The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49´5 kg). The animals received, in a crossover design, each of two rations, hay±grass pellets (1:1 HG) and a mixed concentrate±forage (CF N]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to 15 NH 3 in the digestive tract with subsequent absorption and reconversion to urea. The diets were not isonitrogenous (14´3 v. 17´1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16´3 v. 11´1 g/d; P 0´011 for CF compared with HG and more urea-N entered the GIT (9´9 v. 7´7; P 0´07X A larger proportion of GIT entry was returned to ureagenesis (51 v. 42 %; P 0´047 for the CF diet but a smaller fraction was lost in the faeces (3´3 % v. 7´1 %; P 0´013X In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH 3 ) and the absolute amount available for anabolic purposes was similar between the rations (3´9 v. 4´5 g N/d).

The effect of dietary fiber on endogenous N secretion was studied using a 15N isotope dilution technique in four fistulated Holstein cows. Two isonitrogenous diets differing only in fiber (NDF and ADF) content were used in a crossover design. One diet (HF) contained 37.4% NDF, while the other (LF) contained 23.3%. A new model was developed to estimate endogenous N secretions and losses for the preintestinal, intestinal, and the total sections of the gastrointestinal tract. Three precursor pools: TCA-soluble fraction of plasma, intestinal mucosa, and milk were compared. Although endogenous losses estimated with the model were numerically different for each precursor pool selected (TCA-soluble fraction > mucosa > milk), treatment effects were similar. As intestinal mucosa is probably closest to the precursor pool, these data are discussed. Non-urea N endogenous secretions contributed 13% of the duodenal N flow but were not affected by the fiber content of the diet. The nonurea N endogenous flow at the duodenum was comprised of approximately equal inputs from endogenous N direct, and that incorporated into the microbial biomass. Total endogenous N flows at the duodenum exceeded, by nearly twofold, estimated inputs of urea-N to microbial biomass. Metabolic fecal output averaged 17% of fecal N and was not affected by level of dietary fiber, but net losses from secretions occurring in the small intestine were higher with the low fiber diet. Overall, endogenous N secretions represented 30% of total digestive tract protein synthesis.

No abstract

Square mesh panels are often inserted in the codend or extension of a fishing net to allow under-sized fish an extra opportunity to escape. The effectiveness of the panel can be quantified by placing a small-mesh cover over the panel to catch all the fish that escape through it. This paper develops methodology for modelling the data from such covered panel experiments. The selection process is modelled in two stages: first, selection in the panel area, and second, conventional codend selection. Several different curves describing selection in the panel area are investigated. These include curves that separate the process of fish ''contacting'' the panel from the selection of the panel itself. Parameter estimation, inference, and methods for assessing goodness-of-fit are described. The methodology is illustrated using haddock and whiting data.

It has been suggested that protein synthesis in peripheral tissues: (1) responds in a curvilinear manner to increasing feed intake over a wide range of feeding levels; and (2) has a greater sensitivity to intake than protein breakdown. The aim of the present experiment was to test these hypotheses across the ovine hindlimb. Six growing sheep (6 -8 months, 30 -35 kg), with catheters in the aorta (two), posterior vena cava and jugular vein, received each of four intakes of dried grass pellets (0 : 5, 1 : 0, 1 : 5 and 2 : 5 Â maintenance energy; M) for a minimum of 7 d. A U-13 C-labelled algal hydrolysate was infused intravenously for 10 h and from 3 -9 h para-aminohippuric acid was infused to measure plasma flow. Arterial and venous plasma were obtained over the last 4 h and the concentrations and enrichments of thirteen 13 C-labelled amino acids (AA) were determined by GC -MS. As intake increased, a positive linear response was found for plasma flow, arterial concentrations of the aromatic and branched-chain AA, total flow of all AA into the hindquarters and net mass balance across the hindquarters (except glycine and alanine). Based on two separate statistical analyses, the data for protein synthesis showed a significant linear effect with intake (except for phenylalanine, glycine and alanine). No significant curvilinear effect was found, which tends not to support hypothesis 1. Nonetheless, protein synthesis was not significantly different between 0 : 5, 1 : 0 and 1 : 5 Â M and thus the 2 : 5 Â M intake level was largely responsible for the linear relationship found. There was no significant response in protein breakdown to intake, which supports hypothesis 2.