Digestibility of Ca and P is most correctly determined as standardized total tract digestibility (STTD). Data for the STTD of P in most feed ingredients have been published, and the STTD of Ca has also been determined in many feed ingredients. However, in practical diet formulation, values for STTD of Ca and P obtained in growing pigs are also applied to sows although there is a lack of comparative data between growing pigs and sows.

Therefore, an experiment was conducted to test the hypothesis that no differences exist between gestating sows and growing pigs for basal endogenous losses, STTD, and retention of Ca and P.

Experimental design

A total of 32 gestating sows and 32 growing pigs were used in the experiment. Sows were parity 2 to 6 (average = 2.48) at an average of 40 days of gestation, and growing pigs had an average body weight of 19.8 kg. Sows and pigs were randomly allotted to 4 diets. Two diets were formulated to contain a low or high amount of phytate. Diets were formulated based on corn, soybean meal, limestone, and dicalcium phosphate, and the high-phytate diet also contained 40% full-fat rice bran. A Ca-free diet and a P-free diet were also formulated to determine basal endogenous losses of Ca and P, respectively. Sows were fed at a daily level of 1.5 × maintenance ME requirement and growing pigs were fed 3.0 × maintenance ME requirement. Fecal and urine samples were quantitatively collected, and the basal endogenous losses, and STTD of Ca and P in experimental diets were calculated based on intake and fecal and urine output of Ca and P.

Results

The basal endogenous loss of Ca was 1.58 g/kg dry matter intake and 0.43 g/kg dry matter intake for gestating sows and growing pigs, respectively, and the basal endogenous loss of Ca from gestating sows was greater (P < 0.001) than from growing pigs (Table 1). The basal endogenous loss of P was 0.78 g/kg dry matter intake from gestating sows and this value was greater (P = 0.011) than the basal endogenous loss of P from growing pigs (0.16 g/kg dry matter intake).

The apparent total tract digestibility (ATTD) of dry matter was not affected by physiological state, but pigs fed the low-phytate diet had greater (P < 0.001) ATTD of dry matter than pigs fed the high-phytate diet (Table 2). Phytate level did not affect the STTD of Ca or Ca retention by gestating sows, but the STTD of Ca and Ca retention were greater if growing pigs were fed the low-phytate diet than if they were fed the high-phytate diet (physiological state × phytate level interaction, P < 0.001). Regardless of dietary treatment, gestating sows had reduced (P < 0.001) digestibility and retention of Ca compared with growing pigs. The STTD of P was greater if pigs were fed the low-phytate diet rather than the high-phytate diet, but the difference was greater for growing pigs than for gestating sows (physiological state × phytate level interaction; P = 0.002). Phosphorus retention by growing pigs fed the low-phytate diet was greater than if they were fed the high-phytate diet, but P retention by gestating sows was not affected by phytate level (physiological state × phytate level interaction; P < 0.001). Regardless of dietary treatment, gestating sows had reduced (P < 0.001) digestibility and retention of P compared with growing pigs.

Key points

• Gestating sows have reduced digestibility and retention of Ca and P, but increased basal endogenous losses of Ca and P, compared with growing pigs.
• Response to dietary phytate in terms of digestibility and retention of Ca and P is different between gestating sows and growing pigs.
• It may not always be accurate to formulate diets for gestating sows using STTD values for Ca and P that were obtained in growing pigs.

Table 1. Basal endogenous losses of Ca and P from gestating sows and growing pigs fed Ca-free and P-free diets

Table 2. Apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) and retention of Ca and P in experimental diets fed to gestating sows and growing pigs

^a-cWithin a row, means without a common superscript differ (P < 0.05).

This report is based on unpublished research by Su A Lee and Hans H. Stein.