Reproductive Responses in the NE Index Line Estimated in Pure-line and Crossbred Litters
2002 University of Nebraska-Lincoln Extension Swine Report. The NE Index Line (Line I) has been selected since 1981 only for litter size and as a pure-line has 3.5 to 4 more pigs per litter than its randomly selected control (Line C). Line I has been released to the industry where it is being used in crossbreeding applications, but whether the response realized in the pure-line is expressed in crossbreeding applications is not known. The objective of this experiment was to estimate responses in reproduction in Line I in pure-line sows, in pure-line sows mated to produce F1 litters and in F1 sows mated to produce three-way cross litters. A total of 850 litters were produced over six-year seasons. There were 224 pure-line I and C litters, 393 F1 litters produced from I and C females mated with Danbred USA Landrace (L) or DH (T) boars, and 233 litters by IxL and CxL females mated with T boars. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. Farrowing rate of Lines I and C (93.3 vs 91.8%) did not differ. Averaged across all groups, mean number born alive per litter and number and weight of pigs weaned per litter, both adjusted for number nursed and weaning age of 12 days, were 10.1 pigs, 9.7 pigs, and 75.9 lb, respectively. Direct genetic effects of I were greater (P < 0.05) than C for total born (3.53 pigs), number born alive (2.53 pigs), number of mummified pigs (0.22 pigs), and litter birth weight (4.72 lb). Line I was less than C (P < 0.05) for litter weaning weight (4.15 lb). However, interactions of line effects with crossing system were significant. In pure-line litters, I exceeded C by 4.18 total pigs and 1.76 stillborn pigs per litter; whereas in F1 litters the difference between I and C was 2.74 total pigs and 0.78 stillborn pigs per litter. The contrast between I and C for number weaned and litter weaning weight in pure-line litters was 0.32 pigs and -0.62 lb, respectively, compared with 0.25 pigs and -4.72 lb in F1 litters. Reproductive performance of Line I substantially exceeds that of the control line. Although the response realized in crossbreeding applications was somewhat less than in the pureline, crossbreeding is an effective way to utilize the enhanced reproductive efficiency of the Index line.