Effect of Fasting on the Urinary Excretion of Nitrogen and Purine Derivatives by Zebu(Bos indicus)and Crossbred (Bos indicus x Bos taurus) Cattle

The effects of partial substitution of soybean with urea or slow-release urea on finishing performance, meat quality, and digestion parameters of Nellore steers

The effects of substituting ~50% of the soybeans in the diet of finishing Nellore steers with either urea (U) and/or slow-release urea (SRU) on the steer performance and meat quality were assessed in two experiments. In the first experiment, 46 Nellore steers in a 104-day experiment (Exp. 1) were fed a Control diet with U or SRU or U+SRU. In Experiment 2 (Exp. 2), digestibility and microbial protein (MCP) synthesis were assessed in four steers by using a 4 × 4 Latin square design with 21-day periods. Four corn-based diets were used in both Exp. 1 and 2. (1) Control (CTL): 0% of non-protein nitrogen (NPN). (2) U: 1.66% of NPN. (3) SRU: 1.8% of NPN. (4) U+SRU: 1.72% of NPN. In Exp. 1, final bodyweight, average daily gain, dry matter intake, Gain to Feed ratio, carcass traits and steer meat quality were not influenced by the experimental diets. In Exp. 2, the apparent digestibility was similar for all diets, and the MCP synthesis was affected by dietary treatments (P = 0.065). The NPN treatments showed 25.5% more (P = 0.03) MCP efficiency (g microbial protein/kg of total digestible nutrient content consumed) than the CTL. We conclude that the partial replacement of SBM with U, SRU or U+SRU will provide similar animal performance without negatively impacting carcass and meat quality and improve the efficiency of microbial protein synthesis in Nellore cattle.

Endogenous fraction and urinary recovery of purine derivatives obtained by different methods in Nellore cattle

Two experiments were conducted to assess the endogenous fraction of purine derivative (PD) excretion, urinary recovery, and intestinal digestibility of purines in Nellore heifers. For both experiments, 8 Nellore heifers fitted with ruminal and abomasal cannulas were allocated to two 4 × 4 Latin squares. The diets were based on corn silage and concentrate (60 and 40% DM basis, respectively); feces and urine samples were obtained by total collection, and abomasal DM flow was estimated using indigestible NDF as an internal marker. In Exp. I, 4 of the 8 heifers (BW 258 ± 20 kg) were also fitted with ileal cannula. The planned treatments were 4 different DMI: 1.2, 1.6, 2.0, and 2.4% of BW (DM basis). The endogenous losses and purine recovery as urinary PD were estimated using linear regression between daily urinary PD excretion (Y) and daily abomasal flow of purine bases (X), expressed in millimoles per kilogram of BW(0.75). In Exp. II, the same 8 Nellore heifers (BW of 296 ± 15 kg) were fed at 1.37% BW (DM basis). The treatments were the infusion of purines (RNA from torula yeast, type VI, Sigma) into the abomasum in increasing amounts (0, 33, 66, and 100 mmol/d). All statistical analyses were performed using the PROC MIXED procedure in SAS. In Exp. I, the DMI range was 1.16 to 1.84% of BW and did not affect (P > 0.05) the apparent RNA digestibility in the small intestine, which had a mean of 75.6%, and a true digestibility of 93.0%. The mean ratio of the N-RNA to the total-N in the ruminal bacteria was 0.137. The daily urinary PD excretion (Y, mmol/kg of BW(0.75)) was a function of RNA flow in the abomasum (X, mmol/kg of BW(0.75)): Y = 0.860X + 0.460, where 0.860 and 0.460 were the PD recovery of purines and the endogenous fraction (in mmol/kg of BW(0.75)), respectively. In Exp. II, the daily urinary PD excretion was a function of RNA flow in the abomasum: Y = 0.741X + 0.301, where 0.741 and 0.301 were the recovery of PD in urine of infused purines and the endogenous losses (in mmol/kg of BW(0.75)), respectively. In conclusion, our data suggest that in Nellore heifers the respective values of endogenous PD excretion (mmol/kg of BW(0.75)), urinary recovery of the purines absorbed in the abomasum, and true digestibility of RNA in the small intestine were 0.30, 0.80, and 0.93.

Influence of different levels of concentrate and ruminally undegraded protein on digestive variables in beef heifers

This experiment evaluated the effect of 2 levels of diet concentrate (20 and 40% of DM) and 2 levels of ruminally undegraded protein (RUP: 25 and 40% of CP) on nutrient intake, total and partial apparent nutrient digestibility, microbial protein synthesis, and ruminal and physiological variables. Eight Nellore heifers (233 +/- 14 kg of BW) fitted with ruminal, abomasal, and ileal cannulas were used. The animals were held in individual sheltered pens of approximately 15 m(2) and fed twice daily at 0800 and 1600 h for ad libitum intake. Heifers were allocated in two 4 x 4 Latin square designs, containing 8 heifers, 4 experimental periods, and 4 treatments in a 2 x 2 factorial arrangement. All statistical analyses were performed using PROC MIXED of SAS. Titanium dioxide (TiO(2)) and chromic oxide (Cr(2)O(3)) were used to estimate digesta fluxes and fecal excretion. Purine derivative (PD) excretion and abomasal purine bases were used to estimate the microbial N (MN) synthesis. No significant interaction (P > 0.10) between dietary levels of RUP and concentrate was observed. There was no effect of treatment (P = 0.24) on DMI. Both markers led to the same estimates of fecal, abomasal, and ileal DM fluxes, and digestibilities of DM and individual nutrients. Ruminal pH was affected by sampling time (P < 0.001), but no interaction between treatment and sampling time was observed (P = 0.71). There was an interaction between treatment and sampling time (P < 0.001) for ruminal NH(3)-N concentration. A linear decrease (P = 0.04) over sampling time was observed for the higher level of RUP, whereas a quadratic effect (P < 0.001) of sampling time was observed for the lower level of RUP. The higher level of dietary concentrate led to greater MN yield regardless of the level of RUP. The MN yield and the efficiency of microbial yield estimated from urinary PD excretion produced greater (P < 0.01) values than those estimated by either TiO(2) or Cr(2)O(3), which did not differ (P = 0.63) from each other. However, all methods yielded values that were within the range reported in the literature. In conclusion, no interactions between dietary levels of RUP and concentrate were observed for ruminal and digestive parameters. Neither RUP nor concentrate level affected DMI. Titanium dioxide showed to be similar to Cr(2)O(3) as an external marker to measure digestibility and nutrient fluxes in cattle.

Urinary excretion of purine derivatives inBos indicus×Bos tauruscrossbred cattle

Four experiments were performed to study the kinetics of purine metabolism and urinary excretion in Zebu crossbred cattle. Fasting excretion was established in Expt 1, using eighteen maleBos indicus×Bos tauruscrossbred cattle (261 (se 9·1) kg body weight), six of each of the following genotypes: 5/8Bos indicus, 1/2Bos indicusand 3/8Bos indicus. No significant differences were observed among genotypes in fasting purine derivative excretion (277·3 (se 35·43) μmol/metabolic body weight). In a second experiment we measured the xanthine oxidase activity, which was higher in liver than in duodenal mucosa (0·64 and 0·06 (se 0·12) units/g wet tissue per min respectively;P>0·05) being in plasma 0·60 (se 0·36) units/l per min. The kinetics of uric acid were measured by intravenous pulse dose of [1,3-15N]uric acid (Expt 3). The cumulative recovery of the isotope in urine was 82 (se 6·69) %, and uric acid plasma removal, pool size and mean retention time were 0·284 (se 0·051) per h, 5·45 (se 0·823) mmol and 3·52 (se 0·521) h, respectively. Allantoin was removed from plasma at an estimated fractional rate of 0·273 (se 0·081) per h and mean retention was 3·66 (se 1·08) h. In Expt 4, the relationship between urinary purine derivative excretion (Y; mmol/d) and digestible organic matter intake (X, kg/d) was defined by the equation:Y=7·69 (se 4·2)+5·69 (se 1·68)X;n16, Se 1·31,r0·67.

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

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 W0.75.day v. 414 µmol/kg W0.75.day; combined s.e. 37.2 µmol/kg W0.75.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.