Agriculture 0600 | Paper 1 Mock 01 | Theory

(a) The causative agent of East Coast fever is Theileria parva, a protozoan parasite [1].

(b) Transmission of East Coast fever (3 marks):

1. The disease is transmitted by the brown ear tick (Rhipicephalus appendiculatus), which acts as the biological vector [1].
2. When the tick feeds on an infected animal, it ingests blood cells containing Theileria parasites. The parasite undergoes development stages inside the tick [1].
3. When the infected tick subsequently feeds on a healthy animal, it injects the parasite into the animal's bloodstream through its saliva during feeding [1].

(c)(i) Two other signs of East Coast fever besides swollen lymph nodes and fever (any two for [2]):

1. Discharge from the eyes and nose (lacrimation and nasal discharge) [1].
2. Difficulty breathing (dyspnoea) due to fluid accumulation in the lungs [1].

Also acceptable: diarrhoea; loss of appetite; rough coat; anaemia (pale mucous membranes).

(c)(ii) Two preventive measures explained (each for [2], total [4]):

1. Regular acaricide treatment - dip or spray all cattle with an acaricide on a strict schedule (e.g. every 7-14 days during the tick season). This kills ticks on the animals before they can transmit the parasite, breaking the disease cycle. The dip concentration must be maintained correctly to remain effective [2].
2. Quarantine of new stock - isolate newly purchased animals in a separate holding area for at least 21 days before introducing them to the main herd. This observation period allows any incubating disease to become apparent, preventing an infected newcomer from introducing Theileria into a clean herd [2].

Also acceptable: rotational grazing to reduce tick burdens on pasture; vaccination where available (infection-and-treatment immunisation method).

Labelled answer diagram:

(a)(i) The structures labelled in the diagram of the chicken respiratory system:

• P = Trachea (windpipe) - the main airway connecting the larynx to the bronchi [1].
• Q = Bronchus (primary bronchus) - the branch that carries air from the trachea into the lung [1].
• R = Air sac - the thin-walled extension of the respiratory system unique to birds, which stores air and facilitates unidirectional airflow through the lungs [1].

(a)(ii) How Newcastle disease affects the respiratory system (3 marks):

1. The Newcastle disease virus (a paramyxovirus) attacks and inflames the epithelial lining of the trachea and bronchi, causing swelling and excess mucus production [1].
2. Affected birds show gasping, coughing, sneezing and nasal discharge as they struggle to move air through the inflamed, mucus-clogged airways [1].
3. The air sacs may become clouded or thickened, reducing gas exchange efficiency. In severe cases the respiratory damage allows secondary bacterial infections to establish, worsening the condition [1].

(b) How Newcastle disease spreads between birds (3 marks):

1. Direct contact - healthy birds become infected through close contact with sick birds or their respiratory secretions [1].
2. Airborne droplets - coughing and sneezing release virus-laden aerosol droplets that nearby birds inhale [1].
3. Fomites and environment - contaminated feed, water, equipment, litter and droppings carry the virus. Wild birds, rodents and human visitors can also transport the virus between farms on their bodies or clothing [1].

(c)(i) A suitable vaccination programme for Newcastle disease (3 marks):

1. Vaccinate chicks at day-old with a live attenuated vaccine (e.g. Hitchner B1 strain) administered by eye drop or in the drinking water [1].
2. Give a booster vaccination at 3-4 weeks of age to strengthen immunity as maternal antibodies wane [1].
3. Revaccinate layers every 8-12 weeks (or as recommended by the vaccine manufacturer) to maintain protective antibody levels throughout the laying period. Keep written records of vaccination dates and batch numbers [1].

(c)(ii) Three biosecurity measures apart from vaccination (any three for [3]):

1. Restrict access - limit entry to the poultry house to essential workers only and provide disinfectant footbaths at every entrance, so that pathogens are not carried in on shoes or clothing [1].
2. All-in, all-out management - do not mix birds from different sources or age groups. Bringing in birds of uniform age and origin, then cleaning thoroughly between batches, prevents disease cycling between cohorts [1].
3. Prompt carcass disposal - remove and bury or burn dead birds immediately rather than leaving them on the farm, eliminating a major source of virus amplification and environmental contamination [1].

Also acceptable: netting open sides to exclude wild birds; cleaning and disinfecting feeders, drinkers and equipment regularly.

(a)(i) Two types of milking parlour layout [2]:

1. Herringbone parlour - cows stand at an angle to a central pit, allowing the milker to access udders from below. [1]
2. Rotary (carousel) parlour - cows stand on a slowly revolving platform and are milked as it turns. [1]

Other acceptable answers: tandem parlour (cows stand in a line, one behind another) or abreast parlour (cows stand side by side facing the same direction).

(a)(ii) Three hygiene practices during milking [3]:

1. Wash the udder with clean warm water and dry it thoroughly before attaching the milking unit. This removes dirt and bacteria that could contaminate the milk. [1]
2. Dip teats in disinfectant (teat dipping) after milking. Post-milking dipping seals the teat canal while it is still open, preventing bacteria from entering and causing mastitis. [1]
3. Wash all milking equipment with hot water and detergent after each milking session. Milk residues left in pipes and clusters are an ideal breeding ground for bacteria. [1]

Also acceptable: milker wears clean gloves/has clean hands; foremilk is discarded or tested with a strip cup to check for mastitis.

(b) Why the floor should be concrete with a smooth, sloped surface [3]:

• Concrete is durable and non-absorbent, so liquids do not soak in and harbour bacteria. This makes thorough cleaning with water and disinfectant effective. [1]
• A smooth surface prevents injuries to hooves and allows scrubbing equipment to clean every area without trapping dirt in crevices. [1]
• A sloped surface ensures that waste water, urine and spilled milk drain continuously into a collection channel, preventing pooling. Standing water breeds pathogens and makes the floor dangerously slippery. [1]

(c) Waste water and manure management to prevent pollution [3]:

1. Waste water should be channelled through drains to a soak-away pit or settling tank, where solids settle out and liquids are absorbed or treated before they can reach watercourses. [1]
2. Solid manure should be collected and composted. Composting breaks down pathogens and converts the waste into valuable organic fertiliser for crops. [1]
3. Effluent must never be allowed to enter rivers or streams. Nutrient-rich runoff causes eutrophication: excessive algal growth depletes dissolved oxygen, killing aquatic life. [1]

(d) Two reasons a milking parlour is more efficient than hand milking in the field [2]:

1. Speed - a machine milks each cow faster than hand milking, so fewer labour hours are needed and labour costs fall. [1]
2. Cleanliness - milk in a parlour is collected into a closed system, reducing contamination from dust, flies and field debris that would affect open-bucket hand milking. [1]

Also acceptable: milk can be cooled quickly using in-parlour refrigeration; cows can be fed concentrates during milking, improving nutrition management.

(a) Line breeding is a form of selective breeding in which animals that are related, but not as closely as parent-offspring or full siblings, are mated together (e.g. half-siblings, cousins, uncle-niece). [1] The aim is to concentrate the genes of a particular outstanding ancestor in the offspring, increasing the likelihood that the ancestor's desirable traits are inherited homozygously. [1]

(b)(i) How the breeder would carry out line breeding over three generations to increase litter size:

1. Generation 1: Select the sows in the herd that produce the largest litters and mate them with a boar that is a relative of a high-performing sow (e.g. a half-brother or maternal grandson of an outstanding dam), but not a direct parent or full sibling. [1]
2. Generation 2: From the offspring, select the gilts (young females) that produce the largest litters in their first farrowing. Mate them with a boar from the same family line (e.g. a cousin or half-brother from the same outstanding ancestor). [1]
3. Generation 3: Again select the females with the largest litters from this generation and mate them with a male from the same bloodline, continuing to concentrate the genes associated with prolificacy. [1]
4. Throughout all three generations, always select strictly for large litter size and keep the breeding stock within the family line of the original outstanding ancestor, while avoiding the closest matings (parent x offspring or full sibling x sibling). [1]

(b)(ii) One risk of continuing line breeding for too many generations is inbreeding depression. As relatedness accumulates, harmful recessive alleles become homozygous, leading to reduced fertility, smaller litters, lower disease resistance, and poorer overall performance. [1]

(c) Boar D has the best feed conversion ratio at 2.8. [1] A lower feed conversion ratio means the animal converts feed into body mass more efficiently - it needs fewer kilograms of feed to gain one kilogram of body weight. Therefore Boar D is the most feed-efficient, reducing feed costs per kilogram of pork produced. [1]

(d) A farmer might choose to buy hybrid breeding stock from a commercial breeder rather than running an on-farm programme because:

1. Hybrid stock may display hybrid vigour (heterosis), giving faster growth, better feed conversion, and improved reproductive performance compared to purebred animals. [1]
2. Purchasing ready-made hybrids saves the farmer years of time and the specialist expertise required to maintain pedigree records, conduct progeny tests, and manage a multi-generation selection programme. [1]

(e) Two other characteristics a pig farmer might select for:

1. Backfat thickness / lean meat percentage - consumers and processors prefer leaner carcasses, so selecting for low backfat increases the market value of each pig. [1]
2. Growth rate / daily weight gain - faster-growing pigs reach slaughter weight sooner, reducing the total feed cost per animal and increasing throughput. [1]

(f) One way selective breeding differs from natural selection:

In selective breeding, humans deliberately choose which animals are allowed to reproduce, based on traits the farmer considers economically desirable (such as litter size or growth rate). [1] In natural selection, the environment determines which animals survive and reproduce. Traits that aid survival and reproduction in that environment are favoured, regardless of whether they are useful to humans. Selective breeding is therefore directed towards human goals, while natural selection is driven by environmental fitness. [1]

(a)(i) The average gestation period of a sow is approximately 114 days, often remembered as "3 months, 3 weeks, and 3 days". [1]

(a)(ii) Calculating expected piglets over three years:

Farrowings per year = 2

Over 3 years: \( 2 \times 3 = 6 \) farrowings [1]

Total piglets = \( 6 \times 10 = \mathbf{60} \) piglets [1]

(b) Four management practices to ensure high piglet survival in the first week:

1. Provide a warm farrowing environment: Install a heat lamp or create a heated creep area for the piglets, as newborn piglets cannot regulate their body temperature effectively and are highly susceptible to hypothermia, which is a leading cause of neonatal death. [1]
2. Supervise farrowing and prevent overlaying: Ensure the sow is monitored during and after farrowing. Farrowing crates or rails can be used to prevent the sow from lying on (crushing) the piglets, which is one of the most common causes of piglet mortality. [1]
3. Ensure early colostrum intake: Make sure all piglets suckle colostrum within the first 6-12 hours of birth. Colostrum provides antibodies for passive immunity, and the piglet's gut can only absorb these immunoglobulins during this narrow window. [1]
4. Clip needle teeth and treat navels: Clip the sharp needle teeth of piglets shortly after birth to prevent injury to the sow's teats and to littermates during competition for teats. Apply iodine to each piglet's navel stump to prevent bacterial infection. Administer iron injections within the first few days to prevent iron-deficiency anaemia, as sow's milk is low in iron. [1]

(c) Pregnancy diagnosis determines whether a sow has conceived after mating. Two methods:

1. Non-return to oestrus: If the sow does not show signs of heat approximately 21 days after mating, she is likely pregnant. The farmer watches for behavioural signs of oestrus (restlessness, standing reflex, swollen vulva). This method is simple and cost-free but not completely reliable, as some sows may have a "silent heat" that goes undetected. [2]
2. Ultrasound scanning: A portable ultrasound scanner is applied to the flank of the sow from about 25-30 days after mating. It detects the presence of fluid-filled embryonic vesicles or foetal heartbeats. This method is more accurate, provides earlier confirmation, and can give an estimate of litter size. [2]

(d)(i) Sow A had the best overall reproductive performance. [1] She produced the highest number of piglets weaned (22 from 24 born alive across two litters), meaning 91.7% of her piglets survived to weaning. This combines both high prolificacy (24 born alive) and excellent mothering ability or management conditions (only 2 pre-weaning deaths). [1]

(d)(ii) Sow C had only 14 piglets weaned from 22 born alive (a loss of 8 piglets, or 36%), which is significantly worse than the other sows. Possible reasons include:

1. The sow may have overlaid (crushed) several piglets, particularly if the farrowing pen lacked adequate crate protection or the sow was restless. [1]
2. Piglets may have died from disease, infection, or insufficient milk supply. If the sow had mastitis or poor teat function, weaker piglets could not compete for milk and starved. Alternatively, a disease outbreak (such as scours) may have killed piglets in the early neonatal period. [1]

Labelled answer diagram:

(a) The three parts to label on the cross-section of the hoe blade (Fig. 2.1):

1. (i) Cutting edge - the thin, sharpened lower edge of the blade that contacts the soil and severs weed roots. [1]
2. (ii) Tang - the narrow metal extension that projects upward from the blade and is inserted into the wooden handle to connect them. [1]
3. (iii) Socket (eye) - the opening or sleeve where the wooden handle fits into and is secured to the hoe head. [1]

(b)(i) Two qualities of wood that make it suitable for tool handles:

1. Strong yet lightweight - wood provides enough strength to withstand the forces of digging and chopping while keeping the overall tool light enough for prolonged use. [1]
2. Shock absorption - wood absorbs vibrations from impact (hitting the ground or rocks), reducing the jarring transmitted to the user's hands and wrists. Metal or plastic handles would transmit far more vibration. [1]

(b)(ii) Fitting a new wooden handle to the hoe head:

1. Select a handle of the correct length and diameter for the socket. Shape the insertion end with a rasp or knife so that it tapers to fit snugly into the socket or eye. [1]
2. Push the handle into the socket and tap it firmly against a hard surface (or use a mallet) to seat it tightly. Then drive a wooden or metal wedge into the top of the handle inside the socket; the wedge forces the wood to expand outward, locking it in place and preventing the head from flying off during use. [1]

(c) Metal handles are uncommon for hand hoes because:

1. Heat conduction - metal absorbs and conducts heat from the sun, making the handle uncomfortably hot in tropical or summer conditions, whereas wood remains cool. [1]
2. Vibration and weight - metal transmits impact shock directly to the hands, causing rapid fatigue and blisters during extended hoeing. Metal handles are also heavier than wood, increasing the effort needed for each stroke. [1]

(a)(i) The part where food is temporarily stored before entering the stomach is the crop. [1] The crop is a thin-walled expandable pouch in the oesophagus that holds swallowed food and softens it with moisture before it moves into the glandular stomach.

(a)(ii) Grit serves as a grinding agent inside the gizzard: it mechanically crushes and breaks down food, compensating for the fact that poultry have no teeth. [1]

(a)(iii) The muscular organ in which grit is used is the gizzard (also called the ventriculus). [1]

(b) Poultry do not need to chew because they lack teeth entirely. [1] Instead, mechanical breakdown of food is accomplished in the gizzard, where thick muscular walls contract rhythmically to grind food against ingested grit particles. [1] This internal grinding replaces the function that teeth and mastication serve in mammals.

(c) Two differences between the chicken and pig digestive systems (paired comparisons): [4]

1. A chicken has a crop for temporary food storage in the oesophagus; a pig does not have a crop and food passes directly to the stomach. [2]
2. A chicken has a gizzard (muscular stomach) that grinds food using grit; a pig has no gizzard and instead relies on teeth for mechanical breakdown and a single stomach for both chemical and some mechanical digestion. [2]

Other valid pairs: the chicken has a proventriculus (glandular stomach) that secretes acid and enzymes before the gizzard, while the pig has a single stomach combining these functions; the chicken has two caeca at the small-large intestine junction, while the pig has one caecum.

(a) Three conditions that make wind erosion more likely [3]:

1. Dry, loose or sandy soil with little organic matter. Organic matter acts as a binding agent between particles; without it, individual grains are easily lifted by wind. [1]
2. Flat, open landscape with no barriers. Wind accelerates across unobstructed terrain, building up enough force to detach and transport soil. [1]
3. Bare soil surface with no crop cover or stubble. Vegetation and residue shield the soil from direct wind contact and reduce wind speed at ground level. [1]

Also acceptable: strong or persistent winds; soil that has been finely cultivated (fine tilth is more vulnerable than cloddy soil).

(b) How a windbreak reduces wind erosion [3]:

1. The row of trees reduces wind speed on the sheltered (leeward) side. Air hitting the windbreak is forced up and over, creating a zone of calmer air downwind. [1]
2. Slower wind has less energy to lift and carry soil particles. The critical threshold wind speed for detaching particles is no longer reached in the sheltered zone. [1]
3. The windbreak also traps airborne soil particles that are already in suspension, preventing them from being transported further across the field. [1]

(c)(i) Distance protected by the windbreak [1]:

\[ 10 \times 8 = 80 \text{ m} \] [1]

(c)(ii) Whether the single windbreak adequately protects the entire field [2]:

No, the windbreak protects only 80 m, but the field is 200 m wide. [1] The far side of the field (200 - 80 = 120 m from the windbreak) remains exposed to wind erosion. A second windbreak approximately 80 m from the first, or additional protective measures such as cover crops or mulching, would be needed to protect the entire field. [1]

Labelled answer diagram:

(a)(i) The bacteria found in the root nodules of legumes that convert atmospheric nitrogen into a plant-usable form are Rhizobium. [1]

(a)(ii) The process is called nitrogen fixation (biological nitrogen fixation). [1] Rhizobium bacteria use the enzyme nitrogenase to break the strong triple bond in atmospheric nitrogen gas (\(\text{N}_2\)) and convert it into ammonia (\(\text{NH}_3\)), which is then available to the host plant.

(a)(iii) The process by which nitrates in the soil are converted back to atmospheric nitrogen is denitrification. [1] This is carried out by anaerobic bacteria in waterlogged or poorly aerated soils, and it represents a loss of available nitrogen from the soil.

(b) How growing and ploughing in a legume crop benefits the next crop: [3]

1. While growing, the legume fixes atmospheric nitrogen through its Rhizobium bacteria, enriching both the plant tissue and the surrounding soil with nitrogen. [1]
2. When the crop is ploughed in as green manure, the nitrogen-rich plant material decomposes in the soil. [1]
3. During decomposition, nitrogen compounds are released and converted to nitrates by nitrifying bacteria (mineralisation and nitrification), making this nitrogen available for uptake by the roots of the next crop planted in that field. [1]

(c) Two ways nitrogen can be lost from agricultural soils (any two): [2]

1. Leaching: soluble nitrate ions are washed downward through the soil profile by heavy rainfall or excessive irrigation, moving beyond the reach of plant roots. [1]
2. Removal in harvested crops: every crop harvested takes nitrogen incorporated into its proteins and other organic molecules out of the field permanently. [1]

Other acceptable answers: denitrification by anaerobic bacteria in waterlogged soils; erosion of nitrogen-rich topsoil by wind or water; volatilisation of ammonia from surface-applied manure or urea fertiliser.

(a)(i) Bull C should be selected for future breeding because its calves achieved the highest average daily weight gain of 1.35 kg. [1] This demonstrates that Bull C transmits genes for superior growth rate to its offspring, which will translate into heavier animals at market age, higher carcass weights, and greater profitability. [1]

(a)(ii) The type of test being carried out is a progeny test. [1] It evaluates the breeding value of each bull based on the measured performance of its offspring rather than the bull's own characteristics.

(a)(iii) Each bull was mated with a similar but separate group of cows rather than the same cows to ensure the comparison is fair. [1] If all bulls mated the same cows sequentially, differences in the cows' age, condition, or milk production between matings could confound the results. Using similar groups ensures that any differences in calf performance are attributable to the bull's genetics, not the dam's.

(b) Two advantages of using AI instead of keeping the bull on the farm:

1. Semen from a genetically superior bull can be used even if the bull is far away or no longer alive, because frozen semen stored in liquid nitrogen remains viable indefinitely. This gives access to the best genetics regardless of geography. [1]
2. One semen collection can inseminate many cows, spreading the genetic improvement from Bull C across the entire herd much faster than natural mating would allow. It also eliminates the cost of feeding, housing, and managing a live bull on the property. [1]

(c) After several generations of selecting from the same genetic line, the farmer should introduce unrelated genetics because:

1. Continued selection within a closed population causes the animals to become increasingly related (inbred). The effective population size shrinks and homozygosity rises with each generation. [1]
2. Inbreeding can lead to inbreeding depression, manifesting as reduced fertility, weakened immune function, slower growth rates, and higher calf mortality. Hidden deleterious recessive alleles become expressed when both parents carry copies. [1]
3. Introducing an unrelated bull or semen from a different bloodline restores heterozygosity, brings in new alleles, and can reverse the negative effects of inbreeding while maintaining the accumulated genetic gain for growth rate. [1]

(a)(i) The genotypes of the parents are: boar = EE (homozygous dominant) [1]; sow = ee (homozygous recessive). [1] The boar is stated to be homozygous erect-eared, and the sow has floppy ears which can only occur with the genotype ee.

(a)(ii) The genotype of the F1 piglets is Ee (heterozygous). [1] Each F1 piglet inherits one E allele from the EE father and one e allele from the ee mother. All F1 piglets have erect ears because the dominant E allele masks the recessive e.

(a)(iii) Crossing two F1 piglets (Ee x Ee):

Parents: Ee x Ee

Gametes from each parent: E and e

Offspring genotypes: EE, Ee, Ee, ee [1]

Expected genotype ratio: 1 EE : 2 Ee : 1 ee [1]

Expected phenotype ratio: 3 erect ears : 1 floppy ears [1] (EE and Ee both show the dominant erect-ear phenotype; only ee shows floppy ears.) [1]

(b)(i) Calculating the ratio of erect-eared to floppy-eared piglets from the data:

Erect ears = 34, Floppy ears = 14

\[ \text{Ratio} = \frac{34}{14} : \frac{14}{14} = 2.4 : 1 \] [1] for method (dividing both by the smaller number), [1] for arriving at approximately 2.4 : 1.

(b)(ii) The ratio is not exactly 3:1 because fertilisation is a random event, and the sample size (48 piglets) is relatively small. [1] Chance variation means the actual numbers will fluctuate around the expected ratio; a perfect 3:1 would require 36 erect : 12 floppy, but random sampling produced 34:14 instead.

(c) Heterozygous means having two different alleles for a particular gene - one dominant and one recessive (e.g. Ee). [1] The dominant allele determines the phenotype in a heterozygous individual.

(d) How to use a test cross to determine whether an erect-eared pig is homozygous or heterozygous:

1. Cross (mate) the erect-eared pig with a floppy-eared pig (ee), which is known to be homozygous recessive. [1]
2. If the erect-eared pig is homozygous (EE): all offspring will be Ee, and every piglet will have erect ears. No floppy-eared offspring will appear. [1]
3. If the erect-eared pig is heterozygous (Ee): the expected offspring are Ee and ee in a 1:1 ratio, so approximately half will have erect ears and half will have floppy ears. [1]
4. Therefore, any floppy-eared offspring proves the tested pig is heterozygous (Ee), since a floppy-eared piglet must have inherited a recessive allele from each parent. [1]

Labelled answer diagram:

(a) Definition of sheet erosion [2]:

Sheet erosion is the uniform removal of a thin layer of topsoil over a wide area by shallow overland flow. [1] It is caused by rainwater that flows as a broad, shallow sheet rather than concentrating into defined channels or rills. [1]

(b) Why sheet erosion is more difficult to detect than gully erosion [2]:

1. The soil surface remains relatively smooth with no visible channels or gullies. There is no dramatic physical feature to draw the farmer's attention. [1]
2. The change happens gradually over many seasons. The farmer may not notice the slow thinning of topsoil until the lighter-coloured subsoil becomes visibly exposed or crop yields decline noticeably. [1]

(c) Three ways losing topsoil through sheet erosion reduces crop yields [3]:

1. Organic matter and humus are lost, reducing the soil's natural nutrient supply and its ability to support microbial life that cycles nutrients. [1]
2. Fine clay and silt particles are selectively removed (they are the lightest and first to move), reducing the soil's water-holding capacity. The remaining coarser particles drain too quickly. [1]
3. Soil structure deteriorates, becoming compacted or crusted, which makes root penetration harder and reduces seedling emergence. [1]

Also acceptable: applied fertilisers are washed away before crops absorb them; seed and young seedlings may be displaced or buried by moving soil.

(a)(i) The animal with the longest gestation period is cattle, at 283 days. [1] This is read directly from the table; sheep and goats both have 150 days, and pigs have 114 days.

(a)(ii) The difference in gestation period between cattle and sheep:

\[ 283 - 150 = 133 \text{ days} \]

Cattle gestation = 283 days [1]; sheep gestation = 150 days; difference = 133 days. [1]

(a)(iii) Pigs produce larger litters than cattle because:

1. Pigs are polytocous (naturally adapted to produce multiple offspring per pregnancy), whereas cattle are monotocous (typically producing a single calf). The pig ovary releases many ova during each oestrous cycle, so multiple embryos implant and develop simultaneously. [1]
2. This is an evolutionary and selective breeding adaptation: larger litters compensate for the pig's shorter gestation period and allow rapid population growth, which is advantageous for commercial meat production where high output per sow is the economic goal. [1]

(b) A farmer should keep accurate breeding records for the following reasons:

1. To predict expected dates of parturition (calving, lambing, farrowing), so that the farmer can prepare housing, equipment, and veterinary support in advance. [1]
2. To monitor fertility by identifying animals that repeatedly fail to conceive or have long calving intervals, allowing the farmer to cull poor performers and improve overall herd reproductive efficiency. [1]
3. To track parentage for selective breeding purposes and to avoid inbreeding, which can lead to reduced vigour, lower productivity, and increased susceptibility to disease (inbreeding depression). [1]

(a) Green manuring is the practice of growing a crop (usually a legume) specifically for the purpose of ploughing it back into the soil while the plants are still green and actively growing, [1] in order to add organic matter and nutrients to the soil and improve its fertility. [1]

(b)(i) Two benefits the cowpea crop provides to the soil before it is ploughed in (any two): [2]

1. The cowpea roots bear nodules containing Rhizobium bacteria that fix atmospheric nitrogen, adding nitrogen to the soil even before the crop is ploughed in. [1]
2. The plant canopy covers the soil surface, reducing erosion from rain splash and wind, and suppressing weeds by shading them out and competing for light and space. [1]

(b)(ii) Why ploughing in at the flowering stage is more beneficial than waiting until seed maturity: [2]

1. At the flowering stage, the plant tissue has its highest nitrogen content and is soft and succulent, so it decomposes rapidly once ploughed in. [1]
2. After seed maturity, the stems become woody and lignified, with a high carbon-to-nitrogen (C:N) ratio. Material with a high C:N ratio decomposes slowly, and decomposing bacteria actually draw nitrogen from the surrounding soil to break down the carbon, temporarily reducing the nitrogen available to the next crop (nitrogen immobilisation). [1]

(c) Two other methods of adding organic matter to the soil, apart from green manuring (any two): [2]

1. Applying animal manure (farmyard manure / cattle or poultry manure). [1]
2. Adding compost made from decomposed crop residues and organic waste. [1]

Other acceptable answers: mulching with crop residues; applying biosolids / sewage sludge.