Growth, puberty and pregnancy were studied in 665 crossbred heifers produced by breeding Hereford and Angus cows to Hereford, Angus, Red Poll, Brown Swiss, Gelbvieh, Maine Anjou, and Chianina sires. Estrus was determined from an average of 240 to 476 days of age. Puberty age was defined as age at first observed, standing estrus followed by an estrus within 45 days, except during the last 45 days of estrus detection when it was defined as first standing estrus. Heifers were bred by artificial insemination for 42 days and naturally for 22 days from an average age of 412 to 476 days. Brown Swiss, Gelbvieh, Maine Anjou and Chianina crosses were 5 to 7% heavier (P<.01), while Red Poll crosses were not different (P>.05) from the Hereford-Angus crosses at the 200-day weight. Compared to Hereford-Angus crosses at 400 days of age, Maine Anjou, Chianina and Gelbvieh crosses were 5 to 8% heav ie r ( (P< .01 ) , Red Poll crosses were 4% lighter (P<.01), and Brown Swiss were 3% heavier (P>.05). Sire breed influenced (P<.01) puber ty age and percentage of heifers reaching puberty by 270 to 450 days of age. Sire breed groups divided into three groups for puberty age with Gelbvieh (343 + 5), Brown Swiss (349 +4), and Red Poll (354 -+ 5) crosses the youngest (P<.01), Chianina (401 + 5) crosses the oldest (P<.01), and Maine Anjou (374 -+ 5) and Hereford-Angus (374 _+ 5) crosses intermediate. Chianina crosses were heaviest at puberty (319

An elite, three-generation family from the USDA Meat Animal Research Center twinning population was examined for evidence of ovulation rate quantitative trait loci (QTL). This work was both a continuation of previously reported results suggesting evidence for ovulation rate QTL on bovine Chromosome (Chr) 7 and an extension of a genome-wide search for QTL. Additional markers were typed on Chr 7 to facilitate interval mapping and testing of the hypothesis of one versus two QTL on that chromosome. In addition, 14 other informative markers were added to a selective genotyping genome screening of this family, and markers exhibiting nominal significance were used to identify chromosomal regions that were then subjected to more exhaustive analysis. For Chr 7, a total of 12 markers were typed over a region spanning the proximal two-thirds of the chromosome. Results from interval mapping analyses indicated evidence suggestive of the presence of QTL (nominal P < 0.00077) within this region. Subsequent analysis with a model postulating two QTL provided evidence (P < 0.05) for two rather than one QTL on this chromosome. Preliminary analysis with additional markers indicated nominal significance (P < 0.05) for regions of Chrs 5, 10, and 19. Each of these regions was then typed with additional markers for the entire three-generation pedigree. Significant evidence (P < 0.000026) of ovulation rate QTL was found for Chrs 5 and 19, while support on Chr 10 failed to exceed a suggestive linkage threshold (P > 0.00077).

Breed differences in performance characteristics are an important genetic resource for improving efficiency of beef production. Diverse breeds are required to exploit heterosis and complementarity through crossbreeding and new composite breeds and to match genetic potential with diverse markets, feed resources and climates. This report presents results from the Germplasm Evaluation Program at the Roman L. Hruska U.S. Meat Animal Research Center (MARC) to characterize breeds of cattle representing diverse biological types for bioeconomic traits that influence quantity and value of production.