Comparison of litter adjustment factors in Yorkshire and Landrace data

National Swine Improvement Federation (NSIF) adjustment factors presently used to standardize litter data for age at 21 d, number born alive (NBA), 21-d litter weight, and number after transfer (NAT) were evaluated using 104,884 litters in 1,348 Yorkshire herds and 20,370 litters in 197 Landrace herds. In addition, adjustment factors for number weaned were calculated for standardization of this trait. Number weaned is adjusted for parity and NAT. The mixed-model least squares, maximum likelihood computer program described by Harvey was used in the analyses. Yorkshire and Landrace data were combined to test for breed effects and interactions involving breed. Breed interactions were different (P < .05). Therefore, breed-specific adjustment factors were calculated for Yorkshire and Landrace data sets. Also, adjustment factors were calculated for combined data that might be appropriate to use for breeds without specific adjustments available. Parity adjustment factors for NBA and 21-d litter weight were different (P < .05) from current NSIF recommendations, as was the NAT adjustment for 21-d litter weight. The age-at-weaning multiplicative factors were not different (P > .05) from current NSIF values. However, in all three data sets, the intercepts and linear coefficients of the quadratic regression for age at weaning were different (P < .05) from NSIF's. A Student-Newman-Keuls (SNK) test was used to evaluate the NSIF groupings of parity and number after transfer.(ABSTRACT TRUNCATED AT 250 WORDS)