Experiments show that a high grain diet will result in a dramatic increase of LPS in the bodies of cows. Why are we looking at cows rather than mice, the usual animal model for human beings? The GI tracts of mice are good models for the GI tract of healthy humans without carbohydrate malabsorption because mice have a good capacity to digest grains and starches. People with carbohydrate malabsorption need a different animal model because their digestive system cannot digest the grains and other starches.

Cows are animals that do have some difficulty with carbohydrate malabsorption; when cows are fed high grain diets, they get acidosis. Although cows may not be a perfect animal model for the GI tract of people with carbohydrate malabsorption, the fact that cows get higher levels of LPS with a high grain diet does suggest there is a connection between unabsorbed carbohydrates and LPS levels.

View this article in PubMed
1: J Dairy Sci. 2007 Feb;90(2):856-66.
Ruminal lipopolysaccharide concentration and inflammatory response during grain-induced subacute ruminal acidosis in dairy cows.

* Gozho GN, * Krause DO, * Plaizier JC.

Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.

The effects of grain-induced subacute ruminal acidosis (SARA) in lactating dairy cows on free ruminal lipopolysaccharide (LPS) and indicators of inflammation were determined. Four mid lactation dairy cows were divided into 2 groups of 2 cows and used in a repeated switchover design. During each period, SARA was induced in 2 animals for 5 subsequent days by replacing 25% of their total mixed ration (dry matter basis) with a concentrate made of 50% wheat and 50% barley. The other 2 cows acted as controls and were fed a total mixed ration diet in which 44% of dry matter was concentrate. On average, inducing SARA did not affect milk composition, increased the duration of rumen pH below 5.6 from 187 to 309 min/d, and increased free ruminal LPS concentration from 24,547 endotoxin units (EU)/mL to 128,825 EU/mL. Averaged across treatments, milk fat yield and milk protein yield were 0.66 and 1.00 kg/d, respectively. Rumen pH and milk fat data suggest that control cows also experienced ruminal acidosis, albeit a milder form of this disease than SARA cows. Serum LPS concentration in both control and SARA cows was less than the detection limit of <0.01 EU/mL for the assay. Induction of SARA elevated serum amyloid A concentration from 286.8 to 498.8 mug/mL, but did not affect other markers of inflammation including haptoglobin, fibrinogen, serum copper, or white blood cells. These results suggest that grain-induced SARA in mid lactation dairy cows increases the lysis of gram-negative bacteria and activates an inflammatory response.

PMID: 17235162 [PubMed - indexed for MEDLINE]

* Gozho GN, * Krause DO, * Plaizier JC.

Department of Animal Science, University of Manitoba, Winnipeg, MB, Canada R3T 2N2.

Three rumen-fistulated Jersey steers were gradually adapted to a wheat-barley concentrate over a 4-wk period. Adaptation steps consisted of four 1-wk periods during which steers were fed diets with forage-to-concentrate (F:C) ratios of 100:0, 79:21, 59:41, and 39:61. The forage consisted of chopped hay (CH), and the concentrate consisted of pelleted concentrate containing 50% ground wheat and 50% ground barley. Steers were fed the all-forage diet ad libitum during wk 1. Feed offered in wk 2 to 4 was kept constant at the ad libitum intake during wk 1. On 2 d that were set 3 d apart during wk 5, subacute ruminal acidosis (SARA) was induced in the steers by feeding a diet with an F:C ratio of 24:76 by offering them 0.9 kg of CH at 0900 h followed by 2 meals of 3.0 kg each of wheat-barley pellets (WBP) at 1100 h and 1300 h and 0.9 kg of CH at 1700 h, to depress rumen pH for at least 3 h/d below 5.6. The average concentrate inclusion for the SARA induction diet was 76 +/- 10% DM. During stepwise adaptation, time with pH below 5.6 increased to an average of 121 min/d when the steers were consuming a diet containing 61% DM as WBP. Dietary inclusion of WBP at the rate of 76% DM induced SARA because the steers spent an average of 219 min/d with pH below 5.6. The free ruminal lipopolysaccharide (LPS) concentration increased from 6,310 endotoxin units (EU)/mL with the all-forage diet to 18,197 EU/mL with the 61% concentrate diet. The ruminal LPS concentration increased to 26,915 EU/mL when SARA was induced. Serum haptoglobin increased from 0.53 mg/mL when steers were on the all-forage diet to 1.90 mg/mL with the 61% concentrate diet and were not increased further by inducing SARA. The serum amyloid-A concentration was not affected by increasing dietary concentrate during stepwise adaptation to the concentrate, but increased from 71 to 163 microg/mL when SARA was induced. A gradual increase in dietary concentrate so that the F:C ratio decreased to 39:61 resulted in increased ruminal LPS concentrations. Subsequent induction of SARA further increased ruminal LPS and activated an inflammatory response.

* Goad DW, * Goad CL, * Nagaraja TG.

Department of Animal Sciences, Kansas State University, Manhattan 66506-1600, USA.

We used six ruminally cannulated steers in a two-period crossover design to study ruminal fermentative and microbial changes associated with induced subacute acidosis. Steers were adapted to either an 80% alfalfa hay (hay-adapted)- or corn grain (grain-adapted)-based concentrate diet. After feed was withheld for 24 h, steers were overfed with an all-grain diet at 3.5 x NEm daily for 3 d. Ruminal contents and jugular blood samples were collected before withholding feed and at 0 and 12 h daily for 3 d during the overfeeding period. Ruminal samples were analyzed for pH, lactate, VFA concentrations, and counts of total anaerobic, amylolytic, lactic acid-producing and -fermenting bacteria, and ciliated protozoa. Blood samples were analyzed to assess acid-base status. Ruminal pH declined to a range of 5.5 to 5.0 with increased VFA concentrations, but normal lactate concentrations (<5 mM) were indicative of subacute acidosis. Total viable and amylolytic bacterial counts were higher (P < .05) in grain-adapted than hay-adapted steers. Anaerobic lactobacilli counts increased over time (P < .01) in both groups and were generally higher in grain-adapted than hay-adapted steers. Lactate-utilizing bacteria were initially greater in grain-adapted than hay-adapted steers and increased over time in both groups following grain challenge. Total ciliates were initially higher (P < .05) in grain-adapted than hay-adapted steers and decreased after 48 h in both groups. Blood acid-base changes were minimal. Bacterial changes associated with subacute acidosis resemble those reported during adaptation to grain feeding, and the decline in ciliated protozoa may be the only microbial indicator of a potentially acidotic condition in the rumen.

PMID: 9464904 [PubMed - indexed for MEDLINE]