Early weaned pigs produce insufficient levels of gastric acid which can result in a high stomach pH. As a result, the digestion of nutrients, especially protein is reduced. Moreover, high pH is favourable for the proliferation of diarrhoea-causing micro-organisms in the weaned pig. The use of organic acids has been suggested as a means of lowering gastric acidity in weaned pigs and has been reported to improve growth performance. The benefits that arise from feeding organic acids include an inhibitory effect on pathogenic bacteria, increased amino acid and energy digestibility and an increase in nitrogen retention. The response to organic acids was previously found to be greatest in diets with low levels of dairy products. Dairy products contain lactose which can be fermented to lactic acid thus reducing gut pH. In addition, milk proteins are much more easily digested than vegetable proteins in the immature gut. The response to diet acidification might be expected to be reduced when provided in post-weaning diets to pigs that were provided with creep feed prior to weaning as creep feeding of suckling pigs is thought to benefit post-weaning pig performance by stimulating gastric acid production and enzyme secretion.
Unexpectedly, Lawlor et al. (2005a) found that the response to a dietary acid was not influenced by the level of dairy product in the diet or whether pigs had or had not been creep fed while suckling the sow. Feed intake in one experiment was increased by ~32% in week 1 and by 11% over the first 3 weeks after weaning due to the dietary addition of fumaric acid. This increase in feed intake translated into a ~20% increase in growth rate in the first 3 weeks post-weaning. However, the response to diet acidification was not always consistent between experiments with a response to fumaric acid seen in 2 of the 3 experiments reported and the magnitude of the response varied greatly between the two experiments where a positive response was found. Similar results were found in later work (Lawlor et al., 2006). It was thought that microbial challenge during the post-weaning period has a major influence on the response to fumaric acid supplementation.
Table 9. Effect of pre-weaning creep feeding on response of weaned pigs to dietary fumaric acid (Lawlor et al 2005a)
表9斷奶前料過渡對斷奶仔豬日糧富馬酸反應的影響（勞勒等人，2005）
標準誤差 F檢驗
蠕變 否 否 是 是 添加富馬酸
富馬酸（富馬酸；克/千克） 0 20 0 20
豬體重（千克）
斷奶 6.1 6.1 6.2 6.0 0.31
結果 12.1 12.9 11.9 13.6 0.67 **
采食量（克/天）
第一周 194 233 180 260 19.0 ***
第二周 528 550 533 623 46.0
第三周 658 696 667 711 43.7
總量 466 500 466 535 30.3 *
日增重（克/天）
總量 289 320 273 358 23.6 **
斷奶后微生物挑戰(zhàn)對添加富馬酸的效果有主要影響。
An alternative approach to diet acidification, which can yield similar benefits, is to formulate post-weaning diets to have a low acid binding capacity. Acid binding capacity can be defined as the amount of acid in milliequivalents (meq) of Hydrochloric acid required to lower the pH of 1kg of feed sample to (a) pH 4.0 (ABC-4) and (b) pH 3.0 (ABC-3) (Lawlor et al 2005b). The lower the acid-binding capacity of the feed, the lower the amount of gastric acid that is required to lower its pH and create an acidic environment in the stomach, which is beneficial to pig health and digestion. Lawlor et al. (2005b) published a data set of acid-binding capacity values for a wide range of feed ingredients. There is great variation between ingredients with regard to acid-binding capacity values. For this reason, complete post-weaning diets can be formulated to have a low acid-binding capacity by selection of ingredients from this dataset with low acid-binding capacity and by using the acid-binding capacity value for each ingredient in the diet formulation matrix. Such diets can be used when a high gastric pH is likely to be a problem (e.g., at weaning) and as an effective alternative to diet acidification. When such diets were formulated by reducing calcium and phosphorus content in the diet formulation, feed intake in the first week after weaning was increased by 17% (Lawlor et al., 2006). This is the time where we need to increase feed intake as it has such an influence on subsequent growth performance.
Probiotics are ‘live microorganisms which when administered in adequate amounts confer a health benefit on the host’ (FAO/WHO, 2001). They offer potential as an alternative to antibiotics for pigs, both as a means of controlling enteric pathogens and improving growth performance. Their possible modes of action include modulation of the immune system, competitive exclusion of pathogens in the gut and antimicrobial production. Prieto et al. (2014) evaluated the safety and efficacy of a marine-derived Bacillus pumilus strain for use as an infeed probiotic in newly weaned pigs. The B. pumilus used was pre-screened and selected for its ability to inhibit porcine pathogenic E. coli (Prieto et al., 2013). The Bacillus strain was administered to weaned pigs fed a non-medicated diet and compared to a negative control treatment without antibiotic or pharmacological levels of zinc oxide (non-medicated treatment) and a positive control treatment containing apramycin and pharmacological levels of zinc oxide (medicated treatment). The study herd was at the time experiencing oedema disease during the post-weaning period. The B. pumilus strain decreased ileal E. coli counts in a manner similar to the medicated treatment but without the reduction in growth performance (Table 10) and possible liver toxicity found with the medicated treatment (Prieto et al., 2014).
Table 10. Effect of feeding non-medicated, medicated or B. pumilus treatments for 22 days on post-weaning pig growth performance1,2 (Prieto et al., 2014)
Casey et al. (2007) investigated the effects of oral treatment of pigs with a mixture of five lactic acid bacteria probiotic strains, on both clinical and microbiological signs of Salmonella Typhimurium infection. Following probiotic administration for 6 days, animals were challenged orally with S. Typhimurium and monitored for 23 days post-infection. Animals treated with probiotic showed reduced incidence, severity, and duration of diarrhea, gained weight at a faster rate than control pigs, and had reduced fecal shedding of Salmonella
Prebiotics, like probiotics, are used as a strategy to influence the composition of the gastrointestinal microflora towards a more favorable balance, by reducing the amount of harmful/pathogenic species and promoting the growth of species thought to have beneficial effects on host health (O’Sullivan et al., 2010). A prebiotic is “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity of the gastrointestinal microflora that confers benefits upon the host wellbeing and health”. Prebiotics are resistant to digestion in the upper gut (i.e. resistant to acid and enzymes), a selective substrate for the growth of beneficial bacteria and able to induce luminal or systemic effects that are beneficial to host health. To date only inulin, oligofructose, galactooligosaccharides and lactulose are considered true prebiotics; however, other potential sources of prebiotics such as seaweed-derived compounds are currently being explored (O’Sullivan et al., 2010).