Assessment of Quality Beef Production in Northern Thailand

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The main goal of this study was to assess carcass and meat quality of Northern Thai beef cattle aiming to improve the quality of beef production in this area. The study focused on two specific crossbreeds, Brahman × Thai native (BRA) and Charolais × Thai native crossbred (CHA), which are currently mainly used for fattening in this area. Three specific objectives were set to achieve this goal:
1. Identify the best genotype and the optimum slaughter weight in terms of growth performance, carcass quality, and meat quality for fattening in the area.
2. Evaluate various fat parameters like intramuscular (i.m.) fatty acid composition of the genotypes slaughtered at the different slaughter weights.
3. Evaluate muscle fiber characteristics and their relationship to meat quality parameters.

The study was conducted on a commercial beef farm in Chiang Mai, Northern Thailand. The experiment included 34 BRA and 34 CHA bulls which were progenies of Brahman × Thai native or Charolais × Thai native cows sired by Brahman or Charolais, respectively. Percentage of Brahman and Charolais blood ranged between 75 to 87.5 %, respectively. Mean age at start of fattening and at slaughter of both genotypes were 19 and 29 months, respectively. Mean live weight at start of fattening was 323 and 316 kg for BRA and CHA, respectively. The bulls were housed in a stanchion barn. Animals had free access to fresh water. They were fed ad libitum with roughage, mainly seasonal grass, rice straw, corn and by-products from the agro-industry. Furthermore, the animals received 1 kg concentrate per 100 kg live weight per day. The animals of both genotypes were randomly selected and slaughtered at a mean live weight of 500, 550, or 600 kg, respectively. The experimental design was 2 (genotype) × 3 (slaughter weight) factorial, resulting in 6 groups with 11 or 12 animals per group.

Each animal was weighed at the beginning and the end of the fattening period. When the animals reached the target slaughter weight, they were slaughtered and dressed according to the commercial procedure. Within 1 h postmortem (p.m.), a sample of Longissimus dorsi (Ld) muscle was taken by a biopsy cannula between the 12th and 13th rib, frozen in liquid nitrogen and stored at -65°C in a freezer until subsequent histochemical analysis. Carcasses were chilled for 24 h at 4°C. Growth performance such as average daily weight gain, feeding period, body muscle score and body measurements were evaluated. Slaughter traits including carcass weight, dressing percentage and internal and external organs percentages were determined. Measurements of pH-value of carcasses were performed 1 and 24 h p.m. at the 12th rib of the Ld muscle. After chilling for 24 h, a cut of Ld muscle was removed from the right carcass side for subsequent carcass and meat quality analysis. Carcass quality parameters such carcass measurements, carcass tissue composition, carcass classification, loin eye area and marbling score were evaluated. Furthermore, commercial primal cut percentages were determined from left carcass sides after an ageing period of 14 days at 4°C.

Meat quality parameters were determined as follows: meat colour at 24 h p.m. was measured from the surface of the 12th rib of the Ld cut. Two steaks were prepared from the Ld cut. One steak was homogenized and stored at 20 °C until chemical composition analysis and one was used to determine 48 h drip loss by the bag method. The remaining Ld cut was aged at 4 °C for 14 days and 7 and 14-day ageing loss were determined. After the 14-day ageing period, 2 more steaks were prepared and stored at -20 °C. Both steaks were thawed at 4 °C for 24 h and thawing loss was calculated. One of the steaks was vacuum packed in a polyethylene bag and boiled in a water bath at 82 °C for 45 min to calculate boiling loss percentage. Thereafter, 6 round cores were removed from the boiled meat for shear force value determination using an Instron. The other steak was grilled in an electric air-convection oven until the internal temperature reached 70 ºC to calculate grilling loss percentage. The grilled steaks were subjected for sensory evaluation by eight trained panelists who were asked to grade samples for the following eight-point scale attributes: tenderness, juiciness, beef flavour intensity and overall acceptability. Intramuscular fatty acid composition was performed by extracting and esterifying i.m. fat. Finally, fatty acid methyl esters were analysed by gas-liquid chromatography. The frozen muscle samples from biopsy were sectioned into 12 micron thickness slices by a cryostat microtome. Two main muscle fiber types, slow-twitch and fast-twitch fiber, were distinguished by myofibrillar ATPase (acid pre-incubation) reaction. Fast-twitch oxidative glycolytic and fast-twitch glycolytic fibers were combined. Cross-sectional areas were measured at 3 random frames. Muscle fiber numbers were counted from 3 complete bundles under the microscope using the “Lucia G” image analytic software. The study was divided into 4 parts: (1) growth performance and carcass quality, (2) meat quality, (3) i.m. fatty acid composition and (4) muscle fiber characteristics.

Chapter 3 presents the growth performance and carcass quality of BRA and CHA slaughtered at 500, 550 and 600 kg live weight. CHA had a significantly higher daily weight gain and a shorter feeding period when compared with BRA. Body muscle score was higher for CHA and not affected by slaughter weight. CHA had a significantly heavier carcass weight and higher dressing percentage. Furthermore with higher slaughter weights carcass weight increased significantly, whereas dressing percentage did not differ. Regarding carcass quality, CHA had a significant higher muscle proportion and a lower bone plus connective tissue and fat proportion. Carcass classification was better for CHA caused by a significant higher carcass conformation and lower carcass fat score. Loin eye area was significantly higher for CHA and an increasing slaughter weight increased the loin eye area significantly. Distribution of commercial primal cuts was affected by genotype with greater proportions of brisket, rib eye, loin, rump and round in CHA and a greater proportion of blade plus chuck in BRA. Except for blade plus chuck and rib eye proportions which were not influenced, increasing slaughter weight generally increased commercial primal cut proportions especially of loin, rump and round.

The effects on meat quality are presented in Chapter 4. The results showed that Ld muscle from CHA contained significant higher fat and lower moisture contents and exhibited higher marbling score than those from BRA. Increasing slaughter weight did not influence any of the aforementioned parameters. Soluble, insoluble and total collagen contents and collagen solubility were not significantly affected by genotype. Meat from cattle slaughtered at 600 kg had significant higher concentrations of insoluble collagen when compared with animals slaughtered at 500 and 550 kg. No effect of slaughter weight on soluble and total collagen concentrations and collagen solubility was recorded. Redness (a*) and yellowness (b*) values were higher in CHA, whereas lightness (L*) did not differ between genotypes. No effect of slaughter weight on meat colour was recorded. Meat pH-values at 1 and 24 h p.m. were not affected by genotype or slaughter weight. Shear force value was only affected by genotype with lower values for CHA. Regarding water holding capacity of meat, 7-day ageing, thawing and grilling loss percentages were lower for CHA, whereas drip, 14-day ageing and boiling loss percentages were not significantly affected by genotype. Slaughter weight had no significant effect on water holding capacity. Sensory evaluation by panel test showed no significant differences between genotypes and slaughter weight groups.

Chapter 5. Intramuscular fatty acid composition and contents of triglyceride and cholesterol in Ld muscle were assessed. In comparison to BRA, CHA meat contained significantly higher i.m. fat, triglyceride and cholesterol content. Slaughter weight did not influence any of the aforementioned parameters. The major fatty acids in both BRA and CHA meat were C18:1, C16:0 and C18:0 with overall means of 38.8, 27.2 and 14.6 % FAME, respectively. Total saturated fatty acid (SFA) concentration of Ld muscle did not significantly differ between breeds. Out of the individual SFA only percentage of C17:0 differed, being higher in BRA. CHA meat exhibited higher total monounsaturated fatty acid (MUFA), C14:1 and C16:1 concentration. Total polyunsaturated fatty acid (PUFA) concentration was similar for BRA and CHA while C18:3 omega-3 (n-3) and C22:5 n-3 concentrations were higher in BRA. Total n-3 PUFA concentration was higher for BRA, while total omega-6 (n-6) PUFA concentration was similar for both genotypes. No significant differences were found in i.m. fatty acid composition between slaughter weights. Genotype had no effect on PUFA/SFA ratio, averaging 0.14, but BRA had significantly lower n-6/n-3 PUFA as well as C18:2 n-6/C18:2 n-3 ratios. Significant differences of fatty acid ratios between slaughter weights could not be observed.

Chapter 6 presents muscle fiber characteristics and their relationship to water holding capacity of Ld muscle in BRA and CHA bulls. Both, genotype and slaughter weight, had no significant effect on muscle fiber composition. Percentages of slow- and fast-twitch fibers averaged 24.4 and 75.6 % over all experimental groups, respectively. Muscle fiber cross-sectional area was neither affected by genotype nor by slaughter weight. Cross-sectional area of fast-twitch fibers was almost twice the size of slow-twitch fibers (6,721 and 3,713 µm2, respectively). Muscle fiber type composition had a significant relation to grilling loss. The percentage of slow-twitch fibers was positively correlated with grilling loss, whereas an inverse relation between percentage of fast-twitch fibers was observed. No relationship between muscle fiber composition and other water holding capacity parameters were observed. Cross-sectional areas of both slow- and fast-twitch fibers were negatively correlated to drip loss and 7-day ageing loss. In contrast, positive correlations were found between cross-sectional areas of both fiber types and cooking loss, and between cross-sectional area of fast-twitch fibers and grilling loss. No relationship between muscle fiber cross-sectional area and 14-day ageing and thawing loss were found.

In conclusion, CHA bulls were superior to BRA bulls in growth performance, carcass quality, commercial primal cuts and meat quality. Increasing slaughter weights from 500 up to 600 kg generally increased body size and weight, carcass size and weight, loin eye area and percentage of commercial primal cuts. At the same time they had no significant effects on meat quality. Therefore, to achieve a successfully quality beef production in Northern Thailand, fattening CHA up to 600 kg live weight can be recommended.