The effect of dietary nonphytate P (nPP) and Ca concentration on the Ca appetite in broilers was evaluated. A total of 288 one-day-old male Ross 308 broilers were fed a commercial diet for 7 d then randomly allocated to 1 of 8 dietary treatments for a 28-d study. Diets were corn-soybean meal based and formulated to be nutritionally adequate except for nPP and Ca. Two concentrations of Ca (5.0 and 10.0 g/kg) and 4 of nPP (2.5, 3.5, 4.5, and 5.5 g/kg) were used, and all birds had access to a separate Ca source (CaCO3). Bird performance, nutrient digestibility, and tibia ash were determined. Birds fed 5.0 g of Ca/kg diets consumed more (P < 0.01) of the separate Ca source than birds fed diets containing 10.0 g of Ca/kg. Increased consumption (P < 0.01) of the separate Ca source was associated with increasing nPP concentration. Bird performance was not influenced by dietary treatment. Birds fed 5.5 g of nPP/kg diets had lower (P < 0.01) digestibility of DM, CP, and energy than the other groups. Phosphorus digestibility was reduced in birds fed high Ca diets and those fed 2.5 g of nPP/kg diets (P < 0.001). Birds fed 2.5 g of nPP/kg had lower tibia ash values than those fed higher concentrations of nPP while feeding diets containing 10.0 g of Ca/kg led to higher concentrations (P < 0.05) of tibia ash than for birds fed 5.0 g of Ca/kg. This study confirms previous findings that birds are able to meet their Ca requirement when fed Ca separately from the mixed ration. Consumption of the separate Ca source responded to not only Ca concentration but also to the amount of nPP in the diet. These data suggest that dietary nPP concentration influences the Ca specific appetite of broilers, and this may indicate that birds attempt to regulate their intake of Ca relative to nPP. This may be mediated via a physiological mechanism to maintain an appropriate Ca:nPP intake.

The interaction between calcium (Ca) and non-phytate phosphorus (nPP) in broiler nutrition and skeletal health is highly complex with many factors influencing their digestion, absorption and utilisation. The use of an investigative model such as the geometric framework allows a graphical approach to explore these complex interactions. A total of 600 Ross 308-day-old male broiler chicks were allocated to one of 15 dietary treatments with five replicates and eight birds per replicate. Dietary treatments were formulated to one of three total densities of total Ca + nPP; high (15 g/kg), medium (13.5 g/kg) and low (12 g/kg) and at each density there were five different ratios of Ca : nPP (4, 2.75, 2.1, 1.5 and 1.14 : 1). Weekly performance data was collected and at the end of the experiment birds were individually weighed and the right leg removed for tibia ash analysis. Skeletal health was assessed using the latency to lie (LTL) at day 27. At low Ca and high nPP as well as high Ca and low nPP diets, birds had reduced feed intake, BW gain, poorer feed efficiency and lower tibia ash, resulting in a significant interaction between dietary Ca and nPP (P < 0.05). LTL times were negatively influenced by diets having either a broad ratio (high Ca, low nPP) or too narrow a ratio (low Ca, high nPP) indicating that shorter LTL times may be influenced by the ratio of Ca : nPP rather than absolute concentrations of either mineral. The calculated intake arrays show that broilers more closely regulate Ca intake than nPP intake. Broilers are willing to over consume nPP to defend a Ca intake target more so than they are willing to over consume Ca to defend an nPP target. Overall dietary nPP was more influential on performance metrics, however, from the data it may appear that birds prioritise Ca intake over nPP and broadly ate to meet this requirement. As broilers are more willing to eat to a Ca intake target rather than an nPP intake target, this emphasises the importance of formulating diets to a accurately balanced density of Ca : nPP considering the biological importance of both minerals.

The study herein investigated the effect of mean particle size, calcium (Ca) source, Ca concentration and phytase on broiler performance, mineral digestibility and skeletal integrity from 1 to 28 days post-hatch. Sixteen dietary treatments were arranged in a 2 × 2 × 2 × 2 factorial design consisting of two Ca sources (limestone or a highly soluble calcium, HSC), two Ca concentrations (9.0 or 6.0 g/kg from Day 0 to Day 14 and 8.0 or 5.5 g/kg from Day 15 to Day 28), two Ca particle sizes (<0.5 or >0.5 mm) and two phytase-supplementation levels (0 or 1000 FTU/kg). Overall performance (Days 1–28) showed that the addition of phytase to diets containing 8.0 g/kg total Ca provided by HSC improved feed intake (P < 0.05), but there was no effect of the addition of phytase to birds fed Ca from limestone. Phytase supplementation decreased feed intake in birds fed limestone with a mean particle size >0.5 mm and increased feed intake in birds fed HSC with a mean particle size >0.5 mm, which resulted in a Ca source × Ca particle size × phytase interaction (P < 0.05). Birds fed diets containing HSC had a lower liveweight gain than did birds fed diets containing limestone (P = 0.03). Increasing the dietary Ca concentration from 5.5 g/kg to 8.0 g/kg total Ca decreased liveweight gain (P = 0.01). Phytase supplementation increased final liveweight gain (P < 0.001). Foot ash was observed to be higher in birds that received diets containing 8.0 g/kg Ca (P < 0.05). Phytase supplementation increased foot ash percentage (P < 0.05). Phytase increased Ca digestibility in birds fed diets containing Ca provided by HSC with a mean particle size <0.5 mm and diets containing limestone with a mean particle size >0.5 mm (P < 0.05). Phytase increased Ca digestibility in birds fed 5.5 g/kg Ca, but had no effect on Ca digestibility in birds fed 8.0 g/kg Ca (P < 0.05). The addition of phytase to diets improved the digestibility of phosphorus, especially in birds fed diets containing limestone (P < 0.05), or 8.0 g/kg total Ca (P < 0.05), or diets with a mean particle size >0.5 mm (P < 0.05). The results of the present study are consistent with those of previous studies by the authors, which have shown that low dietary Ca in conjunction with phytase improves broiler performance and mineral digestibility. Phytase improved growth performance, regardless of Ca source or Ca concentration and improved mineral digestibility.

Arginine activity in broiler diets can be supplied by L‐arginine (Arg), guanidinoacetic acid (GAA) and L‐citrulline (Cit), all of which are commercially available. This study was conducted to assess the effects of Arg source and level on broiler performance, nutrient digestibility and carcass parameters. Day‐old Ross 308 cockerels (n = 768) were assigned to one of eight dietary treatments using a completely randomized design: normal protein (NP), low protein deficient in Arg (LP) and LP with two levels of either Arg (0.238% and 0.476%), GAA (0.309% and 0.618%) or Cit (0.238 and 0.476%). The LP was 5 percentage points lower in protein level than the NP. Wheat, sorghum, soya bean meal, canola meal, and meat and bone meal‐based diets were fed over three feeding phases to 6 replicate floor pens with 16 birds each. Compared to NP, birds fed LP had reduced feed intake (FI, p < 0.001), reduced body weight gain (BWG, p < 0.001) and increased feed conversion ratio (FCR, p < 0.001) from day 0 to day 35. Additions of Arg or Cit to the LP at both levels resulted in increased BWG and reduced FCR (p < 0.05). Birds fed LP with GAA added had lower FCR (p < 0.05) but not higher BWG (p > 0.05) compared with the LP observed from day 0 to day 35. Supplementation of Arg, Cit and the low level of GAA to LP resulted in increased carcass yield, bone length, diameter and ash (p < 0.05) but did not increase ileal energy or nitrogen digestibility (p > 0.05). The findings indicate that Cit is an efficacious source of Arg activity in Arg‐deficient diets.

A study was conducted with Hy-Line Brown laying hens to examine the effects of reduced protein diet, deficiency of arginine (Arg), and addition of crystalline Arg, citrulline (Cit) and guanidinoacetic acid (GAA) as substitutes for Arg. Hen performance, egg quality, serum uric acid, liver and reproductive organ weights, and energy and protein digestibility were measured using a completely randomized design with 5 treatments. Treatments were a standard diet (17% protein diet; SP), a reduced diet (13% protein diet deficient in Arg; RP) and RP with added Arg (0.35%, RP-Arg), GAA (0.46% equivalent to 0.35% Arg, RP-GAA) or Cit (0.35%, RP-Cit) to the level of SP. It was hypothesized that performance would decrease with Arg deficient RP diet and the addition of GAA or Cit in RP would allow birds to perform similar or greater than Arg-added RP treatment. The experiment was conducted from 20 to 39 wk of age but the treatment effect was seen only after 29 wk of age. The birds offered RP had reduced egg and albumin weights ( P < 0.01), lower yolk color score ( P < 0.01), lower protein intake and excretion ( P < 0.01) than those offered SP. When Arg or Cit were added to RP to make them equivalent to SP, feed intake (FI) and egg production were not different than those of RP ( P > 0.05). The birds offered RP-GAA decreased FI and egg production ( P < 0.01) compared to those offered RP. The addition of Arg, Cit or GAA to the RP had no effect on egg quality parameters, protein and energy digestibilities ( P > 0.05). However, birds offered the RP-Cit diet tended to have higher Haugh unit ( P = 0.095) and lower shell breaking strength ( P = 0.088) compared to all other treatments while those offered RP-GAA had higher energy digestibility ( P < 0.05) than all other groups but RP. The limited performance response of hens fed RP with added Arg, GAA, or Cit may be due to deficiency of some other nutrients in RP such as phenylalanine, potassium or non-essential amino acids and other components of soybean meal in the diet.

A total of 600 Ross 308-day-old male broiler chicks were used in a 28 day digestibility study to investigate the interaction between dietary calcium (Ca) and non-phytate phosphorus (nPP) on the digestibility of minerals and amino acids. Diets were formulated to be nutritionally adequate except for Ca and nPP. Fifteen mash diets based on corn and soya bean meal with varying concentrations of Ca (6.4 to 12.0 g/kg) and nPP (2.4 to 7.0 g/kg) were used. Diets were clustered around total densities of Ca and nPP of 12, 13.5 or 15.0 (g/kg) and within each density, a range of five Ca : nPP ratios (1.14 : 1, 1.5 : 1, 2.0 : 1, 2.75 : 1 and 4.0 : 1) were fed. Birds had free access to feed and water throughout the study. At day 28, birds were euthanised for the determination of apparent ileal mineral and amino acid digestibility. Data were modelled in R version 2.15 using a linear mixed-effects model and interrogation of the data was performed by fitting a low order polynomial function. At high Ca concentrations, increasing nPP led to an increase in the apparent digestibility of minerals. Apparent ileal digestibility of phosphorus (P) was enhanced with increasing dietary nPP up to 5.5 g/kg beyond which no improvements were found. Maximal Ca digestibility was found in diets with > 8.0 g/kg Ca with concomitant low concentrations of nPP. Diets with a broader Ca : nPP ratio improved the digestibility of Ca but were deleterious to the digestibility of P. In this study, apparent digestibility of amino acids was broadly unaffected by dietary Ca and nPP concentrations. However, interactions between Ca and nPP were observed for the digestibility of glutamine, tyrosine and methionine (all P < 0.001). Nitrogen digestibility showed discrete optima around 10.0 and 5.0 g/kg nPP and Na digestibility was maximised around 8 to 9.0 g/kg Ca and 4.5 to 5.4 g/kg nPP. These data show that the ratio of Ca : nPP is more influential to mineral digestibility than the absolute dietary concentration of each macro mineral.

High inclusion concentrations of dietary calcium (Ca) from limestone may have detrimental effects on broiler performance, such as increased gastric pH and a reduction in phosphorus (P) and amino acid digestibility. To assess the potential for feeding diets with lower total Ca concentrations, the effect of a novel highly soluble source of calcium (HSC) on bird performance, nutrient digestibility and skeletal integrity of 1120 male Cobb-500 broilers was compared with that of limestone. Eight dietary treatments in a 2 × 2 × 2 factorial design consisted of two sources of Ca (limestone or HSC), two concentrations of Ca (6.0 or 7.7 g/kg in the starter and 4.0 or 5.7 g/kg in the grower), two phytase levels (0 or 500 FTU/kg). The effect of dietary treatments on growth performance and feed intake were measured from Day 1 to Day 40 and foot ash and leg health on Day 40. At the end of the starter period, in the absence of phytase, changing Ca source from limestone to HSC at 6.0 g/kg total Ca decreased both bodyweight gain and feed intake (P < 0.05). The addition of phytase to diets containing 6.0 g/kg total Ca provided by HSC increased bodyweight gain (P < 0.05), as well as increasing feed intake (P < 0.05). At the end of the grower period, diets supplemented with phytase increased bodyweight gain (P < 0.001), birds fed the higher Ca concentration were also observed to have an increased bodyweight gain (P < 0.001). Apparent ileal Ca digestibility significantly increased with the addition of phytase to diets containing 4.0 g/kg total Ca provided by HSC (P < 0.05), this was also observed for P digestibility. Replacement of limestone with HSC when fed in conjunction with phytase has the potential to be an effective strategy to improve broiler performance and bone mineralisation.

Heat stress causes significant economic losses in the broiler industry. Dietary supplementation of arginine (Arg) and citrulline (Cit) might increase the performance of broilers raised under warm temperature due to vasodilation effects. This study investigated the effects of L-Arg or L-Cit supplementation in broilers fed a reduced protein wheat-based diet deficient in Arg under thermoneutral (NT) and cyclic warm temperature (WT). Ross 308 cockerels ( n = 720) were randomly allocated to 4 dietary treatments with 12 replicates of 15 birds per pen from d 7 to 21. The 4 treatments were: normal protein (NP), i.e., 22.3% and 20.9% crude protein in grower and finisher, respectively; reduced protein (RP), i.e., 2.5% lower protein and deficient in Arg; and RP supplemented with 0.28% Arg (RP-Arg) or 0.28% Cit (RP-Cit). A factorial arrangement of treatments was applied during the finisher phase (21 to 35 d). Factors were: diet (4 diets above); and temperature, NT (24 °C) or cyclic WT (33 ± 1 °C for 6 h per day) with 6 replicate pens per treatment. During 7 to 35 d and 21 to 35 d, the birds fed the RP diet had lower body weight gain (BWG) and higher FCR compared to the NP diet ( P < 0.01). The addition of Arg or Cit to RP decreased FCR compared to RP ( P < 0.01). During 21 to 35 d, the birds exposed to WT had lower feed intake (FI), lower BWG ( P < 0.001) but similar FCR ( P > 0.05) compared to birds exposed to NT. Diet by temperature interactions were not observed for performance parameters during the period of WT ( P > 0.05). On d 35, the RP-fed birds had a lower yield of thigh and drumstick, higher fat pad, lower femur ash, and breaking strength but similar serum uric acid level and higher nitrogen digestibility on d 21 compared to those offered NP ( P < 0.05). Supplementation of Arg or Cit to RP resulted in increased femur ash on d 35 ( P < 0.05). Thus, feeding the NP diets is necessary to maintain growth performance in broilers regardless of the temperature conditions.