懷孕牛於不同季節及不同降溫模式紓解熱緊迫之生理、行為變化與產後表現

Abstract

隨著全球暖化程度變得越來越嚴重，熱緊迫成為阻礙酪農業發展的最關鍵挑戰之一，龐大的經濟損失也隨之而來。熱緊迫對經濟效益最直接的影響是產乳量的減少與較差的繁殖性能。牛乳是最重要的營收來源，因此，在炎熱季節提供泌乳牛舒適的環境是酪農的首要任務。然而目前已經有一些研究指出如果懷孕牛受到熱緊迫，也會使產前的生理及行為表現受到負面影響，即使在分娩之後都是飼養在有降溫的環境中，這些負面影響仍然會延續到隨後的泌乳期。 由於目前懷孕牛的環境降溫管理仍然不如泌乳牛良好，因而本實驗旨在為懷孕牛找到較適當的環境降溫管理。本研究在台大乳牛場和台南的商業乳牛場進行。在台大乳牛場我們收集熱季（5月至10月）與涼季（11月至4月）懷孕牛的生理和行為資料，以及產後的泌乳表現、繁殖表現以及小牛的生長狀況。涼季的懷孕牛不分組，以涼季資料建立沒有熱緊迫狀況的參考。熱季的懷孕牛在產前分到風扇+灑水組（FS，7頭）和風扇+灑水+噴霧組（FSM，6頭）兩種不同降溫方式的環境，以產前及產後表現來比較兩種不同降溫方式的效果。在台南的商業乳牛場，我們收集熱季 (4頭)和涼季 (5頭)牛隻懷孕末期活動量和產後泌乳表現，以檢查兩個季節之間的差異。 在台大乳牛場，我們發現風扇+灑水+噴霧的環境對懷孕牛來說是更舒適的。這組牛隻的全天呼吸速率較低 (P<0.01)、總產前乾物質採食量較多 (P<0.01)、站立時間有較短的趨勢 (P<0.1)、採食時間較長 (P<0.05)、反芻時間也較長 (P<0.001)。分娩後，FS組發現更多疾病事件。FSM組的乳量有多於FS組的趨勢 (P<0.1)，其差異約為4 公斤/天。乳成分數據顯示FS組乳樣品中的脂肪/蛋白質比超過1.4的比例較高，表示此組牛隻的能量代謝狀況較不佳。在繁殖性能方面，發現FSM組的配種成功率更高 (FSM組67%; FS組36%)。此外，雖然兩組小牛的體重沒有差異，但兩組之間的體重差異隨著小牛年齡的增長而增加。在台南的商業乳牛場，我們發現在同一季節內當溫濕度指數較高時，懷孕牛的活動也會較高。另一方面，熱季的整體活動量低於涼季。熱季的產前平均每小時活動量為42，涼季則為60。熱季與涼季產後平均乳量分別為25.47和27.61公斤/天。 綜合上述，熱季時提供懷孕牛適當的降溫使生理和行為表現以及產後泌乳表現及繁殖性能更好。此外，我們可以使用在涼季觀察到的各項資料作為熱季調整到相對較好的降溫模式之初步參考。

As global warming is getting worse, heat stress becomes one of the most critical challenges hampering the dairy industry today and it causes enormous economic losses. The most immediate impact is lower milk yield, and poorer reproductive performance. Milk is the most important source of income revenue, providing dairy cows good environment especially in hot season is the top priority for dairy farmers. Some research indicated if pregnant cows suffer from heat stress, it will affect their physiology and behavior and the negative influences can be carried over to the subsequent lactation even when they were maintained in a cooling environment following calving. In the light of the environment management of pregnant cows is still not as delicate as lactating cows, the present experiment is intended to find a proper environmental cooling management for pregnant cows. The study conducted at NTU dairy farm and a commercial farm in Tainan. At NTU dairy farm, we collected physiological and behavioral information of pregnant cows during the hot season (May-October) and the cool season (November-April), as well as their postpartum lactation performance, reproductive performance and growth of the calves. The pregnant cows in the cool season were all in one group to establish a performance baseline for no heat stress condition. The pregnant cows in the hot season were divided into fan+sprinkler group (FS n=7) and fan+sprinkler+mist group (FSM n=6) prepartum to compare the effects of two different cooling modules. At commercial farm in Tainan, we collected late gestation activity and postpartum lactation performance in hot (n=4) and cool (n=5) seasons to check difference between two seasons. At NTU dairy farm, we found the environment of fan+sprinkler+mist group for pregnant cows was more comfortable. The pregnant cows in this group had lower respiration rate (P<0.01) and more dry matter intake (P<0.01). FSM group had a trend to be lower standing time (P<0.1), longer feeding time (P<0.05) and rumination time (P<0.001). After calving, more disease events were found in the FS group. The milk yield of the FSM group had a trend to be higher than FS group (P<0.1), and their difference is about 4 kg/day. The milk composition data showed that the fat/protein ratio of greater portion of FS group milk samples was higher than 1.4, indicating worse energy status. Furthermore, on the reproductive performance, it was found that the conception rate of the FSM group was higher (FSM group 67%; FS group 36%). Although there was no difference in calf body weight between the two groups, the body weight difference between two groups inclined as calves grew. At commercial farm in Tainan, we found when the temperature humidity index was higher within the same season, the activity of pregnant cows were higher. On the other hand, the overall activity in the hot season is lower than the cool season. In the hot season, the prepartum average hourly activity was 42, and in the cool season was 60. The average postpartum milk yields were 25.47 and 27.61 kg/day for hot and cool seasons, respectively. In conclusion, cooling pregnant cows appropriately in hot season makes physiological and behavior performance and postpartum lactation and reproduction performance better. Besides, we can use the performance baseline observed in cool season as a preliminary reference for adjusting to a relatively good cooling module in hot season.