|Hutchison, Jana - Edwards|
Submitted to: Journal of Dairy Science
Publication Type: Abstract only
Publication Acceptance Date: 2/28/2005
Publication Date: 7/24/2005
Citation: Kuhn, M.T., Hutchison, J.L. 2005. Factors affecting heifer fertility in US Holsteins [abstract]. Journal of Dairy Science. 88(Suppl. 1):11. Interpretive Summary:
Technical Abstract: Heifer breedings from January 2003 to October 2004 were used to investigate factors affecting heifer fertility. There were 331,469 breedings on 220,624 Holstein heifers. Only artificial inseminations were analyzed. Age at breeding was required to be between 8 months and 3 years. Only 0.33% of breedings occurred at ages > 2.5 years; 98.2% of all breedings were at ages < 2 years. The dependent variable for analysis was 0 (no conception) or 1 (conception). A heifer's last recorded service was considered a success. Breedings were included only if there was at least 2 months for a repeated service to be reported. The linear model for analysis included the fixed effects of herd, year, month, and age-at-breeding, and the covariates of parent average predicted breeding value for milk, SCS, and daughter pregnancy rate (DPR). The overall arithmetic mean conception rate was 0.64 with a 0.48 standard deviation. The only factors that did not have a significant effect on heifer conception were parent average breeding values for milk and SCS. Year accounted for the most variation in heifer conception rate. Year 2004 had a 6% higher conception rate than 2003. This may be a realistic difference between years or it may indicate that additional editing needs to be investigated. Perhaps 2 months is not an adequate amount of time to wait for a reported service in the case of heifers. Month of breeding accounted for the second largest amount of variation with January and February having the poorest conception rates and September and October having the best. Parent average breeding value for DPR accounted for the third most variation with conception rate increasing as DPR increased. Selection on DPR will improve fertility in heifers as well. Age at breeding accounted for more variation than herd; conception rates increased with age. Further research will investigate appropriate edits for heifer breedings and also compare linear model results to results from logistic and probit models.