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

Published online by Cambridge University Press:  11 June 2018

G. V. Kozloski*
Affiliation:
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil
E. M. C. Zilio
Affiliation:
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil
F. Ongarato
Affiliation:
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil
B. C. Kuinchtner
Affiliation:
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil
A. G. Saccol
Affiliation:
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil
T. C. M. Genro
Affiliation:
EmpresaBrasileira de Pesquisa Agropecuária, Centro de Pesquisa Pecuária Sul, Bagé, RS 62010-970, Brazil
L. Oliveira
Affiliation:
Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91540-000, Brazil
B. M. Faria
Affiliation:
Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91540-000, Brazil
I. M. Cezimbra
Affiliation:
Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91540-000, Brazil
F. L. F. Quadros
Affiliation:
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil
*
Author for correspondence: G.V. Kozloski, E-mail: gilberto.kozloski@ufsm.br

Abstract

The current study aimed to test whether organic matter intake by free-ranging ruminants could be estimated from the amount of nitrogen (N) excreted in faeces and to compare this approach to conventional techniques. An equation describing the relationship between excreted N and nutrient intake was developed in indoor digestibility trials conducted with male sheep (n = 36) and cattle (n = 24) housed in metabolism cages and solely fed hay harvested from a local rangeland. Faecal N excretion was linearly related to organic matter (OM) intake without a significant animal species effect. To evaluate the linear equation, data from free-ranging trials conducted with sheep and cattle were used. The faecal N approach was compared with either in situ digestibility plus external marker (n = 123) or n-alkanes (n = 272) to estimate OM intake and digestible OM intake. Estimates obtained through the faecal N approach did not closely fit those obtained with either conventional technique for any variable. Averaging all individual values, the supply of metabolizable energy (ME) estimated through faecal N was similar to the required level, whereas both the in situ and n-alkanes techniques overestimated ME supply. In conclusion, OM intake by free-ranging sheep and cattle can be estimated based on the amount of N excreted in faeces with some advantages over conventional techniques: knowledge about herbage attributes is not required and it accounts for individual variability on selectivity and digestion processes.

Information

Type
Animal Research Paper
Copyright
Copyright © Cambridge University Press 2018 

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