Division of Plant Sciences, University of Missouri, Columbia, MO 65211, USA.
J Anim Sci. 2012 Jan;90(1):387-94. doi: 10.2527/jas.2011-4070. Epub 2011 Aug 19.
The daily BW gain of stocker steers grazing tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbysh. = Schedonorus arundinaceus (Schreb.) Dumort.]-based pastures typically declines during summer. To avoid these declines, in part to mitigate the effects of tall fescue toxicosis, it is commonly advised to move cattle to warm-season forage during this period. A 3-yr (2006, 2007, and 2008) grazing study was conducted to evaluate the effect of replacing 25% of the area of a tall fescue/clover (81% endophyte-infected) pasture system with "Ozark" bermudagrass [Cynodon dactylon (L.) Pers.] overseeded with clover (Trifolium spp.) to provide summer grazing for stocker steers (TF+BERM). The TF+BERM treatment was compared with a grazing system in which tall fescue/clover (TF) pastures were the only type of forage available for grazing. Our objective was to determine if replacement of 25% of the land area in a fescue system with bermudagrass would increase annual beef production compared with a system based solely on tall fescue. The study was conducted at the Southwest Research and Education Center of the University of Missouri near Mt. Vernon. Each treatment was rotationally stocked with 5 steers (248 ± 19.3 kg) on 1.7 ha. Fertilizer applications were applied at rates recommended for each respective forage species. Total forage production, BW gain per hectare, and season-long ADG of steers was greater (P < 0.06) for TF+BERM than for TF in 2006, but none of these measures differed (P > 0.19) in 2007 or 2008. In vitro true digestibility of pastures was greater (P = 0.01) for TF (84.4%, SEM = 0.64%) compared with TF+BERM (80.6%, SEM = 0.79%), even in summer. The decreased in vitro true digestibility of the bermudagrass pastures likely negated any benefit that animals in TF+BERM had in avoiding the ergot-like alkaloids associated with endophyte-infected tall fescue. Renovating 25% of the pasture system to bermudagrass provided some benefit to the system in years when summertime precipitation was limited (2006) but provided no value in wetter years (2007 and 2008). Although renovating endophyte-infected tall fescue pastures to a warm-season forage is a widely used practice to mitigate tall fescue toxicosis, the benefits of this practice are limited if forage quality of the warm season component is poor.
在夏季，放牧高羊茅[Lolium arundinaceum (Schreb.) S.J. Darbysh. =Schedonorus arundinaceus (Schreb.) Dumort.]为主的育肥牛群的日增重通常会下降。为了避免这种情况，部分是为了减轻高羊茅中毒的影响，通常建议在这段时间将牛群转移到暖季牧草上。进行了为期 3 年（2006 年、2007 年和 2008 年）的放牧研究，以评估用“Ozark”百慕大草[Cynodon dactylon (L.) Pers.]替代 25%高羊茅/三叶草（81%内生菌感染）牧场系统的面积对育肥牛（TF+BERM）的影响。TF+BERM 处理与仅使用高羊茅/三叶草（TF）牧场作为放牧的放牧系统进行了比较。我们的目的是确定用百慕大草替代 25%的放牧系统土地面积是否会比仅基于高羊茅的系统增加年度牛肉产量。该研究在密苏里大学西南研究与教育中心附近的芒特弗农进行。每个处理都有 5 头体重（248 ± 19.3kg）为 1.7 公顷的育肥牛轮流放牧。根据各自牧草的建议施肥率进行施肥。2006 年，TF+BERM 的总牧草产量、每公顷 BW 增重和整个季节的 ADG 均高于 TF（P < 0.06），但 2007 年或 2008 年这些措施均无差异（P > 0.19）。即使在夏季，TF（84.4%，SEM = 0.64%）的牧草体外真消化率也高于 TF+BERM（80.6%，SEM = 0.79%）（P = 0.01）。百慕大草牧场体外真消化率的降低可能抵消了动物在 TF+BERM 中避免与内生菌感染的高羊茅相关的麦角生物碱的任何好处。将 25%的牧场系统更新为百慕大草，在夏季降雨量有限的年份（2006 年）对系统有一定的好处，但在多雨的年份（2007 年和 2008 年）没有价值。尽管用暖季牧草将感染内生菌的高羊茅牧场更新是减轻高羊茅中毒的常用做法，但如果暖季牧草成分的质量较差，这种做法的好处就有限了。
