A comparison of the excretion rate of endogenous purine derivatives in the urine of Bos indicus and Bos taurus steers

Abstract

Abstract. Estimates of microbial crude protein (MCP) production by ruminants, using a method based on the excretion of purine derivatives in urine, require an estimate of the excretion of endogenous purine derivatives (PD) by the animal. Current methods allocate a single value to all cattle. An experiment was carried out to compare the endogenous PD excretion in Bos taurus and high-content B. indicus (hereafter, B. indicus) cattle. Five Holstein-Friesian (B. taurus) and 5 Brahman (>75% B. indicus) steers (mean liveweight 326 ± 3.0 kg) were used in a fasting study. Steers were fed a low-quality buffel grass (Cenchrus ciliaris; 59.4 g crude protein/kg dry matter) hay at estimated maintenance requirements for 19 days, after which hay intake was incrementally reduced for 2 days and the steers were fasted for 7 days. The excretion of PD in urine was measured daily for the last 6 days of the fasting period and the mean represented the daily endogenous PD excretion. Excretion of endogenous PD in the urine of B. indicus steers was less than half that of the B. taurus steers (190 µmol/kg W 0.75 .day v. 414 µmol/kg W 0.75 .day; combined s.e. 37.2 µmol/kg W 0.75 .day; P < 0.001). It was concluded that the use of a single value for endogenous PD excretion is inappropriate for use in MCP estimations and that subspecies-specific values would improve precision.Additional keywords: rumen microbial protein, cattle.

Effect of quantity and source of rumen nitrogen on the efficiency of microbial protein synthesis in steers consuming tropical forage

“…The flow of MCP to the intestines of steers was calculated using the equations proposed by Chen and Gomes (1995). These calculations were made using the value for endogenous purine derivative excretion determined for highcontent (>75%) B. indicus cattle by Bowen et al (2006), i.e. 190 mmol/kg W 0.75 .day.…”

Endogenous fraction and urinary recovery of purine derivatives in Nellore and Holstein heifers with abomasal purine infusion

“…Regarding the effect of genetic groups, Bowen et al (2006) found difference (Po0.001) for endogenous losses of PD 0.414 and 0.1898 mmol/kgPC 0.75 , respectively, in B. taurus and B. indicus fasted for 7 days. However, the same authors did not find difference (P¼ 0.2) for the average excretion of PD during the trial period in which the animals were fed at maintenance.…”

“…However, the same authors did not find difference (P¼ 0.2) for the average excretion of PD during the trial period in which the animals were fed at maintenance. Bowen et al (2006) stated that the reason for the low endogenous excretion PD in B. indicus cattle is unclear. Osuji et al (1996) obtained values numerically lower of endogenous losses of DP for crossbred (B. indicus  B. taurus) when compared with Zebu (B. indicus), respectively, 0.108 and 0.172 mmol/kg PC 0.75 for animals fasted for 20 days.…”

“…The endogenous loss of PD proposed by Bowen et al (2006) was replaced in the equation of Chen and Ørskov (2003).…”

“…While Pimpa et al (2001) stated that this fraction is similar between Bos indicus (Nellore) and Bos taurus (Holstein), other authors (Bowen et al, 2006;Chen and Gomes, 1992;Osuji et al, 1996) suggested there are genetic differences between groups. Bowen et al (2006) worked with different genetic groups at the same physiological stage and experimental conditions. However the animals were fasted, which can alter the normal animal metabolism or the rate of degradation of the nucleic acids of tissues.…”