The quantitative relationship between the urinary excretion of <I>TBA</I> and the uptake of <I>PPA </I>and <I>CHCA</I> was examined by continuous intraruminal infusion of <I>PPA</I> (8, 16 or 24 mmol/d) either alone or with <I>CHCA </I>(8 or 16 mmol/d) in sheep nourished by intragastric infusions of all nutrients. The daily excretion of <I>TBA</I> was linearly correlated (<I>r</I> 0.99, <I>P</I><0.001) with the amounts of <I>PPA</I> and <I>CHCA</I> infused. The urinary recovery of infused <I>PPA</I> and <I>CHCA</I> as <I>TBA</I> was 0.79 (<I>s.e.</I> 0.01). Recovery of infused <I>SA</I> (8 mmol/d) as urinary total salicylic acid (<I>TSA</I>) was 0.89 (<I>SD</I> 0.08). Both <I>TBA</I> and <I>TSA</I> excretions were found to be exclusively of exogenous origin, with negligible faecal excretion. It is concluded that urinary <I>TBA</I> is a potential estimator of <I>PPA + CHCA</I> absorption from the digestive tract. <I>SA</I> may have potential as a marker of urine volume. The relationship between urinary excretion of <I>TBA</I> and forage intake was assessed with steers fed different amounts of fresh herbage from pastures comprising oat, rye, vetch and lucerne. Herbage samples collected daily were incubated <I>in vitro</I> with buffered rumen fluid for 48 h. The <I>PPA</I> production per unit of herbage <I>DM</I> incubated was fitted to the exponential function of time <I>Y </I>= <I>a +</I> [<I>b</I>. (1 - <I>e</I><sup>-<I>c.l</I></sup>)]. Regression analysis showed that the <I>TBA:</I>creatine concentration ratio was a good explanatory variable (<I>r</I><sup>2 </sup>0.92-095; <I>P</I><0.001) of herbage intake. <I>TBA</I>:creatinine concentration ratio divided by the product <I>b.c</I>, both constants from the fitted curves of <I>PPA</I> production of herbage cultures, was another good index (<I>r</I><sup>2</sup> up to 0.98). It is concluded that a method for the prediction of herbage intake for grazing animals based on <I>TBA</I> excretion in urine seems promising.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:369561 |
| Date | January 1998 |
| Creators | Pagella, Jose Horacio |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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