Study On The Mechanism Of High Zinc On Preventing Early Weanling Stress Syndrome Of Piglets

An experiment was conducted to examine the effects of high zinc diets (from ZnO or Zn-Met) on the growth performance, serum antioxidative enzyme activities, serum biochemical indexes, serum hormone levels and the contents of copper, iron, zinc in sera and tissues of piglets, in order to study the mechanism by high zinc diets preventing stress syndrome of early weanned piglets and security. One hundred"Duroc×Landrace×Yorkshire"crossbred weanling stress piglets (26 d±2 of age) were randomly divided into 5 groups of 20 piglets each by weight and sex. The piglets in GroupⅠwere fed a basal diet; the piglets in Group II were fed the diets plus 2000 mg·kg-1 Zinc (from ZnO); The piglets in Group III were fed the diets plus 3000 mg·kg-1 Zinc (from ZnO) ; the piglets in GroupⅣwere fed the diets plus 250 mg·kg-1 Zinc (from Zn-Met); the piglets in GroupⅤwere fed the diets plus 500 mg·kg-1 Zinc (from Zn-Met).The trial was conducted for 14 d. Body absolute weights (AW), average daily gain (ADG), average day feed intake (ADFI) and the ratio of feed to gain (F/G) in all piglets were determined on d 0,7,14 postweaned, and diarrhea rates were evaluated. Blood samples in fifty(10 per group) of one hundred piglets were taken from the anterior vena cava on d 0, 7, 14 postweaned for measuring serum CuZn-superoxide dismutase (CuZn-SOD) activities; the serum concentrations of total protein (TP), albumin (ALB), globulin (GLOB), cholesterol (CHL), urea nitrogen (UN), alkaline phosphatase(ALP), glutamic-pyruvic transaminase(GPT) and glutamic-oxalacetic transaminase (GOT),Calcium(Ca),Phophorus(P); the serum levels of growth hormone (GH), insulin (INS), Insulin-like growth factor-Ⅰ(IGF-Ⅰ), triiodothyronine (T3), thyroxin (T4) and cortisol; and the serum contents of copper, iron and zinc were determined at the same time. At the end of the trial, 15 male piglets (3 per group) were bled via the anterior vena cava. Brain, spleen, kidney, heart, thymus and liver were collected for later analysis of trace minerals.The results were as follows:1. The diets adding high zinc can significantly improve growth performance in weanling stress piglets.Compared with the control group, AW of trial groups piglets had no significant difference on d 7 postweaned, but enhanced significantly on d 14 postweaned(P<0.01 or P<0.05); ADG and ADFI of trial groups piglets improved significantly on postweanling (P<0.01) , respectively; F/G and diarrhea index reduced significantly on d 0~14 postweaned (P<0.01 or P<0.05), respectively. Compared with GroupⅡ, ADG in GroupⅢ,Ⅳ,Ⅴpiglets improved significantly during d 0~14 postweaned(P<0.05); ADFI in GroupⅢ,Ⅴpiglets improved significantly during d 0~7 postweaned (P<0.05); the diarrhea indexes in GroupⅢ,Ⅳ,Ⅴpiglets reduced significantly on d 0～14 postweaned(P<0.01).2. Some serum biochemical indexes had been influenced significantly by adding high zinc to the basal diets in weanling stress piglets.The serum concentrations of GOT and GPT in five groups of piglets had no significant changes(P>0.05) on d 0~14 postweaned.Compared with d 0, serum ALB, TP, GLOB , CHL levels in five groups of piglets postweaned decreased significantly(P<0.01 or P<0.05),respectively.Serum UN contents in GroupⅠpiglets increased significantly (P<0.01) on d 7 postweaned, but there had no changes on d 14. Serum UN contents in GroupⅡ,Ⅲ,Ⅳ,Ⅴpiglets had no significant changes on d 0~14 postweaned.Compared with d 0, serum ALP levels in five groups of piglets decreased respectively on d 0~7 postweaned, serum ALP levels in GroupⅠwere decreased again and serum ALP contents in GroupⅡ,Ⅲ,Ⅳ,Ⅴpiglets had no significant changes on d14 postweaned.Compared with the control group, serum ALP levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴpiglets improved respectively by 19.15%(P<0.05),21.45%(P<0.05),18.82%(P<0.05),19.63%(P<0.05)on d 7 postweaned, and improved respectively by 37.78%(P<0.01),49.51%(P<0.01),48.51%(P<0.01),47.59%(P<0.01)on d 14 postweaned. There is no difference among trial groups.Serum Ca, P had the same changes on postweanling, there was no difference in GroupⅠpiglets, but the GroupⅡ,Ⅲ,Ⅳ,Ⅴpiglets decreased significantly respectively(P<0.01 or P<0.05 ) . Compared with GroupⅠ,serum levels of Ca, P in GroupⅡ,Ⅲ,Ⅳ,Ⅴdecreased significantly on d 7, 14 postweaned(P<0.05).There was no difference among trial groups.3. High zinc diets improved significantly serum antioxidative enzyme activities in weanling stress piglets.Compared with d 0, serum CuZn-SOD activities of the control group decreased by 18.98%(P<0.01) on d 7 postweaned, and there were no significant changes on d 14 postweaned ; serum CuZn-SOD activities of GroupⅡ,Ⅲ,ⅣandⅤpiglets had no significant change(P>0.05)between d 0 to d 7 postweaned; and increased on d14 postweaned significantly(P<0.01 or P<0.05). Compared with the control group, serum concentrations of CuZn-SOD in GroupⅢ,ⅣandⅤpiglets enhanced significantly(P<0.01)on d7 postweaned; serum concentrations of CuZn-SOD in GroupⅡ,Ⅲ,ⅣandⅤpiglets improved on d14 postweaned significantly(P<0.01). There had no difference among trial groups.4. High zinc diets had improved significantly hormone levels in weanling stress piglets.Compared with d 0, serum GH, INS, IGF-Ⅰ, T3 levels in GroupⅠpiglets decreased significantly on d 0~7 postweaned (P<0.05), there had no significant difference on d 14 postweaned; serum GH, INS, IGF-Ⅰ, T3 levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴhad no significant difference on d 0~7, but increased significantly on d14(P<0.01 or P<0.05). Compared with GroupⅠ, serum GH, INS, IGF-Ⅰ, T3 levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴwere enhanced significantly on d 7,14 postweaned(P<0.01 or P<0.05),but trial groups had no difference. Serum T4 levels in GroupⅠ,Ⅱ,Ⅲ,Ⅳ,Ⅴhad no difference during the whole experiment.Serum cortiosl levels in GroupⅠpiglets changed significantly on d 0~14 postweaned (P<0.01). Compared with d 0, serum cortiosl levels in GroupⅠpiglets improved by 81.82% (P<0.01) on d 7 postweaned; but serum cortiosl levels decreased significantly on d 14 compared with d 7 postweaned (P<0.01). Serum cortiosl levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴhad no difference postweaned. Compared with GroupⅠ, serum cortiosl levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴdecreased significantly(P<0.01).5. The contents of Cu, Fe and Zn in weanling stress piglets were influenced by feeding high zinc diets.5.1 The contents of serum Cu, Zn in weanling stress piglets had influenced significantly by feeding high zinc diets, but there had no difference in serum Fe.Compared with d 0, serum Cu levels in GroupⅠpiglets declined significantly on d 7 postweaned (P<0.05), and there had no difference on d 14 postweaned; Serum Cu levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴdecreased significantly(P<0.01 or P<0.05)on d7,14 postweaned. Compared with GroupⅠ, serum Cu levels in GroupⅢ,Ⅳ,Ⅴdecreased significantly on d 7 postweaned(P<0.01), Serum Cu levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴdecreased significantlyon d 14 postweaned(P<0.01 or P<0.05). Compared with GroupⅡ, serum Cu levels in GroupⅢ,Ⅳ,Ⅴhad decreased significantly on d 7 (P<0.05), but there had no difference among trial groups on d14 postweaned.Compared with d 0, serum Zn levels in GroupⅠpiglets postweaned declined significantly(P<0.01 or P<0.05), serum Zn levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴhad no changes on d 7 postweaned, and improved significantly(P<0.01 or P<0.05)on d 14 postweaned. Compared with GroupⅠ,serum Zn levels in GroupⅡ,Ⅲ,Ⅳ,Ⅴhad increased significantly(P<0.01)on d 7,14 postweaned, but there had no difference among trial groups.There had no difference of serum Fe levels in the five groups.5.2 The contents of Cu, Fe, Zn in the tissues were influenced by the diets adding high zinc.Compared with GroupⅠ, heart Cu and thymus Cu of the trial groups were decreased significantly(P<0.01 or P<0.05), spleen Cu ,liver Cu, kidney Cu and brain Cu had no difference, and there had not any significant distinction among trial groups .Compared with GroupⅠ, heart Fe, Liver Fe, kidney Fe, brain Fe and thymus Fe in GroupⅡ,Ⅲ,ⅣandⅤpiglets had no difference, but spleen Fe in GroupⅢ,ⅣandⅤpiglets were decreased significantly(P<0.01 or P<0.05).There had no difference among the trial groups.Compared with GroupⅠ, heart Zn, liver Zn, brain Zn and kidney Zn in GroupⅢ,Ⅴpiglets had enhanced significantly(P<0.01 or P<0.05); liver Zn and brain Zn in GroupⅡpiglets were increased significantly(P<0.01 or P<0.05); liver Zn , kidney Zn and brain Zn in GroupⅤpiglets were increased significantly(P<0.01 or P<0.05), and spleen Zn and thymus Zn had no difference in the trial groups. There were no distinctions among trial groups.These results showed that serious stress responses were observed in piglets feeding basal diets during week 1 to 2 after weanling. Weanling stress decreased immunities, disturbed endocrines, and inhibited growth of weanling piglets. But early weanling stress syndrome of weaned piglets were reduced by addition of zinc from ZnO (2000, 3000mg·kg-1) and Zn-Met (250,500 mg·kg-1) in diets. The high zinc diets improved body environments, modulated the regular metabolism, enhanced growth performance, and stimulated growth of weaning piglets efficiently.