The protein/energy ratio is important for the production performance and utilization of available feed resources by animals. Increased protein consumption by mammals leads to elevated feed costs and increased nitrogen release into the environment. Livestock producers use nutritional modifiers in an attempt to increase protein accretion in the muscle, while they often simultaneously reduce fat deposition. The pattern of fat deposition in pigs in the growing-finishing phase affects carcass and meat quality. According to Ph.D candidate LIU Yingying from Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA), the livestock industry faces the challenge of increasing the intramuscular fat (IMF) content of pork so that consumers may have a satisfactory experience, while simultaneously producing minimal visible fat, which is a deterrent to health-conscious consumers.

By using two types of pig breeds, Bama mini-pigs (Sus scrofa domestica), a Chinese indigenous mini-pig breed and Landrace pig, a representative lean genotype, LIU Yingying and her colleagues analyzed the effects of two dietary treatment groups (Chinese conventional diet with low protein/energy ratio or National Research Council diet with high protein/energy ratio) on the growth performance, muscle development, and plasma metabolites (which are indicators of nitrogen metabolism) in two pig breeds at different phases of growth.

The researchers observed significant interactions between breed and diet for total fat percentage, IMF content, protein content in biceps femoris (BF) muscle, and plasma urea nitrogen (UN) concentration in the nursery phase; for average daily gain (ADG), average daily feed intake (ADFI), dry matter, IMF content in psoas major (PM) muscle, and plasma total protein and albumin concentrations in the growing phase; and for drip loss and plasma UN concentration in the finishing phase. Breed influenced growth performance, carcass traits, and meat quality, but not plasma metabolites. Throughout the trial, Landrace pigs showed significantly higher ADG, ADFI, dressing percentage, lean mass rate, and loin-eye area than did Bama mini-pigs, but significantly lower feed/gain ratio, fat percentage, backfat thickness, and IMF content. Dietary protein/energy ratio influenced the pH value, chemical composition of BF and PM muscles, and plasma activities of glutamic-pyruvic transaminase and gamma-glutamyl transpeptidase, and plasma concentration of UN.

This study indicates that Bama mini-pigs showed slower growth and lower carcass performance, but had better meat quality, when compared with Landrace pigs. Moreover, unlike Landrace pigs, the dietary protein/energy ratio did not affect the growth performance of Bama mini-pigs. These results suggest that, in swine production, low dietary protein/energy ratio may be useful for reducing feed costs and minimizing the adverse effects of ammonia release into the environment.

The article has been published on Journal of Animal Science and Biotechnology (DOI 10.1186/s40104-015-0036-x),details can be found at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4537580/