Major forage diseases
In the past, forage diseases of major economic importance were rare in Kenya. The situation has recently changed with reports of smut and stunting diseases affecting Napier grass, one of the most important forages in the country. Outbreaks of smut were reported by Kungu and Waller in 1992 in an unpublished report and of stunting by Jones et al. (2004).1 The diseases reduce Napier grass yields by almost 100% for the affected stools.
1. Napier grass head smut disease
The disease is caused by a fungus, Ustilago kameruniensis. Affected Napier grass flowers early and the head is characterized by a loose black soot-like powder, which is the disease-causing spores.
Affected Napier grass changes in appearance, the leaves become short and narrow, the internodes short, and the plant appears seriously dwarfed. In a stool, it starts with a few stems that when pulled, uproot easily and appear like a parasitic plant. The roots also appear shortened and dwarfed.
The disease is spread by
- planting diseased Napier grass
- transporting disease-causing spores to clean Napier grass by wind or water or through farm tools
- manure from cattle fed on diseased Napier grass (with the spores)
In Kenya, the occurrence of disease has been reported in
- central Kenya in the districts of Kiambu, Kirinyaga, Maragua, Murang’a, Nyeri, and Thika
- eastern Kenya; Meru Central and Meru South
- the Rift Valley: Londiani and Molo
Control
- Uproot the diseased stems or stools and burn; do not feed to cows.
- Apply enough farmyard manure on the Napier grass to increase the yield, although it does not eradicate the disease.
- Avoid applying manure from cows fed on diseased Napier grass.
- Plant disease-resistant Napier grass cultivars such as Kakamega 1 or Kakamega 2, which are available from the Kenya Agricultural Research Institute.
2. Napier grass stunting disease
Napier grass stunting disease is caused by tiny bacterium-like organisms called Phytoplasma. The affected Napier grass appears pale yellow-green, leaf size is seriously dwarfed and internodes are shortened. There is normally a proliferation of tillers from the affected stool. The affected and stunted clumps will later die.
The disease is spread by planting diseased stems and splits and by leafhoppers and planthoppers. The diseased grass is safe for livestock to eat and the disease cannot be spread through manure.
Occurrence of disease
- Bungoma, Butere, Kakamega and Mumias in western Kenya
- Kiambu and Murang’a in central Kenya
- Uganda, in areas bordering western Kenya
- Ethiopia
Solution
- Inspect Napier grass fields regularly, remove diseased stools and burn them.
- Use clean planting material from clean areas.
- Avoid harvesting the same area frequently before the grass is at the recommended height, as early cutting exposes the stools to sap-sucking planthoppers that transmit the disease.
- In areas that are seriously affected, use alternative fodders such as giant panicum, Guatemala grass and fodder sorghum.
No Napier grass cultivars presently known resist the disease.
Cost and quality of commercial concentrates
Commercial concentrates are key to increased milk production as most pastures and forages are of low quality and cannot meet the nutrient demand of high-yielding cows.
The main limitations in using these concentrates are affordability and quality. The farm gate price of milk, which is dictated by the processors, also determines affordability.
Price is dictated by the availability of raw materials, which in some cases are also used for other purposes, especially human food. When there is competition for the use of raw materials as human food, the price increases. Currently, grain-surplus countries are using grains to produce biofuels, leading to an increase in world prices of cereals and cereal by-products.
The quality of these commercial concentrates is also of major concern to the dairy farmer. Though standards exist in different countries to check on quality they are not always enforced. Currently, several laboratories can analyse these concentrates and advise the farmer accordingly.
Farmers should also note that concentrates are supplements and their effectiveness depends on the quality of the basal ration. If the basal ration is very poor, high levels of concentrates will be required to achieve the desired level of production.
Effect of feed contamination on milk quality
Several factors can affect both milk quality and flavour. Off-flavours in milk have been attributed to feed-related causes (80% of cases), oxidation (5%), rancidity (5%), chemical residues (3%), poor hygiene (3%) and other causes (4%). Some feed-related flavours are not objectionable, while others are usually offensive. Table 9.1 indicates examples of feedstuffs that could cause off-flavour in milk.
Table 9.1. Various feedstuffs and their effect on milk flavour
| Little or no feed flavour at normal feeding levels | Off-flavour if fed within 5 hr of next milking | Common weeds causing off-flavour milk |
| Napier grass | Lucerne (green, hay or silage) | Wild garlic and onions |
| Most grasses and hay | Silage | Wild lettuce and carrot |
| Beet tops and pulp | Turnips, cabbage, kale | |
| Carrots and green peas | Fish meal | |
| Maize, barley and oats | ||
| Soybean and cottonseed | ||
| Safflower and sunflower | ||
| Fish meal, 3–4% of ration |
To reduce feed off-flavours in milk, eliminate mouldy feeds and ensure that feeds likely to impart off-flavours are fed either soon after milking or at least 4 to 5 hours before the next milking time. Objectionable flavours from some feeds pass from the rumen and digestive tract, via blood, into the udder and milk. Controlling intake of feeds that impart off- flavours is not always easy, and the amount of time between feeding and milking varies.
Oxidized flavour is characterized by a metallic or cardboard-carton taste and can be prevented by using stainless steel or glass equipment. Plastic and rubber are acceptable but are hard to keep clean. Prolonged exposure of milk to light may also result in oxidation.
Rancidity is characterized by a bitter, soap-like taste. Maintaining the milk at cool temperature helps reduce the problem. High levels of bacteria in milk, as from cows with mastitis, can aggravate the problem.
Chemical flavours: Milk may acquire a medicinal, sometimes minty, taste from disinfectants and cleaning agents used in disinfecting the milking equipment and milking area. Care should be taken to use the correct amount of disinfectant for the appropriatelength of time. Also, care must be taken to properly clean and rinse equipment and to avoid the chemical agent coming in contact with milking equipment during milking.
General hygiene in the milking area can affect the flavour and quality of the milk. Contamination of milk, hence objectionable flavour, can occur through contact with the udder and from milking equipment. Also, tests have shown that flavours can be transmitted from the environment to the udder within 15 minutes, by way of the cow’s respiratory tract.
Another common cause of undesirable milk flavour is mastitis. This is mainly from the effect mastitis has on increasing the salt and decreasing the sugar content of milk. Sometimes a flat or watery taste occurs, or both salty and watery tastes occur at the same time.