PDS Nutritional Summary
PDS Nutritional Summary - SARA
S.A R.A
Introduction
Sub-acute ruminal acidosis (SARA), also known as chronic or sub-clinical acidosis, is a well-recognized digestive disorder that is an increasing health problem in most dairy herds. Results from field studies indicate a high prevalence of SARA in high-producing dairy herds as producers respond to the demands for increased milk production with higher grain, lower fibre diets that maximize energy intake during early lactation. Dairy herds experiencing SARA will have a decreased efficiency of milk production, impaired cow health and high rates of involuntary culling.
What are the symptoms of SARA?
Dairy cows experiencing SARA often do not exhibit any clear, overt clinical symptoms. Often, the most common clinical sign associated with SARA is reduced or erratic feed intake. Dairy cows experiencing an episode of SARA will reduce their feed intake in order to reduce the acid load in their rumen. Cows will start eating again when ruminal pH is above 5.6. This results in erratic feed intake that often goes unnoticed in individual cows experiencing SARA, particularly in large dairy herds where cows are housed and fed in groups. Other clinical signs often observed during
SARA may include:
• reduced rumination (cud-chewing)
• mild diarrhoea
• foamy faeces containing gas bubbles
• appearance of undigested foodstuffs ( ¼ inch or 6 mm) in faeces
• Cows swishing their tails in the absence of flies. This is likely to be associated with irritation caused by the production of acidic urine and faeces. Tail swishing leads to rump faecal soiling, a common finding in affected herds;
• Individual cows will be seen to be ‘off their food’ with no other clear presenting signs. The condition usually resolves spontaneously within 24 – 48 hours; this is attributable to a reduction in appetite, accompanied by a tendency to select and consume forage rather than smaller high energy partocles;
• Reduced milk yield )albeit this may not be recognised on farms where the problem is continuously present);
• Increased numbers of cases of digestive disease, including displacement of the abomasums;
• Reduced dry matter intake;
• Excessive weight loss in early lactation. This can occur as cows affected by SARA fail to increase their dry matter intake as a coping strategy for negative energy balance;
• Increased incidence of ketosis.
• Poor reproductive performance. This is a reflection of both reduced conception rates and a reduction in the intensity and duration of oestrous behaviour.
• Environmental mastitis. Levels may be increased due to poor hygiene and a reduction in the cow’s immune function. Negative energy balance occurring secondarily to SARA is recognised as impacting adversely on immune function
In the long term, dairy herds experiencing SARA usually exhibit secondary signs of the disease, usually 3–6 months after an episode of SARA. These secondary signs include episodes of laminitis, weight loss and poor body condition despite adequate energy intake, and unexplained abscesses. Undiagnosed, the secondary health effects of SARA can lead to high herd culling rates. SARA should be investigated as a cause, if the secondary signs are occurring for no apparent reason.
How to Prevent SARA
It is important to make the appropriate adjustments in feeding and management practices to reduce the incidence of SARA. The rapid or abrupt introduction of fresh cows to high concentrate diets is the most common cause of SARA. Changes in ruminal bacterial populations when exposed to higher concentrate rations require about 3 weeks, and it is recommended that concentrate levels be increased at 5 to 7-day intervals during this period to avoid SARA. The adaptation of ruminal papillae when higher concentrate diets are fed takes longer, approximately 4–6 weeks. Close-up dry cows should consume enough carbohydrates in their ration so that changes in the rumen are minimized when the milking cow ration is offered after calving.
Practical measures to avoid SARA include:
• Avoid over-mixing or over-processing of the TMR that reduces particle size and NDF content
• Minimize separation of feed ingredients during TMR mixing and delivery when feeding a TMR, monitor and minimize sorting in the feed bunker
• Avoid "slug feeding" of higher concentrate rations by allowing adequate bunker space or feed provision so as to reduce meal size
• Avoid the sorting of long fibre within the diet when the fibre in a TMR is longer than 10 cm, cows are likely to sort the food and only consume small particles and short fibres, leaving the long fibre alone. Cows which sort food in this manner will be at risk of developing SARA.
• Ensure adequate length of cut for forages and silage (2.5 to 10 cm)
• A properly defined dry cow transition period of three to four weeks pre-calving to three to four weeks post-calving.
• Post calving diets no more than 10% greater than the transition pre-calving diet.
Nutrition
Excessive feeding of starches and sugars
Excessive feeding of starches and sugars is a common problem, especially soon after calving. Maize silage is a rich source of starches and sugars and this property, together with its lack of effective fibre, means that it is frequently implicated as a factor in the development of SARA. A common scenario is for a farmer and his advisors to counter poor yields or an excessive loss of body condition score during early lactation by feeding additional concentrates in order to supply additional energy. However, often the problem is one of SARA, and feeding additional energy actually makes the situation worse although a temporary increase in milk yield may be observed, probably as a result of small intestinal carbohydrate digestion.