This study aimed to evaluate the supplementation strategies on forage intake and nutrient digestibility, feeding behavior, milk production and composition, feed efficiency, nitrogen balance and body weight change of dairy cows kept in Tanzania grass pastures (Panicum maximum Jacq. cv. Tanzania) in the dry season. We used eight crossbred Holstein and Zebu cows in the final third of lactation, with an average weight of 505±44 kg and initial milk production of 9.0±1.44 kg day -1 , in a double 4X4 Latin square design. The experiment consisted of four experimental periods of 17 days each, with nine days for initial adaptation and eight days to collect data. Treatments consisted of mineral mix and supplements (energy, protein or multiple) provided in the amount of 2 kg per cow day -1 . Supplements promoted increased consumption of dry matter and nutrients (P < 0.05), without changing the forage intake in relation to the mineral mixture. The treatments did not affect the feeding behavior of animals (P > 0.05). There was an increase (P < 0.05) of 19.51% in milk production in the supplemented animals and productive responses approximate marginal 0.64 kg of milk for each kg of supplied supplement, however, the different supplements promoted a drop in the milk fat. There were higher net energy values of animal lactation for protein-energy supplementation and mineral mixture, but no change was observed in feed efficiency and energy efficiency. The performance of dairy cows kept in tropical grass pasture can be improved with the use of a concentrate supplementation of 0.40% of body weight per day -1 without compromising the forage intake of animals. Key words: Concentrate. Digestibility. Forage intake. Milk production. ResumoObjetivou-se avaliar estratégias de suplementação sobre o consumo de forragem e nutrientes, digestibilidade dos nutrientes, comportamento ingestivo, produção e composição do leite, eficiência alimentar, balanço de compostos nitrogenados e variação de peso corporal de vacas leiteiras mantidas em pastos de capim Tanzânia (Panicum maximum Jacq. cv. Tanzânia) no período seco do ano. Foram utilizadas oito vacas mestiças HolandêsXZebu no terço final de lactação, com peso médio de 505±44 kg e produção de leite inicial de 9,0±1,44 kg dia -1 , em delineamento quadrado latino 4X4 duplo. O experimento consistiu de quatro períodos experimentais de 17 dias cada, sendo nove dias inicias para adaptação e oito dias para coleta de dados. Os tratamentos consistiram de mistura mineral e suplementos (energético, proteico ou múltiplo) fornecidos na quantidade de 2 kg por vaca dia -1 . Os suplementos promoveram aumento no consumo de matéria seca e nutrientes (P < 0,05), sem alterar o consumo de forragem em relação a mistura mineral. Os tratamentos não alteraram o comportamento ingestivo dos animais (P > 0,05). Foi observado aumento (P < 0,05) na produção de leite em 19,51% para os animais suplementados e respostas produtivas marginais aproximadas de 0,64 kg de leite para cada kg de suplemento fornecido, no entanto, os...

Animals on pasture generally show higher feed efficiency as a result of the use of antibiotics. This study evaluated the effect of the antimicrobials salinomycin and/or virginiamycin on production and the ruminal parameters of supplemented dairy cows grazing on Panicum maximum cv. Tanzania. Twelve Holstein/Zebu multiparous cows were used, distributed in three Latin squares, one for the evaluation of ruminal parameters, and the others for production parameters. Cows on pasture were fed 50 % of their estimated intake with corn silage and concentrate supplements containing salinomycin, virginiamycin or a combination of additives, in doses of 120 and 150 mg kg −1 , respectively. There were no differences in milk production and composition, energy and nitrogen balance, dry matter digestibility and feeding behavior. However, salinomycin and virginiamycin each reduced pasture and total dry matter intake by about 14 % and 10 %, with a consequent improvement in feed efficiency.

Brasil é o quarto produtor mundial de leite com aumento de 15,9% na sua produção nos últimos cinco anos, apresentando potencial de se tornar o maior exportador mundial de leite. Para isso, é preciso produzir leite com baixo custo e alta qualidade. Minas Gerais é o maior produtor de leite, apresentando 27,3% da produção nacional. A produção de leite no Brasil é desenvolvida principalmente em sistemas de pastagens, o que confere ao leite produzido, baixo custo de produção. Todavia, sistemas de produção de bovinos leiteiros baseados apenas na utilização de pastagens tropicais não atendem a demanda para altas produções individuais e nem mesmo para médias produções. Estudos demonstram o potencial de produção de leite de pastagens intensivamente manejadas, possibilitando incremento da produção de leite por área e com a associação da utilização de alimentos concentrados maximização da produção de leite por vaca. A associação das duas técnicas de manejos possibilitam incremento na produção de leite de forma significativa.Palavras-chave: Concentrado, gramíneas tropicais, produção de leite, pastagem, vacas de leite. Supplementation strategies for dairy cows grazing on tropical grass during the rainyABSTRACT. Brazil is the fourth largest milk producer with 15.9% increase in its production in the last five years, showing potential to become the world's largest exporter of milk.However, for it is necessary to produce milk with low cost and high quality. Minas Gerais is the largest milk producer, with 27.3% of national production.Milk production in Brazil is developed mainly in pasture systems, which gives the milk produced, low production cost. However, production of dairy cattle based only on use of tropical pasture systems does not attend the high demand for individual productions or even for medium productions. Studies demonstrate the potential of milk production from intensively managed pastures, allowing increased milk production per area and the association with the use of feed concentrates maximizing milk production per cow. The combination of these twotechniques managements enables increase in milk production significantly.

This study was conducted to evaluate the effects of the increasing levels of tannin supplementation—0 (control—no additive), 2, 4 and 6 mg/g of dry matter (DM)—versus monensin (0.02 mg/g DM) on in vitro ruminal fermentation of either nitrogen (N)‐fertilized or non‐fertilized Urochloa brizantha cv. Marandu. Ruminal fluid was obtained from two grazing Nellore bulls receiving 0.3% of the body weight of a supplement free of additives. The incubations were conducted for four consecutive weeks with gas production (GP) recorded up to 96 hr, whereas pH and ruminal ammonia (N‐NH3) were measured at 24 and 48 hr, and volatile fatty acids at 48 hr. Additionally, in vitro dry matter digestibility (IVDMD) and in vitro neutral detergent fiber digestibility (IVNDFD) were measured at 24, 48 and 96 hr. The crude protein (CP) contents for N‐fertilized and non‐fertilized forages were 11.77% and 7.75, respectively. There was no interaction between forage and additives (p > 0.05) for fermentation kinetic parameters. Nitrogen fertilization reduced (p < 0.05) the theoretical maximum of gas production (ml) (a), the maximum gas production rate (ml/hr) (b) and the lag time (L). The inclusion of monensin reduced (p < 0.05) b and L compared with control and inclusion of tannin. In general, the inclusion of monensin and tannins reduced (p < 0.05) the IVDMD and IVNDFD. Compared to monensin, tannin reduced (p < 0.05) the N‐NH3 and the acetate:propionate ratio. The use of N fertilization in tropical forage reduces in vitro gas production. Tannins and monensin influence the modulation of ruminal fermentation mainly by reducing neutral detergent fiber (NDF) digestibility. Tannins reduce N‐NH3 concentration regardless of the use of N fertilization of Urochloa brizantha cv. Marandu.

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