Twenty-four multiparous dairy cows (eight with ruminal cannulae) were blocked by days in milk and assigned to six balanced 4 x 4 Latin squares with 21-d periods. The four diets, formulated from alfalfa silage plus a concentrate mix based on ground high moisture ear corn, contained (dry matter basis): 1) 20% concentrate, 80% alfalfa silage (24% nonfiber carbohydrate; NFC), 2) 35% concentrate, 65% alfalfa silage (30% NFC), 3) 50% concentrate, 50% alfalfa silage (37% NFC), or 4) 65% concentrate, 35% alfalfa silage (43% NFC). Soybean meal and urea were added to make diets isonitrogenous with equal nonprotein nitrogen (NPN) (43% of total N). Total urine was collected with indwelling Folley catheters for 24 h during each period. There was no effect of diet on urinary creatinine excretion (average 29 mg/kg of BW/d). There were quadratic effects of diet on total urinary ecretion of allantoin, uric acid, and purine derivatives (allantoin plus uric acid), and on ruminal synthesis of microbial N estimated from purine derivatives; maxima occurred at about 35% dietary NFC. Urinary excretion also was estimated with spot urine samples from creatinine concentration and the mean daily creatinine excretion. Daily excretion of allantoin, uric acid, and purine derivatives estimated from spot urine sampling followed the same pattern as that observed with total collection; differences between measured and estimated urine volume were significant only for 35% dietary concentrate. Spot urine sampling appeared to yield satisfactory estimates of purine derivative excretion. Maximal urea N excretion was estimated to occur at about 31% dietary NFC. Milk allantoin secretion increased linearly with concentrate and accounted for 4 to 6% of the total purine derivative excretion. Microbial yield was maximal at 35% dietary NFC, suggesting that this was the optimal level for utilization of dietary NPN from alfalfa silage and other sources.

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RESUMO -Foram objetivos do presente trabalho estimar a produção de proteína microbiana, utilizando-se a excreção total de derivados de purina (DP); comparar as excreções de DP e uréia obtidas a partir de coletas spot de urina com aquelas observadas em coletas de 24 horas; e avaliar as concentrações de N-uréia no plasma e no leite e as excreções de uréia. Utilizaram-se 16 vacas holandesas em quatro quadrados latinos balanceados 4 x 4, distribuídos de acordo com o período de lactação. Cada período experimental teve duração de 21 dias, sendo sete dias de adaptação e 14 dias para as coletas de amostras. As quatro rações experimentais, isoprotéicas, foram formuladas para conter na base da MS 60% de silagem de milho e 40% de concentrado. Foram utilizados níveis crescentes de uréia no concentrado: 0; 0,7; 1,4; e 2,1%, correspondentes aos níveis de proteína bruta na forma de compostos nitrogenados não-protéicos (NNP) das rações de 2,22; 4,18; 5,96; e 8,09%, respectivamente. O volume urinário foi estimado utilizando amostras de urina obtidas quatro horas após a alimentação (spot), dividindo-se a excreção diária média de creatinina pela concentração de creatinina na urina spot. O volume urinário e as excreções de DP e de uréia, estimados por meio da urina spot, não diferiram daqueles obtidos pela coleta de urina por 24 horas. As produções de N-microbiano estimadas e obtidas apresentaram valores máximos de 198,05 e 196,96 g/dia, nos níveis de compostos nitrogenados não-protéicos de 5,33 e 4,44%, respectivamente. A concentração de alantoína no leite decresceu linearmente com o aumento dos níveis de NNP na dieta e representou 4,5% da excreção total de DP. A excreção de creatinina não foi afetada pelos níveis de NNP na dieta (23,41 mg/kg PV), enquanto as excreções estimada e obtida de uréia, as concentrações de uréia e N-uréia no plasma e no leite aumentaram linearmente com os níveis de NNP na ração. Concentrações plasmáticas e no leite de N-uréia de 19 a 20 mg% e 24 a 25 mg%, respectivamente, representariam valores limites a partir dos quais ocorreriam perdas de compostos nitrogenados.Palavras-chave: creatinina, derivados de purina, compostos nitrogenados não-protéicos, uréia, vacas de leite Microbial Protein Production, Purine Derivatives and Urea Excretion Estimate in Lactating Dairy Cows Fed Isoprotein Diets with Different Non Protein Nitrogen Compounds LevelsABSTRACT -The objectives of the present work were to estimate the microbial protein production using the total purine derivatives (PD) excretion, to compare the PD and the urea excretions, obtained from spot urine collection with that observed in the 24 hours collection and to evaluate the plasma and milk N-urea and urea urinary excretion. Sixteen Holstein lactating cows were assigned to four 4X4 Latin Square with 3-wk periods in accordance with the lactation period. The four experimental isoproteic diets were formulated to contain 60% of corn silage and 40% of corn meal, soybean meal, urea and mineral salt mixture as dry matter basis. Crescent levels of urea in the ...

Two experiments were conducted to assess the endogenous fraction of purine derivative (PD) excretion, urinary recovery, and intestinal digestibility of purines in Nellore heifers. For both experiments, 8 Nellore heifers fitted with ruminal and abomasal cannulas were allocated to two 4 × 4 Latin squares. The diets were based on corn silage and concentrate (60 and 40% DM basis, respectively); feces and urine samples were obtained by total collection, and abomasal DM flow was estimated using indigestible NDF as an internal marker. In Exp. I, 4 of the 8 heifers (BW 258 ± 20 kg) were also fitted with ileal cannula. The planned treatments were 4 different DMI: 1.2, 1.6, 2.0, and 2.4% of BW (DM basis). The endogenous losses and purine recovery as urinary PD were estimated using linear regression between daily urinary PD excretion (Y) and daily abomasal flow of purine bases (X), expressed in millimoles per kilogram of BW(0.75). In Exp. II, the same 8 Nellore heifers (BW of 296 ± 15 kg) were fed at 1.37% BW (DM basis). The treatments were the infusion of purines (RNA from torula yeast, type VI, Sigma) into the abomasum in increasing amounts (0, 33, 66, and 100 mmol/d). All statistical analyses were performed using the PROC MIXED procedure in SAS. In Exp. I, the DMI range was 1.16 to 1.84% of BW and did not affect (P > 0.05) the apparent RNA digestibility in the small intestine, which had a mean of 75.6%, and a true digestibility of 93.0%. The mean ratio of the N-RNA to the total-N in the ruminal bacteria was 0.137. The daily urinary PD excretion (Y, mmol/kg of BW(0.75)) was a function of RNA flow in the abomasum (X, mmol/kg of BW(0.75)): Y = 0.860X + 0.460, where 0.860 and 0.460 were the PD recovery of purines and the endogenous fraction (in mmol/kg of BW(0.75)), respectively. In Exp. II, the daily urinary PD excretion was a function of RNA flow in the abomasum: Y = 0.741X + 0.301, where 0.741 and 0.301 were the recovery of PD in urine of infused purines and the endogenous losses (in mmol/kg of BW(0.75)), respectively. In conclusion, our data suggest that in Nellore heifers the respective values of endogenous PD excretion (mmol/kg of BW(0.75)), urinary recovery of the purines absorbed in the abomasum, and true digestibility of RNA in the small intestine were 0.30, 0.80, and 0.93.

Doze vacas da raça Holandesa, puras e mestiças, foram distribuídas em três quadrados latinos 4 X 4, balanceados de acordo com o período de lactação, com o objetivo de avaliar parâmetros do comportamento ingestivo. As dietas experimentais foram à base de silagem de milho com relação volumoso:concentrado de 60:40, com base na matéria seca, ou à base de cana-de-açúcar, com relação volumoso:concentrado de 60:40 ou 50:50. As vacas foram submetidas à observação visual para avaliação do comportamento ingestivo. Os animais foram observados a cada dez minutos, durante 24 horas, para determinação do tempo despendido em alimentação, ruminação e ócio. Não houve diferença para os tempos médios despendidos com alimentação e ruminação entre as dietas experimentais. Entretanto, na dieta à base de silagem de milho, os animais ficaram menos tempo no ócio, quando comparados àqueles alimentados com cana-de-açúcar. Com relação à eficiência de alimentação, expressa em gFDN/h, não houve diferença entre as dietas experimentais. A eficiência de ruminação, expressa em gMS/h, foi semelhante para as diferentes dietas. A eficiência de ruminação, expressa em gFDN/h (ERU FDN) foi maior para a dieta à base de silagem de milho. Não houve diferença na ERU FDN entre dietas à base de cana-de-açúcar. Vacas alimentadas com dietas à base de cana-de-açúcar apresentaram maior tempo despendido em ócio e menor consumo de MS, quando comparadas àquelas alimentadas com dietas à base de silagem de milho

RESUMO -Doze vacas da raça Holandesa, puras e mestiças, foram distribuídas em três quadrados latinos 4 x 4, com o objetivo de avaliar o consumo e a digestibilidade aparente dos nutrientes, a produção e composição do leite, o pH e a amônia ruminais. As dietas foram constituídas à base de silagem de milho (SM) (AG 1051) com relação volumoso:concentrado (V:C) de 60:40, com base na matéria seca (MS), ou à base de cana-de-açúcar (CA) (RB 855536) com relação V:C de 60:40, com 0,35 ou 1% da mistura uréia+sulfato de amônio (SA) ou V:C de 50:50 com 1% de uréia+SA. O consumo de MS foi de 17,8; 14,9; 14,4 e 15,8 kg/dia, para as dietas, respectivamente. O maior consumo de MS resultou, também, em maior consumo de nutrientes para a dieta à base de SM, com exceção dos carboidratos não-fibrosos, em que se verificou maior consumo para a dieta com CA com 50% de concentrado. A produção de leite (PL) foi maior para a dieta à base de SM, não havendo diferença na PL entre as dietas contendo CA, sendo de 22,0; 19,0; 18,6 e 20,1 kg/dia e a produção de leite corrigida para 3,5% de gordura foi de 23,0; 19,7; 19,4 e 21,3 kg/dia para as dietas SM, CA 0,35%, CA 1%, CA 1% 50:50, respectivamente. Em relação à composição do leite, não foram encontradas diferenças entre as dietas. Os teores de gordura foram de 3,8, 3,8, 3,8 e 3,9% para as dietas, respectivamente. Não foram verificadas diferenças quanto à digestibilidade aparente da MS, matéria orgânica, proteína bruta e carboidratos totais entre as dietas. A digestibilidade aparente da fibra em detergente neutro (FDN) foi maior para a dieta contendo SM (47%). Não houve diferença na digestibilidade da FDN, entre as diferentes dietas com CA, 32, 31 e 31%, respectivamente. Dentro de cada tempo (antes e três horas após a alimentação matinal), não houve diferença nos valores de pH e compostos nitrogenados amoniacais (N-NH 3 ) entre as dietas.Palavras-chave: consumo de FDN, nitrogênio amoniacal, produção de leite, silagem de milho Intake, Apparent Digestibility, Milk Production and Composition and Ruminal Variables of Dairy Cows Fed Sugar Cane Based DietsABSTRACT -Twelve purebred and crossbred Holstein cows were allotted to three 4 x 4 Latin Squares to evaluate the intake, apparent digestibility of nutrients, milk production and composition, ruminal pH and ammonia. The experimental diets were based on corn silage (CS) (AG 1051) with forage:concentrate ratio (F:C) of 60:40, in dry matter (DM) basis, or based on sugar cane (SC) (RB 855536) with F:C of 60:40 with .35 or 1% of urea+ammonium sulfate (AS) mixture or F:C of 50:50 with 1% of urea+AS. DM intake was 17.8, 14.9, 14.4, and 15.8 kg/day, for the diets, respectively. DM intake was higher, resulting in greater nutrient intake for CS based diet, except for the non fiber carbohydrates intake, which showed higher intake for SC based diet with 50% concentrate. Milk production (MP) was higher for the CS based diet, with no difference in MP among the SC based diets, with mean values of 22.0, 19.0, 18.6, and 20.1 kg/day and the 3.5% fat corrected milk prod...

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Twenty-four multiparous lactating Holstein cows were blocked by days in milk and assigned to treatment sequences in a replicated 4x4 Latin square with 21-d periods. The four diets, formulated from alfalfa silage plus a concentrate mix based on ground high moisture ear corn, contained [dry matter (DM) basis]: 1) 20% concentrate, 80% alfalfa silage (24% nonfiber carbohydrates; NFC), 2) 35% concentrate, 65% alfalfa silage (30% NFC), 3) 50% concentrate, 50% alfalfa silage (37% NFC), or 4) 65% concentrate, 35% alfalfa silage (43% NFC). Soybean meal and urea were added to make diets isonitrogenous with equal nonprotein N (43% of total N). Intake of DM and milk yield indicated that adaptation was complete within 7 d of changing the diets within the Latin square. There were linear increases in apparent digestibility of DM and organic matter, and a linear decrease in neutral detergent fiber (NDF) digestibility with increasing dietary NFC. Solutions of significant quadratic equations yielded estimated maxima for intake of DM, organic matter, digestible organic matter, and NDF at, respectively, 37, 38, 43, and 27% dietary NFC. There were linear increases in yields of milk, protein, lactose, and solids not fat with increasing dietary NFC. Feed efficiency (milk/DM intake) yielded a quadratic response with a minimum at 27% dietary NFC. Maxima for milk fat content, fat yield, and fat-corrected milk yield were estimated to occur at, respectively, 30, 34 and 38% dietary NFC. In this short-term trial, maximal DM intake and fat-corrected milk yield indicated that the optimum concentrate for cows fed high moisture ear corn plus alfalfa silage as the only forage was equivalent to 37 to 38% dietary NFC; however, yields of milk, protein and solids not fat were still increasing at 65% dietary concentrate (43% NFC).