EVALUATION OF SIRES AVAILABLE THROUGH PLANNED MATING

A comparison was made between records of daughters of three Holstein sires used in planned mating programs and records of their dams in order to determine the influence of selectivity of mating on sire evaluation. The number of daughter-dam sets ranged from 33 to 44. The results showed that all three sires were mated to cows in above average herds. One sire was mated to cows which averaged above their herd mates by 599 lb. of milk and 31.6 lb. of fat. The other sires were mated to cows averaging nearer to their herd mates: –285 lb. of milk and –1.7 lb. of fat, and 334 lb. of milk, 0.5 lb. of fat respectively. Selection index estimates of daughter superiority were only slightly changed when dam records were considered in addition to daughter records even for the sire mated to cows averaging considerably above their herd mates. Copyright © 1962 American Society of Animal Science. Used by permission. EVALUATION OF SIRES AVAILABLE THROUGH PLANNED MATING L. D. VANVLEcK, C. R. HENDERSON, AND H. W. CARTER Cornell University, Ithaca, New York T H E R E is some concern that methods of sire evaluation which utilize contemporary stablemate averages can be biased by differential genetic merit of the mates of these sires. A little reflection, however, indicates that even if the cows to which some sires are mated are more highly selected than the mates of other sires, this differential merit will not affect seriously the ranking of sires according to the evaluation of their progeny. Until the present, data have not been readily available with which to study the seriousness of this problem. The present study does not deal with the question generally, but attempts only to discover the effect of the estimated genetic merit of dams on the evaluation of three sires which were used in planned matings. The term "planned mating" as understood for this study refers to matings through artificial insemination to sires which are not normally available for service except by special request at additional cost and which are not owned by the distributing organization. The three sires whose matings are studied were from "popular" herds and were older bulls without an evaluation on the basis of their artificially sired progeny. Thus, a situation worse than would normally exist with respect to selected mates seems likely to exist. Da t a and P rocedure The 305 day, 2x, M.E. records of artificially sired progeny of three Holstein sires available through planned mating service which were found in the New York Dairy Records Processing Laboratory and the records of the dams of these progeny were studied. Only the first record of each daughter appearing in the file was used. Most of these were actually first lactation records. Similarly only one record from each dam was selected. I f possible, the selection was such that this record was made during about the same period of time as the daughter record. The number of records in each sire group is listed in table 1. Many of the progeny records did not have corresponding dam records in the file. The daughter average for milk and fat for each sire was computed as well as the corresponding average of adjusted stablemate averages, for all daughters in the file and for those daughters having dam records in the file. Similar averages were computed for the available dam records. These averages are also presented in table 1. The adjusted stablemate average is essentially the average of the herd mates which started records in the same yearseason as the individual adjusted for the regression of true stablemate average on the stablemate average. This procedure was first described by Henderson et al. (1954), and was explained in more detail by Henderson (1956) and by Heidhues et al. (1960). Resul ts and Discuss ion The mates for all three sires were evidently from above average herds as can be seen in table 1. The current 5-year DHIA averages for New York Holsteins are 12,280 lb. of milk and 442 lb. of fat. Only one of the sires was mated to cows whose records were much above their corresponding stablemate averages. In fact, for fat production the mates of two sires were less than 2 lb. above or below their stablemate averages. The milk production of the mates of the same two sires w a s 285 and 334 lb. different from their herd mates. The other sire, however, was mated to cows which were considerably above their herd mates in milk and fat production. I t is necessary to examine the effect of this superiority on the evaluation of the sire. Index procedures will be used to compare evaluation based on only daughter records and evaluation considering also the dam records. In order to correct for known environmental effects the records will be expressed as deviations from their adjusted stablemate averages which removes the effects of the herd, year and season of freshening. The index when using only daughter records is Io=b(Yo-Xo) where Io is the index, b is the regression coefficient for the regression of the true daughter superiority on the daughter average, Yo is the daughter average and Xo is the average of the corresponding adjusted stablemate averages. I t is noted that this expresses the predicted superiority of a sire's 30 EVALUATION OF SIRES 31 T A B L E 1. AVERAGES OF M I L K AND F A T R E C O R D S OF D A U G H T E R S AND M A T E S OF T H R E E P L A N N E D M A T I N G SIRES AND T H E AVERAGES OF T H E I R S T A B L E M A T E A V E R A G E S