The effect of essential oils and calcified marine algae as natural alternatives to ionophore antibiotics on performance of feedlot cattle

Abstract

viii SUMMARY The effect of essential oils and calcified marine algae as natural alternatives to ionophore antibiotics on performance of feedlot cattle by Emile Francois Haasbroek Supervisor: Prof. L.J. Erasmus Department: Animal and Wildlife Sciences Faculty: Natural and Agricultural Sciences Degree: MSc (Agric) Animal Science: Animal Nutrition Ionophore antibiotic supplementation is standard practice in almost all feedlots in the USA, South Africa and many other countries due to its effectiveness to increase feed efficiency and modulate feed intake. Public concern over the emergence of antibiotic resistant bacteria and the consumers’ demand for safe, high quality nutritious food has stimulated the search for natural alternatives to ionophores in ruminant diets. The objectives of this study were: (i) to compare the effect of a specific blend of essential oils (XTract X60 – 7065 (XTract)) and a rumen buffer (Acid Buf) to monensin and its effects on the performance of feedlot cattle under both experimental and commercial conditions (ii) to determine the effect of these feed additives on the health status of feedlot cattle and (iii) to determine whether Acid Buf can replace monensin as feed additive in high energy feedlot diets based on hominy chop. For the experimental growth trial 180 Bonsmara type animals were blocked into two groups and then allocated to 6 pens with 10 animals each per treatment using a randomised complete block design. The basal diets (starter, intermediate finisher and final finisher) were the same for the Control XTract and Acid Buf; the only difference being the Control treatment was supplemented with monensin (21 – 33 mg /kg DM), the XTract treatment supplemented with XTract (1000 – 1200 mg /h /d) and the Acid Buf treatment supplemented with Acid Buf at 0,6% dietary DM. For the commercial trial, animals were blocked according to the same criteria but for each treatment there were 3 pens, standing 130 head of cattle per pen, therefore 390 animals per treatment. The experimental pen trial was designed for evaluation of growth and the commercial pen trial for evaluation of health status and growth under practical feedlot conditions. In the small pen trial there were no differences (P > 0.05) in DMI, FCR or ADG between treatments. In the commercial trial the XTract supplemented cattle had a higher EW (429.3 vs. 417.5 kg) and ADG (1.77 kg /d vs. 1.70 kg /d) (P < 0.05) compared to monensin supplemented cattle and the Acid Buf supplemented cattle tended (P > 0.10) towards a higher EW (425.3 vs. 417.5 kg) and ADG (1.74 vs. 1.70 kg /d) compared to monensin supplemented cattle. The feed conversion ratios were 5.67 and 5.26 for XTract and monensin supplemented cattle and did not differ (P = 0.26). The feed conversion ratios were 5.22 and 5.26 respectively for Acid Buf and monensin supplemented cattle and did not differ (P = 0.86). Treatments affected health parameters in the commercial pens with 78% healthy animals (not pulled) in the monensin supplemented animals compared to 82% for XTract and 66% for the Acid Buf supplemented animals (P < 0.01). Rumen damage occurred in 73% of monensin supplemented animals compared to 51% for the Acid Buf supplemented animals and only 24% of the XTract supplemented animals (P < 0.01). Differences in health parameters did not seem to affect the overall growth performance of the cattle, suggesting a relatively minor effect on performance. Results from this large scale study should provide South African feedlot operators with sufficient information to make informed decisions on natural alternatives when the day comes that ionophores are placed on the banned list of ruminant feed additives. Further research, however, is needed on determining the optimal dose, dietary dependant responses, adaptation of rumen microbial populations and potential additive or synergistic effects when supplemented together with other rumen modifiers. Furthermore, the cost: benefit ratio should be determined under the prevailing conditions in different countries.