EMBRYO MORTALITY IN THE HEAT STRESSED EWE

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Author:
C. J. THWAITES
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DOI:
https://doi.org/10.1530/jrf.0.0190255
Volume/Issue:
Volume 19: Issue 2
Page Range:
255–262
Article Type:
Research Article
Online Publication Date:
Jul 1969
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Summary.

Continuous hot-room exposure during the first 15 days of pregnancy raised the rectal temperatures and respiratory rates of mature Merino ewes to about 104 to 105° F and 170 respirations/min respectively and led to the death of 83% of embryos.

Similar ewes subjected to a diurnally variable heat stress, which raised their rectal temperatures and respiratory rates to about 104 to 105° F and 220 respirations/min during an 8-hr 'day' and allowed them to fall to about 102° F and 140 respirations/min respectively during a subsequent 16-hr 'night', experienced an embryo mortality rate of only 35%.

Control ewes, housed similarly, but at natural temperatures (33 to 65° F), had rectal temperatures and respiratory rates of about 101 to 102° F and 20 respirations/min, respectively, and suffered the loss of 19% of their ova.

The results illustrate the mitigating effects of a daily period of respite from high temperatures and indicate that this, rather than differences in acclimatization to heat and lack of radiant heating in the hot-room, is the major factor to be considered when comparing the effects on embryo mortality of heat stress in the field with those of periods of continuous heat stress in the hot-room.

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Print ISSN:
1470-1626
Online ISSN:
1741-7899