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2019. J. Anim. Sci. 97(2):735-744

https://doi.org/10.1093/jas/sky468.

免疫系統激活提高生長豬蛋白質沉積對蘇氨酸的需要量

Whitney D McGilvray, Hailey Wooten, Amanda R Rakhshandeh, Amy Petry, Anoosh Rakhshandeh

前人的研究發現免疫系統激活會提高蘇氨酸的利用率。但是，由于內源氨基酸可能會彌補日糧氨基酸的不足，所以蘇氨酸利用率的提高并不意味著對日糧需要量的提高。本試驗評估了免疫系統激活對蘇氨酸不同需要量（如維持需要、蘇氨酸沉積率）的影響。

試驗選用39頭商品小母豬（初始重32±2.1kg），分別為單個代謝籠飼養，隨機分為六個處理組。6個日糧中蘇氨酸為第一限制性氨基酸。根據免疫應激組豬蛋白質沉積速度估算其氨基酸需要量，日糧蘇氨酸含量分別為70%、90%、110%蘇氨酸需要量。隨著試驗日糧適應期結束后，隨機注射生理鹽水或大腸桿菌脂多糖（25和35ug/kg體重），48小時后再注射一次。檢測注射后72小時內機體氮平衡情況。監控豬機體溫度變化情況，注射24小時后收集血液樣品，檢測血液化學指標。

血液化學指標和體溫結果表明豬只處于免疫應激狀況（P＜0.03）。所有免疫應激組蘇氨酸線性提高了蛋白沉積（P＜0.01）。從線性方程的斜率可以看出，蛋白沉積利用的標準可消化蘇氨酸的邊際利用效率不受免疫應激狀態的影響。但是，從線性方程的截距來看，免疫應激大幅度的提高了SID蘇氨酸的維持需要量（對照組VS應激組，-11.2 VS -56.3， SE13.2； P＜0.05）。

總之，本試驗結果說明免疫應激下生理狀態的變化提高了蘇氨酸的維持需要，進而導致對日糧蘇氨酸需要要的提高。

Immune system stimulation increases dietary threonine requirements for protein deposition in growing pigs

Whitney D McGilvray, Hailey Wooten, Amanda R Rakhshandeh, Amy Petry, Anoosh Rakhshandeh

Previous studies have reported an increase in the utilization of threonine (Thr) during immune system stimulation(ISS). However, increased utilization of an AA during ISS may not reflect an increased dietary requirement, as endogenous sources may supply AA to meet the need for enhanced utilization. The current study evaluated the impact of ISS on components of dietary Thr requirements, i.e., maintenance requirement and the efficiency of Thr utilization. Thirty-nine gilts (initial BW 32 ± 2.1 kg) of commercially relevant genetics were individually housed in metabolism crates and fed one of six experimental diets in which Thr was the first limiting among other AA. Three levels of dietary Thr were tested within each ISS group: 70%, 90%, and 110% of daily Thr requirements, which were estimated based on the potential of each ISS group for protein deposition (PD). Following adaptation to the experimental diets, pigs from each dietary treatment group were injected with either increasing amounts of Escherichia coli lipopolysaccharide (ISS+; 25and 35 μg/kg BW) or saline (ISS−). Injections were given 48-h apart and whole-body nitrogen balance was measured for 72-h following the first injection. Body temperature (BT) was monitored and blood samples were collected 24 h after initiation of ISS and evaluated for measures of blood chemistry. Blood chemistry and BT results indicated an effective ISS in pigs (P < 0.03). Threonine intake increased PD in a linear fashion in both ISS groups (P < 0.01). The marginal efficiency of standardized ileal digestible (SID) Thr utilization for PD, represented by the slope, was not affected by ISS. However, ISS substantially increased the extrapolated maintenance SID Thr requirements, represented by the intercept at zero PD (ISS−vs. ISS+, −11.2vs. −56.3SE 13.2; P < 0.05). Collectively, our results indicated that the physiological changes associated with ISS increased the dietary SID Thr requirements for PD due to an increase in maintenance requirements.

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