γ-胺基丁酸做為飼料添加劑於改善亞熱帶乳牛之熱緊迫試驗

Abstract

環境因子對乳牛的飼養影響深遠，特別是在高溫高濕的條件下，容易導致乳牛出現熱緊迫及免疫功能受損等問題。當環境溫度與濕度升高時，乳牛會經歷不同程度的熱緊迫，表現出尋找遮蔭、增加飲水量、體溫升高與喘氣等明顯行為，同時其懷孕率、採食量及泌乳量也會下降。在多數國家中，溫濕度指數（Temperature Humidity Index, THI）達68-74 被視為熱緊迫的臨界點。然而，臺灣屬於熱帶及亞熱帶氣候，夏季氣溫常超過30℃，且相對濕度高達75%以上，臺灣每年約有8個月的THI超過熱緊迫臨界值。本研究旨在評估透過添加γ-胺基丁酸（Gamma-aminobutyric acid, GABA）來緩解乳牛熱緊迫的影響。試驗於THI大於72時進行，將20頭泌乳牛分為兩組：試驗組（餵食3公克GABA每頭牛）與對照組（未添加GABA），試驗為期2個月。結果顯示，試驗組乳牛的活動量在第8週顯著低於對照組，且雖然泌乳量無顯著差異，但試驗組在試驗末期泌乳增加量有呈現上升趨勢。此外，試驗組乳品質中的體細胞分數差值在第2週及第3週顯著低於對照組，且於試驗後段時期乳房炎累計發生率，試驗組（3/40）低於對照組（12/40），而於血液學、血清學及糞便評分則無明顯變化皆在正常生理範圍內。綜合而言，作為飼料添加劑，GABA可能具有鎮靜效果，使乳牛活動量穩定，並顯示降低乳品質中體細胞數的潛力。此外，GABA在反芻時間、乳品質檢測及血液學指標上，未見不良影響。因此，在臺灣等高溫高濕地區，GABA可作為有效減緩乳牛熱緊迫深具潛力的飼料添加劑，以減輕熱緊迫對乳牛的影響。

Environmental factors have a profound impact on dairy cow management, especially under conditions of high temperature and humidity, which can easily lead to heat stress and compromised immune function in cows. As environmental temperature and humidity rise, cows experience varying degrees of heat stress, exhibiting obvious behaviors such as seeking shade, increased water intake, elevated body temperature, and panting. At the same time, their conception rate, feed intake, and milk yield tend to decrease. In most countries, a Temperature-Humidity Index (THI) between 68 and 74 is considered the threshold for heat stress. However, Taiwan’s tropical and subtropical climate often features summer temperatures exceeding 30°C and relative humidity above 75%, resulting in over eight months each year with THI values surpassing the heat stress threshold. This study aims to evaluate the effects of supplementing feed with gamma-aminobutyric acid (GABA) in alleviating heat stress in dairy cows. The experiment was conducted when the THI exceeded 72. Twenty lactating cows were divided into two groups: a treatment group (fed 3 grams of GABA per cow) and a control group (no GABA supplementation). The trial lasted for two months. Results showed that the activity level of cows in the treatment group was significantly lower than that of the control group in the eighth week. Although there was no significant difference in milk yield, the treatment group showed an increasing trend in milk production toward the end of the trial. In addition, the somatic cell count (SCC) difference in milk was significantly lower in the treatment group during the second and third weeks compared to the control group. Moreover, during the later stage of the experiment, the cumulative incidence of mastitis was lower in the treatment group (3/40) than in the control group (12/40). Hematological, serum, and fecal score assessments showed no significant changes and remained within normal physiological ranges. In summary, as a feed additive, GABA may exert a calming effect that helps stabilize cow activity levels and shows potential for reducing somatic cell counts in milk. Furthermore, GABA did not negatively affect rumination time, milk quality, or hematological parameters. Therefore, in hot and humid regions such as Taiwan, GABA can be considered an effective feed additive to mitigate the adverse effects of heat stress in dairy cows.