No abstract

Four experiments were conducted in this study. Experiment 1 was carried out to examine mRNA expressions of nuclear vitamin D receptor (nVDR), membrane vitamin D receptor (mVDR), and type IIb sodium-phosphate cotransporter (NaPi-IIb) in the small intestine of broiler chickens. Experiments 2, 3, and 4 were implemented to evaluate effects of age, non-phytate phosphorus (NPP), and 25-hydroxycholecalciferol (25-OH-D3) on mRNA expressions of nVDR, mVDR, and NaPi-IIb in the duodenum of chickens. Results showed that mRNA expression levels of nVDR and NaPi-IIb were highest in the duodenum of 21-day-old broilers, lower in the jejunum, and lowest in the ileum. By contrast, no differences in mRNA expression levels of mVDR were detected among the duodenum, jejunum, and ileum. Age quadratically affected mRNA expressions of nVDR, mVDR, and NaPi-IIb in the duodenum and 25-hydroxylase in the liver of 7- to 42-day-old broilers, with the highest levels observed at 21 d of age. By contrast, age linearly decreased mRNA expression level of 1α-hydroxylase in kidneys. Dietary NPP levels quadratically affected mRNA expression levels of nVDR and mVDR in the duodenum and 25-hydroxylase in the liver of 21-day-old broilers. The highest mRNA expression levels of nVDR and mVDR and lowest mRNA level of 25-hydroxylase were observed at 0.55% NPP. mRNA expression level of NaPi-IIb linearly declined when dietary NPP levels increased from 0.25 to 0.65%. Addition of 12.5 μg/kg of 25-OH-D3 increased mRNA expression level of 1α-hydroxylase in kidneys and those of nVDR, mVDR, and NaPi-IIb in the duodenum of broilers compared with birds fed the diet without 25-OH-D3. These data indicate that mRNA expressions of nVDR and NaPi-IIb are highest in the duodenum, and the greatest mRNA levels of nVDR, mVDR, and NaPi-IIb are observed at 21 d of age. Dietary NPP levels quadratically increase mRNA expressions of nVDR and mVDR but linearly decrease NaPi-IIb mRNA level. 25-OH-D3 up-regulates the above gene transcription.

This study aimed at comparing the growth and mineralization of the femur, tibia, and metatarsus of male and female broiler chicks. On the day of hatch, 100 male and 100 female Ross 308 broiler chicks were transferred stainless cages with 10 birds per cage. On d 7, 14, 21, 28, 35, and 42, five males and five females were sacrificed and their femur, tibia, and metatarsus were collected. Results showed that the tibia was the heaviest and the longest and contained the highest content of ash and calcium (Ca) among the three leg bones. The femur had the greatest diameter. The weight, length, diameter, and ash weight of the femur, tibia, and metatarsus linearly increased with age. The ash, Ca, and phosphorus (P) content in the femur and the tibia quadratically increased with age; by contrast, these parameters in the metatarsus linearly increased with age. The bones grew faster in 1 to 21 d of age. The weight, diameter, and ash weight of the three bones of males were higher than those of females. The Ca to P ratio of the three bones (femur, tibia, and metatarsus) was approximately 2.0:1. These data indicate that there are differences in bone growth and mineralization among the femur, tibia, and metatarsus of male or female broiler chicks.

The objective of this study was to investigate the optimal zinc (Zn) requirement of broiler chickens based on Zn retention. On the day of hatch, 350 male Ross 308 broilers were randomly assigned to seven treatments with five replicates of ten birds each. Zinc was supplemented as ZnSO 4 •7H 2 O at 0, 20, 40, 60, 80, 100, or 120 mg/ kg in the starter diet (fed from 1 to 21 d of age) and at 0, 16, 32, 48, 64, 80, or 96 mg/kg in the grower diet (fed from 22 to 42 d of age). The analyzed Zn levels were 34.98 and 27.57 mg/kg in the basal starter and grower diets, respectively. Supplemental Zn levels did not influence body weight gain, feed intake, feed conversion ratio, or liver Zn content of broilers at 21 and 42 d of age (p>0.05). Tibia ash Zn content of 21-d-old broilers increased when Zn supplementation level increased from 0 to 40 mg/kg Zn in (p<0.05). The highest breast muscle Zn content in 42-d-old broilers was observed when 100 and 80 mg Zn/ kg was supplemented in the starter and grower diets, respectively. Fecal Zn content, Zn intake, Zn excretion, and Zn retention of 31-to 33-d-old broilers linearly increased with supplemental Zn levels (p<0.05). Zinc retention values, calculated as the difference between Zn intake and Zn excretion, were negative, about zero, and positive when starter/grower diets were supplemented with 0/0 and 20/16, 40/32, and 60/48 and 120/96 mg/kg, respectively. These results indicate that supplementing 40 and 32 mg Zn/kg in starter and grower diets, respectively, promote the growth performance of broiler chickens, while reduce Zn excretion in the environment.

1α-Hydroxycholecalciferol (1α-OH-D3) is a vitamin D derivative. The objective of this study was to evaluate the effects of 1α-OH-D3 on the growth and the mRNA expression of vitamin D receptor (VDR) in the small intestine and kidney of chickens. A total of 240 males of one-day-old Ross 308 broilers was randomly assigned to 4 treatments with 5 replicates of 12 birds per replicate. Three levels of 1α-OH-D3 (1.25, 2.5, and 5 μg/kg) were added to a basal diet containing 0.50% calcium (Ca), 0.25% non-phytate phosphorus (NPP), and without supplemental cholecalciferol (vitamin D3). The control diet contained 1.00% Ca, 0.45% NPP, and 25 μg/kg cholecalciferol. Dietary 1α-OH-D3 levels linearly improved the average daily feed intake (ADFI), average daily gain (ADG), femur and tibia mineralization, and plasma Ca concentration, and retained Ca and total phosphorus (tP) amounts in broilers from 1 to 21 d of age (P < 0.05). In addition, 1α-OH-D3 also linearly up-regulated the mRNA expression levels of VDR in the duodenum as well as those of VDR and sodium-phosphate cotransporter NaPi-IIa and NaPi-IIc in the kidney of broilers (P < 0.05). However, 1α-OH-D3 did not affect the mRNA levels of 25-hydroxylase in the liver or NaPi-IIb in the duodenum (P > 0.05). No differences were observed in the ADFI, ADG, bone length, plasma mineral concentration, retained tP amount, or the mRNA levels of the above genes (except for VDR in the kidney) between the birds fed the diet with 5 μg/kg 1α-OH-D3 and the birds fed the control diet (P > 0.05). By contrast, the weight, ash weight, ash percentage, and Ca percentage of the bone, retained Ca amount, and the mRNA level of VDR in the kidney were lower in the birds fed the diet with 5 μg/kg 1α-OH-D3 than in the birds fed the control diet (P < 0.05). These data indicate that 1α-OH-D3 up-regulates the gene expression of VDR in the small intestine and kidney at the transcriptional level, thereby improving the growth performance and bone mineralization of broiler chickens from 1 to 21 d of age.