In analyzing the results with the first 52 Holstein and 45 Jersey cows for which the required data were available, we adjusted the production records of the first lactation to a mature-age basis so as to overcome the effects of differences in age at first calving. We determined separate milk production averages for cows that had received each of the various grades for mammary development when they were calves; that is, animals that were given a grade of one were put in one group, those graded two in another, those graded three in another, and so on. In this way we ascertained the average milk production of cows that were in each of the different degrees of advancement in mammary development as calves.

The increase in average production with successive grades (one, two, three, four, etc.) was marked but somewhat irregular for Holsteins. For Jerseys, each grade had a higher average than the one next below.

The practical test of the significance of degree of advancement of mammary development in calves is to determine whether the animals that are potentially low, medium, or high producers can be identified as calves rather than to attempt to draw fine lines of distinction between those that are good and those that are slightly better or between those that are poor and those that are slightly poorer. Thus it probably is enough to classify calves into three groups—the advanced, the average, and the retarded. The calves that were given grades of seven, eight, and nine for mammary development ( advanced development) were put in one group, those with grades of four, five, and six ( average development) in another, and those with grades of one, two, and three (retarded development) in still another group. The average milk production for the Holsteins that were advanced in mammary development as calves was 3,396 pounds higher than the ones retarded. The corresponding difference for Jerseys was 4,391 pounds.

Separate analyses of grades given calves at various ages indicate that the relative degree of mammary-gland development at from 3 to 5 months is more significant of potential producing ability than the relative degree of development at any other age. Grades given after 6 months were of little significance.

It should be borne in mind that the so-called breed standards and the results shown were based on studies made in one herd—the one at Beltsville. In this herd the continued use of sires proved for their ability to transmit high production to their daughters has resulted in an extremely high and uniform level of production. In this connection it should be pointed out that even the cows graded in the retarded group as calves had production averages that would be considered profitable in most herds. The question is whether the relatively low and the relatively high producers in any herd can be identified while they are calves regardless of the producing level of the herd.

The present need is to give the method a rigid test in other herds. It should be tried in herds where the inheritance for milk production may be at different levels, and where wide individual variation in producing capacity exists. In making such a test it would be necessary to obtain grades on calves in herds that are regularly tested for production. The animals would have to be kept through one lactation period—those that were retarded as well as those advanced in mammary development as calves. Otherwise, it would be impossible to establish the level of their producing ability and the test of the method would fail.

In making such a test, the development of each heifer calf in the herd would be examined by palpation when she is 4 months old. The examination takes only about 10 minutes, and is not difficult. Unfortunately, the method is not readily explained, except by demonstration. The various stages of development can be detected and identified easily by the beginner, without previous experience. Some practice is needed to enable one to evaluate consistently their degree of advancement, but experience in conducting demonstrations in many places has proved that there is little disagreement on whether a calf is to be graded A, B, or C.

The widespread interest of dairymen in the method is indicated by the response from 38 States and several foreign countries, including 800 requests for information and expressions of desire to try the plan. Some breeders already have started to keep records of the mammary development of their young calves.

We must emphasize again that the results are not conclusive, because of the limited number of animals tested, and because all of the results were obtained from one excellent herd. Encouraging as they appear to be, the results must be proved in the field. But the idea is worth the effort—worth, if it is proved to be perfect, 250 million dollars a year.

THE AUTHOR

W. W. Swett is a dairy husbandman in the Division of Dairy Cattle Breeding, Feeding, and Management, Bureau of Dairy Industry. He is a graduate of the University of Missouri and taught dairy husbandry there for 6 years.