Additive and nonadditive genetic effects on lifetime yields of milk and milk components and lifetime profitability were estimated from 5070 cattle in a Holstein pureline, an Ayrshire-based pureline, and 10 crossbred groups of these purelines. Lifetime yields of milk, fat, protein, and lactose and lifetime milk value and annualized discounted net returns were analyzed. Lifetime yields, lifetime milk value, and annualized discounted net returns of the Holstein x Ayrshire-based line F1 and an F1 x (F1 x F1) cross were not significantly different from those for the Holstein pureline. Net reproductive rate for F1 females was 9% greater than that of contemporary Holsteins. The Holstein pureline was superior to the Ayrshire-based pureline for direct additive genetic merit for all traits. Heterosis for the lifetime traits ranged from 16.6% for lifetime milk yield to 20.6% for annualized discounted net returns. Cytoplasmic maternal effect on annualized discounted net return was significant and favored the Ayrshire-based line. Potential economic benefit may derive from development of a crossbred cow that is superior to Holsteins. Maximum exploitation of additive and nonadditive genetic effects on lifetime yields and profitability appears to favor a rotational crossbreeding system with two breeds.
Heritabilities, genetic and phenotypic correlations among growth, forage consumption, and BW changes of heifers and feed consumption, BW changes, and yields of first lactation cows were estimated. Data were from 1266 Holstein progeny of 74 sires born from 1972 to 1985 at three Agriculture Canada research herds. Heavier heifers at 26 wk consumed more feed from 26 to 34 wk than smaller heifers but gained the same BW. The BW gain and feed consumption heritabilities were .17 and .23, respectively; genetic correlation was .44, and phenotypic correlation was .27. During first lactation, feed intake from 8 to 16 wk and measures of milk yield are very tightly intercorrelated both phenotypically and genetically (.78 to .98). Precalving BW gain and BW at calving were genetically uncorrelated with measures of milk yield (-.09 to +.05). Loss of BW during the first 8 wk of first lactation was moderately heritable (.29) and correlated genetically and phenotypically with measures of milk yield in early lactation (.32 to .39) and feed consumption (.26). From 8 to 16 wk, average BW changes were small and had low heritability and weak phenotypic correlations with measures of milk yield or feed intake. The BW at 26 wk and BW gain from 26 to 34 wk were very poor indicators of early first lactation milk yield. Heifer feed intake was weakly correlated phenotypically (-.07 to .16) but moderately genetically correlated (.17 to .23) with early first lactation milk yield and feed consumption.
Data of 6482 lactations from 14 crossbred (Holstein x Zebu) herds in Brazil were used to study breed additive and heterosis effects for first, second, third, and first to fifth lactation milk yields, age at first calving, calving interval, and milk yield divided by calving interval, as well as the effect of age at calving on milk yield. Holstein additive expressed as deviation from Zebu and heterosis effects were highly significant for all traits. For each percentage of Holstein gene contribution an increase of 10.02, 12.02, 12.51, and 12.15 kg of milk were expected for first, second, third, and first to fifth lactation yields, respectively. Corresponding heterosis effects on those traits were 3.80, 3.39, 4.02, and 3.90 kg of milk for each percentage of heterozygosity. Replacement of pure Zebu genes by Holstein genes reduced age at first calving by 6 mo and shortened calving interval by 37 d. Holstein x Zebu heterotic effect decreased age at first calving by 2 mo and calving interval by 39 d. Holstein additive and heterosis effects for milk yield divided by calving interval were 3.4 and 1.3 kg of milk/d, respectively. Fitting breed additive and heterozygosity effects accounted for 99% of the genetic effects except for first to fifth lactation milk yield.
Data from 1341 Holstein heifers of 71 sires were used to study heritabilities of and genetic and phenotypic correlations among milk production traits (308-d milk, front and rear half yields), body measurements (heart girth, withers height, body length, and rump length), udder measurements (front teat length and diameter, rear teat length and diameter, teat distance and udder height), and age at first calving. Genetic and phenotypic parameters were estimated by the multitrait restricted maximum likelihood method. Multitrait estimates of heritability ranged from .37 to .47 for first lactation yield traits, from .19 to .51 for body measurements, and from .08 to .41 for udder measurements. Age at first calving averaged 22.3 mo with a heritability estimate of .11. Milk production traits were all positively correlated with body measurements, suggesting that high producing heifers would be taller, larger, and longer than low producing heifers. Multitrait estimates of genetic and phenotypic correlations between udder height and yield traits were all negative, suggesting that high producing heifers tend to have lower udders. Of four body measurements studied, rump length showed the greatest genetic correlations with yield traits. Among six udder measurements, udder height exhibited the highest degree of associations with yield traits. Thus, rump length and udder height merit greater attention for prediction of lactational performance.
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