Selecting young dairy bulls on differences between relatives and their contemporaries

Effects of genetic and environmental variance on dairy sire evaluation

“…Barr (1962) also found a value of " ^ to be applicable to Canadian herd test data. Concerning the latter two methods above, they are, in effect, simply 'two sides of the same coin'.…”

“…Numbers of records included in each study ranged from 3900 by Hickman Legates et al, 1956;Barr, 1962;Van Vleck et al, 1961b. In selecting the present data from among those available, the only restriction stipulated was that each sire must have daughters in at least two different herds.…”

“…As a result, environmental correlations within some groups of paternal sibs might be expected to contribute to a larger than normal sire component. Barr (1962; see Table 17), in his paternal sib analysis, also included all records of each daughter but calculated them as was done in the present study. He found the sire components for fat and milk to be 5.2 and 2.7 percent, respectively, thus indicating that the resultant bias is probably very small when considering each record separately.…”

Genetic gain in sire selection

“…The mean squares were,equated to their expec tations and the resulting components of variance are given in other studies (Barr, 1962;Van Vleck ^ al., 196ld) have shown that seasons accoi^t for less than 5 percent of the total variance and herds account for more than 25 percent of the total variation. One of the reasons that seasons account for so much more variation in the California data than was found in the other studies is the definite time trend which was present in the California data.…”

“…The effect of sires was not included in Model 1 as it was in other studies of this type (Barr, 1962;Henderson, 1956). Leaving the effect of sires out of the herd-year-season analysis requires the assumption of independence of the sire effect from these environmental effects.…”