"Management" is often a catchall for production problems that do not fit in other areas. Improving reproduction requires attention to careful management of the replacement gilt and many details not easily categorized.
Gilt pool concept. With confinement farrowing facilities, it is important to maintain the size of each sow group to use the farrowing barn efficiently. We know that some sows will not conceive. Therefore, the producer should keep a group of gilts, the gilt pool, ready to breed with each sow group.
The number of gilts in the pool must be large enough to cover the sows culled for poor performance, structural or reproductive unsoundness, non-cycling, or poor conception. The size of this gilt pool depends on: culling rate of sows, conception rate of sows, conception rate of gilts, percentage of gilts cycling normally, percentage of gilts cycling per day, and length of breeding period.
If a producer routinely culled four sows in a sixteen-sow group, bred for 5 days, maintained a 75-percent conception rate in the sows and 65-percent in the gilts, he or she would need 47 gilts in the gilt pool for each group or 6 to 7 gilts per sow culled (see equations below). This number would ensure that enough females would be available for the maintenance of the sow group. The farrowing facilities will then be used at full capacity.
| To determine the number of gilts needed to farrow: | |
Number sows per group less sows culled |
= Number sows for breeding |
Number sows for breeding X conception rate |
= Number sows to farrow |
Number sows per group less number sows to farrow |
= Number gilts needed to farrow |
| To determine gilt pool size: | |
Number gilts needed to farrow / conception rate (gilts) |
= Number gilts to breed |
Number gilts to breed X (days in breeding period / 21) |
= Number gilts needed in gilt pool |
Stimulating and synchronizing estrus. Very seldom are only one or two gilts needed for breeding at one time. Normally, a group of gilts is needed to ensure that every farrowing crate is full. There are several ways to trigger heat in a group of gilts.
Research has shown that moving gilts will stimulate heat. Moving gilts from confinement finishing facilities to dirt lots and loading them in a truck or trailer and hauling them to the gilt pool area will stimulate estrus in 15 to 50 percent within 4 to 6 days after moving. Fence-line contact with a mature boar also stimulates onset of estrus. In gilts 165 days of age or older, 30 to 90 percent of the gilts will cycle within 3 to 7 days after initial contact.
One product, P.G. 600, is approved for "induction of fertile estrus (heat) in healthy prepuberal (non-cycling) gilts over 165 days of age and weighing over 187 pounds." According to the product information, most gilts will show fertile heat in 3 to 7 days after the injection. Most lean gilts should be bred on the second or third heat period to maintain proper body condition later in life. P.G. 600 is also approved for inducing estrus in sows experiencing a delay to estrus after weaning. According to the company, "sows treated with P.G. 600 at weaning are nearly two times more likely to return to estrus within 3 to 7 days than untreated sows." See your veterinarian for more information on this product.
Age at puberty. Selecting gilts that cycle earlier will gradually decrease the age at puberty. More rapid changes can be made by improving management. Overcrowding can delay puberty. During the finishing stage, gilts should be allotted at least 8 square feet per animal and group size limited to twenty-four animals per pen. Confinement can also increase the age at puberty. Moving gilts from confinement to drylots at 180 to 200 pounds will reduce this effect.
Age at breeding. The best time to breed a gilt depends on her age and weight. Breeding too early may cause problems with the second and third litters. Waiting too long to breed a gilt increases production costs and can result in lower productivity from the gilt.
For gilts from high-producing sow lines, age and weight at breeding is even more critical. Average gilts should not be bred before they reach 230 to 250 pounds. Gilts from high-producing lines should weigh 250 to 300 pounds. This means breeding on the second estrus or heat. The 3-week wait should be offset by increased litter size and fewer problems with future litters.
Heat detection. Heat detection in sows can be difficult. In some gilts, it is impossible. About 10 percent of all gilts fail to show heat. Some do not cycle at all, while others cycle but show no outward signs of estrus. Whether breeding gilts or sows, using good heat detection methods following stimulation and synchronization of heat (such as weaning) can increase the number of females bred.
The best way to test for heat is with a boar. Heat can be determined using the boar or hand pressure on the gilt's back in the presence of a boar. For best results, both methods should be used. It is possible to detect heat visually without a boar, but two to four times more females show heat in the presence of a boar.
Time to breed. Standing heat usually lasts no more than 48 hours in gilts and 48 to 72 hours in sows. Ovulation occurs from 36 to 42 hours after the onset of heat. The time of breeding in relation to ovulation affects both conception rate and litter size.
Ideally, a sow or gilt should be bred so the sperm can reach the site of fertilization at the time of ovulation. Breeding too early or too late will result in reduced litter size and lowered conception rate. If heat is checked twice daily, sows should be bred 12 and 36 hours after heat is detected. Breed gilts when heat is detected and 12 hours later. If heat is checked once a day, breed sows and gilts when heat is detected and 24 hours later. In the summer, sows and gilts should be bred when heat is detected and 12 to 24 hours later.
Pen breeding. There is less control over time of breeding, age of breeding, and the number of services when pen-breeding. However, there are ways to improve reproduction. It is important to provide at least one mature boar for every ten females if they cycle throughout a 21-day breeding period. If estrus is synchronized in any way (weaning, transportation), you need more boars. The boars must also be fertile and willing to breed. Boars should be rotated at least every 12 hours.
Boar size. Some gilts, especially smaller gilts, cannot stand up under a large boar. They might be in standing heat, but they will move away from the boar. For best results, gilts should be bred to boars weighing 350 to 400 pounds. Avoid using large mature boars and inexperienced young boars.
Boar use. There are limits to using a boar when improving reproductive efficiency. Use young boars (less than 12 months of age) only once a day and no more than five services a week. Mature boars over 12 months can service two times a day, but no more than 7 times a week. If you wean sows in groups, you need one young boar per sow or one mature boar for every three sows. For continuous weaning programs, you need two young boars or one mature boar for every ten sows.
Boar fertility. Temperature, disease, and use can affect boar fertility. Elevated body temperatures resulting from heat stress or disease result in the production of non-viable sperm. The reduced fertility will last as long as 45 to 55 days. Overuse, as mentioned earlier, also reduces fertility by reducing sperm numbers and motility.
A breeding soundness examination conducted by a qualified technician or veterinarian, will identify problem boars. If fertility does not improve, problem boars should be culled.
Pregnancy checking. Breeding is not complete until it is certain a sow or gilt is pregnant. Bred females should be heat-checked with a teaser boar 18 to 24 days after first breeding. Any sow showing heat can then be rebred or culled. She should not be allowed to waste another 300 to 400 pounds of feed during gestation. Pregnancy can be detected electronically 36 to 48 days after breeding. Sows or gilts with a negative test can then be culled, again saving feed, labor, and space.
The producer can take several steps to improve reproductive efficiency during farrowing and lactation. First, move sows and gilts into the farrowing facility 3 to 5 days before they are due to farrow. This reduces some behavior problems by allowing the female to become accustomed to the new environment. It also makes routine observations easier.
Next, have someone present during the actual farrowing process. Attended farrowings result in an extra live pig per litter, on the average. It is especially important to have someone in the farrowing facility when gilts are farrowing. The farrowing process is a new experience for a gilt, and her instincts are not adequate to handle the trauma of birth in some cases. Some gilts are nervous throughout parturition and will, on occasion, bite at pigs venturing close to the front of the crate. You may want to remove the pigs as they are born, place them in a warm, dry area until farrowing is complete, and then put them back with the gilt. Very rarely will a gilt attack her pigs after farrowing. If a gilt does so, her pigs should be moved to other sows, and she should be culled.
Farrowing difficulties require care and, in some cases, a well-trained veterinarian. All too often, a producer will wait until all hope is lost for the pigs or sow before calling a vet. Oxytocin should be used with caution. Most farrowing difficulties are caused by one extremely large pig in the litter becoming lodged in the birth canal. Administering oxytocin will only make the situation worse, further lodging the pig. If a stuck pig cannot be easily pulled, then a vet should be called. While vets are expensive, their bills are often offset by the cost of replacing a gilt or sow and her litter.
Last, the environment and farrowing-lactation diet must allow for adequate
feed intake. During most of the year, some type of sow cooling is necessary.
Sow feeders should be cleaned and waterers checked daily. During the spring,
summer, and fall, sows fed 4 pounds of feed three times a day will eat more
than sows fed 12 pounds at one time. As in gestation, daily feed intake
should be monitored. Reductions in intake are the first sign of problems.
Low intake during lactation reduces body condition and increases the time
required for a sow to cycle. Sows with less than 0.60 inches of backfat
at weaning, with prominent hook bones (point of the hip), or in poor condition
at weaning are an indication of inadequate feed in lactation.