Oxygen uptake and net flux of metabolites by splanchnic tissues of sheep in response to short-term mesenteric infusion of nitrogenous compounds.

This study was conducted in an attempt to quantify the impact of N load on splanchnic tissues metabolism of sheep. The trial was conducted with four male sheep (45 ± 2.5 kg body weight (BW)) surgically implanted with chronic indwelling catheters into the portal, hepatic and mesenteric veins. Blood flow and metabolic flux through portal-drained viscera (PDV), liver and total splanchnic tissues (ST) were measured daily following a 4 × 4 Latin Square experimental design, where sheep were continually infused into the mesenteric vein with a physiological saline (0.15 m NaCl) solution during 90 min followed by the infusion, during more 120 min, of either solution: physiological saline (control), 0.250 mNH4 HCO3 , 0.250 m L-alanine or 0.125 m L-arginine, all of them infused at a rate of 1.5 ml/min to provide 375 µmol N/min. During the treatment infusion period, the net removal of ammonia N and the net production of urea N by liver were higher (p < .05) in NH4 HCO3 infused sheep. Based on oxygen consumption, and on average of all treatments, the heat produced by liver and ST was on average 6 and 14 kcal/kg BW representing 16% and 38% of the metabolizable energy intake respectively. Linear relationships between variables indicated that gluconeogenesis and ureagenesis occurred concomitantly and both processes accounted for approximately 50% of total liver energy expenditure, two-thirds of it associated with gluconeogenesis. The results of the current study did not present clear evidence of the expected energy costs associated with ammonia N, alanine or arginine metabolism by liver. However, they indicated that gluconeogenesis is on average a more energy expensive process than ureagenesis.

Technical note: Evaluation of urinary purine derivatives in comparison with duodenal purines for estimating rumen microbial protein supply in sheep.

A data set of individual observations was compiled from digestibility trials to examine the relationship between the duodenal purine bases (PB) flow and urinary purine derivatives (PD) excretion and the validity of different equations for estimating rumen microbial N (Nm) supply based on urinary PD in comparison with estimates based on duodenal PB. Trials (8 trials, = 185) were conducted with male sheep fitted with a duodenal T-type cannula, housed in metabolic cages, and fed forage alone or with supplements. The amount of PD excreted in urine was linearly related to the amount of PB flowing to the duodenum ( < 0.05). The intercept of the linear regression was 0.180 mmol/(d·kg), representing the endogenous excretion of PD, and the slope was lower than 1 ( < 0.05), indicating that only 0.43% of the PB in the duodenum was excreted as PD in urine. The Nm supply estimated by either approach was linearly related ( < 0.05) to the digestible OM intake. However, the Nm supply estimated through either of 3 published PD-based equations probably underestimated the Nm supply in sheep.

Relationship between level of forage intake, blood flow and oxygen consumption by splanchnic tissues of sheep fed a tropical grass forage.

Four Polwarth castrated male sheep (42 ± 4.4 kg live weight (LW) surgically implanted with chronic indwelling catheters into the mesenteric, portal and hepatic veins, housed in metabolism cages and offered Cynodon sp. hay at rates (g of dry matter (DM)/kg LW) of 7, 14, 21 or ad libitum, were used in a 4 × 4 Latin square experiment to evaluate the effect of the level of forage intake on blood flow and oxygen consumption by the portal-drained viscera (PDV), liver and total splanchnic tissues (ST). The portal blood flow and the oxygen consumption by PDV linearly increased at increased organic matter (OM) intake. No effect of level of OM intake was obtained for the hepatic artery blood flow and oxygen consumption by liver. As a consequence, the level of OM intake only tended to directly affect hepatic blood flow and oxygen consumption by total ST. Oxygen consumption was linearly and positively related to blood flow across PDV, liver and total ST. The heat production by PDV and total ST, as proportion of metabolizable energy (ME) intake, decreased curvilinearly at increased ME intake. In conclusion, the oxygen consumption by PDV, but not by liver, was directly related to the level of forage intake by sheep. Moreover, when ingested at levels below maintenance, most of ME was spent as heat produced by ST.

Minimum length of the adaptation and collection period in digestibility trials with sheep fed ad libitum only forage or forage plus concentrate.

Two in vivo digestibility trials with sheep were conducted to identify the minimum period length of feeding a new diet to obtain reproducible values of nutritional variables onward and the minimum length of collection period as to obtain maximal precision for each variable. Trial 1 was conducted with ten Polwarth male sheep (34 ± 5 kg body weight (BW)) throughout three 21-day periods, in a completely randomized two-way crossover design. The animals were divided into two groups (Group A and B, n = 5 per group) which were fed ad libitum with a sequence of the following diets throughout the periods: Group A: hay - hay plus concentrate - hay; Group B: hay plus concentrate - hay - hay plus concentrate. The concentrate was included in a proportion of 0.33 of the total diet. The intake, and the faecal and urinary excretion were measured daily throughout the experiment. For evaluating rumen fermentation variables, in Trial 2 four Santa Inês male sheep (65 ± 5 kg BW) fitted with ruminal cannula were used. The animals were randomly divided into two groups (n = 2 per group), and the trial was conducted through four 21 days experimental period, in a three-way crossover design, using experimental diets and feeding management similar to Trial 1. The results indicated that, even though no clear or consistent steady-state condition was identified for rumen fermentation or urinary excretion variables, the adaptation period for measuring OM digestibility in in vivo trials with sheep fed ad libitum where the diet shifts from one of only hay to another containing concentrate, or vice-versa, should be at least 12 days long. Moreover, although no precision improvement was obtained by increasing the collection period above 1 day for measuring OM digestibility, the minimal length of collection period should be 4 days for measuring faecal excretion variables and 7 days for measuring urinary excretion variables.

Technical note: Evaluation of markers for estimating duodenal digesta flow and ruminal digestibility: Acid detergent fiber, sulfuric acid detergent lignin, and n-alkanes.

The amount of digesta flowing to the duodenum is a relevant measurement for the evaluation of nutrient supply to ruminants, which is usually estimated in animals fitted with a duodenal T-type cannula using internal or external markers. This study evaluated acid detergent fiber (ADF) compared with external (C32n-alkane) and internal [sulfuric acid lignin (ADL) and n-alkanes C31 and C33] markers for estimating duodenal flow and(or) ruminal digestibility of dry matter (DM) in cattle and sheep. In the first assay, 4 duodenally cannulated Holstein steers housed in metabolism cages, dosed with C32n-alkane, and fed Avena strigosa plus concentrate and increasing levels of tannin extract to reduce ruminal digestibility, were used in a Latin square design. The mobile-bag technique was used to measure the intestinal disappearance of ADL and ADF from forage (Avena strigosa, Pennisetum purpureum, Cynodon dactylon, and Medicago sativa) and concentrate (corn grain, soybean meal, and sunflower meal) samples that were previously incubated in the rumen of additional fistulated steer for 12, 24, 36, or 48 h. The ADF concentration in residues recovered in the feces was strongly related to the ADF concentration in residues at the duodenum (R(2)=0.93, standard deviation=30.0, n=901). This relationship showed a lower precision for ADL fraction (R(2)=0.88, standard deviation=12.6, n=590). In a second assay, duodenal flow and ruminal DM digestibility were calculated from the duodenal and fecal concentration of either marker. We observed a significant effect of marker type on ruminal DM digestibility values, and the effect of tannin treatments was observed only when ADF or ADL was used as the marker. The lowest residual error was obtained for ADF. Ruminal DM digestibility was, on average, higher for C31 and C(33)n-alkanes, and the use of dosed C(32)n-alkane resulted in a negative value. In the third assay, a data set of 235 individual observations was compiled from digestibility trials to compare ADF and ADL as markers for estimating duodenal digesta flow in wethers (n=204) and cattle (n=31). We observed a strong relationship between markers (R(2)=0.84 in sheep and R(2)=0.88 in cattle), but variance analysis within trials indicated that ADF was more precise than ADL. In conclusion, in digestibility trials in which fecal output was measured and spot samples of the duodenal digesta were obtained, duodenal flow and ruminal digestibility of the DM may be estimated from the relationship between the ADF concentration in feces and that in the duodenal digesta of ruminants.

Faecal nitrogen excretion as an approach to estimate forage intake of wethers.

Data from twenty-two digestibility trials were compiled to examine the relationship between faecal N concentration and organic matter (OM) digestibility (OMD), and between faecal N excretion and OM intake (OMI) by wethers fed tropical or temperate forages alone or with supplements. Data set was grouped by diet type as follows: only tropical grass (n = 204), only temperate grass (n = 160), tropical grass plus supplement (n = 216), temperate grass plus supplement (n = 48), tropical grass plus tropical legume (n = 60) and temperate grass with ruminal infusion of tannins (n = 16). Positive correlation between OMD and either total faecal N concentration (Nfc, % of OM) or metabolic faecal N concentration (Nmetfc, % of OM) was significant for most diet types. Exceptions were the diet that included a tropical legume, where both relationships were negative, and the diet that included tannin extract, where the correlation between OMD and Nfc was not significant. Pearson correlation and linear regressions between OM intake (OMI, g/day) and faecal N excretion (Nf, g/day) were significant for all diet types. When OMI was estimated from the OM faecal excretion and Nfc-based OMD values, the linear comparison between observed and estimated OMI values showed intercept different from 0 and slope different from 1. When OMI was estimated using the Nf-based linear regressions, the linear comparison between observed and estimated OMI values showed neither intercept different from 0 nor slope different from 1. Both linear comparisons showed similar R(2) values (i.e. 0.78 vs. 0.79). In conclusion, linear equations are suitable for directly estimating OM intake by wethers, fed only forage or forage plus supplements, from the amount of N excreted in faeces. The use of this approach in experiments with grazing wethers has the advantage of accounting for individual variations in diet selection and digestion processes and precludes the use of techniques to estimate forage digestibility.

Desempenho animal e produtividade de pastagens tropicais no noroeste do Rio Grande do Sul / Animal performance and productivity of tropical pasture in Northwest of Rio Grande do Sul

Avaliou-se a produtividade do capim-elefante anão e do tifton 85 sob pastejo contínuo no noroeste do Rio Grande do Sul, utilizando-se 12 vacas da raça Holandesa, multíparas e com cerca de 100 dias de lactação. Foi aplicada a técnica dos animais reguladores para ajustes da carga animal de forma a manter a oferta de lâminas foliares de 4 por cento. No primeiro ano experimental, o capim-elefante anão e o tifton 85 apresentaram diferenças significativas quanto às taxas médias de acúmulo de lâminas foliares (31,2 vs 22,6kg/ha/dia) e produção animal (17,4 vs 20kg de leite/vaca/dia). No segundo, o tifton 85 foi superior ao capim-elefante anão quanto à taxa de acúmulo de matéria seca de lâminas foliares (38,8 vs 21,9kg/ha/dia), capacidade de suporte (2157 vs 1084kg de peso vivo/ha) e produções por área (70 vs 41,3kg de leite/ha/dia). No segundo ano, em relação ao primeiro, o tifton 85 manteve 88 por cento da capacidade de suporte e 80 por cento da produção por área, enquanto o capim-elefante anão apenas 46 por cento e 56 por cento. A produção média de 17kg de leite/vaca/dia indica um potencial pouco explorado das gramíneas tropicais em sistemas de produção de leite, especialmente na região Sul do Brasil.

Productivity of dwarf elephantgrass (Pennisetum purpureum Schum. cv. Mott) and tifton 85 (Cynodon dactylon x Cynodon nlemfuensis) pastures was evaluated under continuous grazing, in the Northwest area of Rio Grande do Sul. Twelve multiparous Holstein cows, at 100 days of lactation were evaluated and the put-and-take technique was used to regulate the stocking rate to maintain 4 percent of leaf lamina on offer. In the first year, dwarf elephantgrass and tifton 85 were different in leaf accumulation rates (31.2 vs 22.6kg/ha/day) and animal production (17.4 vs 20kg of milk/cow/day). In the second year, tifton 85 had higher leaf accumulation rates (38.8 vs 21.9kg/ha/day), stocking rate (2,157 vs 1,084kg of live weight/ha), and production per area (70 vs 41.3kg of milk/ha/day) than dwarf elephantgrass. Comparing the second to the first years, tifton 85 maintained 88 percent of stocking rate and 80 percent of production per area, while dwarf elephantgrass only 46 percent and 56 percent, respectively. Average individual production of 17kg of milk/cow/day indicates an unexplored potential of tropical grasses in dairy production systems, especially in the South of Brazil.

Avaliação de métodos laboratoriais para estimar a digestibilidade e o valor energético de dietas para ruminantes / Evaluation of laboratorial methods to estimate the digestibility and energetic value of ruminant diets

Foi avaliada a acurácia dos métodos laboratoriais para estimar a digestibilidade e o valor energético de dietas para bovinos de corte. As dietas experimentais foram isonitrogenadas e compostas por silagem de milho e 25, 40, 55 ou 70 por cento de concentrado. Os valores de digestibilidade medidos in vivo foram comparados com os obtidos nos ensaios in situ, in vitro e in vitro/gases, e com valores estimados a partir de equações matemáticas baseadas na composição química das dietas. O ensaio in vivo foi realizado com quatro bovinos em delineamento em quadrado latino 4×4. Quatro animais foram usados para o ensaio in situ e quatro corridas foram realizadas para os ensaios in vitro. Não houve interação significativa de dietas versus métodos. As taxas de degradação calculadas a partir dos ensaios in situ e in vitro/gases não foram acuradas para estimar o valor nutritivo dos alimentos, e o método in vitro foi o que melhor estimou a digestibilidade das dietas. A equação de Weiss superestimou o valor nutricional das dietas por superestimar a digestibilidade da fibra e por subestimar a excreção endógena fecal, mas essa equação foi mais acurada que as equações de McDowell.

The accuracy of laboratorial methods to estimate the digestibility and energetic value of beef cattle diets was evaluated. Experimental diets were isonitrogenous and composed by corn silage, and 25, 40, 55, or 70 percent of concentrate. Digestibility values measured in vivo were compared to those obtained in situ, in vitro, and in vitro/gases assays, as well to values estimated from mathematical equations based on the chemical composition of diets. The in vivo assay was carried out using four cattle in a Latin Square experimental design. Four animals were used for in situ assay and four runs were carried out for in vitro assays. Significant interaction of method vs. diet was not observed. As single indicators, degradation rates calculated from in situ and in vitro/gas assays were not accurate to estimate the nutritive value of feeds. Among all tested methods, the in vitro assay was the most accurate to estimate the digestibility of diets. Weiss equation overestimated the nutritional value of diets by overestimated fiber digestibility and by underestimated fecal endogenous excretion. However, it was more accurate than McDowell equations.

Energy requirements of Texel crossbred lambs.

Two trials were conducted to determine the energy requirements of feedlot Texel crossbred lambs. In a comparative slaughter trial, thirty 11/16 Texel x 5/16 Ile de France crossbred noncastrated male lambs, weaned at 42 d of age (16.2 +/- 2.1 kg of shrunk BW; SBW), were used. Five lambs were randomly chosen and slaughtered after 10 d of experimental management and diet adaptation (baseline group). Fifteen lambs then were fed for ad libitum intake and slaughtered at 25, 30, or 35 kg of SBW. The remaining 10 lambs were randomly assigned to 2 levels of DMI, either 70 or 55% of the ad libitum intake, and were slaughtered concomitantly with lambs of the 35 kg of SBW group. Total body N, fat, and energy contents were determined. In a digestibility trial, 6 Texel x Ile de France crossbred lambs (30.4 +/- 2.6 kg of SBW) were housed in metabolic cages and used in a replicated 3 x 3 Latin square experiment to evaluate the energetic value of the diet at different feed intake levels. Net and ME requirements for maintenance were 58.6 and 91 kcal/kg(0.75) of SBW, respectively. Consequently, partial efficiency of energy use for maintenance was 0.64. Body fat content varied from 72.7 to 125.9 g/kg of empty BW, respectively, for 13.1 and 28.2 kg of empty BW. Net energy requirements for growth of lambs at 15 and 35 kg of SBW at an ADG of 250 g were 424 and 553 kcal/d, respectively. Partial efficiency of energy use for growth was 0.47. Texel x Ile de France crossbred growing lambs used in this study showed decreased nutritional requirements than those reported by most nutritional systems.

Níveis de fibra em detergente neutro na dieta de cordeiros: consumo, digestibilidade e fermentação ruminal / Levels of neutral detergent fiber in lambs diets: intake, digestibility and ruminal fermentation

Foram utilizados oito cordeiros castrados (35,0±6,0kg peso vivo) em um delineamento duplo quadrado latino 4 ´ 4 para avaliar o efeito de quatro níveis de fibra em detergente neutro (FDN) na dieta (25, 31, 37 e 43 por cento da matéria seca (MS)) sobre o consumo e parâmetros digestivos. O consumo de nitrogênio (N) variou de forma quadrática; o de MS, matéria orgânica (MO) e energia diminuíram (P<0,05) e de FDN aumentou (P<0,01) linearmente com o aumento de fibra na dieta. A digestibilidade da FDN e do N, assim como o pH e as concentrações de peptídeos no fluído ruminal foram similares em todos os tratamentos. A digestibilidade aparente da MS, da MO e da energia, assim como as concentrações ruminais de açúcares diminuíram linearmente (P<0,01) e a síntese de proteína microbiana ruminal, as concentrações ruminais de amônia e de aminoácidos variaram quadraticamente (P<0,05) com o aumento do teor de FDN das dietas. A redução do consumo e da digestibilidade foram mais evidentes somente pela inclusão do nível mais alto de FDN (43 por cento) e, sob o aspecto nutricional, a inclusão em torno de 30 por cento de FDN representa o nível mais adequado para formulação de dietas a base de silagem de sorgo e concentrado oferecido a cordeiros confinados.

Eight castrated raw lambs (35.0± 6.0kg live weight) were used in a replicated 4 ´ 4 latin square design to evaluate the effect of four neutral detergent fiber (NDF) levels (25, 31, 37 and 43 percent of dry matter (DM)) on intake and digestion traits. Nitrogen (N) intake varied quadratically; intake of DM, organic matter (OM) and energy decreased (P<0.05) and that of NDF increased (P<0.01) as fibre level increased. NDF and N digestibility, as well as pH and ruminal concentrations of peptides were similar for all treatments. Apparent digestibility of DM, OM and energy, as well as ruminal concentrations of sugars decreased (P<0.01) and, ruminal microbial protein synthesis and ruminal concentrations of ammonia and amino acids varied in a quadratic way (P<0.05) with increased levels of NDF. The effect of NDF in decreasing intake and digestibillity was more evident only at the highest level (43 percent). The inclusion of about 30 percent NDF represents the most adequate level for sorghum silage and concentrate based diets fed to feedlot lambs.

Cateterizaçäo das veias porta e ramo mesentérico para avaliar a absorçäo do trato gastrintestinal em bovinos jovens / Catheterization of portal and mesenteric veins for evaluation of gastrintestinal absorption in heifers

Em 10 bezerros machos, com idade média de seis meses, foi avaliada a cateterizaçäo das veias porta e ramo mesentérico, como modelo experimental, para estudos da absorçäo gastrintestinal. A técnica utilizada demonstrou ser simples e econômica com a adaptaçäo de sonda intestinal siliconizada como cateter venoso