Rodrigo Peláez

The influence of digestible organic matter and nitrogen intake on faecal and urinary nitrogen losses in sheep

Relationships between dietary characteristics and faecal and urinary nitrogen losses were examined using data from 25 rations fed to Merino ewes. Metabolic faecal nitrogen (MPN) ranged from 153 to 280 mg/kg W”.75, increasing (P < 0.05) with increasing levels of digestible organic matter (DOM) intake (r = 0.96). Endogenous urinary nitrogen (EUN) showed the opposite behaviour, decreasing from 181 to 76 mg/kg W”.75, which could be attributable to urea recycling to the large intestine being enhanced by increasing hindgut fermentation with increasing DOM levels, as the composition of urinary nitrogen suggests. Total endogenous nitrogen (TEN) remained fairly constant, indicating that faeces and urine are complementary routes for the excretion of recyclable nitrogen compounds. The TEN overall mean value was very close to the value adopted by AFRC (AFRC Technical Committee on Responses to Nutrients, 1992. Report No. 9. Nutritive Requirements of Ruminant Animals: Protein. Nutr. Abstr. Rev. Ser. B 62, 787-835.) (333 vs 350 mg N/kg W”.75). 0 1997 Elsevier Science B.V.

Prediction of aspects of neutral detergent fibre digestion of forages by chemical composition and near infrared reflectance spectroscopy

Sixty-two herbage samples, harvested in natural meadows located in the mountains of Leon (north-west Spain), and characterised by a diverse botanical composition and different stages of maturity of the plants, were used to evaluate the ability of chemical composition and near infrared (NIR) spectroscopy to predict in vitro digestibility and in sacco degradability of the neutral detergent fibre (NDF) fraction. In vitro digestibility was performed as described by the Goering and Van Soest procedure. Three dry Holstein-Friesian cows fitted with a rumen cannula were used to incubate the herbage samples. A Bran+Luebbe InfraAlyzer 500 spectrophotometer was used to obtain the NIR spectra corresponding to the 62 original herbage samples. Prediction equations for the estimation of in vitro digestibility and in sacco degradability parameters of the NDF fraction were generated using NIR spectra or chemical data as independent variables. The results showed that the in vitro digestibility and kinetic parameters of degradation of the NDF fraction could not be predicted accurately, probably as a consequence of the errors corresponding to the reference methods. In contrast, these errors did not greatly affect the extent of disappearance of the NDF fraction at later times, so the accuracy of prediction of these parameters was higher, especially when NIR spectra were used as independent variables. This is probably due to the close relationship that the parameters showed with the chemical data, since this kind of information, together with some physical characteristics of the samples, is included in the NIR spectra.