Gorocica-Buenfil M A, Fluharty F L, Reynolds C K, Loerch S C
Department of Animal Sciences, The Ohio State University, Wooster 44691, USA.
J Anim Sci. 2007 Sep;85(9):2243-55. doi: 10.2527/jas.2006-781. Epub 2007 Apr 27.
To determine the effect of duration of dietary vitamin A restriction on site of fat deposition in growing cattle, 60 Holstein steers (BW = 218.4 +/- 6.55 kg) were fed a diet based on high-moisture corn, with 2,200 IU of supplemental vitamin A/kg of DM (control) or no supplemental vitamin A for a long (243 d; LR) or short (131 d; SR) restriction before slaughter at 243 d. The SR steers were fed the control diet for the first 112 d. Steers were penned individually and fed for ad libitum intake. Jugular vein blood samples for serum retinol analysis were collected on d 1, 112, and 243. Carcass samples were collected for composition analysis. Subcutaneous fat samples were collected for fatty acid composition. Fat samples from the i.m. and s.c. depots were collected to measure adipocyte size and density. Feedlot performance (ADG, DMI, and G:F) was not affected (P > 0.05) by vitamin A restriction. On d 243, the i.m. fat content of the LM was 33% greater (P < 0.05) for LR than for SR and control steers (5.6 vs. 3.9 and 4.2% ether extract, respectively). Depth of back-fat and KPH percentage were not affected (P = 0.44 and 0.80, respectively) by vitamin A restriction. Carcass weight, composition of edible carcass, and yield grade were similar among treatments (P > 0.10). Liver retinol (LR = 6.1, SR = 6.5, and control = 44.7 microg/g; P < 0.01) was reduced in LR and SR vs. control steers. On d 243, LR and SR steers had similar serum retinol concentrations, and these were lower (P < 0.01) than those of control steers (LR = 21.2, SR = 25.2, and control = 36.9 microg/dL). Intramuscular adipose cellularity (adipocytes/mm2 and mean adipocyte diameter) on d 112 and 243 was not affected (P > 0.10) by vitamin A restriction. Restricting vitamin A intake for 243 d increased i.m. fat percentage without affecting s.c. or visceral fat deposition, feedlot performance, or carcass weight. Restricting vitamin A intake for 131 d at the end of the finishing period appears to be insufficient to affect the site of fat deposition in Holstein steers.
为了确定日粮维生素A限制持续时间对生长育肥牛脂肪沉积部位的影响，选用60头荷斯坦公牛（体重=218.4±6.55千克），给它们饲喂以高水分玉米为基础的日粮，每千克干物质补充2200国际单位维生素A（对照），或者在243天屠宰前长期（243天；LR）或短期（131天；SR）不补充维生素A。SR组公牛在最初112天饲喂对照日粮。公牛单独圈养，自由采食。在第1、112和243天采集颈静脉血样进行血清视黄醇分析。采集胴体样本进行成分分析。采集皮下脂肪样本进行脂肪酸组成分析。采集来自肌内和皮下脂肪库的脂肪样本以测量脂肪细胞大小和密度。维生素A限制对育肥性能（平均日增重、干物质采食量和料重比）没有影响（P>0.05）。在第243天，LR组公牛的腰大肌肌内脂肪含量比SR组和对照组公牛高33%（P<0.05）（分别为5.6%、3.9%和4.2%的乙醚提取物）。背部脂肪厚度和肾脏、盆腔和心脏脂肪（KPH）百分比不受维生素A限制的影响（分别为P=0.44和0.80）。各处理间胴体重、可食用胴体组成和产量等级相似（P>0.10）。与对照组公牛相比，LR组和SR组公牛肝脏视黄醇含量降低（LR=6.1、SR=6.5、对照组=44.7微克/克；P<0.01）。在第243天，LR组和SR组公牛血清视黄醇浓度相似，且低于对照组公牛（LR=21.2、SR=25.2、对照组=36.9微克/分升；P<0.01）。维生素A限制对第112天和243天的肌内脂肪细胞特性（每平方毫米脂肪细胞数和平均脂肪细胞直径）没有影响（P>0.10）。限制维生素A摄入243天可提高肌内脂肪百分比，而不影响皮下或内脏脂肪沉积、育肥性能或胴体重。在育肥期结束时限制维生素A摄入131天似乎不足以影响荷斯坦公牛的脂肪沉积部位。
