1943
Effects of parity and selection for uterine capacity on sow litter performance traits
Selection for 11 generations for uterine capacity (UC) was previously reported to increase litter size in gilts by 1.6 more fully formed pigs at birth compared to an unselected control line (CO) despite averaging 1 less ova shed. Our objective was to characterize litter performance traits in each line from subsequent sow parities following a shift in management scheme to a continuous flow farrowing system that more closely resembles industry conditions. Gilts entered into the system and were farrowed in contemporary groups of a maximum of 19 litters and maintained in this system through four parities if successfully mated in that contemporary group. A total of 203 litters (90 CO, 103 UC; 101 Parity 1, 49 Parity 2, 33 Parity 3; and 20 Parity 4) were analyzed. A mixed model analysis of variance was conducted. Fixed effects of farrowing group, line, parity (1-4), and two-way interactions involving line were fitted. The random effect of sire (n = 75) of the litter within farrowing group and line was included in the model. UC line averaged 1.3 ± 0.38 greater (P < 0.01) pigs born alive with 0.5 ± 0.14 fewer (P < 0.01) stillbirths than CO. Average pig birth weight was similar (P = 0.99) between lines, thus the UC line exceeded (P < 0.05) the CO line by 1.1 ± 0.38 kg in litter birth weight. UC line averaged 1.6 ± 0.32 greater (P < 0.001) pigs weaned than CO. Average pig wean weight was similar (P = 0.64) between lines, thus the UC line exceeded (P<0.05) the CO line by 6.0 ± 2.07 kg in litter wean weight. Parity effects were observed as expected from first through fourth parities and no interactions of parity effects were observed with line. Improved reproductive performance of the UC line was maintained in sow litters similar to those previously measured in gilts. Selection for uterine capacity improved fetal survival resulting in increased number born alive with a similar average birth weight. This resulted in an increase in total weaning weight of sows through four parities.
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Keywords: Pigs, Selection, Uterine Capacity