Reproduction in Animals Reproduction is the method by which animals pass on their genes to their offspring ensuring survival of the species. There are two types of reproduction: Asexual Reproduction Sexual Reproduction

Asexual Reproduction Asexual Reproduction involves: Only one parent Offspring is genetically identical to the parent. An example is an aphid in spring where only females are present in the population during this time and so an unfertilised egg develops into a female identical to its mother.

Sexual Reproduction Takes place in Vertebrates. Involves males gametes called sperm cells and female gametes called egg cells. Offspring are genetically different to their parents but do have characteristics from each parent.

Hybrid Vigour Hybrid Vigour (Heterosis): when the offspring produced as a result of crossing two genetically different breeds is superior to either of its parents. Example 1: Perennial Ryegrass X Italian Ryegrass = Hybrid Ryegrass. Hybrid Ryegrass has the persistence of perennial ryegrass and longer growing season and the high productivity of Italian Ryegrass. Example 2: Purebred Hereford Bull X Freisian Cow = Blackwhitehead. This blackwhitehead if a female and kept for breeding will produce high milk yields but also pass on beef characteristics to its offspring.

Male Reproductive System Gonads - reproductive organs that produce gametes (sex cells) Testes - produce the male gametes called sperm cells. Scrotum - hangs outside the body cavity to keep it at a lower temperature so that sperm cells develop and mature properly. Sperm - produced in the testes. Epididymis - this is where sperm matures and is stored. Vas Deferens stores sperm. Semen- this is sperm with fluids which give it mobility.

Male Hormones Follicle Stimulating Hormone (FSH) - promotes sperm production. Luteinising Hormone (LH) - controls the production of the hormone testosterone. Testosterone - is responsible for the development of male sex characteristics and male sex organs.

Female Reproductive System Ovaries - these are the female gonads and produce eggs called ova. Fallopian Tubes (Oviducts) - connect the ovaries to the uterus. Fertilisation takes place in the fallopian tube. Zygote - this is the fertilised egg. It moves to the uterus (womb) where it implants itself in the uterine wall. Embryo - an embryo is formed as the cells divide in the zygote. Uterus (Womb) - this is where the embryo grows into a foetus. Cervix - dilates during birth. Vagina - serves as birth canal during birth.

Female Hormones Follicle Stimulating Hormone (FSH) - promotes the development of a follicle that produces oestrogen. Luteinising Hormone (LH) - stimulates ovulation and development of the corpus luteum which secretes progesterone. Progesterone - supports pregnancy, allows the uterus to grow during gestation, inhibits lactation prior to birth, labour and the inhibition of the immune response to the embryo. Oestrogen - promotes the secondary sex characteristics in the female and the growth of the mammary glands. Oxytocin - responsible for contractions in uterine wall at birth and “milk let down”.

Oestrous and Oestrous Cycle Oestrous Cycle - a recurring cycle during which a female mammal comes into heat, releasing an egg which is available for fertilisation by the male. Duration of Oestrous - the length of time during the oestrous cycle which the female is in heat and an egg is available for fertilisation. Gestation - this is pregnancy. The period of development in the uterus from conception to birth.

Polyoestrous Animals that have oestrous cycles throughout the year are described as polyoestrous. Cows and pigs are polyoestrous. Animals that have a number of oestrous cycles but only during a certain time of the year are described as seasonally polyoestrous or seasonal breeders. Sheep are seasonal breeders. Seasonal breeding is determined by the length of day (photoperiod). Sheep are short day breeders, they breed when the length of daylight shortens (autumn and winter)

Length of Oestrous Cycle, duration of Oestrous and Gestation. Animal Length of Oestrous Cycle Duration of Oestrous Length of Gestation Cow 21days 18 to 24 hours 283 days (9.5 months) Sheep 17days 36 hours 149 days (5 months) Pig 2 to 3 days 115 days (3months, 3 weeks and 3 days)

Birth in Cows and Sheep A few days before birth the udder of the cow or ewe swells. The ligaments around the base of the tail relax and pelvic bones widen. The “water bag” which is a membrane of water will come out and the young animals forelegs will appear. After the calf or lamb is born the umbilical cord is cut. The navel is disinfected with iodine to prevent the entry of E. coli bacteria which cause navel ill or joint ill. The cow or ewe licks the new born animal which helps them to warm up and also to form a bond between mother and new born. The new born animal should be fed colostrum as soon as possible.