Study On The Calcium Requirement Of Broilers Fed A Corn-Soybean Meal Diet From 22 To 42 Days Of Age

In this experiment,the effects of different dietary calcium(Ca)levels on the production performance,blood and bone parameters,and the m RNA and protein level of bone Ca metabolism utilization marker in the bones of broilers from 22 to 42 days of age were investigated,and proper sensitive indices were selected to evaluate dietary Ca requirement of broilers fed a corn-soybean meal diet from 22 to 42 days of age.A total of 252 22-day-old commercial Arbor Acres male chicks with similar body weight were randomly divided into 1 of 7 treatment groups with six replicate cages of six birds per cage.The dietary Ca levels were 0.5、0.6、0.7、0.8、0.9、1.0 and 1.1%,respectively,and the non-phytic acid phosphorus level in the diets was fixed at 0.31% for all treatments.The results showed that:(1)Dietary Ca level did not affect the production ferformance indicators of broilers from 22 to 42 day of age(P>0.32);(2)Dietary Ca level did not affect the carcass performance indicators of42-day-old broilers(P>0.29);(3)Dietary Ca level did not affect the meat quality indicators of42-day-old broilers(P>0.08);(4)Dietary Ca level did not affect the serum Ca,P and OC content,ALP activity,tibial ALP and TRACP activity of 42-day-old broilers(P>0.022),however,it affected serum TRACP activity(P<0.05).The serum TRACP activity increased linearly as dietary Ca level increased(P<0.01);(5)Dietary Ca level did not affect the tibial ash percentage and tibial strength of 42-day-old broilers(P>0.07),however,it affected the ash Ca percentage,ash P percentage,bone mineral content(BMC)and bone mineral density(BMD)of 42-day-old broilers(P<0.02).The ash Ca and P percentage of tibia bone increased linearly as dietary Ca levels increased(P<0.04),BMC and BMD of tibia bone increased linearly and quadratically as dietary Ca levels increased(P<0.01),BMC and BMD of the tibia bone reach a plateau at a dietary Ca level of 0.6%;(6)Dietary Ca level did not affect the middle toe ash P percentage of 42-day-old broilers(P>0.24),however,it affected the ash percentage,ash Ca percentage,BMC and BMD of middle toe(P<0.04).BMC and ash percentage of middle toe increased quadratically as dietary Ca levels increased(P<0.03),ash Ca percentage and BMD of middle toe increased linearly and quadratically(P<0.03).Ash percentage,ash Ca percentage and BMC of middle toe reached the highest point at a dietary Ca level of 0.70%,and BMD of middle toe reached the plateaus at a dietary Ca level of 0.60%;(7)Dietary Ca level did not affect the m RNA expression of SOST and TRACP in tibia bone(P> 0.05),however,it affected the m RNA expression of ALP,OPG,OC,DMP-1 and BMP-2 in tibia bone(P< 0.04).The m RNA expression of OPG,OC,DMP-1 and BMP-2 increased linearly as dietary Ca level increased(P< 0.04),the m RNA expression of ALP increased quadratically as dietary Ca level increased(P< 0.01).The m RNA expression of ALP reached the highest point at a dietary Ca level of 0.70%;(8)Dietary Ca level did not affcet the protein expression levels of ALP,OPG,OC,DMP-1,BMP-2,SOST and TRACP in the tibia of 42-day-old broilers(P>0.46);(9)BMC,BMD and ALP m RNA levels of tibia and BMC,BMD,ash percentage and ash Ca percentage of middle toe bone were sensitive indexes,ased on fitted broken-line,quadratic-curve or asymptotic-line models(P < 0.02)of the above indexes,optimal dietary Ca levels were estimated to be 0.55-0.72 mg/kg for broilers fed a corn-soybean meal diet from 22 to 42 day of age.The results from the current study indicate that the optimal dietary Ca level would be 0.72% to support the bone developement and Ca metabolism of broilers fed a practical corn-soybean meal diet from 22 to 42 d of age,which are 20% lower than the current NRC Ca requirement.It is of great significance to ensure the healthy growth of broilers,and reduce the interference of Ca on the palatability of broiler diets and the absorption and utilization of other nutrients,as well as save Ca resources and reduce feed costs.