Dr Shadreck Magonziwa (BVSc, BBA, MCom)
Ticks cause significant economic losses in cattle production. Reduced productivity is due to irritation and loss of condition impacting on fertility, the loss of blood in severe infestation can sometimes lead to death, reduced body weight gains, reduced milk yield in dairy cattle and in addition can create sites for secondary bacterial infection that can often lead to mastitis.
Blackleg – Blackleg is disease of young cattle caused by the bacteria called Clostridium which reproduce in form of spores, making it highly resistant to weather elements in the soil. Feet, legs and the tongue are often the affected areas, hence the name of the disease. Usually lameness (limping or unwillingness to move), loss of appetite, rapid breathing and a fever are the signs seen with the disease. There is often a crepitation when the skin over the affected leg when pressed with hands as the bacteria produces gas. In most cases the animal is found dead without being previously observed sick.Most losses due to blackleg occur when the cattle are between the ages of 6 months and 2 years, although it can occur when they are as young as 2 months. Many blackleg cases occur during the hot and humid summer months or after a sudden cold period, but cases can occur at any time during the year.The use of a clostridial vaccine is the most common and cost-effective preventative measure taken against blackleg. It is often in a combination with Anthrax and botulism vaccines. Burning the upper layer of soil to eradicate spores is the best way to stop the spread of blackleg from diseased cattle although burning should be cleared by the Environmental Management Agency (EMA) official. This should also be in line with the veld management plan. Diseased cattle should be isolated so that they can be tended to separately. Treatment is generally not effective due to the rapid progression of the disease, but penicillin is the drug of choice for treatment and should be prescribed by a registered veterinarian. Treatment is only effective in the early stages and as a control measure.
The Blue Tick – The Boophilus (Rhipicephalus Boophilus) tick commonly known as the blue tick. It is the most common and widespread tick in Zimbabwe, especially in these cooler months of the year. The tick has a wide range of hosts; mainly cattle, although the tick can be found in sheep, goats, pigs and sometimes horses. This tick is economically more important in winter as it can survive up to six months in cooler months. In summer, the blue tick can survive for as long as three to four months without feeding. The female ticks lay up to 4400 eggs, therefore the infestation spreads fairly fast. Heavy infestations of Blue tick cause hides to be downgraded and a source of transmission tick-borne diseases namely Red water (Babesiosis) and Gall Sickness (Anaplasmosis). Dipping or spraying livestock with an Acaricides once a week in summer and once a fortnight is winter helps control blue tick infestation. Farmers are urged to keep dipping in winter as most farmers tend to stop when rains end in May and often end up with problems. It is also important to rotate the dipping chemical so as to avoid tick resistance. It is also critical to apply the Acaracide correctly and at the correct concentration for an effective outcome.
Redwater and gall-sickness disease are transmitted by the Blue tick. Gall-sickness is also transmitted by stamoxys or biting/stable fly and horseflies. Gall-sickness is characterized by very hard dung and on post-mortem the rumen is almost solidified with dry matter. In the case of redwater, symptoms are blood-red urine. The drug of choice is a long-acting tetracycline and in the case of gall-sickness, bowel movement must be induced with liquid paraffin or cod-liver oil and brown sugar or molasses. -By Stu Taylor