Influence of Rumen Protein Degradability and Supplementation Frequency on Ruminants Consuming Low-Quality Forage


Site of Digestion and Microbial Efficiency in Steers

Seven cannulated (rumen and duodenal) Angus´ Hereford steers (264 ± 8 kg BW) consuming low-quality forage (5% crude protein) were used to determine the influence of crude protein degradability and supplementation frequency (SF) on dry matter intake and nutrient digestion using an incomplete 7 × 4 Latin square design with four 24-day periods.  Treatments included an unsupplemented control and degradable intake protein (DIP) or undegradable intake protein (UIP) provided daily, every 3 days, or every 6 days.  The DIP treatments (18% UIP) were calculated to provide 100% of the DIP requirement while the UIP treatments (60% UIP) were provided on an isonitrogenous basis compared with DIP.  The DIP supplement was composed of soybean meal and the UIP supplement was composed of expeller processed soybean meal and blood meal.  Forage dry matter intake was not affected by treatment.  Total dry matter and nitrogen intake, duodenal nitrogen flow, and intestinal nitrogen disappearance increased (P < 0.01) with supplementation.  Dry matter intake and duodenal nitrogen flow responded quadratically (P < 0.04; greatest values on the 3 day treatments) as SF decreased.  However, no differences in nitrogen intake or intestinal nitrogen disappearance were observed because of crude protein degradability or SF.  Duodenal bacterial nitrogen flow and true bacterial nitrogen synthesis (g bacterial nitrogen/kg of organic matter truly digested in the rumen) were increased (P < 0.05) with supplementation.  Also, duodenal bacterial nitrogen flow was greater (P < 0.05) for DIP compared with UIP.  Duodenal non-bacterial nitrogen flow was increased (P = 0.02) with crude protein supplementation and for UIP compared with DIP (P < 0.01).  Supplemental crude protein increased (P < 0.01) total tract dry matter and nitrogen digestibility with no difference due to crude protein degradability or SF.  Results suggest crude protein supplements consisting of 20 to 60% UIP can be effectively used by steers consuming low-quality forage without adversely affecting dry matter intake, nutrient digestibility, and bacterial crude protein synthesis, even when provided as infrequently as once every 6 days.

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Bohnert, D.W., C.S. Schauer, M.L. Bauer, and T. DelCurto. 2002. Influence of rumen protein degradability and supplementation frequency on steers consuming low-quality forage: I. Site of digestion and microbial efficiency. J. Anim. Sci. 80:2967-2977  (DWB PDF #8)

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