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RESEARCH ARTICLE
Contents Vol 47(11)

Growth and carcass characteristics of cast-for-age Merino ewes fed sorghum-based feedlot diets

M. K. Bowen A D E , P. M. Pepper B , E. Patterson A , I. McConnel A and D. J. Jordan C
+ Author Affiliations
- Author Affiliations

A Department of Primary Industries and Fisheries, PO Box 519, Longreach, Qld 4730, Australia.

B Department of Primary Industries and Fisheries, Locked Mail Bag 4, Moorooka, Qld 4105, Australia.

C Department of Primary Industries and Fisheries, PO Box 102, Toowoomba, Qld 4350, Australia.

D Present address: Department of Primary Industries and Fisheries, PO Box 6014, Rockhampton, Qld 4702, Australia.

E Corresponding author. Email: maree.bowen@dpi.qld.gov.au

Australian Journal of Experimental Agriculture 47(11) 1309-1316 https://doi.org/10.1071/EA06145
Submitted: 26 April 2006  Accepted: 15 March 2007   Published: 18 October 2007

Abstract

Grain feeding low bodyweight, cast-for-age (CFA) sheep from pastoral areas of eastern Australia at the end of the growing season can enable critical carcass weight grades to be achieved and thus yield better economic returns. The aim of this work was to compare growth and carcass characteristics for CFA Merino ewes consuming either simple diets based on whole sorghum grain or commercial feed pellets. The experiment also compared various sources of additional nitrogen (N) for inclusion in sorghum diets and evaluated several introductory regimes. Seventeen ewes were killed initially to provide baseline carcass data and the remaining 301 ewes were gradually introduced to the concentrate diets over 14 days before being fed concentrates and wheaten hay ad libitum for 33 or 68 days. Concentrate treatments were: (i) commercial feed pellets, (ii) sorghum mix (SM; whole sorghum grain, limestone, salt and molasses) + urea and ammonium sulfate (SMU), (iii) SMU + whole cottonseed at 286 g/kg of concentrate dry matter (DM), (iv) SM + cottonseed meal at 139 g/kg of concentrate DM, (v) SMU + virginiamycin (20 mg/kg of concentrate) for the first 21 days of feeding, and (vi) whole cottonseed gradually replaced by SMU over the first 14 days of feeding.

The target carcass weight of 18 kg was achieved after only 33 days on feed for the pellets and the SM + cottonseed meal diet. All other whole grain sorghum diets required between 33 and 68 days on feed to achieve the target carcass weight. Concentrates based on whole sorghum grain generally produced significantly (P < 0.05) lower carcass weight and fat score than pellets and this may have been linked to the significantly (P < 0.05) higher faecal starch concentrations for ewes consuming sorghum-based diets (270 v. 72 g/kg DM on day 51 of feeding for sorghum-based diets and pellets, respectively). Source of N in whole grain sorghum rations and special introductory regimes had no significant (P > 0.05) effects on carcass weight or fat score of ewes with the exception of carcass weight for SMU + whole cottonseed being significantly lower than SM + cottonseed meal at day 33.

Ewes finished on all diets produced acceptable carcasses although muscle pH was high in all ewe carcasses (average 5.8 and 5.7 at 33 and 68 days, respectively). There were no significant (P > 0.05) differences between diets in concentrate DM intake, rumen fluid pH, meat colour score, fat colour score, eye muscle area, meat pH or meat temperature.


Acknowledgements

This study was funded by the Australian Sheep Industry Cooperative Research Centre with in-kind contributions from the Department of Primary Industries and Fisheries, Queensland (DPI&F). We are grateful to the Health and Nutritional Biochemistry Laboratory of DPI&F for conducting laboratory analyses and to A. Slacksmith of the University of New England for conducting carcass measurements.


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