Thompson I M T, Tao S, Monteiro A P A, Jeong K C, Dahl G E
Department of Animal Sciences, University of Florida, Gainesville 32611, USA.
J Dairy Sci. 2014 Dec;97(12):7426-36. doi: 10.3168/jds.2013-7621. Epub 2014 Oct 18.
Heat stress in the dry period affects the immune status of dairy cows in the subsequent lactation. We hypothesized that cooling during the dry period improves immune response to postpartum intramammary infection (IMI) by environmental pathogens such as Streptococcus uberis. Cows were dried off 46 d before expected calving and assigned to cooling (CL, n = 15) or heat stress (HT, n = 15). Cooled cows were housed with sprinklers, fans, and shade, whereas the HT group had only shade. All cows were cooled postpartum. Rectal temperature (RT) and respiration rate (RR) were recorded thrice weekly during the dry period. From −46 to 42 d relative to calving, dry matter intake was recorded daily, and both body weight (BW) and body condition score (BCS) weekly. Milk yield and composition were recorded daily after calving. Streptococcus uberis IMI was induced at 5 d postpartum in a subset of cows (CL, n = 5; HT, n = 5). Blood was collected at 0, 12, 18, 24, and 36 h after IMI. Hematological analysis was performed, and neutrophils isolated for RNA extraction. Immune response genes (TLR2, IL1-β, IL6, IL8, IL10, and TNFα) were assessed by real-time, reverse transcription-PCR. Relative to HT cows, CL cows had lower RT and RR during the dry period. The CL cows also consumed more feed prepartum but not postpartum, gained more BW prepartum but lost more BW in lactation, and had higher BCS score prepartum and a lower BCS postpartum. During 40 wk of lactation, CL cows produced more milk (33.8 vs. 30.0 kg/d) than HT cows but milk composition was not affected. Cows in the CL group had greater white blood cell counts and more neutrophils than HT cows during IMI. From 0 to 36 h post-IMI, TNFα mRNA expression decreased, whereas that of IL6 and IL8 increased in both treatments. Additionally, CL cows had lower IL10 mRNA expression at 18 h post-IMI. Expression of TLR2 mRNA decreased over time in both treatments. However, CL cows had greater overall TLR2 mRNA expression than HT. No differences were detected for mRNA expression of IL1-β, IL6, IL8, or TNFα. Cooling cows during the dry period alters immune function and neutrophil response to IMI in early lactation.
干奶期的热应激会影响奶牛随后泌乳期的免疫状态。我们假设，干奶期进行降温可改善奶牛对产后乳房内感染（IMI）的免疫反应，这种感染由诸如乳房链球菌等环境病原体引起。在预计产犊前46天对奶牛进行干奶处理，并将其分为降温组（CL，n = 15）和热应激组（HT，n = 15）。对降温组奶牛提供喷淋装置、风扇和遮阳设施，而热应激组奶牛仅提供遮阳设施。所有奶牛产后均进行降温处理。在干奶期，每周三次记录直肠温度（RT）和呼吸频率（RR）。在距产犊前46天至42天期间，每天记录干物质摄入量，每周记录体重（BW）和体况评分（BCS）。产犊后每天记录产奶量和奶成分。在一部分奶牛（CL组，n = 5；HT组，n = 5）产后5天诱导乳房链球菌IMI。在IMI后0、12、18、24和36小时采集血液。进行血液学分析，并分离中性粒细胞用于RNA提取。通过实时逆转录PCR评估免疫反应基因（TLR2、IL1-β、IL6、IL8、IL10和TNFα）。与热应激组奶牛相比，降温组奶牛在干奶期的RT和RR较低。降温组奶牛产前采食更多饲料，但产后没有；产前体重增加更多，但泌乳期体重损失更多；产前BCS评分较高，产后较低。在40周的泌乳期内，降温组奶牛的产奶量（33.8 vs. 30.0 kg/天）高于热应激组奶牛，但奶成分未受影响。在IMI期间，降温组奶牛的白细胞计数和中性粒细胞数量均多于热应激组奶牛。在IMI后0至36小时，两种处理中TNFα mRNA表达均下降，而IL6和IL8的表达增加。此外，降温组奶牛在IMI后18小时IL10 mRNA表达较低。在两种处理中，TLR2 mRNA表达均随时间下降。然而，降温组奶牛的TLR2 mRNA总体表达高于热应激组奶牛。未检测到IL1-β、IL6、IL8或TNFα mRNA表达的差异。干奶期对奶牛进行降温会改变其免疫功能以及早期泌乳期对IMI的中性粒细胞反应。
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