Liver abscesses and performance in feedlot cattle as influenced by dietary roughage level and tylosin inclusion.
Zemicael, Mulugeta Berhe.
MetadataShow full item record
The focal interest of this study was the problem of liver abscesses that occurs in intensively fed beef cattle. The literature on metabolic disorders and diseases associated with feeding high concentrate diets to beef cattle was reviewed, with special emphasis on liver abscesses (Chapter 1). The antibiotic tylosin is generally included as a feed additive to curb liver abscesses, but has recently been banned as a feed additive in Europe. Whilst tylosin use is still permitted in South Africa, a long-term alternative to its use as a liver abscess control agent is needed . Previous research has shown a linear decline in liver abscesses as the roughage portion of high-concentrate finishing diets increases at the expense of concentrates. Unfortunately, animal performance and profits decline with such an increase in roughage inclusion, apparently due to the lower nutritive value of roughages relative to concentrates. However, if the nutritive value of roughages can be improved sufficiently, for instance by chemical treatment methods such as urea ammoniation, the detrimental effects of concentrate replacement may be at least partially alleviated. This will allow beef cattle finishing operations to use higher dietary roughage levels to reduce the incidence of liver abscesses, without severely compromising animal performance and economic returns. Hence, this study was undertaken to examine: (i) the incidence of liver abscesses in feedlot cattle originating from three feedlots in Kwazulu-Natal province, South Africa (Chapter 2); (ii) the effect of dietary roughage level (20% or 40%), with or without tylosin (10 mg/kg feed) inclusion, on biological and economic performance of feedlot cattle, and the incidence of liver abscesses (Chapter 3); and (iii) the effect of dietary roughage level, with or without tylosin inclusion, on in situ degradation characteristics of dry matter (DM) and crude protein (CP) in dietary concentrates and roughage (either urea ammoniated or untreated), when incubated in the rumen (Chapter 4; dietary roughage levels and tylosin level as for Chapter 3). In the last chapter (Chapter 5), a general discussion of the outcomes of this study is presented. The results of the survey show that the incidence and severity of liver abscesses in the feedlot beef cattle was high (25.4%), and there was a difference among the feedlots studied concerning the incidence of liver abscesses. The results of the feedlot experiment show that tylosin inclusion did not affect the performance and carcass characteristics of the steers. Roughage level had an adverse effect (P<O.Ol) on growth rate and feed conversion ratio. However, average dry matter intake and carcass characteristics were not affected by roughage level. Roughage level and tylosin inclusion did not affect the cost of concentrate feed consumed, carcass income and margin over total feed cost, but cost of roughage consumed differed between roughage level and tylosin treatments (P<O.Ol). In the degradability trial, inclusion of tylosin in the diet did not affect the DM and CP degradation of the untreated and treated veld hay in the rumen. In the concentrates incubated, tylosin affected the potential degradability (PD) of the DM and CP, and the rate of degradation (C) of CP. Roughage level only had a significant effect (P=0.05) on the effective degradability (ED) of CP of the incubated roughage. The CP content of the roughage (veld hay) was increased from 4.01 to 14.11 in the feed lot trial and to 13.10% in the degradability trial due to urea ammoniation. Urea ammoniation also resulted in a decrease of neutral detergent fibre and hemicellulose content of the roughage. However, the acid detergent fibre and lignin content increased due to urea treatment. The DM and CP degradability of veld hay was improved due to urea treatment. In conclusion tylosin had no effect on performance of the steers and degradability of incubated veld hay. Urea treatment of veld hay increased CP content, decreased NDF and hemicellulose contents, and improved the degradability of DM and CP of veld hay in the rumen. Comparable results were found on performance and economical evaluation of beef steers by using either 20 or 40% of treated veld hay in feedlot finishing diets. The diets with 20% and 40% hay also responded similarly to the degradability of incubated hay. Therefore, the diet with 40% treated hay and 60% concentrate mixture (without tylosin) can be used as a strategic alternative to tylosin for combating liver abscesses in finishing cattle, without statistically significant loss in revenue. Further research is necessary to study the most optimal level of treated hay in terms of performance of animals, incidence of liver abscesses and economical value. Further survey work on the incidence of liver abscesses in feedlot cattle, representative of South Africa (and not only KwaZulu-Natal) is also required.