Practical nutritional aspects to prevent Necrotic Enteritis

By José Ignacio Barragan Cos, Associated Professor Veterinary Faculty, University Cardenal Herrera de Valencia, Spain

The feed conversion ratio (FCR) is one of the most important elements to maximise profitability in broiler production. Feeding cost is the combination of feed price and FCR, and is a very important percentage of the total cost, which means that producers around the world are becoming more and more interested in a reduction of the FCR.

A very obvious way to improve FCR is to increase feed concentration. Unfortunately, though, considering the actual price situation, it usually means an increase in the feeding cost. Another way to improve FCR is by reducing mortality; however, due to today’s industrial conditions this is not always possible. An alternative way to improve FCR is by increasing the average daily gain (ADG) of broilers. The earlier we obtain the target weight, the fewer the number of days the birds will need to remain on the farm. This could mean that less feed will be needed to produce the same amount of meat. Also, bear in mind that the older the birds become the more ingested nutrients will be used for maintenance. The higher the daily gain of the broilers, the lower the feed conversion will be (Figure 1).

Controlling daily gain

In bird management, final weight is of course very important, but in fact controlling weekly weights is much more important! Final weight figures will not be able to tell the producer if the intermediate weights were good, or if the gain during the last days were significant. At times, intermediate weights are lower than optimum, which may explain lower final weight figures. It is for good reason, therefore, that one of the most important objectives in company management must be accurate control of weekly bird weights.

In Figure 2 we can compare the total weight increase and the relative weight increase (gain to previous weight) in today’s broilers. The red line represents the broiler weight at each age, and blue line the relative weight (daily gain divided by day weight). As can be seen, during the first 15 days the relative growth is really high and the total weight at the end of production phase is also high. In the medium period, the relative and total weights are generally low. This is the reason why bird weight in the middle of the growing time is often not given much extra attention. This provokes misfortune, since a lack of weight in that period could relate to a reduced final weight, particularly when the broilers do not have enough time to compensate this dip in growth. Compensatory growth is depressed particularly when it is “disbacteriosis time”.

The risk window

Disbacteriosis is a sudden change in the number or in the profile of the bacterial population in the gut. One of the various causes of disbacteriosis is the boosted growth of the bacteria Clostridium perfringens, resulting in Necrotic Enteritis.

Such a spontaneous growth of bacteria, and its associated problems, is related to the presence of undigested nutrients in the gut. All nutrients that a broiler is not able to digest and absorb are available for bacterial multiplication. Therefore, the first objective for producers must be reducing the presence of undigested feed in the gut of animals during the “risk window”, which is shown during day 15-30.

During the “risk window” extra attention should be given to feed concentration and feed digestibility. A high concentration will not cause major problems when the raw materials and feed production is of “optimum quality”. It is often not possible, however, to assure this merit (due to variability in soya quality, high viscosity of some cereals, dangerous inclusions in fats, etc). In that case, it would be better to reduce the feed concentration and improve raw material quality standards. Knowing the soya solubility can help determine the cooking process, and correct, if necessary, amino acids level and digestibility. The use of specific enzymes can reduce the risks associated with viscosity.

Undigested feed

Similar patters can be seen all over the world with regards to undigested feed. At around 10-12 days of age the faeces often look relatively good, but may be slightly wet. Then, just 2-3 days later, faeces appear big and wet. By day 20 it is possible to find orange drops (gut mucosa discharge) in the faeces, and the litter becomes wet. After approx. day 25 we sometimes find undigested feed in the faeces. In case there are no posterior complications, this process will disappear in 2-3 days. Theoretically, it does not appear to be a serious problem, but in reality, however, several days of growth have been lost. Compensatory growth can minimise the loss at the end, but this is not efficient, or guaranteed. In broiler production the aim must be to increase weight, not to (temporarily) reduce it!

One of the problems related to a decrease in growth is that it is not very obvious, so farmers may not recognise the problem when it occurs. Production supervisors or veterinarians most of the time do not visit the farm during the mid-period of production and may not be aware of a problem. They are often more focused on the starter and finishing period.

Control measures

There are several measures that can be taken to control disbacteriosis and prevent a drop in growth halfway the production cycle of broilers. These include:

• Improve digestibility of feed, so no undigested feed remains in the bird, thereby becoming a basis for bacterial multiplication.

• Control water quality by using potable water. Water from own wells should be checked, filtered and made potable to reduce danger of intestinal damages. Chlorination is an excellent option, as well as acidification. A reduction of the pH in the crop can contribute to a reduction of the number of pathogenic bacteria in the gut.

• Medicate. Of course, it is possible to reduce the aggressiveness of the bacterial growth through using antibiotics. Many of these antibiotics have a broadspectrum activity, while others are more specific against Clostridia. In any case it is important to remember that the earlier we start the treatment, the more effective it will be. The functional effect of antibiotics will be dramatically reduced if the producer waits until a problem occurs.

• Use alternative weapons. There are many alternative products available, like plant extracts, essential oils, and organic acids, etc. All of them have a general action against bacteria, and are able to reduce the total bacterial counts in the gut. Some of them have a specific action against Clostridium. The activity of these products has to be confirmed in practical trials.

Finally, it is important to choose the correct preventive method to control gut health. During the first 15 days, the development of gut and immunity status should get the most attention. In case of problems, the use of products with specific action against Clostridium, like vaccines and antagonists bacteria, is advised to reduce the aggressiveness of clostridial infections in broilers, and to avoid gut wall lesions, which allow a better broiler growth and improved feed efficiency.