(a) Classify the minerals required by animals and discuss the functions of calcium in animals. (10 marks) (b) Discuss the…

(a) Classification of minerals and functions of calcium (10 marks)

Minerals are classified by the amount needed:

• Macrominerals (more than about 100 mg/kg of diet): calcium, phosphorus, magnesium, sodium, potassium, chlorine and sulphur.
• Microminerals (trace elements): iron, copper, zinc, manganese, cobalt, iodine, selenium, molybdenum and chromium.

Some elements, such as fluorine, lead and arsenic, are toxic at high levels.

Functions of calcium:

• About 99% is in bones and teeth, giving strength and acting as a reserve.
• Blood clotting, nerve impulse transmission and muscle contraction, including the heart.
• Enzyme activation, membrane permeability, and an intracellular messenger role.
• Milk synthesis and eggshell formation.

Blood calcium (about 9 to 11 mg/dl) is regulated by parathyroid hormone, calcitonin and vitamin D. Deficiency causes rickets, osteomalacia, milk fever and thin eggshells; the dietary Ca:P ratio should be about 1.5 to 2:1.

(b) Development of the feed industry in India and activities of CLFMA (10 marks)

Until the 1960s animals were fed mainly on crop residues, grazing and oilseed cakes. The commercial compound feed industry began in the 1960s with dairy cooperative cattle-feed plants (Amul, Kanjari, 1964) and grew with Operation Flood and the poultry expansion of the 1970s and 1980s, then with broiler, layer, pig and aquafeed. It now produces tens of millions of tonnes a year, poultry being the largest user, with a shift to larger mills, additives and BIS quality standards. Problems are raw-material prices and supply (maize, soybean meal, fish meal), adulteration and the lack of a comprehensive feed law.

CLFMA (Compound Livestock Feed Manufacturers Association of India) represents manufacturers. It puts industry views to government on policy, taxes and raw-material supply; promotes quality and safe feed; holds conferences, exhibitions and training; shares market and technical information; and encourages research and good practice.

(c) Role of blood in regulating body temperature (10 marks)

• Heat transport: blood carries heat from muscles, liver and other organs to the skin and respiratory tract, where it is lost. Plasma water has a high specific heat, so it carries much heat with little temperature rise.
• Skin blood flow: in heat, the hypothalamus causes cutaneous vasodilation; skin, ear and limb flow rises, heat is lost by radiation, conduction and convection, and sweat glands are supplied for evaporation. In cold, vasoconstriction conserves heat.
• Arteriovenous anastomoses and countercurrent arteries and veins shunt flow or exchange heat.
• Selective brain cooling: in ruminants the carotid rete cools blood going to the brain with cooler venous blood from the nose.
• Panting and sweating depend on blood supply, and hormones (thyroxine, adrenaline) carried in blood change heat production.

In dehydration, low blood volume reduces heat loss, so the animal is at risk of heat stress.

(d) Maternal nutrition and uterine environment: prenatal versus postnatal development (10 marks)

Prenatal growth depends wholly on the dam. About two-thirds of fetal growth occurs in late gestation, so under-nutrition then lowers birth weight, viability and vigour. Under-nutrition in mid-gestation can reduce muscle-fibre number and organ development, which is not regained later; this fetal programming has lasting effects on growth, carcass and metabolism.

The uterine environment sets the ceiling on fetal size: uterine size and blood flow, placental size and type, litter size (crowding in pigs), maternal age, size and parity, heat stress and disease. Embryo-transfer studies (large-breed embryo in a small-breed dam) show that the dam's uterus, and not only fetal genes, limits fetal size.

After birth, growth depends on the animal's own genes, colostrum, milk, feed, health and management, so it is far more modifiable, and compensatory growth can recover much of an early setback. Prenatal effects are set early and are less reversible.

(e) Effect of extenders and preservation methods on fertilising capacity of sperm (10 marks)

Extenders dilute semen and protect sperm, so their composition affects fertilising capacity.

• Glucose or fructose gives energy; citrate, Tris or phosphate buffers keep pH and osmotic pressure right.
• Egg yolk (lecithin, lipoproteins) or milk protects against cold shock: egg yolk-citrate for chilled cattle semen, Tris-egg yolk-glycerol for frozen semen.
• Cryoprotectants (glycerol 5 to 7%, DMSO) reduce ice-crystal and osmotic damage, but excess is toxic.
• Antibiotics control bacteria, and antioxidants such as vitamin E limit lipid peroxidation.

Preservation: liquid at 15 to 18 °C (boar, poultry; days), chilled at 4 to 5 °C (bull, ram; one to three days), and frozen in liquid nitrogen at −196 °C (bull, in straws; years). Cooling, freezing and thawing injure the membrane, acrosome and mitochondria, so motility and fertility fall, and only about half of the sperm survive freezing; more sperm per dose are therefore used.