Evaluation of Raw Materials for Poultry: What s up?

Transcription

1 Evaluation of Raw Materials for Poultry: What s up? JAN DIRK VAN DER KLIS* and JAN FLEDDERUS Schothorst Feed Research BV, Meerkoetenweg 26, 8218 NA Lelystad, The Netherlands * Corresponding author: jdvdklis@schothorst.nl Approximately three quarters of the feed costs are represented by costs for dietary energy. Therefore, an accurate estimate of the energetic value of raw materials is extremely important to reduce the price of poultry feed. The quality and composition of raw materials, especially byproducts, can be highly variable. In poultry, several systems are used to describe the energetic value of feedstuffs, like the Apparent and True Metabolisable Energy (both corrected for zero nitrogen balance) values. The basis for including an higher efficiency for fat utilisation in comparison with carbohydrates is given, which is a first modification towards a Net Energy system. Different energy evaluation systems have a clear effect on the ranking of feedstuffs. Finally, different P evaluation systems are compared. Key words: Energetic value, AME, TME, P value, by-products Introduction Essential nutrients for maintenance and (re)production are primarily supplied via feed. In Europe, dietary energy is by far the most costly feed ingredient. To optimise the dietary composition based on the nutrient requirements of the animal in a specific stage of production, the absorption and utilisation of nutrients should be accurately predicted and preferentially be related to feedstuff characteristics. Feeding diets with too low nutrient concentrations will increase feed intake or decrease production performance, whereas too high concentrations or imbalanced nutrient ratios will increase nutrient spillage (if not stored in e.g. fat, liver or bone) or might even reduce production performances. An accurate estimation of the nutrient availabilities in raw materials is therefore crucial for practical poultry feeding. In Europe several energy evaluation systems are used like apparent and true metabolisable energy (corrected or uncorrected for zero nitrogen balance) with growing broilers or adult cockerels as reviewed by MacLeod (2002) and Fisher (2005). Using adult cockerels, force-feeding methods are used feeding the test material as such or as part of a complete diet, whereas broilers are generally fed complete diets to nearly ad libitum intake. The energy content in and the ranking between feedstuffs will be dependent on the energy evaluation system used. In addition to these reviews, in the Netherlands the AME N value for layers takes an extra caloric value for fat into account and a lower energy contribution for digested protein in broilers which already implies a shift towards a net energy system. Like for energy, also different methods are used to estimate the availability of dietary protein (amino acids) data not shown- and of phosphorus. Metabolisable energy (AME and TME) In practical feed formulation, generally the apparent metabolisable energy (AME) content is used. In 1990 Bourdillon described a European reference assay for measurement of this AME value to increase the precision of measurement and the comparability of dietary AME values between laboratories. Their method was based on a quantitative balance technique (i.e. quantitative measurement of nutrient intake via feed and excretion via droppings). The 4-day collection period was started and ended after a 17-h fasting period, using: 1) Adult cockerels fed to 90% ad libitum in order to minimise ingredient selection in the feeders. 2) Three-wk old broilers fed for ad libitum intake. Since then different laboratories have made their own modifications to this reference method. INRA uses a 3- day adaptation period, followed by a one night fast for young birds or 24 hours for cockerels. The balance period

2 (which comprises three days in total) starts and ends after this fasting period. Faeces are collected once daily. In other countries like the Netherlands, adult cockerels are no longer used. In the Netherlands, measurements are done with growing broilers using a minimum 7-day adaptation period, followed by a 4-day balance period. A fasting period at the start and the end is omitted by the CVB as the N-correction is based on the measured nitrogen balance (based on a gross energy content of nitrogenous excretory products of 36.5 kj/g, whereas others use a value of 34.4 kj/g) and not on body weight gain. Faeces are collected thrice daily to avoid fermentation of nutrients in droppings. Determination of the AME value with growing broilers or layers are based on the measurement of energy intake and energy excretion with droppings in birds fed preferably nutritionally adequate test diets, containing minimal 80% of the commercial nutrient recommendations not to compromise production performance, whereas a significant amount of the major energy delivering nutrients should originate from the test feedstuffs for accurate estimations. By subtracting the AME contribution of the basal diet from the AME of the test diet, the AME of the feedstuff can be calculated. Using this methods assumes the absence of interactions between the test feedstuff and other dietary components, and potential synergistic or antagonistic effects are attributed to the test feedstuff. It is well recognised that this approach may have large effects on the estimated AME value of feedstuffs as was shown for wheat varieties using a basal diet with no or 7% added fat. Using the basal diet with the high fat content reduced the determined AME N value for wheat by 3 MJ/kg DM compared to the low fat diet (Van der Klis et al., 1995). The outcome of assays using complete diets can also be largely different from assays where test feedstuffs are fed as such to adult cockerels. In the latter case such interactions between feedstuffs are not possible. If complete diets are used for energy evaluation, the nutrient composition of the basal diet should be as close to normal nutrient concentrations as possible, to avoid unrealistic interaction effects. Feeding test feedstuffs as such (not being part of a complete diet) or prolonged fasting periods of at least 24 h might not be acceptable anymore to animal ethics committees. In Europe several systems 1 are used to calculate the AME N value from digestible nutrient concentrations in feedstuffs. 1) The European Community equation: AME N (MJ/kg) = % C.FAT % CP % total sugar (Luff-Schoorl method) % STARCH (1.1) This equation is based on coefficients determined with adult cockerels, ignoring differences due to species and age and differences in nutrient digestibilities between feedstuffs. Digestibilities are fixed at 0.87, 0.86, 0.96 and 0.79 (Carré, 1990). This equation can be used to calculate the AME N for complete diets. 2) The CVB equations: AME N (kj/kg) = dcp dc.fat dnfe (2.1) AME N (kj/kg) = dcp dc.fat dnfe (2.2) In the Netherlands in principle two different general equations are used: One for adult animals (2.1) and one for growing broilers (2.2), which are based on measured nutrient digestibilities in target animals for each feedstuff. For laying hens an additional correction is made because of a higher efficiency of fat utilisation compared to carbohydrates, which was based on energy retention studies (a specified in a later section). In broilers a lower energy value was introduced for digestible crude protein. This value was obtained from regression analyses between the measured AME N value and the g digested protein, fat and NfE in 15 important feedstuffs for poultry. From this regression equation it was concluded that the energy coefficient for digestible protein for broilers was significantly lower than for adult cockerels, whereas the energy coefficients for the other nutrients were similar. However, the physiological basis for this lower energy coefficient for digested protein used in the CVB table is not clear. 3) The Rostock equation: AME N (kj/kg)= 18.8 dcp dc.fat dstarch dsugars dnfr In the Rostock equation, the NfE fraction of the CVB equation is split into starch, sugars and NFR, which implies that variation in the starch content of a feedstuff is directly related to its AME N value. 1 CP: crude protein; C.FAT: crude fat; NfE: 1000 moisture crude ash - CP- C.FAT- crude fibre; NFR: 1000 moisture crude ash CP - C.FAT STARCH SUGARS; d: digestible; values given as g/kg unless stated otherwise

3 The effect of different feed evaluation systems on the AME N value and on the ranking of feedstuffs is shown in Table 1. Table 1. The effect of different feed evaluation systems on the AME N value and on the ranking of feedstuffs 1. Feedstuff EU INRA Rostock CVB 2 AME N AME N AME N AME N MJ/kg % MJ/kg % MJ/kg % MJ/kg % Maize Wheat Barley Oats Soybean meal Rapeseed meal Sunflower seed meal Peas Tapioca Wheat bran Values have been recalculated based on the feedstuff composition as published by Sauvant et al. (2004). 2 AME N Poultry (no correction for higher efficiency of fat utilisation). It is shown in Table 1 that the variation in energy values differ between the systems used, except for the cereals. Moreover the ranking between feedstuffs varies, which implies that the feedstuff composition based on linear programming of the diets will change due to the energy evaluation system. Results of the dietary AME value are highly dependent on the daily feed intake (Figure 1), which is more or less obvious as in contrast to the TME value, the AME value is not corrected for endogenous losses from the intestinal tract. Especially at low feed intakes endogenous losses can have a great impact on the apparent metabolisable energy content. Due to this correction the outcome of the TME assay is much more constant. Endogenous energy losses can be estimated based on the excreta energy content using graded levels of intake of e.g. a highly digestible starch, sugar, oil (SSO) mixture when extrapolated to 0 intake, like was done by Askbrant and Kalili, (1990). Results are illustrated in Figure 1. It is clear that the gap between the AME and TME is decreased when the intake of the SSO mixture is increased. Moreover, this gap between AME and TME is much smaller when the nitrogen balance correction was carried out, which indicates that this nitrogen correction will create a more constant AME value that can be used in more variable circumstances than uncorrected values. Figure 1. The relationship between TME, TME 0, AME and AME 0 values in relation to the intake of a starch, sugar, oil (SSO) mixture in adult cockerels (Askbrant and Kalili, 1990).

4 Whether or not to correct for endogenous energy? In normal balanced diets, endogenous losses will be more or less constant. Endogenous losses will be proportionally attributed to the test feedstuffs. Composing a complete diet will therefore be corrected for the normal physiological endogenous energy loss. Increased efficiency of fat utilisation compared to carbohydrates Although in general, dietary AME N values from assays with adult cockerels are used for laying hens, these values might underestimate the dietary energy content in highly productive animals. There are indications that energy from fat can be used at a higher efficiency than energy from carbohydrates, as fatty acids can be used as such to form body (or egg) fat. Scheele (1985) estimated the efficiency of fat utilisation in comparison to carbohydrates, using ad libitum fed hens from 24 to 36 weeks of age. Different diets containing 13.0, and 13.5 MJ AME N per kg DM, each with increasing amounts of energy from animal blended fat (3, 6 and 9 g digestible fat per MJ AME N )) in exchange for energy from carbohydrates, were fed for ad libitum intake. Dietary AME N, nutrient digestibilities and retained energy were measured (as total energy retention in body and egg). Results are given in Figure 2. Figure 2. The energy retention (in body and egg) in laying hens fed diets differing in AME N content each containing three levels of dietary energy from fat in exchange for carbohydrates. It can be calculated for diets containing 13.5 MJ AME N /kg DM that an increase in fat energy from 115 to 345 kj (i.e. 3 and 9 g digested fat) per MJ AME N in iso-energetic exchange for carbohydrates resulted in a 16 kj higher energy retention, whereas an increase from 230 to 345 kj (i.e. 6 and 9 g digested fat) per MJ AME N resulted in a 6 kj higher energy retention. This equals (=16/230) and (=6/115) kj RE per kj energy from fat. The intercept value represents a diet with no energy from fat, which equals an energy retention of 314 (dotted line 1) and 320 kj/hen/day (dotted line 2). Finally, it was calculated from these data that the energy retention on 100% fat energy would represent 1000* =384 and 1000* =372 kj/hen/day. Expressed as a percentage of the carbohydrate (and protein) energy this would mean an efficiency of 122% and 116%. Performing similar calculations for the diet with 13.0 MJ/kg DM gives a 114% and 116%. Therefore the energy value from fat in the Dutch CVB system was increased with 15% compared to carbohydrates and for layers an AME value in feedstuffs is calculated as: AME N (kj/kg) = dcp *1.15 dc.fat dnfe (2.3) Using this higher energy value for fat is already a first step towards a net energy system.

5 Starch digestion rate and its amino acid sparing effect Starch is the major energy yielding ingredient for poultry diets. Although the total tract digestibility of starch is often assumed to be 100%, the rate of starch degradation can be highly variable as was shown in vitro (Weurding et al., 2001). As a slower starch digestion rate can improve production performance in broilers, an amino acid sparing effect was assumed when slowly degradable starch was used instead of rapidly degradable starch. This hypothesis was tested by Weurding et al. (2003). Iso-energetic broiler diets (2975 kcal/kg) containing 34% of slowly degradable starch (i.e. peas and corn as starch sources) or rapidly degradable starch (i.e. tapioca and corn as starch sources) were formulated with a low (8.5 g/kg) and high (11.0 g/kg) digestible lysine content. Intermediate lysine contents (9.13; 9.75 and g/kg) were obtained by mixing the low and high lysine diet with the same starch sources. The diets with slowly degradable starch showed consistent better production performances than the diets with the rapidly degradable starch (Figure 3). Slowly degradable starch improved protein and energy utilisation in broilers. The effect of starch source was more pronounced at the lower digestible lysine contents indicating that amino acid and glucose supply might be unbalanced in the RDS diets, which implies that initially after ingestion of a diet more glucose conversion into glycogen or fat is needed in the RDS diet because of the absence of protein. Synchronising glucose and amino acid supply might therefore stimulate energy efficiency. Figure 3. The effect of the dietary digestible lysine content in broilers fed iso-energetic diets with slowly degradable starch (SDS) or rapidly degradable starch (RDS) on feed conversion ratio from 9 to 30 days of age. Phosphorus availability in poultry Optimising phosphorus nutrition in poultry becomes increasingly important for environmental reasons. When the phosphorus level in the diet is attuned to the phosphorus requirements in the respective production phases of the bird, accurate estimations of the biological phosphorus availability in feed ingredients are needed. Currently, phosphorus evaluation in poultry is based on three different principles: 1) The NRC (1994) defines the available phosphorus content as total P phytate P, assuming that inorganic P is completely available, whereas organic P is not available to monogastric animals. If phytate-p in plant feedstuffs is not analysed, it is assumed to be 1/3 of total plant-p. 2) A different approach is based on a bio-assay adding graded dietary phosphorus levels of a test and of a reference phosphate to a phosphorus deficient basal diet. Generally, body weight gain or tibia ash are used as response parameters. The response curve is linear until the phosphorus requirement is met (Figure 4) and its slope is directly related to the availability of phosphorus from the test source. A higher slope indicates a larger response per g of added P (i.e. a higher phosphorus availability). When this slope for the test feedstuff is expressed relative to the slope of a highly available reference P source, the Relative Biological Value (RBV) can be calculated. RBV values for plant and animal feedstuffs and

6 feed phosphates are presented by Sauvant et al. (2004). In their assays mono sodium phosphate is used as a reference. 3) A third approach is based on determination of the P-retention in broilers, using phosphorus deficient diets in which the major part of the dietary P originates from the test feedstuff. The Dutch retainable P system (Van der Klis and Blok, 1997) for poultry is based on this approach. In their studies, experimental diets contained approx. 1.8 g retainable P and 5.0 g Ca per kg diet. P retention was measured in a 3-day balance study with day old broilers following a 10-day adaptation period. A similar technique was used by Leske and Coon (2002). Figure 4. Body weight gain ( ) and tibia ash contents ( ) in broilers fed graded levels of KH 2PO 4 added to a phosphorus deficient diet (containing 1.0 g non-phytate P) and 7.5g Ca. Diets were fed from 8 to 21 days of age (Augspurger and Baker, 2004). Although it is generally assumed that phytate-p is not available to monogastric animals, experiments with broilers fed a low Ca and retainable P content clearly showed that phytate P can be utilised. It was calculated from experiments by Van der Klis and Blok (1997) that the phytate-p degradation could be as high as 60%, which was supported by measurements at ileal level (Table 2). The ileal phytate-p degradation was significantly reduced in all diets by an increased dietary Ca and retainable P level (Table 2). Table 2. The ileal phytate-p degradation at low and normal dietary Ca and retainable P (rp) contents in broiler diets (Van der Klis and Versteegh, 1996). The rp content was increased using monocalcium phosphate. 1.8 g rp 5.0 g Ca 3.0 g rp 6.8 g Ca Lupin Soybean meal Soybeans Wheat Peas Sunflower seed meal Rapeseed meal Maize The results from the three P evaluation systems is summarised in Figure 5 for some plant feedstuffs, which demonstrates substantial differences between these systems. In general the relative biological availability as presented in the INRA tables is lower compared to the retainable P system as used in the CVB table. This differences might be (at least partly) due to the calcium to phosphorus ratio used in the assays. Using the relative biological availability uses a wider Ca:P ratio than the retainable P system as the first is focussed on maximising retention and the second on maximising absorption. Moreover, it was shown by Lima et al. (1997) that the outcome of the relative biological availability might also be dependent on the response parameter chosen. The differences between the feed phosphates were not only more pronounced for the response parameters reflecting a higher P requirements (bone breaking > bone ash > body weight gain), but also a different ranking between these phosphates differed (Figure 6).

7 P-value (% tp) Lupin SBM Maize RSM SSM Wheat non-phytate P (NRC ) available P (INRA) retainable P (CVB) Figure 5. The non-phytate P, available P and retainable P in broilers in different plant feedstuffs A B C D 70 BW Bone ash Bone breaking Figure 6. The relative biological value of four batches of commercial dicalcium phosphates, using dicalcium phosphate dehydrate as a reference (Lima et al, 1997). New raw materials Since the production of biofuels is heavily stimulated worldwide, increasing amounts of dried distiller grains with solubles (DDGS) from corn, barley and wheat and of glycerol and rapeseed by-products become available as a dietary ingredient for poultry. Although the nutritional value of oil seeds and their by-products for poultry is already known, DDGS are new by-products for poultry feeding. Recently some data were published on the TME N value of corn DDGS batches by Batal and Dale (2006), who reported a range from 2490 to 3190 kcal/kg. These authors presumed that differences between batches were related to differences in the composition of the original corn, the production process and the content of solubles added. Relative phosphorus availabilities in corn DDGS were reported by Amaezcua et al. (2004) from 75 to 102%, using potassium phosphate as a reference. As the composition of these products can be highly variable, research needs to be done to enable incorporation of these products into the feeding tables that are based on different feed evaluation systems.

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