(a) Describe about the copper-molybdenum-sulphur inter-relationship in ruminants. (15 marks) (b) Write in detail about the…

(a) Copper-Molybdenum-Sulphur Inter-Relationship in Ruminants

The three-way dietary antagonism among copper (Cu), molybdenum (Mo), and sulphur (S) represents one of the most critical trace mineral interactions in ruminant nutrition. In the anaerobic environment of the rumen, dietary sulphate and sulphur-containing amino acids are reduced by ruminal microflora into inorganic sulphide (S²⁻). Concurrently, dietary molybdate reacts with sulphide ions in a stepwise manner to form thiomolybdates, progressively yielding mono-, di-, tri-, and tetrathiomolybdate (MoO₄²⁻ → MoS₄²⁻).

These thiomolybdates exert antagonistic effects at two primary levels. Within the rumen, thiomolybdates react directly with ionised copper to form highly stable, insoluble copper thiomolybdate complexes (CuMoS₄), preventing copper absorption across the gut wall. Moreover, simple sulphides also bind free copper directly to precipitate unabsorbable copper sulphide (CuS), and dietary iron adds to the antagonism by forming iron-sulphide complexes that also trap copper. Because these reactions depend on the reduction of sulphur in the rumen, the antagonism is far stronger in ruminants than in monogastric animals. Systemically, absorbed di- and trithiomolybdates enter the bloodstream, binding firmly to plasma albumin and circulating copper, rendering systemic copper biologically unavailable to tissues. Systemic thiomolybdates also displace copper from vital cuproenzymes such as ceruloplasmin, cytochrome c oxidase, and superoxide dismutase, accelerating their degradation and renal excretion.

This interaction leads to secondary (conditioned) hypocuprosis, classically manifested as "teart" disease in cattle grazing high-molybdenum pastures (first described in Somerset, England), characterised by persistent profuse watery scouring with gas bubbles, achromotrichia (loss of hair pigmentation around the eyes causing a "spectacle" appearance), reproductive failure, anaemia, lameness and weak bones. In lambs born to copper-deficient ewes it causes enzootic ataxia (swayback), and in Merino sheep 'steely', crimpless wool; severe copper deficiency in cattle can also cause sudden cardiac death ("falling disease"). The dietary Cu:Mo ratio is best kept between about 6:1 and 10:1; below about 2–3:1, molybdenum-induced copper deficiency (molybdenosis) is likely. The reverse also matters: when molybdenum and sulphur are very low, sheep, which store copper readily in the liver, are prone to chronic copper poisoning, and molybdate or tetrathiomolybdate is used to prevent or treat it. In India, molybdenosis has been reported in cattle and buffaloes on alkaline soils in parts of Punjab, since molybdenum uptake by fodder rises with soil pH. Control relies on area-specific mineral mixtures with extra copper, copper sulphate or slow-release copper boluses, and on avoiding excess sulphate in the ration.

(b) Components of the Circulatory System in Animals

The animal circulatory system is a closed vascular network dedicated to maintaining homeostatic transport of oxygen, nutrients, metabolic wastes, hormones, and immune cells. It comprises the heart, systemic and pulmonary vascular circuits, blood, and the auxiliary lymphatic system.

The mammalian heart is a four-chambered muscular pump enclosed within the pericardium. It consists of two thin-walled atria and two thick-walled ventricles, separated by the atrioventricular valves (tricuspid and bicuspid/mitral) and guarding outlet vessels via semilunar valves (aortic and pulmonary). An intrinsic conduction network—comprising the sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibres—regulates rhythmical contraction. The vasculature functions as a double circulatory system: the pulmonary circulation transports deoxygenated blood from the right ventricle to the lungs for gas exchange, while the systemic circulation distributes oxygenated blood from the left ventricle through the aorta, branching into arteries, high-resistance arterioles, exchange capillaries, and collecting veins. Specialized portal systems (hepatic and hypophyseal) provide direct local vascular connections between capillary beds. Arteries have thick, elastic and muscular walls (tunica intima, media and externa) to withstand pressure; veins have thinner walls, a wider lumen and valves that prevent backflow; capillaries have walls only one endothelial cell thick, allowing exchange with tissue fluid.

Blood comprises plasma (containing albumins, globulins, fibrinogen, and electrolytes) and formed cellular elements: erythrocytes for respiratory gas transport, leukocytes (granulocytes and agranulocytes) for immune defence, and thrombocytes or platelets for haemostasis. The complementary lymphatic system consists of blind-ended lymph capillaries, lymphatic vessels, lymph nodes, and lymphoid organs such as the spleen. It drains excess interstitial fluid, absorbs dietary long-chain fatty acids (chyle), and facilitates systemic immune surveillance.

Comparative anatomical distinctions are prominent across classes: mammalian erythrocytes are non-nucleated and mostly biconcave (camelids have oval, still non-nucleated, cells), whereas avian erythrocytes and thrombocytes are oval and nucleated. Furthermore, birds possess a right aortic arch instead of the mammalian left aortic arch and retain a functional renal portal system. The bovine heart contains an os cordis, a small bone in its fibrous skeleton.

(c) Feeding of Breeding Bulls

Nutritional management of breeding bulls aims at maximizing libido, semen volume, and sperm viability while avoiding excessive fat deposition. Overfeeding leads to adipose accumulation in the neck of the scrotum, impairing testicular thermoregulation and causing elevated testicular temperatures, which induces semen abnormalities and depressed libido. Bulls are best kept in moderate condition, a Body Condition Score (BCS) of about 3.0–3.5 on a 5-point scale: thin bulls lose libido and sperm output, while fat bulls produce poorer semen and develop foot and leg problems.

The ration must provide balanced energy (Total Digestible Nutrients) and protein (Crude Protein at 12–14%). Concentrate mixtures should be balanced with non-leguminous and leguminous green fodders to provide rumen-degradable and undegradable protein without causing over-conditioning. Trace mineral supplementation is indispensable: Zinc (Zn) is required for DNA synthesis, testicular development, and carbonic anhydrase activity; Selenium (Se), as a component of glutathione peroxidase, protects sperm cell membranes from oxidative peroxidative damage. Adequate Vitamin A maintains the integrity of the germinal epithelium of seminiferous tubules, while Vitamin E provides antioxidant protection for the lipid-rich sperm membrane. Gossypol in cottonseed cake impairs spermatogenesis, so it is limited or avoided, and long-term excess calcium from legume-heavy rations predisposes older bulls to bone and spinal problems.

During the non-breeding or off-season, bulls are maintained on high-quality roughage supplemented with a maintenance concentrate allowance (2–2.5 kg/day). During the active breeding or semen collection season, the concentrate allowance is stepped up by 1.0–1.5 kg/day alongside ad libitum digestible green fodder to sustain the higher metabolic and spermatogenic demands.

A practical daily ration for an adult bull of about 500 kg is 25–30 kg of green fodder (including some legume), 5–6 kg of dry fodder, 2–3.5 kg of concentrate, about 50 g of mineral mixture and 30 g of salt, with clean water always available. Young bulls that are still growing need more protein and energy. Daily exercise, such as an hour's walk or a bull exerciser, keeps the feet, legs and libido sound.

(d) Use and Abuse of Antibiotics as Feed Additives in Swine Feeding

Antibiotics in swine feeding have historically been administered at sub-therapeutic concentrations (5–50 ppm) as Antibiotic Growth Promoters (AGPs), distinct from their higher-dose therapeutic use for disease treatment. At sub-therapeutic levels, AGPs improve average daily gain and feed conversion efficiency by thinning the intestinal mucosal lamina propria (enhancing nutrient absorption), sparing essential amino acids and vitamins otherwise consumed by gut flora, and suppressing subclinical micro-infections and microbial toxin generation. In Cromwell's review of US trials, daily gain improved by about 16% in starter pigs but only about 4% in finishing pigs, so the benefit is largest in young, weaned pigs kept in poor hygiene. Agents used included tetracyclines (chlortetracycline, oxytetracycline), bacitracin, tylosin, virginiamycin, carbadox and, formerly, avoparcin.

However, the chronic abuse of sub-therapeutic antibiotics has generated critical public health hazards. Continuous low-dose exposure exerts selective pressure that accelerates the emergence and dissemination of Antimicrobial Resistance (AMR), including livestock-associated methicillin-resistant Staphylococcus aureus (MRSA, clonal complex 398 in pigs) and vancomycin-resistant enterococci (VRE), whose spread in Europe was linked to the glycopeptide growth promoter avoparcin (banned in the EU in 1997). These resistance genes can transfer horizontally via plasmids and transposons to human pathogens. Moreover, antibiotic residues enter human food chains, while swine slurry spreads resistant pathogens and unmetabolised active drugs into soil and groundwater ecosystems.

Recognising these risks, Sweden banned growth promoters in 1986, and the European Union banned all antibiotic growth promoters from January 2006 (and high-dose zinc oxide in piglet feed from June 2022). The US FDA's Guidance #213 ended growth-promotion use of medically important antimicrobials from January 2017. In India, the Food Safety and Standards Authority of India (FSSAI) has established strict Maximum Residue Limits (MRLs) in animal food products, while the Ministry of Health and Family Welfare (July 2019) has banned the use of critical drugs like colistin in food-producing animals and feed supplements, and the National Action Plan on AMR (2017) aims to phase out non-therapeutic antibiotic use in food animals. Sustainable swine production requires replacing AGPs with bio-safe alternatives, including probiotics (Lactobacillus, Saccharomyces), prebiotics (mannan-oligosaccharides), organic acidifiers (formic, propionic, and citric acids to lower gastric pH), and phytogenic plant extracts.