Effect of Dietary Fat Level on Dose Response Relationships During Aflatoxicosis in Young Chickens

Abstract

The effect of aflatoxin in poultry is greater on birds fed a low fat diet, but it is not known whether this effect is associated with a lower apparent minimum effective dose (MED), altered slope of the response curve, or both. Aflatoxin at 16 dosages ranging from 0 to 3.797 μg/g of feed was fed to six groups of 15 young chickens per treatment ingesting a 2 or 4% fat diet for 3 wk. The weights of the body, liver, bursa of Fabricius, and spleen and the total lipid content of the liver were measured. Mathematical models were fitted to the data and dose-response curves were predicted as continuous functions of aflatoxin concentration. Quadratic polynomials fit body weight and spleen weight whereas plateau-linear models fit liver weight and liver lipid content in both 2 and 4% fat diets. The weight of the bursa of Fabricius was fit equally well by quadratic and linear plateau models. Dietary fat had negligible effects on the apparent MED (μg of aflatoxin per gram of feed) for body, liver and spleen weights, which were calculated from the modeling approach to be 1.37 and 1.41, 1.68 and 1.69, and 1.49 and 1.46 on 2 and 4% fat diets, respectively. The apparent MED for liver lipid content was appreciably lower for birds fed the 2% fat diet than those fed the 4% fat diet (.88 and 1.62, respectively). Similarly, the apparent MED for the bursa was 1.48 and 1.74 for birds fed the 2 and 4% fat diets, respectively. The lower MED for these two variables on the lower fat diet were accompanied by a lesser slope of the linear response, which could result in either an enhanced or ameliorated effect of aflatoxin, depending on its dose. The response curves for liver lipids and bursa which were upward and downward turning curves, respectively, were essentially mirror images of each other, implying that both variables may be responding to a specific metabolite of aflatoxin. These observations, which add a biological factor to the documented statistical factors controlling the apparent MED of aflatoxin, illustrate some of the difficulties in estimating an MED suitable for practical poultry operations.