季節與芻料變動對乳牛瘤胃菌相與產乳性能之影響

Abstract

本研究旨在探討芻料與季節變化對臺灣荷蘭種乳牛瘤胃微生物群、產乳性能和乳脂肪酸組成之影響。 國內總乳脂肪酸組成的季節性變化及其與飼糧間的關聯性資訊仍然不完整。本研究連續兩年每月收集國內90個乳牛場的總乳樣品，以了解乳成分的季節性變化。此外，自2022年8月至2023年7月，每月從三個乳牛場採集共計36個總乳樣品進行乳成分分析。冷季總乳之產乳量（公斤/天）、乳脂肪（%）、乳粗蛋白質（CP %）、乳真蛋白（%）、乳糖（%）及無脂固形物（SNF %）顯著高於熱季和與暖季（p < 0.05）。相反的，冷季的體細胞數顯著低於熱季與暖季（p < 0.05）。冷季總乳中飽和脂肪酸及肉豆酸（C14:0）濃度顯著高於熱季與暖季（p < 0.05）。而熱季與暖季總乳中油酸（C18:1）濃度顯著高於冷季（p < 0.05）。在不同季節期間，乳牛場A總乳中飽和脂肪酸、新合成型脂肪酸、混合型脂肪酸與棕櫚酸（C16:0）濃度最高（p < 0.05），推測可能與乳牛場A飼糧中脂肪含量較低以及使用乾草代替新鮮飼料或青貯飼料有關。乳牛場 C 總乳中預製型脂肪酸與油酸濃度最高（p < 0.05），則可能與其飼糧中脂肪含量較高有關。採用不同的芻料種類與比例調製相等能量和蛋白質的日糧，並透過兩個試驗評估上述兩個變因對乳牛瘤胃微生物群和產乳性能之影響。試驗一，30頭泌乳牛（產後235 ± 13天；產乳量29.1 ± 1.0公斤/天）分為盤固草組和百慕達草組；試驗二，20頭泌乳牛（產後79.9 ± 8.1天；產乳量34.7 ± 0.6公斤/天）分為盤固草組和燕麥草組。結果顯示，試驗一盤固草組瘤胃微生物Simpson指數顯著高於百慕達草組（p < 0.05）。Weighted UniFrac分析結果指出，兩個試驗中盤固草組、百慕達草組及燕麥草組之間的瘤胃微生物群Beta多樣性群落組成存在顯著差異（p < 0.001）。試驗二盤固草組短普氏菌（Prevotella brevis）相對豐度顯著高於燕麥草組（p < 0.05）。試驗一百慕達草組牛乳中的體細胞數（SCC）、硬脂酸（C18:0）和油酸（C18:1）顯著高於盤固草組（p < 0.05）。試驗二燕麥草組的牛群乳中SNF %顯著高於盤固草組（p < 0.05）；然而，盤固草組牛群乳中尿素氮（MUN）顯著較高（p < 0.05）。 乳牛完全混合日糧中不同的芻料來源與比例會影響瘤胃微生物群和產乳性能。在高纖維含量之完全混合日糧前提下（試驗一），較低比例的芻料替換（盤固草與百慕達草）僅導致瘤胃微生物群多樣性（Beta多樣性或Simpson指數）及產乳性能（乳中SCC、C18:0 及C18:1 濃度）些微的改變。但較高比例的芻料替換時（試驗二盤固草與燕麥草）會導致瘤胃微生物群多樣性（Beta多樣性、微生物群相對豐度與Prevotella brevis）發生更多變化，並且產乳性能表現也受到影響（乳中CP、SNF及MUN）。 總而言之，國內乳牛場之總乳產乳量、乳成分與乳脂肪酸組成皆受到季節變化的影響而且有顯著的差異，而就個別乳牛場的資料可知，完全混合日糧配方中選用之芻料種類或脂肪含量則是造成乳牛群間乳脂肪酸組成差異的可能原因。另外，不同芻料與比例的完全混合日糧，會造成牛群瘤胃微生物群組成及乳成分之改變。本研究結果可提供國內不同季節總乳乳成分與脂肪酸變化基礎值，且為首篇比較國產與進口芻料為主之飼糧配方對瘤胃菌相與產乳性能之影響，期為未來相關研究提供參考依據。

This study explores the effects of forage, seasonal variation, and their combined influence on rumen microbiota, milk production performance, and fatty acid (FA) composition of Holstein dairy cows in Taiwan. Information about seasonal variation in the fatty acid (FA) composition of bulk tank milk and its relationship with dietary factors in Taiwan remains incomplete. Bulk tank milk samples were collected monthly from 90 dairy farms across Taiwan for two years to capture seasonal variations. Additionally, 36 bulk tank milk samples from three farms were collected monthly from August 2022 to July 2023. Milk production (kg/day), fat (%), crude protein (%), true protein (%), lactose (%), and solids-not-fat (%) were significantly higher in the cold season than in the hot and warm seasons (p < 0.05) over the studied period. In contrast, somatic cell counts were significantly lower in the cold season than in the hot and warm seasons (p < 0.05). Total saturated FA and C14:0 concentrations were significantly higher in the cold season than in the hot and warm seasons (p < 0.05). In contrast, the C18:1 concentration was significantly higher in the hot and warm seasons than in the cold season (p < 0.05). However, the C18:0 concentration did not differ significantly by season. Fat and FA concentrations varied significantly among three selected dairy farms (p < 0.05). Milk fat only differed significantly between the three farms in the hot season, with Farm B having the lowest milk fat concentration (p < 0.05). FA concentrations showed significant seasonal effects at all three farms. These results provide an overview of milk FA variation and identify the critical factors influencing variation in bulk tank milk fat and individual farm FA concentrations: dietary ether extract content and forage choice. Different forage sources and proportions were used to formulate rations containing equal energy and protein, and their effects on dairy cows’ rumen microbiota and milk production performance were evaluated in two experiments. In experiment 1, thirty lactating cows (235 ± 13 d postpartum; milk production 29.1 ± 1.0 kg/day) were divided into Pangola and Bermuda groups. In experiment 2, twenty lactating cows (79.9 ± 8.1 d postpartum; milk production 34.7 ± 0.6 kg/day) were divided into Pangola and Oat groups. In experiment 1, the Simpson index for rumen microbiota of the Pangola group was significantly higher than the Bermuda group (p < 0.05). Analysis of the weighted UniFrac distances indicated significant differences in the beta diversity community composition of rumen microbiota between Pangola, Bermuda and Oat groups in both experiments (p < 0.001). The relative abundance of Prevotella brevis was significantly higher in the Pangola than Oat group in experiment 2 (p < 0.05). The somatic cell counts (SCCs), C18:0, and C18:1 in milk were significantly higher in the Bermuda group than Pangola group (p < 0.05) in experiment 1. On the other hand, milk crude protein (CP) and solids-not-fat (SNF) were significantly higher in the Oat group than Pangola group (p < 0.05) in experiment 2; however, milk urea nitrogen (MUN) was significantly higher in the Pangola group (p < 0.05). A switch of forage (Pangola vs Bermuda) at lower proportion of diet under the high total dietary fiber level condition (experiment 1) only caused minor changes in rumen microbiota diversity (Simpson index, beta diversity) and milk production performance (milk SCCs, C18:0 and C18:1). On the other hand, a switch of forage (Pangola vs Oat) at higher proportion of diet under the low total dietary fiber level condition (experiment 2) resulted in more changes in rumen microbiota diversity (beta diversity, relative abundances of bacterial taxa, Prevotella brevis relative abundance) and milk production performance (milk CP, SNF, and MUN). In conclusion, the bulk tank milk production, milk composition, and milk fatty acid composition are all affected by seasonal changes and have significant differences. The data of individual dairy farms shows that the source of forage used in the total mixed ration formula or EE content is a possible cause of differences in milk fatty acid composition between dairy herds. In addition, a total mixed ration with different forage and proportions will cause changes in cattle's rumen microbiota and milk composition. The results of this study provide fundamental values for changes in bulk tank milk composition and fatty acids in different seasons in Taiwan. This thesis is the first study to compare the effects of domestic and imported forage on rumen bacteria and milk production performance and provide a reference for future related research.