Female Puberty and Reproductive Senescence

• Puberty is when the female is sexually mature and able to reproduce
• Puberty precedes the development of physical maturity.
• Although females become capable of reproducing, their efficiency, particularly fecundity (number of offspring), has not reached its maximum
• Juvenile ewes mated just after puberty produce an average of 0.6 lambs weaning, while ewes 1 year older produce 1.2 lambs weaning. This could be from:
• Lower ovulation rate
• Increased fertilization failure
• Embryo loss
• Failure to be mated by the ram
• Environmental influences must be favorable for the "biological clock" to continue once started.
• There isn't a physiological change in domestic species comparable to women's menopause
• Reproductive senescence is reported in killer and pilot whales, which is likely a strategy to boost ecological fitness.
• Recurring cyclic activity in nonseasonal polycyclic animals like cows and sows is interrupted by:
• Pregnancy
• Lactation
• Pathological conditions.
• Seasonally polyestrous animals include mares, ewes, does or nanny goats, and cats.
• Monocyclic animals (bitches) experience a period of sexual quiescence or anestrus.
• Increased growth rate occurs when a female reaches puberty and the genital organs increase in size
• In gilts, the mean length of the uterine horn increases by 58%
• The mean uterine weight increases by 72% The mean weight of the ovaries increase by 32%
• Females of domestic species reach puberty at the following ages:
• Mare: 1 to 2 years
• Cow: 7 to 18 months
• Ewe: 6 to 15 months
• Doe (or nanny goat): 4 to 8 months
• Sow: 6 to 8 months
• Bitch: 6 to 20 months
• Queen cat: 7 to 12 months
• Changes during puberty depend on the activity of the ovaries, which have two functions:
• Production of female gametes
• Hormone synthesis
• Changes occur in the ovary of the heifer calf as at birth, the ovaries contain approximately 150,000 primary or primordial follicles apiece.
• Luteinizing Hormone (LH) is the primary hormone associated with ovarian activity during puberty

Hormones

• Puberty onset depends on ovarian estradiol secretion, which is sufficient to stimulate a preovulatory gonadotropin-releasing hormone (GnRH) and LH surge.
• As puberty approaches, the inhibitory effect of estrogen is reduced in the tonic center (hypothalamus).
• The hypothalamic-gonadal axis becomes more active, increasing the pulsatile frequency of GnRH, FSH, and LH.
• Increased FSH stimulates follicle development, which then secretes estrogen.
• The endocrine trigger for puberty is the loss of feedback inhibition of oestrogen on the tonic center of the hypothalamus.
• The parameters used to define puberty onset in males are:
• Behavioral changes
• Age of first ejaculation
• Quality of ejaculate
• Younger males develop smaller testes and short epididymis, resulting in lower daily sperm production than more mature animals
• Males within a few months of puberty have a reduced capacity to establish a high pregnancy rate.
• The quality of ejaculate determines sperm production which makes the pregnancy reliable
• Puberty in males occurs when hypothalamic sensitivity to estradiol and testosterone decreases
• Male testosterone crosses the blood-brain barrier and an enzyme then converts it to oestradiol. The inhibitory effect is primarily caused by oestradiol.
• As puberty begins the inhibitory effects of estradiol and testosterone on GnRH secreting neurons in the hypothalamus decreases, triggering the release of the GnRH to undergo spermatogenesis
• In males, the rise in LH begins earlier than in females.
• The rise in testosterone is gradual, including the 2 months period required for spermatogenesis in sheep.
• Puberty in gilts occurs at about 24 weeks (160-170 days)
• Puberty in boars occurs at about 28 weeks

Seasonal Breeding

• For seasonal breeders (ewes, mares, and queen cats), the time puberty occurs depends on that time's environmental circumstances
• By definition, seasonal breeders experience a period of anestrus (non-breeding season), and the annual transition to the breeding season is similar to puberty

Melatonin: Puberty, and Seasonality

• The pineal gland plays an important role in controlling:
• reproduction in seasonal breeding species.
• The timing of puberty by influencing the release of FSH, LH, and prolactin
• There is increasing interest in these pineal peptide hormones:
• Arginine vasotocin
• Gonadotrophin
• Prolactin releasing and inhibitory hormones.
• Melatonin drives the reproductive response of ewes to inductive photoperiods.
• When adult ewes are given rhythmic administration of melatonin,it exerts a similar effect to increased hours of darkness by inducing the start of the mating season.
• "Switching" is done by changing the day length for the mare.
• The melatonin concentration in intact mares increases with hours of darkness.
• First estrous: Silent
• The reason for the "silent” first estrous of pubertal animals is that the CNS requires progesterone priming before responding and behavioral signs of heat occur.

Kisspeptin

• Puberty and seasonality are influenced by a number of environmental factors, notably nutrition and fatness.
• Environmental influences mediate this control through presynaptic neurons, which stimulate neuronal GnRH secretion.
• Neurons release Kisspeptin(a protein), which binds to its receptor ,which is expressed on GnRH secreting neurons.
• An intact kisspeptin signalling pathway is a prerequisite for puberty in mammals.
• Kisspeptin-secreting neurons are found in many places:
• Arcuate nucleus
• Proventricular nucleus of the hypothalamus
• Rising estrogen concentrations activate the HPG axis by acting as a positive feedback on Kisspeptin signaling
• Kisspeptin-secreting cells express an essential receptor for feedback effects of estrogen, while GnRH-secreting cells do not have the receptor.
• Kisspeptin influences seasonality.
• Expression of the kisspeptin gene rises when photoperiod diminishes, and seasonal changes occur in the arcuate nucleus of the hypothalamus

Timing and Health

• Genetics determine the time puberty occurs, and smaller breeds tend to be slightly precocious (early) with puberty
• The various external factors influence the timing:
• Nutrition
• Proximity of the male
• Climate
• Disease

Nutrition and Diet

• The onset of puberty is usually closely linked with nutrition in most domestic species:
• Attainment of a critical body weight
• Minimum percentage body fat or metabolic mass
• A critical body weight and minimum percentage body fat are needed
• Dietary restriction delays puberty by an effect on both the frequency and amplitude of GnRH secretion
• A well-fed animals will have a better growth rate and reach puberty sooner
• Protein Leptin comes from fat in tissue is an important link metabolic status and the neuroendocrine axis.
• Leptin doesn't trigger puberty, however, a permissive signal enables puberty to occur.
• Leptin acts like a metabolic 'gate', where an increase in circulating concentration increases with over development

Environment Factors

• Exposure to males will speed up puberty
• Animals in tropics hit puberty faster that animals in more temperament climates
• Diseases hinder growth rate which effect when they hit puberty

Using tools to alter Puberty and Seasonality

• Seasonal breeders need to produce offspring so ability during non-seasonal times have benefits:
• Ability to produce offspring out of season
• Advance the timing of onset activity

Nonhormonal Methods

• Use of controlled lightning
• Lengthening photo periods to simulate the natural light
• Reduce daytime using equatorial lighting to show changes in the climate
• Artificial light, given during the latter part of the day is the same as extending and this works for mares.
• In the ewe, this is not as effective but can be enhanced using melatonin

Management

• Housing with lightning is how the breeding cycle changes

• Gradual, reduce day light

• Ewes are only exposed to light so reduce the chance of decreased light

• Remove nature light

• Mares in late autumn respond better to artificial lightning and have increased periods of oestrous

• Good for animals in the northern hemisphere

• Lighting should be used in December for efficiency

• The amount of extra light they need is 2 hours and 30 minutes

• 1.Well fed mares has a longer period of cyclicity than those on a more restricted diet. Stabling of mares and the provision of good feeding are believed to assist in stimulating the onset of cyclic activity in early spring.

• Another method is to have a male present in the area

Hormonal Intervention

• Using Gonadotrophin to help induce estrous
• However there is little proof to back this up as efficacy is poor
• ACYCLICAL can be from 1.seasonaility 2.monoestrous cyclicity 3.postpartum anestrous
• Using Gonadtrophins extracts from a pituitary or chorionic
• Limited evidence of effects of eCG
• Should be used as a synchronizer
• Reason to not used winter animals: does is large, LH and FSH activity is low
• Progesterone may be used in anestrous to induce estrous as species is polytocous

Managing Melatonin and Health

• Use a melatonin implant for animals like sheep, goats, and horse, and cats
• They can also suppress this with estrous as you can with cats
• If implant is administered, keep from sound for 7 days, and separate until ready
• Mating action is 2/3 of month
• Use in ewe for 2/3 months
• Progesterone implant, implant after insertion to stop receptors from getting used too it

Common Conditions with Progesterone and Hormones

• Anestrous found in cows and is a lack of ovulation
• To solve give a single does of GnRH but with no look
• D. melatonin is how to control the reproductive health with sheep dogs and cats
• To terminate lighting or with an artificial light source
• This does not stimulate when giving the mare winter as it must be larger
• eCG both in the ewe
• Progesterone is polytocus that helps with ewes.
• To advanced date of health that administer implant
• Mating Activity is between 3 week period
• Can advance for a 2,3, with good facility