肉牛肌内脂肪的沉积机制及其营养调控的研究进展

牛肉的肌内脂肪(IMF)含量与肉品质(嫩度、多汁性、风味)呈正相关,而大理石花纹丰富(富含IMF)的牛肉通常来源于饲喂高水平谷实饲料和育肥周期较长的肉牛(30月龄或以上),这种投入产出比较低的模式限制了我国肉牛产业生产高品质牛肉的可持续发展。此外,肉牛肌内脂肪沉积、合成代谢以及营养因素对IMF的影响尤为重要。因此,本文就肌内脂肪细胞发育、合成和降解代谢以及日粮淀粉生糖效率、脂肪消化吸收和维生素等营养因素对IMF沉积的影响展开综述,为肉牛IMF沉积的营养调控提供参考。     

DNA甲基化与去甲基化调控脂肪沉积的研究进展

脂肪沉积是一个复杂的生物学过程,受遗传和表观遗传的调控作用。DNA甲基化和去甲基化是表观遗传修饰的重要方式,可通过与转录因子的相互作用或改变染色质的结构调控基因的表达,进而参与机体生长发育和细胞分化等重要的生命过程。动物脂肪沉积是脂肪细胞增殖分化和肥大的结果,脂肪细胞分化是由多能干细胞经前体脂肪细胞向成熟脂肪细胞转化的过程。相关研究表明,转录因子过氧化物酶体增殖物激活受体γ(peroxi-some proliferator activiated receptorγ,PPARγ)和CCAAT增强子结合蛋白家族(CCAAT enchancer binding proteinfamily,CEBPs)在脂肪沉积过程中起关键调控作用。近期研究发现,DNA甲基化可以通过调控脂肪形成过程中相关基因的表达而参与脂肪细胞的分化和脂肪组织的生长发育。去甲基化也可影响动物脂肪沉积过程,但其具体机制目前尚不清楚。作者主要介绍了DNA甲基化和去甲基化的定义、发生位点、生物学功能、参与DNA甲基化和去甲基化过程中的酶及其作用机制,概述了脂肪沉积过程及PPARγ、C/EBPα等转录因子在脂肪沉积过程中的调控作用,重点阐述了DNA甲基化和去甲基化对脂肪形成相关基因的表达和对脂肪细胞分化的影响,旨在为阐明脂肪沉积机制及改善动物肉质品质提供参考。     

DNA甲基化与去甲基化调控脂肪沉积的研究进展

脂肪沉积是一个复杂的生物学过程,受遗传和表观遗传的调控作用。DNA甲基化和去甲基化是表观遗传修饰的重要方式,可通过与转录因子的相互作用或改变染色质的结构调控基因的表达,进而参与机体生长发育和细胞分化等重要的生命过程。动物脂肪沉积是脂肪细胞增殖分化和肥大的结果,脂肪细胞分化是由多能干细胞经前体脂肪细胞向成熟脂肪细胞转化的过程。相关研究表明,转录因子过氧化物酶体增殖物激活受体γ(peroxi-some proliferator activiated receptorγ,PPARγ)和CCAAT增强子结合蛋白家族(CCAAT enchancer binding proteinfamily,CEBPs)在脂肪沉积过程中起关键调控作用。近期研究发现,DNA甲基化可以通过调控脂肪形成过程中相关基因的表达而参与脂肪细胞的分化和脂肪组织的生长发育。去甲基化也可影响动物脂肪沉积过程,但其具体机制目前尚不清楚。作者主要介绍了DNA甲基化和去甲基化的定义、发生位点、生物学功能、参与DNA甲基化和去甲基化过程中的酶及其作用机制,概述了脂肪沉积过程及PPARγ、C/EBPα等转录因子在脂肪沉积过程中的调控作用,重点阐述了DNA甲基化和去甲基化对脂肪形成相关基因的表达和对脂肪细胞分化的影响,旨在为阐明脂肪沉积机制及改善动物肉质品质提供参考。     

饲粮淀粉水平对生长期肉牛肌内脂肪细胞增殖和分化的影响及其机制

肉牛生长期是肌内脂肪细胞发育的重要时期,此阶段脂肪细胞的增殖和分化受到营养物质特别是淀粉供给的重要影响。但饲粮中淀粉水平过高会产生亚急性瘤胃酸中毒,出现一系列健康问题。因此,本文总结生长期肉牛肌内脂肪细胞发育特点,从肌内脂肪细胞脂肪酸底物利用以及脂肪酶和转录因子等方面阐述了饲粮淀粉水平对生长期肉牛肌内脂肪细胞增殖和分化的调控作用和分子机制,为开展生长期肉牛肌内脂肪代谢调控研究和促进肌内脂肪沉积的应用提供理论依据和实践指导。     

维生素A对动物肌内脂肪的营养调控研究进展

肌内脂肪(Intramuscular fat, IMF)是指肌肉内沉积的脂肪,主要包括磷脂、甘油三酯和胆固醇,其含量是评价肉品质的重要指标。维生素A是基因表达的关键调节因子,通过转录因子、信号通路和表观遗传修饰等途径对肌内脂肪细胞进行调控,影响动物脂肪合成和脂类代谢。本文主要综述了维生素A调控脂肪分化的机理,为通过营养途径调控肌内脂肪提供参考。     

提高肉牛大理石花纹等级的研究进展

肉牛肉质质量等级主要由牛眼肉里的大理石花纹等级即眼肉里的肌内脂肪沉积决定,大理石花纹受酮体背膘的影响。研究具有高等级大理石花纹的脂肪沉积和最低限度的皮下脂肪牛肉体系具有显著的经济价值。国内外从遗传、营养和管理等方面提高肉牛的大理石花纹等级作了大量的研究,本文就此问题的研究进展作一综述。     

影响肉牛肌内脂肪沉积的遗传、管理和营养因素

肌内脂肪在骨骼肌中的含量包括长背肌,也称为大理石花纹脂肪,是决定牛肉质量最重要的因素之一。基因、品种、管理和营养影响肌内脂肪沉积。在此,本文综述了影响肌内脂肪沉积的遗传因素(品种、性别差异和遗传力)和管理因素。阉割公牛会增加大多数品种牛的肌内脂肪沉积。本文还综述了断奶日龄、阉割、屠宰体重、年龄和环境条件等因素对肌内脂肪沉积的影响。营养因素包括脂肪代谢,饲料消化、吸收,葡萄糖、淀粉的有效性,维生素水平。因此,根据消费者对牛肉的偏好,可能需要多种策略的组合来调控肌内脂肪的沉积。     

利用荷斯坦阉牛生产大理石纹牛肉的研究

本文主要从荷斯坦牛肌内脂肪沉积相关基因的研究入手,主要阐述荷斯坦牛大理石纹的影响因素,去势对荷斯坦牛肉品质(大理石纹和牛肉嫩度)影响及营养(营养浓度和维生素A成分)调控对荷斯坦阉牛肌内脂肪沉积的影响展开综述,以期为利用荷斯坦阉牛生产大理石纹牛肉提供参考。     

猪脂肪细胞分化的调控

动物体内脂肪的沉积过程一方面是脂肪组织细胞内脂肪的不断合成、蓄积过程。另一方面是脂肪组织脂肪细胞的不断分化过程。因此，脂肪细胞分化的调控在脂肪沉积的调控中占有重要地位。本文阐述了猪脂肪细胞分化的几种调控措施。包括激素调控、生长因子调控、细胞外基质调控、不饱和脂肪酸调控和分化转录因子调控。     

猪脂肪细胞分化的调控

动物体内脂肪的沉积过程一方面是脂肪组织细胞内脂肪的不断合成、蓄积过程,另一方面是脂肪组织脂肪细胞的不断分化过程。因此,脂肪细胞分化的调控在脂肪沉积的调控中占有重要地位。本文阐述了猪脂肪细胞分化的几种调控措施,包括激素调控、生长因子调控、细胞外基质调控、不饱和脂肪酸调控和分化转录因子调控。     

Fat depot‐specific effects of body fat distribution and adipocyte size on intramuscular fat accumulation in Wagyu cattle

Ectopic fats have been recognized as a new risk factor for metabolic syndrome. In obese humans, ectopic fat accumulations are affected by body fat distribution. Intramuscular adipose tissue is categorized as one of the ectopic fats. Japanese black cattle (Wagyu) are characterized by the ability to accumulate high amounts of intramuscular adipose tissue. In Japan, the marbling level is indicated by the beef marbling standard number (BMS No.), which reflects the intramuscular fat content of longissimus muscle. We hypothesized that the intramuscular fat accumulation is affected by the body fat distribution in Wagyu cattle. In this study, we showed that the BMS No. was not correlated with the subcutaneous and visceral adipocyte diameter. In contrast, the BMS No. was positively correlated with intramuscular adipocyte diameter. These results indicate that the intramuscular adipocyte diameter of Wagyu is hypertrophied with an increase in the intramuscular fat accumulation. In addition, we showed that the BMS No. was positively correlated with the subcutaneous fat percentage. In contrast, the BMS No. was negatively correlated with the visceral fat percentage. These results indicate that highly marbled Wagyu cattle have a higher percentage of subcutaneous fat and a lower percentage of visceral fat.     

影响肉牛大理石花纹形成的主要因素

决定大理石花纹水平的肌内脂肪(IMF)含量是影响牛肉感官质量(包括嫩度、多汁性、风味和颜色)的重要因素之一。肉牛体内IMF的形成始于受孕后6个月左右,并在动物的一生中持续增长。大理石花纹的沉积受到品种、遗传、营养和管理(包括去势、断奶年龄)等多方面因素的影响。本文综述了肉牛大理石花纹沉积的主要影响因素,为品种选择以及在肉牛生长发育过程中有效调整饲料、优化营养、因地制宜改善管理提高牛肉品质提供有效依据。     

Correlations between carcass traits and mRNA levels of CGI-105 and CCAAT/enhancer protein α genes in steers of Korean cattle

To understand the molecular mechanisms that regulate intramuscular fat deposition (marbling), cDNA clones expressed in adipose tissues of Korean cattle were identified and characterized. One clone had a total length of 1262 nucleotides coding for 314 amino acids. It was identified as one encoding bovine homolog of human CGI-105 mRNA. CGI-105 is a member of fumarylacetoacetate hydrolase family. Comparison of the deduced amino acid sequences of bovine CGI-105 with those of human revealed more than 89% identity. High levels of CGI-105 mRNA expression were detected in muscle, heart, and kidney tissues among various bovine tissues. Carcass traits, including backfat thickness, rib eye area, yield index, marbling score, and quality grade were analyzed in steer of Korean cattle. A CCAAT/enhancer binding protein alpha (C/EBPα) is one of adipocyte differentiation factors that may affect deposition of fat in muscle. mRNA levels of CGI-105 and C/EBPα genes were determined in the loin muscle tissues of steers. Correlation between carcass traits and mRNA levels of the genes was estimated by Pearson's correlation coefficient. The mRNA levels of C/EBPα showed strong positive correlation (r = 0.83, p < 0.01) with marbling scores. The results of the present study indicate that the manipulation of the expression of the C/EBPα gene may contribute to the development of a method for enhancing intramuscular fat deposition in beef.     

Restriction of vitamin A and D in beef cattle finishing diets on feedlot performance and adipose accretion

Feedlot producers often exceed NRC recommendations for vitamin A and D supplementation; however, increased concentrations of these vitamins have been shown to limit adipocyte differentiation in vitro. A feedlot trial was conducted using 168 Angus crossbred steers (BW = 284 ± 0.4 kg) allotted to 24 pens. The experiment had a 2 × 2 factorial arrangement of treatments: no supplemental vitamin A or D (NAND), 3,750 IU vitamin A/kg dietary DM with no supplemental vitamin D (SAND), no supplemental vitamin A and 1,860 IU vitamin D/kg dietary DM (NASD), and 3,750 IU and 1,860 IU vitamin A and D/ kg dietary DM (SASD), respectively. Serum, liver, and intramuscular and subcutaneous adipose tissue retinol concentrations were decreased in (P < 0.001) in cattle fed the no supplemental vitamin A diets (NAND and NASD combined) compared with those consuming supplemental vitamin A (SAND and SASD combined) diets. In addition, intramuscular retinol concentration was 38% less than in the subcutaneous depot. Serum 25(OH)D(3) concentrations were reduced (P < 0.001) during the first 70 d when cattle were fed no supplemental vitamin D diets (NAND and SAND combined); however, liver 25(OH)D(3) concentrations remained unchanged (P > 0.10) through d 184. Serum and liver 25(OH)D(3) concentrations increased (P < 0.001) with vitamin D supplementation (NASD and SASD combined). The DMI, ADG, G:F, and morbidity were not affected (P > 0.10) by dietary concentration of vitamin A or D. There were vitamin A and D interactions (P < 0.03) for backfat thickness and USDA Yield grade. Cattle fed the NAND diet had greater (P < 0.03) Yield grades than other treatments because of greater (P < 0.005) 12th rib backfat thickness in NAND steers than the NASD and SAND steers. Vitamin D concentrations were attenuated and minimal carcass adiposity responses to vitamin D supplementation were observed. Feeding a diet without supplemental vitamin A increased (P < 0.05) Quality grades and marbling scores and tended (P = 0.06) to increase ether extractable lipid of the LM. As retinol and 25(OH)D(3) concentrations in feedlot cattle declined as a result of a lack of dietary supplementation, adipose accretion increased, resulting in elevated Quality and Yield grades. Withdrawal of supplemental vitamin A, D, or both from the finishing diet of feedlot beef cattle had minimal impact carcass composition.     

Micronutrients affecting adipogenesis in beef cattle

Beef marbling is an important trait of meat quality and beef marbling influences the tenderness and flavor of beef, which contributes directly to the value of beef especially in the Japanese market. The lipid content of beef depends on the strain, sex, diet and fattening period of the animal. Japanese Black cattle (Wagyu) are well‐known for their ability to produce marbling beef and this is a popular strain in Japan. The development of beef marbling was closely associated with an increase in the number of adipocytes, that is, adipocyte differentiation in the skeletal muscle. This review article describes our experiment and related reports on micronutrients, especially vitamins and minerals, affecting adipogenesis in beef cattle. We pursue the possibility that manipulating the level of dietary micronutrients may become a new technique to promote beef marbling.     

Effects of vitamin A on growth performance and carcass quality in steers

Vitamin A plays a critical role in many essential life processes. In herbivores, it is either derived from plant β-carotene or directly as a dietary supplement. In cattle, vitamin A has the potential to influence various carcass traits that are sought by specific beef markets. A group of 20 Angus steers was removed from pasture and fed a low β-carotene and vitamin A cereal-based ration on a feedlot for 308 days. Ten of the steers were supplemented with vitamin A (retinyl palmitate, 60 IU of vitamin A/100 kg body weight/day) and the other ten received no supplement. The results demonstrated that restriction of vitamin A intake changed intramuscular fat deposition without changing subcutaneous fat depots. Angus steers that had been depleted of vitamin A showed increased intramuscular fat in the longissimus thoracis et lumborum (LTL) by 35% (P < 0.026) and seam fat area at the quartering site by 33% (P < 0.0273), when compared with cattle supplemented with vitamin A. There were no changes in intramuscular fat in the semitendinosus. Visually assessed marbling scores were also higher (19%; P < 0.094) in the non-supplemented, depleted group. There was no effect of vitamin A depletion on cattle growth and other meat traits (eye muscle area, meat colour, pH, meat cut weight), meat eating attributes (tenderness, cooking loss) or muscle fibre diameter. The only difference (P < 0.0177) among the meat traits was fat colour where depleted animals had whiter fat than the controls. Moreover, the fat from the vitamin A depleted group was softer with a lower melting point. We conclude that the reduced vitamin A consumption, leading to vitamin A depletion, increases intramuscular fat. On the other hand, the vitamin A depletion did not increase subcutaneous fat depth or change other meat quality traits, suggesting that marbling and these other traits are not invariably related.