Hostname: page-component-669899f699-vbsjw Total loading time: 0 Render date: 2025-04-25T05:17:19.943Z Has data issue: false hasContentIssue false
  • English
  • Français

Heat stress and development of the conceptus in domestic sheep

Published online by Cambridge University Press:  27 March 2009

G. Alexander  and
D. Williams
G. Alexander
Affiliation:
G.S.I.R.O., Division of Animal Physiology, Ian Clunies Ross Animal Research Laboratory, Prospect, N.S.W., Australia
D. Williams
Affiliation:
G.S.I.R.O., Division of Animal Physiology, Ian Clunies Ross Animal Research Laboratory, Prospect, N.S.W., Australia
Get access Rights & Permissions [Opens in a new window]

Summary

In four series of experiments Merino ewes were exposed to ambient temperatures of about 44 °C and water vapour pressure of 33 mmHg for 9 h daily, and to 32 °C and 18 mmHg for the remaining 15 h daily, during the middle third, the final third or the final two-thirds of pregnancy. Birth weight and the weight of the placenta were considerably reduced by the treatments and the reductions were considerably more than could be accounted for by the partial loss of appetite produced by heating.

There was a close inverse relationship between birth weight and the elevated rectal temperature of heated ewes in several series; but the absence of foetal dwarfing in ewes with elevated rectal temperatures due to daily heating for only 9 h at 44 °C indicates that the elevated rectal temperature of the ewe is not the main cause of dwarfing.

Contrary to previous suggestions, the dwarfed lambs were not proportional miniatures, for the head components, the body lengths, the kidneys and adrenal glands were disproportionately large in heated lambs, while the liver, thyroid and thymus glands and the biceps femoris muscle were disproportionately small, and the ratio of secondary to primary wool fibres was very much reduced. There were cavities in the white matter of the cerebral hemispheres of heat-dwarfed lambs.

The hypothesis that foetal dwarfing is due to stunting of the placenta was examined, but conflicting evidence was obtained in the different series. However, it appears that under some circumstances a heat-stunted placenta is capable of considerable growth in the absence of heating during the final third of pregnancy, when the placenta is normally shrinking, and that placental shrinkage in late pregnancy may be greatly accelerated by the application of heat.

Neither thyroxine nor a preparation of ovine growth hormone, injected into heated ewes, prevented foetal dwarfing; the injections of growth hormone appeared to increase foetal mortality.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 76 , Issue 1 , February 1971 , pp. 53 - 72
Copyright
Copyright © Cambridge University Press 1971

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Article purchase

Temporarily unavailable

References

REFERENCES

Alexander, G. (1964). Studies on the placenta of the sheop (Ovis aries L.): effeofc of surgical reduction in the number of caruncles. J. Beprod. Fert. 7, 307–22.CrossRefGoogle Scholar
Alexander, B. & Williams, D. (1966). Heat stress and growth of the conceptus in sheep. Proc. Aust. Soc. Anim. Prod. 6, 102–5.Google Scholar
Baroroft, J. & Kennedy, J. A. (1939). The distribution of blood between the foetus and the placenta in sheep. J. Physiol., Lond. 95, 173–86.CrossRefGoogle Scholar
Bianca, W. (1958). The relation between respiratory rate and heart rate in the calf subjected to severe heat stress. J. agric. Sci., Oamb. 51, 321–4.CrossRefGoogle Scholar
Blaxter, K. Li., Graham, N. Mcc, Wainman, F. W. & Armstrong, D. G. (1959). Environmental temperature, energy metabolism and heat regulation in sheop. II. The partition of heat losses in closely clipped sheep. J. agric. Sci., Camb. 52, 25–40.CrossRefGoogle Scholar
Carter, H. B. & Hardy, M. H. (1947). Studies in the biology of the skin and fleece of sheep. Bull. Goun. scient. ind. Res., Melb. no. 215.Google Scholar
Cloete, J. H. L. (1939). Prenatal growth in the Merino sheep. Onderstepoorl J. vet. Sci. Anim. Ind. 13, 417–558.Google Scholar
Good, C. A., Kramer, H. & Somooyi, J. (1933). The determination of glyoogen. J. biol. Chem. 100, 485–91.CrossRefGoogle Scholar
Goode, L. (1964). Effects of summer confinement upon ewe productivity. J. Anim. Sci. 23, 906.Google Scholar
Klemm, G. H. (1962). The reactions of unshorn and shorn sheep to hot wet and hot dry atmospheres. Aust. J. agric. Res. 13, 472–8.CrossRefGoogle Scholar
Lyne, A. G. & Verhaoen, A. M. W. (1957). Growth of the marsupialTrichosurus vulpecula and a comparison with some higher mammals. Qrowth 21, 167–95.Google ScholarPubMed
Macfarlane, M. V. (1963). Endocrine funotions in hot environments. In ‘Environmental Physiology and Psychology in Arid Conditions. Reviews of Research’, pp. 153–222. Arid Zones Res. no. 22.Google Scholar
Moule, G. R. (1954). Observations on mortality amongst lambs in Queensland. Aust. vet. J. 30, 153–71.Google Scholar
Shelton, M. (1964a). Relation of environmental temperature during gestation to birth weight and mortality in lambs. J. Anim. Sci. 23, 360–4.CrossRefGoogle Scholar
Shelton, M. (1964b). Relation of birth weight to death losses and to certain productive characters of fallborn lambs. J. Anim. Sci. 23, 355–9.CrossRefGoogle Scholar
Shelton, M. (1965). Effect of heat stress and thyroxine implants during gestation on lambing performance and wool production. J. Anim. Sci. 24, 288.CrossRefGoogle Scholar
Shelton, M. & Huston, J. E. (1968). Effects of high temperature stress during gestation on certain aspects of reproduction in the ewe. J. Anim. Sci. 27, 163–8.Google Scholar
Thomson, W. & Aitken, F. C. (1959). Diet in relation to reproduction and the viability of the young. II. Sheep. Tech. Commun. Gommonw. Bur. Anim. Nutr. no. 20.Google Scholar
Wallace, L. R. (1948). The growth of lambs before and after birth in relation to the level of nutrition. J. agric. Sci., Camb. 38, 367–401.CrossRefGoogle Scholar
Yeates, N. T. M. (1953). The effect of high air tempera-ture on reproduction in the ewe. J. agric. Sci., Canib. 43, 199–203.CrossRefGoogle Scholar
Yeates, N. T. N. (1956). The effect of high air temperature on pregnancy and birth weight in Merino sheep. Aust. J. agric. Res. 7, 435–9.CrossRefGoogle Scholar
Yeates, N. T. M. (1958). Foetal dwarfism in sheep—an effect of high atmospheric temperature during gestation. J. agric. Sci., Camb. 51, 84–9.CrossRefGoogle Scholar