**Core Concept**
The question is testing the understanding of nutritional deficiencies associated with goat's milk ingestion, focusing on the lack of a specific nutrient. Goat's milk is known for its nutritional profile, which differs slightly from cow's milk, particularly in terms of certain vitamin and mineral content.

**Why the Correct Answer is Right**
Given the common association of goat's milk with a particular nutritional deficiency, it's essential to recognize that goat's milk contains less **folic acid** (or folate) compared to cow's milk. Folic acid is crucial for various bodily functions, including DNA synthesis and repair, and its deficiency can lead to several health issues, most notably megaloblastic anemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while goat's milk may have different concentrations of various nutrients, the specific deficiency commonly associated with its consumption is not typically related to the options provided, assuming a common nutritional deficiency.
**Option B:** Similarly, this option does not directly relate to the well-known nutritional deficiency associated with goat's milk ingestion.
**Option C:** This option is also incorrect as it does not correspond to the specific deficiency commonly linked with the consumption of goat's milk.

**Clinical Pearl / High-Yield Fact**
A critical point to remember is that **folic acid deficiency** can be particularly problematic in pregnant women, as it increases the risk of neural tube defects in the developing fetus. Thus, understanding the dietary sources of folic acid and the potential for deficiency with certain types of milk consumption is vital.

**Correct Answer:** D. Folic acid.