Abstract：
Heat stress (HS) is one of the pivotal causes of economic losses in dairy industries and affects welfare and performance, but its effect on milk microbiota remains elusive. It is also unclear if and how different breeds may cope with HS in sustaining productive performance. The objectives of this study were to compare a) the performance of 2 dairy breeds, namely Holstein and Brown Swiss, subjected to HS and b) the different effects of HS on the milk microbiota of the 2 breeds in thermal comfort conditions and HS. The study was carried out on 36 dairy cows, 18 per breed. The HS was induced by switching off the cooling system during a natural heat wave for 4 d. Besides the Temperature Humidity Index (THI), the animal stress was confirmed by measuring respiratory frequency and rectal temperature twice daily at 4 a.m. and 3 p.m. The HS differently impacted the 2 breeds. Rectal temperatures were higher in Holstein cows, while no changes in rectal temperature were found in Brown Swiss. Milk yield recording and sampling were performed during the morning milking of d 1 (at 4.00 a.m.) and afternoon milking of d 4 (at 5.00 p.m.). Productive parameters were also different: milk yield, fat-corrected milk, energy-corrected milk, protein and casein content, and renneting parameters were decreased in Holstein but remained unaffected in Brown Swiss. The HS also modified the milk microbiota of the 2 breeds differently. During HS, the Brown Swiss milk microbiota was richer (α diversity) than the Holstein one. Comparing the time points before and during HS within breeds showed that Brown Swiss milk microbiota was less affected by HS than Holstein\'s. Under the same thermal comfort condition, milk microbiota did not discriminate between Brown Swiss and Holstein. Consistently with α and β diversity, the number of operational taxonomic units (OTUs) at the genus level that changed their abundance during HS was higher in Holstein (74 OTUs) than in Brown Swiss (only 20 OTUs). The most significant changes in abundance affected Acinetobacter, Chryseobacterium, Cutibacterium, Enterococcus, Lactococcus, Prevotella-9, Serratia, and Streptococcus. In conclusion, the present report confirms and extends previous studies by demonstrating that Brown Swiss cows regulate their body temperature better than the Holstein breed. The relative thermal tolerance to HS compared with Holstein is also confirmed by changes in milk uncultured microbiota, which were more evident in Holstein than in Brown Swiss.
摘要：
热应激(HS)是乳制品行业经济损失的重要原因之一,影响乳制品行业的福利和绩效,但它对牛奶微生物群的影响仍然难以捉摸。还不清楚不同品种是否以及如何应对HS以维持生产性能。这项研究的目的是比较a)2个乳品品种的表现，即荷斯坦和布朗瑞士，进行HS和b）在热舒适条件和HS下，HS对2个品种的牛奶微生物群的不同影响。这项研究是在36头奶牛身上进行的，每个品种18个。HS是通过在自然热浪期间关闭冷却系统4d而引起的。除了温度湿度指数（THI）之外，通过每天凌晨4点和下午3点两次测量呼吸频率和直肠温度来确认动物应激。HS对2个品种的影响不同。荷斯坦奶牛的直肠温度较高，而在布朗瑞士没有发现直肠温度的变化。在d1的早晨挤奶（凌晨4点）和d4的下午挤奶（下午5点）进行产奶量记录和采样。生产参数也不同：产奶量，脂肪校正牛奶，能量校正牛奶，蛋白质和酪蛋白含量，荷斯坦州的重新设计参数有所下降，但在布朗瑞士人中未受影响。HS还不同地改变了2个品种的乳微生物群。在HS期间,布朗瑞士牛奶的微生物群（α多样性）比荷斯坦州的微生物群更丰富。在品种内比较HS之前和期间的时间点表明，布朗瑞士牛奶微生物群受到HS的影响小于荷斯坦氏。在相同的热舒适条件下，牛奶微生物群没有区分布朗瑞士和荷斯坦。与α和β多样性一致，在HS期间改变其丰度的属水平上的操作分类单位（OTU）的数量在荷斯坦州（74个OTU）高于布朗瑞士州（只有20个OTU）。最显著的丰度变化影响不动杆菌，金杆菌,Cutubacterium,肠球菌,乳球菌,Prevotella-9,沙雷氏菌,和链球菌。总之,本报告证实并扩展了以前的研究，证明布朗瑞士奶牛比荷斯坦奶牛更好地调节体温。与荷斯坦相比，对HS的相对耐热性也通过牛奶未培养微生物群的变化得到证实，这在荷斯坦比在布朗瑞士更明显。
