Phenotypic relationships between residual measurements of finishing feed efficiency and visceral organ mass of backgrounded beef steers

Abstract Text: Residual measurements of feed efficiency for beef cattle have recently gained popularity among producers, breed associations and researchers alike. Efforts devoted toward identifying the underlying physiological mechanisms have been met with limited success.  Visceral organs play major roles in nutrient digestion, absorption and metabolism, and are considered to be substantial contributors to animal energy requirements for maintenance.  As such, an experiment was conducted to determine phenotypic relationships between individual visceral organ mass (VOM) and residual measurements of finishing feed efficiency of backgrounded beef steers.  Conventionally- and early-weaned steer progeny (N = 105) from four calving seasons within a single herd were finished on a concentrate-based ration for 110 ± 34 d within contemporary group immediately following a 150 ± 60 d backgrounding period.  Finishing ADFI and BW were collected at 28 day intervals throughout the duration of the finishing period and used to calculate average daily finishing residual feed intake (RFI) and residual ADG (RADG) using a relatively large sample population.  A subsample of steers (N = 28) from the sample population utilized to determine RFI and RADG were harvested upon reaching an ultrasound predicted 12^th rib subcutaneous fat thickness of 1 cm and utilized to measure emptied and cleaned individual VOM.  Visceral organs measured included the heart, liver, gallbladder, lungs, kidneys, spleen, rumen, reticulum, omasum, abomasum, small intestine, pancreas, cecum, and colon and rectum.  All statistical analyses were conducted using JMP Pro.  Multivariate analysis of VOM and RFI, as well as VOM and RADG using the multivariate and correlations procedure revealed inverse relationships (P < 0.05) between RFI and mass of the lungs, spleen and rumen (r = -0.57, -0.44 and -0.46, respectively), as well as a correlation (P < 0.05) between RADG and lung mass (r = 0.42).  No relationships existed (P > 0.05) between RFI and mass of the heart, liver, gallbladder, kidneys, reticulum, omasum, abomasum, small intestine, pancreas cecum, and colon and rectum, or between RADG and mass of the heart, liver, gallbladder, kidneys, spleen, rumen, reticulum, omasum, abomasum, small intestine, pancreas, cecum, and colon and rectum.  Collective interpretation of these results suggests a direct phenotypic relationship between mass of the lungs and residual measurements of finishing feed efficiency for backgrounded steers.  Further research is necessary to evaluate the metabolic implications of the lungs and spleen to nutrient metabolism, cattle growth and feed efficiency.

Keywords: beef, efficiency, intake