Effect of a slow-intake urea supplementation on growing kids fed corn stubble or alfalfa with a balanced concentrate

One hundred and sixty Alpine kids (16 kg BW) were studied for 150 days with two diets, evaluating in situ DM disappearance, VDMI, OMI, rumen degradation, rate of passage, ammonia (NH3) and volatile fatty acids (VFA) concentrations, apparent digestibility, pH, total fermentable carbohydrates (FC), and BW gains. Group 1, designated as CS/SIUS (n=80 plus two cannulated goats) was offered corn stubble (CS) 800 g per day and alfalfa hay (AH) 100 g per day, with 150 g per day of a slow-intake urea supplement (SIUS) consisting of 16.5% molasses, 5% urea, 4% fishmeal, 2% limestone, 16% cottonseed meal, 17.5% rice polishing, 14.5% corn, 9.5% poultry litter, 4.1% commercial mineral salt, 0.9% orthophosphate, 2% ammonium sulfate, 1.5% cement kiln dust, and 6.5% animal lard. Group 2, designated as AH/BC (n=80 plus two cannulated goats) were fed 550 g AH per day supplemented with 450 g of a balanced concentrate (BC) per day, consisting of 1.1% mineral salt, 1.2% orthophosphate, 40.0% corn, 25.9% wheat bran, 25.8% barley, and 6.0% soybean meal. VDMI and OMI were similar for 150 days for the two experimental diets fed to goats. NH3 concentration and degradation of potential non-degradable DM fractions were augmented by SIUS (P<0.05). Rumen pH rose to 6.9 by 2 h after CS/SIUS was offered and stayed above 6.6 for 12 h, while the rumen pH in AH/BC goats decreased to 5.57 by 6 h and rose again to 6.50 after 12 h. N intake with CS/SIUS was 18.60 g per day versus 14.57 g per day with AH/BC (P<0.05). In vivo N digestibililty was 76.63% in the CS/SIUS diet and 54.16% in AH/BC (P<0.05). In vivo digestibility of NDF was greater for CS/SIUS (P<0.05) (77.14% versus 65.11% for AH/BC). Degradation rate constant (kd) of NDF also favored the CS/SIUS diet (P<0.05) and non-degradable fiber was less (P<0.05) (35.18% versus 63.32% for AH/BC). Half-time (t(1/2), h) disappearance of cellulose and hemicellulose in the CS/SIUS diet were 29.34 and 29.14 compared to 16.54 and 20.16 in the AH/BC diet, respectively (P<0.05) and passage rates differed similarly (P<0.05). True digestibility of cellulose in CS/SIUS at 46.24% was higher (P<0.5) than that of AH at 33.22%. Growth in 150 days averaged 112±23 g gain per day for CS/SIUS compared to 86±21 g per day for the AH/BC diet (P<0.05). SIUS supplement intake per kg BW ranged from 6.57 to 3.12 g per day for the CS fed goats and 21.02 to 11.80 g per day for the AH/BC fed control goat kids (P<0.05). Rumen NH3 was higher for CS/SIUS (12.3 mg per 100 ml versus 6.8 mg per 100 ml for AH/BC) (P<0.01). Rumen acetic and butyric acids increased with the CS/SIUS diet (P<0.05), while propionic acid was less and total VFA were not different. Supplementation of a high fiber diet with a slow-intake NPN supplement improved rumen fermentation. SIUS supplied critical nutrients to the rumen microflora, improved rate of passage, ruminal pH, NH3 contents, and resulted in higher weight gain than the AH/BC fed control goat kids. Results showed that high fiber forages like CS can be used efficiently by growing goats, when conditions for ruminal microorganisms are improved with a continuous slow-intake N supplementation.