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Abstract
The effect of feeding rations containing approximately 85% concentrate and balanced to contain 20% crude protein (CP) ad libitum to ruminants previously fed all roughage diets was studied in three cattle trials and one sheep trial.
In all three cattle trials, the steers fed the 20% CP ration "came back" on feed more rapidly and exhibited less severe variations in dry matter intake (DMI) than did steers consuming a similar ration balanced at 11% CP. The source of supplemental protein did not effect this response. By the end of the initial 10 or 14 days, respectively, of concentrate feeding, no differences in DMI were observed due to treatment. In addition to early differences in DMI, steers consuming the high protein rations had higher rates of average daily gain (ADG) during the initial 10 or 14 days of concentrate feeding. In the first cattle trial, steers consuming the high protein treatment with soybean meal (SBM) as the source of the supplemental protein gained 1.24 kg/head/day compared to 0.74 kg/head/day for the control treatment. In the second trial, addition of SBM to the hay ration compared to the same hay without supplemental SBM prior to changing to an 85% concentrate diet resulted in higher ADG (1.82 versus 1.35 kg) and DMI (6.36 versus 5.63 kg) during the initial concentrate feeding period. Addition of SBM or urea to the 85% concentrate ration to give a total CP level of 20% also resulted in higher ADG (2.69, 1.16, 0.92 kg) for SBM, urea, or control, respectively, for the initial 10 days of concentrate feeding. In the third trial, cattle consuming SBM rations balanced for 25% CP had higher ADG (1.91 versus 1.32 kg) for the first 14 days compared to the control treatment at 15% CP. In this study, the steers consuming the 25% CP ration had higher fecal pH and lower fecal starch than did the steers fed the 15% CP ration.
Sheep fed a 20% CP, 80% concentrate diet tended to consume more DM than did sheep fed an 11.5% CP, 80% concentrate ration; although the difference was not significant. Sheep on the high protein ration retained 15.3 gm nitrogen/day compared to 5.1 gm/day for the sheep consuming the low protein ration. Rumen volatile fatty acids were higher for the sheep consuming the high protein ration and indicated an increase in microbial activity. Rumen lactates were lower in the high protein fed sheep, especially the L (+) isomer of lactic acid. No significant changes in gastrointestinal tract pH were noted due to protein level of the ration.
