Acidosis is an important nutritional problem for the dairy industry, both in terms of economic impact and as a substantial health problem. Even in well-managed, high-yielding herds, the prevalence of the disorder is reported to be increasing.
However, the reality is that maximising milk production without incurring ruminal acidosis is a challenge for most producers, particularly during the early lactation period, which is the most nutritionally challenging time for dairy cows.
Inevitably, in most high-producing dairy cows, given their high level of dry matter intake and the high proportion of cereals included in diets during lactation, acidosis and related conditions are quite common.
Nevertheless, at farm level, it is crucial to develop an understanding of the factors that put cows at risk of developing acidosis and how feeding and management practices can help minimise this risk.
Acute and Subacute Acidosis
Ruminal acidosis occurs when the rate of volatile fatty acid (VFA) production in the rumen exceeds the rate at which the rumen environment can neutralise or absorb the acids.
Generally, acidosis is caused by digestive upsets. A sudden increase in concentrates after calving or feeding high levels of concentrates containing too much starch or acid ingredients are frequent causes of the problem.
For simplicity, acidosis can be divided into categories of acute or subacute acidosis.
Clinical signs of acute acidosis (pH<5.0) include anorexia, abdominal pain, rapid beating of the heart, diarrhoea, recumbency and death. Cattle that survive acute acidosis can often have a poor thrive, due in part to damage of the gastrointestinal tract and reduced absorptive capacity. Fortunately, the incidence of acute acidosis in dairy herds is very low. Subacute acidosis (SARA; pH 5.0-5.6) occurs more frequently, but is seldom recognised and is usually of greater economic importance than the clinical disease. Studies suggest a prevalence of SARA in 15% to 20 % of early and mid-lactation cows. Even Irish data on a grass-based diet suggests 11% of cows were affected with SARA (pH = < 5.5), while 42% were marginal (pH 5.6–5.8). Repeated bouts of SARA is the basis for future problems and can lead to impaired animal health, including decreased feed intake and milk fat production, lowered body condition, inflammation, liver abscesses, displaced abomasum and laminitis causing lameness.
Risk animals
The key at-risk groups from SARA are cows in early lactation and first calved heifers. Dairy cows in early lactation experience the most challenging time, both nutritionally and physiologically.
During this time, cows are switched from a dry cow diet or transitional diet to a high-energy density lactating diet. This dietary change, along with high nutritional demands of milk production, put this group of animal at great risk of SARA. First calved heifers are particularly susceptible to developing acidosis after calving and studies show a higher prevalence of SARA in first calvers than in older cows.
Signs and diagnosis
To monitor acidosis on-farm, simply build up a herd health profile of your herd. In the case of SARA, monitor the incidences of associated conditions and utilise cow signals as indicators.
Typical cow signals relating to SARA include low milk fat, poor rumen fill, dung with gas bubbles, undigested fibre particles in the dung and laminitis. If you suspect a SARA problem, consult with your vet and confirm with a rumen fluid pH analysis.
On-farm indirect indicators:
Feed behaviour: Feeding behaviour changes in accordance with diets offered and the animal’s health condition, and can be a useful diagnostic tool in dairy cows. Healthy rumen function is when at least 50% of the cows are chewing the cud at any given time, other than when they are eating or being milked. To measure accurately, numerous observations over several days are required.
Faecal changes: Faeces of acidotic stock are more liquid, contain undigested fibre and grain, are often lighter in colour and may contain gas bubbles. The smell of the faeces may be bitter-sweet. Typically, if more than 15% of a herd is scouring, investigate further.
Low milk fat concentration: A milk fat to milk protein ratio of <1.15:1 may indicate a risk of acidosis. If individual cows have milk fat concentrations equal to or below 2.5%, or a rapid fall in milk fat of 0.3% to 0.5% in a week occurs, investigate further.
Lameness: Cows experiencing laminitis and foot problems (>15%), especially first lactation and fresh cows.
Prevention and control
The best strategy to prevent SARA is to gradually adapt the rumen environment to changes in diet composition. Formulate adequate fiber in the diets, prepare diets with adequate particle size distribution to reduce sorting and consider supplements, such as yeats and buffers, to stabilise rumen pH.
Gradual adaptation: Gradual transition of cows from a high-forage dry-cow diet to a lactation diet helps stabilise the rumen environment to dietary changes. Appropriate and planned transition programmes before calving can help reduce the risk of acidosis post-calving.
Diet formulation and fibre: A key to preventing SARA is to supply adequate fibre. Target a minimum of 25% NDF in the total diet, 75% of which is supplied by coarse forage to maintain rumen function and health.
Most diets are formulated for the average cow and are closer to the minimum level of fibre. This may be acceptable for cows in mid- and late-lactation, but diets for cows in early lactation need to account for the higher risk of experiencing acidosis, so ensure a safety margin is factored in.
Monitor the inclusion level of rapidly fermentable ingredients like wheat, barley and steam-flaked grains. Also, wet silage and/or low pH (<4) silages can increase the acid load.
Sorting: Properly formulated diets do not necessarily guarantee healthy digestion. Dairy cows usually sort for the most palatable feed grains.
Depending upon the degree of sorting behaviour, the composition of feed could be substantially different from what is originally formulated.
To reduce sorting, prepare TMR with an appropriate particle size and moisture content. Dry diets not only limit feed intake, they also help to prevent excess sorting. Ideal moisture content in TMR is about 40% to 50%.
Housing and management: Nutritional imbalances, deficiencies or erratic management of feeding programmes should be avoided at all costs.
In terms of the housing requirements, ensure adequate trough space (0.6m per cow) and avoid factors such as limited water availability, poor grouping strategy/overcrowding, excessive time standing after milking and slippery floor at the feed face.
Acidosis is an important nutritional problem for the dairy industry, both in terms of economic impact and as a substantial health problem. Even in well-managed, high-yielding herds, the prevalence of the disorder is reported to be increasing.
However, the reality is that maximising milk production without incurring ruminal acidosis is a challenge for most producers, particularly during the early lactation period, which is the most nutritionally challenging time for dairy cows.
Inevitably, in most high-producing dairy cows, given their high level of dry matter intake and the high proportion of cereals included in diets during lactation, acidosis and related conditions are quite common.
Nevertheless, at farm level, it is crucial to develop an understanding of the factors that put cows at risk of developing acidosis and how feeding and management practices can help minimise this risk.
Acute and Subacute Acidosis
Ruminal acidosis occurs when the rate of volatile fatty acid (VFA) production in the rumen exceeds the rate at which the rumen environment can neutralise or absorb the acids.
Generally, acidosis is caused by digestive upsets. A sudden increase in concentrates after calving or feeding high levels of concentrates containing too much starch or acid ingredients are frequent causes of the problem.
For simplicity, acidosis can be divided into categories of acute or subacute acidosis.
Clinical signs of acute acidosis (pH<5.0) include anorexia, abdominal pain, rapid beating of the heart, diarrhoea, recumbency and death. Cattle that survive acute acidosis can often have a poor thrive, due in part to damage of the gastrointestinal tract and reduced absorptive capacity. Fortunately, the incidence of acute acidosis in dairy herds is very low. Subacute acidosis (SARA; pH 5.0-5.6) occurs more frequently, but is seldom recognised and is usually of greater economic importance than the clinical disease. Studies suggest a prevalence of SARA in 15% to 20 % of early and mid-lactation cows. Even Irish data on a grass-based diet suggests 11% of cows were affected with SARA (pH = < 5.5), while 42% were marginal (pH 5.6–5.8). Repeated bouts of SARA is the basis for future problems and can lead to impaired animal health, including decreased feed intake and milk fat production, lowered body condition, inflammation, liver abscesses, displaced abomasum and laminitis causing lameness.
Risk animals
The key at-risk groups from SARA are cows in early lactation and first calved heifers. Dairy cows in early lactation experience the most challenging time, both nutritionally and physiologically.
During this time, cows are switched from a dry cow diet or transitional diet to a high-energy density lactating diet. This dietary change, along with high nutritional demands of milk production, put this group of animal at great risk of SARA. First calved heifers are particularly susceptible to developing acidosis after calving and studies show a higher prevalence of SARA in first calvers than in older cows.
Signs and diagnosis
To monitor acidosis on-farm, simply build up a herd health profile of your herd. In the case of SARA, monitor the incidences of associated conditions and utilise cow signals as indicators.
Typical cow signals relating to SARA include low milk fat, poor rumen fill, dung with gas bubbles, undigested fibre particles in the dung and laminitis. If you suspect a SARA problem, consult with your vet and confirm with a rumen fluid pH analysis.
On-farm indirect indicators:
Feed behaviour: Feeding behaviour changes in accordance with diets offered and the animal’s health condition, and can be a useful diagnostic tool in dairy cows. Healthy rumen function is when at least 50% of the cows are chewing the cud at any given time, other than when they are eating or being milked. To measure accurately, numerous observations over several days are required.
Faecal changes: Faeces of acidotic stock are more liquid, contain undigested fibre and grain, are often lighter in colour and may contain gas bubbles. The smell of the faeces may be bitter-sweet. Typically, if more than 15% of a herd is scouring, investigate further.
Low milk fat concentration: A milk fat to milk protein ratio of <1.15:1 may indicate a risk of acidosis. If individual cows have milk fat concentrations equal to or below 2.5%, or a rapid fall in milk fat of 0.3% to 0.5% in a week occurs, investigate further.
Lameness: Cows experiencing laminitis and foot problems (>15%), especially first lactation and fresh cows.
Prevention and control
The best strategy to prevent SARA is to gradually adapt the rumen environment to changes in diet composition. Formulate adequate fiber in the diets, prepare diets with adequate particle size distribution to reduce sorting and consider supplements, such as yeats and buffers, to stabilise rumen pH.
Gradual adaptation: Gradual transition of cows from a high-forage dry-cow diet to a lactation diet helps stabilise the rumen environment to dietary changes. Appropriate and planned transition programmes before calving can help reduce the risk of acidosis post-calving.
Diet formulation and fibre: A key to preventing SARA is to supply adequate fibre. Target a minimum of 25% NDF in the total diet, 75% of which is supplied by coarse forage to maintain rumen function and health.
Most diets are formulated for the average cow and are closer to the minimum level of fibre. This may be acceptable for cows in mid- and late-lactation, but diets for cows in early lactation need to account for the higher risk of experiencing acidosis, so ensure a safety margin is factored in.
Monitor the inclusion level of rapidly fermentable ingredients like wheat, barley and steam-flaked grains. Also, wet silage and/or low pH (<4) silages can increase the acid load.
Sorting: Properly formulated diets do not necessarily guarantee healthy digestion. Dairy cows usually sort for the most palatable feed grains.
Depending upon the degree of sorting behaviour, the composition of feed could be substantially different from what is originally formulated.
To reduce sorting, prepare TMR with an appropriate particle size and moisture content. Dry diets not only limit feed intake, they also help to prevent excess sorting. Ideal moisture content in TMR is about 40% to 50%.
Housing and management: Nutritional imbalances, deficiencies or erratic management of feeding programmes should be avoided at all costs.
In terms of the housing requirements, ensure adequate trough space (0.6m per cow) and avoid factors such as limited water availability, poor grouping strategy/overcrowding, excessive time standing after milking and slippery floor at the feed face.
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