(PhD in Animal Nutrition & Physiology) Reproductive Physiology By: A. Riasi (PhD in Animal Nutrition & Physiology) http://riasi.iut.ac.ir Advanced Reproductive Physiology (part 1) Isfahan University of Technology, Isfahan, Iran

Puberty and sexual maturity Physiology of gamete production The topics Puberty and sexual maturity Physiology of gamete production Hormonal & non-hormonal secretions of reproductive in male and female animals Physiology of pregnancy and embryo development

Physiology of parturition Pheromones Abnormality of reproduction The topics (continue) Physiology of parturition Pheromones Abnormality of reproduction Reproductive immunology Recent advance associated with reproductive physiology

References Pathways to Pregnancy and Parturition, P.L. Senger, Second edition, 2011. Reproductive in Farm Animals, By: E.S.E. Hafez, 2000. Improving the Reproductive Management of Dairy Cattle Subjected to Artificial Insemination, By: IAEA-TECDOC-1533, 2007. Review and original papers

What is the difference between puberty and sexual maturity? Puberty is time when animal becomes sexually capable of producing fertile gametes and exhibiting adult reproductive behavior. Puberty should not be confused with reproductive maturity (sexual maturity) that point where the animals reached its maximum reproductive potential. In female, usually considered first estrus. In male, appearance of enough sperm in ejaculate to impregnate females. Average age at puberty for different animals Sheep: 5-9 months Pigs : 3-7 months Cattle : 10-20 months Horses: 15-24 months

Definition of puberty in females: Puberty and sexual maturity Definition of puberty in females: Age at first estrus Age at first ovulation Age at which a female can support pregnancy without deleterious effects.

Definition of puberty in males: Puberty and sexual maturity Definition of puberty in males: Age when behavioral traits are expressed. Age at first ejaculation. Age when spermatozoa first appear in the ejaculate. Age when spermatozoa first appear in the urine. Age when the ejaculate contains a threshold number of spermatozoa.

Hypothalamus controls puberty in animals Two centers in hypothalamus: Puberty and sexual maturity Hypothalamus controls puberty in animals Two centers in hypothalamus: Tonic center Surge center It is well defined that hypothalamus plays a very important role in regulation of onset of puberty. The series of hypophysial and gonadal endocrine events that take place during pubertal onset were dependent on the release from hypothalamic negative feedback mechanism. This could be explained by the concept of “gonadostat hypothesis” which states that prior to puberty, the small amount of estrogens produced from the growing follicles inhibits the surge center of hypothalamus.

Puberty Surge Tonic Surge Tonic

Puberty The tonic secretion of LH prior to puberty was not sufficient for the maturation of follicles. However as the puberty was advanced, the increased LH pulses augments the follicular development with a subsequent increase in production of 17β-estradiol. This was associated with a decreased sensitivity of the tonic center of hypothalamus (ventral) due to fall in estrogen receptors with a simultaneous increased sensitivity of the surge center (anterior). This depicts the positive feedback effect of increasing levels of estrogens produced by the growing follicles on the hypothalamus at the pubertal onset. Stimulation of surge center releases LH in a surge fashion triggering follicular maturation. Ovulation can be made in pre-pubertal animals occur by inducing LH surge, but animals return to anestrus without continuation of the normal cycling activity.

Adapted from Vasantha SKI and Kona SSR. 2016 Puberty Adapted from Vasantha SKI and Kona SSR. 2016

Puberty

Effect of testosterone on male brain Testis T E2 Blood Brain Barrier Surge Center Does not Develop

Effect of estrogen on female brain aFP + E2 E2 Placenta E2 E2 E2 Ovary Blood Brain Barrier Surge Center Develops

Average age of puberty (range) 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) 18 mo (12-19) Human 13 yr 12 yr

Puberty may affected by different factors: Factors affecting puberty Puberty may affected by different factors: Heritability and breed Environmental factors Heat stress, birth month, photoperiod, social condition Nutrition Weight and growth rate Endocrine factors Age at puberty is influenced by several factors: Heritability and Breed: The heritability of age at puberty is much higher than other reproductive traits. Breed can influence age and size at puberty. Dairy heifers reach puberty at younger age (11-12 months) and a lower % of adult weight (35%) than beef heifers(14-15 months and 45-55% weight). Decreasing age at puberty is profitable to producers because animals can start returning investment earlier and total lifetime production will be increased. A useful marker for age at puberty in males is scrotal circumference. Sires with large scrotal circumference tend to have progeny with decreased age at puberty. Larger scrotal circumference indicates higher LH and FSH secretion which induces puberty in males and females. Environmental factors: Heat stress will delay puberty in heifers. By the time fall born lambs reach the right size and weight it is spring. Sheep are short day breeders and the increasing day length will inhibit LH secretion until the next fall. Research has shown ewe lambs need to see a period of long days followed by short days to reach puberty. Ram exposure can induce puberty in ewe lambs. These effects on prepubertal females due to exposure to adult males are caused by pheromones. Nutrition: Nutrients particularly energy and protein are essential to optimize reproduction. Malnourished females lack ovarian activity owing to the suppression of luteinizing hormone in a pulsatile fashion. LH pulse generating system in the hypothalamus and its pre pubertal rise is influenced by the plane of nutrition. Nutrition effects synthesis and release of GnRH, FSH, LH and GH due to its action on hypothalamus and anterior pituitary respectively. The Ovarian follicular growth and steroid synthesis are influenced by nutrition. Acute and chronic dietary restriction results in a gradual reduction of growth rate of dominant follicle. The effects of nutrition on the follicular development mediated by the actions of various growth factors and their receptors. Weight and growth rate: Body weight is more important than age in determining when puberty occurs. Improved growth during 4-7 months of age in heifers is seems enough stimulus to induce the onset. Better growth rates decrease the negative feedback of estradiol on LH secretion and thus stimulate the follicular growth. Endocrine factors: 1. Leptin: It is produced primarily by the adipose tissue with other sites being stomach, skeletal muscle, fetal cartilage, pituitary, mammary tissue and placenta. It signals nutritional status of the organism to the central reproductive axis. An increase in the circulatory leptin at the pubertal onset was reported in rodents and heifers. Its role in the activation of GnRH neurons via hypothalamic proopiomelanocortin system was proposed by Amstalden et al. (2014). It is suggested that leptin may act as a metabolic gate especially at the time of puberty. 2. Growth hormone: Delayed puberty due to declined LH pulses was attributed for the nutrient restriction. This was correlated with changes in mean concentration and amplitude of GH pulses just before puberty. Pubertal onset was positively associated with circulatory IGF-I independent of growth rate, leptin concentrations, and body fat. 3. Insulin: The role of Insulin in setting pace for the pubertal onset by monitoring the nutritional status was proposed and its role through IGF-I. It was proposed that circulatory IGF-I is used as a means for studying interactions between nutrition and reproduction 4. NPY: The role of NPY in the inhibition of GnRH and subsequent LH release was proposed. This was correlated with a fastened puberty in calves whose metabolic status was favorable with increased leptin and decreased NPY levels. 5. Melatonin. Its activity is dependent on the photoperiod. There were few studies depicting its direct role in pubertal development.

Influence of Growth Rate and Bull Exposure on Age of Puberty 500 449 428 422 400 375 High Growth Rate Moderate Growth Rate 300 Age at Puberty (days) 200 100 Heifers only Bull Exposure

Adapted from Vasantha SKI and Kona SSR. 2016 Nutrition affect puberty Adapted from Vasantha SKI and Kona SSR. 2016

Nutrition affect puberty Association of weight:height ratio (W:H) and age at puberty (AP) in crossbred beef heifers. (Adapted from Bras., 2017)

Role of leptin in puberty Effect of a minimum percentage of body fat Serum leptin concentrations Leptin does not serve as triggering signal Leptin acts mainly as a permissive signal that permits puberty to occur Proopiomelanocortin system affect leptin role in GnRH neuron activation

Role of leptin in puberty Model for pathways mediating the nutritional regulation of GnRH release during pubertal development. (Adapted from Marcel Amstalden et al., 2011).

Nutrition affect puberty Association of fat thickness (FAT) and age at puberty (AP) in crossbred beef heifers.(Adapted from Bras., 2017)

Role of insulin in puberty The role of insulin in setting pace for the pubertal onset by monitoring the nutritional status was proposed and its role through IGF-I.

Role of NPY in puberty The role of NPY in the inhibition of GnRH and subsequent LH release was proposed. This was correlated with a fastened puberty in calves whose metabolic status was favorable with increased leptin and decreased NPY levels.

Role of melatonin in puberty Pineal gland activity and melatonin secretion is dependent on the photoperiod. There were few studies depicting its direct role in pubertal development.

Some research papers associated to this lecture Barb, C. R. and R.R. Kraeling. 2004. Role of leptin in the regulation of gonadotropin secretion in farm animals. Anim. Reprod. Sci. 82–83: 155–167. Clarke, I. J. and B. A. Henry. 1999. Leptin and reproduction. Reviews of Reprod. 4: 48–55. Vasantha SKI and Kona SSR. 2016. Physiology of puberty in females: A review. Int. J. Vet. Sci. Anim. Husbandry. 1(2): 23-26.