Daily and alternate-day supplementation of urea or biuret to ruminants consuming low-quality forage: III. Effects on ruminal fermentation characteristics in steers1,2

Abstract

Five ruminally and duodenally cannulated steers (491 +/- 21 kg BW) were used in an incomplete 5 x 4 Latin square with four 24-d periods to determine the influence of supplemental nonprotein N (NPN) source and supplementation frequency (SF) on the dynamics of ruminal fermentation in steers consuming low-quality grass straw (4% CP). Treatments (TRT) included an unsupplemented control (CON) and a urea or biuret supplement that were placed directly into the rumen at 0700 daily (D) or every other day (2D). The NPN treatments were formulated to provide 90% of the estimated degradable intake protein requirement; therefore, the urea and biuret treatments received the same amount of supplemental N over a 2-d period. Daily TRT were supplemented with CP at 0.04% of BW/d, whereas the 2D TRT were supplemented at 0.08% of BW every other day. Forage was provided at 120% of the previous 5-d average intake in two equal portions at 0715 and 1900. Ruminal fluid was collected 0, 3, 6, 9, 12, and 24 h after supplementation on a day of and a day before supplementation for all TRT. Ruminal NH3-N increased (P < 0.04) with CP supplementation on the day all supplements were provided and on the day on which only daily supplements were provided compared with the CON. However, an NPN source x SF interaction (P = 0.03) on the day all supplements were provided indicated that NH3-N increased at a greater rate for urea as SF decreased compared with biuret. Ruminal NH3-N on the day only daily supplements were provided was greater (P = 0.02) for D compared with 2D. On the day all supplements were provided, D increased (P = 0.05) ruminal indigestible acid detergent fiber passage rate and ruminal fluid volume compared with 2D. These results suggest that urea or biuret can be used effectively as a supplemental N source by steers consuming low-quality forage without adversely affecting ruminal fermentation, even when provided every other day.

Daily and alternate-day supplementation of urea or biuret to ruminants consuming low-quality forage: II. Effects on site of digestion and microbial efficiency in steers1,2

“…This could possibly be the result of increased flow of NH 3 -N to the small intestine with the urea treatments. This would coincide with the increased ruminal NH 3 -N noted for urea compared with biuret treatments in a companion paper (Currier et al, 2004b). It is of interest to note that bacterial N flow at the duodenum averaged almost 150% of N intake for all steers, indicating that N recycling played a large role in steer N metabolism.…”

“…They were 0.16, 0.24, 6.90, and 0.80 mM in the studies of Lintzenich et al (1995), Köster et al (1996), Spragg et al (1986), and Bohnert et al (2002a), respectively. Ruminal NH 3 -N in the current study was 1.48 mM (Currier et al, 2004b). Consequently, CP supplementation may have had a more positive effect on ruminal digestion in the studies of Lintzenich et al (1995) and Köster et al (1996) than in the present study.…”

“…This is supported in the current study by the tendency for ruminal NDF digestibility to be greater for D compared with 2D treatments. However, ruminal fermentation characteristics (rumen liquid fill, liquid dilution rate, pH) reported in a companion paper are not consistent with this suggestion (Currier et al, 2004b). The lack of a SF effect on apparent and true (corrected for bacterial OM) ruminal OM digestion suggests that ruminal fermentation was not negatively affected by 2D supplementation.…”

“…It is possible that the slower and more sustained release of ruminal NH 3 -N often observed with biuret compared with urea (NRC, 1976;Bartle et al, 1998) may have allowed for a ruminal environment that supported increased bacterial growth. The slower and more prolonged increase in ruminal NH 3 -N concentration with biuret compared with urea is especially evident with 2D supplementation (companion paper; Currier et al, 2004b). Currier et al (2004b) reported that ruminal NH 3 -N at 3, 6, and 9 h after supplementation on the day all supplements were provided was approximately 12, 6, and 3 mM and 5, 5, and 5 mM for urea and biuret 2D treatments, respectively.…”

“…Ruminal samples were weighed, dried in a forced-air oven (55°C; 96 h), reweighed in order to calculate DM, ground to pass a 1-mm screen in a Wiley mill, and composited within period and day by steer. A complete description of these procedures is provided in a companion paper (Currier et al, 2004b). Ruminal bacteria were isolated from ruminal contents on d 13.…”