3 A farmer keeps a flock of 200 laying hens on a free-range system. The hens have access to pasture during the day and are housed at night. (a) Name the cla...

(a) Class of food nutrient most important for egg production [1]

Protein. [1] Egg white (albumen) is almost entirely protein, and the yolk also contains significant protein alongside fats. A laying hen requires around 16-18% crude protein in her diet to sustain peak egg production.

(b) Two other nutrients required by laying hens [2]

Any two of:

1. Calcium / minerals - essential for forming strong eggshells (each egg shell contains about 2 g of calcium). [1]
2. Vitamins - vitamin A for egg quality and resistance to disease; vitamin D for calcium absorption. [1]
3. Carbohydrates / energy - the hen needs energy for body maintenance and the metabolic cost of producing an egg daily.
4. Water - an egg is about 65% water; hens drink roughly twice the mass of feed they consume.
5. Fats / lipids - a concentrated energy source and needed for yolk formation.

(c) One reason laying hens require calcium [1]

Calcium is needed for the formation of eggshell. [1] The shell is composed mainly of calcium carbonate, and a hen deposits a new shell in the shell gland (uterus) every 20-21 hours. Without sufficient dietary calcium, shells become thin, soft, or absent.

(d) Three possible nutritional reasons for decreased egg production [3]

Any three of:

1. The feed may lack sufficient protein or essential amino acids (especially methionine and lysine), limiting the hen's ability to form egg white and yolk. [1]
2. The feed may be deficient in calcium or other minerals, leading to thin-shelled or shell-less eggs that the hen stops producing. [1]
3. The hens may not be receiving enough total feed (insufficient quantity), so overall nutrient intake falls below the threshold for production. [1]
4. The feed may lack vitamins (particularly A, D, or E), impairing reproductive function.
5. The water supply may be inadequate - dehydration quickly suppresses egg output.
6. The energy content of the feed may be too low for the hens to meet both maintenance and production needs.

(e) Advantage of allowing hens to range on pasture [2]

1. Pasture provides additional nutrients - green plants supply vitamins (A, K, riboflavin), minerals, and insects provide supplementary protein - that complement the formulated ration. [1]
2. This reduces feed costs because the hens obtain part of their nutritional requirement from foraging, so less purchased formulated feed is needed per bird. [1]

(f) What is meant by ad libitum feeding [1]

Ad libitum means the animals have unrestricted, continuous access to feed at all times. [1] Feed is kept constantly available in the trough or hopper so the birds can eat whenever and as much as they choose, rather than receiving set meals at fixed times.