J.A. Guada

Determination of rumen microbial-nitrogen production in sheep : a comparison of urinary purine excretion with methods using 15N and purine bases as markers of microbial-nitrogen entering the duodenum

The present study compares estimates of rumen microbial-N production derived from duodenal flow measurements (15N and purine bases) with those from measurements of the urinary excretion of purine derivatives. Four Rasa Aragonesa ewes fitted with simple cannulas in the rumen and proximal duodenum were used. Four diets consisting of 550 g lucerne (Medicago sativa) hay/d as sole feed or supplemented with 220, 400 and 550 g rolled barley grain/d were given in a 4 x 4 random factorial arrangement. Duodenal digesta flows were determined by the dual-phase marker technique during continuous intraruminal infusions of Co-EDTA and Yb-acetate. Microbial contribution to the non-NH3 N (NAN) flow was estimated from 15N enrichment and purines: N ratio in duodenal digesta and bacterial fractions isolated from the rumen content. Whole tract organic matter (OM) digestibility and duodenal flow of OM and NAN increased (P < 0.001) with the level of barley supplementation. Digestible OM intake ranged from 19.0 to 42.7 g/kg metabolic weight (W0.75) and the duodenal flow of purine bases and the urinary excretion of allantoin increased linearly (P < 0.001) from minimum values of 7.47 (SD 1.524) and 4.65 (SD 0.705) mmol/d respectively on the basal diet to 18.20 (SD 1.751) and 11.62 (SD 0.214) mmol/d on the 400 g barley diet; a further increase in barley supplementation decreased both variables (13.50 (SD 2.334) and 8.77 (SD 0.617) mmol/d respectively). Urinary excretion of uric acid and hypoxanthine showed a slight but significant increase (P < 0.05) over all levels of barley. Molar recoveries of duodenal purine bases as purine derivatives or allantoin in the urine were 0.78 (SD 0.156) and 0.65 (SD 0.130) respectively. The increase on barley supplementation significantly augmented microbial-N, but large differences between microbial markers employed were observed. Mean values of microbial-N estimated from the duodenal purine bases or urinary allantoin excretion were on average 18 and 29% lower than those measured by 15N.

Validation of the n-alkane technique to estimate intake, digestibility, and diet composition in sheep consuming mixed grain:roughage diets

The usefulness of the n-alkane technique to estimate intake, digestibility, and diet composition in sheep fed mixed diets was tested in an experiment with 16 ewes consuming 4 different proportions of barley grain and straw ranging from 15:85 to 60:40. Two cases were considered: (1) straw as one component or (2) straw separated into leaves and stems. The relationship between estimated (Y) and observed (X) proportion of grain in the diet was highly significant (1: Y = 0.2355 + 0.9945X, r 2 = 0.9999; 2: Y = -2.472 + 1.0063X, r 2 = 0.9999). Actual intake was overestimated in (1) by 3.43-12.40%, the largest discrepancies corresponding to the lowest proportions of grain. In (2) actual intake was either overestimated (2.69%) or underestimated (5.38-6.85%), without a clear effect of the diet. A similar pattern was observed for digestibility, which was overestimated in (1) by 1.65-9.59%, and overestimated (by 2.07%) or underestimated (by 3.80-4.62%) in (2). Due to the small discrepancies between observed and estimated values, it may be concluded that the n-alkane technique might be a valid method for estimating intake, digestibility, and diet composition in sheep consuming mixed diets, for the two latter provided that faecal recovery of individual n-alkanes is calculated with enough accuracy. AR02 The nechn s i O. L. Va et al

Contribution of dietary purine bases to duodenal digesta in sheep. In situ studies of purine degradability corrected for microbial contamination

The dietary contribution of purine bases (PB) to duodenal flow was evaluated by the in situ method after correcting for microbial contamination using 15N as microbial marker and rumen solid associated bacteria as reference sample. Four ruminally fistulated sheep were offered at 4 h intervals a mixed diet 2:1 vetch-oat hay:concentrate, and 179 mg of ((15NH4)2SO4) were continuously infused in the rumen during a minimum of 5 days prior to incubation and rumen sampling. The following feeds were tested: meat meal (MM), fish meal (FM), gluten feed (GF), barley grain (BG), corn grain (CG), sunflower meal (SFM), soya bean meal (SBM), dry brewery distilled grain (DBDG), alfalfa hay (AH) and barley straw (BS). The largest residual proportion of microbial purine bases was found in BS followed by AH, CG, BG, DBDG, GF, SFM, MM, SBM and FM, in that order. For all feeds, the extent of degradation of dietary purine bases at the studied fractional outflow rates increased after the correction for microbial contamination. Apparent and true degradability were significantly different (P < 0.05) in DBDG, CG, AH, GF and MM, ranging the feeds in that descending order; whereas they did not differ in BG, SBM, SFM and FM. Correction for contamination of feeds by microbial purine bases did not substantially affect the proportion of dietary purines escaping ruminal degradation ranging from 5 to 17% for AH, BG, GF, SFM, CG, from 11 to 23% for MM, SBM and from 20 to 40% for FM and DBDG when fractional rates of outflow from the rumen of 0.02–0.08 were assumed.

Effect of ammonia treatment and carbohydrate supplementation on the intake and digestibility of barley straw diets by sheep

Abstract The changes in straw voluntary intake and apparent digestibility caused by the ammoniation of straw and energy supplementation in diets fed to adult, non-productive sheep were studied in two experiments. In Experiment 1, untreated (US) or ammonia treated (TS) barley straw were given as the only feed to four ewes in a cross-over design. Ammoniation increased straw dry matter (DM) intake from 30.2 to 50.6 g kg −1 LW 0.75 , organic matter digestibility (OMD) from 0.438 to 0.519 and digestible organic matter intake (DOMI) from 12.5 to 24.7 g kg −1 LW 0.75 , allowing energy maintenance requirements to be met. In Experiment 2, three groups of four ewes received US, with another three groups of four receiving TS, both supplemented with meadow grass hay (H), rolled barley (B) or sugar-beet pulp (P) in a 2 × 3 factorial design. Each supplement was given in amounts of 150, 300, 450 and 600 g day −1 , in a Latin-square design. The type of supplement did not significantly affect straw intake at any level of inclusion. The level of supplementation scarcely affected US intake, whereas DM intake of TS diminished linearly. Substitution rates were 0.49 ± 0.088, 0.61 ± 0.085 and 0.55 ± 0.131 for TS-H, TS-B and TS-P diets, respectively ( P > 0.05). Apparent digestibility of straw was not significantly affected by supplementation. Increases in total DOMI when the level of supplementation was augmented were lower in TS than in US diets, and with H than with B or P as supplements. To reach the DOMI obtained with TS as the only feed, US has to be supplemented with 420, 272 or 269 g DM of H, B or P, respectively.

Validation of use of purine bases as a microbial marker by 15 N labelling in growing lambs given high-concentrate diets: effects of grain processing, animal age and digesta sampling site

The origin of post-ruminal purine bases ( PB) was studied in 24 growing lambs that were given a pelleted concentrate plus barley straw (C) or whole barley grain plus protein supplement ( WB). Six lambs from each treatment were slaughtered at 10 and 30 days post weaning after 15 N labelling of microbial nitrogen (N) and PB. Microbial contribution to digesta nonammonia N (NAN) and PB was lower ( P < 0·01) when estimated from duodenal rather than abomasal samples (0·36 v. 0·52 (s.e.d. 0·021) for NAN and 0·47 v. 0·77 (s.e.d. 0·029) for PB) as a result of endogenous contamination. In comparison with 15 N, total PB/N led to higher estimates ( P < 0·01) of microbial contribution to abomasal NAN in WB treatment (0·62 v. 0·46 s.e.d. 0·049). The difference was removed after correcting for microbial PB, while this effect was not observed with < the C diet, resulting in a marker by diet interaction ( P < 0·05). Abomasal PB flow increased ( P < 0·1) from 10 to 30 days after weaning mainly due to the higher proportion of microbial PB (0·70 v. 0·81 (s.e.d. 0·047)). Rumen apparent PB degradation did not differ between diets in older lambs, but it was proportionally 0·39 lower for WB treatment ( P < 0·05) in younger lambs. When the microbial PB flow was estimated indirectly from labelled microbial N and the PB/N ratio of bacterial extracts the estimates were in agreement with those derived from PB- 15 N in the WB treatment but resulted in unrealistic values in lambs on diet C. Results suggest that significant proportions of dietary PB can escape rumen degradation which may lead to overestimation of microbial contribution to abomasal NAN when the PB/N ratio is used as marker. The extent of the overestimation is affected by the lamb age and grain processing.

The effect of protein restriction during the growing period on carcass, meat and fat quality of heavy barrows and gilts

Nutritional strategies are being researched in pigs to increase fatness and then to improve quality of dry-cured products. A total of 160 Duroc×(Landrace×Large White) pigs, 50% barrows and 50% gilts, were used in a trial. During the growing period (73-118d of age), four feeds were formulated with decreasing levels of crude protein (CP; 21.6, 17.7, 14.7 and 13.5%) to achieve 1.10, 0.91, 0.78 and 0.52% of total Lysine, respectively. From 118d until slaughter, at 123kg (183, 181, 178 or 192d of age, respectively), a common diet was provided (17.7% CP and 0.91% Lysine). Barrows had fatter carcasses than gilts but intramuscular fat (IMF) proportion was similar for both. Dietary CP restriction promoted wider backfat depth and pork with higher IMF percentage which was more monounsaturated and less polyunsaturated. We conclude that CP restriction during the grower period improves desirable carcass and meat traits in barrows and gilts intended for dry-cured products.

Frequency of feeding and form of lucerne hay as factors affecting voluntary intake, digestibility, feeding behaviour, and marker kinetics in ewes

The effects of the form (chopped or ground and pelleted) of a lucerne hay, and its frequency of feeding (once daily with restricted access, twice daily, or once every 2 h) on voluntary intake, digestibility, feeding behaviour, and marker kinetics was studied on 12 Rasa Aragonesa ewe lambs. The results showed that differences between animals fed twice daily or continuously were small and only found in intake and feeding behaviour, whereas feeding once daily with restricted access to the meal resulted in a much lower dry matter and digestible organic matter intake, which in turn affected significantly both the feeding behaviour of the animals and the total mean retention time of liquid and solid markers, but did not influence digestibility coefficients. It is concluded that continuous feeding does not seem to be necessary when studies on marker kinetics based on faecal marker excretion curves are carried out in sheep fed at intake levels close to ad libitum. Grinding and pelleting resulted in a higher dry matter intake and a reduction in organic matter digestibility, which resulted in a higher digestible organic matter intake. Feeding behaviour and rate of passage of Co-EDTA were also affected, although Cr did not show any tendency to pass faster when attached to the pelleted diet.

Contribution of dietary nitrogen and purine bases to the duodenal digesta: comparison of duodenal and polyester-bag measurements

Four ewes fitted with ruminal and duodenalT-piece cannulas were given fourdietsin a 4 × 4 factorial design. Diets consisted of 700 (HF) or 400 (LF) g/day of ammonia-treated barley straw supplemented respectively with 150 or 600 g/day of concentrate made up with barley plus either soya-bean meal (SBM) or fishmeal (FM) as the protein source, offered at 2-h intervals. Duodenal flowsof digestawere estimated by the dual-phasetechniqueusing CoEDTAand Yb-acetate as markers and ( 15 NH 4 ) 2 SO 4 was infusedinto the rumento label microbial N. Bacteria were isolated from the liquid (LAB) or solid (SAB) rumendigesta. Purinebases (PB) were isolated by precipitationin an acid solution of AgN0 3 , and microbial contribution either to the duodenalnitrogen(N) or PB were determinedby 15 N measurements induodenaldigesta and bacteria.Simultaneously, therumen degradation of Nand PB contained in SBM and FM was studiedby incubating supplements in polyesterbags in the rumen.PBcontent (mmol/g dry matter)and guanine: adenine(G/A) ratio of barley strawwas 2·89 and 5·23; barley grain,7·91 and 111;SBM, 18·8 and 1·26; and FM, 58·9 and 6·96, respectively. Duodenal flow ofPB(mmol/day)was significantly higher than PB intake on all diets and G/A ratio showed a meanvalue of 0·97, similarto the ratios determined in SAB(0·80) and LAB (1·04) and muchlower than diets(1·31 to 4·32). Microbial contribution to duodenal Nflow ranged from43·3% to 61·0%, beinghigherin SBM(59·0%)thanin FM(46·7%)diets. However, microbial contribution to duodenal PB was not affected by the experimentaltreatment, accounting for proportionately 0·77 of total PB at the duodenum. Rumen degradability of PB was much higher than that of total N and in both cases degradability was higher in SBM than FM. Direct measurements of non-microbialN were significantly higher than values determined by the polyester-bagmeasurements. However, once corrected forthe endogenousN (52 mgN per kg live weight)contribution, results show edan acceptable agreement. Duodenal flow of PB non-attributable to microbes (unlabelled PB) showed a mean value of 3·25 mmol/daywithouta significanteffect of dietary treatment. However, undegradablePBsupply determinedfor0·02, 0·05 and 0·08 per h fractional out flow rates were proportionately lower than 0·025 with SBM and 0·100 with FM diets of the estimated duodenalPB flow. Despite the magnitudeof the unlabelledduodenalPB, the close agreement between G/A ratios in duodenaldigesta and bacteria suggests thatthe contribution of dietary PB to the duodenalflow was low and seemsto confirm the reliability of values obtained from polyester-bag measurements.

Effects of sex and dietary lysine on performances and serum and meat traits in finisher pigs.

A total of 160 Duroc×(Landrace×Large White) pigs, 50% barrows and 50% gilts, of 28.3 ± 4.52 kg of BW were used to study the effect of lysine (Lys) restriction in the finisher period, on growth performances and serum and carcass and meat quality traits. The grower diet (from 30 to 90 kg BW) was slightly Lys-restricted (7.8 g standardised ileal digestible (SID) Lys/kg) in accordance with results from a previous trial. During the finisher period (90 to 130 kg BW), four experimental diets with decreasing SID Lys contents (6.3, 5.6, 4.2 and 3.2 g/kg) were tested. Each of the eight treatments (two sexes×four levels of Lys) was replicated five times. Each replicate was a pen with four pigs allocated together. When animals achieved 129 ± 2.59 kg were slaughtered and carcass and meat characteristics were evaluated. No significant interaction sex×diet was found. During the finisher period, barrows grew faster (P<0.001) and ate more feed (P<0.001) but tended to be less efficient (P=0.055) than gilts. The Lys restriction affected linearly (P<0.001) all productive performance traits; daily BW gain and feed intake decreased and feed conversion ratio increased. Also, the concentration of serum urea at slaughter tended to be higher in barrows than in gilts (P=0.065) and was reduced quadratically by the restriction of Lys in feed (P<0.001). Carcasses from barrows had higher backfat thickness (P<0.01) and lower weight of main trimmed lean cuts (ham+shoulder+loin; P<0.05) than those from gilts. The Lys restriction during the finisher period decreased carcass yield (quadratic; P<0.001) and the weight of major cuts (linear; P<0.001). Sex and diet had limited effect on meat characteristics; the Lys restriction decreased quadratically the proportion of protein (P<0.01) and increased linearly the intramuscular fat (IMF) content (P<0.001). We can conclude that dietary Lys restriction during finisher period in pigs impaired growth performances and was not successful to increase the carcass fat deposition, although it could have positive effects on IMF proportion of pork.

Net transfer of nutrients to the duodenum and disappearance of n-alkanes in the reticulo-rumen and the hindgut of sheep fed grass/legume combinations

An experiment was carried out to examine the effect of increasing the proportion of Wimmera ryegrass hay in a lucerne hay-based diet on net transfer of nutrients to the intestine, and on the disappearance of n-alkanes in the reticulo-rumen and the hindgut of sheep. Following a latin square design, four adult ewes were fed 1:0, 0·33:0·67, 0·67:0·33 and 0:1 proportions of legume and grass. Increasing the proportion of ryegrass in the diet linearly decreased the intake of DM (P= 0·017), organic matter (P= 0·021) and N (P= 0·001). However, neutral-detergent fibre intake was not affected (P= 0·148), nor was its digestibility coefficient (P>0·10). Diet had no effect on duodenal flows of nutrients (P>0·10), although the proportion of N intake (NI) recovered at the duodenum as non-NH₃ N (NAN) increased linearly with Lolium rigidum in the diet (P= 0·002). Full recovery of NI as NAN was achieved at NH₃ concentrations in the rumen below 110 g/l. Microbial N contribution to NAN varied in a quadratic manner (P< 0·05) with the proportion of grass in the diet, although efficiency of microbial synthesis was not affected (P>0·10). Duodenal recovery of consumed n-alkanes was not affected by diet and was complete for those present in higher concentrations in the forages. Isolated rumen bacteria contained significant amounts of n-alkanes, contributing to the duodenal flow of these hydrocarbons in variable proportions depending on the diet consumed.