RESUMO. Este estudo foi realizado para avaliar modelos de predição de peso corporal (PC), utilizando-se medidas corporais como perímetro torácico (PT), altura de cernelha (AC), largura de garupa (LG), comprimento corporal (CC) e altura de garupa (AG), e desenvolver novas Equações de estimação de PC para novilhas Holandesas e mestiças. Foram testadas Equações de predição (1, 2, 3, 4, 5 e 6) propostas em estudos anteriores e as medidas corporais mais relacionadas com PC foram utilizadas para gerar novas Equações. O perímetro torácico é a medida corporal mais correlacionada com PC. A Equação 4 apresentou os melhores resultados de predição com baixo desvio médio e alta precisão e exatidão. As Equações 1 e 2 apresentaram alto viés de estimação, enquanto 2 teve o menor valor de coeficiente de correlação e concordância, e grande contribuição de erro sistemático. O modelo 3 apresentou alta variabilidade na predição de PC. Tanto para novilhas Holandesas quanto mestiças, as Equações avaliadas não são eficientes em predizer PC. Entre as Equações avaliadas, o modelo usando PT apresentou o melhor ajuste e maior coeficiente de determinação ajustado. As medidas corporais de PT e CC foram as variáveis mais significativas na predição do PC, sendo utilizadas na obtenção da Equação: PC = - 372.89 + 2.8072 × PT + 1.6087 × CC.

ABSTRACT. This study was realized to evaluate prediction models for body weight (BW) using body measurements as heart girth (HG), wither height (WH), hip width (HW), body length (BL) and hip height (HH), and develop new Equations to predict the BW of Holstein and crossbred heifers. Prediction Equations (1, 2, 3, 4, 5 and 6) proposed in previous studies were tested, while body measurements, which were more significant in terms of predicting BW, were used to obtain new Equations. Heart girth was the body measurement with the greater correlation with BW. Equation 4 presented the best prediction results, showing a low average deviation, high accuracy and precision. Equations 1 and 2 predicted with a high presence of bias, while 2 had the lowest value of the concordance correlation coefficient and a great contribution made by systematic error. The 3 model presented a high variability in predicting BW. For both Holstein and crossbred heifers, the Equations evaluated are inadequate for predicting BW. Among the Equations evaluated, the model using HG presented the best adjustment and the greater adjusted coefficient of determination. Body measurements relating to HG and BL were the most significant variables in predicting the BW, resulting in the following Equation: BW = - 372.89 + 2.8072 × HG + 1.6087 × BL.

ABSTRACT This study aimed to evaluate the biometric and chemical characteristics of five sugarcane varieties (RB 863129, RB 867515, RB 92579, RB 943365, and RB 98710) grown in a semi-arid climate for use as forage. The experiment was designed as randomized blocks, in a 5 × 2 factorial arrangement (five sugarcane varieties and two evaluation times, 407 and 483 days). Response variables included dry matter productivity, morphological characteristics, chemical composition, digestibility, and ratios among neutral detergent fiber (NDF), Brix, and Pol. For the biometric analyses, there was an interaction effect between the evaluated varieties and harvest times on the variables fresh matter yield, uncovered internodes, and stalk density (MID -middle internode density). Regarding stalk density (MID), at 407 days, there was no significant difference among the varieties (1.19 g cm−3). For the fractionated parts, there was an effect of harvest time on the amount of fresh matter and dry matter of tops produced, which was highest at 407 days of age. A significant difference was detected among the varieties for contents of dry matter and total digestible nutrients. The variable in vitro neutral detergent fiber digestibility was influenced by the time, decreasing by 53.62 g kg−1 at 483 days. In the analysis of Brix and Pol yields per hectare, it was observed that variables ton of Brix per hectare and ton of sucrose per hectare averaged 15.12 and 10.14 t ha−1, respectively, and the NDF:Brix and NDF:Pol ratios were higher for variety RB 863129, with 2.93 and 3.68, respectively. Variety RB 867515 is suggested for forage production in semi-arid conditions, as it is best adapted to the local soil-climatic conditions and to the water deficit, especially at 407 days.

ABSTRACT The objective of this study was to evaluate the effect of different concentrate levels (40, 50, 60, and 70% on dry matter basis) on intake, digestibility of nutrients, and performance of heifers fed sugarcane bagasse as exclusive roughage. Twenty Girolando heifers, with an average body weight of 198±25.6 kg were assigned to a completely randomized design, established according to body weight. The intake of dry matter (5.12 to 7.73 kg d-1), organic matter (4.72 to 7.32 kg d-1), crude protein (0.71 to 1.05 kg d-1), and digestible organic matter (3.09 to 4.77 kg d-1) linearly increased with the inclusion of concentrate in the diets. The final weight (238 to 299 kg d-1), body weight gain (0.50 to 1.20 kg d-1), and total weight gain (35.2 to 83.6 kg d-1) linearly increased with the concentrate levels. Considering the occurrence of the first calving at 24 months, a 50:50 ratio of sugarcane bagasse to concentrate seems to be the most appropriate for crossbred heifers.

RESUMO Objetivou-se levantar e avaliar os perfis tecnológicos, zootécnicos e socioeconômicos, identificar e quantificar indicadores referência, para sistemas de produção de bovinos de leite, de caráter não experimental, de forma a contribuir para a sustentabilidade e competitividade da pecuária de leite na mesorregião do Agreste pernambucano. Para identificar e quantificar os indicadores referência foram avaliados durante doze meses, trinta e seis sistemas de produção de leite da agricultura familiar e empresarial. Os sistemas foram caracterizados em relação ao perfil tecnológico e aos indicadores de tamanho, zootécnicos e econômicos. Foram determinados os coeficientes de correlação com a taxa de remuneração do capital investido e geradas equações de regressão, para cada indicador, em função de quatro cenários da taxa de remuneração do capital (4, 6, 8 e 10% ao ano). Os indicadores correlacionados foram: produção de leite/vacas em lactação; produção de leite/área; preço médio do leite; custo operacional efetivo, custo operacional total e custo total / preço do leite e lucratividade. A pecuária leiteira no Agreste pernambucano, paga os custos mensais, mas a tendência é a não remuneração adequada da mão-de-obra familiar e a injeção de capital externo para a reposição dos bens. A produtividade dos fatores de produção terra e animal apresentaram maior correlação com rentabilidade, indicando a necessidade do aumento da produção, por meio do aumento da produtividade da terra e da produção de leite/vacas em lactação. A identificação e quantificação de indicadores referência podem contribuir para a identificação dos pontos frágeis da pecuária leiteira no Agreste tornando-a sustentável e competitiva.

ABSTRACT The objective of this work was to identify and assess the technological, zootechnical and socioeconomic profiles and identify and quantify benchmarks for dairy cattle production systems, in a non - experimental approach, aiming to contribute to the sustainability and competitiveness of dairy farming in the Pernambuco Agreste region, northeastern Brazil. Thirty-six milk production systems of family and corporate farming were evaluated during twelve months, in order to identify and quantify the benchmarks. The systems were characterized regarding their size and technological, zootechnical and economic profiles. The correlation coefficients of the return rate on invested capital were assessed and regression equations were developed for each indicator, according to four scenarios of annual return rates (4, 6, 8 and 10%). The indicators evaluated were milk production per dairy cows, milk production per area, average price of milk, effective operational cost, total operating cost, total cost per price of milk and profitability. The dairy farming in the Pernambuco Agreste region pays the production costs, but tends to a not adequate remuneration of family labor and a need of external capital input for replacement of the assets. The productivity of production factors area and animals showed higher correlation with cost-effectiveness, denoting the need for increase the production through increases in land area and milk productivity per dairy cow. The identification and quantification of benchmarks may help to identify the weak points of dairy farming in the Agreste region, making it sustainable and competitive.

RESUMO Objetivou-se avaliar o efeito da levedura seca de cana-de-açúcar em substituição ao farelo de soja em dietas de novilhas leiteiras. Vinte e quatro novilhas leiteiras com peso médio inicial (BW) de 178 kg foram distribuídas em delineamento inteiramente casualizado. Os tratamentos foram níveis de inclusão de levedura seca de cana-de-açúcar em substituição ao farelo de soja (0, 33, 67 e 100% com base na matéria seca (MS)). Não houve diferença para a ingestão de MS, fibra em detergente neutro (FDN), energia metabolizável e volumoso; entretanto, houve aumento na ingestão de carboidratos não fibrosos e concentrados. A ingestão de proteína bruta diminuiu de acordo com o aumento do nível de levedura em substituição ao farelo de soja. Os coeficientes de digestibilidade da MS e FDN não foram alterados. A substituição do farelo de soja pela levedura não promoveu efeito sobre o desempenho, pois o ganho médio diário e as medidas corporais estudados foram os mesmos para todos os animais, em todos os níveis de inclusão. O farelo de soja pode ser completamente substituído por levedura seca de cana-de-açúcar em dietas para novilhas leiteiras em crescimento, pois não afeta consumo, digestibilidade, desenvolvimento físico dos animais e metabolismo de compostos proteicos.

ABSTRACT This study was performed in order to evaluate the effect of dried yeast from sugar cane when replacing soybean meal in dairy heifers' diets. Twenty-four heifers, with an initial body weight (BW) of 178 kg, were distributed in a completely randomized design. The treatments were four levels of inclusion of dried yeast from sugar cane replacing to soybean meal (0, 33, 67 and 100% on a dry matter (DM) basis). While there was no difference in DM, neutral detergent fiber (NDF), metabolizable energy or roughage intakes, the intakes of non-fiber carbohydrates and concentrate were increased. The crude protein intake decreased according to the dried yeast from sugar cane when replacing soybean meal. The digestibility coefficients of DM and NDF showed no difference. Replacement of soybean meal with dried yeast from sugar cane had no effect on performance, because average daily gain and body measurements studied were similar for all animals and inclusion levels. Soybean meal can be completely replaced with dried yeast from sugar cane in diets for growing dairy heifers without restrictions; this will not affect the intake, digestibility, physical development of animals or metabolization of protein compounds.

ABSTRACT The effect of replacing wheat bran with spineless cactus (0, 25, 50, 75, and 100%) in sugar cane-based diets on the intake of nutrients, feeding behavior, and rumen digestibility of steers was assessed using digested samples collected from the omasum. Five crossbred steers (1/2 Holstein-Zebu) were fitted with cannulas in the rumen and then assigned to a 5 × 5 Latin square design. Samples of omasal digesta were collected for three days. Rumen was evacuated via the rumen cannula to determine the rumen pool of dry matter (DM), neutral detergent fiber (NDF), indigestible NDF (iNDF), intake (ki), passage (kp) and degradation (NDF) rates, and the passage of iNDF (kpi). Nutrient intake displayed a quadratic effect, with maximum intakes of DM (5.73 kg d−1), non-fiber carbohydrates (NFC, 4.63 kg d−1), and digestible organic matter (DOM, 3.45 kg d−1) estimated at the replacement levels of 54.63, 60.00, and 43.17%, respectively. The replacement levels showed no effect on feeding, rumination, or idle times. There was a linear increase in the total apparent and ruminal digestibility of CP as the spineless cactus content in the diet was increased. There was no effect on total and partial digestibilities of OM and NDF or on intestinal digestibility of CP. No effect was observed on the rumen pool of DM, NDF, or iNDF. Furthermore, ki, kp, NDF degradation, and iNDF passage rates displayed a quadratic effect, with higher concentrations estimated for replacement levels of 56.07, 56.12, 59.00, and 55.20%, respectively. Replacing 55% wheat bran with spineless cactus in sugar cane-based diets is recommended.

ABSTRACT - The objective of this study was to evaluate the effect of replacing wheat bran by spineless cactus (0, 25, 50, 75, and 100%) in sugar cane-based diets on intake and nutrient digestibility and ruminal parameters of sheep. Five sheep (Santa Inês; average initial weight of 34.0±3.6 kg) were fitted with cannulas in the rumen and then assigned to a 5 × 5 Latin square design. The maximum dry matter (DM; 1414 g d−1), digestible organic matter (658 g d−1), and neutral detergent fiber corrected for ash and protein (NDFap; 425 g d−1) intakes were estimated by replacing 80.2, 89.9, and 50.5% of wheat bran. Dry matter and crude protein digestibility increased by 0.60 and 0.85 g kg-1 of DM. With the replacement of 57.1 and 62.2% of wheat bran, a maximum rate of NDF ingestion (0.70 h−1) and NDF ruminal pool (7.31 g) was obtained. Rumen pH increased with the inclusion of spineless cactus, while the maximum concentration of ammonia N (33.3 mg dL−1) and total volatile fatty acids (57.7 μmol mL−1) were estimated at the levels of 72.3 and 63.7% of replacement of wheat bran. It is recommended to replace 63% of wheat bran by spineless cactus in sugar cane-based diets, to promote better animal performance.

We evaluated the effect of adding four levels (0, 4, 8 and 12 g/kg, as fed) of a mixture (9:1) of urea and ammonium sulfate (UAs) to sugarcane on feed intake and digestibility, productive performance and metabolism of nitrogen compounds of dairy cows. Twelve multiparous Holstein cows (12.6±0.5 kg/d of milk, 225±90 days in milk) were distributed in three 4 × 4 Latin squares, receiving diets with the same amount of nitrogen (125 g crude protein/kg of dry matter). Concentrate feed was supplied at a ratio of 1 kg for each 3 kg of milk produced. The sugarcane presented 21.9 ºBrix. The level of UAs did not affect intake, total digestibility of diet components, milk production or milk components. Increasing UAs level linearly increased concentration of plasma urea nitrogen (PUN), urinary excretion of nitrogen and contribution of non-urea nitrogen in the urinary excretion and linearly reduced milk production/urinary excretion of nitrogen ratio. In spite of the linear increase of PUN with increased urea, the maximum value observed (14.31 mg/dL) was below the threshold value of 20 mg/dL, above which reproductive function may be compromised. In diets with sugarcane for dairy cows with production below 15 kg/day, the UAs level may be raised from 0 to 12 g/kg natural matter without impairing performance.

The objective of this study was to identify and quantify benchmarks of milk production systems. The technological profile and size, livestock and economic indicators of sixteen farms in the region of Triângulo Mineiro were analyzed. Indicators correlated with rate of return on capital (RRC) were identified and quantified in four scenarios of RRC (6, 8, 10 and 12% per year). The correlated indicators and their respective values in the four scenarios were: land (99, 90, 81 and 73 ha); relation of total cows in lactation (74, 77, 79 and 82%); lactating cows per area (0.89; 0.99; 1.11 and 1.22 cows/ha); milk production per lactating cow (12.04; 13.00; 13.96 and 14.92 liters/cow/day); milk production per total cows (9.19; 10.23; 11.27 and 12.31 liters/cow/day); labor productivity (322, 349, 375 and 402 liters/day/man); land productivity (4351, 5236, 6120 and 7004 liters/ha/year); participation of total effective operational cost of activity in the gross revenue of the activity (69, 66, 63 and 60%); participation of total operational cost of activity in the gross revenue of the activity (80, 76, 72 and 69%); participation of total cost of activity in the gross revenue of the activity (93, 88, 82 and 77%); labor cost in relation to milk gross revenue (15, 13, 11 and 9%); profitability (15, 19, 23 and 28%); and capital investment in the activity in relation to daily milk production (922, 829, 736 and 644 R$/liter-day). The productivity of the factors land and animals present more correlation with profitability than labor productivity, regardless of the production size.

The effect of replacing of 0; 0.33; 0.67 and 1.0 (kg/kg) of soybean meal (SBM) by undecorticated castor seed meal treated with calcium oxide (CMT - 60 g/kg) was evaluated on performance and efficiency of nutrient utilization in dairy cows. Sixteen Holstein and crossbred cows were distributed in four 4 × 4 latin squares. Animals received concentrated feed at a ratio of 1 kg for 3 kg of milk produced, in the natural matter. The diets had the same amount of nitrogen (150.4 g crude protein/kg DM), containing 325.6 g of concentrated feed/kg DM. There was no effect on the serum concentration of transaminase and the animals showed no clinical symptoms of intoxication by ricin. The intake of DM, crude protein (CP) and non-fibrous carbohydrates (NFC) reduced from 0.67 replacement of SBM by CMT. The intake of neutral detergent fibers corrected for ash and protein (NDFap) increased from 0.33 replacement of SBM with CMT. Although the digestibility of dietary components decreased from 0.33 replacement, the intake of digestible components only reduced from 0.67 replacement. Because of the reduction of digestible energy, the synthesis of microbial CP and the utilization efficiency of rumen-degradable protein for the synthesis of microbial CP reduced with full replacement of SBM by CMT. Milk yield, milk composition, daily variation of body weight and the efficiency of utilization of the nutrients for the synthesis of N in milk reduced from 0.67 replacement of SBM by CMT. Castor seed meal treated with calcium oxide can replace up to 0.33 of SBM (50 g/kg DM diet DM) in the diet of dairy cows with an average milk production of 20 kg/day.

Avaliaram-se os efeitos das características químicas e da digestibilidade in vivo da FDN (DFDN) sobre o consumo, a digestibilidade e o desempenho de vacas leiteiras em confinamento utilizando-se meta-análise a partir de 285 observações de seis experimentos. Utilizaram-se dados de animais alimentados com dietas à base de silagem de milho (n = 213) ou cana-de-açúcar (n = 72). Apesar do menor teor de FDN da cana-de-açúcar (45,27% da MS) em relação à silagem de milho (54,48%), observaram-se menores consumos de MS e FDN, que refletiram em menor produção de leite. Verificou-se maior redução no comsumo de matéria seca (kg/dia) com aumento do teor de FDNf (FDN de forragem, % da MS) em dietas com canade-açúcar (332,4 g de MS para cada 1% no teor de FDNf) em relação à silagem de milho (96 g de MS para cada 1% no teor de FDNf). O maior efeito de repleção ruminal da FDN da cana-de-açúcar deve-se à fração indigestível, majoritária, apesar da maior taxa de degradação da fração potencialmente degradável da FDN em relação à silagem de milho. A produção de leite não-corrigida (PL) e corrigida para 4% de gordura (PLC) e o teor de proteína do leite reduziram linearmente com o aumento no teor de FDNf, independentemente da fonte de forragem. Porém, a PL e PLC não foram afetadas pelo nível de FDNnf (FDN de não-forragem). Os consumos de MS, FDN e NDT e o teor de gordura no leite reduziram linearmente com aumento na relação lignina:FDN, com maior amplitude em dietas à base de cana-de-açúcar em relação à silagem de milho. O consumo de MS, a produção de leite e a produção de leite corrigida reduziram linearmente e na mesma magnitude entre as fontes de forragens, com o aumento na DFDN da dieta. O efeito do teor FDN e lignina sobre o consumo, a digestibilidade e o desempenho animal depende da fonte utilizada.

It was evaluated the effects of the chemical characteristics and in vivo NDF digestibility (IVNDFD) on intake, digestibility and performance of dairy cows in fedlot by using a meta-analysis procedure from 285 observations of six experiments. It was used data of animals fed diets based on corn silage (n = 213) or sugarcane (n = 72). Despite the lower NDF content of sugarcane (45.27% of DM) compared to corn silage (54.48%), it was noted lower intakes of dry matter (DMI) and NDF, which responded with a lower milk yield. It was observed a greater reduction in DMI (kg/day) with the increase of NDFf (NDF forage, % DM) in sugarcane diets (332.4 g of DM for each 1% of NDFf) in relation to corn silage (96 g of DM for each 1% of NDFf). The greatest effect of ruminal repletion of sugar cane NDF is caused by the indigestible fraction, majoritary, despite the highest degradation rate of NDF potentially degradable fraction in relation to corn silage. Milk production not corrected (MP) and MP corrected to 4% fat (MPC) and the content of milk protein decreased linearly with the increase of NDFf content, regardless of the forage source. However, MP and MPC were not affected by NDFnf (non-forage NDF) level. Intakes of DM, NDF, TDN and milk fat content decreased linearly with increase in the lignin:NDF ratio, with greater amplitude in sugarcane based diets in relation to silage corn. Dry matter intake, MP and MPC reduced linearly and at the same magnitude among forage sources, with the increase in NDFD of the diet. The effect of NDF and lignin on intake, digestibility and animal performance depend upon the source used.

Objetivou-se avaliar os efeitos de três níveis de concentrado (2,0; 4,0 e 6,0 kg/vaca/dia) e dois de proteína bruta (PB) (14 e 16% da matéria seca total da dieta) em comparação à mistura mineral (controle) no consumo, na digestibilidade aparente, na produção e composição do leite e na eficiência alimentar e de utilização de concentrados de vacas sob pastejo de capim-elefante (Pennisetum purpureum, Schum) na época das águas. Vinte e uma vacas Gir linhagem leiteira com média de 426 kg de peso vivo e produção de 13,0 kg de leite/vaca/dia, aos 55 dias de lactação, foram distribuídas em delineamento de blocos casualizados, com sete dietas (tratamentos), em arranjo fatorial 3 × 2 + 1 e três repetições, num período de 84 dias. O consumo de matéria seca de forragem não foi influenciado pelas dietas, mas o consumo de matéria seca total aumentou 45% com a inclusão de concentrado na dieta. Entretanto, a produção de leite aumentou apenas 17% (1,76 kg a mais de leite por dia) com o uso de concentrado. Para vacas Gir linhagem leiteira em pastagens de capim-elefante na época das águas, 2 kg de concentrado/vaca/dia e 14% de PB na dieta total proporcionam melhor resposta produtiva sem prejudicar o peso corporal.

The objective of this work was to evaluate the effects of three levels of concentrate (2.0, 4.0 and 6.0 kg/cow/day) and two levels of crude protein (CP) (14 and 16% total dietary dry matter), in comparison to mineral mixture (control) on the intake, apparent digestibility, milk composition and yield and on feed efficiency and use of concentrates of cows grazing elephant grass (Pennisetum purpureum, Schum) in the rainy season. Twenty-one milking Gyr cows with average body weight of 426 kg and yield of 13.0 kg of milk/cow/day at 55 days of lactation were distributed in randomized blocks design, with seven diets (treatments) in a 3 × 2 + 1 factorial arrangement and three replications, in a period of 84 days. Forage dry matter intake was not influenced by the diets, but total dietary dry matter intake increased by 45% with the inclusion of concentrate in the diet. However, milk yield increased by only 17% (1.76 kg more milk per day) with the use of concentrate. For dairy Gyr cows grazing elephant-grass during the rainy season, 2 kg of concentrate/cow/day and 14% of CP in the total diet provided the best productive response without harming body weight.

Avaliou-se a resposta de novilhas leiteiras alimentadas com dieta à base de silagem de milho e com 1,3 kg/dia de concentrado em comparação a três dietas à base de cana-de-açúcar corrigida com 1% de ureia + sulfato de amônio (9:1) (ureia), com 1,3; 2,0 e 2,7 kg/dia de concentrado. Foram utilizadas 20 novilhas (12 da raça Holandesa e oito da raça Pardo-Suíça) em delineamento de blocos casualizados, com cinco blocos formados de acordo com o peso inicial e a raça dos animais. Os consumos de matéria seca, matéria orgânica e fibra detergente neutro não diferiram entre a dieta à base de silagem de milho e aquelas à base de cana-de-açúcar. Maior consumo de extrato etéreo foi observado quando fornecida a dieta à base de silagem de milho em comparação àquelas à base de cana-de-açúcar. Os consumos de carboidratos totais e carboidratos não-fibrosos diferiram entre a dieta com silagem de milho e as dietas à base de cana-de-açúcar (1,3 e 2,0 kg de concentrado). O consumo de nutrientes digestíveis totais observado com o fornecimento da dieta à base de silagem de milho foi menor que o obtido com a cana-de-açúcar (2,0 kg de concentrado). As dietas tiveram efeito significativo nos coeficientes de digestibilidade de proteína bruta, extrato etéreo, carboidratos totais e fibra em detergente neutro. Não houve diferença significativa no ganho de peso total nem no ganho médio diário entre a dieta à base de silagem de milho e aquela à base de cana-de-açúcar com 2,7 kg de concentrado em relação às dietas com cana-de-açúcar. O pH ruminal não diferiu nos tempos de coleta entre as dietas experimentais. A concentração de nitrogênio amoniacal mais baixa foi observada 3 horas após a alimentação nos animais alimentados com dieta à base de silagem de milho. A cana-de-açúcar corrigida e com maior participação de concentrado (relação volumoso:concentrado ± 45:55, na base seca da dieta) pode ser utilizada em substituição à silagem de milho em sistemas de produção de leite com idade ao parto próxima dos 24 meses.

This study evaluated the response of dairy heifers fed corn based silage with 1.3 kg/day of concentrated in comparison with three sugar cane-based diets corrected with 1% of urea + ammonium sulphate (9:1) (urea), with 1.3; 2.0 and 2.7 kg/day of concentrate. A total of 20 heifers were used (12 Holstein breed and 8 Brown Swiss breed heifers) in a randomised block design, with 5 blocks formed on the basis of initial live weight and breed. The consumption of dry matter, organic matter and neutral detergent fiber did not differ between corn-silage based diet and sugar-cane based diet. Higher consumption of ether extract was found when diet based on corn silage was supplied in comparison to those based on sugar cane. Intakes of total carbohydrate and non-fibrous carbohydrates differed between corn silage diet and those based on sugarcane (1.3 and 2.0 kg concentrate). Total digestible nutrient intake observed with supply of the diet based on corn silage was lower than that obtained with sugar cane (2 kg concentrate). Diets had a significant effect on coefficients of digestibility of crude protein, ether extract, total carbohidrates and neutral detergent fiber. There was no significant difference on total weight gain neither on average daily gain between the corn-silage based diet and the sugar-cane diet with 2.7 kg of concentrate in relation to the sugar-cane diets. Ruminal pH did not differ at collection times among experimental diets. The lowest concentration of N-NH3 was observed in animals fed corn silage-based diet 3 hours after feeding compared to the sugar cane-based treatments. A milk production system with heifers calving at 24 months and fed a diet containing moderate to high concentrate levels (± 45:55, forage:concentrate), sugar cane forage added with 1% of a mixture of urea + ammonium sulfate (9:1, urea:ammonium sulphate) can be a substitute for corn silage.

Adotou-se uma metodologia para estimar o nível ótimo de alimentos concentrados para vacas leiteiras em pastos tropicais com base na teoria da análise marginal. Um modelo empírico foi desenvolvido e validado para aplicação da metodologia, utilizando-se um banco de dados formado por 62 médias de tratamentos oriundos de 31 estudos em que a produção de leite foi avaliada em relação aos níveis de alimentação concentrada. A produção de leite (PL) apresentou comportamento quadrático em resposta ao consumo de concentrado (CC): PL (kg/vaca/dia) = 10,554 + 1,5855CC - 0,0552CC². A avaliação dos valores de produção de leite observados sobre os preditos de PL apontou a não-rejeição da hipótese de nulidade, indicando que o modelo pode ser aplicado na predição da produção de leite e, consequentemente, do nível ótimo de suplementação. No entanto, a avaliação da partição do quadrado médio do erro de predição do modelo indicou a necessidade de ajustamentos. A resposta produtiva marginal (RPMa) apresentou comportamento linear decrescente ao nível de CC: RPMa (kg leite/ kg de concentrado adicionado) = 1,5855 - 0,1104CC. O consumo de concentrado que maximiza o lucro por animal (CCótimo) é estimado pela seguinte equação: CCótimo (kg/vaca/dia, com base na matéria natural) = (1,5855 - (Px/Py))/0,1104; em que Px e Py são, respectivamente, os preços do concentrado (R$/kg de matéria natural) e do leite recebido pelo produtor (R$/kg). Sugere-se a realização de novos estudos para incorporar ao modelo indicadores de desempenho reprodutivo e outros fatores que afetam a resposta produtiva à suplementação com alimentos concentrados. Recomendações de níveis de suplementação com alimentos concentrados para bovinos devem basear-se nos pressupostos da teoria da análise marginal sob o risco de uso irracional dos nutrientes.

It was adopted in this work a methodology to estimate the optimal level of concentrate food for dairy cows on tropical pastures based on the theory of marginal analysis. An empiric model was developed and validated for application of the methodology using a database composed of 62 means of treatments from 32 studies in which milk production was evaluated regarded to the levels of concentrate feeding. Milk production (MP) showed quadratic behavior in response to concentrate intake (CI): MP (kg/cow/day) = 10.554 + 1.5855CI - 0.0552CI². Evaluation of the MP values observed over the predicted ones pointed the non-rejection of the null hypothesis, indicating that the model can be applied on the prediction of milk production, and consequently, on the optimal level of supplementation. However, evaluation of the partition of mean square error of prediction indicated the need for adjustments. The marginal production response (MPR) presented decreasing linear effect at CI level: MPR (kg milk/kg concentrate added) = 1.5855 - 0.1104CI. The intake of concentrate that maximizes profit per animal (CIoptimum) is estimated by the following equation: CIoptimum (kg/cow/day, as fed basis) = (1.5855 - (Px/Py))/0.1104; in which Px and Py are, respectively, the prices of concentrate feeds ($/kg, as fed basis) and of the milk at farmgate ($/kg). It is suggested the realization of new studies to include in the model, indicators of reproductive performance and other factors that affect the productive response to supplementation with concentrate feeds. Recommendations on levels of concentrate feeding for bovines should be based on presuppotions of marginal response theory, in order to avoid irrational use of nutrients.

Avaliou-se a influência do fornecimento de concentrados à base de farelo de soja ou farelo de algodão em dietas com silagem de milho sobre o balanço de nitrogênio e a produção de proteína microbiana em fêmeas leiteiras em crescimento. As dietas foram constituídas da combinação de dois níveis de concentrado (1 ou 2 kg) e duas fontes proteicas (farelo de soja ou farelo de algodão). Os animais que consumiram concentrado na quantidade de 2 kg/dia apresentaram maior consumo de nitrogênio total, entretanto não houve efeito significativo sobre o N-fecal, N-urinário e o balanço de nitrogênio. A interação entre o nível de concentrado e a fonte proteica influenciou o nitrogênio ureico na urina (N-urina), mas não alterou os níveis de nitrogênio ureico no plasma. Os níveis de concentrado e as fontes proteicas não afetaram as concentrações de purinas totais e alantoína na urina, a porcentagem de alantoína em relação às purinas totais, os níveis de ácido úrico na urina e nitrogênio microbiano nem a eficiência microbiana. O fornecimento de 1 ou 2 kg de concentrado contendo farelo de soja ou farelo de algodão como fontes proteicas para novilhas leiteiras em crescimento não afeta a eficiência microbiana, entretanto o fornecimento de 2 kg de concentrado aumenta a excreção de nitrogênio nas fezes.

The objective of this work was to evaluate effect of based-soybean or cottonseed meal concentrate rations in diets with corn silage on nitrogen balance (NB) and microbial protein production in growing dairy females. diets consisted of the combination of two levels of concentrate ration, 1 or 2 kg, and two protein sources, soybean meal or cottonseed meal. The animals that consumed 2 kg of concentrate ration showed greater total nitrogen intake, however, there was no significant effect on fecal-N, urine-N and nitrogen balance. The interaction among the concentrade levels and the protein source affected the urine uric N (N-urine) but did not change the levels of ureic nitrogen in the plasma. Levels of concentrate and protein sources did not affect concentrations of total purine and allantoin in the urine, the percentage of allantoin regarded to total purine, the levels of uric acid in the urine, microbial nitrogen neither the microbial efficiency. The supply of 1 or 2 kg of concentrate ration for growing dairy heifers, using soybean meal or cottonseed meal as protein sources does not affect microbial efficiency, although the supply of 2 kg of concentrate ration causes N waste in feces.