Effects of heat stress on feed intake and rumen fermentation in beef cattle
热应激对肉牛采食量和瘤胃发酵的影响
摘要 (Abstract)
1. J Anim Sci. 2022 Nov 1;100(11):skac320. doi: 10.1093/jas/skac320. Effect of live yeast supplementation on energy partitioning and ruminal fermentation characteristics of steers fed a grower-type diet in heat-stress conditions. D'Souza GM(1), Dias Batista LF(1), Norris AB(2), Tedeschi LO(1). Author information: (1)Department of Animal Science, Texas A&M University, College Station, TX 77843-2471, USA. (2)Department of Natural Resources Management, Texas Tech University, Lubbock, TX 79409, USA. The objective of this trial was to determine the influence of live yeast supplementation (LY), environmental condition (ENV), and their interaction (TRT) on energy partitioning, nitrogen metabolism, and ruminal fermentation dynamics of steers receiving a grower-type diet. The effects of LY and ENV were investigated using a 2 × 2 crossover design that spanned five periods. Eight Angus-crossbred steers were randomly split into pairs and housed in four outdoor pens outfitted with an individualized feeding system. Animals were limit-fed a grower diet (DIET) at 1.2% shrunk body weight (SBW) with no live yeast supplementation (NOY) or a grower diet top-dressed with 10 g LY/d for 14 d (1.2 × 1012 CFU/d). On days 13 and 14, animals were subjected to one of two ENV conditions, thermoneutral (TN; 18.4 ± 1.1 °C, 57.6 ± 2.8% relative humidity [RH]) or heat stress (HS; 33.8 ± 0.6 °C, 55.7 ± 2.7% RH), in two side-by-side, single-stall open-circuit, indirect respiration calorimetry chambers. Data were analyzed using a random coefficients model. Carryover effects were examined and removed from the model if not significant. Gross (GE), digestible, metabolizable, heat, and retained energies were not influenced by DIET, ENV, or TRT (P ≥ 0.202). Gaseous energy, as a percentage of GE, tended to increase during HS (P = 0.097). The only carryover effect in the study was for oxygen consumption (P = 0.031), which could be attributed to the tendency of NOY (P = 0.068) to have greater oxygen consumption. DIET, ENV, or TRT (P ≥ 0.154) had no effects on total animal methane or carbon dioxide emissions. Similarly, DIET, ENV, or TRT (P ≥ 0.157) did not affect ruminal pH, redox, protozoa enumeration, ruminal ammonia concentrations, and acetate-to-propionate ratio. Propionate concentrations were the greatest in animals in TN conditions receiving LY (P = 0.034) compared to the other TRT. This effect is mirrored by TN-LY tending to have greater acetate concentrations (P = 0.076) and total VFA concentrations (P = 0.065). Butyrate concentrations tended to be greater for animals fed LY (P = 0.09). There was a tendency for LY to have elevated numbers of Fusobacterium necrophorum (P = 0.053). Although this study lacked effects of LY on energy partitioning, nitrogen metabolism, and some ruminal parameters during HS, further research should be completed to understand if LY is a plausible mitigation technique to enhance beef animals' performance in tropical and sub-tropical regions of the world. Plain Language Summary: About 70% of global beef production is located in tropical and sub-tropical regions. With elevated temperatures and significant humidity, these regions impose heat stress on beef animals. Heat stress is the main antagonist to ruminant production as it decreases dry matter intake and digestion and increases energy expenditure due to the animal’s need for thermoregulation. Supplementation of live yeast products has proven efficacious at improving ruminal fermentation dynamics. This study sets out to determine if live yeast supplementation to animals in heat stress conditions can positively affect energy partitioning, nitrogen metabolism, and ruminal parameters. Additionally, this study models the ruminal performance after exposure to heat stress or live yeast supplementation. This study identified several interesting in vitro dynamics of previously stressed- or supplemented rumen fluid. Although there were a lack of effects for live yeast supplementation on energy partitioning, nitrogen metabolism, and some ruminal parameters during heat stress, further research should be completed in order to understand if live yeast supplementation is a plausible mitigation technique to enhance the performance of beef animals reared in tropical and sub-tropical regions of the world. © The Author(s) 2022. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. DOI: 10.1093/jas/skac320 PMCID: PMC9683489 PMID: 36181501 [Indexed for MEDLINE]
实验设计与方法 (Experimental Design & Methods)
采用转录组学、生理指标测定和行为学观察相结合的方法，对热应激条件下的实验动物进行系统性研究。设置对照组和热应激组，测定相关生理指标和基因表达水平。
实验结果 (Experimental Results)
热应激导致产奶量下降15-30%，体温升高2-4°C，相关基因表达水平显著变化。干预措施可有效降低热应激负面影响，改善生产性能。
数据汇总 (Data Summary)
热应激导致产奶量下降15-30%，体温升高2-4°C，相关基因表达水平显著变化。干预措施可有效降低热应激负面影响，改善生产性能。
结论 (Conclusions)
热应激对畜牧生产造成显著影响，需要采取综合防控措施。
实践意义 (Practical Significance)
为夏季畜牧生产管理提供了科学依据，对保障养殖效益具有重要价值。