Validation of intake estimates in grazing beef cattle

Abstract

SUMMARYGrowing beef cattle grazed six pasture types (all-grass or grass-legume mixtures) for 4 months on each. Live weight (mean of ten animals) and dietary energy concentration were measured at 2- or 3-weekly intervals. Values for feed intake estimated by back-calculating from feeding standards were on average 2·5% higher (range, 10% less to 12 % higher) than intake values estimated directly from dietary energy concentration and live weight. In contrast to this level of agreement of means, differences between methods within pastures were so large as to suggest the presence of overriding effects on predictors of voluntary intake. It was concluded that until these overriding effects are explained, there are no means of validating measured intakes in grazing cattle, or of accurately predicting the amount of beef produced from pasture.

Effect of pasture growth rate on live-weight gain of grazing beef cattle

“…However, there is another component of pasture growth that has the reverse effect. During growth there is young tissue present which has high digestibility; just how high can be gauged, for example, in pangola grass with cell-wall values at the lower end of the range of little more than 50% of the forage organic matter (Moir et al 1982). Such values can be expected to lead to true digestibilities of the total grass organic matter approaching 100% and a narrowing margin between true and apparent digestibility (Moir, 1982).…”

“…Data were drawn from experiments conducted at the Coolum Research Station as described by Moir et al (1982) and Moir & Ebersohn (1983). Only data from pastures that supported live-weight gain were used.…”

“…Large variation in the magnitude of live-weight gain of beef cattle grazing tropical pasture, for little or no change in dietary-energy concentration, has been reported by Moir, Ebersohn & Evans (1982) and Moir & Ebersohn (1983). High live-weight gain was not explained by intake; for the amount of faeces voided digestibility would need to have been much higher than is normally attributed to tropical pasture.…”

“…Four fistulated cattle and a 15-30 min collection period over three consecutive days were used in the derivation of each intake value. Intake by these means was measured in three series of experiments conducted during 1977-9 as described by Moir et al (1982).…”

“…The procedure of Moir et al (1982) was used. Dietary-energy concentration was estimated via cell wall in separated pasture fractions, and then this value was used to estimate D.M.…”