Question

Dairy cattle reach puberty when the bodyweight is what percentage of the bodyweight of the adult?

• A. 60-70%
• B. 50-60%
• C. 30-40%
• D. 20-30%

Hint:

Bovine Growth Benchmarks:
Puberty = 50%--60% of adult body weight.
First Service Breeding = 60%--65% of adult body weight.
First Calving = 80%--85% of adult body weight.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Bovine growth and reproductive maturity: the onset of puberty (first ovulatory estrus) is triggered by metabolic body size thresholds reaching 50--60% of mature adult body weight.
Key Formula or Approach:
\[ \text{Body Weight at Puberty} = 50\% - 60\% \text{ of Mature Adult Body Weight (Breeding Weight } \approx 60-65\%) \]

Step 2: Detailed Explanation:
In bovine reproductive growth physiology:
- The onset of puberty (activation of pulsatile hypothalamic GnRH release and first ovulatory estrous cycle) in dairy heifers is governed primarily by physiological body weight and adipose accumulation (leptin signaling) rather than chronological age.
- Dairy heifers consistently reach Puberty when they achieve 50% to 60% of their expected mature adult body weight (e.g., $220 - 260\text{ kg}$ in zebu/crossbreds with mature weight of $450\text{ kg}$).
- Heifers are subsequently bred at first breeding size ($60 - 65\%$ of adult weight).

Step 3: Final Answer:
Hence, dairy cattle reach puberty at 50-60% of adult bodyweight, matching option (B).