In mammals that are seasonal brreeders, females are receptive only once in a year. This is called

Options

A. a follicular cycle
B. an estrous cycle
C. a menstrual cycle
D. a luteal cycle

Answer

To solve the question regarding what it is called when females of seasonal breeding mammals are receptive only once a year, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Seasonal Breeders**:
- Seasonal breeders are animals that breed only during specific seasons of the year. This means that their reproductive cycles are closely tied to environmental factors such as temperature and food availability.

2. **Identifying Female Receptivity**:
- In the context of seasonal breeders, female mammals are only receptive to mating during a specific time frame each year. This period is crucial for successful reproduction.

3. **Exploring the Options**:
- The options provided are:
- Follicular cycle
- Estrus cycle
- Menstrual cycle
- Luteal cycle

4. **Analyzing Each Cycle**:
- **Follicular Cycle**: This phase refers to the maturation of follicles in the ovary, primarily seen in the menstrual cycle of primates.
- **Menstrual Cycle**: This cycle occurs in female primates and includes various phases, but it is not specific to seasonal breeders.
- **Luteal Cycle**: This phase follows ovulation and is also part of the menstrual cycle, not specific to seasonal breeding.
- **Estrus Cycle**: This cycle is characterized by a period of receptivity to mating, which occurs only during specific times of the year in seasonal breeders.

5. **Conclusion**:
- Given that the question asks for the term describing the period when females are receptive only once a year in seasonal breeders, the correct answer is the **estrus cycle**.

### Final Answer:
The term for when females of seasonal breeding mammals are receptive only once a year is the **estrus cycle**.

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