Gordon King, Animal Science Department, University of Guelph, Canada

The Importance of Reproductive Performance

No presently available procedure allows prediction of current or future fertility. Thus, accurate monitoring of immediate past performance is essential to identify problems quickly and to initiate solutions before consequences become too severe. Some considerations for the assessment of performance and suggestions for problem solving are presented later in this section.

Boar Selection

• The boars have more impact than the females. Select wisely and carefully.
• Concentrate on performance trait(s) of economic importance and select from source that test or record as many boars as possible (high selection intensity)
• Make certain only healthy replacements selected. This is especially critical if boars are purchased.
• Select for physical soundness: strong feet and legs, watch them walk, no buckling of front legs or stiffness in hind. Boar must have good general conformation and willingness to breed (good libido).

Boar Management

• Feed to keep fit, not fat, usually receive sow gestating diet;
• If purchased, isolate for 3-6 weeks, allow 3-4 weeks to settle in;
• Can use to breed at 6-7 months of age - occasional service;
• Ensure that first mating is successful. Use a small, quiet sow or gilt in good estrus.
• Mating in boar's pen may be the best location since the male is not distracted by new surroundings.
• Wait until 7-8 months of age before regular use, 2-4 times per week until one year of age.
• Mature boars can perform 6-10 services per week.

Boar to Sow-Gilt Ratios

AI + natural - 1 boar for every 20-30 females

All AI - 1 boar for every 40-50 females. Larger herds require fewer boar's

Gilt Management

• Select from dams with good prolificacy and mothering ability.
• Important traits are sound feet & legs, good growth rate & back fat, 14 or more well spaced teats with none inverted and sexually mature by 220 days of age.
• Within herd selection makes genetic evaluation easier and provides fewer health concerns but must watch out for inbreeding.
• Purchase from other breeder or hybrid producing company simplifies within herd breeding program but should make certain of genetic quality and health status
• Isolate all additions for 3-4 weeks.

Factors Influencing Puberty

Nutrition
- restricted feed intake can delay puberty slightly.
recommend to allow only 0.5 kg gain per day after market weight.
- obesity interferes with normal ovarian function.

Distress
- moving or mixing gilts - fight
- tends to cause puberty 4-7 days later
- contact with boars may advance puberty
- related to pheromones
- direct exposure most effective
- exposure should not be too early (after 155 days of age)
- older boars more effective.

Light
- some evidence for advantage of increase light
- may decrease age at puberty
- may increase litter size

When to mate

• litter size related to number of heats more than age or weight
• fewest ova at first estrus (heat) = smallest potential litter
• increase by about 1 ovum each for 2nd, 3rd heat so potential litter size increases
• normally breed in 2nd or 3rd heat so gilts farrow by 10-11 months of age.

Selecting the proper time to breed replacement gilts is an important part of reproductive management. A few precocious females may begin estrous cycles and show estrous signs by five months but most do not reach sexual maturity until around six months of age. Since the ovulation rate increases at each subsequent estrus period, many farmers delay mating until the second or even the third cycle to increase litter size. Although the number of piglets born will increase if mating is postponed, there are other factors to consider in making the decision about when to mate gilts. The results from a number of research trials comparing litter size after mating at the first or third estrus are shown in the following table.

	Mating estrus		Piglet increase per day of delayed mating
	First	Third
Brooks & Cole, Livst. Prod. Sci. 7:67	8.8	9.9	0.026
Pay & Davis, Anim. Prod. 17:85	7.9	9.3	0.033
MacPherson et al, Anim. Prod. 24:333	8.4	10.4	0.062
Young & King, J. Anim. Sci. 53:19	9.6	10.6	0.023

Mating gilts on the third observed estrus resulted in larger litters but also required feeding the dams for an additional six weeks. Depending on costs for feed and housing, the extra piglets may or may not compensate for the additional expenses.

Pregnancy rates were 69.6% for animals bred at first estrus and 77.4% when mated at the third estrus in the study conducted by Young and King. Although this difference was not statistically significant in this trial, subsequent experience also indicated a somewhat lower fertility at the first cycle. An even lower pregnancy rate is usually obtained in the University of Guelph research herd when sexual maturity is induced with hormone injections (about 55% for six month old gilts inseminated on the induced estrus vs. 80% in sows).

Perhaps the best practical advice for producers is to wait for the second or later heat whenever this is convenient. However, if replacement animals are needed to fill groups and no older females are available, gilts can be mated on their first estrus. If gilts are mated at the first cycle, use herd boars rather than expensive semen purchased from an outside supplier.

Estrous signs

• Swelling, reddening of vulva - not positive
• Ears erect (especially in Yorkshire breed)
• Standing reflex - response to pressure on back (see Back Pressure Test described below). Boar presence may be necessary, especially for gilts
• Allows mounting and copulation
• Characteristic grunt (or song)

Good Practices for Detecting Estrus

• Use a sexually motivated boar in an adjacent pen or introduce the boar directly into the pen containing the females to be tested.
• Boars used for estrus testing should be 9 months of age or older.
• Be certain that the boar is familiar with and comfortable working in the testing environment.
• Allow sufficient time to do a thorough job in all pens.
• Change boars regularly.
• Allow no more than 15 - 20 seconds of vigorous courtship.
• Supervise the testing procedure at all times.
• Keep accurate records of weaning, suspicious and actual mating dates.

Back Pressure Test

• Whenever possible, allow boar and females to have head-to-head access through pen partition or gate.
• If in or very near estrus, a female should show definite interest in the boar almost immediately.
• Rub the interested female's flanks and scratch her back.
• Gently put firm pressure on loin region or sit on her rump. Animals in estrus will allow this but others will not. A positive response is when any female stands still and allows the tester to place full weight on her back, Gilts may only respond if a boar is near. Most sows will show a positive response anytime that they are in estrus.
• Retest any animals showing suspicious signs in a few hours.

Mating Practices

• Group recently weaned sows and replacement gilts near boars.
• Design all pens for easy access to facilitate entry and exit of both people and animals during estrus detection and mating.
• A proper mating area requires ample space for all courtship and mating activities.
• Provide nonslip footing with roughened concrete and sand or grit spread as needed.
• Remove any objects or projections, such as feeders or nipple drinkers, that might cause injury during courtship-mating.
• Try to mate animals of approximately equal sizes.
• It is perhaps best to move the female into the boar's pen for mating since she may be easier to get out after the mating.
• Supervise all matings to insure that the boar's penis penetrates into the vagina, not into the anus.
• A proper mating-ejaculation sequence should last at least three minutes. If shorter, repeat the service.
• Remove the female quickly after the boar dismounts unless the copulation was interrupted before three minutes.
• Always be gentle when handling animals.
• Record all events accurately and quickly.

Timing & number of services

• Ovulation occurs about 36-40 hours after the beginning of standing heat
• Optimum insemination is 6-12 hours prior to ovulation
• Therefore, mate 24 hours after initiation of standing heat and rebreed 8-16 hours later if female will still accept the boar or is still showing a positive (standing) response to the Back Pressure Test.
• A different boar might be used at each service if breeding only for market pigs.

Feeding Replacement Gilts

• If gilts are placed on a restricted level after selection, increase feed intake by 50% 10-14 days before breeding. This process, called flushing, might increase ovulation rate.
• If flushed, reduce feed intake after breeding
• Some believe that heavy feeding during early gestation increases embryonic loss but most evidence indicates that this is not true!

Housing for Breeding Females

• Group housing is preferred.
• Tethering or over-crowded confinement hampers breeding ability through difficulties in detecting estrus

Pregnancy Diagnosis

Sows and replacement gilts require considerable attention in the mating area but only casual observation once they are pregnant. Thus, producers usually place pregnant females in a gestating area but need some reliable method to check that conception occurred before animals are moved from the mating unit. All attendants should be aware that domesticated animals rarely exhibit any signs of sexual behavior one cycle interval after a fertile mating. Thus, for animals mated on known dates, demonstration of sexual receptivity when the next estrus period is due indicates no conception from the previous service. In contrast, the absence of sexual behavior is strong evidence for pregnancy. Sows and replacement gilts should remain in the mating area, with daily boar contact to check for estrus, for around 25 days after service. Once they pass three weeks without estrus signs they can be presumed pregnant and moved to the gestating area.

Other methods for pregnancy testing are also available.

Livestock producers must recognize that there is one inherent problem that will continue to be associated with even the most reliable pregnancy test. No matter how accurate the procedure, the results are only valid for the time when the sample was collected or the physical examination conducted. There can be no guarantee that the embryonic or fetal piglets present at the time of testing will continue to develop normally throughout the remainder of gestation.

Early Embryonic Mortality

Preparation for Farrowing

• Follow an All-In All-Out system.
• Treat females with anthelmintic about 3-4 weeks before they are due.
• Feed a laxative diet for the week before moving into the farrowing crate or pen.
• Thoroughly clean and disinfect all farrowing crates between occupants
• Wash the sow thoroughly to remove dirt and parasite eggs and place in the farrowing location about one week before her expected date of parturition.

Go to section on farrowing considerations.

Seasonal Influences on Pig Reproduction

Assessing Reproductive Performance

Many producers delude themselves, or try to impress their neighbors, by omitting culled females and gilts from the calculation. However, all members of the breeding herd are part of the overhead and should be included in any efficiency calculation. Gilts may be added to the monthly inventory as soon as they pass market weight and are retained as potential breeding stock or when they are first mated. When the performance is calculated on an annual basis, proportional figures can be used for females kept for periods less than a full year. Litter sizes are sometimes calculated and even published in official production statistics with gilt litters excluded. Since gilts produce 30 to 50% of total litters in commercial piggeries, such figures may look impressive but are quite misleading.

Another simple way to monitor productivity of a large continuously farrowing sow unit is by calculation of the Piglets Weaned per Sow per Month in operations where weaner pigs are sold or Finished Animals Marketed per Sow per Month in Farrow-to Finish herds. The actual number of piglets weaned or marketed is divided by the total number of mature females on the herd inventory. A monthly average of 1.7 corresponds to over 20 piglets per sow per year and this figure should be maintained or exceeded in most problem-free operations.

Suggestions for Performance Targets and Potential Problem Values for Pig Reproduction

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