Evaluation of collection days and times to estimate urinary excretion of purine derivatives and nitrogen compounds in grazing Nellore cattle

Estimating purine derivatives and nitrogen compound excretion using total urine collection or spot urine samples in grazing heifers

“…Pereira (2009) evaluated the effect of urine collection on the creatinine ratio every 2 h with Nelore heifers in feedlots and found no significant difference in PD:creatinine for the different collection periods. Silva Júnior et al (2018), evaluating the effect of total urine collection days/ periods in similar conditions, also did not find an effect of treatments on the AL:creatinine, UA:creatinine and PD:creatinine ratios. Thus, as treatment, collection day and CT had no effect on the AL:creatinine, UA:creatinine and PD:creatinine ratios, it was possible to infer that TA B L E 7 Adjusted means for urinary nitrogen (UN) excretion and urinary urea nitrogen (UreaN) excretion, in mmol, and the ratios of UN:Cre and UreaN:Cre, in function of collection time (CT), per 4 h and their p-value (probability) for the effects collection day (CD), CT and treatment (Tre) in Zebu cattle kept in pasture *Means in the same column followed different letters are different (p < 0.05).…”

“…Júnior et al (2018). The ratios of urinary nitrogen and UreaN with creatinine were also not influenced by treatment, collection day, CT or their interactions.…”

“…These variables are important for studies that aim to improve livestock production systems by maximizing microbial efficiency and nitrogen (N) utilization (Newbold & Ramos-Morales, 2020;Whittet et al, 2019). However, to properly quantify PD and NC excretion in urine, accurate estimates of their concentrations in urine and urinary volume are essential (Berchielli et al, 2000;Cochran et al, 1986;Silva Júnior et al, 2018;Whittet et al, 2019).…”

“…In this context, the use of spot sampling techniques is promising to make feasible estimates of PDs and NCs in nutrition trials, even under feedlot conditions (Chizzotti et al, 2008;Pereira, 2009). The spot sampling technique is based on using creatinine as a marker to estimate daily urinary excretion given its relative stability in excretion per unit of body weight (BW) in cattle (Chizzotti et al, 2008;Costa e Silva et al, 2012;Silva Júnior et al, 2018;Valadares et al, 1997).…”

“…However, variations in PD and creatinine ratios during the day can be observed because of nutritional and metabolic aspects, and more than one spot sampling a day might be required (Pereira, 2009). Under grazing conditions, evidence shows that NC concentrations in urine vary throughout the day, but the PD concentration seems more stable (Silva Júnior et al, 2018).…”