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)

Parts of digestive tract

The digestive tract, also known as the alimentary canal, is a tube like structure extending from the mouth to anus. The different parts of the digestive tracts of ruminants and non-ruminants are illustrated in figures. The alimentary canal is comprised of the following parts,

1. Mouth (lips, tongue, gums and teeth) and pharynx
2. Oesophagus
3. Stomach (In ruminants, the stomach includes the rumen, reticulum, omasum, and abomasum)
4. Small intestine (duodenum, jejunum, and ileum)
5. Large intestine (caecum, colon, and rectum)
6. Anus

In addition to the above, the following accessory organs/glands also take part in the process of digestion: salivary glands, liver, gall bladder, and pancreas.

Among domestic animals, the proportion of the digestive tract to total body weight is higher in ruminants than in non-ruminants, as shown in table. Horses, for example, have a large caecum (15.6% of the total alimentary tract) where extensive microbial fermentation of plant materials takes place. Similarly, rabbits also have a well developed caecum. In ruminants, the stomach compartments (rumen, reticulum, omasum, and abomasum) occupy the major part (62%) of the digestive tract. Large variations in the proportion of different parts of the digestive tract in farm animals reflect differences in their feeding habits. These variations have evolved over time, and the animals have gradually adapted to various feed resources.

	Cattle	Buffaloes	Sheep/Goats	Horses	Dogs
Body Weight (Kg)	450	600	50	450	20
	Volume in liters, and proportion of body weight (percent)
Stomach
Reticulo-rumen	97.6 (48)	130.3 (48)	10.7 (56.7)	-	-
Omasum	15.8 (7.6)	20.9 (7.6)	0.6 (3.3)	-	-
Abomasum	11.8 (5.8)	15.7 (5.8)	1.3 (6.7)	8.0 (8.9)	1.0 (63)
Small Intestine	50.9 (25)	67.7 (25)	3.8 (20)	27.0 (30.0)	0.37 (23.0)
Caecum	7.7 (3.8)	10.3 (3.8)	0.6 (3.3)	14.0 (15.6)	0.02 (1.0)
Large Intestine	19.7 (9.5)	26.0 (9.5)	1.9 (10.0)	41.0 (45.6)	0.21 (13.0)
Total	203.5	270.9	18.9	90.0	1.6

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.

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.

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.

Transporting livestock by train and vehicle

Transport facilities for livestock are grossly inadequate in Pakistan. The stock owner has to use one of five ways to transport: by ship, train, plane, vehicle, or hoof. Transport by plane or ship, of course, isi usually reserved for costly race horses, zoo animals, and imported pure bred exotic cattle, etc. For long distances, rail transport, affords a savings on maintenance and handling charges, tolls, and other incidental expenses. Also, weight loss and death, potential consequences of transport by foot, can be avoided.
If rail transport is chosen, the wagons which are to carry livestock should always have a roof, provide for free passage of air, and have battened or non-slippery floors. In Pakistan wagons used for goods transport are generally used for transport of animals too. In such a wagon a 10 - 15 cm thick layer of sand should be spread on the floor. This prevents the animals from slipping, soaks up urine and makes lying down comfortable. The side doors should be left open for ventilation. Partitions of suitable size should be made using wooden poles to keep the animals on their feet while the train is moving.
Sheep should be packed in a wagon closely enough to prevent them from being thrown about during transit. Animals should be so grouped that those of approximately the same size and condition are loaded together. Horned cattle should be secured by the horns to the side of the wagon. They should stand head to tail so that alternate animals face the opposite directions.
It is necessary to carry the local feed and utensils for feeding, watering, and milking of animals during the journey. Two experienced attendants who can perform these tasks should accompany the wagon or truck load. Simple medicines for diarrhoea, bloat, fever, and injury should also be carried.
In the winter, the stock should be watered every 12 hours, once in the morning and once in the evening. In the summer, watering frequency should be at least three times a day. When a journey is of more than three days, off-loading for feed and rest is essential to maintain the health and well-being of animals.
Transport of livestock by vehicle has many advantages. It is very convenient to load the animals at the farm and directly transport them to their destination. Thus, the problems of repeated handling and associated disturbances, such as weight loss, can be avoided. On the other hand, if the journey is long and the roads unsurfaced, the cost of transport per Km is somewhat greater than it is by rail, and an extra strain is placed on the animals. Nevertheless, the advantages of vehicle transport outweigh the truck can then be taken to an earthen mound or any other raised geoplogical feature of convenient height and the animals loaded from the mound.
The precautions to be followed while transporting livestock by road are the same as for rail transport. An ordinary goods truck can take four to five cattle and buffaloes, or 20-25 small animals depending on their age and condition.
If goats are being transported in a vehicle, they should not be allowed too much space, otherwise they will be knocked against the sides as the vehicle moves. If only a few are to be transported, spare space can be filled with bales of straw. These must be firmly tied in place and should not provide the goats with any climbable surfaces or ledges. The ideal floor is a rubber mat covered with a thin layer of straw. Horned and dehorned goats should not be carried together in the same compartment. Goats should never be transported in a vehicle without a division between them and the driver.

Transporting animals: Sheep and Cattle

It is much easier to move a group of sheep than to try to separate one or a few from a flock. It is sometimes more efficient to sort (draft or cut a small group from a large flock using a gate. A well trained dog or another person is essential. It is often easier to take the whole group to the yards even when just a few are needed.
There is a high risk of smothering when a large group of sheep is run through a narrow gap, such as a gate in a rotational grazing system. The risk is reduced by adopting the following measures.

1. Move the group uphill where possible
2. Place a person immediately before the gap to cut off the flow
3. Be particularly careful when a downhill movement leads to a stream crossing, culvert, gate, or other narrow area
4. Stresses such as the presence of dogs and noise should be eliminated if possible to let the sheep look ahead to see where they are going. When there is too much stress, sheep mill around climb on each other's backs.

Sheep can be driven easily by dogs or people. Sheep that are kept in restricted spaces like fields learn to respond to dogs by forming a group. Feral sheep, on the other hand scatter when attempts are made to muster them with dogs. Once domestic sheep are in a group, they try to maintain a certain distance (flight distance) between themselves and the dog and so move away on the dog's approach. Single sheep also maintain a flight distance. Whey they cannot escape, they are likely to turn and face the dog or run past it to escape from confinement.
When driving sheep along public roads, have one person at the front to warn oncoming traffic and control the rate of movement and a more experienced person behind to move them forward. Sheep are "followers" animals, and will therefore naturally follow other sheep. They will also follow people who feed them regularly.
For cattle and buffaloes, as well as sheep, driving is the most economical way to move the animals, at least for short distances. It is essential that an adequate supply of food and water be available at suitable points along the route. All farm stock should be kept to a a well defined track because,

1. Facilities for feeding and watering will often be available, 
2. Wandering animals may spread diseases in the region through which they pass and can be properly checked by authorities on well defined roads.

Animals lose body weight while moving, THis loss can be minimized by proper scheduling of feeding and watering. Indigenous cattle are well served if ad libitum water supply points are locaated about 20 Km apart. Mutton sheep going to market should get water at intervals of about 10 Km, otherwise they will lose a large amount of body weight.
Cattle, including buffaloes, can be driven easily for about 30 - 35 Km a day, and sheep for half that distance. In summer, driving during the hottest part of day should be avoided. Whenever possible, animals should be driven on soft ground and not on hard roads.

Handling Animals: Sheep

Preparation: Prior to actual handling, it is wise to have though through all the tasks and possible responses of the sheep. Are all the facilities, tools, chemicals, and protective clothing ready? Are there sufficient people on hand having the necessary skill? Is the route ready, with all unnecessary avenues blocked off? Once handling has started, such preparation helps the job to go smoothly and lessens delay due to unforeseen events.
Risk of injury: Because of the relatively small size of sheep, we tend to lift and move them manually, often with a bent back. Such action may cause low-grade back injury with a cumulative effect.
Although sheep are generally not aggressive towards people, they sometimes cause injuries. Rams, particularly during the mating season, may attack with sufficient force to cause serious leg or back injury. Remember that sheep do not sense their environment in the same way as humans. They have eyes at the sides of their heads and can almost see behind themselves without turning their heads.
Arousal: Here are some common factors that tend to incite or arouse sheep:

1. Visual isolation from other sheep
2. Proximity of dogs or people
3. Hunger or thirst
4. Sexual activity
5. New environments
6. Unusual loud or high frequency sounds

The following factors decrease arousal:

1. Proximity of other sheep
2. Low-frequency noises such as the "rumble" call of a ewe to her lamb, or the courting ram to an oestrous ewe
3. Low illumination, as in covered yards.

Handling and restraining of farm animals

Handling, controlling, restraining, transporting, and casting farm animals sometimes causes them distress even when they are being well managed. Three principles should be kept in mind when conducting these procedures to avoid harming the animals or affecting their productivity.
- The stock man should try to minimize any stress experienced by the animals or the workers handling them.
- These procedures should be carried out in such a manner that the animal are not injured.
- These procedures should be carried out in such a way that the workers are not injured.
In order to meet these objectives, the stock man should ensure before starting that proper equipment is available for the procedure and that the equipment is clean and in good working order. He should know how to use the equipment properly, efficiently and quietly. People assisting a procedure should also know the procedure and feel comfortable while performing it. Fear is perhaps the most dangerous emotion when working with livestock, since a frightened person seldom considers the consequences of his actions. His fear may also be communicated to the animals and upset them, thus making handling more difficult.