Effects of castration age, protein level and lysine/methionine ratio in the diet on colour, lipid oxidation and meat acceptability of intensively reared Friesian steers.

A total of 64 intensively reared Friesian steers were used in a 2×2×2 design to study the effects of age of castration (15 days old v. 5 months old), dietary protein level (14.6% v. 16.8%; DM basis) and lysine/methionine (lys/met) ratio (3.0 v. 3.4) on meat quality. The lys/met ratio of 3.0 was reached with supplementation of protected methionine. Animals were slaughtered at a live weight of 443.5 ± 26.2 kg at around 12 months of age. Colour and lipid oxidation were measured in the longissimus thoracis muscle throughout the 14 days of display under modified atmospheric and commercial display conditions. A panel of 17 consumers assessed daily the visual acceptability of the meat on display. A consumer acceptability eating test was also performed with 120 consumers in meat aged for 7 days under vacuum conditions. Lipid oxidation was not influenced by castration age and the protein level in the diet. Castration age did not affect meat colour, but meat from the low protein level diet and the low lys/met ratio showed higher redness (a*) from 3 days of display onwards. Nevertheless, from 6 days onwards, consumer visual acceptability was below the level of acceptance in all treatments, and even from 5 days onwards in those animals that underwent early castration and were fed either a high protein diet or a combination diet low in protein content and high in lys/met ratio. The best accepted treatments throughout the display period were those from late castrated animals fed a low protein diet, probably related to other visual aspects. However, the best accepted meat after consumption was that from late castrated animals fed high protein and high lys/met. The addition of protected methionine to reach lys/met levels of 3.0 did not improve beef acceptability, with the high protein diet being preferred by consumers in terms of palatability in late castrated animals.

Effects of castration age, dietary protein level and lysine/methionine ratio on animal performance, carcass and meat quality of Friesian steers intensively reared.

The effects of castration age, dietary protein level and the dietary lysine/methionine (lys/met) ratio on animal performance, carcass characteristics and meat quality were studied in 64 intensively reared Friesian steers. Animals underwent castration procedures at 15 days old or at 5 months old. Dietary treatments started at 90 days old, with eight animals from each castration age randomly allocated to each treatment: 14.6% v. 16.8% CP (DM basis), and 3.0 v. 3.4 lys/met, on a 2×2×2 design. The recommended ratio of 3.0 was reached with supplementation of protected methionine. Steers were slaughtered at 443.5±26.2 kg live weight when they reached 12 months old approximately. Average daily gain, cold carcass weight or carcass classification were not affected by any studied effect. Muscle moisture (P=0.024), C18:2n-6 percentage (P=0.047), polyunsaturated fatty acid/saturated fatty acid (P=0.049) and n-6/n-3 (P=0.003) were higher in late castrated animals. Both high levels of dietary protein (P=0.008) and lys/met ratio (P=0.048) increased the percentage of muscle in the carcass. A level of 16.8% of CP in the diet also increased the percentage of monounsaturated fatty acids in the intramuscular fat (P=0.032), whereas a ratio lys/met of 3.4 decreased the percentage of saturated fatty acids (P=0.028). Thus, it is recommended using diets with a high protein level (16.8%) and a high lys/met ratio (3.4) in animals slaughtered at a young age, in order to obtain carcasses with high muscle content without negatively affecting productive traits or intramuscular fat composition.