The objective of this study was to determine the effect of genotype and carcass conformation class on the slaughter quality of 200 young bulls, including 108 crossbred beef bulls and 92 Holstein- Friesians (HF), aged 21-22 months, selected in the lairage. The lean meat content was estimated and body measurements were taken before slaughter. After slaughter, the carcasses were graded according to the EUROP system, and carcass quality parameters were determined. Intramuscular fat was extracted from samples of m. longissimus dorsi, and the fatty acid profile of extracted fat was determined by gas chromatography. 61.11% carcasses of crossbred beef bulls were graded in the conformation class R, and 56.53% carcasses of Holstein-Friesians were classified as O. The majority of carcasses belonged to fat class 2, which was not consistent with intramuscular fat content. Within the same conformation classes, crossbred beef bulls were characterized by higher slaughter quality than Holstein-Friesian bulls. Meat from hybrid beef bulls had a higher (by 0.42% on average) content of fat with a more desirable composition. Since the population size of beef cattle will probably not increase in the nearest future, efforts should be continued to optimize the production of high-quality beef from dairy cattle herds.
The aim of the study was to determine the effect of ultrasound gain level, chemical composition and histological structure of musculus longissimus dorsi on pre-slaughter ultrasound evaluation of intramuscular fat content in m.l.d. of beef bulls. The study was conducted on 217 young bulls of six breeds: Red Angus, Charolais, Hereford, Limousin, Salers, and beef type Simmental. Measurements were conducted with an ultrasound system Aloka SSD-500 at five gain levels (90, 85, 80, 75, 70). After slaughter the content of intramuscular fat, total protein, connective tissue and muscle fibre type and diameter of m.l.d. were determined. Ultrasound evaluation of the intramuscular fat depended on the actual intramuscular fat and the total protein content (P<0.01) in most of the measurements. The correlation between actual and ultrasound measurement of intramuscular fat content ranged from 0.2 to 0.36, and was highly significant for most of the ultrasound gain levels. There were highly significant (P<0.01) and significant (P<0.05) negative correlations between the total protein and ultrasound fat content (r = -0.17 to -0.31). The connective tissue percentage showed a significant effect on the ultrasound fat measurements at gains of 75 and 85. Ultrasound intramuscular fat content was positively correlated with the connective tissue in the m.l.d. at gain levels of 75 and 85 and the average ultrasound intramuscular fat measurement (r = 0.16, 0.20, 0.16). Highly significant and significant correlations between each ultrasound measurement were observed.
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