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ISSN : 1598-5504(Print)
ISSN : 2383-8272(Online)
Journal of Agriculture & Life Science Vol.52 No.5 pp.81-89
DOI : https://doi.org/10.14397/jals.2018.52.5.81

Manipulating Growth Performance and Carcass Characteristics of Hanwoo Heifers by Dietary Means during Growing and Early Fattening Period

Joung Yong Kim,Seongjin Oh,Chaehwa Ryu,A-leum Lee,Sangbuem Cho,Nag-Jin Choi*
Department of Animal Science, Chonbuk National University, Jeonju, 54896, Korea
*Corresponding author: Nag-Jin Choi
Tel: +82-63-270-2579
Fax: +82-63-270-2612
March 12, 2018 August 14, 2018 August 27, 2018

Abstract


This study was conducted to improve growth performance of Hanwoo heifer and to produce high quality of meat with dietary means during growing and early fattening period. Particularly, additional energy diet to relieve estrus stress was main purpose in this study. The results of in vitro rumen fermentation indicated that there was no negative effect by additional energy diet as treatments. In the feeding trial, twenty Hanwoo heifers(average 10 months age) were allocated and distributed into two treatments in randomized block design based on body weight. There were three growth stages such as growing, early fattening and late fattening periods in this feeding program, respectively. In growing stage, there were two treatments consisting of only total mixed ration(TMR) as a control and TMR with additional energy treatment. The experimental diets were fed twice a day, and water and mineral were freely accessed. In additional energy treatment, 500 g of concentrate diet was fed daily to relieve estrus stress due to obese with high energy intake. Not outstandingly differences were found across the treatments during entiretrial period. While, unexpectedly greater feed conversion ratio in treatment compared to the control was found during late fattening period. It seems that the blood cortisol decreased with addition energy supplementation compared with the control during trail period. Carcass characteristics including carcass weight, back fat thickness, marbling score, meat color, fat color, maturity and texture were not significantly different each other. Rib-eye area, however, was greater in the control compared to the treatment(p<0.05). In addition, it appears that yield index was tended to be greater in the control. In conclusion, it is suggested that additional energy supplementation to Hanwoo heifer could get a potential in improving meat quality and relieving estrus stress.



초록


    Introduction

    Recently, there are a lot of interests in producing high quality of Hanwoo heifer beef in accordance to consumer’s demand in Korea. If the heifer could not be pregnant due to disturbance of recurrent estrus or late stage, they used to be fattened. In fact, Korean consumers prefers to consume beef meat of heifers due to the better meat quality than steers. Previous studies reported that fat deposition in heifer occurred in lower body weight than steers and bulls(Berg & Butterfield, 1976) but the rate of marbling deposition was similar(Zinn et al., 1970).

    However, heifers are comparatively less efficient fatteners because of negative production effects by estrus stress, which is the main limitation to fatten heifers. Therefore, a simple, economic and nonsurgical method of inhibiting estrus stress has been interested and sought to improve growth performance in feedlot heifers. The previous study reported that inadequate supply of energy with overfeeding protein might be associated with decreases of fertility in heifers during breeding season and early gestation(Elrod & Butler, 1993). In the other side, the information and data concerning proper fattening period with growth stages for Hanwoo heifers are limited. Therefore, nutritionally overfeeding strategy to relieve estrus stress during puberty(growing period) in fattening Hanwoo heifer was used to investigate its effect on growth performance and carcass characteristics.

    Materials and Methods

    1 In vitro rumen fermentation

    Rumen contents were collected from two ruminally cannulated Hanwoo(Korean native) steers before morning feeding. The cannulated steers were fed twice a day(08:00 and 17:00 h) with mixed of hay and commercial concentrate at 1:1 ratio. The collected rumen fluid was contained in thermo bottle and transported to the laboratory within an hour. The rumen fluid was further strained through 4 layers of cheese clothes on arrival at the laboratory. In vitro rumen fermentation was performed according to Tilley & Terry(1963). The strained rumen fluid was then mixed with McDougall’s buffer(pH 6.8) according to Troelsen & Donna(1966). For diet preparation, rice straw and concentrate diet(used for additional dietary energy in feeding trial) was mixed in ratio of 6:4 (DM basis) and assigned to control. Two TMR diets were prepared for treatments. TMR diet for growing period, timothy and concentrate diet were mixed in different ration according to treatments(TMR: Timohty: concentrate diet): 8:2:0(T1), 7.5:1.9:0.7(T2) (Table 1). Prepared diets were finely ground using hammer miller equipped with 1 mm screen. Aliquot 50 mL of buffered rumen fluid was dispensed into individual 250 mL serum bottle including 0.5 g diet. Carbon dioxide gas was used to maintain headspace anaerobically. Bottle were sealed with rubber stoppers and aluminum caps prior to start incubation(39℃). At the end of incubation(12 h), total gas production was measured by way of displacing a glass syringe. The pH was measured using a standard pH meter(Mettler- Toledo AG, Schwerzenbach, Switzerland). The culture fluid was centrifuged at 3,000×g at 4℃ for 20 min, and 1 mL supernatant was stored at 20℃ for further analysis including ammonia nitrogen and volatile fatty acid (VFA). The VFA was analyzed according to Erwin et al.(1961) with modification. Liquid sample(1 mL) was pre-treated with 0.2 mL of 25% metaphosphoric acid and incubated for 30 min, then re-centrifuged at 12,300×g using a table-top centrifuge(Gyrozen mini, Seoul, Korea). The supernatant was injected into the gas chromatography(GC-7890A, Agilent Technologies) equipped with flame ionizing detector(FID) and a capillary column(NucolTM, Fused silica capillary column, 0.25 mm×0.25 μm×30 m, Supelco, Bellefonte, USA). The temperatures of oven, injector and detector were 180℃, 220℃ and 200℃, respectively. Ammonia nitrogen(NH3-N) was determined as specified according to Chaney & Marbach(1962).

    2 Feeding trial

    The feeding trial was performed for 760 days at farm located Kimje city, Korea. Twenty Hanwoo heifers (228.41±40 kg) were used in a completely randomized design to determine the effects of additional energy supplementation in the growing period. Addition of dietary energy(ADE) treatment was prepared by providing 0.5 kg of concentrate diet per herd for a day. Five heifers were assigned to a pen with rice husks bedding. Three growth stages were employed: growing(6-15 months of age), early fattening(15-28 months of age), and last fattening(29-32 months of age), respectively. Concentrate for ADE was offered as top-dressing on the TMR during growing period. All groups received ad libitum TMR throughout the feeding trial until slaughter. Concentrate, timothy hay, and TMR were purchased from Jeonbuk Hanwoo cooperative. Heifers were fed diets twice a day at 08:00 and 17:00 h and had free access to mineral block and water. Nutrient contents of diets weremeasured according to the AOAC(1990) and Van Soest et al.(1991). Heifers were weighed before the morning feeding(at 08:00 h) every month during the experimental period. Refused diet was collected and weighed every day to estimate dry matter intake. Feed conversion ratio was expressed as average dry matter intake per average daily gain. Heifers were slaughtered at 32 months of age. Carcasses were chilled at between 0-2℃ for 24 h. The carcasses were then graded for quality and yield factors from the longissimus muscle taken at 13th rib. Carcass characteristics such as yield and quality grades were assessed at 24 h post-mortem by an experienced carcass grader of the Animal Products Grading Service (APGS, 2009), Korea. Quality trait(marbling score, meat color, fat color, texture and maturity) and yield trait(cold carcass weight, back fat thickness and rib-eye area) were recorded. The quality grade was determined by assessing the degree of marbling and firmness in the cut surface of the rib-eye, in relation to the maturity, meat color and fat color of the carcass. The rib-eye area was measured from longissimus muscle taken at the 13th rib and back fat thickness was also measured at the 13th rib. Yield index was calculated as follows: Yield index; 68.184(0.625 × back fat thickness(mm)) + (0.130 × rib-eye area(cm2)) + (0.024 × dressed weight amount(kg))+3.23. The degree of marbling was evaluated with the Korean Beef Marbling Standard, and the scores of meat color and fat color were made using the color standard (APGS, 2007). The scores for texture and maturity were made using the APGS reference index(APGS, 2007). The grading ranges were 1 to 9 for marbling score with higher numbers for better quality(1= devoid, 9=abundant); meat color(1=bright red, 7=dark red); fat color(1=creamy white, 7=yellowish); texture (1=soft, 3=firm); maturity(1=young, 9=old). Plasma was stored at 20℃ until assayed. Plasma cortisol concentrations were measured by a direct radioimmunoassay method as described(Sulon et al., 1978; Garcia-Ispierto et al., 2009).

    3 Statistical analysis

    Effect of treatment was analyzed using general linear model. Multiple comparison was accessed using Duncan’s post-hoc test for In vitro rumen fermentation. Mean comparison was performed using Student’s t-test for feeding trial. Statistical analysis was performed by SPSS program(version 18, IBM, USA).

    Results and Discussion

    1 In vitro rumen fermentation parameters

    Rumen fermentation parameters are summarized in Table 2. Rumen pH in all groups was ranged between 6.79 and 6.90. The pH of T2 showed significantly lower than others(p<0.05). Significantly greater gas and NH3N production were detected at T2(p<0.05). Significantly great VFAs production was detected in order of T2, T1 and control(p<0.05). Higher pH and lower production of gas and VFAs in control than the treatments reflected more available nutrients in diet composed of TMR-timothy and concentrates. Significantly greater production of gas, NH3N and VFAs(p<0.05) in T2 which contained more energy than T1 did not show any negative effect on rumen fermentation.

    2 Growth Performance of Hanwoo heifers

    The growth performance of Hanwoo heifers at different growth stages is shown in Table 3. Dry matter intake(DMI) was not differed among experimental groups during trial. Measured DMI in this study was 8.0 kg/d and it was relatively greater than the previously reported(7.2-7.5 kg/d) (Lee et al., 2013). During growing period treatment trended greater average daily gain(ADG) than the control(p=0.059). ADG in control, while, tended to greater than the treatment during late fattening period(p=0.051). No difference between control and treatment in ADG during early fattening and overall period was detected (p<0.05). This might be attributed to propitious physiological conditions which heifers grow at faster rate with additional concentrate during growing period, and this availability of excess energy for heifers not only to fulfill maintenance requirements but also to grow and develop body reserves. While, the ADG was interestingly tended to be lower in treatment compared with the control during late fattening period. Difference of daily gain between control and treatment during late fattening period could be explained kind of compensatory growth with different energy level. Choi et al.(2002) and Kim et al.(2002) reported that average body weight of fattening Hanwoo heifers at 30 months ages ranged 514.9- 540.0 kg. While, the heifers in present study resulted 593.6-606.0 kg at 28 months of age. The relatively greater body weight of heifers in the present study compared with the previous results could be caused by differences of genetic improvement and nutrition. Similar to previous study(Lee et al., 2013), the daily gain was decreased as increased fattening period. This was also similar to results of Hanwoo steers (Kwon et al., 2009; Kim et al., 2011). It appears that heifers in control gain less rapidly than in the ADE treatment during growing period possibly due to estrus stress in relation to its relatively higher amount of cortisol production(Fig. 1), but it was recovered during late fattening period possible reflecting compensatory growth in the control. Feed conversion ratio was not significantly different between control and treatment at growing and early fattening period, but it was beneficially lower in the control compared to treatment at late fattening period(p<0.05). Feed efficiency was increased as fattening period increased, and the present results are in agreement with other Hanwoo investigations(Cho et al., 2009; Kim et al., 2011; Lee et al., 2013).

    3 Carcass characteristics

    All heifer was slaughtered at 32 months of age; the carcass characteristics are summarized in Table 4. The carcass weight, back fat thickness and yield index were not significantly different between the two groups. Yang & Ahn(2001) reported that back fat thickness and marbling score were increased as increases of carcass weight in Hanwoo steers. Kwon et al.(2009) explained that marbling score and back fat thickness could be increased as increasing fattening period with feed intake. However, no significant differences between the treatments in the present study were found in back fat thickness, carcass weight, marbling score and feed intake. Carcass weight at 32 months age in the present study was approximately 382 kg, and it is relatively greater than previous study(Lee et al., 2013) which reported approximately 358 kg at same age. While, the rib-eye area increased in control group compared with ADE treatment(p<0.05), and it might be associated with results that back fat thickness tended to be greater (13.8 vs. 17.1 mm) in ADE treatment compared with the control despite of no statistically significance. Lee et al.(2013) reported that back fat thickness was approximately 14.1 and 17.7 mm in Hanwoo heifers at 32 and 36 months of age, respectively.

    Occurrence ratio of yield grades(A:B:C) were 6:0:4 and 1:4:5 in the control and the ADE treatment, respectively. In carcass quality traits, meat color, fat color, texture and maturity were similar between the two groups. While, marbling score in treatment was numerically greater compared with control group. Appearances of quality grade ratios(1++:1+:1:2) were 0:3:6:1 and 1:4:4:1 in the control and the treatment, respectively. This result could be explained that intramuscular fat deposition which is marbling is increased because animals are exposed to an earlier fattening period with additional dietary energy during growing period in ADE treatments compared with control. Also, the increased marbling seems to be due to an enlargement of the adipocytes with storage reservoirs with additional energy supply during growing period.

    Acknowledgement

    This work was supported by Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries(IPET) through(Agri- Bioindustry Technology Development Program), funded by Ministry of Agriculture, Food and Rural Affairs (315017-5).

    Figure

    JALS-52-81_F1.gif

    Cortisol concentration in blood at different growth stages.

    Table

    Ingredient and chemical composition of experimental diets

    Effects of different diet on In vitro rumen fermentation

    Growth performance of Hanwoo heifers at different growth stages

    Carcass characteristics of Hanwoo heifers at different growth

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