Genetic Trends of Protein Deposition and Amino Acid Needs of Pigs

Abstract Genetic selection and nutrition are two key factors contributing to improved efficiency and profitability in swine production. As pigs are increasingly selected for leaner carcasses and faster growth, understanding the associated genetic trends in protein deposition becomes critical. Such insights allow precise prediction of Lysine requirements, ensuring nutrition does not constrain the expression of genetic potential. The objective is to describe the genetic trends of PIC commercial growing finishing pigs, progeny of PIC Camborough sows and PIC 337 or 800 boars, and to explain how the genetic trends of protein deposition align with PIC Lysine recommendation. Knap et al. (2025) modeled genetic trends of protein deposition and Lysine requirement with a factorial approach using EBV of carcass growth rate, backfat, and loin depth of PIC 337 and PIC 800 progenies from Jan 2013 to May 2023. For either PIC 337 or 800, the results showed that lifetime carcass growth rate increased by 61.1 g/d, loin muscle depth increased by 5.7 mm with minor fluctuation in backfat depth in 10 years. Consequently, lean growth rate increased by 5.6 g/d per year, and average protein deposition increased by 1.8 g/d per year for 20- to 120-kg pigs. The greater capacity of lean growth largely reflects a higher plateau of protein deposition and reaching this plateau at a heavier body weight (Zaragoza et al., 2024). With more efficient lean growth, modern pigs require less time to reach the target market weight, as a greater proportion of daily nutrient pivots towards growth rather than maintenance, leading to improved feed efficiency. The daily SID Lysine requirement of growing finishing pigs (20 to 120 kg) is estimated to increase by 0.14 g/d per year according to genetic trends, this estimate using the factorial model also aligns with results from growth performance trials on Lysine response, which is 0.15 g/d per year according to PIC 2008 and 2021 PIC SID Lysine recommendation, with a minimum change in Lysine per kg gain. In addition to the overall increase in the volume of protein deposition, evidence suggested that the efficiency of lysine utilization is similar for pigs with different protein deposition (Batterham et al., 1990). Thus, changes in dietary lysine requirements will be proportional to increases in protein deposition. As pigs have been selected for faster carcass growth, this has also led to an increase in voluntary feed intake. However, the genetic trends for voluntary feed intake do not progress at the same speed as protein deposition, and the magnitude of this difference varies among genetic lines. Therefore, genetic trends in protein deposition and feed intake can provide guidance for adjusting the dietary SID Lysine to energy ratio or how frequently to update requirement estimates.