Is visceral organ size related to feed efficiency in tropical hair sheep?

Abstract

The residual feed intake (RFI) and residual intake and gain (RIG) are indices that measure ruminant feed efficiency. Their application has become alternatives to improve the profitability of intensive lamb production systems. This study aimed to evaluate the accuracy of RFI and RIG to measure the non-carcase organ size and cavitary fat of lambs. Thirty non-castrated male lambs were fed for 92 days and slaughtered, and non-carcase organs were weighed. RFI and RIG were classified in low, medium and high efficiency groups, and correlated to carcase and non-carcase organ size. The average RFI values were 0.07, 0.00, and −0.07 kg DM/d and the RIG values were 1.86, −0.20, and −1.91, for high, medium and low, respectively. Low-RFI lambs had lower (p < .05) dry matter intake (DMI) and percentage of DMI standardised by metabolic weight. High-RIG lambs had a higher feed conversion ratio (p ≤ .05) and tended (p < .10) towards higher average dairy gain. The efficient lambs (low-RFI and high-RIG) had a higher heart weight (p ≤ .05). Trends (p < .10) towards higher blood volume and lower relative weight in omental and total cavitary fat deposits were found in lambs with low RFI. Lambs classified as low-RFI and high-RIG had larger hearts, which could be related to improved cardiovascular performance and feed efficiency. Highlights Heart size is related to feed efficiency. Lambs with improved feed efficiency have larger hearts. High-RIG lambs have higher intestinal mass.