Fattening Rambouillet lambs with corn stubble or alfalfa, slow intake urea supplementation or balanced concentrate

One hundred and sixty Rambouillet lambs (15.925 +/- 0.350 kg/BW) were studied for 90 days with two treatments evaluating in situ DM disappearance, voluntary DM and OM intake, rumen degradation, rate of passage, NH3 and VIA concentrations, apparent digestibility, ruminal pH, total fermentable carbohydrates, and weight gains. The first diet (80 lambs plus two carmulated sheep) offered 1000 g corn stubble (CS) per day, 200 g alfalfa hay (AH) per day, and 200 g of a slow-intake urea supplement (SIUS) per day, consisting of 12.0% molasses, 5.0% urea, 4.0% fish meal, 3.0% salt, 2.5% orthophosphate, 3.2% limestone, 12.0% cottonseed meal, 12.0% rice polishing, 25.0% corn, 8.0% poultry litter, 1.5% mineral salts, 2.0% ammonium sulphate, 1.8% cement kiln dust, and 8.0% animal lard. The second group (80 lambs plus two carmulated sheep) was fed 800 g AH per day and 600 g of a 18% CP balanced concentrate (BC) per day. VDMI, OMI, DM digestibility and rumen NH3 concentrations were highest (P < 0.05) in CS/SIUS fed sheep. Rumen pH rose at 2 h with CS/SIUS and stayed above 6.4 for 12 h, while the pH in AH/BC fed sheep decreased to 5.6 by 4 h and rose to 6.2 after 12 h. N intake was 65.61 g per day with the CS/SIUS diet versus 28.93 for AH/BC (P < 0.05). In vivo N digestibility of CS/SIUS was 79.12% versus 56.14% for AH/BC (P < 0.05); OM, NDF, cellulose and hemicellulose in vivo digestibilities differed similarly. In situ DM disappearance differed also among diets at all hours of incubation, being slightly higher for CS/SIUS and significantly lower for CS. Digestion rate of NDF constant (k(d)) favored the CS/SIUS diet (P < 0.05), its passage rate (k(p), h(-1)) was 0.082 h(-1) for CS/SIUS (P < 0.05) versus 0.061 h(-1) for AH/BC (P < 0.05). True digestibility of NDF was 48.33% in the CS/SIUS diet compared to 34.11% for AH/BC (P < 0.05). In situ digestion rate (kd) for cellulose was 0.060 for CS/SIUS and 0.055 for AH/BC, but half-time disappearance of CS/SIUS was 30.34 h versus 17.54 h for AH/BC (P < 0.05). True digestibility of cellulose for CS/SIUS was 48.26% compared to 34.22% for AH/BC (P < 0.05). Indigestible fiber was 48.22% in the AH/BC diet compared to 32.93% for CS/SIUS (P < 0.05). Passage rate of hemicellulose was higher (0.034 h(-1)) for CS/SIUS and than for AH/BC (0.029 h(-1)) (P < 0.05). Half-time disappearance of hemicellulose was 31.14 h for CS/SIUS versus 22.14 h for AH/BC (P < 0.05). The CS/SIUS diet was consumed in 8-10 h, while the AH/C diet took only 30 min. Weight gain was 351 g per day (+/-46) for CS/SIUS compared to 315 g per day (+/-58) for the AH/BC diet (P < 0.05). Rumen acetic acid production increased in CS/SIUS compared to the AH/BC diet (P < 0.05), while propionic acid was reversed (P < 0.05). Results showed that high fiber forages, such as CS can be used efficiently by lambs, when ruminal conditions are improved with a non-protein N (NPN) slow-intake supplementation. (C) 2003 Elsevier B.V. All rights reserved.