Male Reproduction PDF

Male reproduction Need to be able to label: − bladder The male anatomy − urethra − penis − testis Testis − epididymis – male gonads – responsible for − vas...

Male reproduction Need to be able to label: − bladder The male anatomy − urethra − penis − testis Testis − epididymis – male gonads – responsible for − vas deferens production/formation of sperm − secondary glands i.e., the seminal vesicle, spermatogenesis prostate, and cowper’s – formation of sperm glands (bulbo-urethral occurs within glands) – the seminiferous tubules – Hormone production - androgens main one - testosterone  The male anatomy The male anatomy Vas deferens and accessory glands Epididymis – what is its – connect epididymis to the urethra role/function – transport of sperm from testes to vas – contracts during ejaculation to add in the movement deferens of spermatozoa from the epididymis to the urethra – concentration of sperm (~4 billion – at ejaculation sperm are mixed with secretions from spermatozoa per ml) the accessory glands – storage of sperm seminal vesicles, prostate, and cowper’s glands – maturation of sperm (motility and (bulbo-urethral glands) fertility) Contain buffers, nutrients, and other substances – secretion of nutrients to sustain needed to assure optimum motility and fertility of sperm sperm – absorption of older unused sperm – these secretions make up 95% of the seminal fluids the mix of sperm and seminal fluid is called “semen” The male anatomy Scrotum Ejaculation times, ejaculate volumes and sperm concentration for – two-lobed sac that enclose the testes males of a number of farm species (study guide Table B1) Penis Species Ejaculation time Ejaculation Sperm Sperm per – organ of copulation volume Concentration ejaculate – erection is due to more blood entering via (ml) (per ml) the arterial supply than that which leaves via the veins. Ram and Buck 1 second 0.8-1.5 3-6 x 109 1.5-6.0 x 109 – straightening of the sigmoid flexure (in those species which have one) causes the penis to Bull 1 second 5-10 1-2 x 109 5-15 x 109 protrude from the sheath Boar 5-20 minutes 150-300 200-300 x 106 30-60 x 109 Urethra Stallion 10-60 seconds 30-100 150-300 x 106 5-15 x 109 – fine duct within penis that provides for the release of either the semen (from epididymis) or urine (from bladder)  The male anatomy Sperm structure Spermatozoa - has four main structures – head shape differs between species haploid cell - contains half the autosomes contain X or Y chromosome (determines sex of offspring) – acrosome membranous sac on sperm head that adds in the penetration of the egg (hydrolytic enzymes) – mid piece of tail contains densely packed mitochondria – which are thought to help with motility – end piece of tail - locomotion Sperm movement  Male physiology – hormonal control Male physiology – hormonal control Gonadotrophin releasing hormone (GnRH) FSH (follicle stimulating hormone) and LH (luteinizing stimulates the release of both FSH and LH hormone) – gonadotrophins which promote testicular function Negative feedback loop (i.e. higher levels of testosterone reduce GnRH, FSH and LH secretion) – FSH promotes spermatogenesis Testosterone itself can also directly - - suppress LH release. Promotes ABP production + High concentrations of FSH can result in – LH increased production of the protein inhibin, produced in sertoli cells which suppresses promotes androgen secretions (mainly testosterone) FSH release but not LH + Male physiology – hormonal control Thermoregulation of the testis Androgens (male sex hormones) – involved in the development of sexual characteristics To maintain normal functionality and fertility the testes must more rapid growth remain higher mature weight – generally 2 – 5oC cooler than the internal body cavity (core ~38.5- greater muscling 39.5oC) lower body fat growth of horns/antlers To do this aggression – the skin of the testis is thin with little hair or wool libido – the skin has sweat glands – evaporative cooling – chemicals which – the scrotum can be contracted (muscles do not respond to changes can taint meat (“boar taint”) in temperature until near the age of puberty - must first be – can induce sensitized by testosterone) reproductive activity in females (pheromones) – the direction of blood flow is such that arterial blood entering the testis is cooled by venous blood leaving it  Puberty in the male Venous Peripheral heterothermy: Arterial heat is exchanged by convection arteries and veins are Puberty is defined as arranged so that Heat is – the time at which the male has the capability to fertilise the transferred from the outward-flowing arterial female blood in to the inward- – production of viable sperm flowing venous blood. Arterial Venous Like the female onset of puberty is driven by – weight (30-60% mature BW) and genetic factors As in the female puberty does not mean sexual maturity – i.e. sexual behaviour is not fully developed and sperm levels is less than in mature male, still growing Management of reproductive Management of reproductive performance in the male performance in the male Reduced fertility caused by disease The main issues in management of male fertility relates to – brucellosis (which results in the formation of a hard swelling in the situations in which fertility must be eliminated epididymis and consequently low fertility or complete sterility) – pizzle-rot (in which a bacterium growing in the sheath produces – either because the males are being grown for meat ammonia from the urea excreted in the urine and as a result causes production (and are not of adequate genetic merit to be a scalding effect on tissues of the penis and sheath) used as flock or herd sires) – infection of the external genitalia, particularly the scrotum, i.e. from severe shearing cuts in rams. – or because they are to be used as “teasers”. – What else could reduce fertility via mating?  Management of reproductive Management of reproductive performance in the male Burdizzo performance in the male Castration – a castrated male - characteristics – removal of the testis is infertile – results in a infertile animal has no libido (no hormones) – results in very low levels of is not aggressive androgens has slower growth rates than an entire male has lower muscle levels and tends to have higher fat Effect this has on the animal levels for a given live weight (~like a female) depends on when this procedure is does not grow the large horns/antlers undertaken – i.e. if undertaken prior to puberty the – These animals are used on farm to effects observed are more pronounced ensure no unwanted pregnancies and when high growth rates are not the main target of the production system COMMON NAMES FOR MALE FARM ANIMALS (TABLE B2) Management of reproductive performance in the male Short-scrotum Species Entire male name Castrated male name – Pushing the testis up against (generally not within) the body cavity by shortening the scrotum length with a rubber ring – ‘cooking’ the Cattle Bull Steer testis (sometimes called a rig) Sheep Ram Wether Cryptorchid Goat Buck (Billy) Wether – Natural failure of testis to descend is correctly known as – Farmers inter-change the terms Pig Boar Barrow Horse Stallion Gelding Physical and hormonal characteristics of these Chicken Rooster Capon animals – still produce androgens (not affected by temp) – have very low sperm viability (mostly considered infertile)  Management of reproductive Management of reproductive performance in the male performance in the male – Characteristics of a short scrotum male Vasectomy has growth rates similar to an entire male – cutting vas deferens (and generally tied) is ‘considered’ infertile – often called ‘teasers’ has libido (due to hormones) can still display aggression – Physical and hormonal characteristics: is lean like an entire male still produce androgens can still grow the large horns/antlers there is no sperm in ejaculate – These animals are used on farm – Generally used on farm to either when high growth rates are wanted without the risk identify females in heat of unwanted pregnancies or induce breeding activity in females Management of reproductive performance in the male – Characteristics of a vasectomised male has growth rates similar to an entire male is infertile has libido (has hormones) can still display aggression is lean like an entire male can still grow the large horns/antlers