Article

Part Lactations. III. Progeny Testing with Part Lactation Records

Journal of Dairy Science - J DAIRY SCI 01/1961; 44(5):921-927. DOI: 10.3168/jds.S0022-0302(61)89833-0

ABSTRACT Analyses of monthly records of artificially-bred cows indicate that under New Zealand conditions records accumulated up to a specified test day early in lactation are suitable for progeny testing. Heritability slightly exceeds that for lactation yield and the genetic correlation between the part record and lactation yield exceeds 0.90. As a result, the rate of progress in improving additive genetic merit for lactation yield when selecting on part records differs very little from when selecting on lactation yield. Approximately 40, 60, and 80 daughters in sire proofs using part records give the same information about lactation yield as a proof using lactation yield on 30, 40, and 50 daughters, respectively. Proofs evaluated on both kinds of records for the same group of sires were highly correlated and the part lactation proofs were just as repeatable as those based on lactation yields.

0 Bookmarks
 · 
16 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The first two USDA-DHIA Prelimi- nary Sire Summaries were compared with official summaries on the same hulls. Preliminary summaries were avail- able an average of 6.0 and 5.5 me before official summaries. For six breeds, cor- relations between preliminary and offi- cial Predicted Differences for milk ranged from .93 to .98 for the June, 1973, preliminary and .96 to .99 for the October summary. Corresponding re- gressions of official Predicted Difference on preliminary Predicted Difference ranged from .89 to 1.09 and .99 to 1.05 for milk. ,The average absolute differ- ences in Predicted Difference for milk varied directly with breed yield so were largest for Holstein's (35 and 27 kg). The accuracy of current projection fac- tors appears to vary with season of calv- ing, but this variation did not affect seri- ously sire selection based on records deviated from herdmates. Selecting young bulls on the preliminary evalua- tion may increase the rate of genetic im- provement in sires by as much as 10%.
    Journal of Dairy Science - J DAIRY SCI. 01/1975; 58(4):551-557.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A significant change in the methods of progeny-testing dairy sires in recent years has been the discarding of daughter-dam comparisons in favor of comparing daughters with their herd-mates. These involve comparing records of daughters with those of their herd-mates made in the same year, and as such are often referred to as contemporary comparisons, or sometimes as stable-mate comparisons. They were first used on a widespread scale in New Zealand in 1950, with refinements added in 1957. They were introduced in Great Britain in 1954 and were also being used in New York State at about the same time. This paper discusses some of the underlying principles of progeny-testing based on such contemporary comparisons, and presents details of the methods used in these places, all three of which have large sire-proving routines in regular operation.
    Journal of Dairy Science - J DAIRY SCI. 01/1964; 47(4):402-413.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A total of 418,139 mature-equivalent (ME) lactation records representing cows of five dairy breeds calving from October, 1964, to September, 1965, was used to esti- mate the intrasire regression of daughters on herdmates. Differences in the regressions from breed, lactation number, trait, and region were studied. Regressions for first lactations were generally lower than those for later lactations. Guernseys and Hol- steins had the highest regressions for milk and fat yield, followed by Ayrshire, Jer- seys, and Brown Swiss. Holsteins and Ayr- shires had the highest regressions for fat per cent. Regional differences in the Hol- stein regressions were substantial. New England, the South, and California had the highest regressions for yield. The South and California had the highest regressions for fat per cent, but the Northeast was intermediate. The accuracy of the adjust- ment of sire evaluations for performance of herdmates can be improved by consider- ing these differences. Regressions for first- lactation fat per cent were around 0.7, indicating that the deviation of herdmates from breed average should be considered in evaluating sires.
    Journal of Dairy Science - J DAIRY SCI. 01/1970; 53(10):1461-1468.