Perkins S D, Key C N, Marvin M N, Garrett C F, Foradori C D, Bratcher C L, Kriese-Anderson L A, Brandebourg T D
Department of Animal Sciences, Auburn University, Auburn, AL 36849.
J Anim Sci. 2014 Apr;92(4):1451-61. doi: 10.2527/jas.2013-7020. Epub 2014 Feb 10.
The relationship between heat stress, meat quality, and residual feed intake (RFI) is unknown in growing steers. To address this issue, high RFI (HRFI) and low RFI (LRFI) individuals were compared by assessing RFI in 48 Angus-sired steers during a 70-d feeding trial conducted during July through September to identify steers with calculated RFI at least 2 SD apart. The association of RFI with indices of meat quality and expression of genes within hypothalamic and adipose tissue was then determined in LRFI and HRFI steers. While on test, feed intake was recorded daily with BW and hip heights recorded every 14 d. Ultrasound measurements of rib eye area (REA) and backfat (BF) were recorded initially and before harvest. Carcass and growth data were analyzed using a mixed model with RFI level (LRFI and HRFI) as the independent variable. The least square means for RFI were -1.2 and 0.99 kg DMI/d, respectively, for the LRFI and HRFI cohorts (P < 0.0001). Dry matter intake was higher for the HRFI individuals versus the LRFI steers (P < 0.0001) while on-test gain was not different (P < 0.95). Marbling score was greater in LRFI than HRFI steers (P < 0.05). However, there were no differences in REA (P < 0.53), BF (P < 0.65), yield grade (P < 0.24), or objective Hunter color measures between LRFI and HRFI steers indicating there was no consistent relationship between RFI and indices of meat quality. Hypothalamic neuropeptide Y (NPY), agouti related protein (AGRP), relaxin-3 (RLN3), melanocortin 3 receptor, and relaxin/insulin-like family peptide receptor 1 (RXFP1) mRNA were expressed 280, 185, 202, 183, and 163% greater, respectively (P < 0.01), while proopiomelanocortin (POMC) mRNA was expressed 42% lower in LRFI than HRFI animals (P < 0.05). Hypothalamic GnRH mRNA expression was 67% lower while gonadotropin inhibiting hormone (GnIH) mRNA was 209% higher in LRFI than HRFI animals (P < 0.01). Pituitary expression of FSHβ and LHβ correlated to hypothalamic GnRH levels (P < 0.05) indicating changes in gene expression within the hypothalamus had functional consequences. Leptin mRNA expression levels were not different between adipose tissue of LRFI or HRFI steers (P < 0.84). These data indicate that animals with superior RFI evaluated during warm conditions have higher expression of orexigenic neuropeptide genes independent of the expression of adipose-derived leptin. Furthermore, the gonadotropin axis may also influence feed efficiency under these conditions.
在生长育肥牛中，热应激、肉质和剩余采食量（RFI）之间的关系尚不清楚。为解决这一问题，在7月至9月进行的为期70天的饲养试验中，通过评估48头安格斯种公牛的RFI，比较了高RFI（HRFI）和低RFI（LRFI）个体，以识别计算出的RFI至少相差2个标准差的公牛。然后在LRFI和HRFI公牛中确定RFI与肉质指标以及下丘脑和脂肪组织内基因表达的关联。在试验期间，每天记录采食量，每14天记录体重和髋部高度。最初和屠宰前记录肋眼面积（REA）和背膘（BF）的超声测量值。使用以RFI水平（LRFI和HRFI）作为自变量的混合模型分析胴体和生长数据。LRFI和HRFI组的RFI最小二乘均值分别为-1.2和0.99 kg DMI/d（P < 0.0001）。HRFI个体的干物质采食量高于LRFI公牛（P < 0.0001），而试验期增重无差异（P < 0.95）。LRFI公牛的大理石花纹评分高于HRFI公牛（P < 0.05）。然而，LRFI和HRFI公牛之间的REA（P < 0.53）、BF（P < 0.65）、产量等级（P < 0.24）或客观亨特颜色测量值没有差异，表明RFI与肉质指标之间没有一致的关系。下丘脑神经肽Y（NPY）、刺鼠相关蛋白（AGRP）、松弛素-3（RLN3）、黑皮质素3受体和松弛素/胰岛素样家族肽受体1（RXFP1）mRNA的表达分别高出280%、185%、202%、183%和163%（P < 0.01），而阿黑皮素原（POMC）mRNA在LRFI动物中的表达比HRFI动物低42%（P < 0.05）。LRFI动物的下丘脑促性腺激素释放激素（GnRH）mRNA表达低67%，而促性腺激素抑制激素（GnIH）mRNA高209%（P < 0.01）。垂体促卵泡素β（FSHβ）和促黄体生成素β（LHβ）的表达与下丘脑GnRH水平相关（P < 0.05），表明下丘脑内基因表达的变化具有功能后果。LRFI或HRFI公牛脂肪组织中的瘦素mRNA表达水平没有差异（P < 0.84）。这些数据表明，在温暖条件下评估的具有优异RFI的动物，其促食欲神经肽基因的表达较高，与脂肪来源的瘦素表达无关。此外，在这些条件下，促性腺激素轴也可能影响饲料效率。
