THE EFFECTS OF TRYPANOSOMA BRUCEI INFECTION ON REPRODUCTION IN FEMALE PIGS
The objective of this work was to study the reproductive performance of pigs experimentally infected with T. brucei. In doing so attention was focused on the effects of the parasite on the following parameters:-
Age of attainment of puberty, duration of puberty, fertility and pregnancy.
2.1 LITERATURE REVIEW
Puberty in Gilts
This is the age when reproduction becomes possible. It is usually considered to be the age at first estrus (Cupps et al., 1969). Ovulation is also known to occur at this time (Roberts, 1986). Puberty does not signify full or normal reproduction capacity which develops later, however its attainment is a slow and gradual process which depends upon the anterior pituitary (Roberts, 1986). Puberty occurs in gilts at 6 to 8 months of age. However gilts have reached puberty as early as 4 months and as late as 9 months (Cupps et al., 1969).
The age at which puberty is attained may be influenced by the level of nutrition, social environment, bodyweight, season of the year, breed of the pigs, infectious or non infectious diseases, parasitic diseases, management practices and genetic factors (Hafez et al., 1969; and Roberts, 1986). The age of the gilts is more important than weight and nutrition in determining the onset of puberty (Hughes and Valey, 1980; Hurtgen, 1981; Hurtgen, 1982).
Puberty is hastened in the gilts by cross breeding and by the presence of the male. However it is delayed in gilts penned individually as compared to those penned in a group. Delay in attainment of puberty is also noticed in gilts that are on diet restricted in protein and those raised under stressful conditions (Hafez 1975; Zimmerman and Cunningham, 1975; Roberts, 1986).
This is the phase in the estrus cycle in which the female will accept coitus (Cupps et al., 1969; Sorrensen, 1979). The period is well defined, and it is characterized by sexual desire and immobility in the presence of the male (Roberts, 1986). Estrus may begin at any time of the day (Cupps et al., 1969), its duration varies with individual animals. Various periods have been reported in pigs, these are, 59.3 hours (Cupps et al., 1969), 44 hours (Sorrensen, 1979), 24 to 96 hours (Roberts, 1986). However it is generally accepted that estrus begins with the time of the first acceptance of the male and ends with the last acceptance of the male (Roberts, 1986). It is influenced by factors such as parity, season, stress, boar effects, and when weaned piglets are removed from their mother (Weitze et al., 1994; Kemp and Soede, 1996; Soede and Kemp, 1997).
Noticeable changes of the vulva and behavioral patterns are seen during estrus and they vary with the time of estrus in individual animals. At the beginning of estrus the vulva swells, it becomes congested or red. The animal at this time becomes easily disturbed. Other animals in the pen begin to mount it, but it usually will not stand to be mounted. The mammary glands at this stage begin to develop. Later, the vulva reddening starts to subside, mucus discharge is noticed, and the animal begins to mount other females and stands to be mounted. Other females are also known to emit high pitched grunts during this time which is said to be characteristic. Appetite decreases, ears become erect; lordoses response is noticed and rub marks are also seen on the back of the animal (Hafez et al., 1969; Sorrensen, 1979; Carr, 1996).
Estrus has also been shown to occur immediately after delivery of the conceptuses. This is referred to as post partum estrus. It frequently occurs within 1 to 3 days after parturition. If mated the sow fails to become pregnant (Dunne and Leman, 1975).
INFERTILITY IN THE SOW
Reproductive failure has been considered to be the main reason why sows and gilts are culled. However, only a small proportion of the animals that are culled are found to be permanently sterile (Arthur et al., 1983).
The incidence of infertility in sows may approach that seen in cattle, but because of their lower values and difficulties in diagnosis and treatment, this has not been studied as much as infertility in cattle and horses (Roberts, 1986).The best index of accessing infertility in pigs is to determine the Percentage of females which farrow to the first service; this should be about 70-80% (Arthur et al., 1989).
The causes and type of reproductive failure are as a result of structural or functional abnormalities and infections (Arthur et al., 1983; Roberts, 1989). The structural defects of the genitalia of the female pig are congenital rather than acquired. They are seen more in gilts than in sows (Wilson et al., 1949). These lesions include double vagina, septae or strings in the vagina, hymeneal residue and hymeneal stricture (Teige, 1957).
Functional infertility is due to impairment of estrus, ovulation and gestation as a result of hereditary and environmental factors (Arthur et al., 1983). Lack of estrus is one of the chief components of female infertility in the pigs (Perry, 1956). Where management and nutrition are satisfactory, poor estrus manifestation in gilts is as a result of hereditary factors, persistent corpora lutea, pyometra and luteal cyst.
Ovulation is either absent or occurs at a low rate when gilts first show estrus at about 6 months of age (Arthur et al., 1983). Stress factors as well as diet affect ovulation. Supplementation of diet is known to increase the number of ovulations in the pigs, but if continued after estrus it predisposes to embryonic death. Hereditary differences in ovulation rate occur between breeds and between families within breeds. (Arthur, 1983; Barbet et al., 1979).
A considerable degree of embryonic mortality is regarded as a characteristic feature of normal porcine gestation and the death of 40% of fertilized ova is considered normal with mummification, abortion and maceration accounting for one third of the 40% while embryonic death makes up the remaining two third (Arthur,1983)
Specific infections of the genital tract that cause infertility in swine include brucellosis, leptospirosis, porcine parvovirus, porcine enterovirus, and pseudorabies (Floss and Tubbs, 1993).
ABORTION IN PIGS
Abortion is defined as the expulsion before full term of a conceptus incapable of an independent life. It differs from premature delivery which is the expulsion before full term of a fetus capable of independent life (Hubbert, 1971). Since abortion occurs before the gestation period is over, there is, therefore, fetal immaturity, and the newly aborted fetus is generally dead or dies shortly thereafter (Dunne and Leman, 1975).
Abortion may be spontaneous or induced, infectious or non infectious with the non spontaneous type being due to genetic, chromosomal, hormonal or nutritional factors whilst spontaneous abortions may also occur in animals bred immediately after puberty or immediately after parturition (Roberts, 1986).
Other causes of abortion include infections due to bacteria, viruses, parasites, nutritional deficiencies, toxemias, poisoning, genetic factors, management and miscellaneous factors like starvation, mastitis, metritis and fatal stomach ulcer (Dunne and Leman, 1975).
Infectious Abortions in Pigs
Blood and Radostists (1989) reported that infectious abortions in pigs are due to; brucellosis, leptospirosis, parvovirus infections, Aujeszky disease, still birth, mummification, embryonic death and infertility virus SMEDI, and erysipelas. They described the various clinical pictures of each disease where brucellosis and leptospirosis cause abortion in the 3rd trimester. Also in brucellosis the herd history of infertility, orchitis in the boar and high neonatal mortality may give a general idea of the causative agent while in leptospirosis, hepatic necrosis in fetuses that have been aborted may help in the presumptive diagnosis. Distinguishing between the two diseases is usually by laboratory examination. Parvovirus infection can cause outbreaks of abortion involving all ages of sows with a concurrent occurrence of early embryonic death and infertility in association with still birth, mummified fetuses and small litter size. Aujeszky disease in early pregnancy may result in embryonic death or abortion but there is early return to heat. The condition is usually accompanied by abundant vaginal discharge. The disease also causes abortion in the late pregnancy and birth of mummified fetuses. Parvovirus infections and SMEDI closely resemble pseudorabies in their reproductive inefficiency and they require laboratory and serological testing to differentiate them. Erysipelas causes abortion like other systemic bacterial infections that cause severe systemic reactions.
All the inoculated pigs developed clinical trypanosomosis. The disease took a short, severe and acute course killing two pigs. Later a mild but debilitating chronic disease developed in the six remaining ones. In the acute phase of the disease, the clinical signs observed were; fever, slightly pale mucous membranes, anorexia, dullness, reduced weight gain, recumbency and death.
The chronic phase of the disease exhibited, weight loss, on- coordinated movements, emaciation, mucopurulent ocular discharges, hyperemia of the skin, lethargy and abortion. The abortion occurred in the third trimester. Other clinical signs noticed were reduction in feed intake weakness and wobbling of the hindquarters. The weakness and wobbly movements became more pronounced as the disease progressed, especially in the pregnant pig. Even after it had aborted, the pig progressively got weaker till the experiment was terminated.