The objectives were to examine melatonin-mediated changes in temporal uterine blood flow (UBF), vaginal temperatures (VTs), and fetal morphometrics in 54 commercial Brangus heifers (Fall, n = 29; Summer, n = 25) during compromised pregnancy. At day 160 of gestation, heifers were assigned to one of the four treatments consisting of adequately fed (ADQ-CON; 100% National Research Council [NRC]; n = 13), global nutrient restricted (RES-CON; 60% NRC; n =13), and ADQ or RES supplemented with 20 mg/d of melatonin (ADQ-MEL, n = 13; RES-MEL, n = 15). In the morning (0500 hours; AM) and afternoon (1300 hours; PM) of day 220 of gestation, UBF was determined via Doppler ultrasonography, while temperature data loggers attached to progesterone-free controlled internal drug releases were used to record VTs. At day 240 of gestation, heifers underwent cesarean sections for fetal removal and morphometrics determination. The UBF and VT data were analyzed using repeated measures of analysis of variance (ANOVA), while the morphometrics was analyzed using the MIXED procedure of SAS. Seasons were analyzed separately. In Fall, a nutrition by treatment interaction was observed, where the RES-CON heifers exhibited reduced total UBF compared with ADQ-CON (5.67 ± 0.68 vs. 7.97 ± 0.54 L/min; P = 0.039). In Summer, MEL heifers exhibited increased total UBF compared with the CON counterparts (8.16 ± 0.73 vs. 6.00 ± 0.70 L/min; P = 0.048). Moreover, there was a nutrition by treatment by time interaction in VT for Fall and Summer heifers (P ≤ 0.005). In Fall, all groups had decreased VT in the morning compared with the afternoon (P < 0.05). Whereas, in Summer, VT increased for ADQ-CON and RES-CON (P < 0.0001) from morning to afternoon, the ADQ-MEL and RES-MEL remained constant throughout the day (P = 0.648). Furthermore, the RES-MEL-PM exhibited decreased VT compared with ADQ-CON-PM (38.91 ± 0.09 vs. 39.26 ± 0.09 °C; P = 0.018). Lastly, in Fall, a main effect of nutrition was observed on fetal weights, where the RES dams had fetuses with decreased body weight when compared with ADQ (24.08 ± 0.62 vs. 26.57 ± 0.64 kg; P = 0.0087). In Summer, a nutrition by treatment interaction was observed on fetal weights where the RES-CON dams had fetuses with reduced weight when compared with ADQ-CON and RES-MEL (P < 0.05). In summary, nutrient restriction decreased UBF and melatonin supplementation increased UBF depending on the season. Additionally, melatonin appeared to decrease VT and rescue fetal weights when supplemented in the Summer.

中文翻译：

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褪黑激素在妊娠晚期营养限制期间以季节依赖性方式改变牛子宫动脉血流动力学、阴道温度和胎儿形态测量

目的是检查 54 头商业 Brangus 小母牛（秋季，n = 29；夏季，n = 25）在妊娠受损期间，褪黑激素介导的时间子宫血流 (UBF)、阴道温度 (VT) 和胎儿形态测量学的变化。在妊娠第 160 天，小母牛被分配到四种处理中的一种，包括充分喂养（ADQ-CON；100% 国家研究委员会 [NRC]；n = 13）、全球营养限制（RES-CON；60% NRC； n = 13），ADQ 或 RES 补充 20 mg/d 褪黑激素（ADQ-MEL，n = 13；RES-MEL，n = 15）。在妊娠第 220 天的上午（0500 小时；上午）和下午（1300 小时；下午），通过多普勒超声测定 UBF，而连接到无孕酮的受控内部药物释放的温度数据记录器用于记录 VT。在妊娠第 240 天，小母牛接受剖宫产以进行胎儿切除和形态测量学测定。使用重复测量方差分析 (ANOVA) 分析 UBF 和 VT 数据，而使用 SAS 的 MIXED 程序分析形态计量学。季节单独分析。在秋季，观察到治疗相互作用的营养，与 ADQ-CON 相比，RES-CON 小母牛的总 UBF 降低（5.67 ± 0.68 对 7.97 ± 0.54 L/min；P = 0.039）。夏季，MEL 小母牛的总 UBF 比 CON 小母牛增加（8.16 ± 0.73 对 6.00 ± 0.70 L/min；P = 0.048）。此外，秋季和夏季小母牛的VT中存在时间交互作用的营养（P≤0.005）。秋季，各组上午与下午相比，VT均降低（P＜0.05）。鉴于，在夏天，ADQ-CON 和 RES-CON 的 VT 从早上到下午增加（P < 0.0001），ADQ-MEL 和 RES-MEL 全天保持不变（P = 0.648）。此外，与 ADQ-CON-PM 相比，RES-MEL-PM 的 VT 降低（38.91 ± 0.09 对 39.26 ± 0.09 °C；P = 0.018）。最后，在秋季，观察到营养对胎儿体重的主要影响，与 ADQ 相比，RES 大坝的胎儿体重下降（24.08 ± 0.62 对 26.57 ± 0.64 kg；P = 0.0087）。夏季，在胎儿体重上观察到治疗相互作用的营养，其中与 ADQ-CON 和 RES-MEL 相比，RES-CON 母系的胎儿体重减轻（P < 0.05）。总之，营养限制降低了UBF，而褪黑激素补充增加了UBF，具体取决于季节。此外，