Measuring Broiler Response when an Antibiotic Growth Promotor is Removed and Replaced with Therapeutic Feed Additives

I. Introduction

The World Health Organisation has raised concern regarding increasing antibiotic resistance to commonly used antimicrobial drugs. In response, the use of antibiotic growth promoters in livestock production is being reduced each year, directed either by local government legislation or the pressure of consumer preferences. The objective of this study was to evaluate the effectiveness of several active compounds in maintaining bird health and performance when an antibiotic growth promotor was removed from the diet.

II. Method

1,365 Ross 308 broiler chicks were allocated to 5 treatments with 13 replications, using 21 chicks per experimental unit. Treatment periods were 0-10 days of age, 11 to 24 days of age and 25 to 35 days of age. Birds were fed a corn/soybean meal-based diet and raised to breed manual specifications as seen in Table 2. The treatments can be seen in Table 1. Samples of intestinal tissue (jejunum and ileum) were collected from 2 birds per pen at 35 days of age for the measurement of villus length, villus width, crypt depth and villous:crypt ratio. Analysis of all zootechnical data was conducted using Analysis of Variance. Treatment effects were significantly different at P < 0.05. Variables having a significant F-test were compared using the Duncan’s new multiple range test function of SAS. Statistical significance was declared at P ≤ 0.05, with 0.05 < P < 0.10 considered as a near-significant trend.

Table 1 - Dietary Treatments

Table 2 - Nutrient composition of experimental diets¹

Table 2 - Nutrient composition of experimental diets1

III. Results

No significant differences were observed in mortality or morbidity among dietary treatments. During 0-10 days of age, birds fed the protease (T5) had lower feed intake (P < 0.05) than negative control (T2) and T4 but not positive control (T1) or T3. Growth performance during this period was equal among all treatments; however feed conversion ratio followed the significant difference of feed intake with T5 showing better efficiency (P = 0.01) than T2 and T4 but not different than T1 or T3. During 11-24 days of age, birds fed T3 grew heavier (P < 0.05) than T2 but not different than other treatments. By the end of the study, at 35 days of age, there were no significant differences of growth performance among treatments as seen in Table 3.

When stress and immunity measurements were taken using blood from one bird per pen at 35 days the only significant difference found was for T3, T4 and T5 which had higher interleukin 2 (IL2) (P = 0.007) than T2, with T5 the only treatment to have a significantly higher IL2 than both T1 and T2.

Table 3 - Effect of in-feed therapeutics on performance of broilers

There was no significant difference among treatments for measurements of villus architecture in the ileum tissue section; however in the jejunum section, treatments T4 and T5 had significantly shallower crypt depth than T1 and T2 (P < 0.05) and this led to significantly greater villus to crypt ratios (P = 0.0002) for T4 and T5 to all other treatments as seen in Table 4. This result is similar to responses seen to the same additives when reported in conjunction with water acidification by Bekker et al, 2019.

Table 4 - Effect of in-feed therapeutics on intestinal morphology

IV. Discussion

In this study, all treatments resulted in similar overall performance to the positive antibiotic control. As there were no significant differences for overall performance between positive and negative control it must be assumed that there was no chronic disease or bacterial dysbiosis. While these performance indicators showed no significant differences to 35 days when birds were processed, there were positive phases for additional protease on top of pre-starter diets and encapsulated essential oils with organic acid in the grower phase. Significant differences in intestinal morphology were also seen for protease and copper treatments. These specific results support the previous data and will allow for refinement in future studies that may show where each feed additive component could be applied most effectively in the absence of AGPs.

Presented at the 33th Annual Australian Poultry Science Symposium 2022. For information on the next edition, click here.