Animal and
Veterinary Science Department
AVS 222
(Instructor Dr. Amin Ahmadzadeh)
THE ONSET
OF PUBERTY
Puberty is defined in both the male and female as the
ability to accomplish reproduction successfully (acquiring reproductive
competence).
- Visual signs of sexual receptivity
- May not reflect acquisition of full reproductive
capability
B. Age at
first ovulation
- Acquisition of a proper body size, body composition, and metabolic
status
- It is important from management point of view in farm animals
A. Age at first sexual behavioral
activities
- Mounting and erection
- Not sperm production
B. Age at first ejaculation
- Development of muscles, nerves, accessory glands
C. Age at first ejaculation with
spermatozoa
D. Age when the ejaculate contains enough sperm cells to accomplish fertilization
Species |
Male |
Female |
Bovine |
11
Mo (7-18) |
11
Mo (9-24) |
Ovine |
7
Mo (6-9) |
7
Mo (4-14) |
Porcine |
7
Mo (5-8) |
6
Mo (5-7) |
Equine |
14
Mo (10-24) |
14
Mo (12-19) |
Adapted from Dr. Senger
IV. The Key to Initiation of Puberty
(Figures 6-3 & 6-4)
A. Release of GnRH in high frequency pulses and high
amplitude from hypothalamic neurons
B. High GnRH secretion and thus LH and FSH release for initiation of follicular growth in the female or initiation of spermatogenesis in the male
C. High LH pulses and amplitudes and thus preovulatory LH surges do not occur unless
hypothalamic sensitivity to gonadal estradiol increases
- Before
puberty, females have low ovarian estradiol and low hypothalamic sensitivity to
estradiol, resulting in low frequency GnRH pulses
A) Genetic
and Breeds (see table 6-2)
B) Body Size and Composition
1. Degree of
fatness and body weight (see figure 6-6)
- Body growth, shifts in nutrient
requirements, and energy balance send metabolic signals
2. Metabolic
signals (see figure 6-5 and 6-7)
- Insulin, Glucose, and Fatty acids may influence GnRH neurons activity
C. Environmental factors
1. Season (see figure 6-8)
2. Photoperiod
3. Presence of the opposite sex (see figure 6-9
&6-10)