Estimating forage intake of lactating dual-purpose cows using chromium oxide and n-alkanes as external markers

Dimas Estrasulas De Oliveira,Sila Carneiro Da Silva,Luís Januário Magalhães Aroeira,Sérgio Raposo De Medeiros,Luis Orlindo Tedeschi

doi:10.1590/s0103-90162007000200001

Dimas Estrasulas De Oliveira, Sila Carneiro Da Silva + Show 3 more

Open Access

https://doi.org/10.1590/s0103-90162007000200001

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Abstract

The n-alkanes have been used to estimate forage dry matter intake, digestibility and the diet composition in grazing animals. The objective this study was to compare chromium oxide and n-alkanes techniques used to estimate forage intake. Twenty lactating dual-purpose cows receiving two sources of fat (treatments: conjugated linoleic acid (CLA) or Megalac (control)) plus 4 kg of concentrate were dosed with n-alkanes and chromium oxide to estimate the intake of stargrass (Cynodon nlemfüensis Vanderyst var. nlemfüensis). The in vitro dry matter (DM) digestibility of the stargrass and concentrate were used to estimate the nutritive value of the digesta. The n-alkanes between C23 and C36 were quantified in the digesta and feces. The regression between metabolizable energy requirement (MEr, Mcal d-1) and supply derived from forage DM intake estimated using chromium oxide was ME IntakeCr = 19.1 + 0.62 MEr (R² = 0.27) and the same relationship estimated using C35:C36 n-alkane ratio was ME IntakeC35:C36 = 9.3 + 0.77 MEr (R² = 0.52). There was a treatment effect on fecal concentration of chromium oxide with daily and period variations. For the n-alkane technique, treatment and period effects and a linear effect of day of collection on the fecal concentrations of C35 were found. For C36 fecal concentrations, there was a treatment effect and a quadratic effect of collection day. There was no treatment effect on the fecal concentration of the C35:C36 ratio, but a period effect and a linear effect of day of collection were found. Estimates of daily intake using the two markers were different, but those obtained using the C35:C36 pair of n-alkanes were more precise than those obtained using chromium oxide and in vitro digestibility. Management of experimental animals could have influenced the concentration of markers in the feces, determining variations and inconsistencies that partially explain the inaccuracy of the estimates.

Highlights

Pasture is the main source of nutrients for grazing animals
The most common methodology for estimating forage intake by grazing ruminants is the calculation of fecal output and forage dry matter (DM) digestibility
Because the two treatments (CLA and control) had the same intake of concentrate and there was no difference in body weight and body condition score (Oliveira, 2003), the intake of metabolizable energy was assumed to be the total of the maintenance and lactation requirements in a steady-state condition

Summary

Introduction

Pasture is the main source of nutrients for grazing animals. They modify their diet by selecting different species and/or parts of plants, and this confers complexity to the determination of the diet composition, intake, and digestibility under grazing conditions. The aliphatic saturated hydrocarbons (n-alkanes) in the cuticular wax of plants have been extensively used to estimate forage DM intake (Mayes et al, 1986; Dove & Mayes, 1991; Genro et al, 2000) and digestibility (Mayes & Lamb, 1984; Oliveira et al, 2000). This technique allows the study of the botanical and/or morphological composition of plants available in a pasture or ingested by the grazing animals (Dove, 1992; Dove & Moore, 1995; Oliveira et al, 2003)

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