Impacts of Rumen Degradable or Undegradable Protein Supplementation with or without Salt on Nutrient Digestion, and VFA Concentrations

SIMPLE SUMMARY: Ruminant animals have two specific protein requirements: the protein required by the animal, and the protein required by the microorganisms that exist within the rumen of the animal. These requirements are satisfied by rumen undegradable (RUP) and rumen degradable protein (RDP), respectively. Within the rumen, RDP is hydrolyzed, while RUP is digested and absorbed in the small intestine. As these proteins are digested differently, we studied their impact on the digestion process of low-quality forage. Overall, we found that a RDP supplement, when fed in a self-fed form, may enhance the digestion and use of low-quality forages. This may assist producers in selecting supplementation programs for their operation. ABSTRACT: The objectives of this study were to evaluate the effect of differences in protein type and delivery method on rumen dynamics and nutrient digestion. Cows were allotted to rumen degradable protein (RDP) or rumen undegradable protein (RUP) and self-fed (SF) salt-limited pressed blocks or hand-fed (HF) loose supplement, resulting in four dietary treatments. There was a delivery effect (p = 0.04) on neutral detergent fiber (NDF) intake, as the SF animals consumed more NDF than HF animals. The RDP-SF animals had greater NDF digestibility (p = 0.04) and water intake (p = 0.03) than the three other treatments. Supplement intake displayed a protein type effect (p = 0.03), as RDP-supplemented animals consumed more supplement on a g·kg body weight (BW)(−1) d(−1) basis than RUP animals. There was an effect of protein type (p = 0.02) and delivery method (p = 0.03) on fluid flow rate, with RUP and HF cows having greater liquid flow rates. Ruminal pH was lower (p < 0.01) in RDP-HF cows than RDP-SF cows at all hours, except 4-h post-feeding. RDP-SF animals had the greatest (p < 0.01) concentrations of ruminal ammonia. Valerate ruminal concentrations were greater (p = 0.04) in RDP supplemented animals compared to RUP supplemented animals. In conclusion, self-fed supplements containing RDP may enhance the use of low-quality forages and increase ruminal ammonia concentrations.