Lysozyme - an alternative to antibiotics for piglets

Tuesday, June 5, 2012

U.S. research demonstrates that 10-day-old pigs fed granulated lysozyme in their diets showed improved small intestinal morphology and decreased Campylobacter prevalence in the digestive tract

by JANICE MURPHY

Swine producers are continually being pressured to reduce, or even remove, in-feed antibiotics.   Antibiotics have been used at sub-therapeutic levels as growth promoters for over 50 years, and the majority of swine operations in North America use in-feed antibiotics at some point during production. Their use is especially prevalent in the early stages of production, when the young pig's immune system is still developing. To ease this pressure, the search continues for products that might help to reduce or eliminate the need to use antibiotics in swine facilities.

Lysozyme is a muramidase, an enzyme that has antimicrobial properties. By breaking certain linkages in the peptidoglycan component of bacterial cell walls, it causes cell death. Previous research in pigs reported benefits in intestinal morphology and microflora, as well as improved metabolite profiles, suggesting that inclusion of lysozyme may be a viable alternative to antibiotics in swine feed.

Researchers at the University of Arkansas and the U.S. Department of Agriculture in Nebraska recently set out to compare the effect of adding a purified granulated lysozyme against antibiotics, on growth performance, small intestinal morphology and Campylobacter shedding in 10-day-old pigs.

Forty eight pigs with an initial body weight of four kilograms were weaned at 10 days of age, and assigned to pens according to a randomized complete block design. Each block was assigned to consume one of three liquid diets for 14 days – a control diet (unmedicated milk replacer), the control diet + lysozyme (100 mg/kg of diet), or the control diet + antibiotics (neomycin and oxytetracycline, 16 mg/kg of diet). The diet was prepared daily and new supplies were added twice daily to ensure the diet was fresh and the pigs were able to consume diets ad libitum.

Pig weights were recorded and blood samples taken on days 0, 7, and 14. Blood was analyzed for plasma urea nitrogen (PUN) and Immunoglobulin A (IgA). After 14 days on the experimental diets, pigs were euthanized and samples of the jejunum and ileum were collected for measurement of villus height and crypt depth. Rectal swabs were taken on days 0, 7, and 14, and samples of the contents of the ileum and cecum were collected at the end of the experiment to test for the presence of Campylobacter.

During the first week of the experiment, the pigs gained at the same rate, regardless of dietary treatment (Table 1). However, during the second week, pigs fed the lysozyme and antibiotic treated diets gained at a significantly greater rate compared to control pigs, resulting in an overall higher Average Daily Gain (ADG) over the course of the study. This faster rate of gain with the antibiotic and lysozyme treated diets translated into heavier pigs at the end of the study, compared to control pigs.

Feed consumption rates across treatments were similar up to day 7. During the second week, pigs fed the antibiotic treated diets consumed more feed than pigs fed the control diet. Overall, over the course of the study, pigs fed the antibiotic and lysozyme treated diets consumed significantly more feed than pigs fed the control diet.

Feed efficiency (G:F) over the 14 days was not affected by dietary treatment. The same was true of circulating (IgA) or (PUN) concentrations. The IgA levels did decrease significantly over the course of the experiment, with pigs fed the lysozyme-treated diet showing the greatest decrease. PUN concentration increased over the course of the experiment, but the same patterns were evident across all treatments.

Muscle growth occurs at an extremely rapid rate in young, growing pigs. For this reason, researchers often use PUN concentration as a reliable indirect measurement of the oxidation of dietary amino acids from the process of protein synthesis. These levels were not different between treatments in this experiment, suggesting that the pigs receiving the lysozyme diet were using amino acids for protein synthesis in a similar manner to pigs consuming the other two diets.

Examination of the morphology of the small intestine is traditionally used as an estimation of intestinal health in pigs. Crypt depths in pigs fed the antibiotic and lysozyme treated diets, compared with pigs consuming the control diet, were significantly greater in both the jejunum (60.0 and 62.2, respectively, versus 50.7 µm) and ileum (76.0 and 72.2, respectively, versus. 52.4 µm).  

Villus height did not differ in the jejunum but was significantly higher in the ileum of pigs consuming the lysozyme- and antibiotic-treated diets, compared with pigs fed the control diet (312 and 314, respectively, versus 263 µm). Based on this data, the increase in villus height provides a greater surface area to allow absorption of nutrients in the small intestine, which could be the mechanism by which lysozyme and antibiotics are able to improve growth rates.

Pigs consuming lysozyme for 14 days exhibited less Campylobacter shedding compared to pigs on the control diet. Campylobacter shedding was observed in 27 per cent of samples collected from pigs on the control diet, compared to only five and eight per cent of samples from pigs on the antibiotic and lysozyme diets, respectively. Usually, the higher the level of Campylobacter shedding, the poorer the performance in growing pigs.

Campylobacter is a gram negative organism, so it is not clear how lysozyme would cause a reduction in shedding. Campylobacter is, in fact, resistant to lysozyme. In light of this, it is likely that the results observed in Campylobacter levels was due, in part, to changes in the health of the  gastrointestinal tract and microflora profile by lysozyme that indirectly reduced the ability of Campylobacter to colonize and shed.

This experiment is touted to be the first to demonstrate that the addition of lysozyme can result in improved growth performance in pigs. Pigs fed lysozyme also showed improved small intestinal morphology and decreased Campylobacter prevalence in the digestive tract. Based on the results of this experiment, the researchers concluded that granulated lysozyme is a suitable alternative to antibiotics in 10-day-old pigs consuming liquid diets. BP

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.

Source: K. D. May, J. E. Wells, C. V. Maxwell and W. T. Oliver. 2012. Granulated lysozyme as an alternative to antibiotics improves growth performance and small intestinal morphology of 10-day-old pigs. J. Anim. Sci. 2012, 90:1118-1125.