Dairy Production and Reproduction in Holstein-Friesian and Guzera Crosses

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Abstract
Data on 660 first and second lactations and on 506 calving intervals were used to characterize six red and white Holstein-Friesian .cntdot. Guzera crossbred groups (1/4 to .gtoreq.31/32 European grade) on 65 farms stratified into high and low management classes. Milk, fat, and protein yield per lactation and per day of calving interval were analyzed with models including effects of management, farm, and year-season of freshening. Within-class regressions were fitted for direct gene effects and heterosis, or, alternatively, crossbred classification effect and its interaction with management class. The interaction between crossbred group and management class was important for most traits. In the high management class, component yield per day of calving interval declined slightly with increased European grade above the F1 for 3/4, 7/8, and .gtoreq. 31/32 crosses in the first lactation, but the four groups had similar second lactation performance. Grades 1/4and 5/8 (inter se) had very poor performance due to short lactations. In the low management class, performance declined substantially as the European gene fraction departed from 1/2. The additive breed difference (Holstein-Friesian minus Guzera) were large and positive for yield traits, and so were heterosis effects. The additive-dominance model adequately fitted F1 and backcross data but not inter se data.