Effects of organic zinc on tibia quality, mineral deposit, and metallothionein expression level of aged hens.

The study aimed to determine the effects of methionine hydroxy analog chelate zinc on the tibia quality, mineral deposit, apparent retention of nutrients, and liver metallothionein (MT) expression level of aged laying hens. A total of 960 layers (Hy-Line Grey, 57 wk old) were randomly assigned into 4 groups, and each group had 8 replicates of 30 hens. During the first 2 wk, groups were fed a basal diet without extra zinc (Zn: 35.08 mg/kg). During the ensuing 14 wk, 4 levels of Zn (inorganic Zn: 80 mg/kg; organic Zn: 20, 40, 80 mg/kg) were added to the diet. The results indicated that both the Zn source and level did influence tibia strength and calcium (Ca) and Zn concentrations of tibia (P < 0.05), whereas there were no differences in the copper (Cu) and phosphorus (P) concentrations of the tibia and the tibia length (P > 0.05). Moreover, dietary supplementation with 40 or 80 mg/kg of organic Zn showed higher Zn and Ca concentrations in the tibia and higher tibia strength. The Cu concentration in the liver showed no difference among the 4 treatments, whereas the Zn concentration in the liver increased with the increasing Zn level. The apparent retention of P, iron (Fe), and manganese (Mn) was not affected by the Zn level or source (P > 0.05). However, the organic Zn group increased the apparent retention of Cu, Zn, Ca, crude protein (CP), and energy, and the group supplemented with 40 or 80 mg/kg of organic Zn obtained significant effects (P < 0.05). Moreover, dietary supplementation with 40 or 80 mg/kg organic Zn increased the MT mRNA expression of the liver at week 72, whereas 20 mg/kg of organic Zn decreased it (P < 0.05). In conclusion, this study suggested that an optimum dietary (40 mg/kg) organic Zn level plays a key role in promoting the apparent retention of minerals and nutrients, trace element deposit, and MT mRNA expression.

Effects of methionine hydroxyl analog chelated zinc on laying performance, eggshell quality, eggshell mineral deposition, and activities of Zn-containing enzymes in aged laying hens.

The study aimed to determine the effects of methionine hydroxyl analog chelated zinc (MHA-Zn) on laying performance, eggshell quality and mineral deposits, and the activities of Zn-containing enzymes on aged laying hens. A total of 960 layers (Hy-Line Grey, 57 wk old) were fed a basal diet (Zn: 35.08 mg/kg) without extra zinc for 2 wk. During the ensuing 14 wk, birds were randomly divided into 4 groups according to body weight and laying rate, with 8 replicates per treatment, and each group had 8 replicates of 30 hens. Four levels of Zn (ZnSO4: 80 mg/kg; MHA-Zn: 20, 40, 80 mg/kg) were added to the diet, respectively. The results shown that dietary Zn did not affect laying rate, average egg weight, average daily feed intake, or feed conversion ratio (P > 0.05); however, compared to the inorganic group, dietary supplementation with 40 or 80 mg/kg MHA-Zn decreased broken egg rate significantly in the whole period (P < 0.05), while significantly increased eggshell weight in week 62 to 72, eggshell thickness and eggshell strength in wk 66 to 72, eggshell weight percent and eggshell density in week 62 to 72 (P < 0.05). Besides, dietary supplementation with different sources and levels of Zn did not affect ash concentration of eggshell (P > 0.05), whereas dietary supplementation with 80 mg/kg MHA-Zn improved the Zn and Ca concentrations of eggshells and carbonic anhydrase (CA) activity of liver, and 40 mg/kg MHA-Zn increased Zn concentration of liver (P < 0.05). Moreover, no significant differences in alkaline phosphatase activity were observed among the treatment groups (P > 0.05). Therefore, dietary supplementation with 40 mg/kg MHA-Zn can improve eggshell quality by promoting Ca deposition and CA activity.

Effects of dietary threonine levels on growth performance, serum biochemical indexes, antioxidant capacities, and gut morphology in broiler chickens.

A dose-response experiment was conducted to investigate the impacts of dietary threonine (Thr) levels on growth performance, serum biochemical indices, antioxidant capacities, and gut morphology of broiler chickens. Four hundred and thirty-two 1-d-old commercial broilers were allocated to 4 treatments consisting of 6 replicates of 18 birds. The experimental treatments received the same Thr-deficient basal diet and were labeled as follows: 85%, 100%, 125%, and 150% of NRC (1994) recommendations. The results demonstrated that on 21 d and 42 d, average daily weight gain (ADG, 22 to 42 d, 0 to 42 d) increased quadratically or cubically as the inclusion of Thr increased, while feed conversion ratio (FCR, 0 to 21 d, 0 to 42 d) decreased quadratically or cubically as dietary Thr increase from 85% to 150%. Excess dietary Thr levels triggered plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities. The concentrations of total protein (TP) and globulin (GLO) increased quadratically with increasing Thr level, and the highest concentrations of TP and GLO were obtained at the 125% Thr level. Moreover, the plasma uric acid (UA) concentration decreased linearly or quadratically with the increase in dietary Thr level. Likewise, the serum glutathione peroxidase (GSH-Px) and total superoxide dismutases (T-SOD) activities increased quadratically as dietary Thr increased, and the highest activity of GSH-Px was obtained at the 125% Thr level, while the highest T-SOD level occurred in the 100% Thr group. Gut morphology of birds showed significant response to different graded concentrations of Thr level. Villus height (VH), crypt depth (CD), and VH:CD ratio (VH/CD) were increased linearly or quadratically by Thr supplementation. Therefore, the present study suggests that the NRC (1994) recommendations Thr level that was optimum for growth performance, and 125% of the NRC (1994) recommendations Thr level had better effects on biochemical indices, antioxidant function, and gut morphology of broilers.

Effects of dietary supplementation of synbiotics on growth performance, intestinal morphology, sIgA content and antioxidant capacities of broilers.

Today, several strategies are being used to decrease the serious effects of antibiotics abuse on broilers industry and public health, among which synbiotics are one of the most promising antibiotic alternative. This study was undertaken to assess the effects of synbiotics, which composed of probiotics (Bacillus subtilis) and prebiotics (xylooligosaccharide and mannanoligosaccharide), on growth performance, intestinal morphology, sIgA content and antioxidant parameters of broilers. Four hundred and fifty one-day-old commercial Cobb48 broilers were assigned to five treatments consisting of six replicates of 15 birds each pen. Five dietary treatments include basal diets (control), basal diets plus antibiotics (4 mg/kg Xanthomycin), basal diets plus 1 g of probiotics B. subtilis product/kg of diets (4 × 108  cfu/kg), basal diets plus 150 mg/kg xylooligosaccharide (35%) and 1 g/kg mannanoligosaccharide (75%), and basal diets plus synbiotics (1 g of probiotics B. subtilis product/kg of diets (4 × 108  cfu/kg), 150 mg/kg xylooligosaccharide (35%) and 1 g/kg mannanoligosaccharide (75%). The results demonstrated that on 21 and 42 days, dietary supplementation of the synbiotics significantly increased daily weight gain (p < 0.05), feed efficiency (p < 0.05), the villus height and villus:crypt ratio in the duodenum, jejunum and ileum (p < 0.05), as well as intestinal mucosa sIgA content (p < 0.05), serum T-SOD activity (p < 0.05) and lysozyme content (p < 0.05), comparing with control group. In conclusion, synbiotics (B. subtilis and xylooligosaccharide and mannanoligosaccharide) is one of the safe and ideal dietary supplementations to increase broilers' growth performance by improving small intestinal morphology, sIgA content and antioxidant capabilities.

Dietary vitamin A can improve immune function in heat-stressed broilers.

This experiment was undertaken to evaluate the effect of dietary vitamin A on the performance and immune competence of broilers under heat stress (HS). A total of 180 birds, at 22 days of age, were randomly assigned to be reared either at 24°C (thermoneutral, TN, 24°C, constant) or 24°C to 38°C (heat stress, HS, cycling) until the age of 42 days. Birds were then supplemented with vitamin A at 750, 1500, 15 000 IU/kg. Each of the 2 × 3 factorially arranged treatments were replicated in six cages, each containing five birds. Humoral immunity was assessed by intravenous injection of 7% sheep red blood cells (SRBC) followed by evaluation of serum for antibody titers in primary and secondary responses. Cell-mediated immunity was assessed by using a Sephadax stimulation method to recruit abdominal exudate cells (AEC) to evaluate macrophage phagocytic ability. Body weight (BW) and feed conversion were significantly affected by dietary vitamin A (P < 0.05). HS significantly reduced BW, feed intake and feed conversion (P < 0.05). Numbers of AEC, percentage of macrophages in AEC, phagocytic macrophages, internalized opsonized and unopsonized SRBC were increased by dietary vitamin A (P < 0.05). Both primary and secondary antibody responses were characterized by increasing titers of antibody to SRBC by dietary vitamin A when birds were exposed to HS (P < 0.05). Lymphoid organ weights, antibody responses, incidence of macrophages in AEC and phagocytic ability of macrophages were all significantly reduced under HS. These results indicated that HS severely reduced performance and immunocompetence of broilers, whereas the immune response of broilers improved by dietary vitamin A supplementation under HS.

Effects of yeast culture in broiler diets on performance and immunomodulatory functions.

A study was conducted to evaluate the effect of supplemental yeast culture (Diamond V XP Yeast Culture; YC) in broiler diets on performance, digestibility, mucosal development, and immunomodulatory functions. One-day-old Arbor Acres chicks (n = 960) were randomly assigned to 1 of 4 dietary treatments based on corn and soybean meal and containing 0, 2.5, 5.0, and 7.5 g/kg of YC in the diet for 42 d. Each treatment consisted of 12 replicates of 20 broilers each. Nutrient digestibility was determined on d 15 and 35 by total fecal collection. On d 21 and 42, 12 birds per treatment were sacrificed to evaluate gut morphology and secretory IgA. Broilers were vaccinated with Newcastle disease vaccine by eye drop on d 7 and 28 and antibody titer was determined on d 14, 21, 35, and 42. Dietary supplemental YC at 2.5 g/kg improved average daily gain and feed conversion during grower and overall periods (P 0.05) protein retention and energy digestibility. Villus height to crypt depth ratios in the duodenum and jejunum (d 42) and ileum (d 21) were increased (P