The importance of Fibre when feeding Angora goats
By Dr Mackie Hobson BSc(Agric),BVSc

1. Diseases

The importance of Fibre when feeding Angora goats- Acidosis

Sub-optimal rumen conditions are sometimes seen in Angora goats when supplementary feed is introduced. The overfeeding of carbohydrate in relation to good quality fibre may occur during times of drought, flush feeding, pregnancy and lactation may lead to acidosis. Decreased palatable fibre and periods of hunger can also lead to sub-optimal rumen pH conditions.

What is acidosis?

Acidosis is the ruminal inflammation resulting from the fermentation of an oversupply of a grain/high starch and low fibre diet. The carbohydrate in the rumen rapidly ferments rather than being digested normally. Bacteria in the rumen produce lactic acid, resulting in acidosis, ruminitis, slowing of the gut, dehydration, subsequent laminitis and often death. Subclinical acidosis is also often associated with stress and stress related periods such as early postpartum and weaning.

A brief explanation of acidosis   

Excess carbohydrate leads to an increase in Volatile Fatty Acids (VFA) and lactic acid production so results in reduced rumen pH (acidic).

The lowered Rumen pH leads to:

1. A change in the rumen micro flora.

• As the pH of the rumen drops the Gram –ve bacteria and protozoa die off and Gram + bacteria start taking over (Streptococcus and lactobaccilus). Thiamine deficiency (Vit B1) can occur as a result.

2. Rumen stasis.

• As the pH drops the rumen contractions decline due to central inhibition through lowered blood pH and absorption of endotoxins suppressing the gastric centre.
• A decrease in motility results in a decrease in rumination and less production of saliva. Saliva contains high concentrations of bicarbonate ions and is an important buffering mechanism for the rumen.

3. Formation of toxic breakdown products.

• Dead Gram –ve bacteria form endotoxin results in endotoxaemia

4. Change in rumen epithelium.

• Chemical irritation of the rumen wall and degeneration of papillae result leading to increased toxin and bacterial penetration and abomasal ulceration.

Excess protein in the diet leads to decreased VFA (Volatile fatty acids) and increased ammonia leading to an alkalosis which does NOT cause acidosis.

Clinical signs of acidosis:

Indirect indicators of ruminal acidosis in goats include

• Chewing time: goats with sub-clinical acidosis tend to stop chewing their cud.
• Appetite is reduced
• Faecal changes: Affected goats pass faeces of a lighter colour which may have an acidic smell and diarrhoea may occur
• Laminitis/lameness: Laminitis is seen in sub-clinical cases, with goats being reluctant to move and have a tender gait.
• Lactating ewes fed a diet comprised mainly of cereal grain and affected with sub-clinical acidosis will produce lower milk production
• Young goats will have a reduced daily weight gain
• Depressed appearance
• Lying down
• Dehydration and thirst
• Bloating (of the left side of the abdomen)
•  

Treatment of Acidosis

On-farm treatments include

• Dosing a mixture of vegetable oil and activated charcoal.
• Dosing milk of magnesia (ant-acid) OR magnesium oxide 15-40g per goat OR
• Calcium carbonate (Bicarb) 30-60g per goat
• Injecting with long-acting antibiotic (penicillin) and thiamine (B1).
• Stomach tubing ‘Rumex’ or ‘Protexin’ to re-establish bacterial flora (or ideally the rumen content of a healthy slaughtered goat)
• Anti-inflammatory injection for pain
• Feed Lucern Hay (long stem hay)

Following acidosis, the rumen lining may take up to six weeks to repair, so recovering goats will show poor growth rates during this time.

Some animals may develop secondary infections, including abscesses in the liver and other organs. These animals tend to become long-term poor doers.

Preventing acidosis

• Gradually introducing animals to grain or pellets
• During the introduction phase, feed pellets or grain daily. Increase rations proportion every 5 days over at least 15 days. Maximum 50g per head until a target amount is fed.
• Ensure goats always have access to roughage when feeding concentrate. At least 20% -30% of ration. The average daily weight gain will increase when given access to fibre.
• Monitor your flock for signs of severe acidosis: scouring, depression, lethargy and lameness, which will indicate that the amount of grain being fed is being increased too fast.
• If kids are to be fed concentrates after weaning start feeding ewes about 50g on 4 separate occasions over 2 weeks before weaning.
• In feedlot conditions rumen modifiers can be added to feed. Lasalocid acid (improve weight gain and coccidiosis) Include lasalocid acid at 1mg/kg body weight to feed.
• Check pulpy kidney vaccinations are up to date and vaccinate if necessary before feeding.
• Attempt to keep feeds in rough form rather than milling/grinding/pelleting (although increases wastage) as it leads to increased saliva production.

The role of Saliva and Fibre in maintaining a normal rumen pH.

Rumen bacteria operate at an ideal pH of between 6.2-6.8. A rumen pH outside these parameters results in an inefficient digestive system with secondary problems.

• A high fibre diet results in increased rumination (40-50 minutes/kg Dry Matter) which leads to increased saliva production 12-14L/kg DM which results in low VFA and pH of 6.0-6.8.(Ruminant).
• Saliva production, associated with chewing time, may also be an important physical measurement for effective fibre. At least 50% of ruminants should be chewing when evaluating a flock.
• Saliva acts to buffer acids produced during ruminal fermentation of feeds, thereby promoting fibre digestion. Eating and ruminating stimulate the flow of saliva, although some flow continues constantly.
• Saliva secretion is estimated to be 1.5 to two times higher during chewing compared with resting (Cassida and Stokes 1986).
• The rate of eating is important in determining the buffering of the feed-saliva mixture (Van Soest 1994). High concentrate and pelleted forage diets are characterised by less net saliva flow than diets higher in roughage (Van Soest 1994). Beauchemin et al. (1989) estimated that total saliva production for cows increased by 7 litres per day when silage diets were supplemented with hay producing one hour’s increased chewing time.l
• Chewing time is particularly important in the prevention of ruminal acidosis. This action stimulates the flow of saliva and buffers the rumen in a pH range between 6 and 7. Chewing time is increased when long-stem forages are fed and reduced when particle size is decreased, either by reducing forage particle size (Krause et al. 2002)
• The chop length of the lucerne hay will further influence ruminal pH of the ruminant, with short milled hay reducing chewing and rumination time and, therefore, saliva production (Sudweeks et al. 1975; Grant et al. 1990; Grant et al. 1990; de Boever et al. 1993).

It is interesting to note that a cow produces up to 180 litres of saliva per day. Buffering capacity is normally influenced by factors altering the amount or quality of saliva production. The average pH of saliva is about 8.0 (Counotte et al. 1979). When the rumen pH is less than 6.0, the loss of water from the rumen and decrease in bicarbonate concentration and therefore buffer capacity poses a potential threat to the animal. Below pH 5.5, lactate-fermenting bacteria are unable to grow, partly because of their need for bicarbonate, which is not present in these conditions, allowing lactic acid to build up in the rumen, further depressing pH.

The role of fibre length, particle size and heat treated pellets on rumen function.

• Particle size is negatively correlated with chewing activity per kilogram of DM (Allen 1997; Mertens 1997) and positively with ruminal pH (Allen 1997). For practical purposes, greater than 25% of the forage component of the diet should contain forage with a length comparable with the muzzle width of the animal grazing.
• The processing of grain decreases ruminal pH (Krause et al. 2002). This response reflects less saliva production and more rapid breakdown of carbohydrates in the rumen.
• Heat treated concentrate (pellets) also leads to lower rumen pH.

The role of maintaining an optimal rumen pH when feeding additional concentrate must be kept in mind and the importance of good quality long stem fibre (hay) fed alongside the concentrate is critical.

Dr Mackie Hobson

Reference:

Ruminal Acidosis – understandings, prevention and treatment

A review for veterinarians and nutritional professionals June 2007