Diarrhea is one of the main problems for pigs during the post-weaning period. Traditionally, antibiotic growth promoters have been used to control post-weaning diarrhea, but consumers are increasingly concerned about this practice and there is therefore an interest in feeding diets that contain no antibiotics. However, feeding pigs without antibiotic growth promoters requires alternative strategies to control post-weaning diarrhea, but feeding low protein diets may be one way to reduce the incidence of post-weaning diarrhea. However, there is a lack of knowledge about consequences of reducing the protein level in diets fed to weanling pigs.

Feeding low protein diets to pigs results in increased net energy in the diet, reduced water intake by pigs, and reduced nitrogen excretion. This will result in reduced volume of manure and also reduced concentrations of ammonium in manure. However, if formulation of low protein diets results in feeding diets with concentrations of indispensable AA that are below the requirements, deposition of protein in pigs may be greater and deposition of fat may be increased compared with pigs fed a diet containing higher level of protein. However, it is not known if feeding a diet low in protein to weanling pigs also results in changes in carcass characteristics of market pigs.

Therefore, the objective of this experiment was to test the hypothesis that feeding a low-protein diet to pigs during the post-weaning period will result in reduced diarrhea during this period, but no effects on growth performance from wean to finish and no changes in carcass composition of pigs when they reach market weight.

Requirements for P for growing pigs are expressed as the requirement for standardized total tract digestible (STTD) P, whereas requirements for Ca are usually expressed as requirements for total Ca. It is, however, recognized that diets for pigs are most accurately formulated based on a STTD Ca:STTD P ratio, and recent work has generated values for STTD of Ca in most Ca containing feed ingredients, which makes it possible to formulate diets based on STTD Ca.

Recent data from the University of Illinois have indicated that if STTD P is at the requirement, a ratio between STTD Ca and STTD P that is less than 1.35:1, 1.25:1, and 1.10:1 maximizes growth performance of pigs from 25 to 50 kg, 50 to 85 kg, and 100 to 130 kg, respectively. However, the STTD Ca:STTD P ratio needed to maximize bone ash is greater than the ratio needed to maximize growth performance. An attempt to estimate the requirement for STTD Ca by pigs from 11 to 25 kg was also made, but due to a reduction in ADG and G:F as dietary Ca increased, an optimal STTD Ca:STTD P ratio could not be estimated.

Calcium may be absorbed by transcellular or paracellular transport. Transcellular transport is the primary route if dietary Ca is low, but if dietary Ca is adequate or high, Ca is mainly absorbed using the paracellular route via the tight junctions. However, there are limited data demonstrating effects of dietary Ca concentration on abundance of genes related to transcellular and paracellular transport of Ca in the small intestine of pigs.

Therefore, the objectives of this experiment were to test the hypotheses that a STTD Ca:STTD P ratio less than 1.40:1 maximizes growth performance of pigs from 11 to 25 kg and that increasing dietary Ca downregulates abundance of genes related to transcellular absorption of Ca and tight junction proteins in the small intestine.

Sorghum is used as an alternative to corn due to its lower cost and wide availability. However, conventional sorghum contains high concentration of tannin and phytate, which act as antinutritional factors. Use of microbial phytase may hydrolyze phytate and subsequently improve P absorption. High-lysine sorghum is a new variety of sorghum which may be comparable to other cereal grains and may serve as alternative to corn for pigs. However, there are at this point no data for effects of adding phytase to diets containing sorghum and no data to demonstrate the nutritional value of high-lysine sorghum.

Therefore, 2 experiments were conducted to test the hypothesis that inclusion of 500 phytase units (FTU)/kg of microbial phytase improves the standardized total tract digestibility (STTD) of P in sorghum varieties. The second hypothesis was that the STTD of P, as well as concentrations of digestible energy (DE) and metabolizable energy (ME) in high-lysine sorghum is not different from that of corn and other sources of sorghum.

Casas, G. A., M. F. Overholt, A. C. Dilger, D. D. Boler, and H. H. Stein. 2018. Effects of full fat rice bran and defatted rice bran on growth performance and carcass characteristics of growing-finishing pigs. J. Anim. Sci. 96:2293–2309. Link to abstract

Blavi, L., J. N. Broomhead, and H. H. Stein. 2018. Effects of a novel phytase on growth performance, bone measurements, and Ca and P digestibility in diets fed to growing pigs. J. Anim. Sci. 96(Suppl. 2):163 (Abstr.) Link to abstract (.pdf)

Casas, G. A. and H. H. Stein. 2018. Young Scholar Presentation: Nutritional value of rice coproducts fed to pigs. J. Anim. Sci. 96(Suppl. 2):143 (Abstr.) Link to abstract (.pdf)

Campbell, J. M., J. D. Crenshaw, J. Polo, D. Mellick, M. Bienhoff, and H. H. Stein. 2018. Impact of formaldehyde treated pig feed containing spray dried plasma on weaned pig growth performance. J. Anim. Sci. 96(Suppl. 2):138-139 (Abstr.) Link to abstract (.pdf)

Espinosa, C. D., S. R. Fry, J. L. Usry, and H. H. Stein. 2018. Copper hydroxychloride improves growth performance and reduces diarrhea frequency of weanling pigs fed a corn-soybean meal diet. J. Anim. Sci. 96(Suppl. 2):131-132 (Abstr.) Link to abstract (.pdf)

Last month's newsletter included a research report on research into a novel E. coli phytase expressed in corn, called GraINzyme. Results of that research indicated that adding GraINzyme phytase to diets fed to young growing pigs increased growth performance, digestibility of calcium and phosphorus, and bone mineralization. The comparative effects of GraINzyme and a commercial phytase was not tested in the previous study. Therefore, an experiment was conducted to compare effects of addition of GraINzyme phytase to the commercial phytase AxtraPhy in diets fed to growing pigs.