Effects of Gamma-Ray Irradiation of Bacteria Colonies in Animal Feeds and on Growth and Gut Health of Weaning Piglets

Abstract

Animal feeds contain a substantial number and diversity of microorganisms, and some of them have pathogenic potential. The objectives of this study were to investigate the effects of different doses of gamma (γ)-ray irradiation on the bacteria count in different types of feed and then to test the effect of γ-ray-irradiation-treated fishmeal on the gut health and growth performance of weaning piglets. In trial 1, three fishmeal samples, two feather meal samples, three meat meal samples, three soybean meal samples, and three vitamin complexes were treated with γ-ray irradiation doses of 0, 3, 6, or 9 kGy. The 6 and 9 kGy doses eliminated most of the bacteria in the feed but also resulted in a loss of vitamin C and B1. In trial 2, 96 weaning piglets were fed one of the following three diets with eight replicates (pens) per group over a 14-day period: (1) the control diet-the basal diet supplemented with 6% fishmeal with a low bacteria count (40 CFU/g) and no E. coli; (2) the fishmeal-contaminated diet (FM-contaminated) diet-the basal diet supplemented with 6% fishmeal with a high bacteria count (91,500 CFU/g) and E. coli contamination; and (3) the irradiated fishmeal (irradiated FM) diet-the basal diet supplemented with γ-ray-irradiation-treated E. coli-contaminated fishmeal. The piglets that received the FM-contaminated diet had significantly lower average daily gain and a greater diarrhea index compared to those fed the control diet, whereas γ-ray irradiation treatment abrogated the negative effect of the E. coli-contaminated fishmeal. Collectively, γ-ray irradiation at a dose of 6-9 kGy was sufficient to eliminate the microorganisms in the feed, thereby benefitting the growth performance and gut health of the weaning piglets.

Keywords: E. coli; feed bacteria; fishmeal; piglets; γ-ray irradiation.

Figure 1

Effect of γ-ray irradiation doses on the bacterial counts of fishmeal samples. (a–c) The bacterial counts of fishmeal samples A, B, and C at γ-ray irradiation doses of 0, 3, 6, and 9 kGy. Values are means ± S.E.; n = 3 per sample. N.d., not detected or below detection limits. The bacteria count in the column for n.d. groups was set as 5 CFU/g. The numbers in brackets denote the average values of the bacteria counts in each sample.

Figure 2

Effect of γ-ray irradiation doses on the bacterial counts of feather meals. The bacterial counts of feather meal samples A (a) and B (b) at γ-ray irradiation doses of 0, 3, 6, and 9 kGy. Values are means ± S.E., and n = 3 per sample. n.d., not detected or below detection limits. The bacteria count in the column for n.d. groups was set as 5 CFU/g. The numbers in brackets denote the average values of the bacteria counts in each sample.

Figure 3

Effect of γ-ray irradiation doses on the bacterial counts of meat meal samples. (a–c). The bacterial counts of meat meal samples A, B, and C at γ-ray irradiation doses of 0, 3, 6, and 9 kGy. Values are means ± S.E., and n = 3 per sample. n.d., not detected or below detection limits. The bacteria count in the column for n.d. groups was set as 5 CFU/g. The numbers in brackets denote the average values of the bacteria counts in each sample.

Figure 4

Effect of γ-ray irradiation dosage on the bacterial counts of soybean meals. (a–c) The bacterial counts of soybean meal samples A, B, and C at γ-ray irradiation doses of 0, 3, 6, and 9 kGy. Values are means ± S.E., and n = 3 per sample. n.d., not detected or below detection limits. The bacteria count in the column for n.d. groups were set as 5 CFU/g. The numbers in brackets denote the average values of the bacteria counts in each sample.

Figure 5

Effect of γ-ray irradiation dosage on the bacterial counts of vitamin complex. (a–c) The bacterial counts of vitamin complex samples A, B, and C at γ-ray irradiation dosages of 0, 3, 6, and 9 kGy. Values are means ± S.E., and n = 3 per sample. n.d., not detected or below detection limits. The bacteria counts of the columns for n.d. groups were set as 5 CFU/g. The numbers in the brackets denote average value of the bacteria counts in each sample.

Figure 6

Effect of γ-ray irradiated fishmeal on the fecal E. coli counts of weaning piglets. The FM-contaminated diet was supplemented with 6% FM with high bacteria count and contaminated with E. coli. The irradiated FM diet was supplemented with 6% contaminated FM with γ-ray irradiation at a dose of 6kGy. ** denotes statistical significance at p < 0.01.

Figure 7

Effect of γ-ray irradiated fishmeal on the serum concentrations of immune-related cytokines in weaning piglets. The FM-contaminated diet was supplemented with 6% FM with high bacteria count and contaminated with E. coli. The irradiated FM diet was supplemented with 6% contaminated FM with γ-ray irradiation at a dose of 6kGy. * denotes p < 0.05, and ** denotes p < 0.01.