Swine Reproduction Papers
Introducing replacement gilts into a breeding herd is necessary and desirable for making genetic improvement and when replacing less productive sows. However, along with the benefits of replacement, gilts do have lowered reproductive performance when compared to sows of higher parities (2-8). Problems associated with gilt breeding include: greater difficulty in identifying estrus females due to inexperienced sexual behavior, short estrus, higher anxiety and fear levels, higher levels of anestrus, delayed puberty, difficulty in breeding due to an intact hymen, smaller reproductive organ size, lowered reproductive rates due to lowered ovulation rate, shorter interval from estrus to ovulation, reproductive tract abnormalities, and lower pregnancy rates and litter sizes, and higher incidence of stillborn pigs. Collectively, these factors severely limit reproductive performance in gilts.
Detection of Estrus
Detection of estrus in gilts is more difficult than sows. Certain factors can inhibit expression (or detection) of estrus in gilts. Some factors that inhibit detection are feeding, stress (crowding), and fear. Do not detect estrus near feeding time. Remove all feed from the detection area. Gilts should not be moved to a new or novel pen at time of estrus, since exploratory behaviors can predominate over sexual behaviors. The primary problems involve inappropriate boar exposure. Excessive boar exposure from housing females too close (adjacent) or for too long, leaving boars next to or with gilts for too long before checking for estrus, induces refractory behavior. This results when females in estrus fail to stand for boar and occurs because physiologically, females cannot sustain muscle rigidity for much longer than 15-30 minutes at a time. In contrast, too little boar exposure from an inactive or immature boar (less than 8 months of age), for too short of a time period, or at too great a distance from the gilts, may not provide the necessary stimuli to allow expression of estrus.
Breeding the Gilt
Natural breeding of gilts is achieved by placing a boar of similar size (weight) in with the female. Females that are not in estrus tend to move away and squeal when mounted. These females should be removed to prevent physical harm from occurring when and an excited boar attempts to mount or flank stimulate the gilt. A gilt in estrus will become immobilized when physical contact with the male is established. This detection period may require can take from 2-10 minutes. For a female that is in estrus, the male will often mount and once he extends the penis, will insert it into the female vagina. Sometimes, there remains an intact hymen. This is a thin tissue membrane that will tear at 1st breeding. This is sometimes painful for the gilt, and she may not allow intromission again until the next day of estrus. In other females, no pain is evident when the hymen is ruptured.
AI of gilts is standard with respect to timing and procedures. However, the insertion of the catheter is somewhat more snug due to the smaller size of the reproductive tract and the cervix. The type of catheter does not influence the effectiveness of AI in gilts. Two to three AI doses are usually required to produce optimal pregnancy rates, although the third dose provides little significant effect on pregnancy rate or litter size. Gilts should only be mated that exhibit the standing response. Time the AI doses relative to estrous detection frequency. For example if once daily detection is practiced, then AI should occur at roughly 0-12 and 24-36 hours after onset of estrus.