Ruminal Availability of Crude Protein (CP) for Microbial Growth and Digestion
Ruminants have the ability to derive nutrients and energy from fibrous feedstuffs because of the microorganisms that inhabit the digestive tract, particularly those in the rumen and reticulum, consisting of bacteria, protozoa, and fungi. These microbes have nutrient requirements in some ways similar to those of the host animal. Notable among these requirements is the need for nitrogenous compounds or CP that can be degraded by the microbes. If the availability of ruminally degraded CP is low, then microbial growth and(or) digestion is limited, which indirectly limits protein and(or) energy available to the host animal.
The requirement for ruminally available CP has not been extensively studied with goats compared with other ruminant species. For beef cattle, without considering ruminal recycling of nitrogen, the requirement of consumed ruminally degradable CP, or degraded intake protein (DIP), has been suggested as 13% of total digestible nutrient (TDN) intake (NRC, 2000). If recycling is also accounted for, the requirement is slightly lower (e.g., 10% of TDN). It has been suggested that ruminal nitrogen recycling is more extensive in goats compared with other ruminant species (Silanikove, 2000), suggesting that the DIP requirement might be lower. In this regard, Soto-Navarro et al. (2003) did not observe limitations in digestion or microbial growth with dietary DIP levels as low as 7% of TDN intake. However, to be conservative and as a safety factor, this calculator estimates the DIP requirement as 9% of TDN intake.
In order to estimate the DIP requirement, it is necessary to know feed intake and concentrations of TDN or metabolizable energy (ME) in the diet. To evaluate whether or not the DIP level in the diet is adequate to allow unhindered microbial growth and digestion, it is also necessary to estimate the concentration of DIP. This is determined from concentrations of CP in dry matter (DM) and DIP in CP. DIP concentrations are listed in the table given below for various feedstuffs.
Use this DIP calculator to estimate the daily requirement of DIP for all classes of goats. Enter the data into the table below and then click the Calculate DIP Requirement button. The results will be displayed in the table at the bottom of the page. The requirements are given in the first set of three boxes and intakes are in the second set. If values in the second set of boxes are less than in the first, then there is a deficiency of DIP that might limit microbial growth and(or) digestion. Hence, the formulation of the diet should be altered to correct this deficiency.
As an example, let's assume 1 kg of DM intake and a dietary ME concentration of 10 MJ/kg DM, which equates to a TDN concentration of 63.8%. This results in a DIP requirement of 57.4 g (1000 g DM intake x 0.638 x 0.09) or 5.74% of DM intake. With 10% CP in the diet, and a DIP concentration of 75% of CP, actual DIP intake is 75 g or 7.5% of DM intake (1,000 g DM intake x 10% CP in the diet x 0.75). Hence, the dietary level of DIP is adequate. However, if the dietary CP concentration is 8% of DM and the DIP level is 50%, then DIP intake is inadequate (40 g DIP intake and 4.0% of DM intake).
Sources used in this calculation method are:
NRC. 2000. Nutrient Requirements of Beef Cattle, 2000 Update. National Academy Press, Washington, DC.
Preston, R. L. 2000. Typical composition of feeds for cattle and sheep. In: Beef 36(10), 10-20. Intertec Publ. Co. Overland Parks, KS.
Silanikove, N. 2000. The physiological basis of adaptation in goats to harsh environments. Small Ruminant Research 35:181-194.
Soto-Navarro, S. A., A. L. Goetsch, T. Sahlu, R. Puchala, and L. J. Dawson. 2003. Effects of ruminally degraded nitrogen source and level in a high concentrate diet on site of digestion in yearling Boer x Spanish wether goats. Small Ruminant Research. 50:117-128.