Interaction of Maternal Grandsire with Region of United States and Herd for Calving Ease, Birth Weight and 205-day Weight

Field records supplied by the American Simmental Association from 2-yr-old dams were used to study maternal grandsire • region of the U.S. and maternal grandsire • herd within region (herd/region) interactions. Regions were 1) Montana, North Dakota and South Dakota, 2) Kansas and Nebraska, 3) Texas and Oklahoma and 4) Alabama, Florida, Georgia, Louisiana and Mississippi. Analyses were conducted pairwise with respect to region with the following number of animals in each comparison: 1 (3,964) vs 2 (2,239), 1 (3,996) vs 3 (1,660), 1 (3,418) vs 4 (474), 2 (2,033) vs 3 (1,709), 2 (1,666) vs 4 (443) and 3 (1,372) vs 4 (430). Independent variables were the fixed effects of region, sex of calf, Simmental percentage of the calf (75 to 88%) and the random effects of herd/region, maternal grandsire, maternal grandsire • region and maternal grandsire • herd/ region. Records were adjusted to account for the direct effect of maternal grandsire in the maternal grandsire component. Dependent variables were calving ease score, birth weight and 205-d weight. Region was significant in all analyses except for 1 vs 2, 1 vs 3 and 2 vs 3 for calving ease score and 2 vs 3 for birth weight and 205-d weight. Herd/region was significant in all analyses. Maternal grandsire was significant in all analyses for calving ease score and birth weight and for 1 vs 2 for 205-d weight. Maternal grandsire X region was not significant in any analysis. Maternal grandsire X herd/region was significant in four of six analyses for birth weight and 205-d weight, but was not significant in any analysis for calving ease score. Maternal grandsire, maternal grandsire X region interaction and maternal grandsire • herd/region interaction accounted for an average of 4, 0 and 1%; 3, 0 and 5%; and 0, 0 and 3% of the total variation for calving ease, birth weight and 205-d weight, respectively. Genetic correlations of maternal grandsires' progeny performance in different herds ranged from .20 to .74 for birth weight and from .05 to .34 for 205-d weight, indicating significant changes in rank from herd to herd. (