Forage intake and botanical composition of feed for cattle fed Brachiaria/legume mixtures

Abstract

A key contribution to study the cycling of nutrients in soil/plant/animal systems is the evaluation of the consumption of forage and their nutrients by cattle. The objective of this study was to test techniques to evaluate faecal production, in vitro digestibility, forage consumption and the proportion of legume in the acquired diet. Five Zebu steer calves were confined and fed five diets of different combinations of Brachiaria dictyoneura and Desmodium ovalifolium. All quantities of faeces were collected per animal and these values were found to compare favourably with those derived from using the chromium oxide technique. In vitro digestibility ranged from 7 to 10% higher than the actual in vivo digestibility. Faecal samples from steers fed with diets with 25% or more of grass in the mixture were found to be depleted in δ 13 C between 1.7 and 2.1‰, but no depletion was observed when the diet was 100% D. ovalifolium. There was a positive linear regression (r 2 = 0.97***) of the δ 13 C of the diet with the δ 13 C of faeces, but if the acquired diet contained a very high proportion of legume, the legume content could be underestimated by as much as 10%. None of the internal indicators, such as lignin or ash content of the diets, were useful to predict feed intake, but the chromium oxide external indicator performed satisfactorily. The 13 C analysis of the faeces was an effective predictor of the proportion of the legume in the consumed diet. Key words: Brachiaria dictyoneura, Desmodium ovalifolium, 13 C abundance, digestibility, forage intake Consumo e composição da forragem ingerida por bovinos alimentados com Brachiaria e uma leguminosa RESUMO: Uma contribuição fundamental para o estudo da ciclagem de nutrientes no sistema solo/planta/ animal é a avaliação do consumo pelo gado de forragem e dos nutrientes nela contidos. Testaram-se, sob condições controladas, técnicas para avaliar a produção fecal, digestibilidade in vitro, consumo de forragem e a proporção de leguminosa ingerida na dieta. Cinco novilhos de Zebu foram confinados e alimentados com quantidades conhecidas de cinco rações com diferentes proporções de Brachiaria dictyoneura e Desmodium ovalifolium. Todas as fezes bovinas foram recolhidas e pesadas e estes valores foram comparáveis com as estimativas da produção fecal derivadas do uso da técnica de óxido de cromo. A digestibilidade in vitro variou de 7 a 10% acima da digestibilidade in vivo atual. Amostras de fezes de novilhos alimentados com dietas com 25% ou mais de capim na mistura apresentaram abundância de 13 C por entre 1,7 e 2,1‰, mas este empobrecimento isotópico não foi observado quando a dieta era com 100% D. ovalifolium. Houve correlação positiva linear (r 2 = 0,97***) entre δ 13 C da dieta com o δ 13 C das fezes, mas o conteúdo de leguminosa foi subestimado em mais de 10% quando a dieta ingerida foi de 100% de leguminosa. Nenhum dos indicadores internos, como o conteúdo de lignina ou cinzas, foram úteis para prever o consumo de forragem, mas os resultados da técnica utilizando ó...

Productivity of Brachiaria humidicola pastures in the Atlantic forest region of Brazil as affected by stocking rate and the presence of a forage legume

“…There was a slightly lower forage intake in the mixed grass/legume pastures which increased the protein content of the diet due to the presence of the legume, but further investigation showed that the animals benefited only marginally (Boddey et al in preparation). High polyphenol/tannin content of the D. ovalifolium can lead to the formation of polyphenol/protein complexes (Macedo et al 2008). Allinson and Osbourn (1970); Norton and Ahn (1997) demonstrated that the presence in the diet of forage with high tannin content leads to the formation of these tannin-protein complexes which renders much of the N unavailable for microbial degradation.…”

“…These data were then used to compute the total annual forage intake ha -1 (Table 6). Desmodium ovalifolium is often high in tannin, which is responsible for its low palatability (bitter flavour) and leads to low consumption of this legume (Cadisch et al 1996;CIAT 1997;Macedo et al 2008). However, the manual evaluation of the proportion of the legume in the acquired diet show that this ranged from 40 to 58% over the whole year except in January 1989, and was little affected by stocking rate or sampling time (data not shown).…”

“…In a recent investigation of the relationship between IVD and the true digestibility determined by total faecal collection for mixtures of Brachiaria dictyoneura and Desmodium ovalifolium, it was found that the IVD overestimated the true digestibility by between 7 and 15% depending on the proportion of the legume in the diet (Macedo et al 2008). The relationship could be expressed by the formula: in vivo digestibility = 0.359 [IVD] ?…”

“…Pearson regression coefficients of daily LWG head -1 for the periods immediately preceding the evaluations of forage intake with estimated forage intake were computed and were highly significant (P \ 0.001). Coefficients of regression (r 2 ) were 0.46 for the grass alone B. humidicola pasture and 0.62 for the mixed Macedo et al (2008) B. humidicola/D. ovalifolium pastures (Fig.…”

From production to consumption: tracing C, N, and S dynamics in Brazilian agroecosystems using stable isotopes

“…) Veldkamp (Syn. Brachiaria dictyoneura)] forage (Macedo et al, 2010). Colleta et al (2012) were able to separate barn vs. free-range chicken according to their diet, in which the latter had more C 4 in their diet and higher δ 15 N values, which the authors attributed to the ingestion of animal protein.…”