Department of Animal Science, Cornell University, Ithaca, NY 14853.
Department of Animal Science, Cornell University, Ithaca, NY 14853; Dipartimento di Scienze Mediche Veterinarie, Università di Bologna, Bologna 40064, Italy.
J Dairy Sci. 2023 Apr;106(4):2904-2918. doi: 10.3168/jds.2021-21724. Epub 2023 Feb 14.
To evaluate the effects of heat stress environmental conditioning and dietary supplementation with organic acid and pure botanicals (OA/PB) on growth in dairy calves, we enrolled 62 bull (noncastrated) and heifer calves in a study with a completely randomized design. Calves were assigned to 1 of 5 groups (n = 11 to 14/group): (1) thermoneutral conditions (TN-Con), (2) HS conditions (HS-Con), (3) thermoneutral conditions and pair-fed to match nutrient intake with HS-Con (TN-PF), (4) HS with low-dose OA/PB [75 mg/kg of body weight (BW); 25% citric acid, 16.7% sorbic acid, 1.7% thymol, 1.0% vanillin, and 55.6% triglyceride; HS-Low], or (5) HS with high-dose OA/PB (150 mg/kg of BW; HS-High). Supplements were delivered as a twice-daily bolus via the esophagus from wk 1 through 13 of life; all calves, including those on the control treatments, received an equivalent amount of triglyceride used for microencapsulation. Calves were raised in TN conditions from birth until weaning. After weaning, calves (62 ± 2 d; 91 ± 10.9 kg of BW) were transported to a new facility and remained in TN conditions [temperature-humidity index (THI): 60 to 69] for a 7-d covariate period. Thereafter, calves remained in TN or were moved to HS conditions (THI: diurnal change 75 to 83 during night and day, respectively) for 19 d. Clinical assessments were performed thrice daily, BW was recorded weekly, and blood was sampled on d 1, 2, 3, 8, 15, and 19. Upon experiment completion, calves from HS-Con and TN-Con were euthanized, and hot carcass and visceral organ weights were recorded. The mixed model included calf as a random effect; treatment, day, hour (when appropriate) as fixed effects, and the interactions of treatment × day and treatment × hour (when appropriate). Rectal and skin temperatures and respiration rates were greater in HS-Con than in TN-Con. During heat stress exposure, dry matter intake (DMI), average daily gain (ADG), and gain to feed (G:F) were lower in HS-Con relative to TN-Con. Comparing HS-Con and TN-PF, ADG and G:F were similar. Plasma fatty acid concentrations were elevated in TN-PF compared with HS-Con and TN-Con. Despite tendencies for increased aspartate aminotransferase, HS conditions did not overtly influence liver and inflammation markers. Liver weights were lower in HS-Con relative to TN-Con. During the first week of heat exposure, DMI was greater for HS-Low relative to HS-Con. Supplementation of OA/PB at low and high levels had a similar G:F to HS-Con. We conclude that reductions in DMI accounted for production losses during HS conditioning and that dietary OA/PB supplementation was not able to improve growth performance in heat-stressed calves.
为了评估热应激环境调节和膳食补充有机酸和纯植物（OA/PB）对奶牛犊牛生长的影响，我们将 62 头公牛（未去势）和小母牛纳入一项完全随机设计的研究中。犊牛分为 5 组之一（每组 11 至 14 头）：（1） 热中性条件（TN-Con），（2） 高温条件（HS-Con），（3） 热中性条件和与 HS-Con 相匹配的等量喂养（TN-PF），（4） 低剂量 OA/PB [75mg/kg 体重（BW）；25%柠檬酸、16.7%山梨酸、1.7%百里香酚、1.0%香草醛和 55.6%甘油三酯；HS-Low]，或（5） 高剂量 OA/PB（150mg/kg BW；HS-High）。补充剂通过食道每天两次给药，从生命的第 1 周到第 13 周；所有的小牛，包括接受对照治疗的小牛，都接受了等量的用于微胶囊化的甘油三酯。小牛在 TN 条件下从出生到断奶期间饲养。断奶后（62±2d；91±10.9kg BW），小牛被运送到一个新的设施，并在 TN 条件下停留 7d 作为协变量期（温度湿度指数[THI]：60 至 69）。此后，小牛要么留在 TN 条件下，要么转移到 HS 条件下（THI：夜间和白天分别为 75 至 83 的日变化）19d。每日进行三次临床评估，每周记录一次 BW，并在第 1、2、3、8、15 和 19 天采血。实验完成后，将 HS-Con 和 TN-Con 中的小牛安乐死，并记录热胴体和内脏器官的重量。混合模型包括小牛作为随机效应；处理、天、小时（适用时）作为固定效应，以及处理×天和处理×小时的交互作用（适用时）。直肠和皮肤温度以及呼吸率在 HS-Con 中高于 TN-Con。在热应激暴露期间，与 TN-Con 相比，HS-Con 的干物质摄入量（DMI）、平均日增重（ADG）和增重与饲料比（G:F）较低。与 HS-Con 和 TN-PF 相比，血浆脂肪酸浓度升高。尽管天门冬氨酸氨基转移酶有升高的趋势，但 HS 条件并未明显影响肝脏和炎症标志物。HS-Con 中小牛的肝脏重量低于 TN-Con。在热暴露的第一周，与 HS-Con 相比，HS-Low 的 DMI 更高。低水平和高水平补充 OA/PB 对 HS-Con 的 G:F 相似。我们得出结论，DMI 的减少导致 HS 调节期间的生产损失，并且膳食 OA/PB 补充不能改善热应激小牛的生长性能。
