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Effects of inbreeding and age at first calving on milk yield and failed services in first lactation of bST and non-bST treated Holstein cows
Production and reproduction records on first lactation Holstein cows were used to study effects of inbreeding (F) and age at first calving (AFC) on milk yield and failed services (FS). For milk yield (305d), records of 123,639 registered Holstein heifers were used to compare linear regression, fixed factor, saturated and cubic spline (CS) for modeling effects of F and AFC under bST and non-bST treatments. Thirty seven models were compared using Lack of Fit test and Akaike Information Criteria while fixing the animal genetic variance. Four models were detected as best fitting the data: CS for F at 4, 5, 6 and 7 knots with CS for AFC at 5 knots. There were no significant differences in effects of F and AFC under different bST treatments. Cows treated with bST produced 434 kg more milk than non-treated cows. Inbreeding greater than 6.25% significantly reduced milk yield. Milk yield significantly increased with increases in AFC. Heritability of milk yield was estimated to be 0.33. For FS, treated as a binary trait, reproduction records of 121,518 first lactation cows were used. Cows with at least one bST treatment prior to first service were considered bST treated animals. Cows with three or more FS received a score of 1 indicating reproductive problems. Effects of F and AFC were not significantly different under different bST treatments. Odds of three or more FS were 11 times greater in bST treated cows. For F, odds of three or more FS were highest for inbreeding between 12.5% and 18.75%. For AFC, heifers calving between 22 and 26 months had significantly smaller odds of three or more FS than heifers calving at earlier or later ages. Heritability was 0.37 on the underlined normal scale and 0.158 on the observed scale.^
Biology, Animal Physiology|Agriculture, Animal Culture and Nutrition
Geha, Makram J, "Effects of inbreeding and age at first calving on milk yield and failed services in first lactation of bST and non-bST treated Holstein cows" (2009). ETD collection for University of Nebraska - Lincoln. AAI3352316.