Effect of carbohydrate source on ammonia utilization in lactating dairy cows1

Abstract

This study was conducted to investigate the effect of dextrose, starch, NDF, and a carbohydrate (CHO) mix on utilization of ruminal ammonia in dairy cows. Four ruminally and duodenally cannulated Holstein cows (BW = 788 +/- 31 kg; 217 +/- 35 d in milk) were allocated to four treatments in a 4 x 4 Latin square design trial. Cows were fed an all alfalfa diet at 12-h intervals (DMI = 22.2 +/- 0.25 kg/d). Treatments were control, white oat fiber (NDF); corn dextrose (GLU); cornstarch (STA); and a CHO mix (25% of each): apple pectin, GLU, STA, and NDF (MIX). Carbohydrates were introduced intraruminally during feeding at 20% of dietary DMI. Ruminal ammonia was labeled with (15)N. Ruminal pH was the highest for NDF followed by STA and MIX and GLU (P < 0.001). Ruminal ammonia concentration and pool size were decreased by GLU and STA compared with NDF (P < 0.001 and P = 0.03, respectively). Acetate, isobutyrate, isovalerate, and total VFA concentration in the rumen were decreased (P = 0.009 to 0.001), and butyrate was increased (P < 0.001) by GLU compared with the other CHO. Microbial N flow to the duodenum was decreased (P < 0.05) by NDF compared with the other CHO, and the flow of microbial N formed from ammonia was greater for STA compared with GLU and NDF (P = 0.04 and 0.03, respectively). Urinary N loss was decreased (P = 0.05) by GLU and STA, but overall (feces plus urine) N losses were not affected (P = 0.73) by treatment. Milk urea concentration was lowered by GLU and STA compared with NDF and MIX (P = 0.002). The proportion of bacterial N synthesized from ammonia in the rumen was greater with STA than with NDF and MIX and was least for GLU (P = 0.02). Irreversible ammonia loss and flux were lower (P = 0.09 and 0.02, respectively) for GLU than for STA and NDF. As a percentage of the dose given, cumulative secretion of (15)N ammonia in milk protein was greater for STA than for GLU or NDF (P = 0.01 and 0.001, respectively). This experiment demonstrated that provision of readily fermentable energy can decrease ammonia concentrations in the rumen through decreased ammonia production (GLU), or through enhanced uptake of ammonia for microbial protein synthesis (STA). Rapidly fermentable energy in the rumen decreased ammonia production and flux, but the overall efficiency of ammonia utilization for milk protein synthesis was only increased by enhancing ruminal microbial ammonia uptake.

In Vitro Yield of Microbial-N from Fermentation of Glucogenic and Lipogenic Diets Provided by Different Sources of Rumen Degradable Amino Acids

“…This may be related to the synchrony between ruminal protein and carbohydrate digestion. Microbial protein synthesis depends largely on the available amount and fermentation rate of carbohydrates and N in the rumen [29]. The results of the present study were consistent with those of a previous study pertaining to the reduction of in vitro ammonia concentrations with steam flaking.…”

“…Additionally, in vitro TSD were observed to have a high correlation with gas production [22], and F containing diets had higher parameter (b) than SB. There was no significant difference of ammonia for microbial protein synthesis [29]. The rate of substrate fermentation was roughly proportional to the rate of microbial growth, with more rapidly fermented substrates yielding more microbial mass.…”

In situ Rumen Degradation Kinetics of High-Protein Forage Crops in Temperate Climates

“…Since microbial population growth is highly dependent on the availability of fermentable carbohydrates, its insufficient supply with respect to protein should reduce microbial protein synthesis, increasing N loss through urine and reducing the supply of amino acids (Hristov et al, 2005). The most limiting factor for efficient N utilization is the type and amount of carbohydrates available in the rumen.…”

Metabolismo de nutrientes em ovinos alimentados com casca de soja em substituição ao feno de coastcross

“…Henning et al (1993) também reportaram que a alta concentração e a ineficiência na utilização do nitrogênio amoniacal do rúmen podem refletir em aumento da excreção de nitrogênio pela urina. Além disso, ao melhorar a utilização de amônia no rúmen, transfere-se a excreção de nitrogênio da urina para as fezes (Hristov et al, 2005).…”

“…Assim, é possível que a casca de soja, por ser mais rapidamente digerida que o feno de coastcross, possibilite melhor sincronismo entre os nutrientes. Hristov et al (2005) reportaram que o fornecimento de carboidratos rapidamente fermentescíveis pode diminuir a concentração de amônia no rúmen, em razão da melhor utilização da amônia na síntese microbiana ou da incorporação em aminoácidos pré-formados.…”