PSXII-30 - Changes in ruminal digesta and ruminal ammonia-N concentration with differing durations feed restriction for sheep

Abstract: During transient periods of feed restriction (FR), ruminal ammonia-N (NH3-N) concentrations and fluid volume may parallel the reduction in feed and water intake. However, changes in ruminal digesta characteristics and NH3-N during FR have not been characterized. Thus, the objective was to determine how FR duration impacts ruminal digesta weight and the liquid and solid fractions, and ruminal NH3-N concentration. Lambs (n = 9 wethers and 12 rams, stratified by BW and castration status) were fed ad libitum (AL, n = 7) or subjected to 5-d (FR5, n = 7) or 10-d of FR (FR10, n = 7) at 30% of AL intake. Lambs were killed 4 h post-feeding to excise the gastrointestinal tract and ruminal digesta was weighed. Sub-samples of digesta were collected for separation into solid and liquid fractions using a winepress, used for DM determination, and another was strained and preserved with sulfuric acid to analyze ruminal NH3-N concentration. Data were analyzed with PROC GLIMMIX (SAS 9.4) with the fixed effect of treatment and random effects of lamb specified to the R-sided matrix. Linear regression (PROC REG) was used to evaluate the relationship between ruminal NH3-N concentration and quantity relative to ruminal fluid weight and PROC CORR was used to generate Pearson correlation coefficients. The ruminal digesta weight did not differ (P = 0.97) among treatments but AL ruminal digesta was drier (P < 0.01) than FR5 and FR10 digesta (40.2% decrease in DM% relative to AL). As such, FR5 and FR10 had 0.7 ± 0.16 kg less (P = 0.01) ruminal solids than AL while they tended to have more (P = 0.09) ruminal fluid. Ruminal NH3-N concentration was greater (P < 0.01) for FR5 and FR10 compared to AL (2.4 and 2.0 vs. 0.4 ± 0.52 mg/dL, respectively). The quantity of ruminal NH3-N (mg) followed the same pattern with FR5 and FR10 having, on average, 51.5 ± 18.39 mg NH3-N more (P < 0.01) in their ruminal fluid than AL. The quantity of ruminal NH3-N was strongly correlated (ρ = 0.87, P < 0.01) to the total ruminal fluid such that 75% of the variance was explained by the relationship. The strength of the correlation (ρ = 0.81, R² = 0.66, P < 0.01) between ruminal NH3-N concentration and total ruminal fluid was slightly lesser, but the two parameters were still strongly associated. From these data, we surmise that FR is associated with a reduction in ruminal DM content and may increase ruminal liquid that correspond to increased ruminal NH3-N, independent to the duration of exposure.