|Goodling, Jr., R|
Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/24/2011
Publication Date: 6/30/2011
Citation: Dechow, C.D., Norman, H.D., Goodling, Jr., R.C., Wright, J.R. 2011. The association of high and low parent average with daughter performance for yield, somatic cell score, and productive life in individual herds. Journal of Animal Science 89(E-Suppl. 1)/Journal of Dairy Science 94(E-Suppl. 1):28(abstr. M70). Interpretive Summary:
Technical Abstract: There have been efforts to demonstrate to dairy producers the value of genetic selection by evaluating response to selection within their own herds. The objective of this study was to evaluate how frequently results conform to expectations for various traits and for herds of varying sizes. Parent averages (PAVG) and standardized records of milk yield, fat yield, protein yield, somatic cell score (SCS), and productive life (PL) were obtained from the Animal Improvement Programs Laboratory at USDA for 1,042,361 sire-identified Holstein cows that calved from 2005 through 2009 in 3334 Pennsylvania herds. Parent averages were obtained from evaluations occurring before a cow’s first calving date to prevent part-whole bias. The top 25 percent (Q1) and bottom 25 percent (Q4) of cows for PAVG were identified within each herd and year of calving for each trait. The mean milk, fat and protein yield, SCS, and PL in Q1 and Q4 was determined for all herd-years. Results conformed to expectations when the average for Q1 exceeded the average for Q4. A majority of herd-years had higher values for Q1 cows than Q4 cows regardless of the number of sire-identified daughters present in the herd, with results ranging from 60 percent for PL to 78 percent for fat yield. The mean difference in PA from Q1 to Q4 for fat yield was 34 kg, which was close to the phenotypic difference in fat yield (36 kg). For productive life, the mean difference in average PA from Q1 to Q4 (4.8 months) was greater than the phenotypic difference (1.5 months). Greater than 89 percent of herd-years met expectations for yield traits when the number of cows exceeded 10 in each quartile, compared with 74 percent of herd-years for SCS and 67 percent of herd-years for PL. All herds with 125 or more cows per quartile met expectations for yield traits compared with 98 percent for SCS and 68 percent for PL. Within-herd comparison of top and bottom cows for PAVG demonstrated a favorable response to selection for yield traits even in herds with relatively few sire-identified daughters. Results were less predictable for lower heritability traits, but the majority of herd-years still conformed to expectations.