Dietary nitrogen reduction enhances urea transport across goat rumen epithelium1

Abstract

Ruminants are very capable of adapting their N homeostasis to a reduced dietary N intake. However, the limits of this physiological adaptation are still unknown. The aim of the present study was to determine the quantity of dietary N intake at which the needs of the animal are still satisfied. A study was performed in young White Saanen goats under conditions of dietary N reduction. Different semisynthetic diets with 19 to 7% CP were fed. Urea transport rates across the rumen epithelium from the blood into the ruminal fluid were quantified by Ussing chamber experiments. Reduced N intake increased urea transport rates across the mucosa, which could be inhibited by phloretin. The role of parietal urease in driving urea transfer across the epithelium was negligible because its activity was inhibited by antibiotics during in vitro incubations of the epithelium. Concentrations of ammonia in the ruminal fluid were decreased by reducing dietary N intake, accompanied by diminished urease activity at the smallest dietary N intake. Over the range of plasma urea concentrations observed in the different feeding groups, salivary urea concentrations were 73% of plasma urea concentrations. By plotting plasma urea concentrations against serosal to mucosal urea flux rates, a threshold at 1.75 mmol of urea/L of plasma could be assessed, below which urea flux was strongly increased. This indicates that rumen urea transfer could be stimulated by decreased plasma urea concentrations via unknown mechanisms. The physiological relevance of this adaptation of the rumen epithelium is that it is considered a central mechanism in the N homeostasis of growing goats under reduced N intake.

Proteomic Analysis of a 14.2 kDa Protein Isolated from Bali Cattle(Bos Sondaicus/Javanicus)Saliva Using Single Dimension Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis and Matrix-Assisted Laser Desorption Ionization Time-of-Flight Tandem Mass Spectrometer

“…Mixed saliva was obtained from oral cavity of 4 healthy, non-pregnant and non-lactating female Bali cattle (Bos sondaicus/javanicus) by means of sponge gags (Muscher et al, 2010;Yisehak et al, 2011). The cattle were raised in the Teaching Farm of the Faculty of Animal Sciences, Mataram University, Indonesia.…”

Nutritional aspects applied to grazing cattle in the tropics: a review based on Brazilian results

“…It can be inferred that low RAN concentrations can increase the proportion of urea that is recycled to the rumen (HARMEYER; MARTENS, 1980; MARINI; VAN AMBURGH, 2003;MARINI et al, 2004;WICKERSHAM et al, 2008;MUSCHER et al, 2010;. To some extent, that mechanism seems to be responsible for the negative nitrogen balance in the rumen of non-supplemented animals (Figures 9 and 10).…”

Incorporating farmed goats into sustainable rangeland grazing systems in southern Australia: a review

“…The capacity of goats to perform better than other ruminants in harsh environments has been variously attributed to their smaller body size and higher efficiency of utilisation of ingested nutrients (Silanikove 1997), low metabolic rates (Munn et al 2012), ability to reduce metabolism (Silanikove 1997), efficient N economy (Muscher et al 2010), efficient use of water (Silanikove 2000), and their ability to select a relatively highquality diet from the variety of forage available (Ramirez 1999;see below). The extent to which these traits enable them to maintain growth under poor seasonal conditions is highly relevant to their use as livestock in the southern rangelands.…”