Production responses and problems relating to the use of maize and sorghum grain in feedlots

Though there is very little New Zealand experience on the feeding to cattle of rations containing high levels of maize or sorghum grain, there has been wide experience overseas. For maize this is particularly so in the U.S.A. where some 90o/o of production is fed back to livestock. There has been reasonably wide experience with sorghum grain in Australia and the U.S.A., in the latter in fact Black et al. (1943) were reporting cattle performance on sorghum for preceding decades. Certain general principles have been well established regarding grain feeding to beef cattle. With the higher energy grains at least, an increase in grain level in the diet will lead to an increase in growth rate and a lower feed conversion rate (Pryor, 1970). At such high levels, the nature of the roughage component does not have much effect on performance. Thus performance quoted here must be considered in the light of these principles. There are numerous reports of cattle performance on high maize feeding although average daily gains obtained will be influenced by the percentage of grain in the ration. Preston and Willis (1974) reported data up to 1970 on maize feeding to cattle where no roughage was fed. Daily gains were within the range of 0. 73-1.40 kg per day and feed conversions within the range of 5.00-7.44. A reasonable summary of U .S.A. experience is that gains of about 1 kg/day are obtained for British cattle breeds where maize is fed and some roughage provided. There are very few data in the literature where direct comparisons have been made between maize and sorghum feeding at the same feeding level. Even if there were more, the interpretation could be rather imprecise since such factors as origin of grain and chemical composition will vary from location to location. In published tables Hewitt (1961) records maize as having a starch equivalent value of 77% and a gross digestible energy content of 79% whereas the values recorded for sorghum are 68% and 74% respectively. There seems little scientific basis for such low values for sorghum though at the time of publication, limited U.S.A. data may have influenced them. Morrison (1959) in the U.S.A. however quotes a TDN value in the range of 78.5-81.9% for most corn grains and a value of 79.9% for sorghum grain which is almost the mean of the corn value. Overseas authorities, particularly the Arizona workers, have for some years inclined to the view that sorghum is inferior to maize in respect of feed conversion, though some have recognised that growth performance may be a little better with it. In the Arizona work it is distinctly possible that protein, processing or other limitations may have been occurring. Hale (1973) has recently stressed that there appears a close relationship between apparent protein disgestibility of grain and NFE utilisation of grain by cattle. Although few or no direct comparisons have been made, it is my view that in Australia sorghum has performed quite comparably to maize. For example, the Australian data on sorghum performance, e.g. Mossis (1966 a) reveals feed conversions of down to 4.8 on all grain sorghum