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Digestibility of Calcium in Pig Diets

14 August 2014

Diet complexity, phytase, phytate and fibre affected the digestibility of calcium in pig diets containing fishmeal in two studies at the Hans H. Stein Monogastric Nutrition Laboratory but fat level did not.

The two studies Effect of Phytase, Fibre and Fat on Calculated Values for Apparent and Standardised Total Tract Digestibility of Calcium in Fish Meal showed the presence of phytate in swine diets reduces the digestibility of calcium because phytate is able to bind calcium from organic sources and some inorganic sources, making it inaccessible to the pig. Microbial phytase breaks down phytate and increases the availability of calcium.

An experiment was conducted to test the hypothesis that inclusion of microbial phytase increases the apparent (ATTD) and standardised (STTD) total tract digestibility of calcium in fish meal in diets containing phytate from corn and corn germ.

Besides phytate, corn and corn germ also add fibre and fat to diets, so it is important to know how fibre and fat affect calcium digestibility. Therefore, a second experiment was conducted to test the hypothesis that the values of ATTD and STTD of calcium obtained from corn starch and corn based diets may differ, and to determine the effect of dietary fibre and fat on the ATTD and STTD of calcium in fish meal.

Experiment 1. Effect of phytase on calcium digestibility in diets with no phytate and with phytate

The first experiment was designed to determine the effect of phytase on the ATTD and STTD of calcium in fish meal in diets that either contained phytate or did not contain phytate.

Forty growing pigs with an average initial body weight of 19.16kg were fed one of five diets. The fish meal and corn starch based diet contained no phytate, whereas the fish meal and corn-corn germ based diet contained 0.7 per cent phytate.

Two levels of microbial phytase (0 and 500FTU per kg) were added to each diet, for a total of four experimental diets. Fish meal was the only source of calcium in these diets. A calcium-free diet was also used to determine basal endogenous losses of calcium.

The ATTD and STTD values for calcium in pigs fed the corn-corn germ based diet were greater (P<0.001) than the ATTD and STTD in pigs fed the corn starch based diets (Table 1).

The addition of phytase increased (P<0.05) the ATTD and STTD of calcium in the corn-corn germ based diet, but did not affect the ATTD and STTD of calcium in the corn starch based diets.

Table 1. Apparent and standardised total tract digestibility of calcium in diets containing fish meal without or with phytate and without or with microbial phytase
ItemFish meal + corn starch-based dietFish meal + corn-corn germ-based dietP-value
0 FTU500 FTU0 FTU500 FTUDietPhytaseDiet × Phytase
ATTD of Ca, % 51.22 57.27 73.07 84.01 <0.001 0.009 0.421
STTD of Ca, % 53.87 60.07 76.21 86.88 <0.001 0.009 0.462

Experiment 2. Effect of type of diet, fibre and fat on calcium digestibility

The second experiment used 50 growing pigs with an average initial body weight of 19.36kg.

Two diets were formulated based on fish meal and corn starch. Solka floc was added to one of the diets to evaluate the effect of fibre. Two additional diets were formulated based on fish meal and corn, with soybean oil added to one of the diets to evaluate the effect of fat. As in Experiment 1, a calcium-free diet was also used.

The ATTD and STTD values for calcium were greater (P<0.05) in pigs fed corn-based diets than in pigs fed corn starch based diets (Table 2).

The addition of fibre to corn starch diets increased (P<0.001) the digestibility of calcium. The level of fat in the diets did not affect the ATTD or STTD of calcium.

Table 2. Apparent and standardised total tract digestibility of calcium in diets containing fish meal and either corn starch or corn, and differing levels of fibre and fat
ItemDietContrast P-value
1234Corn starch vs. cornFibreFat
Fish meal - corn starchFish meal - corn starch + fibreFish meal - cornFish meal - corn + fat1 vs. 31 vs. 23 vs. 4
ATTD of Ca, % 40.42 57.08 84.24 82.91 <0.001 <0.001 0.623
STTD of Ca, % 45.64 62.23 88.99 88.14 <0.001 <0.001 0.754

Key Points

ATTD and STTD of calcium were greater for pigs fed diets based on corn and corn germ than for pigs fed a corn starch-based diet.

Adding phytase to diets increased the ATTD and STTD of calcium when phytate was present in corn starch-based diets.

Addition of fibre to diets increased ATTD and STTD of calcium but addition of fat did not affect calcium digestibility.

The increase in ATTD and STTD of calcium in corn-corn germ based diets relative to values in corn starch-based diets may be due to the greater fibre concentration in corn and corn germ.

The data indicate that the digestibility of calcium in synthetic diets based on corn starch is not always representative of the digestibility in practical diets.

This report is based on unpublished data by Caroline González-Vega, Carrie Walk and H.H. Stein.

August 2014

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