Clemmons Brooke A, Shin Sung B, Smith Timothy P L, Embree Mallory M, Voy Brynn H, Schneider Liesel G, Donohoe Dallas R, McLean Kyle J, Myer Phillip R
Department of Animal Science, University of Tennessee, Knoxville, TN 37996, USA.
U.S. Meat Animal Research Center, Clay Center, NE 68933, USA.
Animals (Basel). 2021 May 27;11(6):1561. doi: 10.3390/ani11061561.
Feed accounts for as much as 70% of beef production costs, and improvement of the efficiency with which animals convert feed to product has the potential to have substantial financial impact on the beef industry. The rumen microbiome plays a key role in determining feed efficiency; however, previous studies of rumen microbiota have not focused on protozoal communities despite the estimation that these organisms represent approximately 50% of rumen content biomass. Protozoal communities participate in the regulation of bacterial populations and nitrogen cycling-key aspects of microbiome dynamics. The present study focused on identifying potential associations of protozoal community profiles with feed efficiency. Weaned steers ( = 50) 7 months of age weighing approximately 260 kg were adapted to a growing ration and GrowSafe for 2 weeks prior to a 70-day feed efficiency trial. The GrowSafe system is a feeding system that monitors feed intake in real time. Body weights were collected on the first day and then every 7 days of the feed efficiency trial, and on the final day, approximately 50 mL of rumen content were collected via orogastric tubing and frozen at -80 °C. Body weight and feed intake were used to calculate residual feed intake (RFI) as a measure of feed efficiency, and steers were categorized as high ( = 14) or low ( = 10) RFI based on ±0.5 standard deviations about the mean RFI. Microbial DNA was extracted, and the eukaryotic component profiled by amplification and sequencing of 18S genes using degenerate primers that can amplify this locus across a range of protists. The taxonomy of protozoal sequences was assigned using QIIME 1.9 and analyzed using QIIME and SAS 9.4 with significance determined at α ≤ 0.05. Greater abundances of unassigned taxa were associated with high-RFI steers ( = 0.03), indicating a need for further study to identify component protozoal species. Differences were observed between low- and high-RFI steers in protozoal community phylogenetic diversity, including weighted beta-diversity ( = 0.04), Faith's phylogenetic diversity ( = 0.03), and observed Operational taxonomic unit (OTU) ( = 0.03). The unassigned taxa and differences in phylogenetic diversity of protozoal communities may contribute to divergences observed in feed efficiency phenotypes in beef steers.
饲料成本占牛肉生产成本的70%之多，提高动物将饲料转化为产品的效率有可能对牛肉行业产生重大财务影响。瘤胃微生物群落在决定饲料效率方面起着关键作用；然而，尽管据估计这些原生动物占瘤胃内容物生物量的约50%，但先前对瘤胃微生物群的研究并未聚焦于原生动物群落。原生动物群落参与细菌种群的调节和氮循环，而氮循环是微生物群动态的关键方面。本研究聚焦于确定原生动物群落谱与饲料效率之间的潜在关联。50头7月龄、体重约260千克的断奶公牛在进行为期70天的饲料效率试验前，先适应生长日粮和GrowSafe系统两周。GrowSafe系统是一种实时监测采食量的饲喂系统。在饲料效率试验的第一天、然后每隔7天收集体重，在试验最后一天，通过口胃管收集约50毫升瘤胃内容物并在-80℃下冷冻。利用体重和采食量计算剩余采食量（RFI）作为饲料效率的指标，并根据平均RFI上下±0.5个标准差将公牛分为高RFI（n = 14）或低RFI（n = 10）。提取微生物DNA，并使用可在一系列原生生物中扩增该位点的简并引物通过18S基因的扩增和测序对真核成分进行分析。使用QIIME 1.9对原生动物序列进行分类，并使用QIIME和SAS 9.4进行分析，显著性水平设定为α≤0.05。未分类类群的丰度较高与高RFI公牛相关（P = 0.03），这表明需要进一步研究以确定原生动物组成物种。在低RFI和高RFI公牛的原生动物群落系统发育多样性方面观察到差异，包括加权β多样性（P = 0.04）、Faith系统发育多样性（P = 0.03）和观察到的操作分类单元（OTU）（P = 0.03）。未分类类群和原生动物群落系统发育多样性的差异可能导致在肉牛饲料效率表型中观察到的差异。
