Shimala Yadav, Veena Mani, Lamella Ojha, Shahid Hassan Mir, Ravi Prakash Pal and Gaurav Pratap SinghICAR-National Dairy Research Institute, Karnal-132001
Livestock sector plays an important role in Indian economy and is an important sub-sector of Indian Agriculture. Ever increasing population, urbanization, industrialization, climatic change which has threat on sustainability of agricultural field, under those conditions livestock sector plays a great avenue for a source of income to a large chunk of the Indian society. India rank first in cattle population in world containing 190 million numbers of animals (Livestock census, 2012). Nutrition play key role to influencing the performance, health and welfare of the animals. Generally high producing dairy animals are required to be fed on high concentrate diets to meet their nutritional requirements which impose risk for ruminal acidosis or sub-acute ruminal acidosis (SARA). SARA is a common and costly metabolic disease in high yielding dairy cattle which characterised by moderate decrease of ruminal pH from <5.6 for more than 3 h/day due to production of VFA (Plaizier et al., 2008) .
- • Excessive amounts of rapidly fermentable carbohydrates
- • Engorging
- • Rapid diets changes
- • Lack of coarse fiber (peNDF)
- • Feed sorting
- • Errors in delivery of the rations
- Reduced dry matter intake.
- Reduced the fiber digestion (20-25%)
- Reduced absorptive capacity of rumen
- Reduced efficiency of production
- Milk fat syndrome
- Liver abscesses
- Increasing culling rate and death loss
Financial losses result from decreased milk yield, decreased efficiency of milk production, premature culling and increased death loss in lactating animal. Bipin et al., (2016) observed that a reduced in milk production by 3 kg/cow/day, milk-fat production by 3g/kg of milk and milk protein production by 1.2g/kg of milk. This will account to almost 900 L/year/animal and cause a loss of more than Rs. 20,000/- at the present milk prices.
Difficulties with the diagnosis of SARA are caused by lack of specific pathognomonic signs, diurnal fluctuations in rumen fermentation and problems in obtaining representative rumen fluid samples for rumen pH measurement. However some monitoring parameters mentioned below considered likely to become relevant under field conditions.
a. Feeding pattern: Changes in feeding behavior, refuses feed due to a drastic fall in rumen pH and increased osmolality of the rumen fluid and rumination time may be reduced (normally recommend that 40% of all cows should be ruminating at any one time) (Maekawa et al., 2002)
b. Faeces: In SARA cases, the faeces are bright, yellowish, have a sweetsour smell, appear foamy with gas bubbles, and contain more than normal amounts of undigested fiber or grain (Hall, 2002).
c. Rumen fluid parameters: If the pH is ≤5.5 the case should be considered as SARA positive and pH ≥5.8 as negative when ruminal fluid collected by rumenocentesis (Kleen et al., 2009).
d. Milk parameters: The field study on a large dairy farm in New York State found that SARA reduced milk yield by 2.7 kg/day, milk fat production by 0.3% points and milk protein production by 0.12% points (Stone, 1999).
e. Blood parameters: Brown et al., (2000) demonstrated decreased blood pH and bicarbonate as well as base excess (metabolic acidosis) in steers and increased LPS (Lipopolysaccharide) in peripheral blood (Gozho et al., 2007).
f. Urine parameters: Assessment of the renal net acid-base excretion (NABE), determined by urine titration, is claimed to be more accurate than pH determination because acidosis conditions cause excretion of increased amounts of inorganic phosphate into the urine, acting as a buffer.
Practical feeding guidelines to mitigate SARA
The basic principles of preventing SARA in dairy herds including limiting the intake of rapidly fermentable carbohydrates, providing adequate ruminal buffering and allowing for ruminal adaptation to high-grain diet (Krause, 2006)..
1. Limiting the intake of rapidly fermentable carbohydrates: Cows should not receive 3-5 kg of DM from grain in the first week after calving and grain feeding increase by 110-220 g/cow/day until peak grain feeding is reached at 6-8 weeks post calving and net energy of a ration can be safely increased in 10% increments (Radostits et al., 2006).
Physical form of grains is a useful adjunct test when assessing the risk for SARA in a dairy herd that is grains-finely ground, steam-flaked, extruded and very wet will ferment more rapidly and completely in the rumen than unprocessed or dry grains and starch from wheat or barley is more rapidly and completely fermented than starch from corn.
2. Providing adequate ruminal buffering: Coarse, fibrous feeds contain more effective fiber and stimulate more saliva production during eating than do finely ground feeds or fresh pasture and fibre particles must be at least 4 cm in length, should not less than 7% and should not more than 15% tend to stimulate mat formation in rumen.Buffering capacity of the diet depend on DCAD value of feed and fodders, for early lactation cows and mid- lactation cows is approximately +400 and +275 to +400 mEq/kg of DM respectively.Formulating diets with a high DCAD requires the addition of buffers such as sodium bicarbonate or potassium carbonate. Alfalfa forages tend to have a higher DCAD than corn silage and concentrate feeds typically have low or negative DCAD (Radostits et al., 2006).
3.Ruminal adaptation to high-grain diets: Gradually introducing dairy animals to higher grain diets over a period 3 to 5 weeks, this is important for microbial adaptation (particularly the lactate-utilizing bacteria, which grow more slowly than the lactate-producing bacteria) and ruminal papillae length (longer papillae promote greater VFA absorption and thus lower ruminal pH) (Radostits et al., 2006).
Some additional nutritional interventions that might prevent SARA without limiting grain feeding are summarized below.
a. Enhancing ruminal lactate utilizers: Supplementation with specific yeast strains may enhance lactate utilization within the rumen under certain dietary conditions (Krause, 2006).
b.Preconditioning microbes to handle lactate: Adding lactate to the diet or using feed ingredients high in lactate may improve the ability of the rumen to adapt to sudden increases in lactate production (Oetzel et al., 2007).
c. Supplementation with ionophores: Feeding ionophores reduces ruminal lactate production; this effect appears to be caused by inhibition of lactate-producing bacteria, competitive enhancement of lactate utilizers (Oetzel et al., 2007). Monensin is now approved for use in lactating dairy cattle in the US.
SARA is one of the most important metabolic diseases in modern dairy industry that impairs cow performance and health & concern of animal welfare reasons due to laminitis lead to lameness. The economic losses associated with SARA have been estimated at 20,000/cow/year. Shortage of ruminal buffers experienced during SARA can be met by addition of NaHCO3 can increase DMI, milk production and milk fat percentage. Adding Direct-fed-microbes such as Enterococcus faeciumand Saccharomyces cerevisiaewere administered intraruminally, they improve digestion and reduce diurnal ruminal acidity. Dietary supplementation with ionophores which reduced ruminal lactate production by inhibition of lactate-producing bacteria, competitive enhancement of lactate utilizers.The success of a directed effort against SARA depends on cooperation between veterinary and nutritional researchers.
References are available on request.