Ross T T, Goode L, Linnerud A C
Department of Animal Science, North Carolina State University, Raleigh, NC 27695-7621 USA.
Theriogenology. 1985 Aug;24(2):259-69. doi: 10.1016/0093-691x(85)90190-6.
The effects of high ambient temperatures on rectal temperature (RT), respiration rate (RR), fetal development and serum thyroxine (T(4)) concentrations were stuaied in two experiments involving 35 ewes and 26 lambs from the following ewe groups: 1) Barbados Blackbelly (B), a tropical breed; 2) Dorset (D), a temperate breed; and 3) Blackbelly x Dorset crosses (BxD). Data were obtained on four B, five D and five BxD ewes exhibiting estrus during the summer (Exp. 1). In Exp. 2, eight B, seven D and six BxD ewes were maintained in two environmental chambers (cool, 22.2C; hot, 33.8C) from day 125 of gestation to seven days before the expected lambing date for each breed group (D and BxD, 140+/-1; B, 144+/-1 day of gestation). The B and BxD ewes were more heat-tolerant than D ewes as measured by significantly lower RT and RR in each experiment. Mean lamb birth weight, crown-rump length, number of functional uterine caruncles and caruncle weight and size did not vary significantly among breed groups or temperature chamber (Exp. 2), and there was no indication that the high temperature imposed caused fetal dwarfing in lambs removed from the uterus at a standard age of seven days before expected parturition. Serum T(4) varied markedly among breed groups (P<0.05) in each experiment with B ewes having the lowest and BxD ewes the highest concentration. In Exp. 1, follicular stage T(4) concentrations in B and BxD ewes were lower (P<0.02) than those during the luteal stage of the estrous cycle. The decrease in D ewes was not significant. High ambient temperature (Exp. 2) depressed T(4) levels in D ewes (P<0.05) and also depressed the pituitary-thyroid response to thyrotropin releasing hormone in D lambs. Such was not the case in B and BxD ewes and their lambs.
在两项实验中，研究了高环境温度对直肠温度（RT）、呼吸频率（RR）、胎儿发育以及血清甲状腺素（T4）浓度的影响，这两项实验涉及来自以下母羊组的35只母羊和26只羔羊：1）巴巴多斯黑腹羊（B），一种热带品种；2）陶赛特羊（D），一种温带品种；3）黑腹羊×陶赛特羊杂交种（BxD）。在夏季，从四只B、五只D和五只BxD发情母羊身上获取了数据（实验1）。在实验2中，从妊娠第125天到每个品种组预期产羔日期前七天（D和BxD为妊娠140±1天；B为妊娠144±1天），将八只B、七只D和六只BxD母羊饲养在两个环境舱中（凉爽，22.2℃；炎热，33.8℃）。在每项实验中，通过显著更低的RT和RR测量发现，B和BxD母羊比D母羊更耐热。各品种组或温度舱之间，平均羔羊出生体重、顶臀长度、功能性子宫肉阜数量、肉阜重量和大小没有显著差异（实验2），并且没有迹象表明在预期分娩前七天的标准年龄从子宫中取出的羔羊中，高温导致了胎儿发育迟缓。在每项实验中，各品种组之间血清T4差异显著（P<0.05），B母羊的浓度最低，BxD母羊的浓度最高。在实验1中，B和BxD母羊卵泡期的T4浓度低于（P<0.02）发情周期黄体期的浓度。D母羊的下降不显著。高环境温度（实验2）降低了D母羊的T4水平（P<0.05），并且还降低了D羔羊垂体 - 甲状腺对促甲状腺激素释放激素的反应。B和BxD母羊及其羔羊则并非如此。
