J Anim Sci. 2017 Dec;95(12):5547-5562. doi: 10.2527/jas2017.1843.
Selection for high productivity has resulted in ruminants adversely affected by heat stress (HS) due to their high metabolic rate and feed intake. One mechanism to ameliorate HS is to reduce the forage-to-concentrate ratio in the diet, although the inclusion of readily fermentable grains can reduce heat tolerance. The aim of these experiments was to investigate a chemical method for reducing the rate of fermentation of wheat and its effect on improving heat tolerance in sheep. In the first experiment, fermentation kinetics and buffered rumen fluid pH variation during in vitro incubation of corn, wheat, and 3% NaOH-treated wheat grains were compared. This experiment showed that corn and 3% NaOH-treated wheat had a slower (-23 and -22%, respectively; < 0.001) rate of gas production and elevated buffered rumen fluid pH ( < 0.001) compared with wheat. In the second experiment, 31 Merino × Poll Dorset wethers were housed in 2 climate-controlled rooms and were fed either corn grain plus forage (42.7% starch; were fed either corn grain plus forage (CD), wheat grain plus forage (WD) or 3 % NaOH-treated wheat plus forage (TWD) during 3 experimental periods: period 1 (P1), which consisted of 7 d of thermoneutral conditions (18 to 21°C and 40 to 50% relative humidity) and 1.7 times maintenance feed intake; period 2 (P2), which consisted of 7 d of HS (28 to 38°C and 30 to 50% relative humidity) and the same feed intake as in P1; and period 3 (P3), which consisted of 7 d of HS as in P2 and 2 times maintenance feed intake in a randomized control experiment. Water was offered ad libitum. The impact of HS was quantified by increases in rectal temperature, respiration rate (RR), and flank skin temperature (FT); variations in blood acid-base balance; and glucose, NEFA, and heat shock protein 70 (HSP-70) plasma concentrations. All physiological variables were elevated during HS, especially when wethers had greater feed intake (P3). Wethers fed CD had lower RR, rectal temperature, and FT than wethers fed WD ( < 0.001) and wethers fed TWD had lower RR and FT than wethers fed WD during HS ( < 0.05). There were reductions in blood CO, HCO3, and base excess concurrent with increases in blood partial pressure of O and pH during HS ( < 0.05). Heat stress reduced plasma NEFA and glucose concentrations whereas it increased prolactin ( < 0.05). Prolactin and HSP-70 plasma concentrations were greater for WD-fed wethers ( < 0.001) associated with Prolactin and HSP-70 plasma concentrations were greater for WD fed wethers (P < 0.001) during HS. These data indicate that the slow rate of rumen fermentation of CD and TWD can reduce the heat released during feed fermentation in the rumen, improving heat tolerance in sheep.
选择高生产力导致反刍动物由于高代谢率和采食量而受到热应激（HS）的不利影响。一种改善 HS 的机制是降低饲料中的粗饲料与精饲料的比例，尽管可快速发酵的谷物的添加会降低耐热性。这些实验的目的是研究一种降低小麦发酵速度的化学方法及其对提高绵羊耐热性的影响。在第一个实验中，比较了玉米、小麦和 3%NaOH 处理的小麦粒在体外培养过程中的发酵动力学和缓冲瘤胃液 pH 变化。该实验表明，与小麦相比，玉米和 3%NaOH 处理的小麦的气体产生速率较慢（分别为-23%和-22%；<0.001），缓冲瘤胃液 pH 升高（<0.001）。在第二个实验中，31 只美利奴×多赛特杂交羊被安置在 2 个气候控制室内，分别饲喂玉米粒加饲料（42.7%淀粉）（CD）、小麦粒加饲料（WD）或 3%NaOH 处理的小麦粒加饲料（TWD），在 3 个实验期：第 1 期（P1），包括 7 天的常温条件（18-21°C，相对湿度 40-50%）和 1.7 倍维持饲料采食量；第 2 期（P2），包括 7 天的高温高湿条件（28-38°C，相对湿度 30-50%）和 P1 相同的饲料采食量；第 3 期（P3），包括 7 天的高温高湿条件和 P2 相同的饲料采食量，在随机对照实验中，饲料采食量增加 2 倍。自由饮水。通过直肠温度、呼吸率（RR）和侧腹皮肤温度（FT）的升高来量化 HS 的影响；血液酸碱平衡的变化；以及葡萄糖、非酯化脂肪酸（NEFA）和热休克蛋白 70（HSP-70）的血浆浓度。所有生理变量在 HS 期间均升高，特别是当绵羊的采食量增加时（P3）。与 WD 组相比，CD 组绵羊的 RR、直肠温度和 FT 较低（<0.001），TWD 组绵羊的 RR 和 FT 也较低（<0.05）。HS 期间，血液 CO、HCO3 和碱剩余减少，同时血液部分压力 O 和 pH 增加（<0.05）。HS 降低了血浆 NEFA 和葡萄糖浓度，而增加了催乳素（<0.05）。WD 组绵羊的催乳素和 HSP-70 血浆浓度更高（<0.001），与 HSP-70 血浆浓度相关（<0.001）。这些数据表明，CD 和 TWD 的瘤胃发酵速度较慢可以减少瘤胃发酵过程中释放的热量，从而提高绵羊的耐热性。
