Impact of dried skim milk in production diets on Lactobacillus and pathogenic bacterial shedding in growing-finishing swine

Aims: To determine the possible effects of inclusion of dried skim milk (DSM) in swine diets on indigenous Lactobacillus spp. and Escherichia coli, and its potential for controlling pathogen shedding and affect animal growth in growing-finishing swine. Methods and Results: Animals were fed over three dietary phases to match production needs from age 10-14 weeks, 14-18 weeks and 18-22 weeks. For each feeding phase, diets were formulated to contain 0 or 10% DSM (balanced for metabolizable energy and true ileal digestible amino acids). Animals were weighed every 2 weeks and faecal samples were collected from 40 animals (20 with DSM and 20 without DSM) at week 10 (d 0 on diets), 14, 18 and 22 of age, and were analysed for Lactobacillus spp., Enterobacteriaceae, coliforms, E. coli, Salmonella, Campylobacter and E. coli O157:H7. At the start of the study (week 10), faecal bacterial counts (log(10) CFU g(-1) faeces) were 9.55, 7.26, 7.01 and 6.93 for Lactobacillus, Enterobacteriaceae, coliforms and E. coli populations respectively. The Enterobacteriaceae, coliform and E. coli populations decreased through week 14 and 18, but were higher in animals fed with the DSM diet compared with the basal diet without DSM. The Lactobacillus populations at weeks 14 and 18 were lower in the animals fed the diet without DSM, whereas feeding DSM maintained the Lactobacillus counts from week 10. At week 22, populations of Enterobacteriaceae, coliforms and E. coli were > week 18 for the animals fed the diet without DSM, less change was observed with the feeding of DSM, and no differences between the diets were observed at week 22. However, in week 22 the animal gain was positively correlated with Lactobacillus numbers and negatively correlated with E. coli numbers. Subtraction of the E. coli population (log(10)) from the Lactobacillus population (log(10)) yielded a positive value termed 'effective'Lactobacillus that correlated well with animal gain and may better define a beneficial function in the intestine. Salmonella were detected in over 60% of the animals at week 10 and 14, and < 20% at week 18 and 22. Campylobacter were detected rarely at weeks 10, 14 and 18, but were found in 25% of the animals at week 22. The DSM did not affect Salmonella or Campylobacter shedding, but examination of individual animals over the entire experiment indicated that fewer recurring incidences of Salmonella shedding occurred in animals that maintained higher Lactobacillus. In addition, at week 22, Salmonella and Campylobacter shedding was associated with lower levels of effective Lactobacillus and lower animal weight gains. Conclusions: The DSM did not directly affect the animal performance or pathogen shedding via the Lactobacillus spp. population at any phase of production. However, analysis of data from all animals revealed that faecal Lactobacillus affected Salmonella shedding and in the finishing phase, animal growth and pathogen shedding also were affected, as reflected by the 'effective'Lactobacillus-associated observations. Significance and Impact of the Study: In the swine intestine, any benefits from gastrointestinal Lactobacillus may be compromized by the E. coli population, and this antagonism may explain responses observed with prebiotics or probiotics in some swine.