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Importance of Adequate Non Fiber Carbohydrates (Starch & Sugar) for Maximum Microbial Synthesis of Rumen Undegradable Protein

Microbes in the rumen use (1) rumen degradable protein - RDP (ammonia, amino acids & peptides - short chains of amino acids) and (2) non fiber carbohydrates - NFC (starch & sugar) as their food source. An important part of rumen nutrition is to supply rations on which the rumen microorganism proliferate maximally. Growing maximum amounts of rumen microbes is important as these bugs then become food for the cow when they reach the small intestine. Rumen microbes are mainly protein. As such, they are an important source of digestible rumen undegradable protein (RUP). Under some forage conditions, the rumen is awash in RDP (grasses that are green or immature, all legumes and where lots of protein supplement is fed). It is important that the cow be fed enough NFC (grains) for her rumen microbes to capture as much of the RDP as is possible. By adding more NFC (grains) to the diet, there may be a milk response that is due indirectly, to the added NFC allowing the rumen microbes to synthesize more microbial protein that becomes more RUP for the cow and more amino acids to the udder for milk synthesis. Adding soybean meal (SBM) to the diet may elicit a milk response that could be obtained by feeding more grain. I discussed this possibility in my report to UNDP on our favorable results of feeding SBM to cows and nursing ewes on green pasture in Srebrenica. To test this hypothesis I ran two different ration simulations through the U.S. NRC Dairy 2001 software. Both rations were formulated to support 40 liters of milk on cows eating lush legume pasture. In one ration (low NFC) I added only SBM. In the other ration (high NFC) I added mostly corn (up to cow's ability to eat dry matter) plus a little SBM. Rations and nutrient parameters are shown below. Notice what happened.

Comparison of feeding two different rations to lactating cowsNFCHigh
Ration (same vitamins & minerals) + 2 kg Wheat BranNFCLow
Legume Pasture, lush, kg86.786.7
Corn, ground. kg6.050.00
Soybean Meal, 44% solvent. kg0.603.00
Dry Matter Intake, kg 26.423.2
Predicted Maximum Dry Matter Intake, kg26.426.4
NElactation will support liters of milk44.138.4
Metabolizable protein supports liter of milk40.040.0
Weight Change of cow per day, kg+0.6-0.2
NFC, % of Total Ration Dry Matter 39.630.1
Metabolizable Protein from Microbial Synthesis, gm/day14021224
% RDP Total Ration Dry Matter formulated for 40 liters/milk/day16.320.6
% RUP needed in TRDM to support 40 liters milk/day6.47.6
% Total Protein in TRDM needed to support 40 liters milk/cow/day22.728.2

To support the same level of milk production (40 liters), the ration with corn added to the maximum ability of the cow to eat dry matter (in comparison to added SBM only) supports greater rumen synthesis of metabolic protein (1402/1224 = 17.7 % improvement), the cow will gain weight (+0.6 kg/day) rather than lose it (-0.2 kg/day) and the feed ration needs to contain less crude protein (22.7% vs. 28.2%). This assumes adequate RDP is available. On rations low in RDP and RUP (mature grasses), it will be necessary to add RUP to the ration to improve milk flow. Study the situation to decide.

Roy Chapin, Ph.D. Animal Nutritionist

11145 Chapin Lane, Amity, Oregon 97101
Phone: 503-835-7317
Fax: 503-835-3333
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© Roy Chapin, 2018
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