In this study the effects of animal age combined with feeding regime and the utilisation of a betaagonist (within a grain-fed system) on proximate composition and fatty acid profile of M. longissimus lumborum (LL), M. biceps femoris (BF), and M. semitendinosus (ST) were determined. Eighty Bonsmara steers consisting of A-age (0 permanent incisors) grain-fed (AC) and grain-fed supplemented with a betaagonist, zilpaterol (AZ) (n = 20) grass-fed AB-age (1 -2 permanent incisors; AB) (n = 20), and B-age (3 -6 permanent incisors; B) (n = 20) animals were used. These four groups are representative of cattle slaughtered in South Africa and were treated as four production systems. The chemical composition of all three muscles showed that zilpaterol increased protein and reduced muscle fat contents of meat. All the muscles of both grass-fed groups (AB and B) had significantly higher content of certain desirable fatty acids (FAs) such as conjugated linoleic acid (CLA), omega-3 (n-3) FAs, branched chain saturated phytanic acid, and a lower omega-6/omega-3 (n-6/n-3) ratio than the two grain-fed groups (AC and AZ). The FA composition of grain-fed beef muscle was generally not influenced by the use of zilpaterol except for a tendency towards higher n-6 polyunsaturated fatty acid (PUFA) in beta-agonist produced beef. This was mainly due to higher levels of linoleic acid in LL and ST muscles and higher CLA in BF muscle of AZ animals. Phytanic acid was also higher in BF muscle of the AZ group compared to AC. Differences in animal age among grass-fed animals (AB vs. B) had minimal effect on FA composition of grass-fed beef. We can conclude that differences in FA composition of the three muscles are influenced mainly by feeding regime and less by differences in production factors within feeding regimes. ______________________________________________________________________________________

This study indicates that beta-agonists may influence variation in tenderness within an age class more than age or feeding regime. © 2016 Society of Chemical Industry.

The South African classification system describes beef carcasses in regard to visual fat cover, conformation and age by dentition. Animal age provides a fairly accurate description of expected eating quality in regard to tenderness in an industry where other sources of variation in tenderness are limited. Since deregulation in the beef industry in the 90s many changes have occurred in all parts of the value chain. This paper presents a number of case studies that focussed on the sources of variation in meat quality, but in particular on sources of changes in meat tenderness over the past two decades. These sources include feeding regime, the use of beta agonists, post mortem ageing and electrical stimulation. In some studies these factors are integrated with age or interactions among two or more of these factors are investigated.Keywords: Age, beef, classification, dentition, grading

Feeding systems and other factors associated with processing influence meat quality, and therefore sensory attributes. This study was conducted to assess the meat quality attributes of young grain-fed and older grass-fed steers that mostly affect consumer acceptability of beef. Eighty Bonsmara steers consisting of 20 each of A-age (0-tooth) grain-fed (AC) and grain-fed supplemented with zilpaterol (AZ), 20 each of grass-fed AB (1-2 teeth) and B-age (3 - 6 teeth) animals were used. This combination represented the typical feeding systems of South Africa and other countries using similar classification systems, therefore describes the typical feeding systems of the South African beef industry. The longissimus lumborum (LL), semitendinosus (ST), and biceps femoris (BF) muscles were tested for colour, moisture properties, lipid oxidation and sensory attributes. It was found that diet in combination with animal age influenced meat colour. Muscles of the older grass-fed steers were generally darker and duller (darker red) compared to muscles of young grain-fed animals. Moisture loss was consistently higher in zilpaterol supplemented meat samples compared to the feedlot controls, while muscles of the grass-fed animals had lower moisture loss. A sensory panel clearly distinguished between cuts of grain-fed (AZ and AC) and grass-fed carcasses (AB and B) on the grounds of flavour characteristic. The AB and B cuts scored higher for grassy, animal-like and rancid flavour overtones and lower for roasted flavour and sourness than AZ and AC grain-fed cuts. This indicated that typical flavours related to diet define expected eating quality. Keywords: age, grain, grass, meat quality, zilpaterol