The world population is expected to hit 9 billion people by the year 2050. The need to efficiently and sustainably produce high quality nutritious food will be a key challenge for producers. Meat is a complete source of protein, B-vitamins, and other macronutrients, and a necessity for a balanced diet [1-2]. As the world population continues to grow and developing countries become more affluent, the demand for meat will increase. In order to efficiently and sustainably produce enough meat to satisfy the demand, research must be conducted to establish the biological differences between animals with differing feed efficiencies. It has long been established that traits such as breed, sex, age, and season (temperature) impact the ability of an animal to efficiently convert dietary energy to metabolic energy (ATP). However, these aforementioned factors do not explain all of the variations in efficiencies. These variations can be partly explained by calculating residual feed intake (RFI). The concept of RFI was developed to account for the difference between actual feed consumption and expected consumption given average daily gain [3] and backfat [4]. A low RFI value would indicate the animal is more efficient in the converting dietary energy to metabolic energy than its contemporaries. Similarly an animal with a high RFI value would consume more than expected based on average daily gain and backfat.

To understand and improve efficiency in meat production, the molecular differences between high and low RFI animals need to be better characterized. One of the end products of the conversion of dietary energy to metabolic energy is ATP. ATP is the metabolic currency of the cell. The mitochondria, known as the "power house of the cell," generates up to 90% of ATP produced by the cell. The molecular make up of the mitochondria may impact the efficiency of an animal. Investigations into the electron transport chain and the protein profile of mitochondria may provide evidence for the observed differences in efficiencies from animals genetically selected from RFI.

The electron transport chain is responsible for the conversion of the metabolic products originating from the TCA cycle into an energy gradient that is used to synthesize ATP from ADP. Superoxide anions are a form of reactive oxygen species (ROS) that originate from electron transport. Superoxide anions can cause oxidative stress and damage to cells and proteins. Energy is required to repair this oxidative damage, potentially leading to the partitioning of dietary energy away from protein accretion and growth towards cellular repair and replacement. In addition to ROS damage, the protein profile of mitochondria may hold clues as to the overall molecular differences between animals genetically selected for high and low RFI. Changes in the abundance of proteins related to ATP production, antioxidant defenses, and cell rescue could provide clues for the observed differences in RFI. Our overall objective was to determine potential molecular differences in the mitochondria using pigs genetically selected for RFI status as a model.

Our data show there is a tissue specific increase in ROS production from the mitochondria in the less efficient, high RFI line. Coupled with the increase in ROS, proteins related to ATP production and cellular rescue were more abundant in the more efficient low RFI line. In addition to the data comparing RFI lines, a minimal difference in the protein profile was observed when animals separated by RFI phenotype irrespective of line.

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[2] Murphy MM, Spungen JH, Bi X, Barraj LM. Fresh and fresh lean pork are substantial sources of key nutrients when these products are consumed by adults in the United States. Nutrition Research. 2011;31:776-83.

[3] Boddicker N, Gabler NK, Spurlock ME, Nettleton D, Dekkers JCM. Effects of ad libitum and restricted feeding on early production performance and body composition of Yorkshire pigs selected for reduced residual feed intake. Anim. 2011;5:1344-53.

[4] Koch RM, Gregory KE, Chambers D, Swiger LA. Efficiency of feed use in beef cattle. J. Anim. Sci. 1963;22:486-94.