Evaluation of the Impact of Pig Birth Weight on Grow-Finish Performance, Backfat Depth, and Loin Depth

The effect of birth BW on pig growth was studied in 1,932 barrows and gilts. The pigs were weighed at birth, weaning, and exiting the nursery. The pigs were weighed and measured ultrasonically at approximately 28-d intervals from 74 to 158 d of age. Daily feed intake data were recorded via an electronic feeder from 38 kg BW to the end of test. The relationships of the pig growth variables, carcass predicted percentage lean, and predicted days to achieve 125 kg BW to birth BW were evaluated via regression analyses. Equations fitting ultrasonic loin depths at 46.7, 64.6, 83.5, and 102.5 kg BW included significant (P < 0.05) linear, quadratic, and cubic birth BW variables. At market BW, pigs with birth BW of 1.0 kg had 1% less predicted lean than pigs with birth BW of 2.0 kg. Pig ADG had linear-quadratic relationships (P < 0.001) to birth BW in the gilts and linear-quadratic-cubic relationships (P < 0.02) to birth BW in the barrows. Regression equations predicted that increasing the birth BW of pigs with below-average birth BW had a greater impact on increasing the ADG than increasing the birth BW of pigs with average or above-average birth BW. No relationships (P > 0.60) were found between daily feed intakes and birth BW. Feed conversion (feed:gain) had linear or linear-quadratic relationships (P < 0.05) to birth BW. Pigs with birth BW less than 1.1 kg had greater feed:gain, more days to achieve 125 kg, and decreased predicted percentage lean than pigs with birth BW greater than 1.1 kg.