Grass, Rain and Lambs: Resources on a Sheep Farm

Use a grazing trial and five years of farm records to explain how the grass supply affects sheep.

The paddock trial

Read the passage and Table 1, then answer the questions.

How Much Grass Is Enough?

1Nnamdi Eze, a seventh grader, spends most weekends on his aunt Chiamaka's farm in a valley of rolling hills. The farm raises sheep on 40 hectares of pasture and grows hay, a crop of grasses and clover that is cut, dried and stored to feed the flock in winter. Like most farms in the valley, it depends on rain to grow its grass. For his science fair project, Nnamdi used a summer trial and the farm's records to study how the amount of grass affects the sheep.

2For most of the year, fresh grass is the sheep's main food. A pasture grows only a certain amount of grass in a season, and the amount depends mostly on rain and temperature. All the sheep in a field graze from that same supply, and so do any rabbits or deer that wander in.

3For the trial, his aunt split one pasture into four paddocks of 1 hectare each. The paddocks had the same kind of grass, the same slope and the same water trough. In June, she placed young lambs of about the same age and weight in each paddock: 5 lambs in Paddock A, 10 in B, 15 in C and 20 in D. The lambs grazed for 8 weeks (56 days) and ate only the grass in their own paddock, with no extra hay or grain. Nnamdi weighed every lamb at the start and at the end, and he measured the grass height in each paddock every week.

4The farm's records cover five years. The flock always had 120 adult female sheep, called ewes. Each fall the ewes are bred, and their lambs are born the next spring. A ewe can have one lamb or twins. Farmers have long noticed that ewes in good body condition at breeding time are more likely to carry twins. In dry years, the hay field also yields less, so the farm stores fewer bales for winter.

Table 1. Paddock Trial (8 weeks)
Paddock	Lambs per hectare	Grass height at end (cm)	Average gain (g/day)
A	5	12	280
B	10	8	240
C	15	5	170
D	20	3	110

Over the 56 days, about how many more kilograms did an average lamb in Paddock A gain than an average lamb in Paddock D? (1 kg = 1,000 g) kg

Which pattern does Table 1 show?

A. The paddock with the most lambs kept the tallest grass, because the lambs trampled it less.
B. The grass height changed, but each lamb gained about the same amount per day.
C. More lambs per hectare made each lamb grow faster, because the lambs raced to eat.
D. As the number of lambs per hectare rose, the grass left and the daily gain both fell.

Which explanation for the slow growth of the lambs in Paddock D fits the passage and Table 1 best?

A. Twenty lambs shared 1 hectare, so each lamb got less grass to eat.
B. The lambs in Paddock D were younger and lighter at the start.
C. Paddock D had a different kind of grass that lambs digest poorly.
D. Paddock D had a smaller water trough than the other paddocks.

Suppose a fifth 1-hectare paddock held 25 lambs for the same 8 weeks. Based on the pattern in Table 1, which result is most likely?

A. An average gain of about 280 g/day, the same as Paddock A
B. An average gain between 170 and 240 g/day, like Paddocks B and C
C. An average gain above 280 g/day, with grass taller than 12 cm
D. An average gain below 110 g/day, with grass shorter than in Paddock D

Five years of farm records

Use paragraph 4 and Table 2. The lambs in each row were born in the spring after that summer.

Table 2. Farm Records (120 ewes every year)
Year	Summer rain (mm)	Grass grown (kg per ha)	Hay harvest (bales)	Lambs born next spring
2020	260	3,600	900	198
2021	240	3,400	850	192
2022	90	1,500	400	138
2023	230	3,300	820	180
2024	270	3,700	920	204

How many fewer lambs were born in the spring after the 2022 summer than in the spring after the 2021 summer? lambs

Which pattern links the rain, grass and lamb data in Table 2?

A. The number of lambs rose each year, whatever the rain and grass did.
B. Summers with less rain grew more grass, because the grass roots grew deeper.
C. Drier summers grew less grass, and fewer lambs were born the next spring.
D. Rain changed the hay harvest, but the grass grown stayed about the same.

The farm had 120 ewes every year, yet far fewer lambs were born after the 2022 summer. Which explanation fits the passage and the data best?

A. The lambs born in spring 2023 found too little grass, so many were never born.
B. With little grass, many ewes were thin at breeding time, so fewer carried twins.
C. The large hay harvest in 2022 replaced the grass, so the ewes ate less.
D. The drought killed about a third of the ewes before the fall breeding.

How many lambs per ewe were born in the spring after the 2024 summer? lambs per ewe

Complete the chain of causes that the data show for the 2022 drought.

Word bank: rain · grass · lambs · wool · water

Less summer → less for each ewe → thinner ewes at breeding time → fewer born the next spring

10.

Aunt Chiamaka is thinking about keeping 160 ewes instead of 120 on the same 40 hectares. Which prediction do Tables 1 and 2 support best?

A. Each sheep would get less grass, so lambs would likely gain less, mainly in dry years.
B. The ewes would eat less in total, so more grass would be left over.
C. The lambs would grow just as fast, since grass height did not matter in the trial.
D. The extra ewes would make the pasture grow faster, so each sheep would get more grass.

11.

A neighbor says, “Fewer lambs were born in spring 2023 because the summer of 2023 was too dry.” Do you agree? Write a claim, use evidence from Table 2 and paragraph 4, and use Table 1 to explain how the grass supply affects individual sheep.