Modeling the Impact of Birth and Twenty-Day Body Weight on the Postweaning Growth of Pigs

A stochastic pig BW growth model was developed to reproduce the nonlinear relationships between birth, weaning, and nursery exit BW to later grow-finish BW. Serial grow-finish BW measurements of barrows and gilts were fitted to mixed model generalized Michaelis-Menten equations. Two random effects of the generalized Michaelis-Menten equations were predicted as linear-quadratic functions of birth and 20-d weaning BW. Equations were developed to produce a population of pigs that reproduced the variances and covariance of the random effects. The stochastic model reproduced the variances of the random effects, serial BW, and days to achieve 125 kg BW. The simulation model also reproduced the nonlinear relationships of 20-d and 70-d BW with days to achieve 125 kg and 168-d BW. The simulation data slightly over-predicted 168-d BW and under-predicted days to reach 125-kg BW of barrows with 20-d BW less than 5 kg. Overall, the relationships between days to achieve 125 kg BW and 168-d BW with 70-d BW were similar for the actual and simulated data. The sorting of pigs into light and heavy groups based on weaning or nursery exit BW was evaluated. Sorting based on nursery exit BW was more effective in producing groups of pigs with large differences in days to 125 kg BW than sorting based on weaning BW. The model could be used to identify the optimal management of pigs to reduce variation in BW growth.