Diagnostic tools for detecting sub-acute ruminal acidosis in dairy cows
by A.C. Berge, published in Dairy Solutions Newsletter, 2010, No 6.
Sub acute ruminal acidosis (SARA) is a disease condition that is increasingly seen in our high producing dairy cows being fed a high concentrate diet. SARA can be defined as a condition characterized by rumen pH below 5.8,
an increased total concentration of short chain fatty acids, an increased concentration of lactic, propionic and butyric acid.(Garrett et al., 1999) The disease complex is often not diagnosed due to the lack of typical disease signs, daily fluctuations in rumen metabolism and problems in obtaining representative rumen fluid samples. A good diagnosis involves evaluating the productivity and health of the cows, feed composition and evaluation of ruminal fluid. A diagnosis can be obtained by observing and correlating multiple aspects of the condition. Research is currently performed for finding improved diagnostic tools that can be used in the field.
Clinical signs of SARA
On a herd basis, SARA can be a difficult condition to diagnose because its appearance is subtle. There are numerous clinical signs that are associated with SARA, but none of them can be used in isolation to make a diagnosis (Garrett et al., 1999; Enemark et al., 2004). However, clinical evaluations are highly recommended to assist in the diagnosis, as there are currently no good diagnostic tools for SARA. The clinical signs include decreased dry matter intake, loss of condition, depression in milk fat, changes in faecal consistency, colour and odour, pulmonary bacterial emboli, displaced abomasum, mastitis, metritis and low fertility. Some of the clinical signs may occur after the SARA episode, such as laminitis. There can be an increased culling rate and post-mortem signs could include parakeratosis or rumenitis and liver abscesses or inflammatory processes in other internal organs.
Rumen fluid collection
Rumen cannula in animals has been very valuable in improving ruminant nutrition. Rumen cannulas have been used across the world for research purposes to study rumen wall physiology, as well as ruminal content in live animals. Animal welfare concerns have been raised about this surgical procedure, even though very few detrimental health or behavioural effects have been seen. It is not a practical commercial diagnostic method for study the rumen fermentation. Oral stomach tube is one way of obtaining ruminal fluid, but care must be taken with the oral stomach tube for collection of ruminal fluid, so that the sample is not contaminated with the alkaline saliva.(Nordlund and Garrett, 1994) Rumenocentesis is a common field technique for collecting rumen fluid for SARA diagnosis and this slightly invasive procedure should be performed by a veterinarian(Nordlund and Garrett, 1994). It involves inserting a needle (16-gauge, 10 cm long) into the ventral rumen and withdrawing a sample of ruminal fluid using a 10-mL syringe. A study evaluating this technique indicated that it had no negative impact on animal health and welfare of lactating cows (Gianesella, 2008). Rumenocentesis should be performed 2-4 hours after the cow is offered a concentrate meal or 4-8 hours after total mixed ration.
Blood samples Several blood parameters may be indicative of SARA, however, no parameter was specific (Enemark et al., 2004).
Milk evaluations Depressed milk-fat content is commonly used as a diagnostic tool for SARA. The basis for this is that low pH suppresses fiber digestion in the rumen and the end products of fiber digestion are necessary for milk-fat synthesis. Normal milk-fat test results in Holstein dairy cows is above 3.5%, so a milk-fat test of < 3% can indicate SARA. However, bulk tank testing of milk fat is inappropriate to diagnose SARA at the herd level. Individual cows with SARA may have a low milk-fat test, but pooling their milk with that of the rest of the herd will mask detection of SARA. Individual milk-fat tests provide a better indicator of SARA.
Odd and branched chain fatty acids are of microbial origin and studies of ruminal fluid and intestinal fluids have indicated that these can be used to evaluate ruminal bacteria composition (Vlaeminck et al., 2006) The pattern of odd- and branched-chain fatty acids in milk fat reflects rumen microbial activity and proportions of different rumen microbial groups (Craninx et al., 2008). Therefore, these milk fatty acids can be used to predict rumen proportions of volatile fatty acids, duodenal flow of microbial protein and occurrence of rumen acidosis. It has been found that certain fatty acid changes in the milk can indicate sub-clinical ketosis in dairy cows (Van Haelst et al., 2008). Active research is carried out in the field and a technique using infrared spectroscopy is currently being evaluated (Rutten et al., 2009). Another technique being developed is fast and ultrafast gas chromatography (Fievez, 2010).
Conclusions
The diagnosis of sub-acute ruminal acidosis (SARA) is difficult due to the subtle and non-specific clinical signs, the delayed impact of SARA and the lack of good diagnostic methods. Rumenocentesis performed on a herd basis can be a good diagnostic tool. Methods are currently being investigated looking at the of fatty acid profiles of milk to detect changes in ruminal fermentation.
References
Craninx, M., Steen, A., Van, L.H., Van, N.T., Martin-Tereso, J., De, B.B., Fievez, V., 2008. Effect of lactation stage on the odd- and branched-chain milk fatty acids of dairy cattle under grazing and indoor conditions. J. Dairy Sci. 91, 2662-2677.
Enemark, J.M., Jorgensen, R.J., Kristensen, N.B., 2004. An evaluation of parameters for the detection of subclinical rumen acidosis in dairy herds. Vet. Res. Commun. 28, 687-709.
Fievez, V., 2010. Rumen fermentation characterized by odd and branched chain fatty acids in milk. Rumen Health: A 360º Analysis , Utrecht, NL.
Garrett, E.F., Pereira, M.N., Nordlund, K.V., Armentano, L.E., Goodger, W.J., Oetzel, G.R., 1999. Diagnostic methods for the detection of subacute ruminal acidosis in dairy cows. J. Dairy Sci. 82, 1170-1178.
Gianesella, M., 2008. Subacute rumen acidosis in Italian dairy herds: occurrence and diagnostic tools.
Nordlund K.V., Garrett E.F., 1994. Rumenocentesis - a technique for collecting rumen fluid for the diagnosis of sub-acute rumen acidosis in dairy herds. Bovine Practitioner 28, 109-112.
Rutten, M.J., Bovenhuis, H., Hettinga, K.A., van Valenberg, H.J., van Arendonk, J.A., 2009. Predicting bovine milk fat composition using infrared spectroscopy based on milk samples collected in winter and summer. J. Dairy Sci. 92, 6202-6209.
Van Haelst, Y.N., Beeckman, A., Van Knegsel, A.T., Fievez, V., 2008. Short communication: elevated concentrations of oleic acid and long-chain fatty acids in milk fat of multiparous subclinical ketotic cows. J. Dairy Sci. 91, 4683-4686.
Vlaeminck, B., Fievez, V., Demeyer, D., Dewhurst, R.J., 2006. Effect of forage:concentrate ratio on fatty acid composition of rumen bacteria isolated from ruminal and duodenal digesta. J. Dairy Sci. 89, 2668-2678.
an increased total concentration of short chain fatty acids, an increased concentration of lactic, propionic and butyric acid.(Garrett et al., 1999) The disease complex is often not diagnosed due to the lack of typical disease signs, daily fluctuations in rumen metabolism and problems in obtaining representative rumen fluid samples. A good diagnosis involves evaluating the productivity and health of the cows, feed composition and evaluation of ruminal fluid. A diagnosis can be obtained by observing and correlating multiple aspects of the condition. Research is currently performed for finding improved diagnostic tools that can be used in the field.
Clinical signs of SARA
On a herd basis, SARA can be a difficult condition to diagnose because its appearance is subtle. There are numerous clinical signs that are associated with SARA, but none of them can be used in isolation to make a diagnosis (Garrett et al., 1999; Enemark et al., 2004). However, clinical evaluations are highly recommended to assist in the diagnosis, as there are currently no good diagnostic tools for SARA. The clinical signs include decreased dry matter intake, loss of condition, depression in milk fat, changes in faecal consistency, colour and odour, pulmonary bacterial emboli, displaced abomasum, mastitis, metritis and low fertility. Some of the clinical signs may occur after the SARA episode, such as laminitis. There can be an increased culling rate and post-mortem signs could include parakeratosis or rumenitis and liver abscesses or inflammatory processes in other internal organs.
Rumen fluid collection
Rumen cannula in animals has been very valuable in improving ruminant nutrition. Rumen cannulas have been used across the world for research purposes to study rumen wall physiology, as well as ruminal content in live animals. Animal welfare concerns have been raised about this surgical procedure, even though very few detrimental health or behavioural effects have been seen. It is not a practical commercial diagnostic method for study the rumen fermentation. Oral stomach tube is one way of obtaining ruminal fluid, but care must be taken with the oral stomach tube for collection of ruminal fluid, so that the sample is not contaminated with the alkaline saliva.(Nordlund and Garrett, 1994) Rumenocentesis is a common field technique for collecting rumen fluid for SARA diagnosis and this slightly invasive procedure should be performed by a veterinarian(Nordlund and Garrett, 1994). It involves inserting a needle (16-gauge, 10 cm long) into the ventral rumen and withdrawing a sample of ruminal fluid using a 10-mL syringe. A study evaluating this technique indicated that it had no negative impact on animal health and welfare of lactating cows (Gianesella, 2008). Rumenocentesis should be performed 2-4 hours after the cow is offered a concentrate meal or 4-8 hours after total mixed ration.
Blood samples Several blood parameters may be indicative of SARA, however, no parameter was specific (Enemark et al., 2004).
Milk evaluations Depressed milk-fat content is commonly used as a diagnostic tool for SARA. The basis for this is that low pH suppresses fiber digestion in the rumen and the end products of fiber digestion are necessary for milk-fat synthesis. Normal milk-fat test results in Holstein dairy cows is above 3.5%, so a milk-fat test of < 3% can indicate SARA. However, bulk tank testing of milk fat is inappropriate to diagnose SARA at the herd level. Individual cows with SARA may have a low milk-fat test, but pooling their milk with that of the rest of the herd will mask detection of SARA. Individual milk-fat tests provide a better indicator of SARA.
Odd and branched chain fatty acids are of microbial origin and studies of ruminal fluid and intestinal fluids have indicated that these can be used to evaluate ruminal bacteria composition (Vlaeminck et al., 2006) The pattern of odd- and branched-chain fatty acids in milk fat reflects rumen microbial activity and proportions of different rumen microbial groups (Craninx et al., 2008). Therefore, these milk fatty acids can be used to predict rumen proportions of volatile fatty acids, duodenal flow of microbial protein and occurrence of rumen acidosis. It has been found that certain fatty acid changes in the milk can indicate sub-clinical ketosis in dairy cows (Van Haelst et al., 2008). Active research is carried out in the field and a technique using infrared spectroscopy is currently being evaluated (Rutten et al., 2009). Another technique being developed is fast and ultrafast gas chromatography (Fievez, 2010).
Conclusions
The diagnosis of sub-acute ruminal acidosis (SARA) is difficult due to the subtle and non-specific clinical signs, the delayed impact of SARA and the lack of good diagnostic methods. Rumenocentesis performed on a herd basis can be a good diagnostic tool. Methods are currently being investigated looking at the of fatty acid profiles of milk to detect changes in ruminal fermentation.
References
Craninx, M., Steen, A., Van, L.H., Van, N.T., Martin-Tereso, J., De, B.B., Fievez, V., 2008. Effect of lactation stage on the odd- and branched-chain milk fatty acids of dairy cattle under grazing and indoor conditions. J. Dairy Sci. 91, 2662-2677.
Enemark, J.M., Jorgensen, R.J., Kristensen, N.B., 2004. An evaluation of parameters for the detection of subclinical rumen acidosis in dairy herds. Vet. Res. Commun. 28, 687-709.
Fievez, V., 2010. Rumen fermentation characterized by odd and branched chain fatty acids in milk. Rumen Health: A 360º Analysis , Utrecht, NL.
Garrett, E.F., Pereira, M.N., Nordlund, K.V., Armentano, L.E., Goodger, W.J., Oetzel, G.R., 1999. Diagnostic methods for the detection of subacute ruminal acidosis in dairy cows. J. Dairy Sci. 82, 1170-1178.
Gianesella, M., 2008. Subacute rumen acidosis in Italian dairy herds: occurrence and diagnostic tools.
Nordlund K.V., Garrett E.F., 1994. Rumenocentesis - a technique for collecting rumen fluid for the diagnosis of sub-acute rumen acidosis in dairy herds. Bovine Practitioner 28, 109-112.
Rutten, M.J., Bovenhuis, H., Hettinga, K.A., van Valenberg, H.J., van Arendonk, J.A., 2009. Predicting bovine milk fat composition using infrared spectroscopy based on milk samples collected in winter and summer. J. Dairy Sci. 92, 6202-6209.
Van Haelst, Y.N., Beeckman, A., Van Knegsel, A.T., Fievez, V., 2008. Short communication: elevated concentrations of oleic acid and long-chain fatty acids in milk fat of multiparous subclinical ketotic cows. J. Dairy Sci. 91, 4683-4686.
Vlaeminck, B., Fievez, V., Demeyer, D., Dewhurst, R.J., 2006. Effect of forage:concentrate ratio on fatty acid composition of rumen bacteria isolated from ruminal and duodenal digesta. J. Dairy Sci. 89, 2668-2678.