Estimation of endogenous contribution and urinary excretion of purine derivatives from the total digestible nutrient intake in Nellore heifers

• Published in: Revista brasileira de zootecnia Vol. 41; no. 8; pp. 1899 - 1906
• Main Authors: Braga, Jercyane Maria da Silva, Valadares, Rilene Ferreira Diniz, Pellizzoni, Samantha Gusmão, Valadares Filho, Sebastião de Campos, Prates, Luciana Louzada, Costa e Silva, Luiz Fernando
• Format: Journal Article
• Language: English; Portuguese
• Published: Sociedade Brasileira de Zootecnia 01.08.2012
• Subjects: AGRICULTURE, DAIRY & ANIMAL SCIENCE; cattle; endogenous excretion; microbial protein; VETERINARY SCIENCES; microbial protein; cattle; endogenous excretion
• ISSN: 1516-3598; 1806-9290; 1516-3598; 1806-9290
• DOI: 10.1590/S1516-35982012000800014

The objectives of this experiment were to estimate the endogenous excretion of purine derivatives (PD), the intake and digestibility of nutrients, the urinary excretion of PD from the intake of total digestible nutrients (TDN) and digestible organic matter (DOM) in Nellore heifers. Eight heifers, 267±17 kg body weight (BW), were assigned to two 4 × 4 latin squares. The planned treatments were four dry matter intake (DMI) levels: 10, 14, 18 and 22 g/kg BW. The diet contained 70% corn silage and 30% concentrate. The endogenous losses were obtained by regression between excretion of PD (mmol/BW0.75) and DMI (g/BW0.75). When PD excretion (mmol/d) was related to the intake of DOM and TDN (kg/d), the following equations were obtained: ŶPD= 32.98 + 21.94*DOM and ŶPD= 32.47 + 20.40*TDN, respectively. The excretion of PD (mmol/d) was a function of DMI (kg/d): ŶPD = 0.605 + 0.014 x (r² = 0.46), and 0.60 mmol/BW0.75 was the endogenous fraction of PD. The endogenous losses of PD and nitrogen compounds obtained when the animals were fasted for 5 d, with free access to water, were 0.332 mmol/BW0.75 and 0.384 gN/BW0.75, respectively. The net protein requirement for maintenance was estimated at 2.4 g/BW0.75. Creatinine excretion is not affected by feed restriction.