| Low calcium levels in the diet of goslings can reduce growth performance,while high levels can increase feeding costs and reduce economic benefits.Vitamin D3 is a sterol derivative essential for poultry as a fat-soluble vitamin.It can promote the absorption and metabolism of calcium and phosphorus in food in organs such as the intestine,liver,and kidneys,promote the growth and differentiation of bone cells,and maintain bone health.Previous research indicated an interaction between vitamin D3 and calcium in recent years,which jointly affected animal growth performance and economic benefits.The effects of vitamin D3 and calcium and their interactions on goslings’ growth performance,calcium absorption,and bone calcium retention are still unclear.This study adopted a 2×3 factorial design using 360 1-day-old Jiangnan White female goslings.Geese were randomly divided into six treatment groups with six replicates in each group,with ten goslings per replicate.A basal diet used corn and soybean meal as the primary raw materials.Two levels of vitamin D3 addition(0 IU/kg,1800 IU/kg)and three levels of calcium(0.50%,0.85%,1.20%)were set as treatment factors.Feeding experiments,metabolic tests,physicochemical tests,tissue sectioning staining techniques,scanning electron microscopy,and real-time fluorescence quantitative PCR(RT qPCR)were conducted.The growth performance,bone growth,intestinal tissue morphology,absorption and utilization rates of calcium and phosphorus,morphology and ultrastructure of cartilage,and serum vitamin D3 and vitamin D3 retention in the liver of different age goslings were measured.The study aimed to explore the impact of dietary vitamin D3 and calcium on the growth performance of goslings,calcium absorption,and bone calcium retention.The results indicated that:(1)The body weight and average daily gain of goslings were increased,and the feed-togain ratio was reduced by vitamin D3(P<0.05);When the dietary calcium levels were 0.85%and 1.20%,the body weight and average daily gain of the goslings were increased(P<0.05),while the feed to weight ratio of the goslings was reduced(P<0.05);The interaction between vitamin D3 and calcium increased the body weight and average daily gain of goslings(P<0.01),and decreased the feed to weight ratio of goslings aged 1-28 days(P<0.01).(2)The retention of 25-(OH)-D3 in the liver of 63-day-old goslings was increased by vitamin D3(P<0.05).The retention of 25-(OH)-D3 in the liver of goslings increased with the increase in dietary calcium levels(P<0.01).The interaction between vitamin D3 and calcium did not affect the retention of 25-(OH)-D3 in the liver of goslings(P>0.05).(3)The calcium and phosphorus content in the feces of goslings was reduced by vitamin D3(P<0.05),and the absorption and utilization rate of calcium and phosphorus by goslings was increased by vitamin D3(P<0.05).The absorption and utilization rate of calcium by goslings increased with dietary calcium levels(P<0.05).The interaction between vitamin D3 and calcium reduced the calcium content in goslings’ feces(P<0.05)and increased the absorption and utilization rate of calcium(P<0.05).The dietary calcium level and the interaction between vitamin D3 and calcium did not affect the fecal phosphorus content or absorption and utilization rate of phosphorus in goslings(P>0.05).(4)Vitamin D3 did not affect the slaughter performance of 63-day-old goslings(P>0.05).The increase in dietary calcium levels affected the breast muscle rate of goslings(P<0.05).When the dietary calcium level was 0.85%,the breast muscle rate of goslings reached the maximum value of 10.67%.The interaction between vitamin D3 and calcium did not affect the slaughter performance of 63-day-old goslings(P>0.05).Vitamin D3 had no significant effect on the meat quality of the 63-day-old geese(P>0.05).Higher dietary calcium levels increased the muscle redness value of 63-day-old goslings(P<0.05).The interaction between vitamin D3 and calcium did not affect the meat quality of 63-day-old goslings(P>0.05).(5)The tibia width,strength,coarse ash content,calcium retention,and phosphorus retention(P<0.05),femur width,calcium retention,and phosphorus retention(P<0.05),and metatarsal length,coarse ash content,and calcium retention(P<0.05)were increased by vitamin D3 in goslings.The increase in dietary calcium levels increased the tibial strength(P<0.05),femur length,weight,coarse ash content,calcium retention(P<0.05),metatarsal length,crude ash content,calcium retention,and phosphorus retention(P<0.05)of goslings.The effects of vitamin D3 and calcium on bone growth-related indicators have a time accumulation effect.This effect on bone growth and bone calcium retention in goslings mainly manifests after 14 days of age.Vitamin D3 and calcium have interactions(P<0.05)on the length,strength,crude ash content,femur length,width,relative defatted weight,crude ash content,metatarsal length,relative defatted weight,crude ash content,calcium retention,phosphorus retention of the tibia in different age goslings,promoting bone growth and calcium retention.When the diet was not supplemented with vitamin D3 or the calcium level was low(0.50%),the collagen fibers of proximal tibial cartilage were disordered and loose,and the growth of the tibial growth plate was blocked.(6)The duodenal villi height in goslings and the thickness of duodenal muscle layer in 63-day-old goslings(P<0.05),the jejunal villi height and the thickness of jejunal muscle layer in 28-day-old goslings(P<0.05),and the height and thickness of ileal villi and muscle layer in goslings(P<0.05)were increased by vitamin D3.The ileal crypt depth in 63-day-old goslings was reduced by vitamin D3(P<0.05).The higher dietary calcium levels can increase the villus height and muscle layer thickness of the duodenum,jejunum,and ileum in goslings(P<0.05)and reduce the ileal crypt depth of 63-day-old goslings(P<0.05).The interaction between vitamin D3 and calcium increased the height of duodenal and ileal villi,as well as the thickness of the jejunal muscle layer in 28-day-old goslings,as well as the height and thickness of jejunal villi and muscle layer in 63-day old goslings(P<0.05),and reduced the depth of ileal crypt in 63-day old goslings(P<0.05).(7)The relative expression levels of vitamin D receptor(VDR)and calcium-binding protein(CaBP-D28k)mRNAin the duodenum of 28 and 63-day-old goslings were increased by vitamin D3(P<0.05).The higher dietary calcium levels increased the relative expression of CaBP-D28k mRNA in the duodenum of 28-day-old goslings and the relative expression of VDR and CaBP-D28k mRNA in 63-day-old goslings(P<0.05).The interaction between vitamin D3 and calcium increased the relative expression of CaBP-D28k mRNA in the duodenum of 63-day-old goslings(P<0.05).To sum up,a low calcium level(0.50%)diet without vitamin D3 reduced the retention of 25-(OH)-D3 in the liver of the goslings and hepato-intestinal circulation of vitamin D3,which may lead to inadequate absorption of calcium and other nutrients in the small intestine by down-regulation of the relative expression of vitamin D receptor(VDR)and calcium-binding protein(CaBP-D28k)in the duodenal mucosa of the goslings,reducing the absorption and utilization rate of calcium in the goslings,leading to skeletal dysplasia and the decrease in mineralization rate,ultimately reducing the growth performance of goslings.Adding vitamin D3 to the diet can effectively reduce the adverse effects of insufficient dietary calcium on the growth of goslings. |
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