Estimation of net ruminal protein synthesis from urinary allantoin excretion by bulls given tropical feeds

Abstract

An experiment was carried out to determine net microbial protein supply to ruminants from 15 tropical feeds. The study was done at Lyamungo research institute, on the slopes of Mt. Kilimanjaro, Tanzania in 1993. Twenty Bos Taurus × Bos Indicus bulls were used in three periods in a completely randomised design. The initial 19 days of each period were for adaptation by the bulls to their new environment and diets, followed by 2, 7 and 7 days for total urine collection, spot urine sampling and digestibility, respectively. The feeds included urea treated and untreated maize stover (3 feeds), green maize stover (3 feeds), bean straw (2 varieties), cultivated forage (5) and banana plant residues (2). Both total and spot urine collections were made for estimation of allantoin. Daily excretion of allantoin ranged from 5.63 to 48.89 mmol/day for banana leaves and 5% urea treated maize stover, respectively. Excretion of allantoin increased with level of dry matter intake (DMI) for all the feeds. Microbial N supply (MNS) and efficiency of microbial N supply (EMNS) followed the same trend (4.1–35.5 g N/day and 5.5–17.4 g of N/kg DOMR (digestible organic matter in the rumen) for banana leaves and 5% urea treated maize stover, respectively. Correlation coefficients between allantoin excreted ( A e), DMI and BW 0.75were r = 0.79 and r = 0.54, respectively. That between MNS, DMI and BW 0.75were r = 0.80 and r = 0.52, respectively, while that between EMNS, DMI and BW 0.75were r = 0.78 and r = 0.54, respectively. It was concluded that all the tropical feeds tested were poor sources of MNS and EMNS