Wilting of herbage prior to ensiling: effects on conservation losses, silage fermentation and growth of beef cattle

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Abstract
A sward of perennial ryegrass was either directly ensiled at 181 g dry matter (DM) per kg fresh weight with formic acid applied at 3·6 1/t fresh material or wilted for 65 h to achieve a DM concentration of 407 g DM per kg. Physical and respiration loss were measured in the field and losses during ensiling were estimated from buried bags. The silages were offered to 58 British Friesian steers, initially 3 months of age and 101 kg live weight (LW). Ten steers were allocated to an initial slaughter group and the remainder were offered the two silages either ad libitum or at two restricted levels of feeding. These animals were slaughtered after a mean period of 112 days to estimate the increments in the components of the body.Loss of DM in the field increased from 4·3 to 86·6 g/kg on wilting and proportionately 0·75 of this additional loss was due to respiration. The fermentation characteristics of the silages were broadly similar except that the concentration of ethanol was higher in the unwilted than in the wilted silage (57·6 v. 5·6 g/kg DM). Losses of DM during ensiling were slightly higher with the unwilted (104·4 g/kg ensiled) than with the wilted (80·1 g/kg) material. Losses of nitrogen were relatively higher and energy losses lower than was the loss of DM.Wilting significantly depressed the digestibility of gross energy from 0·651 to 0·631 (P < 0·001) and at the ad libitum level steers ate proportionately 006 more wilted silage (P > 0·05) resulting in similar intakes of digestible energy. At the ad libitum level of feeding steers given wilted silage gained more LW (+55 g/day) and empty-body weight (+64 g/day) than those given unwilted silage (P < 0·05). However, steers given wilted silage contained less fat and energy in the empty body at slaughter than those given unwilted silage. Thus, wilting did not influence the efficiency of utilization of digestible energy for energy retention nor the efficiency of utilization of dietary protein for protein gain. Since efficiencies by the animal were similar and also the increased field loss on wilting was partly compensated for by a reduced silo loss, it is concluded that the proportion of energy and protein in the standing crop retained by the steers is unaffected by wilting (65 and 64 kJ/MJ and 125 and 138 g/kg N for unwilted and wilted systems respectively). Further work is needed to establish the effect of wilting for a shorter period than in the current trial by increasing the drying rate of herbage.