Final answer:
If the farmer selects for cows with higher milk butterfat, it is highly likely that milk protein content will also increase due to the high heritability and strong positive correlation between these traits.
Step-by-step explanation:
If the farmer selects for cows producing more butterfat in their milk, the most likely effect on milk protein content in the next generation, given a heritability of 0.76 for milk protein content and 0.82 for butterfat, with a correlation coefficient of 0.91 between the two traits, would be an increase in the milk protein content. This is because the high correlation indicates that when butterfat increases, protein content tends to increase as well. Furthermore, the high heritability values imply that a significant portion of the variance in these traits is due to genetic differences, meaning selection will be effective.
The term heritability in a narrow sense refers to the proportion of the total variance in a trait that is due to additive genetic variance. Selection on a trait with high heritability is generally more effective, as more of the variation in the trait is due to genetic factors that can be passed on to the next generation. The strong positive correlation between milk protein and butterfat indicates that genetic factors that affect butterfat content are likely to also influence protein content. Therefore, selection for higher butterfat content will most likely lead to an increase in protein content as well.