Sows often encounter problems such as foot and hoof disease, less breast disease, weaker stillbirth, mastitis, and metritis. The occurrence and development of these diseases are closely related to the level of feeding management. To alleviate or avoid the above problems. The role of vitamins is special and complex. They mostly participate in the digestion, absorption and metabolism of various nutrients in the form of coenzymes, and regulate the secretion of hormones and affect the immunity of animals. The way and size of vitamin action depends on the supply of other nutrients and is closely related to the level of feeding management. Therefore, sows have diverse and inconsistent responses to vitamin supplementation. Compared with other nutrients, the current nutrition research on sow vitamins is less and not systematic and in-depth. The research mainly includes the effects of VA, β-carotene, VE, folic acid and biotin on the reproductive performance of sows, and the biochemical mechanism of vitamin action. The vitamin's potency, the relationship between vitamins and sow immunity, vitamin needs and supplies. This article will comprehensively analyze the mechanism of action of major vitamins, the effect of vitamin supplementation in feed, and the need and supply of vitamins in sows.
1 The mechanism and effect of vitamins on sows
1.1 Mechanism of action of VA and β-carotene and its effects
VA is a substance necessary for maintaining the integrity of all epithelial tissues. In the absence of VA, squamous keratinous changes occur in epithelial cells of tissues such as the reproductive system, causing inflammation and reducing the immunity of animals. VA is involved in sow ovarian development, follicular maturation, corpus luteum formation, improvement of oviductal epithelial cell function, and embryonic development. Retinoic acid and triiodothyronine promote the synthesis of placental prolactin to stimulate mammary gland development. When sows lack VA, embryo malformation rate, stillbirth rate, and postpartum mortality increase in piglets. It is generally believed that the number of ovulations in sows is 15-20, and the fertilization rate of eggs is 90%-95%. Therefore, the sows have about 14-18 embryonic cells during pregnancy, and the embryo mortality rate in early pregnancy is 30%-40% (Anderson , 1978; Pope, 1988, 1990), sow uterus can support the development of 12 to 14 fetuses (Christenson et al, 1987; Chen et al, 1993), but the average sow litter size is 10 heads, visible, still There is potential to increase litter size in sows (Pusateri et al., 1999). Pope et al. (1990) argue that the more synchronized embryos are, the higher the embryo survival rate. Whaley et al (1997, 2000) respectively fed a high-energy diet (ME 45.9 MJ/d) to a sow that was injected 1 × 106 IU VA on the 7th or 15th jugular vein of the second estrus cycle to promote pre-ovulation. Oocyte development improves the consistency of early embryo development and increases embryo survival. Coffey et al. (1993) injected 200 mg of β-carotene into piglets at the time of weaning, increased litter size, and injected VA or β-carotene into sows during weaning, estrus or 7 days of estrus. The litter size increased by 0.6. Brief et al. (1985) showed that jugular injection of VA or β-carotene was more effective than oral administration in improving the survival rate of VA.
The effect of β-carotene on the reproductive performance of sows has an independent effect, probably because β-carotene has oxidative activity or acts as a local precursor of VA, altering the metabolism of vitamins in the uterus (Antipatis, 2004). Tokach et al. (1994) injected β-carotene, VA or a mixture of VA and β-carotene into sows at weaning, and no effect on reproductive performance was observed. Pusateri et al. (1999) showed that the injection of 1 × 106 IU VA into the jug of the sow at any time during the weaning of the piglets did not increase litter size. Pusateri et al. (1999) suggested that VA had a slight improvement in the survival rate of embryos, and it may be difficult to show an increase in litter size in actual breeding environments; or that VA improved the survival rate of early embryos in the first trimester; or sows Multiple injections of VA or slow-release VA or beta-carotene are required to maintain a high embryo survival rate.
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