COMPARING BULLS

Hawke's Bay Herald-Tribune, Volume 81, Issue 19, 15 October 1937, Page 43 (Supplement)

COMPARING BULLS

How the Index System Works DATEY farmers who have found the production xecords of their cows so helpful in planning their breeding op6rations are showing increasing interest in the "bull index" question, and discussions as to the most practicable system for determining the xelative merits of different sires are becoming increasingly common. The latest contiibution to these discussione comes from Mr. A. T. Hewitt, dairy herd manager of the State research farm, Werribee, Victoria, who, after apply* ing to the vaxious sires that have been used. in the Victoria stud a number of bull indices, has come to the concluaion that the simplest and most practicable method is that afforded by the "equal parent" index, the principles of which were outlined in a special article in these , columns some time ago. The conditions obtaining at Werribee, where a comparatively large herd of purebred Eed Polls and Friesians ba« been maintained under carefullycontrolled conditions for many years. and where very complete- xecords are available make Mr. Hewitt 's analysis a particularly valuable contribution to the bull index question. As he points out, milk and butterfat yielding capacity is known to be an inherited characteristic, but the study thereof is complicated by the fact that . the genetic characters reeponsible for these yields, depepd on many factors, and the inherent yields cannot be accnrately determined, beeause they are influenced so much by environment. Thus, a cow which may hav.e inherited the capacity to produce, say, 5001b. of butter fat under one set of conditions may produce under different conditions not more than 3001b. That yield factors are inherited according to fairly definite Mendelian proportions has been ehown in a number of tests. The equal influence of 'the parents has been de.monstrated in a comprehensive experiment, commenced in. "1906, in whieh 66 Jersey bulls whose dams had butterfat perceutages ranging 'from 4.7 to 6.5, and averaging 5.57 per cent., were bred to 108 Ked Bane cows whose average test was 3,4 per cent. The 108 first cross cows "that resulted had an average test of 4-39 per cent. These firet cross cows were mated back to both Jersey and Ked Bane sires, the average tests of the back crosses being 4.82 per cent. and 4.04 per cent. xespectively. It Will he noted that in each case the average test of the daughters is approximatciy " half way between that of the uams and that of the sires' dams, which may be taken as the "test" of the sirea since the numbers were large and jepresentative, This experiment, which has been confirmed by munerous others, indicates very cleaiiy that the sire and the dam have an equal influence on the test of their offspring. To avoid as much as possible differeaces yield due to cixanges ln environment, Mr. Hewitt used for hif cal- - culatiec# only the 273 days' performancts of Ked Poll cows in the Victoria stud under the regulations gove'rning the Standard Herd Test. This eliminated changes of environment that occur when cows from the Werribee herd have been tested on other farms under different conditions, although it does not eliminate local changes of environment that occur from time to time, nTid which undoubtedly affect the tecords. The usual allowances were made for age, but no attempt. was made to correct the xecords to any etandard conditions of feeding, seasonal conditions, ete. The production of the dam has long been xegarded as a xeasonable basis for valuing a bulL Most production-bred bulls sold to-day are sold on that basis. This policy is recommended as a satisfactory one where no other more valuable information is available1— such. as Ihe production index of the., bull liiuiself. That the bull from the higherproduction dam tends to throw the higher-producing daughters ik illustrattsd in the accompanying table, in whieh ara set out the "inature equivalent" productions oi the dams and the sires used in the Werribee herd and the average "mature equivalent" yields of the daughters of those sires. The only bulls ineluded in the table are .those with more than five tested daughters from tested dams. A glance at this table shows that, with the exception of Victoria Bit o' Bacca, the bull from the higher-producing dam has thrown the higher-producing daughters. Tbe explanation of the apparent failuro oi Victoria Bit o' Bacco lies in the fact that ten of his eighteen tested daughters were very closely bred, and averaged 581b. butterfat less than the average of their dams. His eight line-bred daughters averaged 91b. butterfat more than the average of their dams. The daughters of Victoria Volcano and Victoria Air Marshal were all line bred.

A bull index ilidicates tlie ability of 4 bull in begetting high-producing hei-

fers. For convenience it is desirable that such indices should be expressed in terms Of pounds of milk, percentage. test and pounds of butterfat in just the same way as the record of a cow is set out. To give a reasonably accurate index it is found that oue needs the xecords of at least five tested daughters of the bull; these daughters must be from tested dams, and, if there are more than five tested daughters, tlio ones whose records are considered must. be selected at random. The more daughters considered and the larger th© difference between the bull index and the herd average, the more significant will the index be. The "equal parent" index is based on the fact, as shown in the experiment already referred to, that the "test" of an cow lies midway between those of her dam and her sire. Similarly there is no doubt in the minds of research workers that the milk and butterfat yields of Ihe daughters also lie midway between those of their parents, although this fact is not so easily demonstrated, since yields are affected maro by environment than 5s test?. The equal parent index, then, assumes that yield, test and butterfat yield of the daughters lie midway between those of the parents. In the case of Victoria Volcano, for example, the average yield of butterfat of his tested daughters is 4361b., whereas the dams of those daughters had an average yield of 4171b. Since the yield of the daughters lies midway between the yields of the parjents, 4321b. must represent the average of the two and, if we multiply the average yield of the daughters by two and subtract the average yield of the dams, we will get the "yield," or rather, the "equal parent" index of the bull, Thus we find the index of Victoria Volcano to be 4551b. butterfat. The equal parent for each of the sires shown in the previous table is set out in Table 2.

It will be seen from the above tables that this index gives what experienc-e has shown to be a reasonable guide to the effect the bull will have on the production capacity of his daughters* Since it most' nearly complies with practieal considerations and, at the same time, is sound in pxineiple, the equal parent index is recommended for general use by dairy farmers who wi«h to compare the relative merits of two or more bulls, or to determine whether a bull that has a number of tested daughters in another herd is likely to improve the production capacity of their own herds. The index is simply to apply and is sufficiently accurate to meet all practieal considerations. Thi3 index is furtheri simplified by the fact that it can be applied to butterfat yields alone, as butterfat yield is economically the- most important faetor in the production of the dairy cow, this is all that is usually required.

Dam of Da .ghters Bull. of Bull. Butter- Butterfat. fat. Bull. lbs. lbs. Victoria Volcano .. 432 436 Victoria Air Marshal 387 404 Nicotine — 373 Earl of Beaconsfield 306 375 Belligerent ........ — • 378 Longford Major ... — - 344 Vice Kegal 292 365 Victoria Bit o' Bacca 462 • 360 Tabacum ......... — 320

MATURE EQUIVALENT PEODUCTION.

—Equal Parent Index — ter Milk. Test. Fat. Bull. lb. P.C. lb. Victoria Volcano .. 10,170 4.45 455 Victoria Air Marshall 9,820 4.69 444 Nicotine ......... 9,980 4.13 400 Earl of Beaconsfield 7,260 5.19 385 Belligerent " 8,390 4.53 372 Longford Major ... 8,520 3.81 331 Vice Kegal ........ 7,250 4.61 327 Victoria Bit o ' Bacca 6,890 4.84 326 Tabacum ........ 5,500 5.37 298