Plasma urea dilution patterns in Southdown ram lambs from high
and low backfat selection lines
A.Y. Abdullah, R.W. Purchas, S.N. McCutcheon, P.C. Van Dinther
Department of Animal Science, Massey University, Palmerston
North, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1990, 50: 105-108
The response of ram lambs from the Massey university backfat
selection lines to a urea load were measured in order to ascertain
whether there were line effects on urea space and to evaluate
relationships between urea space and empty body water content. Thirty-
six 6-8 month-old ram lambs held in metabolism crates and fed lucerne
chaff at 1.3 maintenance, were given 120mg urea/kg through jugular
catheters. Plasma urea levels were measured in samples taken before and
after the urea load. All animals were slaughtered within 7d of the urea
challenge and total body water was determined. In contrast to previous
studies, baseline plasma urea levels were not significantly higher in the
high-backfat-line animals and were not related to carcass fat or water
content. The increases in urea levels following the urea load were
greater for the high backfat line at 15min, but not at subsequent
sampling times. Clearance rates following the load did not differ
between the lines. Correlations between empty body water and estimates
of urea space were low, suggesting that this is not a useful means of
obtaining body composition information for live sheep at this stage.
Urea space estimated in several ways was significantly higher for the
low backfat line group.
Keywords: NZSAPAB;
Plasma urea; ram lambs; backfat; selection lines
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Last Updated 25-01-1997
