Excretion of purine derivatives by ruminants: effect of exogenous nucleic acid supply on purine derivative excretion by sheep

Abstract

The present study examined the relationship between the supply of exogenous nucleic acid (NA) purines and their recovery as the derivatives hypoxanthine, xanthine, uric acid and allantoin in urine. Six lambs, totally nourished by intragastric infusions of volatile fatty acids (VFA) and casein (i.e. no rumen fermentation), were given by abomasal infusion a microbial NA concentrate at six levels (from zero to 24.5 mmol purines/d). The true digestibility between the abomasum and terminal ileum of the NA purines was measured in a separate experiment using three lambs. The relative proportion of urinary allantoin increased, and that of other derivatives decreased, as the amount of NA infused was increased. The relationship between total excretion of purine derivatives ( Y; mmol/d) and exogenous purines absorbed (X, mmol/d) was Y = 0~84X+0~150W0~7see-0~25x, where W is body-weight (kg). This implies that the endogenous contribution to the total excretion of derivative decreased as the supply of exogenous purines increased, with an associated progressive replacement of de n o w synthesis by exogenous purines. The model also implies that 0.16 of the purines were eliminated through routes other than derivative excretion in urine. Once excretion exceeded 0.6 mmol/kg WO." per d, endogenous excretion was effectively zero and thus Y = 084 X. In normally fed sheep, derivative excretion should therefore relate to the microbial purines and, hence, microbial protein absorbed according to these models. The changing proportions of allantoin and other derivatives in urine were probably due to changes in the relative importance of endogenous and exogenous purines as precursors. Nucleic acids: Purine derivatives: SheepStudies on the urinary excretion of purine derivatives by ruminants have been stimulated by the possible use of their excretion as an estimator of the rumen microbial protein supplied to the host animal. This is because in ruminants nucleic acids (NA) flowing to the small intestines are essentially of rumen microbial origin (McAHan & Smith, 1973). Absorbed purines are degraded to hypoxanthine, xanthine, uric acid and allantoin, which are excreted in urine, and should relate quantitatively to the amount of purines and, hence, microbial protein absorbed.The excretion of allantoin has been shown to be correlated with the amount of NA infused post ruminally to sheep (Antoniewicz et al. 1980;Sibanda et al. 1982;Giesecke et al. 1984;Lindberg, 1985;Fujihara et al. 1987). However, recoveries of NA-nitrogen as allantoin-N reported by these authors varied from 0.12 to 0.47 (i.e. purine recoveries of 0.22-0.79). Since uric acid, xanthine and hypoxanthine were not measured, it is not possible to assess whether the recovery of absorbed purines as the derivatives in the urine was complete in these studies. It is also not clear from the existing information whether, and to what extent, exogenous purines would be retained by the animal body.In the studies to be reported here the intragastric infusion technique (0rskov et al. 1979) was e...

Modelling purine derivative excretion in dairy goats: endogenous excretion and the relationship between duodenal input and urinary output

“…Initially proposed to be applied in sheep (Pé rez et al, 1998), the method based on the urinary dilution of labelled exogenous purines allows determination of the endogenous component of the urinary PD without having any adverse physiological effect on the animals. Using that method in sheep, the above authors obtained an endogenous excretion of 115.2 mmol/kg LW 0.75 , which was in the range (92 to 150 mmol/kg LW 0.75 ) reported by non-isotopic studies based on intragastric or digesta draining methods (Ørskov et al, 1979;Giesecke et al, 1984;Chen et al, 1990;Balcells et al, 1991). Furthermore, the technique has been used in lactating cows , showing that recycling of exogenous PB into the tissues by the salvage mechanism was negligible .…”

“…The urinary recovery of PD in lactating goats was in the range observed in cattle 0.75 to 0.8 (Orellana-Boero et al, 2001;Verbic et al, 1990) sheep, (0.7 to 0.8; Balcells et al, 1991;Chen et al, 1990) and camels (0.72; Guerouali et al, 2004), but was higher than the recovery in buffaloes (0.11, Pimpa et al, 2003).…”

Estimation of microbial protein supply in ruminant animals based on renal and mammary purine metabolite excretion. A review

“…Disappearance of RNA due to digestion and absorption has been shown to be almost complete as digesta enters the jejunum (McAllan, 1980;Schonhusen et al, 1999). When corrected for endogenous losses, true digestibility coefficients of 0.859, 0.780-0.871 and 0.913, have been reported for microbial NA-N (Storm and0rskov, 1983), RNA-N Schonhusen et al, 1999) and purines (Chen et al, 1990a), respectively.…”

“…In vitro studies of purine absorption in the hamster have shown that hypoxantine, xanthine and to a lesser extent uric acid are preferentially excreted rather than absorbed across the intestine (Berlin and Hawkins, 1968), while studies in sheep have indicated that the capacity of the small intestine to absorb allantoin is limited (Chen et al, 1990b). Nucleic acids, free bases (except xanthine) and PDs entering the large intestine do not appear to be absorbed due to extensive degradation by indigenous microbes (Sorensen, 1960;Ellis and Bleichner, 1969a;Chen et al, 1990a), and therefore purines excreted in faeces appear to be primarily derived from microbes residing in the caecum (Surra et al, 1997b). Furthermore, variations in the supply of NAs entering the caecum and the extent of hindgut fermentation do not appear to affect urinary PD excretion, but there is evidence to suggest that it is positively influenced by the flow of undigested fibre in the duodenum (Surra et al, 1997b).…”

Effects of alfalfa silage storage structure and roasting corn on ruminal digestion and microbial CP synthesis in lactating dairy cows

“…Purine derivative excretion is an indirect method that does not account for these differences. Some purine derivatives also may be of dietary origin, and excretion route may vary with the nutritional and physiological status of the animal (Chen et al, 1990;Gonzá lez-Ronquillo et al, 2004). Thus, relative differences between dietary treatments in microbial CP flow may not be detected using this method.…”