CHARACTERIZATION OF THE MONTANA LINE 4 INBRED HEREFORD HERD

Records for 1971 calves produced in the Line 4 Hereford herd at the Northern Agricultural Research Center (NARC) in Havre, Montana from 1976 to 2004 were analyzed to determine the current status of this closed herd. From 1976 to 1995, selection in this line was performed using an index of adjusted yearling weight minus 3.2 times adjusted birth weight. Since 1995, selection has been based on single trait selection for scrotal circumference. Records available across the majority of years included birth weight, weaning weight, weaning wither height, and weaning condition score. The average inbreeding coefficient for calves born in 2004 was 36.4%. Genetic parameters for all traits were analyzed using a univariate model. Estimates of direct heritability (and associated s.e.) were 0.51 (0.09), 0.21 (0.07), 0.28 (0.11), and 0.24 (0.09) for birth weight, weaning weight, weaning wither height, and weaning condition score, respectively. Estimates of maternal heritability were 0.08 (0.04), 0.09 (0.06), 0.13 (0.07), and 0.09 (0.07), respectively. The estimate of the direct-maternal genetic correlation was non-significant for most traits with estimates of 0.15 (0.26), -0.12 (0.35), -0.52 (0.22), and -0.48 (0.29), respectively. The proportion of variance due to maternal permanent environmental effects was only significant for weaning weight and weaning condition score with estimates of 0.30 (0.05) and 0.14 (0.04), respectively. Birth weight direct breeding value (DBV), maternal breeding value (MBV), and phenotypic trends were estimated to be -0.005, -0.004, and -0.034 kg/yr, respectively. Weaning weight trends were estimated to be +0.289, +0.082, and +0.276 kg/yr, respectively. Weaning wither height trends were +0.025, +0.010, and -0.130 cm/yr, respectively. Weaning condition score trends were +0.0061, - 0.0002, and +0.0040 score/yr. Trends for these traits are relatively flat for the period of time studied.