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Effect of switching diets on growth and digesta kinetics of cattle.

An approach was developed for describing live weight gain and the contribution of wet gut fill gain to live weight gain in growing cattle. In a continuous growth study, energy densities of winter:spring diets were used to define four treatment groups of cattle. Concentrates and forages were the major ingredients of higher and lower energy-density diets, respectively. Cattle receiving high and low energy sequences (HH and LL) were designated as control groups and were compared with two change-over groups: high to low (HL) and low to high (LH). Switches involved simultaneous changes in several feed characteristics. Every 2 wk for 4 mo, 39 heifers and 19 steers were weighed. Switching young cattle to another diet affected growth during the 2 wk immediately after the switch. After being switched to the lower energy-density diet (i.e., pasture), HL and LL groups lost (P less than .001) from 3.5 to 27.4 kg in both fed and fasted weight. Neither fed nor fasted weights of HH and LH steers changed during the switch to the higher energy-density diet (i.e., concentrates); HH and LH heifers continued to gain (P less than .001). Throughout the remainder of the study, growth rates of cattle were similar for HH and LH groups and for HL and LL groups. In spring, cattle consuming concentrate diets (HH and LH) had greater fill (P less than .001) than pasture-fed contemporaries (HL and LL). Less frequent measurement of growth characteristics would have obscured important facets of growth. A loss of weight followed by continuous gain is not equivalent to a reduced growth rate.