Farmers who rear animals for meat try to obtain as much growth as possible from the food the animals are given, because feed is expensive and much of its en...
Question 1 Report
Farmers who rear animals for meat try to obtain as much growth as possible from the food the animals are given, because feed is expensive and much of its energy is lost rather than turned into body mass. A cattle rancher in Argentina wanted to produce more beef from the same quantity of feed. To do this he kept his cattle in barns so that they moved about less, and he chose the fastest-growing animals to breed from over several generations.
Fig 3.1 is a chart comparing the feed conversion of two different breeds of cattle. A lower value on the chart means that the breed turns its feed into growth more efficiently. Using the chart and your understanding of energy transfer and selective breeding, answer questions about which breed uses its feed better, comparing values taken from the chart, explaining why keeping the cattle in barns increases growth, describing how the fastest-growing animals can be bred together, and considering the concerns raised by this way of keeping animals.
Fig. 3.1
Answer Details
(a) Which breed uses its feed more efficiently [2]: Breed Y [1]; it needs less feed, only 6 kg of feed per kg of gain (a lower value means more efficient conversion) [1].
(b) Difference between the two breeds [1]: \(8-6=2\text{ kg}\) of feed per kg of gain [1].
(c) Why keeping the cattle in barns increases growth [3]: keeping them in barns reduces their movement / activity [1]; so less energy is used in respiration / movement / keeping warm [1]; therefore more of the energy from the food is available for growth / gain in body mass [1].
(d) How the fastest-growing animals are bred together [4]:
- Select the fastest-growing animals as the parents [1].
- Breed these selected animals together [1].
- Select the fastest-growing offspring from the next generation [1].
- Repeat over many generations so the desired characteristic increases in the herd [1].
(e) Two concerns about this way of keeping animals [2]: any two: keeping animals indoors with restricted movement raises animal-welfare concerns [1]; the build-up of waste / methane, or the faster spread of disease in the crowded conditions [1].
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