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INCREASE GILT REPRODUCTIVE EFFICIENCY

Introduction

A successful swine breeding unit is dependent upon the reproductive efficiency of the breeding herd.

Maintaining an optimum litter size at birth and increasing the overall efficiency of the breeding herd offer two good opportunities for assuring a productive swine unit. Because 30 to 40% of the sow herd is replaced by gilts each year, introduction of gilts into the breeding herd is an important aspect of herd productivity.

pig production is shifting from small, non-confined units to larger, total confinement units that may be foreign to the pig’s natural habitat. This environmental change and the selection for the meat-type pig may have altered the behavioral patterns and physiology of gilts.

To overcome the problems associated with introduction of gilts into the breeding herd, swine producers have established “gilt pools” to increase the probability of cyclic gilts for breeding.

Management for Pubertal Development

Several factors that influence puberty and the continuation of regular estrous cycles in gilts have been identified. These include

1) Detection of estrous

2) Genetics

3) Season of the year during sexual development

4) Confinement environment

5) Boar exposure,

6) Nutrition

7) Disease.

It has been concluded that under normal conditions of feeding and management, nutrition will have a minimal influence on gilt development.

Detection of Estrus.

The detection of estrous behavior in gilts is a critical factor for establishing puberty, estrous activity or breeding in gilts, and for the efficient operation of a swine breeding program. Detection of estrus is a simple technique. It involves placing the male and female pig in close proximity on a regular basis (once or twice daily) and observing behavioral changes in the female.

Moving a group of gilts once or twice daffy to a large pen, in the presence of a mature boar, has proved to be a satisfactory method.

Genetics.

The influence of individual breeds and mating systems on age at puberty in swine reared under non-confinement conditions has been reported differences in age at puberty associated with mating types within the purebred and crossbred systems, as well as the effect of heterosis on reducing age at puberty in swine.

Landrace gilts showed the highest estrous activity (number of gilts showing regular estrous cycles/number of gilts x 100) between 5 and 7 month of age, and the percentage of Landrace gilts showing regular estrous cycles at 6 month of age was higher (P<.01) than that of Hampshire, Large White, Yorkshire and Duroc gilts (69 vs. 11, 4, 3, 0%, respectively).

Therefore, introduction of early maturing breeds or crossbred lines may be advantageous for reducing age at first estrus in some herds.

Season.

Climatic conditions (season), whether modified by confinement management or not, are factors that influence the process of sexual development in gilts. It has studied reproductive tract development in slaughter-weight gilts throughout the year.

Collectively, these Studies suggest that the summer climatic conditions cause a delay in sexual development of gilts. However, in a continuous farrowing production system, swine of most reproductive stages (i.e., pubertal development, breeding, early and late gestation) are adversely influenced by summer climatic conditions; therefore from a managerial standpoint, it is difficult to avoid the adverse influence of summer climatic conditions.

Confinement Environment.

The shift from many small, non-confined swine production units to fewer larger, total confinement units has increased both the reproductive problems in gilts and our awareness of such problems.

Boar Exposure.

Exposure of gilts to a mature boar (12 month of age or older) induces puberty at an earlier age in non-confinement reared gilts and in confinement reared gilts than occurs for gilts isolated from boars. Zimmerman have reported that exposure to a mature boar enhances the synchrony of estrus among gilts, particularly if gilts are approaching pubertal age. But, puberty may be delayed if boar exposure is initiated when gilts are too young.

Management for Improved Ovulation Rate

Gilts are polytocous animals, and the rate of ovulation varies considerably with 9 to 17 ova being the usual range. Genetics, nutrition and sexual age are the primary factors that have been shown to influence ovulation rate in gilts.

Genetics.

Although breed differences in ovulation rate have not been investigated extensively, the available evidence indicates that some breeds show a consistently higher ovulation rate than others.

Inbreeding usually reduces ovulation rate, whereas crossing purebred/ inbred lines of gilts increases markedly the number of ovulations.

Nutrition.

Plane of nutrition has been shown to affect ovulation rate significantly in swine. Robertson et al. (1951) and Self et al. (1955) reported that gilts provided continuous ad libitum feeding prior to second estrus produced greater numbers of ova than gilts restricted to about two-thirds of the ad libitum amount of feed.

Sexual Age

Physiological development is not completed with the attainment of puberty, as shown by increases in ovulation rate with successive estrous periods.

However it is reported no increase in ovulation rate with sexual age.

Management for Improved Embryonic/Fetal Survival

Fertilization rate in gilts is usually greater than 95%, and is essentially considered to be an all-or-none process. In swine, conception rate is used to signify those animals in which most ova are fertilized and pregnancy is established. The percentage of gilts mated that conceive varies considerably but in well managed herds, a conception rate of 75% to 85% is not unusual. Embryonic/fetal mortality is a factor of considerable magnitude in the pig. At least 40% of the ova shed are not represented at parturition, and a majority (85%) of this loss occurs during the first third of gestation. Major influences on conception rate and embryonic/fetal survival include.

1) The boar and its environment

2) The gilt and its environment.