The effect of energy supplementation on nitrogen utilization in lactating dairy cows fed grass silage diets.

An experiment was conducted to examine the effect that various isoenergetic diets, containing different quantities of soluble carbohydrate and fiber and different types of starch, have on nitrogen (N) balances. Six lactating dairy cows in early to midlactation consuming grass silage diets with not less than 600 g/kg total DMI as forage were used in the experiment. Four concentrates were prepared that had higher amounts of either fiber, soluble sugars, corn (low degradable starch source), or barley (high degradable starch source). Overall N utilization by the cows was poor, rarely exceeding 0.30 g milk N/g of dietary N intake. Fecal N outputs accounted for more than half of total N excreted in all treatments except for diets supplemented with high degradable starch, in which urinary N excretion was significantly higher compared with the other treatments. Milk yield was unaffected by concentrate type, averaging 19.9 kg/d, but milk protein content decreased from 32.9 for starch-based diets to 30.9 and 30.0 g/kg for the soluble sugar- and fiber-based diets, respectively. The efficiency of N utilization improved in the low degradable starch treatment, which had lower N excretion (65%) and higher protein concentration in milk. Furthermore, feeding cows corn-based concentrates reduced urinary N excretion by almost 30% compared with barley-based concentrates; therefore, feeding corn-based diets is recommended for the reduction of nitrogen pollution in lactating dairy cows.

The effect of protein supplementation on nitrogen utilization in lactating dairy cows fed grass silage diets.

The study set out to examine the effects of supplementing grass silage with various levels of protein concentration and degradability on dietary nitrogen (N) excretion in lactating dairy cows consuming at least 60% forage. Six Holstein/Friesian cows in early to midlactation were offered six diets comprising two levels of crude protein (210 and 290 g/kg DM) and three levels of protein degradability in the concentrate achieved using different amounts of untreated or formaldehyde-treated soybean meal. Despite a difference of almost 100 g/d in N intake, apparent fecal and milk N outputs were not significantly affected. Protein degradability also had no effect on N outputs in feces and milk. However, there was a major effect of both level and degradability of CP on urinary N output. Moreover, an interaction between level and degradability of CP was detected, such that the rate at which urinary N increases with increasing CP degradability was higher on the high-CP than on the low-CP diet. A low level of protein (150 g/kg DM in the diet) and medium to low rumen-degradable protein supplements provided a significant reduction in N excretion without compromising lactational performance (mean 24.8 kg/d), in terms of both milk yield and composition. This study also demonstrated that a high efficiency of N utilization could be achieved on low-CP diets (supplying less than 400 g N/d), with feces being the main route of N excretion, whereas an exponential excretion of urinary N was observed as N intake exceeded 400 g N/d.

Fatores que afetam os valores de degradabilidade in situ da matéria seca de forrageiras tropicais: III. Tamanho de partícula da amostra / Factors affecting in situ dry matter degradability of tropical forage: III. Sample particle size

Amostras de feno de cameroon (Pennisetum purpureum Schum) e jaraguá (Hyparrhenia rufa (Ness), moídas com tamanhos de partículas de 1,3 e 5mm, foram incubadas em sacos de naílon por 6, 24 e 96 horas no rúmen de três bovinos mestiços. Os animais eram alimentados às 8 e 17h, utilizando dieta basal diária de feno de coast-cross (Cynodon dactylon x Cynodon nlemfuensis) ad libitum, 2,4kg de concentrado com 22 por cento de proteína bruta e 25g de mistura mineral. O objetivo era verificar como o tamanho de partícula das amostras afeta os parâmetros da equaçäo de degradaçäo da matéria seca in situ daquelas amostras (DMS=A-B.e elevado a -ct). Os resultados revelaram que, para o feno de cameroon, os valores dos parâmetros näo variaram muito conforme o tamanho de partícula. Para o feno de jaraguá, o valor de "C" aumentou com o menor tamanho de partícula

Avaliaçäo de quatro gramíneas tropicais em diferentes idades de corte pela técnicas "in situ" / Evaluation of four tropical grasses at different growth stages through the in situ technique

Foram avaliadas pela técnica "in situ" quatro forrageiras tropicais: Jaraguá (Hyparrehnia rufa Ness.), Cameron (Pennisetum purpureum Schum. cv cameron), Andropogon (Andropogon gayanus Kunth) e Tobiatä (Panicum maximum Jacq. cv Tobiatä) coletadas com 28, 56, 84 e 112 dias de rebrota. Incubaram-se 4g de amostra em cada saco de dracon, por períodos (t) de 6, 24 e 96 horas em bovinos fistulados. Na comparaçäo entre gramíneas nas diversas idades, o capim Cameron foi o que apresentou maior degradaçäo ruminal. O capim Jaraguá se destacou pela estabilidade de degradaçäo ruminal ao longo dos 112 dias de ciclo vegetativo/reprodutivo. O campim Tobiatä foi o que apresentou efeitos mais acentuados de queda de degradaçäo à medida que amadureceu. Nos estágios iniciais de crescimento, o efeito de idade foi mais acentuado que o de espécie. Em estágios mais avançados, as espécies apresentaram diferenças marcantes em degradaçäo ruminal (y). A equaçäo y = A-B.exp(-Ct) foi utilizada para estabelecer parâmetros de potencial e taxa de degradaçäo. O potencial de degradaçäo ruminal (A) diminuiu à medida em que as gramíneas amadureceram, e houve diferença neste aspecto entre as espécies. Para a taxa constante de degradaçäo (C), os valores se equivaleram tanto para as espécies comparadas como para as idades de corte