Improving growth performance of weanling pigs

Direct fed microbials increase energy and nutrient digestibility

By Maryane S. F. Oliveira and Hans H. SteinDirect fed microbials, sometimes also called probiotics, are among the additives that are often included in diets for weanling pigs. Direct fed microbials are believed to be able to colonize in the intestinal tract of pigs, which allow them to secrete specific enzymes that may improve energy and nutrient digestibility, and thus, possibly increase feed conversion.There are, however, a large number of different products available and each product is based on unique strains of microbes that have unique characteristics. Over the last few years, four experiments with different sources of direct fed microbials were conducted at the University of Illinois to test the hypothesis that direct fed microbials may increase energy and nutrient digestibility and growth performance of weanling pigs.Experimental procedures
In two digestibility experiments, pigs with cannulas in the distal ileum were used to determine ileal digestibility of energy and amino acids in diets without or with direct fed microbials (Blavi et al., 2019; Oliveira et al., 2022). Fecal samples were also collected and total tract digestibility of energy was calculated.In two growth performance experiments, weanling pigs were fed diets without or with direct fed microbials for 35 days (Casas et al., 2020) or 43 d (Jaworski et al., 2017). The direct fed microbials that were used included Bacillus amyloliquefaciens and Bacillus. Subtilis (Chr. Hansen, Hørsholm, Denmark; Blavi et al., 2019), Bacillus toyonensis, (Rubinum, S. A., Spain; Oliviera et al., 2022), C. Butyricum (BASF, Florham Park, NJ; Casas et al., 2020) and a spore forming bacillus based product (Danisco Animal Nutrition, Marlborough, UK; Jaworski et al., 2017).Diets in both digestibility experiments were based on corn, soybean meal and DDGS, whereas diets in the growth performance experiments contained corn, soybean meal and wheat middlings (Casas et al., 2020), and corn and soybean meal without (low fiber) or with DDGS and wheat middlings (high fiber; Jaworski et al., 2017).Increased ileal digestibility of energy and some amino acids
Inclusion of Bacillus amyloliquefaciens or Bacillus toyonensis in diets increased (P < 0.05) ileal digestibility of energy, but this did not translate into an increased total tract digestibility of energy.It therefore appears that use of direct fed microbials may shift the digestibility of energy from the hindgut to the small intestine. This may increase the utilization of energy because energy in the form of glucose absorbed from the small intestine is utilized with a greater efficiency than energy in the form of volatile fatty acids absorbed from the hindgut. Indeed, the ileal digestibility of starch tended (P < 0.10) to increase if Bacillus toyonensis was used (Table 1), indicating that Bacillus toyonensis may have secreted amylase to aid in starch digestion.Inclusion of amyloliquefaciens in diets increased (P < 0.05) or tended to increase (P < 0.10) the ileal digestibility of all indispensable amino acids except histidine, lysine and phenylalanine, whereas Bacillus toyonensis tended (P < 0.10) to increase the ileal digestibility of methionine.It therefore is likely that the direct fed microbials colonized and secreted digestive enzymes in the small intestine, thus increasing nutrient and energy digestibility.Increased feed efficiency with direct fed microbials
Inclusion of C. Butyricum in diets increased (quadratic, P < 0.05) average daily gain and gain to feed ratio during the e post-weaning period with the greatest responses obtained with the lowest inclusion rate of C. Butyricum (Table 2).There were no differences in average daily gain or gain to feed ration between the positive control diet that contained Mecadox and the diets containing C. Butyricum.In contrast, pigs fed the negative control diet without Mecadox and with no C. Butyricum had lower (P < 0.05) average daily gain than pigs fed the positive control diet demonstrating that C. Butyricum could replace Mecadox in the diet without negative effects on growth performance.Pigs fed the diets with C. Butyricum also had greater (P < 0.05) crypth depth and tended (P < 0.10) to have taller villi than pigs fed the diet without C. Butyricum, which may have aided in increasing nutrient absorption.Increased (P < 0.05) gain to feed ratio was also observed if the three-strain spore forming bacillus was included in diets for weanling pigs regardless of the concentration of fiber in the diets (Table 3).In this experiment, it was also demonstrated that expression of one of the transporters that are needed for absorption of volatile fatty acids increased (P < 0.05) in the ileum and tended (P < 0.10) to increase in the liver of pigs fed a diet containing the direct fed microbial.This observation indicates that the direct fed microbial increased intestinal fermentation of fiber, and therefore, increased synthesis of volatile fatty acids, which may have been the reason for the improved gain to feed ratio in the experiment.Overall conclusions
Results of four experiments indicated that inclusion of direct fed microbials in diets for weanling pigs results in positive responses on digestibility of energy and nutrients or improved growth performance. Although not all mechanisms of direct fed microbials are known, results indicate that direct fed microbials likely colonized in the intestinal tract and secreted digestive enzymes that resulted in increased nutrient absorption and increased fermentation of fiber. These effects in turn resulted in increased feed efficiencies in pigs fed diets containing direct fed microbials.

Item	Basal diet	Basal diet + Bacillus toyonensis	SEM	P-value
Dry matter	66.92	70.67	0.76	0.026
Crude protein	71.56	72.79	1.06	0.458
Starch	90.19	92.28	0.65	0.051
Gross energy	68.89	72.18	0.72	0.041
Table 1. Apparent ileal digestibility of dry matter (DM), crude protein (CP), acid hydrolyzed ether extract (AEE), starch and amino acids (AA) in pigs fed diets without or with a Bacillus toyonensis (Oliveira et al., 2022)¹
¹Pigs fed the diet containing Bacillus toyonensis tended (P<0.10) to have a greater apparent ileal digestibility of methionine than pigs fed the basal diet.

Item	Treatment PC	NC	NC+1250 cfu	NC+2500 cfu	NC+3500 cfu	SEM	P-value Linear	Quad³	PC vs. CB	PC vs. NC
Initial wt, kg	6.44	6.42	6.43	6.41	6.44	0.24	0.978	0.972	0.977	0.969
Final wt, kg	20.69	19.50	20.85	20.14	19.79	0.44	0.886	0.051	0.406	0.064
ADG, g	408	374	412	393	382	10.92	0.849	0.006	0.243	0.010
ADFI, g	633	584	628	602	622	15.67	0.213	0.421	0.403	0.033
G:F	0.646	0.641	0.657	0.653	0.617	0.01	0.133	0.013	0.780	0.749
Table 2. Growth performance (day 1 to 35 post-weaning) of weanling pigs fed the positive control diet (PC), the negative control (NC) or diets containing different doses of C. butyricum (CB), (Casas et. al., 2020)^1,2
¹Each least squares mean represents 11 observations. ²C butyricum was added to provide 1,250 x 10⁸cfu/kg of complete diet, 2,500 x 10⁸ cfu/kg of complete diet, or 3,500 x 10⁸ cfu/kg of complete diet. ³Quad = quadratic effect.

Dietary Fiber Direct-fed microbial	Low _	Low +	High -	High +	SEM	P-values Dietary fiber	DFM²
Initial BW, kg	6.336	6.276	6.298	6.309	0.268	0.802	0.048
Final Bw, kg	26.929	27.127	26.117	26.037	1.202	0.024	0.883
ADG, g/d	479	485	461	459	24.24	0.025	0.835
ADFI, g/d	700	702	691	646	43.94	0.048	0.192
G:F, g/g	0.685	0.695	0.667	0.702	0.013	0.592	0.022
G:F, kg/Mcal NE	0.275	0.279	0.276	0.290	0.005	0.138	0.020
*Table 3. Growth performance (day 1 to 43 post-weaning) of weanling pigs fed low- or high-fiber diets without or with a Bacillus-based direct-fed microbial (Jaworski et al., 2017)¹*
¹No interactions between dietary fiber and direct fed microbials were observed. ²DFM = direct fed microbial.

References
Blavi, L., J. J. Jorgensen, and H. H. Stein. 2019. Effects of Bacillus amyloliquefaciens and Bacillus subtilis on ileal digestibility of AA and total tract digestibility of CP and gross energy in diets fed to growing pigs. J. Anim. Sci. 97:727-734. Doi. 10.1093/jas/sky432.Casas, G. A., L. Blavi, T. W. Liu Cross, A. Lee, K. Swanson, and H. H. Stein. 2020. Effects of Miya Gold on growth performance and intestinal microbial profile of weanling pigs. J. Anim. Sci. 98:1-12. doi:10.1093/jas/skz372Jaworski, N. W., A. Owusu-Asiedu, M. C. Walsh, J. C. McCann, J. J. Loor, and H. H. Stein. 2017. Effects of a 3 strain Bacillus-based direct-fed microbial and dietary fiber concentration on growth performance, intestinal concentrations of volatile fatty acids, and expression of genes related to absorption and metabolism of volatile fatty acids in weanling pigs. J. Anim. Sci. 95:308-319. doi.org/10.2527/jas.2016.0557Oliveira, M. S. F., G. Jimenez., and H. H., Stein. 2022. Effects of a probiotic Bacillus Strain on ileal digestibility of crude protein, starch, energy and fat and total tract digestibility of energy and dietary fiber in diets fed to weanling pigs. Abstract # 272. ASAS-CSAS Annual Meeting.

Oliveira is a postdoctoral research fellow and Stein is a professor of animal sciences, both at the University of Illinois.