Economic weights for feed intake in the growing pig derived from a growth model and an economic model

Economic weights are obtained for feed intake using a growth model and an economic model. The underlying concept of the growth model is the linear plateau model. Parameters of this model are the marginal ratio (MR) of extra fat and extra protein deposition with increasing feed intake (FI) and the maximum protein deposition (Pd_max). The optimum feed intake (FI₀) is defined as the minimum feed intake that meets energy requirements for Pd_max. The effect of varying FI and MR on performance traits was determined.An increase in FI results in a larger increase in growth rate with lower MR. For a given MR, feed conversion ratio is lowest when FI equals FI₀. Lean meat percentage (LMP) is largest for a low MR in combination with a low FI. The decrease in LMP with higher FI is largest when FI exceeds FI₀.Economic weights for FI, MR and Pd_max depend on FI in relation to FI₀.Economic weights for FI are positive when FI is less than FI₀ and negative when FI is larger than FI₀. The MR has only then a negative economic weight, when FI is below FI₀.Economic weights of FI and MR have a larger magnitude with lower MR and lower FI. In contrast, economic weights for growth rate and FI derived from the economic model only change in magnitude and not in sign with different levels of these traits. The economic model always puts a negative economic weight on FI since it expresses profit due to a decrease in FI with constant growth rate and LMP. This holds the risk of continuous decrease in FI in pig breeding programs. In contrast, the use of growth models for genetic improvement allows direct selection for an optimum feed intake which maximizes feed efficiency in combination with maximum lean meat growth. It is concluded that recording procedures have to be adapted to collect the data necessary to implement growth models in practical pig breeding applications.