Analysis of Pig Growth from Birth to Sixty Days of Age1

Abstract Alternative versions of common nonlinear growth functions were evaluated on 433 pigs (220 gilts and 213 barrows) from birth to 61 d of age. Pigs were weighed at birth, weaning (19 d of age; SD = 2.4 d), 19 d postweaning, and 42 d postweaning. The model with the best fit based on residual standard derivation (RSD) was BW = exp [(b 0 + b 1 (age + 35) + b 2 (age + 35) 2 )], which fit each individual pig’s BW data to the function. Although the function resulted in the smallest RSD (0.336 kg), it did not predict birth BW (R = 0.65) as precisely as it predicted weaning BW and later BW (R = 0.96 to 099). Also, the RSD was different at the four weigh dates and ranged from 0.04 to 0.45 kg. Birth BW had a linear-quadratic relationship with subsequent BW. Increasing birth BW of pigs with lighter birth BW had a much greater impact on increasing subsequent BW than increasing birth BW of the heaviest pigs. Also, BW taken at 19 and 42 d postweaning had linear-quadratic relationships with weaning BW. The linear-quadratic relationships between the actual BW were predicted by fitting the exponential function to each pig’s BW data. The relationships amongst the b 0 , b 1 , and b 2 values of the pigs were nonlinear and complex. The results indicate that increasing the BW of the lightest birth BW pigs could increase the mean and decrease the variance in BW at subsequent ages.