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

Abstract

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, NH 3 and VFA concentrations, apparent digestibility, ruminal pH, total fermentable carbohydrates, and weight gains. The first diet (80 lambs plus two cannulated 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 cannulated 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 NH 3 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 ( k d) 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/BC 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.