EFFECTS OF FEEDING FREQUENCY AND SOYBEAN MEAL SUPPLEMENTATION OF ALFALFA SILAGE ON DUODENAL NITROGEN SUPPLY TO SHEEP
Eight rams fitted with ruminal and duodenal cannulae were assigned to four treatments in an 8 × 4 crossover design. Treatments were a factorial combination of two feeding frequencies (1 × or 4 ×/d) and two diets fed at 2% of body weight (alfalfa silage with or without 10% soybean meal (SBM), dry matter basis). Diets were made isocaloric by the addition of corn. Supplementary SBM did not affect concentration of most rumen metabolites, except for increasing ammonia levels (P < 0.05). Rumen liquid kinetics were not affected by supplementation with SBM. However, SBM increased (P < 0.05) duodenal flow of microbial and residual N as well as efficiency of microbial protein synthesis when the diet was fed more frequently. Four times feeding increased the turnover rate of rumen liquid (P < 0.05). In addition, the diurnal variation of all rumen parameters was reduced, suggesting more stable rumen conditions and more uniform fermentation. Nevertheless, site and extent of organic matter and cell wall digestion were not affected. Nitrogen retention was improved (P < 0.05) with both diets due to 4 × feeding. Neither N flows to the duodenum nor efficiency of microbial protein synthesis were influenced when the control diet was fed frequently. Key words: Feeding frequency, soybean meal, alfalfa silage, duodenal nitrogen, rumen fermentation, sheep