(a) Give a detailed account of the impact of water, air and soil pollution on animal health and production. (20 marks) (b)…

(a) Impact of water, air and soil pollution on animal health and production (20 marks)

Pollution harms animals through what they drink, breathe and eat, and it also passes residues into milk, meat and eggs, which is a public health problem.

Water pollution: sources are industrial effluent, sewage, runoff of fertilisers and pesticides, mining, and natural contamination.

• Toxic chemicals: heavy metals (lead, cadmium, arsenic, mercury), fluoride (dental and skeletal fluorosis, lameness and reduced production in endemic areas), nitrate and nitrite (methaemoglobinaemia, abortion), pesticides, and high salinity.
• Biological: pathogens (Leptospira, Salmonella, Cryptosporidium, parasites) and cyanobacterial blooms in eutrophic ponds, whose toxins can kill animals within hours.
• Effects: reduced water and feed intake, growth, milk and egg yield and fertility, and acute or chronic poisoning; also loss of fish production.

Air pollution: sources are gases and dust from intensive housing (ammonia, hydrogen sulphide, carbon dioxide, methane, dust), fumes from industry, smelters and brick kilns (sulphur dioxide, fluoride, particulates, lead), smoke and vehicle emissions, and greenhouse gases.

• Effects: irritation and damage to eyes and respiratory tract (bronchitis, pneumonia, keratoconjunctivitis in poultry), reduced immunity, growth and egg production, carbon monoxide or hydrogen sulphide poisoning in closed sheds, and fluorosis near industrial sources, through contaminated pasture. Heat and climate change add heat stress, which lowers milk yield, fertility and immunity.

Soil pollution: sources are industrial and mining waste, sewage sludge, pesticides, fertilisers, plastics and radionuclides.

• Animals are exposed through grazing (they also ingest soil) and contaminated fodder; the toxins pass into milk, meat and eggs.
• Effects: heavy metal poisoning (lead near batteries, cadmium, arsenic), pesticide residues, mineral imbalance such as molybdenum-induced copper deficiency or selenium toxicity, persistence of spores (anthrax) and parasites, and ingestion of plastic causing rumen impaction. Residues of veterinary drugs (diclofenac) in carcasses caused the crash of vulture populations in India.

Prevention: treatment of effluent and waste, enforcement of the Water (1974), Air (1981) and Environment Protection (1986) Acts, monitoring of water, fodder and milk, good ventilation and litter management, safe fodder cultivation, and prompt diagnosis of poisoning.

(b) Conditions causing dehydration in animals; pathogenesis, clinical symptoms and treatment (15 marks)

Dehydration is a deficit of body water, with or without loss of electrolytes.

Conditions (causes):

• Reduced intake: water not available or frozen, and inappetence, painful mouth or throat, and illness in neonates that will not suckle.
• Excess loss: diarrhoea (the commonest cause, especially in calves, lambs and piglets), vomiting, polyuria (kidney disease, diabetes), sweating, panting and heat stress, fever, burns, haemorrhage, and sequestration of fluid in the gut (obstruction, rumen acidosis, peritonitis).

Pathogenesis: water loss exceeds intake, so extracellular and then intracellular fluid volumes fall. The plasma volume drops (hypovolaemia), with haemoconcentration, so venous return and cardiac output fall, tissues are poorly perfused and become hypoxic, and metabolic (lactic) acidosis results. The body responds with thirst, antidiuretic hormone, and the renin-angiotensin-aldosterone system, which retain water and sodium. Severe cases proceed to renal failure, shock and death.

Clinical symptoms: delayed return of a skin fold (skin tenting), sunken eyes, dry, tacky mucous membranes, prolonged capillary refill, weak rapid pulse, cold extremities, depression, weakness, and little urine. Severity by percentage body weight: 5 to 6% mild, 8 to 10% moderate (recumbent calves), and above 10 to 12% severe, near death.

Treatment: correct the cause (antibiotics, antidiarrhoeals) and replace fluid.

• Mild to moderate, with a suckle reflex: oral rehydration solution (glucose, glycine, sodium, potassium and alkalinising agents such as acetate) in frequent feedings.
• Severe or unable to drink: intravenous isotonic fluids (0.9% saline, Ringer's lactate, with dextrose and sodium bicarbonate for acidosis), and hypertonic saline (7%) in small volumes with oral water in emergencies.
• Volume: deficit (% dehydration × body weight in kg = litres) plus maintenance (about 40 to 60 ml/kg/day) plus continuing losses, given over 12 to 24 hours, with monitoring of hydration and urine output.

(c) Chemoprophylaxis for controlling bacterial, parasitic and vector-borne diseases in animals, with advantages and limitations (15 marks)

Chemoprophylaxis is the use of chemicals or drugs in healthy animals, or in animals at risk, to prevent infection or disease, or to limit spread.

Bacterial diseases: metaphylactic antibiotics (oxytetracycline, tulathromycin) to groups arriving at feedlots at risk of respiratory disease; dry cow therapy against mastitis; antibiotic cover for surgery; and post-exposure treatment in some diseases.

Parasitic diseases: strategic deworming (albendazole, ivermectin) timed to the pasture cycle; anticoccidials (amprolium, toltrazuril, monensin) in poultry and young stock; prophylaxis of babesiosis (imidocarb) and theileriosis (buparvaquone); and trypanocide (isometamidium) protection.

Vector-borne diseases: acaricide dipping and spraying (deltamethrin, cypermethrin, amitraz), ear tags and pour-ons against ticks, flies and lice, which lower the transmission of babesiosis, theileriosis, anaplasmosis and trypanosomosis, and monthly ivermectin or milbemycin to prevent canine heartworm.

Advantages: lower morbidity, mortality and losses at times of high risk (transport, weaning, seasonal outbreaks); useful when no vaccine exists (parasites); fast, cheap protection; better productivity, welfare and lower treatment costs.

Limitations: antimicrobial and anthelmintic resistance, and acaricide resistance; residues in milk, meat and eggs (withdrawal periods must be obeyed); toxicity and environmental effects (ivermectin on dung fauna); protection is temporary, so repeated dosing is needed; cost and compliance; it may mask infection; and it is not a substitute for vaccination, hygiene and biosecurity. Use should follow veterinary advice, with limits on antimicrobials as growth promoters.