藉由環境及營養的調整策略改善熱季泌乳羊生產表現

Abstract

臺灣熱季時間長，氣候高溫多濕，環境溫濕度指數（temperature-humidity index, THI）往往高於熱緊迫之標準，因此熱緊迫一直是酪農首要克服的問題。熱緊迫會造成泌乳羊體溫上升、呼吸速率加快並伴隨有喘氣行為的出現，此外採食量下降以及飲水量增加也是熱緊迫下典型的表現。在生產表現上會造成羊隻乳產量下滑，乳成分表現亦受負面影響，乳脂率、乳蛋白質以及非乳脂固形物會下降。甚至在熱季，非乳脂固形物無法符合生羊乳國家標準已是常態。解決的辦法除了選拔較耐熱的品種之外，在環境改善方面，可以加裝蒸發降溫的設備如灑水、噴霧，另外透過營養方面的調控，調整日糧能量、蛋白質、芻精比等，希望能彌補熱季採食量不足的問題。 本試驗分做兩個部分，第一部分在臺大試驗農場，選用12隻已過泌乳高峰之阿爾拜因（Alpine）山羊，依據乳量、胎次將羊隻平均分配成兩個處理（對照組、日糧調整組），兩組羊隻分別飼養於兩個大欄位。試驗期間包含三週開啟噴霧降溫設備以及關閉噴霧降溫設備後的4天，期間收集剩料、羊乳樣品以及呼吸速率，並記錄試驗環境溫度及濕度以計算THI。第二部分在嘉義及臺南共三間商業乳羊場，預先收集採食量、日糧配方、呼吸速率、乳產量以及乳成分作為初始參考值，將日糧做調整包括調降芻精比例、增加蛋白質含量、提高能量濃度等等。收集調整後泌乳羊採食量、乳產量以及乳成分等資料，將調整前後做對照，評估日糧調整對於羊隻熱季表現的改善效果。 第一部分結果顯示，在開啟噴霧降溫的三週前後，日糧調整組的羊隻，採食量增加了36%（1621.2 g/head/d vs 1188.0 g/head/d），乳產量也增加了11.7%達到顯著差異，乳蛋白質及非乳脂固形物雖無顯著差異，但在三週後也有提升的現象。而在關閉噴霧後，採食量及乳產量皆在一天之內下降，乳產量呈顯著下滑。對照組羊隻的呼吸速率及採食量甚至出現有起伏的不穩定表現，由此可見熱季的蒸發降溫系統的必要性。但在噴霧關閉的前後，泌乳羊呼吸速率並無顯著差異，因此噴霧降溫的效果並不如預期，仍需更多試驗找出最佳的設定。 第二部分試驗在三間商業乳羊場做日糧調整，105年A乳羊場芻精比從76:24降低至65:35，日糧粗蛋白質含量自10.51%提升至15.11%並增加過瘤胃蛋白含量，結果採食量提高，乳產量提高20%，乳蛋白質及SNF皆有上升；105年B乳羊場日糧精料比例高達60%，日糧粗蛋白質自14.16%提高至17.45%同時增加過瘤胃蛋白質，結果採食量增加，乳產量增加8.8%，乳蛋白及SNF些微提升；106年A乳羊場增加日糧蛋白質（14.56% vs 12.97%）並提高過瘤胃蛋白，結果乳產量增加8%，乳成分沒有變化；106年C乳羊場僅將品質差的苜蓿草換成品質較佳的苜蓿乾草，使得日糧粗蛋白質含量自12.36%提高至16.45%，結果乳產量增加3.6%，乳蛋白質及SNF也有提升的情形。 綜合上述，熱季提高日糧精芻比例和粗蛋白質含量，並提高過瘤胃蛋白質比例，對於改善泌乳羊生產表現，如乳產量、乳蛋白質及SNF皆有正面的效果，可作為熱季泌乳羊調整日糧的主要原則。噴霧降溫能夠幫助泌乳羊紓解熱緊迫，但設定的細節仍需要更多試驗去支持。

It is hot and humid in the long hot season in Taiwan. Heat stress is very common in hot season and is a problem must be solved first in dairy industry. Heat stress will increase rectal temperature and respiration rate. Panting is a typical behavior in heat stressed goats. Dry matter intake (DMI) decreases and water consumption increases during heat stress. Heat stress also decreases lactation performance. Milk production, milk fat, milk protein, and milk solids-non-fat (SNF) decline during heat stress. There are three methods to reducing the effects of heat stress: selecting heat tolerant goat breed/strain, physical modification of environment such as water sprinkling and mist cooling, and nutritional management to counteract the declined intake during hot season. There are two parts of this experiment. First part was at NTU farm. Twelve Alpine dairy goats were assigned according to milk yields and parities into two different two treatment groups (control diet and nutrition-modified diet). During the experiment period, we recorded temperature and relative humidity to calculate THI. Refusals, milk samples, and respiration rate of goats were also collected and measured. Then we monitored changes in compositions of nutrient intake and milk compositions. The second part of the experiment was conducted at three commercial farms in Chiayi and Tainan. The monitored items were the same as first part of experiment. The nutrition modification included decreasing forage to concentrate ratio, increase crude protein density and energy density. About a month after feeding nutrient-modified diet, we collected all the items again to compare the differences before and after diet modification. In the first part, DMI increased 36% and milk production increased 11.7% significantly in nutrient-modified group with water mist and fan cooling. Milk protein and SNF increased a little. When the mist cooling turned off, DMI and milk production decreased immediately. Besides, in control group, DMI and respiration rate were unstable. This implicated the importance of evaporative cooling. However, respiration rate was not significantly different with mist cooling or not. It was not effective as we expected. So, it still needs more experiments to find out the best settings for better cooling. In the second part, the forage: concentrate ratio in A farm in 2016 was lowered (76:24 vs 65:35), and the protein ratio increased (10.51% vs 15.11%) by adding rumen undegradable protein (RUP). As a result, DMI increased and milk production increased 20%. Milk protein and SNF also increased. The concentrate ratio in B farm in 2017 was 60%. We increased protein ratio and RUP of the diet (14.16% vs 17.45%) and we found that DMI and milk production increased. Milk protein and SNF increased a little. We increased protein ratio and RUP in A farm in 2017 and found that milk production increased 8% with no change in milk contents. In C farm in 2017, we changed high quality alfalfa forage to raise dietary protein content (12.36% vs 16.45%). Milk yield was increased by 3.6% with higher milk protein and SNF. In conclusion, by increasing concentrate: forage ratio, protein ratio, and RUP in diet, there were positive effects on lactation performance such as milk yields, milk protein, and SNF in hot season. It could be a useful principle in hot season for nutritional modification for dairy goats. Evaporative cooling as water mist can help to decrease the negative effects of heat stress, but it needs more experiments to find out water mist settings for better cooling effect.