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The Effect of Concentrate Supplementation on Nutrient Flow to the Omasum in Dairy Cows Receiving Freshly Cut Grass

¹ MTT Agrifood Research Finland, North Savo Research Station, FIN-71750 Maaninka, Finland
² MTT Agrifood Research Finland, Animal Production Research, FIN-31600 Jokioinen, Finland

Corresponding author: H. Khalili; e-mail: hannele.khalili{at}mtt.fi.

An experiment was carried out to determine the effect of increasing the amount of grain-based concentrate (0, 3, or 6 kg/d) on nutrient flow to the omasum, rumen fermentation pattern, milk yield, and nutrient use of dairy cows. Harvested timothy-meadow fescue grass was fed individually 3 times daily to 6 rumen-cannulated Holstein-Friesian cows in a duplicated 3 x 3 Latin square experiment. Grass was offered as 6 equal meals daily, and concentrates were fed as 2 equal meals daily. Nitrogen, microbial N, and neutral detergent fiber (NDF) flow from the rumen were measured using an omasal sampling technique in combination with a triple marker method [CoEDTA, Yb, and indigestible NDF (INDF) as markers]. Concentrate supplementation linearly decreased ruminal pH, N degradability, ammonia N concentration, and molar proportion of acetate and increased the molar proportion of butyrate. Supplementation of grass with concentrates linearly increased dry matter intake (DMI), microbial N synthesis, N, and NDF flow to the omasum, and ruminal and total tract NDF digestibility decreased linearly. Decreases in NDF digestibility in response to concentrates was primarily related to a decrease in the rate of digestion. Increased DMI overcame the negative effects of concentrate on NDF digestion, resulting in a linear increase in total metabolizable energy intake and milk production. Physical constraints were found not to limit grass DMI. Concentrate supplementation increased the apparent use of dietary N for milk production because of a reduction in N intake, rather than thorough improvements in N capture in the rumen.

Key Words: dairy cow • grass • concentrate • nutrient flow

Abbreviation key: C0 = no concentrate supplementation, C3 = 3 kg of concentrate, C6 = 6 kg of concentrate, DNDF = potentially digestible NDF, DOM = digestible OM, ECM = energy-corrected milk, INDF = indigestible NDF, LP = large particle phase, ME = metabolizable energy, MPS = microbial protein synthesis, RDN = rumen-degradable N, SP = small particle phase, SR = substitution rate.

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