Recent studies conducted in our laboratory have determined values for standardized total tract digestibility (STTD) of calcium in feed ingredients fed to pigs. However, there is a lack of information about the requirement for STTD calcium in diets for pigs. Therefore, an experiment was conducted to measure calcium balance at different levels of STTD calcium in diets fed to 11 to 25 kg pigs.
Materials and methods
Eighty weanling pigs with an initial average body weight of 13.12 kg were fed eight diets based on corn, soybean meal, and lactose. Six diets contained 0.36% STTD phosphorus and either 0.32, 0.40, 0.48, 0.56, 0.64, or 0.72% STTD calcium. According to NRC (2012), the STTD phosphorus requirement for 11 to 25 kg pigs is 0.33%. Two additional diets containing 0.72% STTD calcium and 0.33% or 0.40% STTD phosphorus were also prepared. The diet with 0.33% STTD Ca was used to determine if there were any negative effects of using 0.36% phosphorus in the experimental diets. The diet with 0.40% STTD P was used to confirm that calcium retention was not limited by the amount of digestible phosphorus in the diet.
Fecal and urine samples were collected and analyzed to determine calcium absorption, retention, and excretion.
Results
Calcium absorption, retention, and excretion in grams per day increased linearly (P < 0.001) as the level of STTD calcium in the diets increased (Table 1). Fecal and urine calcium output, and amount of calcium retained and excreted in grams per day increased linearly (P < 0.001) and quadratically (P < 0.05) as the level of STTD calcium increased. Calcium retention in percentage and ATTD of calcium decreased linearly (P < 0.001) as the level of STTD calcium increased.
The observation that increasing levels of digestible calcium increased the amount of calcium absorbed from the intestines and increased the excretion of calcium in the urine indicates that calcium requirement is mostly regulated at the renal level.
Calcium retention increased as the level of STTD phosphorus increased. Urinary calcium output, and calcium excretion in percentage and grams per day decreased as the level of STTD phosphorus increased.
Fitted broken line analysis and quadratic analysis were used to determine the STTD calcium requirement to maximize retention in grams per day. The intersection of the two analyses was 0.60% STTD calcium.
Key points
- Calcium retention in grams/day increased, but ATTD and retention in percentage decreased as STTD calcium increased.
- The requirement to maximize calcium retention in grams per day is 0.60% calcium when feeding 0.36% phosphorus. This corresponds to a digestible calcium:digestible phosphorus ratio of 1.67.
Table 1. Calcium balance and apparent total tract digestibility (ATTD) of Ca for pigs fed diets containing between 0.32 and 0.72% standardized total tract digestible (STTD) Ca and 0.36% STTD P
|
Item |
Diets |
||||||||
|
STTD Ca, % |
0.32 |
0.40 |
0.48 |
0.56 |
0.64 |
0.72 |
|
P-Value |
|
|
STTD P, % |
0.36 |
0.36 |
0.36 |
0.36 |
0.36 |
0.36 |
SEM |
Linear |
Quadratic |
|
Feed intake, g/d |
771 |
759 |
781 |
746 |
782 |
761 |
29 |
0.964 |
0.953 |
|
Ca intake, g/d |
3.10 |
4.14 |
5.33 |
6.07 |
7.45 |
8.30 |
0.26 |
<0.001 |
0.985 |
|
Fecal Ca output, g/d |
0.82 |
1.19 |
1.54 |
1.93 |
2.34 |
3.03 |
0.10 |
<0.001 |
0.039 |
|
Urine Ca output, mg/d |
122 |
204 |
383 |
731 |
1124 |
1534 |
65 |
<0.001 |
<0.001 |
|
Absorbed Ca, g/d |
2.28 |
2.96 |
3.79 |
4.14 |
4.95 |
5.25 |
0.19 |
<0.001 |
0.283 |
|
Ca retention, g/d |
2.16 |
2.75 |
3.41 |
3.41 |
3.78 |
3.95 |
0.15 |
<0.001 |
0.018 |
|
Ca retention, % |
69.74 |
66.34 |
64.03 |
56.17 |
53.11 |
47.83 |
1.62 |
<0.001 |
0.385 |
|
Ca excretion, g/d |
0.94 |
1.39 |
1.92 |
2.66 |
3.46 |
4.55 |
0.14 |
<0.001 |
<0.001 |
|
Ca excretion, % |
30.26 |
33.66 |
35.97 |
43.83 |
46.89 |
52.17 |
1.62 |
<0.001 |
0.385 |
|
ATTD of Ca, % |
73.68 |
71.35 |
71.13 |
68.15 |
68.25 |
65.24 |
1.52 |
<0.001 |
0.889 |
Table 2. Calcium balance and apparent total tract digestibility (ATTD) of Ca for pigs fed diets containing 0.72% standardized total tract digestible (STTD) Ca and from 0.33 to 0.40% STTD P
|
Item |
Diets |
|
||||
|
STTD Ca, % |
0.72 |
0.72 |
0.72 |
|
P-Value |
|
|
STTD P, % |
0.33 |
0.36 |
0.40 |
SEM |
Linear |
Quadratic |
|
Feed intake, g/d |
748 |
761 |
717 |
30 |
0.412 |
0.465 |
|
Ca intake, g/d |
8.19 |
8.30 |
7.70 |
0.26 |
0.158 |
0.326 |
|
Fecal Ca output, g/d |
2.89 |
3.03 |
2.56 |
0.11 |
0.021 |
0.035 |
|
Urine Ca output, mg/d |
1677 |
1534 |
1096 |
73 |
<0.001 |
0.243 |
|
Absorbed Ca, g/d |
5.09 |
5.25 |
5.03 |
0.20 |
0.774 |
0.450 |
|
Ca retention, g/d |
3.64 |
3.95 |
4.25 |
0.16 |
0.008 |
0.804 |
|
Ca retention, % |
44.63 |
47.83 |
54.51 |
1.65 |
<0.001 |
0.611 |
|
Ca excretion, g/d |
4.69 |
4.55 |
3.47 |
0.14 |
<0.001 |
0.031 |
|
Ca excretion, % |
55.37 |
52.17 |
45.49 |
1.65 |
<0.001 |
0.611 |
|
ATTD of Ca, % |
65.88 |
65.24 |
67.95 |
1.57 |
0.322 |
0.431 |
This report is based on unpublished research by Caroline González-Vega and Hans H. Stein.