The effects of increasing dietary total Ca/total P ratios on growth performance, Ca and P balance, and bone mineralization in nursery pigs fed diets supplemented with phytase

Abstract

The objective of this study was to investigate the effects of increasing dietary total Ca/total P ratios on growth performance, digestibility of Ca and P, bone mineralization, and concentrations of Ca and P in urine and plasma in nursery pigs. There were 6 diets in a randomized complete block design, including 1 positive control and 5 diets corresponding to 5 total Ca/total P ratios: 0.55, 0.73, 0.90, 1.07 and 1.24 (analyzed as 0.58, 0.75, 0.93, 1.11 and 1.30). These 5 diets were deficient in P but supplemented with 1,000 phytase units/kg feed. Each diet was fed to 6 pens of 8 pigs (4 barrows and 4 gilts per pen). All diets contained 3 g/kg TiO2, and fecal samples were collected from each pen on days 5-7 of trial. At the end, one pig per pen was sacrificed to collect the right tibia and urine in bladder. The results showed that increasing dietary Ca/P ratio to 0.93 increased gain:feed but then gain:feed decreased as the Ca/P ratio was increased to 1.30 (linear and quadratic, P < 0.05). Although average daily gain and final BW were unaffected by changing Ca/P ratio in diet, dry bone weight; weights of bone ash, Ca and P; and bone Ca/P ratio increased linearly (P < 0.001) with increasing dietary Ca/P ratio. The percent bone Ca showed a tendency to increase (P = 0.064). Increasing dietary Ca/P ratio decreased apparent total tract digestibility (ATTD) of Ca and P linearly (P < 0.05) and the concentration of digestible P linearly (P < 0.001), but increased the concentration of digestible Ca (linear and quadratic effects: P < 0.01) and the digestible Ca/P ratio (linear effect: P < 0.001). In plasma, the concentration of Ca increased both linearly (P < 0.01) and quadratically (P = 0.051), whereas concentration of P tended (linear and quadratic, P < 0.10) to decrease with increasing dietary Ca/P ratio. Similarly, in urine, the concentration of Ca increased both linearly and quadratically (P < 0.05), whereas concentration of P decreased linearly (P < 0.01). In conclusion, increasing the dietary Ca/P ratio reduced feed efficiency but increased bone mass and the amounts of Ca and P deposited in bone of nursery pigs fed diets supplemented with 1,000 FYT/kg phytase. The increases in bone growth led to a reduction of urinary P excretion that exceeded the decreased digestible P supplied in diet with the widening dietary Ca/P ratios.

The effects of concurrent increases in supplementation of calcium and phytase on growth performance, balance of Ca and P, and bone mineralization in nursery pigs

“…In our previous study ( Zhai et al, 2023 ), increasing dietary Ca/P ratio reduced ATTD of P and the concentration of digestible P in diets supplemented with 1,000 FYT/kg feed. In consideration of phytase as something with a potential counterbalance to the negative effects of high dietary Ca on P absorption, we hypothesized that the P digestibility and the digestible P content in a diet will not be impaired if we increase the dose of phytase as we increase the supplementation of Ca.…”

“…Each pen or pig was an experimental unit. ATTD of Ca and P, and ATTD Ca and P were calculated as described by Zhai et al (2023) .…”

“… Qian et al (1996) reported a linear decrease in apparent total tract digestibility (ATTD) of P with increasing total Ca/total P ratio from 1.2 to 2.0 in weaner pigs fed diets supplemented with phytase, which paralleled the adverse effects on growth performance and bone characteristics. In our previous study, increasing total Ca/total P ratio from 0.6 to 1.3 decreased ATTD of P, but increased bone mineralization in weaner pigs supplemented with phytase because the pigs conserved enough P through reduction of P excretion through urine to compensate for the decreased digestible P from diet ( Zhai et al, 2023 ). In these studies, a fixed dose of phytase was supplemented.…”