaggerated influence of the dams, it was quite clear that with low heritability in milk production little error is introduced by ignoring the dam's production en- tirely. Consideration of daughter's production by itself was thought adequate to establish the breeding value of a bull. This reduces to a formula, I = D, where I is index and D is daughter's average production.

Extensive use of artificial insemination in the dairying countries resulted in use of bulls in several herds at the same time. Indices calculated on these bulls from information on daughters brought to light serious biases that may be introduced on the breeding values of bulls estimated from herds with different levels of production. The simplest method designed to eliminate this bias was to express the average production of' the daughters of a bull as a deviation from the average of the contemporary cows performing in the same herd. The index thus would be I = U + (D-C.A)~ where U is breed average or average of the different herds involved, D is daughter's average production, and C.A is contemporary average. Hiekman (3) reports the use of this method in Canada to estimate breeding values of daily bulls from Canadian R.O.P. records. When the portion D-C.A is used to express the value of a bull the assumption made is that the differences between herds or the differences between periods within herds are essentially due to environmental forces. Henderson et al. (2) discuss the role of contemporary average in appraising progeny tests of bulls used in several herds. They estimated that the intrasire regression of daughter's record on contemporary herd average was 0.6. To adjust the progeny average in accordance with this estimate of herd effect, they reduced 0.6 (later revised to 0.9, as indicated :below) of the amount by which the un- weighted mean of the contemporary herd average exceeded the average of all herds in the population from the average production of the progeny of a particular bull. These methods, however, do not give any consideration to differences in numbers of daughters used to estimate the breeding value of bulls used in different herds through artificial insemination. VanVleck et al. (11, 12) give a suitable formula which considers this factor as well: Estimated Breed-

m ing Value -~ U q D - b ( X - U ) - U , where

m + 12

m is the number of daughters of a sire, U is breed average for the preceding 5 yr, D is average performance of daughters, b intrasire regression of daughter's record on adjusted stablemate average (estimated to be 0.9), and X mean of the adjusted stablemate average associated with daughter records. With a value as high as 0.9, the formula, for all practical

m purposes, reduces to E . B . V . = U - t - -

m + 12

( D - X ) . These workers compared their method with 17 other methods, involving averages, deviations from stablemate average, etc. They

1500 D. SUNDARESAN, M. GURNANI, AND S. P. SIDIIU

found that when the number of daughters per bull was less than 20, no method was found as good as this method. With more than 50 daughters per sire, procedures using the average for daughters gave as much information as the standard.

Breeding values of the 30 Tharparkar bulls and 18 Sahiwal bulls of the N.D.R.I. herd were estimated by the five methods just enumerated, for both milk production and age at first calving as a measure of reproductive maturity. Among these five methods two involved the use of daughter-dam production and the three others only daughter's production.

The methods used are: 1) I = 2D-M; 2) I = D - b (M-H); 3) I = D ; 4) I : U d -

(D-C.A); 5) I : U + n k (D_C.A)" Where n +

I : index, D : average of daughters, b : intrasire regression of daughter on dam, M : average of mates, H ---- U is herd average, C.A is contemporary average, n : number of daugh-

ters, and k is a constant used to make n n -4- /c

an appropriate regression for the character studied, for instance, milk production or age at first calving in this study. The value of k is based on the ratio of components of variance,

~-s 2 where &~ is an estimate of the sire

~/-' + ~.o-°/n component of variance and &~ is an estimate of the error component of variance applicable to the comparison, and n. is the number of

~-e 2

daughters. On this basis, lc ~ ~-7.. - Using this (3" s

argument, from components of variance obtained with the Tharparkar data lc values were obtained as 12 for milk production and 6 for age at first calving. Thus, the regression to be

used in Method 5 is n n d- ~ for milk production

and - n for age at first calving. n-4-6

R E S U L T S A N D D I S C U S S I O N

Indices on the 30 Tharparkar bulls and 18 Sahiwal bulls used in the herd, calculated by the five methods for each bull, for both milk production and age at first calving are given in Tables 1-4.

Indices for the Tharparkar and Sahiwal bulls are presented separately, since the two herds performed in different periods and had different averages for both age at first calving and

milk production. Also, these two herds repre- sent two Indian dairy t)reeds considered dis- tinctly different.

A sire index to be useful should be accurate. Accuracy is measured by repeatability of the index. A reliable method of indexing will tend to give consistently similar ranking to a bull, as the index is calculated with information from additional daughters available in course of time. Heidhues et al. (1) studied the accuracy of sire proofs under the New York system of testing. Predictions of production of future daughters were obtained from ten successive groups of ten daughters and from cumulative groups of ten, 20 ................ 100 daughters. The production of the next 200 daughters was as- sumed to be a close approximation of the true breeding value of the sire; 53 sires, with at least 300 daughters each, were used in the study. Correlations in their study between the various preliminary tests and the estimate of the true breeding value were about the same, giving evidence that the first few daughters gave as nmeh information on the true breeding value of the sire as additional daughters. A few bulls of the Institute had a larger number of daughters than the rest of the bulls. Those bulls which had nmre than 15 daughters with necessary information were separated for the investigation on repeatability of the indices. On these bulls, two sets of indices on each of the five methods were calculated, one on the first six daughters and the other on all daughters available. The first index is essentially a preliminary progeny test and the second is the best available estinmte on the breeding value of the bull. The correlation coefficient of the preliminary progeny test with the final test was calculated for each method separately. Results obtained arc given in Table 5.

In the correlations between the preliminary evaluation of sires, based on the sample of first six daughters and the final index obtained using all daughters, there is an element of criticism. Since the preliminary sample is in- eluded in the final index, this is a correlation between a part and a whole, which automatically produces a correlation greater than zero. I f a sufficiently large number of daughters were available for each bull, the preliminary sample could have been ignored from the final index while calculating correlation between the preliminary index and the final index. I f this is done in this study, the final index will be based on very few daughters and will not be a reliable estimate of the breeding value of the bull.

The repeatability values on Sahiwal were obtained on only six to eight bulls and the

BREEDING YALUE OF BULLS

TABLE 1

Sire indices on Tharparkar bulls (first lactation 305 days' production)

1501

l-%Tallle

1

U + - - No. of D-b U + n + 12 daugh- 2 D-M (M-.H) No. of D (D-C.A) (D-C.A) ter-dam I II daugh- III IV V

pairs (kg milk) (kg milk) ters (kg milk) (kg milk) (kg milk)

2 3 4 5 6 7 8

Jung 11 2,119 2,302 12 2,385 2,617 2,390 Tikka 43 2,390 2,368 49 2,427 2,403 2,356 Mahesh 9 2,336 2~227 13 2,262 2,516 2,346 Nabha 55 1,775 2,104 60 2,143 2,352 2,320 Latif 20 1,937 2,164 21 2,225 2,409 2,319 Balwant 21 2,128 2,222 21 2,273 2,289 2,243 Kulwant 14 2,467 2,224 14 2,163 2,313 2,243 Gama 5 2,284 2,404 2,233 Maharaja ~2 3109~ 21550 33 2,526 2,251 2,227 Alum 22 2,648 2,505 23 2,592 2,251 2,220 Qais 20 2,991 2,512 23 2,554 2,245 2,216 Prince 5 2,963 2,412 6 2,128 2,308 2,211 Azad 10 1,714 2,071 11 2,091 2,262 2,210 Gope 6 1,723 1,984 6 2,011 2,220 2,181 Neta 5 1,231 1~792 5 1,855 2,192 2,171 Kaura 5 2,051 2,189 2,170 Ejaz 17 21432 2:360 18 2,440 2,103 2,127 Partap 8 2,130 2~041 8 1,971 2,065 2,123 Ranfurlay 44 2,832 2,340 52 2,179 2,109 2,119 Ranjit 37 1,373 1,870 39 1,896 2,099 2,114 l~udra 35 1,707 1,968 39 1,941 2,098 2,113 Waryam 10 1,790 2,168 10 2,296 2,052 2,112 Hakim 15 2,51.9 2,425 17 2,414 2,020 2,079 :Raja 6 370 1,505 8 1,515 1,901 2,058 Pathan 6 ],989 2,195 8 2,251 1,843 2,034 Inam 7 740 1,644 7 1,772 1,781 2,022 Faizal 14 1,677 2,085 14 2,196 1,861 2,000 E.I 19 1,457 1,836 1,962 Lear i() 2:060 21020 15 1,792 1,685 1,897 Sikander 8 1,218 1,61] 11 1,893 1,470 1,831

TABLE 2

Sire indices on Sahiwal bulls (first lactation 305 days' production)

~-~qame

1

No. of D-b U -t- daugh- 2 D-M (M-H) No. of D (D-C.A)

ter-dam I I I daugh- I I I IV pairs (kg milk) (kg milk) ters (kg milk) (kg milk)

2 3 4 5 6 7

U + - - n + 1 2

(D-C.A) V

(kg milk) 8

Daulat 5 2,460 2,568 2,315 Lala 15 21211 21363 26 2,375 2,336 2,296 Neera 27 2,262 2,334 29 2,301 2,317 2,286 Govind 24 2,276 2,296 24 2,331 2,306 2,274 Clmndu 7 2,476 2,390 8 2,390 2,349 2,266 Ganesb 6 2,650 2,379 2,266 Mistri 18 21002 21i52 18 2,183 2,282 2,253 Kundan 18 1,766 2,092 18 2,162 2,247 2,232 Asoka 9 1,623 2,068 26 2,339 2,304 2,206 Barkash 5 2,171 2,189 2,204 Balwan "'7 21~42 21310 16 2,265 2,189 2,198 Gulam 13 1,701 2,016 13 2,057 2,149 2,174 R,ana . . . . . . . . . . . . . . . . . . . . 6 2,100 2,088 2,169 Siphai . . . . . . . . . . . . . . . . . . . . 8 2,200 2,078 2,157 Indersen . . . . . . . . . . . . . . . . . . . . 5 2,457 2,001 2,149 Chalaki 8 1,785 1,926 2,096 Jeewan 27 ~i073 ~i~5 35 2,034 2,040 2,083 Mohan . . . . . . . . . . . . . . . . . . . . 6 1,811 1,753 2,058

1502 D. SUNDAI~ESAN, 1~. GUi~NANI, AND S. P. SIDI-IU

T A B L E 3

Sire indices on Tharparka r bulls (age at first calving)

U + - - No. of D-b U + n + 6 daugh- 2 D-M (M-H) No. of D (D-C.A) (D-C.A)

ter-dam I I I daugh- II][ IV ¥ Name pairs (months) (months) ters (months) (months) (months)

1 2 3 4 5 6 7 8

Rudra 46 39.6 39.5 52 40.5 35.7 36.1 K a u r a . . . . . . . . . . . . . . . . 6 40.5 33.6 35.8 E . I 28 46.2 36.5 37.1 P a t h a a 7 31.0 32.6 9 30.8 35.9 36.7 P a r t a p 20 44.1 41.9 20 43.5 36.8 36.5 Ejaz 21 31.2 30.1 21 31.7 36.9 37.4 Mahesh 15 49.0 43.1 17 42.6 36.9 37.5 Nabha 76 47.1 42.9 80 42.6 37.1 37.5 Faizal 15 32.5 34.1 15 32.6 37.1 37.4 Lear 18 43.3 40.8 23 32.4 37.1 37.6 Tikka 51 39.8 37.9 53 36.8 37.2 37.9 Alam 26 30.0 33.0 26 31.8 37.4 37.6 J u n g 13 45.0 40,3 14 39.4 38.0 38.3 Hakim 17 29.8 32.8 17 31.5 37.8 38.1 Mahara ja 33 27.8 32.5 36 32.5 38.0 38.0 Raj a 6 64.2 50.2 10 47.4 38.2 38.5 Prince 5 30.4 35.0 6 36.2 38.6 38.5 Ranfur ly 57 26.4 35.2 69 34.6 38.1 38.5 Ran j i t 55 47.2 42.6 57 42.6 38.1 38.3 Ku lwan t 32 43.3 45.0 32 43.3 38.2 38.3 La t i f 23 55.0 45.3 23 43.8 38.2 38.6 Gama 5 40.4 38.2 5 37.0 38.8 38.8 Neta 5 60.4 48.8 5 48.4 39.1 38.6 Sikandar 14 30.7 33.6 15 32.7 38.5 38.8 Waryam 15 42.3 38.8 15 37.2 39.1 39.3 Qais 24 29.8 33.5 25 33.3 38.9 39.1 Balwant 25 47.4 41.5 25 39.9 39.1 39.2 I n a m 7 46.5 40.5 7 38.3 40.4 39.7 Azad 13 53.0 46.3 14 45.2 39.6 39.2 Gepe 9 27.5 34.2 9 36.6 41.2 36.1

TABLE 4

Sire indices on Sahiw'tl bulls (age at first calving)

n

U ÷ - - No. of D-b U + n + 6 daugh- 2 D-M (M-H) No. of D (D-C.A) (D-C.A)

ter-dam I I I daugh- I I I IV V Name p~irs (months) (months) ters (months) (months) (months)

1 2 3 4 5 6 7 8

Mistrl 19 37.1 39.2 19 38.4 40.0 40.2 Govind 30 43.3 41.8 30 40.2 40.8 40.6 Siphai . . . . . . . . . . . . 9 30.1 41.1 41.2 Neera 31 48.3 40.0 32 42.5 41.6 41.2 Indersen . . . . . . . . . . . . . . . . 5 27,4 40.8 41.4 Mohan . . . . . . . . . . . . . . . . 7 29.3 41.1 41.0 Prakash 5 30.4 41.7 43.4 J iwan 32 51:7 45.0 38 40.4 42.1 41.8 Rana 6 34.3 42.3 41.8 K . n d a . ~ 3~:9 40:5 21 40.9 42.6 42.5 Gulam 14 40.9 41.6 14 41.6 42.7 42.4 Asoka 9 48.7 42.8 29 34.8 43.0 42.4 Cha]aki . . . . . . . . . . . . . . . . 8 45.8 44.0 42.7 Ganesh 6 31.2 44.6 42.8 Cbandu 9 55:6 ~ : 6 10 43.7 44.1 42.9 Lala 15 52.2 44.7 26 41.2 44.0 43.3 Daula t 6 70.4 53.3 7 49.0 45.2 43.4 Balwan 7 58.8 48.8 16 44.1 44.5 43.4

B R E E D I N G V A L U E O F B U L L S 1503

TABLE 5

Repeatability of sire indices (Correlation between the two tests, preliminary on 6 daughters and final on more than 15

daughters)

Methods

Details No. of bulls 1 2 3 4 5

First-lact. prod., Tharparkar 14-18 0.65* 0.62* 0.71 ~ 0.57* 0.64 ~ Sahiwal 6-8 0.89 * 0.95* 0.78 ** 0.67 0.18 Age at first calf, Tharparkar ~8-20 0.47 *~ 0.56 ** 0.70 ~ 0.58* 0.36 ~ Sahiwal 6-8 0.38 0.0 0.41 0.60 0.66 *~

* P < 0.01. ** P < 0.05.

results vary a great deal among the different methods. However, for Tharparkar these values were obtained on 14-18 bulls and for both characters studied, lactation production and age at first calving, all the five methods of evaluating the breeding value of bulls seem to be of about equal repeatability. This would indicate that although the different methods of evaluating bulls may assign varying breeding values to a bull, in each of the methods a preliminary test on the first six daughters explains only 30-50% of the variation among indices calculated, using performance of all daughters, 15-60 in number.

A few bulls in the Tharparkar and Sahiwal herds had 24-60 daughters perform in the herd. Information from these were used to find whether a preliminary test on a higher number of daughters (than the six used before) would give more reliable information on the breeding value of the bulls. The correlation between preliminary test using 15 daughters and index using all available daughters (24-60) for the five different methods using milk production and age at first calving is given in Table 6.

From Table 6 i~ is clear that a preliminary test on 15 daughters explains more variance on the breeding value of a bull than the test with six daughters, as much as 40-80% of variation among indices by 15 daughter test compared to 30-50% by 6 daughter test. IIere, Method Five gives a better repeatability than the four other methods; it explains as much as

81% of' the variation among indices, calculated using all daughters.

The index given to a bull by method 1---- 2 D - M in many cases differs very severely from the indices given to that bull by the four other methods, among which there is some degree of agreement. This is more so in the Tharparkar herd than in the Sahiwal herd. For instance, Bull Inam has a 2 D - M index of 740 kg of milk production, whereas the four others range from 1,644 to 2,022 kg; similarly, Bull Maharaja has a 2D-M index of 3,092 kg, whereas the four others range from 2,227-2,550. The ob- vious cause of this is the exaggerated importance given to the dam's performance in 2 D - M method. This introduces serious bias when there are major differences in production from period to period, as in the Tharparkar herd. Sire's breeding value is adversely affected if dams performed during a favorable period and daughters during an unfavorable period, and vice versa. Also, poor performance, due to chance, of a few dams will bias the indices.

From information presented it would seem

n ( D - C . A ) , 1~ =- clear that Method 5, U + - ~ - ~

12 or 6, provides better repeatability than the other methods. Therefore, one can say that among these five methods Method Five is the most accurate. The design of the method itself provides correction for environmental differences and variation in numbers of daughters

TABLE 6

Repeatability of sire indices (Correlation between the preliminary ~,est on 15 daughters and index using all daughters)

(Tharparkar and Sahiwal combined)

Methods

Details No. of bulls 1 2 3 4 5

Firstqact. prod. 11 0.70* 0.63 *~ 0.74* 0.78* 0.90 .2 Age at first calving 21 0.85 0.87 0.81 0.88 0.89

P < 0.01. ** P < 0.05.

1504 D. SUNDARESAN, 5L GUI~NANI, AND S. P. SIDI-IU

used to evaluate a bull. To estinmte how closely the other methods approach this method, i.e., Method Five, correlations between the indices obtained by each of the first four methods and the last method were calculated. Results are given in Table 7.

There is a vel T high relat ionship between the four th and fifth methods. The other methods have not shown any consistent pa t te rn of relationship with the fifth. Under certain circumstances some of the other methods also give about the same informat ion as the fifth method. In Sahiwal there were no ma jo r changes in product ion or age at first calving during the period of study, 1945-60, which could be at t r ibuted to environmental differences. Under these circumstances, Methods 1, 2, and 3 also have given appreciable relat ionship to the fifth method. On the other hand, with the Tha rpa rka r herd subjected to serious environmental differences, all other methods except Method 4 have very poor relationship with the fifth method. Thus, there is evidence to believe that under field conditions of progeny testing,

where the bulls are either used in several herds of different levels of production or in the same herd over a long period of time with differ- enees in product ion f rom period to period, most of which differences are due to feeding and nmnagemental conditions, the methods using contemporary average to correct for en- vi ronmental differences give a reliable estimate of the breeding value of the bull.

Wi th large-scale applicat ion of artificial insemination in progeny-test ing in Europe and America, the problem of differences between herds confounding sire test has been recognized fo r a long time. I n Denmark, to overcome this difficulty, special progeny-test ing stations were instituted, where samples of daughters of a bull f rom different farms are brought into the station for measuring their performances. How- ever, studies of the results f rom these special test ing stations have not confirmed their need or importance. Robertson and Mason (9) compared the progeny- tes t ing of bulls by special stations, using' data from the field. They found that the wa' iance between progeny groups in

TABLE 7

Relationship among sire evaluation methods (Correlation between each of the first four methods with the l:~st method)

No. of No. of Details bulls r 15 r 25 bulls r 35 r 45

First-laet. prod., Tharparkar 27 0.18 0.33 30 0.39 *~ 0.70 ~ Sahiwal 10 0.44 0.70 '~~ 18 0.65 ~* 0.88 ~ Age at first calf, Tharparkar 28 0.62 ~ 0.30 30 0.08 0.93 * Sahiwal 11 0.69 ~ 0.66 ** 18 0.44 0.95 ~

* P ~ 0.01. ** P ~ 0.05.

1, 2, 3, 4, and 5 are the methods: 2 D-M, D-b(M-H), D, U+ (D-C.A), and U + - -

(D-C.A) /c = 12 or 6, respectively.

/ t

n + / c

the testing stations, even between those tested in the same year, was nmch more than in the field data with the same progeny groups, and that the repeatabi l i ty of special station results in the field was very low, the regression of field results on station test being only 0.2 in herds at all levels of production. Touebberry et al. (10) also studied this question in detail. Their data consisted of milk and fa t records of daughters of bulls tested at special testing stations and records on some of the same sires tested in fa rmers ' herds. They obtained heri tabil i ty estimates f rom 1) station data (between sires within years within stat ions) , 2) field data a f te r removing herd differences, and 3) field data expressed as a deviation f rom contemporaI T average. F o r milk production, the heri tabil i ty estimates by three methods, respectively, were

0.66, 0.29, and 0.23. A highly inflated herita- bil i ty estimate was obtained for milk production by the station data. The estimate of genetic eorrelation for milk production between station test and field test was 0.68, whereas the genetic correlat ion between independent field tests was 0.94. The above two findings would suggest that ei ther a large interaction between sires and levels of management existed or that the sire component of station data is inflated with enviromnental differences. The lat ter is more possible, since many investigations in the past have indicated absence of sire-herd interaction in milk production. The authors, a f te r a comparison of station and field testing with reference to numbers of daughters used fo r test ing a sire, came to the conclusion that i f the number of daughters per sire is seven or

BREEDING VALUE OF BULLS 1505

more, the expected genetic supe r io r i ty resul t - ing f rom selection based on field da ta is g rea t e r t han tha t r esu l t ing f rom s ta t ion tests.

Thus, i t is c lear t h a t since one 's aim is to find the best method of p r o v i n g bulls to give the m a x h n u m genetic super io r i ty u n d e r eco- nomical ly feasible condi t ions and f o r appl ica- t ion in the field fo r i m p r o v i n g nfilk p roduc t ion , ou r efforts should be a imed at des ign ing sta- t is t ical p rocedures to correct fo r env i ronmen ta l differences t ha t p l ay any m a j o r role in sire evaluat ion, r a t h e r t han nmking a t t empts , a t p roh ib i t ive cost, to reduce env i ronmen ta l va r i a - t ion by s teps not app l icab le u n d e r p rac t i ca l condit ions. The eva lua t ion of bulls, t ak ing in to account the c o n t e m p o r a r y average of the daughters, is quite s imple and effective in increas ing accuracy, as is seen f rom resul ts ob ta ined in this s tudy wi th T h a r p a r k a r and Sahiwal bulls, sp read over a long period.

ACKNOWLEDGMENT

Grateful acknowledgment is given to Dr. K. K. Iya, Director of Dairy Research, for the keen interest taken in this work, and to Dr. S. N. Ray, Head of the Division of Dairy Husbandry of this Inst i tute, for the facilities provided. Thanks are expressed to Shri T. R. Purl, Research Officer (Stat is t ics) , N.D.R.I., Karnal , for reading the manuscripts and offering valuable suggestions.

REFERENCES

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(2) HENDERSON, C. R., CARTER, H. W., AND

GODPREY, J. T. 1954. Use of Contemporary Herd Average in Appraising Progeny Tests of Dairy Bulls. J. Animal Sci., 13: 959.

(3) HICK~AN, C. G. 1961. Est imat ing Breeding Values of Dairy Bulls from Canadian R.O.P. Records. Canadian J. Dairy Sci., 41: 40. [Animal Breeding Abstrs., 30: 157. 1962.]

(4) HOP~EYER, JAN. 1955. A Study of Danish and Swedish Progeny Testing Methods for Dairy Bulls. Kgl. Lantbruks-Hogskol. Ann., 22 : 425.

(5) KR~S]~NAN, K. S. 1956. A New Index for Milk Production. Indian J. Vet. Sci., 26: 149.

(6) LUSH, J. :L. 1945. Animal Breeding Plans. Iowa State University Press, Ames.

(7) ROBERTSON, ALAN. 1953. Tile Use and In- terpretat ion of Progeny Tests in Livestock Improvement. Proc. Bri*ish Soc. of Ani- mal Production.

(8) ROBERTSON, ALAN. 1957. Optimum Group Size in Progeny Testing and Family Selec- tion. Biometrics, 13: 442.

(9) ROBERTSON, ALAN, AND MASON, I. L. 1956. The Progeny Testing of Dairy Bulls: A Comparison of Special Stat ion and Field Results. J. Agr. Sci., 47: 376.

(10) TO,UCHBEI~RY, R. ~¢~T., ROTTENSTEN, K., AND ANDERSON, H. A. 1960. Comparison of Dairy Sire Progeny Tests Made at Special Danish Testing Stations with Tests Made in Farmer Herds. J. Dairy Sci., 43: 529.

(11) VANVLECK, L. D., O'BLENESS, G. ~., AND HENDERSON, C. R. 1961. Comparison of Procedures Used for Evaluat ing Sires Used in Artificial Insemination. J. Dairy Sci., 44: 708.

(12) VANVLECK, L. D., HEID~JES, T., ANn HEN- nElSON, C. R. 1961. Analysis of Deviations of Dairy Records from Different Con- temporary Averages. J. Dairy Sci., 44: 269.

Documents

Evaluation of Breeding Value of Bulls Used in Two Herds in India