Dietary clays help prevent diarrhea in weaned pigs

Monday, February 20, 2012

Experiments at the University of Illinois provide strong evidence that clays can be useful in preventing diarrhea in weaned pigs, but more research is needed to discover how this works

by JANICE MURPHY

Clays are naturally occurring materials that have been widely used in swine diets to bind mycotoxins, which can otherwise prove detrimental to animal health and production. In addition, several literature reviews have suggested that clays may have antibacterial or antidiarrheic properties.

Since there are a wide variety of clays available on the market, each with their own individual chemical structure, there may be a large variation in the mechanism involved and the ultimate level of protection.

There are a number of potential mechanisms by which clays could prevent or reduce diarrhea:

1.    Clays may attract bacterial cells with enough force to tear the cell membrane, resulting in death of the invading cells.
2.    Clays may adsorb or detoxify bacterial toxins and protect against intestinal permeability and damage by the toxins.
3.    Clays may attach to mucous membranes in the gastrointestinal tract, thereby reinforcing the physical mucous barrier, resulting in some protection against enteric diseases caused by bacteria and/or toxins.
4.    Clays may absorb water and, as a result, directly influence the presentation of diarrhea.
5.    The ion exchange capacity of clays may modify the characteristics of the environment within the gastrointestinal tract (pH, oxidation state, etc.) and influence the growth of specific bacteria.

Since the experimental evidence for the antidiarrheic effect of clays in pig diets is limited, researchers at the University of Illinois set out to determine whether three different clays reduce diarrhea in weaned pigs experimentally infected with a pathogenic strain of E. coli.

An equal number of barrows and gilts were housed in individual pens within disease containment chambers for 16 days (four days before and 12 days after the first challenge). The E. coli used in the study (isolate number UI-VDL 05-27242; an F-18 fimbria+ E. coli strain) was isolated from a field disease outbreak and provided at a dose of 1010 cfu/3 mL to cause mild diarrhea.

The complex nursery control diet was formulated to meet or exceed the NRC (1998) nutrient requirements for weaned pigs. The researchers did not include spray-dried plasma, antibiotics or zinc oxide in order to avoid any antibacterial or physiological effects from these compounds. The experimental diets were introduced at weaning, containing three clays belonging to classes of smectite, kaolinite and zeolite.

In Experiment 1, a total of 48 pigs (6.9 kilograms initial body weight, 21 days old) were subjected to one of the following four dietary treatments, with half of the pigs on each treatment subjected to the E. coli challenge:

1)    Complex nursery control diet throughout the experiment (CON)
2)    CON + 0.3 per cent smectite throughout the experiment (0.3SM)
3)    CON + 0.6 per cent smectite throughout the experiment (0.6SM)
4)    CON until the challenge and then CON + 0.3 per cent smectite (C/0.3SM)

Treatment 4 was included in order to determine whether or not there was any advantage from feeding clays prior to the pigs becoming infected.

Overall, the clay treatments did not affect average daily gain (ADG) over the duration of the experiment. The unchallenged pigs on the clay treatments grew significantly slower than the control treatment during the early part of the experiment, but more rapidly later on (Table 1). Among the unchallenged pigs, the clay treatments also significantly improved feed efficiency (G:F) during the last six days and over the entire experiment.

The E. coli challenge did not affect diarrhea scores or frequency of diarrhea, but the presence of clay in the diet significantly reduced both the diarrhea score and frequency of diarrhea. Based on these results, the researchers concluded that there is no benefit from feeding more than 0.3 per cent smectite and no advantage to feeding clays prior to the pigs becoming infected.

In Experiment 2, a total of 128 pigs (6.7 kilograms initial body weight, 21 days old) were subjected to one of the following eight dietary treatments, with half of the pigs on each treatment subjected to the E. coli challenge:

1)    Control diet (CON)
2)    CON + 0.3 per cent smectite (SM)
3)    CON + 0.3 per cent kaolinite (KL)
4)    CON + 0.3 per cent zeolite (ZL)
5)    CON + 0.15 per cent of each smectite and kaolinite (SM+KL)
6)    CON + 0.15 per cent of each smectite and zeolite (SM+ZL)
7)    CON + 0.15 per cent of each kaolinite and zeolite (KL+ZL)
8)    CON + 0.1 per cent of each smectite, kaolinite, and zeolite (SM+KL+ZL)

Overall, the E. coli challenge significantly reduced average daily feed intake (ADFI), ADG and feed efficiency during this experiment. The clay treatments did not affect growth rate compared with the control treatment and there were no differences among the clay treatments.

The E. coli challenge significantly increased diarrhea scores for the majority of the experiment and significantly increased the frequency of diarrhea. The clay treatments in the E. coli-challenged pigs significantly reduced the diarrhea score in most time periods and the frequency of diarrhea for the entire experimental period.

There was a lack of consistency in the differences among the clay treatments over the length of the experiment, but in general the treatments including zeolite or a combination of smectite and zeolite showed the most promise in decreasing the frequency of diarrhea.

The results from both experiments show clearly that clays reduce diarrhea in the face of an experimental challenge with pathogenic E. coli as indicated by reductions in both diarrhea scores and frequency of diarrhea.

The researchers were careful to point out that certain aspects of their study differ from conditions in practical swine operations. For example, within their carefully controlled environment, all pigs became sick at the same time and recovered at the same time, with no reliance on pig-to-pig disease transfer.

Since it is unclear whether a reduction in diarrhea would be more significant where pig-to-pig transfer exists, they urged some caution in extrapolating the growth data from these experiments to practical situations and suggested further studies are necessary in order to verify the responses.

The researchers also clearly stated that the growth performance of pigs fed clays has been inconsistent, with some showing improvements and still others yielding no change.

Although clays can protect against enteric disease, they may also bind nutrients or have other impacts in the digestive tract that could turn out to be beneficial or detrimental.

Clearly, further research is needed in this area to explore the mechanisms involved.

In this study, dietary clays were effective in alleviating diarrhea in weaned pigs, as evidenced in the reduction of diarrhea scores and frequency of diarrhea. This study did not identify clear differences in protection against diarrhea between the different clays tested, suggesting that each of them may be beneficial in their own right.

The responses to the clay treatments in both experiments provide strong confidence that clays can be useful in prevention of diarrhea. The next step will be identifying and understanding the mechanisms by which each clay exerts these effects. BP

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

Source: M. Song, Y. Liu, J. A. Soares, T. M. Che, O. Osuna, C. W. Maddox and J. E. Pettigrew. 2011. Dietary clays alleviate diarrhea of weaned pigs. J ANIM SCI published online September 9, 2011. http://jas.fass.org/content/early/2011/09/09/jas.2010-3662