Relationship between carcase traits of Bos taurus genotypes and ultrasound measurements across six stages of growth from weaning through to long-feedlot finishing

Abstract

<p><b>Context.</b> Identification earlier in life of beef cattle with capacity for increased marbling, improved carcase yield and/or reduced subcutaneous fatness can facilitate more rapid genetic improvement and identification of cattle more appropriate for feedlot or pasture finishing. Earlier in life, ultrasound predictions have potential for significant improvements in compliance with market specifications and overall efficiency of beef production systems. <b>Aims.</b> To assess the relationships just prior to slaughter and earlier in life between measurements of intramuscular fat, subcutaneous fat and eye-muscle (Longissimus thoracis et lumborum) cross-sectional area made using ultrasound, and carcase fatness, muscling and yield measurements following slaughter of Bos taurus steers that differed genetically in potential for subcutaneous fatness and marbling. <b>Methods.</b> Ultrasound measurements of intramuscular fat (IMF),rib fat (RFT), P8 rump fat (P8FAT), eye-muscle area (EMA) and retail beef yield (RBY) of cattle heterogeneous for marbling and fat distribution were made at six stages of growth from weaning to long-feedlotting. Carcase measurements of the same traits were made at five stages of growth from weaning through to long-feedlotting. <b>Key results.</b> IMF ultrasound scans 168 days post-weaning were more strongly correlated (<i>r</i> ≤ 0.79) with marbling in the carcase following long-feedlotting than were IMF ultrasound scans at the end of backgrounding (<i>r</i> ≤ 0.71, 326 days post-weaning), short-feedlotting (<i>r</i> ≤ 0.69, 431 days) and during (<i>r</i> ≤ 0.59, 521 days) and at the end of long-feedlotting (<i>r</i> ≤ 0.53, 585 days). P8FAT was the trait with the highest and most consistent accuracy across all stages of life (<i>r</i> = 0.80) between ultrasound and carcase measurements of P8FAT. <b>Conclusions.</b> The results of the present study showed that ultrasound scanned measures of carcase IMF, subcutaneous fat and EMA can be used to predict carcase characteristics with good accuracy earlier in life. <b>Implications.</b> The finding that prediction of marbling in the carcase of long-feedlot-fed cattle was stronger by using ultrasound measurement of IMF in younger post-weaned cattle than in older post-weaned cattle warrants further investigation for genetic improvement and management applications, including using newer scanning technologies.</p>