Functions of various parts of the digestive tract: Mouth, Oesophagus

Mouth:

The primary function of the mouth include prehension (grasping), mastication (chewing), and mixing of feed with saliva as preparatory steps for subsequent digestion in the remaining parts of the alimentary canal. The lips, tongue, and teeth are used to pick and hold feed while it is in the mouth. The teeth grind the feed, and the tongue mixes it with saliva. The lips of sheep, goats, and horses are flexible, while those of cattle and buffaloes are relatively stiff and immobile. In horses, the upper lip is very sensitive and mobile and is used to feel the feed and direct it towards the moouth. Horses also have both upper and lower incisors which cut herbage like scissors and help in prehension. The mastication of feed with grinding molars is also very efficient in horses. In cattle, buffaloes, and sheep, the upper incisors are absent. Instead, they have a hard pad called the dental pad. During grazing, the tongue is used to guide feed into the mouth, and plants are grasped between the dental pad and lower incisors and torn away.

Saliva is a watery solution containing small amounts of mucin, inorganic salts and enzymes. It is secreted into the mouth from three pairs of salivary glands (paratoid, sub-maxillary, and sub-lingual). Secretion of saliva increases during mastication of feed. Cattle and buffaloes produce 130 - 200 litres, sheep and goats 2 - 3 litres, and horses 10 - 12 litres of saliva per day. Saliva lubricates the ingested feed and thus facilitates swallowing. It also helps in maintaining optimum pH in the rumen and provides a mechanism for recycling urea in ruminants.

Oesophagus:

This is a muscular tube extending from the back of the mouth (pharynx) to the stomach. Ingested feed is forced through the oesophagus by its wavelike muscular contractions.

(Note: In next Post, find about Function of stomach in digestive system of farm animals)

Introduction to Digestion in Farm Animals

Digestion in animals involves mechanical, enzymatic, and microbial processes in the gastrointestinal tract, which convert large feed particles to a size which can be absorbed, transported, and used by the animals. The digestive systems of all farm animals are not the same, rendering them less competitive and able to adapt to a wide range of available feed resource niches. Based on the structure and functions of the digestive tract, farm animals are divided into two major groups:  ruminants or polygastrics, e.g. cattle, buffaloes, sheep, and goats; and non-ruminants or monogastrics, e.g. horses, donkeys, rabbits, dogs and cats. The key difference between these two groups of animals lies in the structure of the stomach. Ruminants, as opposed to non ruminants, have three additional stomach compartments where digestion takes place in different environments. In general, for farm animals the processes associated with digestion include prehension, ingestion, grinding or mastication, digestion of feed, absorption of nutrients, and excretion of waste products.

Artificial Insemination (AI)

Artificial insemination (AI) is the deposition of semen in the cervix by the artificial means. It is a useful technique devised for the genetic improvement of farm animals. Artificial insemination is widely used for breeding cattle, buffaloes, sheep, goats, horses, dogs and a variety of laboratory animals.
Advantages of artificial insemination

• The greatest advantage of artificial insemination is the opportunity to spread superior germ plasm by the wide use of carefully tested and selected sires. On average, a bull can sire 50,000 progeny per year through artificial insemination compared to 40 - 50 progeny through natural mating. 
• Artificial insemination plays an important role in the control of various diseases, particularly the venereal diseases disseminated by natural mating. 
• It helps to maintain complete and accurate breeding records, leading to better herd management and the identification of infertility problems. 
• Artificial insemination is more economical than natural mating. 
• The mating of animals of different sizes becomes possible without any accidental injury. 
• Artificial insemination extends the usefulness of sires of high genetic merit which for physical reasons are unable to copulate normally.

Limitations of artificial insemination
There are few disadvantages of artificial insemination even if it is properly performed. The major limitations are due to lack of trained personnel to provide proper service. Poor breeding efficiency may occur in herds when owners do not watch their animals closely for estrus and the inseminator does not breed them at the proper time. The inseminator may be, if not careful, a means of spreading infections from one herd to another. Herd owners should avoid intensive use of a limited number of sires, which may increase inbreeding in the herd. Increased inbreeding is usually associated with low fertility and decrease in vigor and overall productivity.
Semen and its collection
One of the most important steps in an artificial insemination program is the collection of semen and its proper handling. The following methods are used for the collection of semen from bulls.

1. Artificial vagina method 
2. Massage Method 
3. Electro-ejaculation method

The best procedure and practical method for collecting semen is with an artificial vagina. Various sizes and shapes of artificial vagina are used, but all consists of a heavy rubber cylinder with a rubber lining inside. This enables a clean, complete ejaculate to be collected in the glass tube fitted on the lower end of the artificial vagina.
In the massage method, the operator's hand is inserted about 10 inches into the rectum of the bull. The vesicular glands are picked up with the fingers by carefully feeling the rectal wall. They are then massaged gently causing a slightly turbid fluid to appear which cleanses the path for semen. Then the operator massaages the ampulla of the vas deferens until the sperm containing semen appears. The semen is collected in a test tube placed in front of the sheath.
Electro-ejaculation is the method used for males that refuse to serve the artificial vagina or when injuries makes this impossible. A rectal probe with either a ring or straight electrode is used to provide the necessary electrical stimulation.
After the semen is collected, it is evaluated for quality (live and dead sperm, motility etc) and diluted with suitable extenders (diluent). Then it is stored in liquid form in the refrigerator at 5 Degrees Celsius or in frozen form in liquid nitrogen at below 196 Degrees Celsius.
Insemination procedure.
Detection of heat (estrus) of the female is the first step. When a female is found to be in heat, the inseminating rod is passed through the spiral folds of the cow's cervix by the recto-vaginal technique. Part of the semen is deposited in the uterus, just inside the cervix, and the remainer in the cervix while the rod is withdrawn. Extra care must be exercised in the case of those animals that have been inseminated previously. If pregnancy is suspected in an animal, insemination should not be repeated.
Spermatozoa can survive in the genital tract of a cow or buffalo for a little over 24 hours. The egg has a short survival time, about 6 hours at the most. Optimum fertility is obtained when inseminations are performed 13-18 hours before ovulation. Reasonably good results are obtained even during the period 7-12 hours before ovulation. The cows should be checked twice daily with a teaser bull to detect estrus. As a rule of thumb, cows showing estrus in the morning should be bred the same day in the afternoon, and cows showing estrus in the afternoon should be inseminated the next morning.

Reproductive cycle in farm animals

Reproduction in female is a complicated process, and normal reproduction ivolves synchronization of many functions. It is subject to many adverse effects at certain stages. Different aspects of reproduction in cows and buffaloes along with the physiological mechanisms involved are discussed in the following paragraphs.
Puberty or sexual maturity
Puberty is defined as the age at which reproduction becomes possible. In the female this is usually considered to be the age of first estrus. Puberty occurs before full mature body size is attained. The average age at puberty in cows is average 34 months and in buffaloes is 38 months. In cross breeds, the age at puberty is 9 - 18 months.

Trait	Species
	Sahiwal Cow	Holstein Cow	Buffalo	Sheep	Goat	Horse
Age at first service (days)	1030-1052	596-628	1137-1151	195	195	495
Gestation Period (days)	282	282	310	144-151	146-152	340
Dry Period (days)	298	-	191
Service Period (days)	154-221	144	215
Calving interval (days)	500	426	520
Length of estrus cycle (days)	21	21	21	16-17	20-21	21
Duration of estrus (hours)	17	17	17-24	22-36	24-48	4-8 Days
Post-estrus time ovulation (hours)	10-11	10-11	18-45	24-30	24-36	1-2 Days
Best time to Breed	Late estrus or shortly after Estrus	Late estrus or shortly after Estrus		Middle of Estrus		Every other day beginning 2nd day of Estrus
Fertile life of sperm in the female genital tract (hours)	30-48	30-48		30-48		72-120
Fertile life of ovum (hours)	20-24	20-24	N/A	10-25	N/A	6-8

The onset of puberty depends upon a change in the balance between the output of gonadotropins from the gonads and growth hormones secreted by the anterior pituitary gland. The pituitary gland is located in a bony depression at the base of the brain. It consists of two distinct parts, known as the anterior (front) and the posterior (rear) pituitary glands. The pituitary is controlled by certain physiological functions involving the gonads and the anterior pituitary gland, and is influenced by several environmental (season, temperature, nutrition) and genetic factors.
Breeding season
The term breeding season refers to the period of time during the year when females of a species come into estrus. Most species of wild animals have a definite breeding season which is initiated at a time when environmental conditions are conducive to the survival, growth, and development of the young one after birth. For example, the gestation period in sheep and goats is 144 - 152 days, and the breeding season in these species starts in fall so that the young are born in spring. In cattle, where pregnancy on average lasts for nine months, the female breeding season occurs in the early summer so that the calves are born in the spring when the temperature is optimum for the growth of the newborn. Green fodder and forages are also available, which support sufficient milk production by the dams.
Domestication of farm animals has resulted in some variation of breeding season. Due to the intervention of modern production techniques, farm animals are now capable of breeding throughout the year. Among the farm animals, cows and buffaloes are polyestrous, showing diestrous cycles throughout the year. Mares, ewes, and does are seasonally poly estrous, showing diestrous cycles during a definite breeding season. The breeding season of ewes and does is confined largely to fall and winter. In Indian sub continent, buffaloes breed from October to December, when day length is decreasing. The stimulus for the initiation of reproduction during certain seasons results from the action of light, via the eye and optic nerve, on the pituitary gland. This stimulus causes the pituitary to release gonadotropic hormones, which activate the functioning of the gonads. One of the limiting factors influencing the productivity of the buffalo is the seasonality of breeding, which may be due to either anestrus or silent estrus during the hot, dry months of summer.
Estrus Cycle
Estrus occurs in non-pregnant females in characteristic rhythmic cycles. The interval between two consecutive estrus periods is known as the estrus cycle. The estrus cycle in farm animals is characterized by cyclic changes in the morphology of the reproductive organs as well as in the behavior of the animals.
The estrus cycle is divided into four different phases; these are known as proestrus, estrus, metestrus and diestrus. 

Proestrus is the phase of estrus in which the reproductive system is beginning preparation for the release of the mature ovum from the ovary. Estrus is defined as that phase of the cycle when females are receptive to coitus. Metestrus is the short transitional stage following ovulation in which the effects of estrogen are declining. The recently ruptured follicle is reorganized, and the secretion of progesterone is rising. During this phase, the uterus gets prepared for the implantation of the embryo. If pregnancy does not occur, the reproductive tract goes into a period of rest called diestrus. In cows and buffaloes the estrus cycle averages 21 days in length. Sheep and goats usually have a shorter estrus cycle ranging from 16 - 21 days.
Signs of estrus are somewhat similar in females of different species. In cows and buffaloes, estrus is characterized by the manifestation of heat. The cows may bawl frequently, become very active and restless, or mount other females and remain mounted. The vulva swells and the vestibule may be come deep-red. The swelling subsides with the end of estrus. There is marked discharge of clear, viscid mucus secreted by the cervix from the vulva. The excessive secretion at estrus acts as a lubricant during copulation.
Ovulation: Ovulation may be defined as the discharge of the ova from the Graafian follicle. Ova develop from germ cells in the ovaries. Numerous germ cells are present in the ovaries at birth, but few of the follicles surrounding them mature to rupture and shed ova. Follicles grow under the influence of the follicle stimulating hormone (FSH). The layers of follicular tissue become thinner with growth, the follicle rupturees and ova are released. This process is stimulated by the luteinizing hormone (LH). The released ova are swept by muscular and ciliary movements into the oviduct towards the uterus. If mating or articficial insermination takes place, spermatozoa and ova meet in the oviduct.
Esturs and ovulation are more or less synchronized in females to increase the chances of fertilization, the union of an ovum with a spermatozon. Synchronization of ovulation and insemination is essential because the life of the ovum once it is shed and that of the spermatozoa in the female reproductive tract is limited to a few hours.
Gestation: Gestation is the process that begins with the fertilization of the ovum by the sperm and terminates with the birth of a young one. The period of gestation varies considerably among species of farm animals. The average gestation period of cattle is 282 days, buffaloes 310 days, and sheep and goat 151 days. Generally, male calves are carried one day longer than female calves.
Parturition: Parturition is the physiological mechanism that enables the uterus to expel fetus after a certain period of development and nourishment. The process is called "foaling" in mares, "calving" in cows and buffaloes, "lambing" in ewes, and "kidding" in goats.
Signs of Parturition. The dam shows a number of signs of approaching parturition, which are usually divided in to following four stages.
(a) Preliminary stage: This stage may last for hours or even days. The ligaments in the pelvic region and around the tail head begin to relax and sink a few days before calving. The dam exhibits difficulty in movement. The external genitalia are swollen, enlarged, and flabby, and strings of mucous are seen. The mammary glands are enlarged and become tender. A clear, waxy fluid oozes out of the teats when pressure is applied.
(b) Dilation of the cervix: This stage merges with preliminary stage. Uneasiness increases and the animal may lie down and get up frequently. Frequency of micturition (urination) increases. At this time the cervix is fully dialted, and the next stage follows without any appreciable break in the sequence of events.
(c) Expulsion of the fetus: This staage begins with the fetus entering the dilaated cervix and the birth canal. During this time, uterine contractions occur at about two-minute intervals and the amnion is not ruptureed. There is a rush of fluid from the uterus when the water bag rupturees, and the animal appears relieved. Normally, the forefeet, with the muzzle lying behind and over them, appear at the vulva. The young one is expelled from the fetal membranes by a forceful and painful effort by the mother.
(d) Expulsion of membranes: The expulsion of the fetal membranes is commonly known as the delivery of the afterbirth. COntinued contractions of the uterus disjoin the fetal cotyledons, and the placenta is expelled within half an hour to eight hours after partuirition.

Reproductive Hormones

Hormones are organic substances secreted by certain specialized cells (glands) in the body, which are diffused or transported to some other part of the body and bring about certain changes. A number of hormones are directly or indirectly involved in vaarious aspects of reproduction. The secretion of these hormones is essential for the maintenance of a proper internal environment to ensure successful reproduction. The hormones involved in reproduction may be divided into two groups: 

(a) Primary hormones of reproduction

(b) Secondary hormones of reproduction

(a) Primary hormones of reproduction:

Gland	Hormone	Important Function
Anterior Pituitary	Follicle stimulating hormone (FSH)	Spermatogenesis; ovarian follicular growth.
	Lutenizing hormone (LH) (ICSH)	Androgen release; ovulation.
Posterior Pituitary	Oxytocin	Parturition; uterine contractions; milk letdown.
Testis	Testosterone	Maintenance of male reproductive duct system and secondary sexual characteristics; male sexual behavior; spermatogenesis
Ovary	Estradiol	Maintenance of female reproductive duct system and secondary sexual behavior; mammary gland stimulation.
	Progestrone	Implantation; pregnancy maintenance; mammary gland stimulation.
	Relaxin	Relaxation of uterine cervix and pubic symphysis; inhibition of uterine contractions.
Placenta	Human chorionicgonadotrophin (HCG [primate])	LH-Like
	Pregnant mare's serum (PMS [horse])	FSH-Like

(b) Secondary hormones of reproduction:

Gland	Hormone	Important Function
Anterior Pituitary	Somatotropin releasing hormone (STH)	Body growth; protein synthesis.
	Thyroid stimulating hormone (TSH)	Stimulation of thyroid gland; thyroxine release and iodine uptake by thyroid.
	Adrenocorticotropic hormone (ACTH)	Stimulation of adrenal cortex; release of adrenal corticoids
Posterior Pituitary	Vasopressin (antidiuretic horomne) (ADR)	Water balance.
Thyroid	Thyroxine	Body growth; development of maturation; oxidation of feeds.
Adrenal Cortex	Aldosterone	Electrolyte and water metabolism.
	17-OH corticoids (cortisone) (cortisol) (corticosterone)	Carbohydrate, protein, and fat metabolism.
Pancreas	Insulin	Carbohydrate, fat, and protein metabolism.
Parathyroid	Parathormone	Calcium and Phosphorus metabolism.

 

The primary hormones are directly involved in various aspects of reproduction, such as spermatogenesis, oogenesis, and ovulation. The secondary hormones are needed for the normal functioning of the organisms which makes it possible for reproduction to occur.

Reproduction In Farm Animals: Female Reproductive System

Female Reproductive Tract - Cow (Courtesy: fao.org)

The female not only contributes the female sex cell (ovum) but also provides the necessary environment in which the new individual is nourished during the early days of its life. These functions are performed by the primary and secondary organs of the reproductive system. A pair of ovaries are the primary organs of reproduction and produce not only ova but also the hormones required for the normal sexual behavior of females. The secondary organs of reproduction are a pair of oviducts (Fallopian tubes), the uterus, the cervix, the vagina, and the vulva. The mammary glands are also considered an accessory sex organ as they are closely related to the completion of reproduction by the nourishment of the young one.

The development of the reproductive organs starts before birth during the embryonic stage, but they remain quiescent. After birth, the reproductive organs develop gradually until the female attains a specific weight at a certain age when she becomes sexually mature, i.e. capable of producing viable gametes. The age at which a female becomes sexually mature is called puberty.

(a) Ovaries: The cow or buffalo has two ovaries situated on either side of the medial line, deep in the pelvic cavity almost at the border of the abdominal cavity. The right and left ovaries are connected with the uterine cornua of each side by tortuous Fallopian tubes. The ovaries of the buffalo are irregularly oval or spherical in shape and variable in size, while the ovaries of the cow are usually ovoid or spheroidal. The size and weight of active ovaries change frequently due to the formation of Graffian follicles and corpora lutea. A functional ovary develops from outer germinal epithelium from which the Graafian follicle develops.

The ovaries are the primary organs of reproduction because they produce not only the egg cells (ova) but also the sex hormones essential for female sexual activities. Willingness to mate (libido), ovulation, and many processes related to development, maintenance, and delivery of the calf are regulated by the female sex hormones. Hormone production in the ovaries is primarily controlled by the gonadotropic hormones of the pituitary gland. Under the stimulation of the pituitary hormones, the ovaries produce a follicular stimulating hormone (FSH), which is an estrogenic substance. Estrogens induce the psychic manifestations of estrus (heat). They also bring about glands of the cervix to secrete, and promote development of the mammary duct system. The characteristics behavior of the female and the secondary sex characteristics of the female are largely due to the influence of estrogens.

When ovulation takes place, the ruptured cells form the corpus luteum. The corpus luteum becomes a temporary endocrine organ under the influence of the luteinizing hormone  (LH) of the anterior pituitray. The corpus luteum secretes a hormone called progestrone which prepares the endometrium for the implantation of fertilized ovum and the maintenance of pregnancy. Progestrone also prevents ripening of additional follicles and ovulation, thus preventing the occurrence and manifestation of heat. It also stimulates the growth of the alveoli of the mammary glands and depresses the production of luteinizing hormone by the pituitary. The corpus luteum also produces another hormone known as relaxin, which causes decalcification of the pelvis. This results in the relaxation of the birth canal during parturition.
(b) Tubular Genitalia:
The tubular genitalia consist of the oviducts or Fallopian tubes, the uterus, the cervix, the vagina, and the vulva.
Oviduct or Fallopian tube. The oviduct is a tortuous, tubular structure of muscular and epithelial tissues. It reaches from the ovaries to the tapered end of the uterine horn. In cattle of different ages, the oviduct varies in length from 20 - 35 cm, while the length of the oviduct in buffalo varies from 20 - 25 cm. On the basis of diameter and internal structure, the oviduct consists of three parts: the isthmus or narrow portion which adjoins the uterine horns; the ampulla, which is slightly wider; and the infundibulum, which opens into the peritoneal cavity.
Uterus. The uterus consists of a body and two "horns". It is a muscular and irregularly tubular organ, the size of which increases during successive pregnancies. In heifers, it is situated 25 - 40 cm from the vulvular opening, just anterior to the cervix.
Cervix. The cervix or the neck of the uterus is a small muscular tube which extends from the uterus to the vagina. The muscular wall of the cervix is thick and its mucosa contain a large number of mucus-secreting cells. The mucosa form thick folds; opposite folds tend to overlap, forming a spiral passageway through the cervix. This makes possible the tight closure of the cervix with a cervical plug that is formed during pregnancy. This structure and secretions from the mucus secreting cells protect the uterus from microorganisms commonly present in the vagina. The cervical muscles relax during estrus and at the time of parturition. At parturition the cervix dilates, allowing the calf and fetal membranes to be expelled.
Vagina. The thin but elastic-walled tubular connection of the cervix with the vulva is called the vagina. It is a common passage for the reproductive and the urinary tract. The epithelial lining of the vagina undergoes changes during the estrus cycle. During natural breeding, semen is deposited in the vagina near the cervix.
Vulva. The external opening of the female genitalia is called the vulva. It includes the clitoris and the vestibule. The clitoris is a structure of erectile tissue (homologous with the male penis) located just inside the lower junction of the vulvular lips. The external opening of the reproductive tract of the cow lies just below the anus. It is about 12 cm long and has a wide, rounded dorsal angle and a narrow ventral angle. The thick labia majora are covered with fine hair.

Restraining animals: Special Procedures

Lifting a foot or leg: To lift the front foot of an animal like a cow, the animal must first be restrained. Tie its head so that it cannot move about. Then stand beside the animal facing backwards, reach down and lift the foot, and bend it at the knee. Be ready; the animal will probably lean its weight on you as the foot comes off the ground. Lifting the hind leg is difficult and should not be tried without a proper stock to confine and support it. To get an animal to lift its foot a little, e.g. if its foot is on a rope you are working with, exert upward pressure with your foot on the underside of the dew claw of the appropriate foot. This will usually cause the animal to lift its foot off of the ground and replace it. Frequently, it will put its foot down in its former position, so you must be alert and free your rope while the foot is in the air. 

Holding: It is easiest to keep a standing sheep still by holding it against the pen side with your arms and knees. In an open area where there is no fence, the sheep can be straddled if it is not too large. Place one hand under the animal's chin, keep your back straight, and stand as far back as it is comfortable. A standing sheep can also be held in a neck yoke.

Lifting the animal: Many sheep farmers suffer "bad backs" each year from lifting sheep. Sheep are heavy, difficult to hold against your chest, likely to struggle, and cannot be gripped easily. All of these factors increase the risk of back injury. If possible, gates or ramps should be used instead of lifting. If, however, lifting is unavoidable, 

• Do warm-up exercises
• Keep a straight back
• Bend your knees and legs to lift the weight
• Lift smoothly and continously

Once goats are caught, they can be restrained by a firm hold around the neck at the base of the skull. If a difficult procedure is to be carried out, a collar should be used. As previously mentioned, fibre-producing goats such as Angoras should not be restrained by holding their fleece as this will cause excessive bruising under the skin.

Shearing: Two types of goats are kept for their fibre. Angoras produce mohair, whilst a variety of long haired types produce soft under hair or down known as cash-mere. Long haired Angora goats are restrained for shearing in much the same way as sheep are restrained for foot trimming. Cashmere may be harvested by combing or shearing with the goat normally restrained in a standing position. Both types may suffer cold shock after shearing and therefore may need proper housing for at least a few days depeending on the weather and the time of the year.

Artificial insemination: The preferred method for restraining the female goat to be inseminated is to hold her up with her head facing back between the handler's legs. Her rear end is raised up by lifting the bent back position makes the inseminator's job of locating the cervix using an illuminated speculum much easier. The insemination "gun" is inserted into, but rarely through, the cervix.

Parturition: Dairy goats are prolific. Thus the chance of two or three kids being dropped is high. This increases the possibility of malpresentation and the problem of kids becoming mixed up. Handler assistance at the time of birth is therefore a must. A dramatic but often successful method of inducing breathing in a newborn kid to is to hold the kid by the hind legs and swing it backwards and forwards or over and over with the kid describing a circle. This forces fluid out of the lungs and is often enough to stimulate breathing. If newborn kids are too weak to suck their mother's teat, it will be necessary to feed colostrum via a stomach tube. Care should be exercised to ensure that the tube is in the oesophagus and not in the trachea. Insertion of the tube is facilitated by holding the kid's head up with the neck extended.

Turning up sheep: If sheep are to be controlled for a long time, they are turned up with bare hands. First, the handler should stand on the left side of the sheep and place his left hand under the sheep's jaw. He should keep his right hand free to place behind the animals buttocks should it try to run backwards. After steadying the animal in this position, the handler should pass his right hand over the back to the other side, as far under the belly as possible and grasp the wool. The sheep's forelegs should be raised off the ground with the left hand, and with right hand the animal should brough to a sitting position on its hind legs and supported against the handler's legs. Hornless sheep are held in this position by holding their forcannons, while horned sheep can be held by their horns.