Our research group demonstrated that vitamin A restriction affected meat quality of Angus cross and Simmental steers. Therefore, the aim of this study is to highlight the genotype variations in response to dietary vitamin A levels. Commercial Angus and Simmental steers (n = 32 per breed; initial BW = 337.2 ± 5.9 kg; ~8 months of age) were fed a low-vitamin A (LVA) (1017 IU/kg DM) backgrounding diet for 95 days to reduce hepatic vitamin A stores. During finishing, steers were randomly assigned to treatments in a 2 × 2 factorial arrangement of genotype × dietary vitamin A concentration. The LVA treatment was a finishing diet with no supplemental vitamin A (723 IU vitamin A/kg DM); the control (CON) was the LVA diet plus supplementation with 2200 IU vitamin A/kg DM. Blood samples were collected at three time points throughout the study to analyze serum retinol concentration. At the completion of finishing, steers were slaughtered at a commercial abattoir. Meat characteristics assessed were intramuscular fat concentration, color, Warner-Bratzler shear force, cook loss and pH. Camera image analysis was used for determination of marbling, 12th rib back fat and longissimus muscle area (LMA). The LVA steers had lower (P < 0.001) serum retinol concentration than CON steers. The LVA treatment resulted in greater (P = 0.03) average daily gain than the CON treatment, 1.52 and 1.44 ± 0.03 kg/day, respectively; however, there was no effect of treatment on final BW, DM intake or feed efficiency. Cooking loss and yield grade were greater and LMA was smaller in LVA steers (P < 0.05). There was an interaction between breed and treatment for marbling score (P = 0.01) and percentage of carcasses grading United States Department of Agriculture (USDA) Prime (P = 0.02). For Angus steers, LVA treatment resulted in a 16% greater marbling score than CON (683 and 570 ± 40, respectively) and 27% of LVA Angus steers graded USDA Prime compared with 0% for CON. Conversely, there was no difference in marbling score or USDA Quality Grades between LVA and CON for Simmental steers. In conclusion, feeding a LVA diet during finishing increased marbling in Angus but not in Simmental steers. Reducing the vitamin A level of finishing diets fed to cattle with a high propensity to marble, such as Angus, has the potential to increase economically important traits such as marbling and quality grade without negatively impacting gain : feed or yield grade.

我们的研究小组证明，维生素 A 限制会影响安格斯杂交牛和西门塔尔阉牛的肉质。因此，本研究的目的是突出响应膳食维生素 A 水平的基因型变异。商业安格斯和西门塔尔肉牛（每个品种n = 32；初始体重 = 337.2 ± 5.9 kg；约 8 个月大）饲喂低维生素 A ( LVA ) (1017 IU/kg DM) 的背景日粮 95 天以减少肝脏维生素 A 储存。在育肥过程中，以基因型 × 日粮维生素 A 浓度的 2 × 2 因子排列将公牛随机分配到处理组。LVA 处理是没有补充维生素 A 的整理饮食（723 IU 维生素 A/kg DM）；控制（CON) 是 LVA 饮食加上补充 2200 IU 维生素 A/kg DM。在整个研究的三个时间点收集血样以分析血清视黄醇浓度。完成后，公牛在商业屠宰场被屠宰。评估的肉类特性是肌肉内脂肪浓度、颜色、Warner-Bratzler 剪切力、蒸煮损失和 pH 值。相机图像分析用于确定大理石花纹、第 12 肋背脂肪和最长肌面积 ( LMA )。LVA 阉牛的血清视黄醇浓度低于 CON 阉牛( P < 0.001)。LVA 处理导致更大的 ( P= 0.03) 与 CON 处理相比，平均日增重分别为 1.52 和 1.44 ± 0.03 kg/天；然而，处理对最终体重、干物质摄入量或饲料效率没有影响。LVA 肉牛的蒸煮损失和产量等级较大，LMA 较小（P < 0.05）。大理石花纹分数 ( P = 0.01) 和美国农业部 ( USDA ) Prime等级的胴体百分比 ( P )之间存在交互作用= 0.02)。对于安格斯公牛，LVA 处理导致大理石花纹分数比 CON 高 16%（分别为 683 和 570 ± 40），27% 的 LVA 安格斯公牛被评为 USDA Prime，而 CON 为 0%。相反，西门塔尔阉牛的 LVA 和 CON 之间的大理石花纹分数或 USDA 质量等级没有差异。总之，在育成期间饲喂 LVA 日粮会增加安格斯牛的大理石花纹，但不会增加西门塔尔阉牛的大理石花纹。降低饲喂大理石倾向性高的牛（如安格斯牛）的最终日粮中的维生素 A 水平，有可能提高经济上重要的性状，如大理石花纹和质量等级，而不会对增重：饲料或产量等级产生负面影响。