Effects of Added Calcium Carbonate on Weanling Pig Growth Effects of Added Calcium Carbonate on Weanling Pig Growth Performance Performance

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Introduction
Acid binding capacity (ABC), or buffering capacity, is a feed ingredient's ability to change gastrointestinal pH.A low stomach pH (< 4) improves protein digestion and intestinal health, whereas a high gastric pH has been observed to result in negative gastrointestinal challenges including increased intestinal microflora. 2 For this reason, ABC has been used as a means of evaluating diets.The ABC -4 is the amount of acid in Swine Day 2021 Kansas State University Agricultural Experiment Station and Cooperative Extension Service milliequivalents (mEq) required to lower the pH of 1 kg of feed to 4. Therefore, ABC -4 of diets is indicative of a low stomach pH which may improve protein digestion and growth performance.Some minerals have been shown to have high ABC in comparison to common ingredients used in swine diets such as cereal grains, vegetable proteins, fat sources and crystalline amino acids. 3Calcium, in the form of calcium carbonate, is one such mineral with a relatively high ABC due to its cationic properties that would then increase the ABC of the diet and increase stomach pH.Because calcium carbonate is the main source of Ca in most swine diets, lowering dietary Ca may improve growth performance due to a decrease in ABC.However, bone mineralization would be a concern with prolonged feeding of low Ca diets.Therefore, the objective of this study was to investigate the effects of calcium carbonate level immediately post-weaning on growth performance and fecal dry matter of nursery pigs.

Materials and Methods
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment.The study was conducted at the Kansas State University Segregated Early Weaning Facility in Manhattan, KS.The facility has two identical barns that are completely enclosed, environmentally controlled, and mechanically ventilated.Each pen contains a 4-hole, dry self-feeder and a cup waterer to provide ad libitum access to feed and water.Pens (4 × 4 ft) had metal tri-bar floors and allowed approximately 2.7 ft 2 /pig.A total of 695 barrows (DNA Line 200 × 400; initially 12.9 ± 0.05 lb) were used in two groups in a 28-d study with 5 pigs per pen and 27 or 28 pens per treatment.Pigs were randomly assigned to pens and then pens were allotted to 1 of 5 dietary treatments.Dietary treatments were formulated to provide 0, 0.45, 0.90, 1.35, and 1.80% calcium carbonate at the expense of corn (Table 1).This corresponded with final calculated ABC -4 values of 424, 481, 539, 597, and 655 mEq., respectively.A common phase 2 diet was formulated to contain 0.90% calcium carbonate which corresponded to a calculated ABC -4 of 475 mEq.Treatment diets were fed from d 0 to 14 and a common phase 2 diet was fed from d 14 to 28.Treatment diets were fed in both meal (group 1) and pellet (group 2) form, with the common phase 2 diet fed in meal form.A single base diet was manufactured at Hubbard Feeds in Beloit, KS, with calcium carbonate and corn additions mixed and pelleted (group 2) at the O.H. Kruse Feed Technology Innovation Center at Kansas State University, Manhattan, KS.Pig weights and feed disappearances were measured on d 0, 14, and 28 of the experiment to determine ADG, ADFI, and F/G.
Complete diet samples of each treatment were taken with a grain probe from every other bag upon completion of manufacturing and were stored at -4°F (-20°C).Six sub-samples of each diet were ground with a food processor to create a homogeneous sample and then submitted for analysis of Ca and P (K-State Research and Extension Soil Testing Laboratory, Manhattan, KS).

Swine Day 2021 Kansas State University Agricultural Experiment Station and Cooperative Extension Service
On d 10 of the experiment, feces were collected from 3 piglets per pen and dried at 130°F for 48 h to determine fecal dry matter.Pigs were removed for welfare concerns if they were observed to lose 2.0 lb or more through d 10 or were unthrifty.

Statistical analysis
Data were analyzed as a completely randomized design with pen serving as the experimental unit.Treatment was included in the statistical model as a fixed effect and block was incorporated in the model as a random effect, which accounted for initial pen average body weight and group.Data were analyzed using R Studio (Version 3.5.2,R Core Team, Vienna, Austria).Contrasts were used to test for linear and quadratic responses between treatments with results considered significant at P ≤ 0.05 and marginally significant at 0.05 < P ≤ 0.10.
From day 0 to 14 (treatment period), ADG and d 14 BW decreased (linear, P < 0.010) as calcium carbonate increased (Table 3).Likewise, F/G worsened (linear, P < 0.001) as calcium carbonate increased with no evidence (P > 0.10) for difference in ADFI.From d 14 to 28 (common period) and for the overall experiment (d 0 to 28), there was no evidence (P > 0.10) for differences in growth performance between treatments.
For mortalities, there was a tendency for a quadratic (P = 0.078) response with intermediate levels of calcium carbonate having greater mortalities than the high and low dietary levels.However, there was no evidence (P > 0.10) for differences in removals or total mortality and removals.For fecal dry matter, there was a quadratic (P = 0.091) tendency where pigs fed the highest and lowest calcium carbonate diets had the greatest dry matter.In summary, increasing calcium carbonate in the diets of nursery pigs decreased daily gain and worsened feed efficiency immediately after weaning.Despite the linear response, ADG decreased from 0 to 0.45% calcium carbonate, with no change thereafter.Interestingly, feed intake was not changed, thus indicating potential changes in feed utilization as influenced by the ABC -4 of the diets.More research is needed to confirm if this response is indeed reflective of the ABC -4 of the diets or if lower levels of calcium carbonate improved the phase 1 nursery pig growth performance.

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Table 1 .
Phase 1 and 2 diet composition (as fed basis) 1 Kansas State University Agricultural Experiment Station and Cooperative Extension Service Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Table 1 .
Phase 1 and 2 diet composition (as fed basis) 1 Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Table 3 .
Effects of increasing calcium carbonate on weanling pig growth performance 1