Table 1 shows a trend of increasing milk yield for cows. Part of the increase in milk production can be attributed to improved nutrition and health protocols for dairy cows.

Table 1. Average milk production per cow (in kilograms per cow per year)
Year Average Annual Milk Production (kg/cow)
1924 2,300
1937 2,300
1950 2,600
1963 3,400
1976 4,800
1989 6,400
2002 8,400
2015 10,000

Based on the information provided, which of the following best describes the source of the rapid increase in milk production from 1976 to 2015?

Question

Table 1 shows a trend of increasing milk yield for cows. Part of the increase in milk production can be attributed to improved nutrition and health protocols for dairy cows.

Table 1. Average milk production per cow (in kilograms per cow per year)
Year	Average Annual Milk Production (kg/cow)
1924	2,300
1937	2,300
1950	2,600
1963	3,400
1976	4,800
1989	6,400
2002	8,400
2015	10,000

Based on the information provided, which of the following best describes the source of the rapid increase in milk production from 1976 to 2015?

BlackTom AI · Accepted Answer

Analyzing the data in Table 1 and the accompanying description, we’re asked to identify the source of the rapid increase in milk production between 1976 and 2015.
Option 1: 'From the 1970s to the early 2000s, dairy cows were not used for beef production.' This statement focuses on beef use and does not address changes in milk yield. It does not explain the substantial rise in milk production, so it misattributes the trend by discussing an aspect (beef cross-use) that is not connected to the mechanism increasing milk yield.
Option 2: 'Starting in the 1970s, farmers increased the selective breeding of cows and bulls for offspring that produced more milk.' This explanation aligns with the known impact of genetic selection and breeding programs aimed at higher milk output. By improving genetics, nutrition would support higher production, and the rate of increase observed (especially post-1976) matches the influence of selective breeding on dairy herd productivity.
Option 3: 'Reproduction rates in cows and bulls increased significantly in the 1970s.' While reproductive rates can affect herd size, the data provided shows milk yield per cow increasing, not just more cows producing milk. Higher reproduction rates would influence total milk production through more cows, but the table discusses average production per cow, so this option does not correctly describe the source of per-cow yield increases.
Option 4: 'Cows were healthier after the 1970s, so they lived longer and produced more milk during their lifetime.' Improved health could extend productive years, but the question points to rapid increases in annual milk production per cow, which is more directly explained by genetic selection and improved management practices that boost yield per lactation rather than simply longer lifespans. This option attributes the rise to longevity rather than per-cow output changes, making it a less precise explanation for the observed pattern.

In summary, option 2 provides the most direct and widely supported mechanism for the rapid rise in milk production per cow during that period, namely genetic gains from selective breeding that increased milk output in offspring. The other options either mischaracterize the data or point to factors less closely tied to per-cow yield increases.

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