(a) Describe the various blood biochemical tests and discuss their importance in health status of animals. (20 marks) (b)…

(a) Blood Biochemical Tests

Blood biochemistry serves as a critical diagnostic window into the physiological status of livestock, reflecting metabolic homeostasis, organ function, and nutritional adequacy. Systematic analysis of serum constituents allows veterinarians to detect subclinical diseases before clinical signs manifest, thereby optimizing herd health and productivity.

Liver Function Tests (LFTs) Hepatic enzymes and pigments are primary indicators of liver integrity. Alanine Transaminase (ALT) and Aspartate Transaminase (AST) are released into the bloodstream upon hepatocellular damage. Elevated ALT is liver-specific in dogs and cats but of little value in ruminants (hepatic ALT activity is low), while AST elevation may also indicate muscle damage. Alkaline Phosphatase (ALP) rises in cholestasis and in growing or diseased bone, but its wide normal range limits its value in cattle; in ruminants and horses gamma-glutamyl transferase (GGT) is the preferred marker of cholestasis, while glutamate dehydrogenase (GLDH) and sorbitol dehydrogenase (SDH) indicate acute hepatocellular damage. Serum bile acids assess overall liver function. Bilirubin levels rise in obstructive jaundice (mainly conjugated bilirubin) or hemolytic anemias (mainly unconjugated bilirubin), indicating impaired excretion or excessive red blood cell breakdown.

Kidney Function Tests (KFTs) Renal health is assessed via Blood Urea Nitrogen (BUN) and Creatinine. BUN is influenced by protein intake and hydration status; elevated levels suggest renal impairment, dehydration, or high-protein diets. Creatinine, being a stable metabolite of muscle mass, is a more specific marker for glomerular filtration rate (GFR) decline. Electrolyte profiles, specifically Sodium (Na+), Potassium (K+), and Chloride (Cl-), are vital for assessing acid-base balance and dehydration. Hypokalemia, for instance, is common in anorexic cattle and abomasal displacement (with hypochloraemic metabolic alkalosis), while hyperkalemia may indicate acute renal failure or urethral obstruction (for example, urolithiasis in male goats and calves).

Metabolic and Protein Profiles Glucose levels reflect energy status; hypoglycemia is a hallmark of ketosis in early lactation dairy cows, confirmed by raised β-hydroxybutyrate (BHBA above about 1.2 mmol/L indicates subclinical ketosis), while non-esterified fatty acids (NEFA) above about 0.4 mmol/L before calving show negative energy balance. Lipid profiles, including cholesterol and triglycerides, help diagnose metabolic disorders like fatty liver syndrome. The Total Protein profile, split into Albumin and Globulin, provides insight into nutritional status and immune response. Albumin, synthesized in the liver, decreases in malnutrition or liver failure. The Albumin:Globulin (A:G) ratio is a sensitive indicator of chronic inflammation or protein-losing enteropathy; a low ratio suggests chronic disease, while a high ratio may indicate low globulin (e.g., failure of passive transfer); in calves, serum IgG below 10 g/L in the first week confirms failure of passive transfer.

Mineral and Metabolic Profile Tests Serum calcium below about 2.0 mmol/L indicates subclinical hypocalcaemia (clinical milk fever is usually below 1.4 mmol/L), magnesium below about 0.8 mmol/L indicates risk of grass tetany, and low inorganic phosphorus is linked to post-parturient haemoglobinuria in buffaloes and to infertility; copper, zinc and selenium reflect trace-mineral status. Creatine kinase (CK) and AST indicate muscle damage (e.g., white muscle disease), and acute-phase proteins such as haptoglobin and fibrinogen indicate inflammation (mastitis, metritis, traumatic reticuloperitonitis). The Compton metabolic profile test (1970) applied these tests to groups of cows at different stages of lactation to detect herd-level nutritional imbalance before production falls.

Importance for health status: blood tests detect subclinical disease, confirm diagnosis and prognosis, monitor treatment, check the adequacy of rations and guide herd feeding, provided results are read against species-, age- and lactation-specific reference ranges and with the clinical picture.

(b) Classification of Antinutritional Factors (ANFs) Antinutritional factors are substances in feeds, produced by the plant's own metabolism, that reduce feed intake, nutrient digestion or utilisation, or cause toxicity. Based on the nutrient they interfere with (Kumar, 1992), they are classified as:

1. Factors affecting protein digestion and utilisation:

• Protease (trypsin) inhibitors in raw soybean and other legumes reduce protein digestion and cause pancreatic hypertrophy;
• Lectins (haemagglutinins) in raw soybean, kidney bean and castor (ricin) bind the gut epithelium and damage villi;
• Tannins (polyphenols) in sorghum, sal seed meal, oak and many tree leaves bind proteins and enzymes; condensed tannins at about 2–4% of dry matter protect protein from rumen breakdown and reduce bloat, but higher levels depress intake and digestibility;
• Saponins in lucerne, soybean and mahua (mowrah) cake reduce palatability and cause haemolysis and frothy bloat.

2. Factors affecting mineral utilisation:

• Phytates in cereal grains, brans and oilseed cakes bind P, Ca, Zn and Fe (mainly a problem in pigs and poultry, since rumen microbes produce phytase);
• Oxalates in Setaria, hybrid Napier, para grass and beet tops bind calcium, causing hypocalcaemia, nutritional secondary hyperparathyroidism ('big head' in horses) and kidney damage;
• Glucosinolates (goitrogens) in rapeseed-mustard cake and brassicas interfere with iodine uptake and cause goitre;
• Gossypol in cottonseed cake binds iron and lysine.

3. Antivitamins:

• Dicoumarol in mouldy sweet clover antagonises vitamin K (haemorrhage);
• Thiaminase in bracken fern and raw fish destroys thiamine;
• Avidin in raw egg white binds biotin;
• Lipoxygenase in raw soybean destroys carotene, the precursor of vitamin A.

4. Miscellaneous toxic factors:

• Cyanogenic glycosides in young or drought-stressed sorghum, linseed and cassava release HCN, which blocks cytochrome oxidase;
• Mimosine in Leucaena (subabul) causes hair loss and goitre (its metabolite DHP is goitrogenic);
• Nitrates in heavily fertilised fodder cause methaemoglobinaemia;
• BOAA (ODAP), the neurotoxin of khesari (Lathyrus sativus), causes lathyrism;
• Phytoestrogens in subterranean clover cause infertility in ewes;
• Mycotoxins such as aflatoxin in mouldy groundnut cake and maize are contaminants rather than true ANFs but act similarly.

ANFs can also be grouped as heat-labile (protease inhibitors, lectins, goitrogens, antivitamins), which cooking, toasting or extrusion destroys, and heat-stable (tannins, saponins, phytates, oxalates, gossypol, mimosine, cyanogens), which need soaking, fermentation, alkali or polyethylene glycol treatment (tannins), added iron salts (gossypol), phytase enzyme, dilution with safe feeds, or rumen bacteria adapted to degrade them (Synergistes jonesii for the DHP of Leucaena).

(c) Diagrammatic Representation of the Kidney The kidney is a bean-shaped organ divided into an outer Cortex and an inner Medulla. The Cortex contains the renal corpuscles (glomerulus and Bowman’s capsule) and the proximal/distal convoluted tubules. The Medulla consists of renal pyramids containing the loops of Henle and collecting ducts. Urine drains from the pyramids into minor calyces, then major calyces, the renal pelvis, and finally the ureter. The diagram shows a multipyramidal kidney with calyces, as in the pig. The bovine kidney is externally lobulated (about 12–25 lobes) and has no renal pelvis, its calyces draining into two major branches of the ureter, whereas the horse, sheep, goat and dog have a unipyramidal kidney whose papillae fuse into a single renal crest projecting into the pelvis.

The functional unit, the Nephron, facilitates urine formation through three processes:

1. Filtration: Blood enters the glomerulus, where plasma is filtered into Bowman’s capsule.
2. Reabsorption: The Proximal Convoluted Tubule (PCT) reabsorbs approximately 65–70% of filtered water and sodium and nearly all filtered glucose. The Loop of Henle creates the medullary concentration gradient. The Distal Convoluted Tubule (DCT) fine-tunes electrolyte balance under hormonal control.
3. Secretion: The DCT and Collecting Duct secrete hydrogen ions and potassium. The Collecting Duct, regulated by Antidiuretic Hormone (ADH), determines the final water reabsorption, concentrating urine to conserve body water. Blood reaches the kidney through the renal artery (dividing into segmental, interlobar, arcuate and interlobular arteries) and leaves through the renal vein; peritubular capillaries and the vasa recta around the loops of Henle carry the reabsorbed water and solutes away. The juxtaglomerular apparatus (the macula densa of the DCT plus renin-secreting JG cells in the afferent arteriole) regulates GFR and blood pressure through the renin–angiotensin–aldosterone system. Juxtamedullary nephrons with long loops of Henle, as drawn below, build the concentrated medulla; desert species such as the camel have especially long loops.