Lipid Characteristics of the Muscle and Perirenal Fat in Young Tudanca Bulls Fed on Different Levels of Grass Silage

Beef derived from grass-fed cattle is a specific quality criterion. The effect of grass silage intake on quality characteristics, i.e., fatty acids, fat-soluble vitamins, and lipid-derived volatile composition of intramuscular and perirenal fat from fattening bull weaners were studied. Visible (VIS) and near-infrared (NIR) spectra were also obtained from perirenal fat. Perirenal fat analysis was performed for feeding differentiation purposes. A total of 22 Tudanca breed 11-month-aged bulls were finished on three different diets: grass silage and a commercial concentrate ad libitum (GS-AC), grass silage ad libitum and the commercial concentrate restricted to half of the intake of the GS-AC group (GS-LC), and barley straw and concentrate ad libitum (Str-AC). Feeding had a significant effect (p < 0.05) on γ-linolenic acid and the ratio n-6/n-3 fatty acids. Furthermore, β-carotene content was greater in beef from silage groups than in the Str-AC group. Feeding also affected the perirenal fat composition. Beef from silage-fed bulls and straw-fed bulls could be differentiated by fatty acid percentages, especially 18:0, t-18:1, and c9-18:1, β-carotene content, b* colour value, and carotenoid colour index. However, the VIS or NIR spectra data showed poor differentiating performance, and the volatile composition did not have appreciable differentiation power.

The Colour, Composition and Eating Quality of Beef from Late- or Early-Maturing Suckler Bulls Finished at Pasture with or without Concentrate Supplementation

Carcasses from pasture-finished early-maturing (EM), rather than late-maturing (LM), breed bulls may be more suited to meet the minimum carcass fatness classification of 2+ (6.0 on a 15-point scale) required for some markets. The comparative colour and eating quality of beef from grass-fed bulls of different maturities are unknown. Sixty yearling suckler-bred bulls were assigned to a 2 (maturities: EM and LM) × 2 (finishing strategies: grass only (G0) or grass + 4.0 kg concentrate daily (GC)) factorial design. Bulls were at pasture from 7 April, concentrates were introduced (or not) 97 days later, and bulls were slaughtered at 192 d post-turnout (approximately 19 mo of age). Carcass fat scores averaged 5.02, 6.20, 6.33 and 7.30 for LMG0, LMGC, EMG0 and EMGC bulls, respectively. Muscle colour did not differ between treatments. Muscle from LM had lower intramuscular fat concentration, collagen solubility and a tendency (p < 0.1) towards lower ratings for tenderness, texture, and acceptability of 14 d aged beef. Concentrate supplementation decreased the ratings for muscle tenderness but ratings for acceptability were not affected. Achieving the minimum carcass fatness was therefore not required to produce beef of acceptable eating quality and suckler bulls can access the “grass-fed” beef market.

Does Finishing at Pasture Influence the Colour of Muscle from Suckler Bulls and Can Colour Be Used to Authenticate Their Pre-Slaughter Diet?

The primary objective of this study was to compare the colour of muscle from bulls finished at pasture or indoors on a high concentrate diet. The ancillary objectives were to identify possible explanations for any differences in the colour observed and the potential of muscle colour to discriminate between bull beef from different production systems. Growth, longissimus muscle colour, fibre type composition and metabolic profile were measured in late-maturing breed sired suckler bulls slaughtered at 19 months of age after 199 days at pasture (G0), 100 days indoors after 98 days at pasture (G0AL) and indoors for 199 days (AL). When compared to bulls finished indoors and offered a high concentrate ration, the carcass weight of G0 bulls was lower, their carcasses were leaner, and their longissimus muscle was similar in lightness but less red and had a lower glycolytic metabolism. The temperature at which the longissimus muscle reached pH 6.0 was lower (19.7 °C) for G0 than for G0AL (29.9 °C) and AL (31.6 °C), which did not differ. Co-variate adjustment for this variable removed the differences in redness. Adjusting the chill settings appears to be a practical strategy for abattoirs to minimise early post-mortem differences in muscle colour between lighter grass-fed and heavier concentrate-fed carcasses. The preliminary results demonstrate the potential of both L*, a*, b* values and the visible reflectance spectra of muscle to discriminate between grass- finished and concentrate-finished bull beef, but further refinement and validation of the models is required.