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Appreciation is expressed to Guido Geeroms and Daniel D'Haese, who supplied the pigs; and to Annie Lejeune, Frederik Colin, Sabine Buyle and the staff of the abattoir Lokerse Vleesveiling cvba and the cutting plant Van Ruyteghem for their technical support.

IntroductionAs a result of the unavailability of the main fraction of vegetable phosphorus for monogastric farm animals, feed phosphates, are almost always incorporated in the diets of pigs and poultry. Among the commercially available feed phosphates, calcium phosphates (Caphosphates) are by far the most important. However, different Ca-phosphates show differences in availability that largely determine the price differences between them, but also, partly, the polluting effect of pig manure in areas with intensive animal production. In the Netherlands and on the sandy soils of northern Belgium, for example, as well as in other regions with intensive animal production, nitrogen (N) and phosphorus (P) excretion by animal husbandry, per unit arable land, largely exceeds the recommendations for reasonable crop production.However, an overview of the available digestibility figures of Ca-phosphates, in terms of 'apparent digestible P' reveals a tremendous variation. For di-hydrated dicalciumphosphate (CaHPO, .2H,O) the authors have found digestibility figures varying between 52 and 71 %; for anhydrous dicalciuniphosphate (CaHPO,) between 54 and 87%, and finally, for monocalciumphosphate (Ca(H,PO,),) between 64 and 91 % (Table 6). It is somewhat difficult to explain this variation only as a result of impure products and the presence of phosphate forms, other than those labelled. Other factors must also be involved, such as the high variation in the digestibility of Ca and P by pigs. The variation coefficients of the Ca and P digestibility figures of pig diets, in the authors laboratory, are five to more than ten times higher than those of dry matter, crude protein or energy.This fact requires, in the case of digestibility studies with feed phosphates on as high as possible supplementation level (eventually in one or two steps). This, in turn, is only possible when young animals and/or semi-synthetic diets, very low in P, are used, while the digestibility of feed phosphate must be measured at below the physiological requirements.Moreover, the use of markers can be criticized. WALZ and PALLAUF (1993) among others, used cromium (111) oxide (Cr,O,) as a marker substance in their feed phosphates digestibility studies with pigs and found a recovery of only 77% o n average. MROZ et al. (1991) cited a recovery of 92 %. In two unpublished experiments with young pigs, the authors came to the same conclusions as WALZ and PALLAUF (1993) when using 4 N HCI insoluble ash as a marker substance (MCCARTHY et al. 1974). Comparing the total faeces collection technique and the marker technique led to the conclusion that only f 8 0 % (Exp. 1) and * 9 0 % (Exp. 2) of the marker was recovered, although the supplemented Celite (Hyflo Supercel, UCB, Belgium) was carefully checked for in vitro recovery after 4 N HCI treatment. U. S. Copyright Clearance Center Code Statement: 093 1-2439/97/7702-0053 $ 14.00/0 54 W. Eeckhout and M . De PacpeAnothcr possiblc source of error is the frequently observed discrepancy bctwecn formulated P supplementatio...

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238 samples, representing 19 vegetable feeds, were analysed for total and phytate phosphorus. Phytase activity was estimated in a limited number of feeds with an activity of >100 units/kg. Near infrared reflection spectra (NIRS) were taken between 1100 and 2500 nm in steps of 4 nm. By means of principal component analysis the feeds were grouped in starch- (n = 150) and protein-rich feeds (n = 88). NIRS-calibrations were developed using partial least square regression and tested by cross-validation. Total P varied from 0.22 to 1.25% and phytate P from 0.05 to 1.02% for high-starch feeds and, respectively, from 0.46 to 1.37% and from 0.22 to 0.56% for protein-rich feeds. Within these broad ranges, NIRS-values were highly correlated to measured total and phytate P with prediction errors of 0.08 and 0.08%, respectively, for high-starch feeds and 0.08 and 0.04%, for protein-rich feeds. However, considering the mostly small deviation of mean or calculated values for the individual feeds, NIRS is practical for predicting total P for wheat byproducts and phytate P for maize gluten feed. On the other hand, NIRS could be used for unknown or not tabulated products. Spectral signals from total and phytate P are partly based on direct responses from organic complexes but also on secondary relations through protein and fat. It was concluded that NIRS seemed not sensitive enough to detect phytase.