**Core Concept**
Colostrum is a **nutrient-rich** fluid produced by the mammary glands of female mammals, including humans, immediately after giving birth. It is **highly concentrated** with essential nutrients and antibodies. The primary function of colostrum is to provide newborns with **immunoglobulins** and other vital substances.

**Why the Correct Answer is Right**
Colostrum is indeed **rich in immunoglobulins**, which are crucial for providing newborns with **passive immunity**. This helps protect them from infections during the first few months of life. Additionally, colostrum **contains more protein than milk**, which is vital for the newborn's growth and development.

**Why Each Wrong Option is Incorrect**
**Option A:** Secreted after 11 days of childbirth is incorrect because colostrum is secreted immediately after childbirth.
**Option D:** Contains less fat than milk is incorrect because colostrum actually has a similar fat content to mature milk.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that colostrum is **rich in immunoglobulins**, which is essential for the newborn's immune system.

**Correct Answer:** B. Rich in Immunoglobulin