Faecal nitrogen excretion as an approach to estimate forage intake of wethers

Abstract

Data from twenty-two digestibility trials were compiled to examine the relationship between faecal N concentration and organic matter (OM) digestibility (OMD), and between faecal N excretion and OM intake (OMI) by wethers fed tropical or temperate forages alone or with supplements. Data set was grouped by diet type as follows: only tropical grass (n = 204), only temperate grass (n = 160), tropical grass plus supplement (n = 216), temperate grass plus supplement (n = 48), tropical grass plus tropical legume (n = 60) and temperate grass with ruminal infusion of tannins (n = 16). Positive correlation between OMD and either total faecal N concentration (Nfc, % of OM) or metabolic faecal N concentration (Nmetfc, % of OM) was significant for most diet types. Exceptions were the diet that included a tropical legume, where both relationships were negative, and the diet that included tannin extract, where the correlation between OMD and Nfc was not significant. Pearson correlation and linear regressions between OM intake (OMI, g/day) and faecal N excretion (Nf, g/day) were significant for all diet types. When OMI was estimated from the OM faecal excretion and Nfc-based OMD values, the linear comparison between observed and estimated OMI values showed intercept different from 0 and slope different from 1. When OMI was estimated using the Nf-based linear regressions, the linear comparison between observed and estimated OMI values showed neither intercept different from 0 nor slope different from 1. Both linear comparisons showed similar R(2) values (i.e. 0.78 vs. 0.79). In conclusion, linear equations are suitable for directly estimating OM intake by wethers, fed only forage or forage plus supplements, from the amount of N excreted in faeces. The use of this approach in experiments with grazing wethers has the advantage of accounting for individual variations in diet selection and digestion processes and precludes the use of techniques to estimate forage digestibility.

Faecal N excretion as an approach for estimating organic matter intake by free-ranging sheep and cattle

“…Alternatively, a strong correlation has been reported between organic matter (OM) intake and faecal nitrogen (N) excretion (Lancaster, 1949; Peripolli et al , 2011), and linear equations have been proposed to estimate OM intake by sheep based on the amount of N excreted in the faeces (Azevedo et al , 2014; David et al ., 2014; Kozloski et al ., 2014). However, these equations were developed with data obtained in trials conducted with animals fed only one type of forage or forage supplemented with concentrate feedstuffs, and no information on the reliability of this technique on estimating nutrients intake by free-ranging ruminants was provided.…”

Consumo de forragem por ovinos ingerindo grama missioneira gigante com ou sem acesso a amendoim forrageiro

“…A consistência na estimativa do consumo de MO com base na PBf, utilizando a equação gerada no presente trabalho, possibilitou o seu uso no experimento subsequente e demonstra que a confiabilidade dessas estimativas depende do uso de equações geradas com as mesmas espécies forrageiras a serem avaliadas em situação de pastejo. Isso pode ser explicado pelo fato de que, mesmo sendo o N excretado nas fezes predominantemente de origem metabólica, o qual é linearmente afetado pela ingestão diária de alimento (Kozloski et al, 2014), também existe uma fração do N fecal originado da proteína indigestível de origem alimentar (Vérité e Peyraud, 1989). Considerando que forragens com teores semelhantes de proteína indigestível podem proporcionar diferentes consumos voluntários de MO, conclui-se que o uso generalizado de equações para estimativa do consumo com base em indicadores de índice fecal pode ser criticável.…”

“…Para confirmar a acurácia da estimativa proposta pela equação gerada neste trabalho, em comparação a dados de literatura, os consumos médios observados nos animais do presente estudo foram comparados de maneira descritiva com valores estimados a partir de equações publicadas por autores que trabalharam com pastos de clima tropical (Kozloski et al, 2014;Boval et al, 1996), sendo os resultados apresentados na Tabela 4. ., v.71, n.2, p.623-630, 2019 Pode-se observar que, pelas equações de Kozloski et al (2014), as melhores estimativas foram aquelas que utilizaram os dados provenientes de avaliações com gramíneas tropicais mais leguminosas tropicais. Contudo, mesmo nessa situação, o consumo de MO ainda foi subestimado em 14%.…”

“…Entretanto, a estimativa acurada do consumo de forragem por animais em pasto depende do uso de técnicas que devem preferencialmente ter sido precedidas de alguma validação local (Carvalho et al, 2007). Entre essas, destaca-se o uso de indicadores de índices fecais (Boval et al, 1996;Carvalho et al, 2007), os quais podem ser de grande valia desde que sejam construídas equações específicas para cada situação, como demonstrado por Kozloski et al (2014).…”

<b>Methods to determine forage intake by lambs on Italian ryegrass

“…Fecal excretion has been more often estimated with the use of external indicators and, among them, the most widely used by the Brazilian scientific community is chromium oxide (Cr 2 O 3 ), despite their known deficiencies (Carvalho et al, 2007;Zeoula et al, 2002). On the other hand, fecal nitrogen has been recently used as a marker for estimates of intake and digestibility of forage (David et al, 2014;Kozloski et al, 2014;Peripolli, Prates, Barcellos & Neto, 2011). According to Peripolli et al (2011), the use of excretion and fecal nitrogen concentration can promote, with high accuracy, estimates of forage intake and digestibility.…”