Abstract:
Ionophore antibiotic supplementation is standard practice in almost all feedlots in South Africa and many other countries due to its effectiveness in increasing feed efficiency and modulating feed intake. Public concern about the emergence of antibiotic resistant bacteria and consumers’ demand for safe, high quality nutritious food has stimulated the search for natural alternatives to ionophores in ruminant diets. A study was conducted to evaluate the effect of a buffer (calcified marine algae) and/or plant extract (capsicum) in combination with or replacing an ionophore on the performance of lambs in a commercial feedlot. A total of 2340 lambs were randomly allocated to six different treatments with six pens per treatment; with a pen as the experimental unit. Treatments were as follows: (1) Ionophore (18 ppm) (Monensin); (2) Calcified marine algae (5 kg/ton) (AB); (3) Capsicum (25 g/ton) (Caps); (4) AB (5 kg/ton) + Mon (18 ppm); (5) Caps (25 g/ton) + Mon (18 ppm); and (6) AB (5 kg/ton) + Caps (25 g/ton). All supplement concentrations were measured on an “as is” basis. Average starting weight of lambs was 30.9 kg ± 5 kg. The lambs were individually weighed on days 0, 10, 21, 35, 50, and at slaughter. All lambs were slaughtered at a pre-determined end weight of ± 48 kg. Average daily gain, dry matter intake, feed conversion ratio, cold carcass mass, dressing percentage, rumen fluid pH, and rumen scoring were among the parameters that were
vii
determined. The basal diets (starter, grower, and finisher) were the same for all treatments albeit with adjustments to the specific supplementation treatments. Days on feed were significantly longer for the AB + Caps treatment compared to the other treatments (P<0.001). Rumen pH values between day 1 and day 3 as well as days 13 and 30 were different between treatments (P<0.05). Other performance parameters measured did not differ between treatments. Results suggest that an ionophore such as monensin can be successfully replaced in lamb feedlot diets with natural alternatives (AB and/or Caps), with minor differences in production parameters (ADG, FCR, DMI, carcass weight and Dressing %). Further research, however, is needed to determine the potential adaptation of rumen microbial populations to the experimental treatments over time. Furthermore, the cost-benefit ratio should be determined under the prevailing conditions in different countries.
