1. An experiment was conducted to investigate whether a linear regression approach is a suitable tool for determining the amino acid (AA) digestibility up to the terminal ileum of broiler chickens. Solvent-extracted rapeseed meal (RSM) was used as the model ingredient. 2. Ten diets with 5 different inclusion rates of RSM (60, 120, 180, 240 and 300 g/kg, corresponding to crude protein concentrations from 170 to 250 g/kg in the diet), each without or with a supplementation of phytase (500 U/kg), were fed ad libitum to broiler chickens between 14 and 21 d of age. Seven pens of 12 chickens were allocated to each treatment. Digesta were sampled on a pen basis from the section of the gastrointestinal tract between Meckel's diverticulum and 2 cm anterior to the ileo-caeco-colonic junction. Titanium dioxide was included as an indigestible marker. 3. The amounts of crude protein and AAs digested up to the terminal ileum constantly increased with increasing AA intake over the entire range of intakes. When the amount of an AA digested at the terminal ileum is linearly regressed against its intake, the deviation of the slope from 1 is caused by both the unabsorbed AA from RSM and from specific endogenous losses related to RSM. These slopes varied between 0.68 and 0.88 for individual AAs, and the slopes were unaffected by phytase supplementation. 4. It is suggested that a linear regression approach be adopted to study the AA digestibility of raw materials in chickens. Digestibility determined this way does not need any correction for basal endogenous loss.

The responses of broilers to increments of dietary P concentration in P retention and P prececal digestibility were studied in 2 experiments using Ross 308 broilers in their fourth week of age. The low-P basal diet was mainly based on corn, potato protein, and corn starch. Titanium dioxide was used as the indigestible marker. Monobasic calcium phosphate was added in 6 (experiment 1) or 5 (experiment 2) graded levels up to a maximum of 8.1 g of P/kg of the diet. Five (experiment 1) and 6 (experiment 2) replicated pens of 10 birds were used. Excreta were collected from trays underneath the pens. Birds were asphyxiated by carbon dioxide exposure and the ileum (from Meckel's diverticulum to 2-cm anterior to the ileo-ceca-colonic junction) was dissected. Digesta was collected from the entire section (experiment 1) or from 3 subsections of equal lengths (experiment 2). Excretion of P increased linearly with increasing dietary P concentration up to a level of about 5.2 g of P/kg of the diet and increased nonlinearly with further increase in dietary P. In contrast, P flow in the ileum increased linearly over the entire range of P intake. Up to the level of 5.2 g of P/kg of the diet, P excretion was slightly lower than P flow in the ileum, but responses in P excretion and P flow in the ileum were similar, suggesting that P excretion with urine is very low and unaffected by P intake when the birds are supplied with P below their requirement. Between the 3 subsections of the ileum, calculated digestibility was significantly different for the basal diet and the diet with the 3 lowest levels of P supplementation. We concluded that the response in P prececal digestibility to increments in dietary P concentration is linear over a wider range of dietary P than the response in P retention. When digesta is collected from the ileum for determination of P prececal digestibility, the first third of the ileum should not be considered.

We studied whether the availability of P is different among poultry species. A basal diet was mixed mainly based on corn, potato protein, and dried egg white. It was calculated according to the recommendations for young turkeys with the exception of P and Ca concentrations, which were deficient. Monobasic calcium phosphate (MCP) was added in graded levels, and analyzed P concentrations in the 7 diets were (in g/kg of dry matter) 2.9, 3.7, 4.5, 5.3, 6.2, 7.2, and 7.7. Four experiments were conducted with 3-wk-old broiler chickens, turkeys, ducks, and quails. Birds were kept in balance crates, and 8 individuals were allocated to each treatment diet. Birds were fed the treatment diets for 10 d, and excreta were quantitatively collected during the last 5 d. P utilization was calculated as the proportion of P intake that was accreted by the birds. The P accretion response of birds to incremental MCP intake was described with sigmoidal functions, and the marginal efficiency of P utilization ((delta)y/(delta)x) was calculated. Utilization of P from the unsupplemented basal diet was 58% in broilers, 55% in quails, 46% in ducks, and 39% in turkeys. Supplementation of MCP significantly increased P accretion in all species. Ninety-five percent of the estimated ymax in P accretion was achieved with 8.4, 7.3, and 4.8 g P/kg of dietary DM in broilers, ducks, and quails. No plateau in P accretion was achieved in turkeys. These differences correlate well with the differences in the feed/gain ratio, which was 1.3 in turkeys, 1.7 in broilers, 1.9 in ducks, and 3.5 in quails. The maximum in marginal efficiency of supplemented P was 96% in ducks, 81% in turkeys, 74% in broilers, and 77% in quails. These maxima were achieved at different levels of MCP supplementation. We concluded that differences in P availability exist between poultry species for plant and mineral P sources. Quails can be used as model species for broilers in P availability studies, but dietary P levels need special adjustment.

Titanium dioxide (TiO2) is a viable marker in digestibility studies using different animal species. The photometrical analysis is based on an intense orange colour following the addition of hydrogen peroxide to an acid solution. The measurement using inductively coupled plasma optical emission spectrometry (ICP-OES) is a method for analysing more than one element from the same sample preparation. The present study was conducted to investigate whether an established ICP-OES element analysis following acid-based hydrolysis is appropriate for titanium analysis. Defined amounts of TiO2 were added to samples obtained in studies with cows, pigs and turkeys and recoveries were determined. It was shown that supplemented TiO2 can be determined in samples of feeds, faeces or excreta, and digesta using a method based on photometric or ICP-OES measurement. The differences between the true and measured titanium concentrations indicate that using the ICP-OES method leads to a higher accuracy of determination.

Effects of a supplementation of 80 mg L-carnitine per kg diet were studied in broiler chicken at two dietary levels of fat (4 and 8%) and different feeding levels (ad libitum in a growth trial, 95 and 85% of ad libitum in a balance trial). A low-carnitine basal diet adequate in amino acid concentration was used. In the growth trial, each diet was fed to 9 groups of 10 birds each for 16 days from day 5 of live onwards. Growth and feed intake were determined. At the end of the trial, birds were killed and homogenised for subsequent empty body analysis. Accretion of protein and energy was determined using a representative blank group killed at the beginning of the trial. In the balance trial, 8 individual birds were used per treatment. Birds were offered the feed at approximately 85 and 95% of ad libitum intake, which was determined with separate birds for both fat levels. Excreta were quantitatively collected three times daily for 8 consecutive days beginning on day 17 individually for each bird. Supplemented L-carnitine did not significantly affect any response criterion. However, growth and feed conversion tended to be improved by about 5% in the carnitine supplemented diets when fed ad libitum. An interaction between carnitine and fat level occurred with regard to feed conversion, indicating that carnitine had a positive effect at the high fat level, but not at the low fat level. L-carnitine did not positively affect the metabolisability of energy (ME/GE) and the efficiency of energy utilisation (RE/GE or RE/ME). Similarly, no significant carnitine effect was determined with regard to N accretion and the efficiency of utilisation of dietary protein in both trials. It is concluded that endogenous carnitine synthesis is not the limiting factor for energy utilisation in broiler chicken, even at high dietary fat concentration. Occasionally reported positive effects of supplemental carnitine were likewise caused by reasons other than improved energy or protein utilisation. Further studies on amino acid utilisation and catabolism should consider marginal amino acid supply.