Principles of pig production

Feeding and digestion 

The first 72 hours after birth are very critical for the baby pig. During this period the colostrums of the sow has a high content of antibodies and the piglet intestine is able to absorb intact proteins. As the piglet has very little of its own resistance to disease, it is essential that it gets a good suck of colostrums andacquires passive immunity from the sow. 
Failure to take in sufficient colostrums will invariably result in the pig succumbing to infection before it can develop active immunity of its own. Once the piglet has established a teat position, which normally occurs in the first 24 hours after farrowing, it will retain this position for the remainder of the suckling period. As long as milk production continues the dam suckles her litter every 60 to 90 minutes. 

Pig's Alimentary canal 

Although pigs in tropical regions may eat a lot of fibre they are simple�stomached animals and not ruminants which possess a complex stomach with a large microbial population which enables them to digest large quantities of fibrous material. Thus, their ability to digest and utilize fibre is restricted to that digested by the microbial population in the caecum which is of relatively small volume when compared with the rumen. It has been claimed that unimproved breeds found in Africa have 
an enhanced ability to utilize fibrous feeds compared with exotic breeds. 
While this may be so to a small extent, there are no anatomical differences of the digestive tract between the two types. Accordingly, with all pigs, high-fibre diets will have the effect of diluting the amount 
of nutrients available to the animal. In contrast to ruminants, pigs are unable to utilize non-protein sources of nitrogen for the production of microbial protein in the rumen. This makes them dependent on both the amount and quantity of protein in their diet. 
The alimentary tract of the pig is designed to digest and absorb concentrate feeds. Feed taken in at the mouth is ground into a pulp by mastication. At the same time it is moistened and mixed with saliva. 
Saliva contains the enzyme ptyalin which initiates the breakdown of starch to simpler carbohydrates. The feed then passes on into the stomach, which provides an acid environment due to the presence of hydrochloric acid. The gastric juice contains the enzyme pepsin which 
begins the breakdown of protein.
The small intestine is the major site where feed absorption occurs and digestive juices from the pancreas, liver and the small intestine complete the process of digestion as follows. 
Starch is hydrolyzed to maltose byamylase from the pancreatic juice. 
Specific enzymes break down maltose and other disaccharide sugars in the intestinal juice, e.g. maltase, lactase and sucrose into monosaccharides such as glucose and fructose. These are then absorbed 
through the gut wall. 
Trypsin in the pancreatic juice acts on protein to produce polypeptides, which are then broken down to amino acids by various peptidases in the intestinal juice and subsequently absorbed. 
Bile, which is secreted by the liver, serves to emulsify fats into smaller globules, which are then broken down by the enzymes lipase into fatty acids and glycerol ready for absorption. Lipase is present in both the pancreatic and intestinal juices. 
Pigs are omnivores and will consume a wide range of feeds from both plant and animal sources. The natural inclination of the pig is to eat on a ‘little and often’ basis, and this is likely to maximize both total feed intake and the efficiency of feed utilisation. 

Growth and Development of pigs

In practical terms, growth is measured as the increase in body weight with time, and is largely dependent on the amount of feed or total nutrient intake. However, there are major differences between the feed 
intake of different breeds of pig and this affects their growth response per unit of feed ingested. Because man has selected pigs for high growth rates in order to improve biological efficiency, he has selected for a large mature size. In consequence, unimproved types of pig common in developing parts of the world which have not been selected for increased growth rates will tend to grow more slowly to a smaller mature size 
when compared with improved breeds. It follows that if unimproved pigs are slaughtered at the same weight as their exotic counterparts, they will be relatively more mature and therefore at a different stage of development. 
Equally important as rate of growth is how the pig develops. Selection has resulted in a greater propensity to lay down protein tissue in improved breeds. Thus the plateau for maximum growth potential in an improved breed can be 600g compared with 400 g for an unimproved pig. As the level of feed intake increase, the unimproved pigs will deposit more fat in comparison with improved types. Because too much fat is neither a consumer desirable, nor is it cheap to produce  (approximately five times the nutrient cost of lean tissue deposition), it is critical that pigs are fed according to their ability to grow and lay down lean tissue. 
Entire male pigs grow faster; have leaner bodies and convert feed more efficiently than females. If males are castrated the case is exactly opposite. Traditionally, pigs have been castrated in order to improve 
carcass quality and to prevent boar ‘taint’ or odour in the meat, which tends to occur as boars approach puberty. Nowadays, modern pigs grow faster and are slaughtered at younger ages and the problem of taint is considerably reduced. Unless pigs are grown slowly or are required for a highly sophisticated market, there would appear to be no justification for castration in pigs destined for meat production. 
Baby pigs are born with less than two per cent of fat in their bodies, which makes them particularly susceptible to cold stress. Thereafter they deposit fat rapidly, and will usually have a body fat level of over 15 per cent by the time they are three weeks old. This serves as a reserve of 
energy as they adapt to a reduction in milk intake and to overcome the stress associated with weaning. 

Reproduction in pigs

Males pig reproductive system 

The male reproductive system is characterised by a pair of relatively large testes, which can weigh over 300 g each in some exotic breeds. 
Together with the secretions from the accessory sex glands, the testes can produce up to a liter of semen in a single ejaculate. 
To facilitate the transfer of these large quantities of semen at coitus, the end of the penis of the boar is spiral in shape which enables it to lock, into the cervix of the sow. The duration of coitus varies but may last for 20 minutes. 
Puberty, or the ability of the boar to serve a sow, generally occurs around four months of age, but may be earlier in unimproved breeds. 
However, boars should not normally be used until seven months old. 
Young boars are susceptible to bullying by mature sows. And this may adversely affect their subsequently mating performance. 

Reproductive system of Female pigs

The female reproductive tract is distinguished from other farm species 
by the long, convoluted uterine horns (700 to 800 mm in length), which are designed to accommodate large numbers of foetus. The sow will ovulate simultaneously from both ovaries, normally shedding between 
11 and 24 eggs. Puberty, marked by the onset of oestrous cycles, occurs between five and seven months, but may be as early as three months in unimproved breeds. The number of eggs shed at ovulation, and therefore potential litter-size, increases gradually over the first few oestrous cycles. 
The sow will cycle and show heat every 21 days (range 18 –24). She will not cycle when she is either pregnant or lactating, although sows will sometimes show heat during lactation when run in groups. A heat last from one to three days, and ovulation occurs by the second day of 
estrous or any time thereafter. 
After coitus and fertilization have occurred, the embryos space themselves evenly throughout the entire uterus before implantation. 
Competition for space, nutrients and other unknown factors results in uneven growth rates in utero, which gives rise to variation in piglet birth weight. The lighter pigs then suffer a disadvantage in the competition of early post-natal life. This problem tends to be accentuated in older sows, due to the effects of wear and tear on the uterus. 
Pregnancy lasts for 114 days but will tend to be extended slightly with smaller litters. Farrowing may vary in duration from 2 to 24 hours and will tend to be longer the more piglets that are produced. However, due to the relative difference in size between piglets and the dam, and the 
type of placentation in sows, farrowing is normally a straightforward process. The incidence of stillborn piglets, which may be due either to death in utero or during the birth process, is greater in large than in smaller litters. 
Overall, reproduction in the sow results from a complex hormonal interplay between the brain, the pituitary gland, the ovaries and the uterus. These complex relationships must be borne in mind by the pig keepers when management strategies are designed, otherwise optimum reproductive performance by the sow will not be achieved. 

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