The efficiency of piglet production is affected by four main factors:
- Length of lactation period: Reducing the lactation time reduces fertility and number of piglets born. However, the sooned the piglets are weaned, the sooner the sow comes into heat and can be inseminated.
- Time from weaning to insemination: Sows come into heat twice after weaning. First heat is two days after weaning, but insemination at that time does not lead to fertilization. The other heat is 4-7 days after weaning. If the sow is not inseminated then, it takes three weeks before it comes into heat again.
- Mortality of piglets: Reducing mortality directly increases piglet production. More piglets die in large farrows, so increasing farrow size is not the only solution.
- Number of piglets in a farrow: To avoid high mortality, large farrows must be evened out between lactating sows. Mortality rate can be over 40% in farrows of 18 piglets or more. Each sow has fourteen teats, so they cannot nurse more piglets than that. Breed of the sow also affects its "efficiency". Mixed breed sows (local breed + yorkshire) have larger farrows and have their first farrow younger than purebreds.
The ideal time to inseminate a sow for the first time is at 210-230 days of age. The sow's heat lasts 20-72 hours, usually 36-48 hours. Ovulation occurs 30-36 hours after the heat begins, but the eggs live only 8 hours after ovulation. Sows should be serviced (inseminated or mated) 10-30 hours after the heat starts, before the ovulation. Sperm cells need six hours in the uterus to adapt, before they can fertilize the eggs. If the sow is serviced during the optimum time, she will have a better chance of getting pregnant and a to have larger farrow.
Young sows release 10-20 eggs in one ovulation, and older sows 15-25 eggs. Free feeding before service increases the amount of eggs released. Eggs, which are fertilized, stay 12 days floating free in the uterus. Up to 30 % of the fertilized eggs will die during this phase.This phase is called preimplantation. The implantation phase is on days 13-40 from insemination. During implantation the eggs attach to the uterus, the placenta develops and fetuses are formed. The fetus phase lasts until the end of the pregnancy. Sows are pregnant "3/3/3": three months, three weeks and three days. Approximately 115 days after the insemination the sow will give birth.
In intensive production unproductive sows are easily culled. Culling unproductive sows is done to ensure profitability, but also to avoid unhealthy piglets. Sows are often removed, if
- they haven't come into heat at 8,5 months of age
- less than 18 piglets are weaned from their two first farrows
- the sum of days it takes for the sow to come into heat after two first farrowings is over 21 days
- it isn't pregnant after service during two heats
- it has farrowed twice or more, but produces less than 20 piglets a year
- the sow is ill, doesn't nurse the piglets, has feet problems or loses much weight during lactation
- there have been malformed or weak piglets in several farrows
- their estimated breeding value decreases
- they have farrowed more than six times, after which the litter size decreases
Nutrition of a pregnant and lactating sow
Each sow should be fed individually during gestation. In practice they follow two phase diet. During gestation, they need 40-43 MJ ME/day, gilts needing more than older sows. Sows with a lot of moving space need slightly more feed. The feed must be fibrous, so the sows need to spend time eating and feel more satiated. It should have 5 g of intestinally digestable lysine per feed unit, or 12-14 % of crude protein. The feed can be "lactation feed" which has been diluted with grains. Young sows need more feed than old, because they still grow themselves.Thin sows (condition score 2 or 3) can be given 3 units a day. Five days before farrowing the amount of feed is cut drastically to less than 2 units a day. This will empty the intestines of the sow, making farrowing easier. Hay or straw should be given freely to avoid constipation.
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Inadequate feeding during lactation increases the dry matter content of the milk, but decreases total milk yield and protein content. Underfed sows also lose more body fat and muscle. Their piglets grow less, and have less protein and more fat than piglets from an ideally fed sow. It is more effective for a sow to get energy using its own tissues than from feed, so some weight loss is likely even for an ideally fed sow.
See details from Formulating farm-specific swine diets (University of Minnesota).
Caring for pigletsPiglets are born without any immunity or ability to thermoregulate ( = to regulate their body temperature). The temperature inside the sow's womb is nearly 40 C, but only 20 C in the piggery, so piglets are cold and need a heat source to stay warm. The pen has to be clean, desinfected and have enough straw or other dry litter. New-born piglets weigh about 1,5 kilograms. 50-70 % of new-born piglets weighing less 800 g die soon after birth.
First born piglets get to the sow's teats sooner than others, and usually grow faster. They need colostrum during the first hours to build immunity, and to get energy for maintaining body heat. Colostrum is also rich in fat, lactose, vitamins, minerals and proteins. Piglets cannot mobilize their own tissues to get energy. Lack of milk causes the blood glucose level to drop, which makes the piglets drowsy and weak, and unable to seek nutrition. As their body heat and glucose levels continue to decrease, the piglets will fall into come and die. Weak and last-born piglets can be guided to the teats.
After the first week solid food should be offered to the piglets. For some piglets this becomes an important source of nutrition. Their intestinal epithelium, enzymatic activity and stomach acid formation develop faster if they get solid food in addition to milk. At weaning these piglets are better prepared to eat only solid feed. Their chance to get diarrhea and lose weight is decreased. They also may be calmer if they've used the feed as a stimulus. Best ingredients for piglet feed are wheat and peeled oats. Small amounts of oats, barley, and whey can also be used.
At three weeks of age the piglet starts to develop its own immune system, and is no longer dependent on milk. This is also the time they are weaned, and the stress combined with low level of immunity often causes diarrhea and even deaths. If the piglets are weak or small, it is recommended to postpone weaning until the piglets are four or five weeks old.