Glycerol to dairy calves : effects on intestinal health and fluid balance

Abstract: The bacterium Lactobacillus reuteri, which natural habitat is in the intestine of mammals and birds, uses glycerol as a substrate for production of the antimicrobial compound reuterin. Glycerol has been shown to decrease the number of Escherichia coli in human feces and it is believed to be due to in situ production of reuterin. E. coli belongs to the large family of Enterobacteriaceae, naturally occurring in the intestine, and pathogenic strains of E. coli have been shown to be one of several bacteria causing diarrhoea in calves. Consequences of diarrhoea are dehydration and energy deficiency and without treatment, i.e. addition of oral rehydration solution (ORS), the situation can be life threatening for the calf. Besides the nutritional value of glycerol, it has been shown that glycerol can maintain the fluid balance in humans, rats and steers. There seems to be no studies done concerning ORS containing glycerol given to calves.One aim of the present study was to investigate if glycerol, by stimulating the formation of the substance reuterin and thus decreasing the amount of Enterobacteriaceae in calf feces, has a positive effect on the intestinal flora in healthy young calves compared to glucose and water. Secondly, the aim was to evaluate if glycerol can contribute to maintenance of the fluid balance. Furthermore the aim was to investigate if glycerol supplementation may ameliorate effects on metabolism of 24 h feed and fluid deprivation. Twenty dairy calves of the Swedish Red Breed, one to three weeks old at the start of the experiment were used. The calves were randomly divided to one of three oral supplementations: glycerol (0.67 g glycerol/kg BW and 0.33 g glucose/kg BW) (n=8), glucose (1g glucose/kg BW) (n=8) and control (without addition of ORS) (n=4). The calves were provided with 400 ml of ORS twice a day during the adaptation period, day 1 to 11. Day 11 to 12, the calves were deprived of feed, milk and water for 24 h accepts for 800 ml ORS at 16.00 hr day 11 and 08.00 hr day 12. Blood and feces samples were collected 2 to 3 days before the start of the treatment (day 0) and after 11 days of treatment (day 11). Further, blood samples were collected after the 24 h long deprivation period (day 12). The blood was analyzed for packed cell volume (PCV), total plasma protein (TPP), plasma osmolality and plasma concentration of glycerol, glucose and insulin. The feces were analyzed for the concentration of short-chain fatty acids, lactate and 1,3-propandediol using a HPLC assay, and bacterial quantification of lactobacilli and enterobacteria was determined by plate counts. Detection of reuterin producing lactobacilli and E. coli and determination of 16S rRNA gene sequences of Lactobacillus isolates were also performed. The PCV, concentration of TPP in plasma and osmolality increased from day 11 to 12 for all treatments, however, no differences among treatments were found within or between days. The effect of treatment showed that calves provided with ORS containing glycerol had higher values for plasma osmolality and a tendency to lower amount of PCV in blood, compared to the other treatments. The concentration of glycerol in plasma was shown to be higher for calves provided ORS with glycerol day 11 and 12 compared to calves treated with glucose and control calves. The concentration of glucose in plasma increased from day 11 to 12 in calves provided ORS with either glycerol or glucose whereas the glucose concentration in plasma tended to decrease in control calves. The insulin concentration in plasma increased from day 11 to 12 in calves treated with glucose. The concentration of short-chain fatty acids, lactate and 1,3-propandediol in feces remained unchanged irrespective treatment and day. The number of Lactobacillus and Enterobacteriaceae in feces was not affected by treatment. The number of Enterobacteriaceae decreased from day 0 to 11, whereas the number of Lactobacillus remained unchanged. L. reuteri and E. coli was detected in feces regardless of treatment both day 0 and 11. It can be concluded that ORS containing a mixture of glycerol/glucose can maintain the fluid balance in calves in greater extent as ORS containing glucose. Calves receiving pure glucose ORS were markedly hyperglycemic and hyperinsulinemic, whereas calves receiving ORS containing a mixture of glycerol/glucose did not develop hyperglycemia and insulin fluctuated less. ORS containing a mixture of glycerol/glucose was shown to not change the amount of lactobacilli and E. coli in these healthy young calves. Probably glycerol was efficiently absorbed in the small intestine and thereby not available for the intestinal microbiota. Further studies are needed to determine whether glycerol, alone and not in a mixture with glucose, possesses health promoting properties in calves. It is also suggested that further studies focus on the effect of glycerol on either fluid balance or intestinal flora in calves.