Why is the pregnancy rate of sows low in summer?
1. Nutritional factors
(1) Insufficient nutrient intake In the hot summer, due to the thick subcutaneous fat and poor heat dissipation ability of pigs, the feed intake and activity of pigs decreased accordingly, and the nutrient intake required for sow reproduction was insufficient, which led to the disorder of estrus and ovulation of sows, thus affecting mating and conception, and the stillbirth and weak fetus appeared.
(2) Vitamin deficiency or deficiency In summer and high temperature season, the stability of vitamins in feed is destroyed, especially fat-soluble vitamins A and E are the most basic and effective vitamins to maintain the normal reproductive activities of sows. The stability of vitamins is destroyed, which leads to vitamin deficiency in feed, low pregnancy rate of sows and abnormal embryo development.
(3) Malnutrition, lack or insufficiency of green feed, reduced feed intake of breeding pigs in summer, incomplete nutrient intake or lack of certain nutrients (such as selenium, vitamin A and vitamin E), and insufficient supply of green feed affect the normal breeding activities of breeding pigs.
2. Environmental temperature factors
The sperm motility of boars is negatively correlated with environmental temperature. The higher the ambient temperature, the lower the sperm motility. In summer, the temperature of piggery in some farms is as high as 38 ~ 40℃, or even higher. If the temperature is too high, it is easy to cause the boar's sexual desire to decrease, the semen quality is thin and fine, the vitality is obviously decreased, and the dead sperm and weak sperm are increased. If the sow breeding time is not timely, it is easy to cause the sow to be barren. This factor is the most direct factor leading to the low pregnancy rate of sows in summer.
4. Insufficient exercise
The summer weather is hot, and the exercise of breeding pigs is relatively reduced. In addition, some pig farms use positioning bars for breeding pigs, and the amount of exercise is even less. Too little exercise of boars will lead to the decline of sperm motility and directly affect the pregnancy rate; Insufficient exercise of sows will affect the normal estrus and ovulation of sows, and at the same time, it will also make sows weak in limbs and affect mating and conception.
5. Disease factors
(1) Parvovirus disease affects the reproductive performance of sows, which mainly depends on the stage of infection. Generally, it will lead to estrus, infertility, abortion, stillbirth, weak fetus, mummified fetus and reduced litter size of sows. The infection of empty pregnant sows can affect the normal estrus of sows, and some sows will continue to estrus. Infection in the early stage of sow breeding will lead to neither estrus nor pregnancy and farrowing. Early pregnancy infection in sows will lead to premature death of some embryos and be absorbed by the mother; In the second and third trimester of pregnancy, sow infection will lead to the death of some fetuses, the fetal water will be absorbed by the mother, the abdominal circumference of sows will be reduced, or stillborn fetuses, weak fetuses, mummified fetuses or few piglets will be born. Generally sows are infected with the disease after 70 days of pregnancy. Although sows can normally give birth to some piglets, piglets are usually infected and become a new source of infection. To prevent parvovirus disease, it is generally necessary to immunize reserve sows or sows with 2 ml of parvovirus vaccine before breeding. Sows should be immunized every 3 weeks.
(2) Atypical swine fever will lead to the decline of immunity of pigs and the reproductive disorder of sows. Sows infected before 10 days of pregnancy will lead to early embryo death or be absorbed by sows, and sows will return to love or reduce litter size; Sows are infected within 10 ~ 15 days of pregnancy, and the number of stillbirths will increase. Infection in the second and third trimester of pregnancy will lead to stillbirth, fetal weakness and fetal growth and development after delivery; Sows are infected about 1 week before delivery, which does not affect the survival of piglets, but will affect the growth and development of piglets. To prevent atypical swine fever, the swine fever vaccine should be immunized 15 ~ 30 days before the breeding of reserve sows or fertile sows, and the dose is 2 ~ 4 sows per sow.
(3) Japanese encephalitis, mainly spread by mosquitoes and flies, occurs frequently in summer. After infected with Japanese encephalitis, boars mainly show orchitis, decreased sexual function and decreased semen quality. Sows infected with Japanese encephalitis are prone to acute abortion, and the antibodies in the blood of multiparous sows are high, which are characterized by mating difficulties, abortion and stillbirth. Generally, the mortality rate of stillbirth, mummified fetus and newborn piglets of sows is above 40%. To prevent Japanese encephalitis, boars are generally vaccinated against Japanese encephalitis once in spring and autumn, and sows are vaccinated once every three weeks.
(4) Leptospirosis can cause stillbirth and abortion in pregnant sows and reduce the survival rate of piglets. The incubation period of the disease is 1 ~ 2 weeks; Infection in the second month will cause fetal death, sow abortion and fetal mummification; In the third month, the infection caused the sow to miscarry, the offspring were weak, and the survival rate of piglets decreased. In order to prevent leptospirosis, sows can be vaccinated with leptospirosis vaccine before mating in frequent areas. When the pathogen is not identified, sows should be vaccinated with multivalent vaccine.
(5) Chlamydia psittaci is generally endemic. The excreta and secretions of sick pigs and their latent infected pigs can be infected with virus, which can harm pigs of all ages, but pregnant sows are the most sensitive, and pathogens can penetrate into uterus through placental barrier, leading to fetal death. Generally, primiparous sows and young sows not only have obvious symptoms, but also have a relatively high incidence rate, while multiparous sows generally have no obvious symptoms, only stillbirth. The prevention of chlamydia psittaci should focus on preventing the introduction of the disease. In epidemic areas, chlamydia vaccine should be inoculated from suckling pigs to breeding pigs.
(6) Brucellosis easily infects adult boars and adult sows, leading to acute or chronic orchitis and epididymitis in boars; Sows miscarry and give birth to stillbirths and weak fetuses. The prevention of the disease should focus on preventing the introduction of the disease. In the old epidemic areas where the disease is prevalent, it is necessary to strengthen the general survey and treatment of breeding pigs and vaccinate them regularly.
(7) Blue milk, abortion, premature delivery, stillbirth and weak fetus of blue-eared sows. The prevention of the disease should focus on preventing the introduction of the disease, and blue ear disease vaccine can be inoculated before and after weaning, with 3 ml per sow.
(8) Eperythrozoon suis can be infected by pigs of all ages, and sow infection with this disease will cause anemia, emaciation, diarrhea, abortion, stillbirth and low pregnancy rate. To prevent the disease, it is necessary to clean the pig house in summer, eliminate blood-sucking insects such as mosquitoes and flies, and prevent the bite of blood-sucking insects from spreading the disease to sows.
(9) Toxoplasma gondii will cause miscarriage, stillbirth and weak fetus in pregnant sows, and lead to acute postpartum death of piglets.
(10) The reproductive tract infection of sows is mainly caused by poor sanitary conditions, pollution sources, large primipara, dystocia of sows, improper remedial measures or untimely treatment, resulting in reproductive tract diseases such as metritis, endometritis and vaginitis. , leading to estrus, abnormal estrus, repeated infertility or abortion in pregnant sows.
6. Utilization coefficient of boars
In hot summer, the heat stress of boars is obvious. Some farms (households) still use boars to collect sperm and breed during the day in hot weather, and do not pay attention to the rational use of boars. Over time, it is very harmful to boars, which easily leads to the decline of sexual function of boars, the thinning of semen quality, the decline of sperm vitality, and the increase of dead sperm and weak sperm, thus seriously affecting the pregnancy rate of sows.