Abstract
Ca digestibility and utilisation in growing pigs are not well understood, and are usually neglected in diet formulation. This has implications not only for the accurate determination of its requirements but also for its interactions with other nutrients. A systematic review and meta-analysis (meta-regression) of published trials was carried out to quantify factors affecting Ca absorption and utilisation, and to derive an estimate of Ca endogenous excretion. The analysis was carried out on the data from forty studies, corresponding to 201 treatments performed on 1204 pigs. The results indicated that although Ca absorption and retention (g/kg of body weight per d) increased with increasing Ca intake (P<0·001), non-phytate-P intake (P<0·001) and exogenous phytase supplementation (P<0·001), these values decreased with increasing phytate-P intake (P<0·05). Interactions between exogenous phytase and Ca intake, indicating reduced efficacy of this enzyme (P<0·001), and between phytate-P intake and exogenous phytase, counteracting the direct negative effect of phytate-P (P<0·05) on Ca absorption and retention, were also detected. There were no effects of animal-related characteristics, such as pig genotype in Ca absorption and retention. The large amount of variance explained in Ca absorption (90 %) and retention (91 %) supported our choice of independent variables. Endogenous Ca losses obtained via linear regression were 239 mg/kg of DM intake (95 % CI 114, 364). These outcomes advance the current understanding of Ca digestibility and utilisation, and should contribute towards establishing requirements for digestible Ca. Consequently, pig diets will be more correctly formulated if digestible Ca values are used in estimating requirements for Ca.
Highlights
Ca and P play important roles in bone mineralisation and development[1], as well as in many non-skeletal physiological processes[2,3]
The results of this study further enhance the current understanding of Ca digestion and metabolism in pigs, and should contribute towards the development of a dietary formulation system based on both digestible Ca and digestible P
To illustrate how the two types of total P intake (TP) affected Ca absorption, we considered a scenario without any additional exogenous phytase intake (ExPhyt)
Summary
Ca and P play important roles in bone mineralisation and development[1], as well as in many non-skeletal physiological processes[2,3]. There has been limited research on the subject of Ca digestibility in growing and finishing pigs, and only recently experiments have established these values for several plant-based and inorganic sources of Ca[14,15,16,17] This absence of information reflects the difficulty in the accurate determination of Ca requirements and to a certain extent of P utilisation. Current National Research Council[19] guidelines for Ca content in pig diets are expressed on the basis of total Ca, which ignore endogenous losses and the process of digestion This fact often leads to over-supplementation of inorganic Ca, which promotes the formation of indigestible Ca–phytate-P (PP) complexes in the small intestine of pigs, reducing P digestibility[20]. The results of this study further enhance the current understanding of Ca digestion and metabolism in pigs, and should contribute towards the development of a dietary formulation system based on both digestible Ca and digestible P
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