The objective ofthis trial was to study the effects of increasing dietary levels of crude protein(CP) on microbial protein synthesis of lactating dairy goats. The microbialmarkers purines bases and purine derivatives (PD), measured in spot urine samplesor in urine samples from total collection, were used to estimate microbial proteinsynthesis. Sixteen lactating goats (four fitted with ruminal cannula) were randomlyassigned to four replicated 4 x 4 Latin squares and were fed the following dietaryCP levels [dry matter (DM) basis]: 11.5, 13.5, 15.5 or 17.5%. No significantdifferences were observed between techniques for estimating microbial proteinsynthesis. Therefore, 12 non-cannulated goats were used to evaluate the effectof dietary CP level on PD excretion, microbial nitrogen flow and microbial efficiencyusing either total or spot collection of urine. Because creatinine excretiondid not differ among treatments, the average value 26.05 mg of urinary creatinineexcreted per kg of body weight was used for estimating the volume of urine usingspot samples. Urinary volume estimated using spot samples was similar to thatmeasured with total urine collection. In both cases, an increase on the amountof absorbed purines was observed when the dietary CP level increased in thediet. In brief, PD can be used for estimating microbial protein synthesis inlactating goats and spot samples were a good alternative for total collectionof urine.
