Embryo Mortality in the Heat Stressed Ewe

A technique, developed for the objective histological evaluation of the corpus luteuin of the sheep, was applied to normal cyclic and pregnant ewes as well as to ewes subjected to various experimental treatments. Gross histological regression of the corpus luteum progressed rapidly between days 15 and 17 of the estrous cycle. Similar regressive changes did not occur in pregnant ewes; up to day 40, the oldest stage studied, corpora lutea of early pregnancy were similar in appearance to those of mid-cycle.Stresses such as high environmental temperature and acute undernutrition, which may lead to embryo mortality, had no significant effect on corpus luteum histology. Exogenous progesterone slightly depressed the size and weight of the corpus luteum but was without significant effect on its histology. Exogenous cortisol, and more particularly corticotropin, were sometimes associated with marked histological regression of the corpus luteum, although in ewes treated with these hormones there was no significant reduction in embryo survival at the time of autopsy.The observations do not support the suggestion that corpus luteum failure is a frequent cause of embryonic death in the ewe. The technique presented is considered sufficiently sensitive to detect quite small changes in the histological appearance of the corpus luteum, although the relationship of these changes to progesterone secretion is not known. However, the dramatic regression observed between days 15 and 17 of the estrous cycle fits the known pattern of progesterone secretion at this time.

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Effects in mice of high and low environmental temperature on the maternal and fetal toxicity of 2‐sec‐butyl‐4,6‐dinitrophenol (dinoseb) and on disposition of [¹⁴C]‐dinoseb

Preache

Gibson

1975

Teratology

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Swiss-Webster female mice were treated with 2-sec-butyl-4,6-dinitrophenol (dinoseb) and maintained in an increased environmental temperature (32 degrees C) for 24 h or a decreased temperature (0-6 degrees C) for 1.5-4 h. In two experiemtns animals maintained at low temperature were kept wet during the cold exposure, to enhance the reduction in body temperature, by rinsing them with water at approximately 30 min intervals. Results from nonpregnant females indicated that increased temperature lowered the LD50 for single injections of dinoseb from 20.2 to 14.1 mg/kg and that reduced temperature for 4 h had no effect on the LD50. A 24 h exposure to 32 degrees C enhanced the effect of 3 daily dinoseb treatments of pregnant mice; it increased maternal mortality, decreased fetal body weight, and increased frequency of fetal anomalies. Fetal body weight and the frequency of malformations were the same in groups exposed to low temperature and maintained at room temperature. Disposition of [14 C] dinoseb was also determined in nonpregnant mice exposed to temperatures of 0, 24, and 32 degrees C. The periods of environmental temperature studied (3-24 h) had no effect on the rate of disappearance of dinoseb from plasma or other tissues examined.

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Embryo Mortality in the Heat Stressed Ewe

Cited by 16 publications

References 40 publications

Birth Weight of Lambs: Influences and Consequences

Birth Weight of Lambs: Influences and Consequences

Histology of the corpus luteum in the ewe: Changes during the estrous cycle and early pregnancy, and in response to some experimental treatments

Effects in mice of high and low environmental temperature on the maternal and fetal toxicity of 2‐sec‐butyl‐4,6‐dinitrophenol (dinoseb) and on disposition of [¹⁴C]‐dinoseb

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Embryo Mortality in the Heat Stressed Ewe

Cited by 16 publications

References 40 publications

Birth Weight of Lambs: Influences and Consequences

Birth Weight of Lambs: Influences and Consequences

Histology of the corpus luteum in the ewe: Changes during the estrous cycle and early pregnancy, and in response to some experimental treatments

Effects in mice of high and low environmental temperature on the maternal and fetal toxicity of 2‐sec‐butyl‐4,6‐dinitrophenol (dinoseb) and on disposition of [14C]‐dinoseb

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Product

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Effects in mice of high and low environmental temperature on the maternal and fetal toxicity of 2‐sec‐butyl‐4,6‐dinitrophenol (dinoseb) and on disposition of [¹⁴C]‐dinoseb