The aim of the study was to investigate the changes in
renal function in late pregnant and early
lactating Corriedale ewes. Compared with the non-productive
state, plasma urea concentration was
increased by 67% during pregnancy, whereas it decreased by
36% during lactation. Urine flow, urea
clearance, renal plasma flow and glomerular filtration rate
were significantly reduced (P<0·05)
during both late pregnancy and early lactation. Filtered load
of urea and the amount of urea
eliminated were significantly reduced (P<0·05)
only in lactating ewes. No changes were noted in the
fractional excretion of urea, the filtration fraction and the
urine osmolality during both late
pregnancy and early lactation. It was concluded that, as in
other breeds, Corriedale ewes can adapt
to increased nitrogen requirements during late pregnancy,
and especially during early lactation, by
increasing the renal conservation of urea. Unlike other
breeds, however, Corriedale ewes restrict the
urine urea losses mainly by reducing renal plasma flow and
glomerular filtration rate, without any
modification of the tubular reabsorption of urea during
both late pregnancy and early lactation.