A comparison of various methods of estimating digestibility, voluntary intake or average daily gains for beef cattle fed mixed rations

Since feedlot trials are the most useful and accurate method of determining nutritive value of feeds for beef cattle, they are the standard to which all other methods are compared. Considerable time, labor and expense are required to conduct feedlot trials; hence, the number of trials which can be conducted is limited. Therefore, accurate, simple, timesaving and cheap methods of estimating nutritive value of feeds need to be developed. These methods could be used to select the more desirable rations, which can then be fed in the feedlot for further evaluation. However, they probably will never replace feedlot trials. For many years, digestibility trials have been used to estimate nutritive value of feeds. However, it has recently been recognized that the amount of feed eaten by ruminants is also an important factor in assessing its nutritive value.

Numerous laboratory methods are being used to estimate in vivo digestibility and forage intake, which also give an indication of nutritive value of feeds. Using forages, several investigators have shown high correlations between results from laboratory evaluations and in vivo digestibility and/or feed intake. However, since forages are seldom fed alone, it would be advantageous to have a laboratory procedure to evaluate the total mixed ration rather than just the forage alone.

Therefore, the major objective of this study was to determine the relationship between various laboratory evaluations and in vivo digestibility, feed intake and animal performance (average daily gains) when mixed rations are used. The second objective was to determine the relationships among and/or between in vivo digestibility, feed intake, total digestible nutrient intake above maintenance, laboratory evaluation data and animal performance.