Effects of selection for ultrasound intramuscular fat percentage in Angus bulls on carcass traits of progeny

Abstract

Angus bulls (n = 20) from three pure-bred herds in Georgia were acquired to determine the impact of selecting sires based on phenotypic yearling ultrasound intramuscular fat percentage (UIMF) or UIMF EPD on marbling score of steer progeny. Each year in each herd, pairs of bulls were selected to create large differences based on their age adjusted phenotypic yearling UIMF measurements. The average UIMF, weighted by number of progeny per sire, was 3.75% (SD = 1.10%) and 1.70% (SD = 0.53%) for high UIMF (HU) and low UIMF (LU) bulls, respectively. All available ultrasound measurements collected in the purebred co-operator herds were combined with other ultrasound records collected by the American Angus Association for the computation of genetic values for ultrasound fat thickness, ribeye area, and intramuscular fat percentage. Each year bulls were randomly mated to 14 to 30 commercial Angus females. Carcass weight, fat thickness at the 12th rib, ribeye area at the 12th rib, marbling score, yield grade, and quality-grade measurements were collected on 188 steer progeny. Carcass data were linearly adjusted to 480 d of age at slaughter. Steer progeny sired by HU bulls had higher age-adjusted marbling score and quality grade (P < 0.05), and smaller age-adjusted ribeye area (P < 0.05) than steer progeny sired by LU bulls. No significant differences between phenotypic UIMF lines were found for age-adjusted fat thickness (P = 0.84) and yield grade (P = 0.33) in the steer progeny. The regression of age-adjusted carcass marbling score and quality grade of the steer progeny on ultrasound intramuscular fat percentage EPD of the sires produced highly significant regression coefficients of 90.50 and 49.20, respectively. Thus, yearling Angus bulls selected for high-phenotypic UIMF and UIMF EPD can be expected to produce steer progeny with significantly higher amounts of marbling and quality grade. It also appears that marbling can be increased without corresponding increases in external fat thickness and yield grade.

On the determination of residual feed intake and associations of infrared thermography with efficiency and ultrasound traits in beef bulls

“…However, marbling is affected by breed (Zembayashi, 1994), fattening period (Lengyel et al, 2003) and diet (Andrae et al, 2001). In addition, animal category can also influence marbling content, despite the fact that yearling bulls have much lower levels of intramuscular fat than finished cattle (steers and heifers), sires selected for marbling content based on their own scanned marbling score produce steer progeny with greater amounts of marbling (Sapp et al, 2002). Therefore, marbling might be relevant for RFI determination under situations where the factors affecting marbling exhibit a greater variation than that observed in the present study.…”

Intramuscular fat content in meat-producing animals: development, genetic and nutritional control, and identification of putative markers

“…As marbling score in these animals is genetically highly correlated with muscle lipid content (r G 5 0.91), selection based on the former may lead to a correlated improvement in tenderness (for review, see Hocquette et al, 2006). This relationship explains most of the efforts dedicated to the development of live scanning for IMF content as a selection tool in the United States and Australia (Reverter et al, Intramuscular fat content in meat-producing animals 2000; Hassen et al, 2001;Sapp et al, 2002). However, as marbling is positively genetically correlated to the carcass fatness, the undesirable side effects of selection on the basis of IMF content or marbling are often the increase in carcass fatness.…”

Prediction of intramuscular fat by ultrasound in lean cattle

“…The heritability for USIMF in yearlings has been reported varying from 0.23 (Devitt and Wilton, 2001) to 0.50 (Hassen et al, 2003). Sapp et al (2002) reported higher marbling and quality grade in carcasses of offspring from Angus bulls selected for high USIMF. This was in accordance with Devitt and Wilton (2001), who estimated a genetic correlation (r g ) of 0.80 between steer carcass marbling score and bull USIMF based on half-sib relationships.…”