Relationships among sow productivity traits within purebred and crossbred litters

The purpose of this study was to evaluate the relationships of litter weaning weight (LWW), number weaned (NW), mean pig weaning weight (PWT), litter birth weight (LBW), and survival percentage (%S) with number after transfer (NAT) and number born alive (NBA) on purebred and crossbred litters. Data consisted of purebred Duroc (29,297), Landrace (34,177), and Yorkshire litters (40,301) as well as Yorkshire×Landrace (8061) and Landrace×Yorkshire (4028) crossbred litters. The data were distributed into 4 time periods of 1980 through 1997, 1998 through 2002, 2003 through 2008, and 2009 through 2011. All variables were initially modeled with the fixed effects of litter breed, period, NAT, farm, parity-age class (P-AC) groupings and interactions, and random effects of sow and contemporary group. Non-significant variables and interactions (. P>0.05) were removed from final models. Periods 1 and 2 as well as 3 and 4 were combined based on non-significant main effects and interactions. The effect of NAT on LWW differed by time period (. P<0.01) such that heavier litters were achieved at larger litter sizes (NAT>11) in Landrace and Yorkshire litters (. P<0.05) in period 2. Mean PWT decreased as NAT increased with less effect on PWT during the second time period. Also %S decreased in a linear fashion from 6 to 12 NAT then decreased at an increasing rate for NAT>12, with a slight increase in %S over time for all breeds. Number weaned increased in a linear fashion up to NAT equal to 11 then increased at a decreasing rate to a maximum value depending on breed; above that value of NAT, NW decreased. There were no significant (. P>0.05) NBA by parity interactions for traits that were measured after processing and transfer. In every statistical analysis, farm was a significant and major source of variation. Also %S, and NW were greatly affected by NAT, and LBW was greatly affected by total number of pigs born (TNB). As litter size increases, greater emphasis should be placed on preweaning survival. The data indicate the effects of NAT on LWW, and PWT should be revaluated periodically.