ALONGSIDE agriculture, the livestock sector is considered a major part of the economy of Zimbabwe and an important part of food security for the nation. 

As we enter the New Year 2024, climate change still presents both direct and indirect challenges for livestock production and health. With more frequent extreme weather events, including increased temperatures, livestock health is greatly affected by resulting heat stress, metabolic disorder, oxidative stress and immune suppression, resulting in an increased propensity for disease incidence and death. 

The indirect health effects of climate change and rains the country is experiencing relate to the multiplication and distribution of parasites, reproduction of virulence, and transmission of infectious pathogens and/or their vectors. 

Cattle are particularly vulnerable to changes in weather patterns – that is, changes in rainfall, variability and extremes, temperature (average and extremes), humidity and evaporation. These climactic changes can affect livestock directly and also indirectly through pasture growth, forage crop quantity and quality, as well as spatial and environmental changes in disease and pest distribution. 

The greatest risks for cattle farmers stem from extreme events such as droughts, heat-waves and heavy precipitation, such as currently being experienced in Zimbabwe, as they are less predictable and much more difficult to adapt to than gradual changes. 

Dairy cows are particularly affected by heat waves, which can not only reduce milk production, but can cause illness or death. Furthermore, after days of severe heat stress, the negative effects on milk production and the protein content of the milk can last for several weeks. 

There is also an increased risk of contracting infection from water-borne diseases through direct contact with polluted waters, such as wound infections, dermatitis, conjunctivitis as well as ear, nose and throat infections, though they are not epidemic-prone. 

In Zimbabwe, the rain seasons are synonymous with tick-borne and soil-borne diseases. In the course of duty, I have often attended to several domestic pets and small livestock that succumb to tick-borne diseases during this time. 

The current hot, wet season, which presents the ideal environmental conditions for the breeding of the deadly blood-sucking ticks is the peak period for livestock to contract tick-borne diseases that spread from one animal to another. 

Apart from physical damage, ticks transmit a variety of other debilitating and fatal diseases, chiefly: Theileriosis, babesiosis, anaplasmosis, heartwater, red water and gall sickness which account for 47 percent of cattle deaths recorded annually in Zimbabwe in the last eight years since 2017. 

Other diseases of cattle associated with the rains are: black leg or black quarter leg, lumpy skin disease (LSD); helminths and bloat. 

Cattle become particularly prone to these diseases, especially if there is a shortage of pasture in grazing areas. As the animals feed on very short grass, it forces them to ingest soil and, in the process, take up disease-causing agents and vectors that are found within the soil. Many soil-borne diseases can also come from muddy water sources. Over the years, it has been studied and recorded that the major soil-borne diseases that occur in Zimbabwe are anthrax, black leg and botulism. 

Black leg and black quarter leg are soil-borne acute specific infectious diseases of livestock that cause huge mortalities in cattle. The disease-causing agent is very similar to the one that causes anthrax, usually resulting in death in a very short space of time after contracting the disease. 

Black leg disease peaks at the end of the dry season and beginning of the rain season. The most common clinical sign is swelling in the upper part of the front leg, causing the animal to limp for one-two days before it dies. 

Lumpy skin disease (LSD) is a mosquito-borne disease that causes multiple small lumps all over the body of the animal. The peak period for lumpy skin disease is the middle of the rain summer season in Zimbabwe which coincides with the peak mosquito period. 

Affected animals usually do not feed well and lose weight, becoming the source of infection for other animals in the herd and for animals in surrounding through vaccination. Farmers should vaccinate their herds for lumpy skin as soon as, or before, the onset of the rain season. 

Gall sickness or anaplasmosis is caused by the red-legged tick, naplasma marginale a, and transmitted principally by b. decoloratus. Anaplasma is a very small parasite in the shape of a granule of chromatin with no protoplasm. It is found mainly in cattle, of which four species are recognised — a.marginale, a. centrale, a. ovis, and a. mutans. 

Gall sickness can also be spread among cattle by blood transmission, for example by biting insects, dehorning and injecting the animals with the same needle. 

Ticks can also infect cattle with red water known technically as bovine piroplasmosis or medically as haemoglobinuria and heartwater, a tropical and sub-tropical disease commonly referred to as bushveldt sickness, boschziekte or inapunga in South African native vernacular terms. 

Older animals are more at risk than young animals for gall sickness and red water. European breeds imported and adapted to Zimbabwe tend to be at greater risk from this disease than indigenous and Brahman type breeds. 

Red water (babesiosis) is a tick-borne disease listed with the World Organisation for Animal Health. It can often be transferred between animals when farmers vaccinate multiple animals with the same needle. 

Cattle infected with red water will have red or brown urine (blood in the urine) and a high temperature of between 41°C and 42°C. (The norm is 37°C to 38°C.) The mucosa of the eye is pale. Infected animals will not eat, are listless, and their skin may have an unsmooth appearance. The disease can lead to deaths if animals are not treated in time. Infection of the unborn calf can occur, resulting in abortion or death of the calf shortly after birth. 

Asiatic and African red water are responsible for many cattle deaths in Southern Africa. Although red water cannot be transmitted to humans, infected animals cannot be slaughtered, as the carcass will have been affected. 

Helminths, internal parasites, are also a major challenge to animal health, especially in the rain season as the environmental conditions are conducive for them to multiply. Cattle should be de-wormed at least three times a year in Zimbabwe. This should be carried out just before the onset of the rains — between October and November —, in the middle of the rain season — between January and February — and at the end of the rain season — between April and May. Animals may fail to realise their full potential in weight gain from the abundant grazing available at this time of the year if not properly de-wormed. 

Similarly, bloat in cattle in Zimbabwe can result from improved pastures, due to increased good rains when cattle tend to over-feed after a prolonged diet of dry feed and consume too much in one feeding. Bloat caused by rapid gas formation in the rumen, or first compartment of the stomach, is sometimes fatal unless relieved. 

It is a form of indigestion marked by excessive accumulation of gas in the rumen. Immediately after cattle consume a meal, the digestive process creates gases in the rumen. Most of the gases are eliminated by eructation (belching). Any interruption of this normal gas elimination results in gas accumulation or bloat. 

Trapped gases that are not eructated (belched) may foam or froth in the rumen, further preventing elimination of gases. Froth can be formed by many factors resulting from interactions among the animal, rumen microorganisms, and differences in plant biochemistry. Bloat may also be present with no evident froth or foam, described respectively as frothy (pasture) bloat and non-frothy (dry) bloat. The most common is frothy bloat where gas builds up in a foam or froth above the liquid/semi-liquid fraction of the rumen content and the normal belching is inhibited. 

Preventing bloat is necessary not only to reduce deaths but also to reduce the negative effect of bloat on cattle performance. Prevention of all tick-borne diseases is accomplished by stringent tick control, as well as vaccination. 

Dr Tony M. Monda BSc. DVM. DPV. is conducting veterinary epidemiology, agronomy, food security and agro-economic research in Zimbabwe and Southern Africa. E-mail: tonym. MONDA@gmail.com