以隧道式抽風水簾牛舍紓解荷蘭種泌乳牛於臺灣夏季熱緊迫問題之可行性

Abstract

夏季高溫高濕的熱緊迫一直是國內泌乳牛性能表現的瓶頸，改善牛舍降溫環境是紓解熱緊迫最有效與最直接的方法，本試驗目的在評估應用隧道式抽風蒸發冷卻牛舍 (簡稱水簾牛舍) 來紓解夏季荷蘭種泌乳牛熱緊迫的可行性。2005年試驗採用每期30日的交叉設計，平均乳量26.2 kg的42頭泌乳牛分成二組，分別飼養於水簾牛舍或挑高的太子樓牛舍 (簡稱傳統牛舍)。長方形水簾牛舍可飼養48頭牛隻，一端設置整排八臺抽風扇，對應牆面設置L型整面水簾，兩側以厚塑膠捲簾密閉形成隧道，抽風扇依氣溫升高而啟動，提供牛隻周遭最高風速每秒1.66 m與牛舍空氣交換速度每分鐘2次，空氣抽入時經過水簾上的流水而降溫；傳統牛舍共懸掛四臺全日開啟的風扇，採食區另設置每日六次每次30分鐘的噴水吹風降溫處理。試驗結果顯示，水簾牛舍可以較傳統牛舍降低日間最高舍溫2.4℃，並減少牛隻曝露於中度熱緊迫狀況 (78 < 溫濕度指數 (THI) ≤ 84) 的時間2.5 h；但水簾牛舍內持續高的相對濕度 (全日相對溼度 > 93%) 與低的風速增加牛隻熱負荷，牛隻在4 a.m.的呼吸數 (62 vs. 50次/分鐘)、4 a.m.的直腸溫度 (39.58 vs. 39.31℃) 及2 p.m.的直腸溫度 (39.75 vs. 39.47℃) 都顯著高於傳統牛舍牛隻，牛隻血液CO2分壓 (41.4 vs. 43.8 mmHg) 降低，血液pH值顯著增加。同時，水簾牛舍飼養環境顯著減少牛隻的採食活動，使牛隻乾物質採食量降低7.6% (17.0 kg vs. 18.4 kg)，4%乳脂校正乳量降低10.1% (23.1 kg vs. 25.7 kg)，乳蛋白質濃度也顯著降低，但水簾牛舍環境並不影響瘤胃的消化，牛隻的瘤胃pH值、揮發性脂肪酸與氨態氮濃度都相近。為改善水簾牛舍的氣候環境，2006年增加牛舍內的抽風扇數量，並安裝與傳統牛舍相同的噴水處理，提供白天最高風速2.38 m/s與3.2次/min的空氣交換速度，夜間環境估計分別為1.17 m/s與1.4次/min。2006年試驗採用一個3 x 3拉丁方設計，將36頭泌乳牛分組飼養於傳統牛舍、水簾牛舍或水簾+噴水牛舍，試驗每期21日。結果顯示，水簾兩組在降低牛舍日間溫度與THI的效率高於傳統牛舍，每日增加舍內氣溫 < 26℃的時間達4.2小時，但全日相對濕度 > 96%。水簾兩組牛隻3 a.m.的呼吸數與體表溫都顯著高於傳統牛舍組牛隻。水簾組牛隻陰道溫度持續高，但噴水兩組牛隻陰道溫度可隨噴水與擠乳處理後明顯下降0.4 – 0.6℃。三種牛舍環境對牛隻採食活動、瘤胃消化及泌乳性能的影響相近，但水簾兩組牛隻採食量顯著較高，且水簾+噴水組牛隻乳量有高於傳統組的趨勢 (25.4 kg vs. 24.7 kg, P = 0.10)。由2006年試驗結果顯示，三種牛舍環境雖仍無法完全紓解泌乳牛熱緊迫，但經由增加風速與噴水降溫處理，水簾兩組牛隻的採食與泌乳都已相當於或優於傳統組牛隻表現，因此水簾牛舍在高濕地區的使用值得繼續研究。除了影響泌乳牛生理反應與泌乳性能，熱緊迫也嚴重影響乳牛的熱季繁殖效率。2005年調查傳統牛舍與水簾牛舍牛隻的血清助孕素濃度，得知在同期化發情處理過程中，12頭泌乳牛助孕素濃度相近。於2007年熱季將40頭泌乳牛分組飼養於傳統牛舍或水簾+噴水牛舍90天 (換氣速度3.2次/min)，進行兩次前列腺素注射的發情同期化處理。試驗結果顯示，不論在一般傳統牛舍或水簾+噴水牛舍，熱季期間牛隻對標的配種計畫的反應皆不理想，全期試驗每次人工授精受孕率分別為20.7%與17.4%，全期懷孕率分別為30%與21.1%。收集接續三年期間 (2008 - 2010) 的田間紀錄，以2 x 2複因子設計，分析泌乳牛繁殖效率受畜舍降溫處理 (一般傳統牛舍或水簾+噴水牛舍) 及季節 (涼熱兩季) 之影響。結果顯示，泌乳牛熱季 (5 - 10月) 懷孕率，在一般傳統牛舍或水簾+噴水牛舍分別為29.0%與26.4%，全年則分別為40.2%與36.3%，無顯著性差異。綜合三次試驗結果，顯示水簾牛舍的高濕度問題可藉由提高風速來減緩，水簾牛舍內再配合噴水降溫處理，可以有效協助牛隻排熱，提高牛隻泌乳性能，但仍無法解決熱季繁殖效率的低落，如何增加牛舍內通氣量與降低相對濕度，為往後繼續努力的方向。

Heat stress from high temperature and humidity is always the bottleneck in enhancing lactation performance of dairy cows in Taiwan. Improving the barn environment is the most effective and direct method to alleviate cow heat stress. The feasibility of heat stress alleviation for Holstein lactating cows by a tunnel-ventilated, water-padded (TP) barn was assessed in this study. In 2005, a crossover designed experiment was conducted for 30 days a period. A total of 42 head of cows with milk yield of 26.2 kg a day were assigned into the TP barn or the conventional barn. The rectangle TP barn has a raising space for 48 head of lactating cows. Eight exhaustive fans and an L shape water-pad were set at the two end walls in the TP barn. Heavy plastic curtains formed both long side walls contributed the tunnel effect. The exhaustive fans would be turned on following the increasing air temperature and provided the highest daytime air speed of 1.66 m per second and air exchange rate of two times per minute. Evaporating water in the pad absorbs heat from the incoming air and cools the air. Four hung fans operated all day long were set in the conventional barn. Additional six 30-min sprinkler cooling cycles a day were arranged along the intake alley. The results indicated that TP barn could effectively cut down 2.4℃ more at the highest daytime temperature, and decreased 2.5 h more for cows suffering the medium heat stress (78 < THI ≤ 84) than conventional barn did. However, the persistently high relative humidity (> 93%) and low air speed inside the TP barn increased the heat load for cows. Cows raised in the TP barn had the higher 4 a.m. respiration rate (62 vs. 50 breaths/min), 4 a.m. rectal temperature (39.58 vs. 39.31℃), and 2 p.m. rectal temperature (39.75 vs. 39.47℃) than those raised in the convention barn. TP barn environment decreased the partial pressure of CO2 in cow blood (41.4 vs. 43.8 mmHg), thus increased the blood pH. Meanwhile, TP barn environment significantly decreased cow intake activity and resulted in the lower dry matter intake and 4% fat corrected milk yield by 7.6% (17.0 kg vs. 18.4 kg) and 10.1% (23.1 kg vs. 25.7 kg), respectively. Percentage of milk protein was also decreased. But rumen digestion pattern was kept the same. Diurnal rumen pH, NH3-N and volatile fatty acid productions were not influenced by barn environments. To improve the TP barn environment, fan numbers were increased and same sprinkling program as that in the conventional barn were applied in 2006. The highest daytime air speed at cow level and air exchange rate reached 2.38 m/s and 3.2 times/min after the modification. Both parameters at night in the TP barn were estimated to be 1.17 m/s and 1.4 times/min, respectively. In 2006, 36 cows allocated in a 3 x 3 Latin square with 21 days a period were raised in three barn cooling treatments: the conventional barn like in 2005 trial, a TP barn and a TP barn with sprinkler cooling (TP+SP). Both TP barns were more efficient in reducing the daytime temperature and the temperature humidity index. The barn temperature was less than 26°C for an extra 4.2 h per day, but the relative humidity was above 96% in both TP barns. Cows in both TP barns had higher 3 a.m. respiration rates and skin temperatures than cows in the conventional barn. Vaginal temperature was persistently high in cows in the TP barn; in the two barns with sprinkler cooling, vaginal temperature could effectively decreased 0.4 to 0.6°C following the sprinkling and milking. The intake activity, rumen digestion, and milking performance of cows raised in the three environments were similar. Cows in both TP barns ingested more dry matter. Cows in the TP+SP barn tended to produce more milk than those in the conventional barn (25.4 vs. 24.7 kg, P = 0.10). Although cows’ heat stress was not completely alleviated in these three barns, the TP+SP treatment resolved the negative impact of a previous TP barn built in 2004 on intake and milk yield by increasing air speed and using sprinkler cooling. Thus, it is expected that TP+SP barns will be beneficial in areas of high humidity. Except for the physiological responses and milking performance, the reproductive efficacy of cows is also influenced by the environmental heat stress. The serum progesterone levels during synchronization treatment were similar from 12 cows raised in the conventional barn and TP barn in 2005. In 2007 summer, a total of 40 cows were assigned into the conventional barn or the TP+SP barn (air exchange rate of 3.2 times/min) for a period of 90 days. A target breeding program with two consecutive prostaglandin injections at 14-d interval was applied. No matter cows were raised in the conventional barn or the TP+SP barn, responses to prostaglandin treatment of cows in hot summer was not ideal. Conception rate per AI of cows in these two barns were 20.7% and 17.4%, and for the whole period pregnancy rate were 30% and 21.1%, respectively. From 2008 to 2010, reproductive field data of lactating cows were collected. Data were categorized and statistically analyzed in a 2 x 2 factorial design including barn cooling treatments, conventional barn or TP+SP barn, and seasons, cool or hot season. Results showed that conception rate of cows were not affected by the barn treatment. In hot season (May to Oct.), conception rate of cows in conventional barn and TP+SP barn were 29.0% and 26.4%, and were 40.2% and 36.3% for the whole year, respectively. Results from all three studies suggested that the high humidity problem in TP barn could be mitigated by the higher air speed. The application of sprinkler cooling in TP barn is beneficial for cows to dissipate their body heat so that to promote the milking performance. However, poor reproductive efficacy in the hot summer is not resolved by the TP+SP barn. Adequate air speed and lower humidity are likely to be key factors for further TP barn study.