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Abstract

An investigation was conducted to study the effect of body
weight loss and regain on the relationship between the excretion and
retention of nitrogen and sulphur in mature, cross-bred wethers. A
reduction in dry matter intake from 800g/day to 200g/day resulted in
about 25% loss of live weight after 7 weeks. The greatest loss
occurred in the fat stores (5kg or 50% of initial weight). When re- fed
the maintenance diet (i.e. rehabilitation) the wethers
failed to fully recover their lost live weight over 10 weeks and
total body water accounted for, on average, 88% of the live weight
gain, protein 10% and ash 2%, fat made very little or no contribution
to the weight regain. Reasons for the failure to completely recover
the lost live weight, such as inadequate dietary energy, protein
and/or minerals have been discussed.
The balance trial indicated that during undernutrition therOtas'greater:
retention of sulphur relative to nitrogen within the body, pre
sumably for wool growth. The N:S excretion ratios, 15-37:1, were gen-
erally wider than the 15:1, which would be expected if the excretion
ratio reflected tissue protein catabolism. By including the losses
of nitrogen and sulphur in wool grown during undernutrition, the N:S
excretion ratios decreased to 9-15:1. During positive balance (i.e.
rehabilitation) the N:S retention ratios of 10-15:1 were similar to
those observed by other workers, but the deduction of nitrogen and
sulphur deposited in wool resulted in wider ratios of 19-45:1. The
- plasma levels of urea nitrogen and inorganic sulphate sulphur were
not greatly affected by either undernutrition or rehabilitation.
A subsequent balance trial which considered the effect of
body weight loss, in respect to nitrogen and sulphur depletion in
tissue,and nitrogen and sulphur balance, revealed that there was a
disproportionate loss of nitrogen and sulphur from muscle tissue
in that there was a greater retention of sulphur in muscle tissue
particularly in the sheep which were fed higher dietary levels of
nitrogen. However, there was no evidence to suggest that the
higher dietary nitrogen levels in any way influenced overall body
protein loss.
There were large discrepancies between the results for
protein depletion as assessed by the protein prediction equation
of Donnelly and Freer (1974) and those obtained by nitrogen balance
determinations, for both experiments. Of the possible errors
discussed, it appears that the loss of ammonia from the urine before
analysis, may be the major source of error even though precautions
were taken to minimize such losses. The use of the measured amounts
of sulphur in muscle tissue and sulphur balance data gave the better
estimates of wool growth than-nitrogen balance data and accepted N:S
tissue ratio of 15:1, when compared with the results obtained from
dye-bands or shearing.
The third experiment studied the effect of body weight loss
and regain on the storage of copper, zinc and vitamin B 12 in liver.
The losses of fat, water, protein and ash were not completely re-
covered by refeeding the maintenance diet. Total body water regained,
on average, 95% of its lost weight, protein 60%, ash 63% and fat only
32%. The loss of liver protein was accompanied by losses of copper,
zinc and vitamin B12 but serum levels were not elevated during under- nutrition.
The recovery of the undernourished animals were not
improved by higher dietary levels of copper and cobalt. The excess
trace elements were apparently excreted.
The inadequate supp1y of energy was probably the major
determinant of the failure of the sheep to completely recover their lost live weight
in the present experiments.
Wool growth was significantly reduced by undernutrition
but there was very little evidence of reduced sulphur concentration
in wool (experiment 2). Refeeding improved wool growth but not
necessarily to the levels prior to undernutrition (experiment 3).
The sulphur concentration in wool was reduced during the recovery
period (experiment 1). However, the levels of copper and zinc in
wool were not influenced by either undernutrition or rehabilitation.

Item Type:	Thesis - PhD
Authors/Creators:	Mucha, Christine Sandra Dearn
Keywords:	Sheep, Sheep, Nitrogen, Sulfur
Copyright Holders:	The Author
Copyright Information:	Copyright 1980 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1980. Bibliography: l. 380-426. Financial support provided by the Australian Meat Research Committee
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