Growth performance , meat quality , and carcass characteristics in growing and fattening Hanwoo steers fed bentonite

Thirty-six castrated, seven months-old Hanwoo steers (initial body weight: 184 ± 5.2kg) were assigned to three treatments over 23 months to evaluate the effects of supplementation with bentonite (0, 0.1 and 0.3%) on growth performance and carcass and meat characteristics. A completely randomized design with three replicates was used. The inclusion of a bentonite-supplemented diet had an influence on final weight, total weight gain, and average daily gain. Bentonite supplementation had no significant effect on proximate composition and meat quality. For carcass characteristics, there were no significant differences in yield traits and quality traits between treatments (but not cold carcass weight, marbling score, and quality grade). It was concluded that supplementation with bentonite (0.1 and 0.3%) improved growth performance, cold carcass weight, marbling score and quality grade compared with the control, except for meat quality.


Introduction
Bentonites are a clay raw material with strong colloidal characteristics that increase absorption and have high ion exchange capacity because of the presence of hydrated cations (Tiller, Gerth, & Brummer, 1984).Bentonite mostly consists of silicon dioxide (SiO 2 ), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ) and sodium oxide (Na 2 O) (European food safety authority [EFSA], 2012).
Several studies have demonstrated that bentonites have the ability to absorb toxic products during digestion and to decrease the accumulation of toxic substances in tissues, which results in the reduction of internal disorder occurrences (Fenn & Leng, 1989;Walz, White, Fernandez, Gentry, & Blouin, 1998).For example, bentonites in animal diet effectively bind aflatoxins from the animals' digestive tract, which makes mycotoxins unavailable for absorption.This led to the reduction of their absorption into the organism due to its adsorbent capability (Grant & Phillips, 1998;Phillips, Lemke, & Grant, 2002).Therefore, the addition of bentonite could be used as a dietary supplement in animal rations to improve their nutritive value.Moreover, after supplementation of diets with bentonite or peat with minerals, an improvement in productivity, meat quality, and carcass characteristics has been observed in swine and Hanwoo steer (Kim, Lee, Song, & Cho, 2000;Kang et al., 2002 , 2010).This means that bentonite supplementation is a potential method to improve the quality of meat from slaughtered animals.The use of bentonites as feed additives for all animal species has been proposed.However, EFSA (2011) recommended a maximum level of 0.5% bentonite to be safe for all animal species because of the inconsistency in the currently available data.Thus, using a bentonite (under 0.5%) supplement in a direct-rice straw-based diet might enhance the growth performance and improve meat quality in Hanwoo steer.The objective of this investigation was to evaluate the effects of supplementation with bentonite on growth performance and the carcass and meat characteristics of growing and fattening Hanwoo steers.

Animal experiment and treatment
The experimental protocol was approved by the Taemok farm animal care committee and the animals were conducted according to guidelines of the Taemok Farm Council on Animal Care (Reference No.12-01, Yeongcheon, South Korea).The study included 36 castrated, 7 months-old Hanwoo steers (initial live weight: 184 ± 5.2 kg), that were assigned to three different treatments three replications using a completely randomized design.The treatments were kept in 9 pens with four Hanwoo steers per pen in a stall with a slatted floor.
The animals were fed one of three diets; the control group received a concentrate mix and rice straw, the first treatment group (T1) received the control diets plus 0.1% bentonite, the second treatment group (T2) received the control diets plus 0.3% bentonite.These dietary treatments were given as growing (8 months), fattening (8 months), and finishing (7 months) phase in experiment of Hanwoo steer.The chemical composition of the experimental diets for growing, fattening, and finishing Hanwoo steer are present in Table 1.Animals were fed twice a day at 9 and 17h and had free access to fresh water during the whole period.
For growth performance, Hanwoo were weighed monthly throughout the study.The total body weight gain and average daily gain were calculated as the difference between the final body weight and the initial body weight divided by the length of the experimental period.

Carcass evaluation, analytical procedures and sample preparation
Chemical analysis (for dry matter, crude protein, ether extract, crude ash, Ca, and P) of experimental diets was performed according to the methods of Association of Official Analytical Chemists (AOAC, 2005).To determine meat and carcass characteristics, the Hanwoo were fasted for 24h at the end of the experimental period before slaughter.Thirty-six castrated Hanwoo were transferred to a local municipal slaughterhouse and slaughtered using conventional methods.After slaughtering, carcasses were washed and immediately moved to a chilling room.After a 24-h period of carcass chill, cold carcass weights were measured.Meat samples were obtained to determine moisture, crude protein, and ether extract, following the methods of AOAC (2005).The pH of each sample was determined 24h postmortem using a pH meter.Approximately 10 g of minced meat was mixed with 90 mL of distilled water and homogenized for 1 min.The pH values were measured immediately.
At the same time, about 100 g of meat samples for determination of cooking loss were placed in a polyethylene bag.The samples were placed in a water bath at 70°C for 30 min.and cooled at room temperature for 30 min.Cooking loss percentage was determined as the ratio of the difference of meat before and after cooking.Shear force values were measure with a rheometer (CR-300, Sun Scientific Co., Tokyo, Japan).Load cell with 5 kg applied at a cross-head speed of 30 mm min. - .Each core sample was sheared parallel to the muscle fibers.Water holding capacity (WHC) was analyzed using a modification of the method described by Kristensen and Purslow (2001) device and compressed for 2 min.WHC was calculated from duplicate samples as a ratio of the meat film area to the total area.WHC (%) was calculated using the following equation: WHC (%) = 100 − (total meat area/meat film area × 100).
The yield and quality grade of each carcass were evaluated using the Korean carcass grading procedure classified in the Korean Livestock Enforcement Regulation (KMAF, 2007).The left side of the carcass was cut between the 13th rib and the 1st lumbar vertebrae to measure backfat thickness and the longissimus muscle area.Yield index was calculated as follows: Yield index = 68.184-(0.625 × back fat thickness (mm)) + (0.130 × longissimus muscle area (cm 2 )) -(0.024 × cold carcass weight (kg)) + 3.23.
Yield grades were divided into three groups: grade A (lean; higher than 67.5), grade B (higher than 62.0 and lower than 67.5), and grade C (fat; lower than 62.0).The degree of marbling was determined according to the Korean Beef Marbling Standard (Korea Institute for Animal Products Quality Evaluation [KAPE], 2012).Marbling score was graded from 1 (poor) to 9 (excellent), with 9 being the highest higher numbers for better quality.The scores of meat and fat color were measured according to the color standard (KAPE, 2012).The score of meat color range goes from 1 (scarlet) to 7 (dark red) and fat color can be graded from 1 (white) to 7 (dark yellow).The scores for texture ranged from 1 (good) to 3 (bad) and maturity is graded from 1 (fully mature) to 9 (least mature), according to the KAPE reference index (KAPE, 2012).For Korean quality grade, five quality grade groups of carcasses were classified as 1++ (best), 1+, 1, 2 and 3 (poorest).

Statistical analysis
The three treatments were allocated to Hanwoo steers according to a completely randomized design.Pen (n=4) means was considered as the experimental unit for statistical analysis.All data were subjected to analysis of variance according to the General Linear Model procedure (Statistical Analysis System [SAS], 2002).The mean values of the different treatments were compared using Duncan's multiple range test at p < 0.05 level.

Results and discussion
Growth performance of Hanwoo steers supplemented with bentonite during the complete growth period is presented in Table 2.
Initial body weight was not different among treatments (p > 0.05).The inclusion of 0.1% and 0.3% bentonite in a diet has an influence on final body weight, total body weight gain, and average daily gain compared with the controls.The data clearly showed that dietary supplementation with bentonite improves growth performance of Hanwoo steers.In the current study, the improvement in growth performance might be due to bentonite activity, which resulted in the enhanced digestibility of nutrients owing to a delay in the passage of food particles through the gut.These findings disagree with the results of Lee et al. (2010) who found no differences in body weight gain of Hanwoo steers after supplementation with 1% bentonite and concentrate mix during the feeding trials.Berthiaume, Ivan, and Lafrenière (2007) also reported that the average daily gain (ADG) was not affected by the supplementation with bentonite neither in any particular period nor overall, and there was no remarkable interaction between silage types and bentonite additives for this variable.
The comparison of the two levels of bentonite showed no significant effect (p > 0.05) in growth performance.According to Southern, Ward, Binde, and Hebert (1994), the addition of bentonite (5% levels) to chicken fed different-type nutient deficient diets can improve growth performance.The studies regarding the efficacy of bentonite are inconsistent.The variation in growth performance may be explained by the type of animal diets and the different levels of bentonite used.In order to evaluate the effectiveness of bentonite supplementation, it is necessary to understand the correlation between present and previous studies that may play a relevant role.Table 3 shows the approximate composition and meat quality of the longissimus muscle of Hanwoo steers supplemented with bentonite.However, no effect (p > 0.05) of the bentonite supplement was noticed for proximate composition.In the current study, no significant difference in the pH, cooking loss, shear force and water holding capacity values (p > 0.05) was observed among treatments.In other words, the addition of bentonite to the diets of growing and fattening Hanwoo steer did not affect meat quality.Kim et al. (2014) performed a study where pigs were fed with Kaolinite (Macsumsuk) and herb mixtures, and reported that there was no significant reduction in cooking loss of the pork from that the control, except for shear force and water holding capacity. 2)Scored: grade A = 1 (lean), B = 2, C = 3 (fat). 3)Scored: grade 1 = poor, grade 9 = excellent. 4)Scored: grade 1 = scarlet, grade 7 = dark red. 5)Scored: grade 1 = white, grade 7 = yellow. 6)Scored: grade 1 = good, grade 3 = bad. 7)Scored: grade 1 = fully mature, grade 9 = least mature. 8)Scored: grade 1++ = 4, 1+ = 3, 1 = 2, 2 = 1.
Table 4 summarizes the characteristics of Hanwoo steers supplemented with bentonite.Cold carcass weight, marbling scores and quality grade were significantly different among treatments (p < 0.05), and treatments with 0.3% bentonite had more cold carcass weight (478.29 kg), marbling score (7.12) and quality grade (1+=3.31)than other treatments.This may be due to the increase in growth performance observed in Hanwoo steers fed diets with 0.3% bentonite.Marbling scores are often used as the primary predictor of beef palatability among carcasses or as the most important factor in evaluating the beef quality (tenderness, juiciness, flavor, maturity and color of fat) as mentioned by the United States Standards (USDA, 2001) and Kim and Lee (2003).Lee et al. (2010) and Kwak, Kim, Lee, Lee, & Choi (2015) observed no effect of the dietary supplementation of Na-bentonite or a trace minerals-fortified microbial culture (TMC) on carcass yield and quality traits of Hanwoo steer.
In contrast to our expectations, all treatments had no effect (p > 0.05) on yield traits (backfat thickness, longissimus muscle area, yield index and yield grade) and quality traits (meat color, fat color, texture and maturity).However, backfat thickness, longissimus muscle area, yield grade and maturity tended to increase with increasing levels of bentonite, while meat color gradually tented to reduce as bentonite levels increased (but not yield index, fat color and texture).These results are in accordance with that of Walz et al. (1998) in which the inclusion of 0.75% clay mineral to lamb diets had no significant effect on longissimus muscle area, backfat thickness, and yield grade.Constantino et al. (2014) did not observe any significant difference in cold carcass weight, marbling, and fat thickness in ewes supplemented with magnesium oxide.
With the exception of certain parameters such as cold carcass weight, marbling score and quality grade, the effects of bentonite additives on yield traits and quality traits of growing-fattening Hanwoo steer is still unknown.

Conclusion
Supplementation of Hanwoo steer diets with bentonite did bring slight improvement in growth performance, carcass weight, marbling score and quality grade compared with controls.However, growth performance, meat quality, and carcass characteristic were not affected by the inclusion of 0.3% bentonite in comparison with 0.1% bentonite in Hanwoo steer diets.

Table 2 .
Growth performance of Hanwoo steers supplemented with bentonite during the whole period.

Table 3 .
Proximate composition and meat quality in the longissimus muscle of Hanwoo steers supplemented with bentonite.

Table 4 .
Carcass characteristics for Hanwoo steers supplemented with bentonite.