Fatty acid intake and rumen fatty acid composition is affected by pre-grazing herbage mass and daily herbage allowance in Holstein dairy cows

Rafael A Palladino,David A Kenny,Michael O´Donovan

doi:10.5424/sjar/2014123-5578

Abstract

The objective of this study was to investigate the effect of level of pre-grazing herbage mass (HM) and daily herbage allowance (DHA) on the fatty acid (FA) intake and composition of ruminal content of grazing dairy cows. Four rumen fistulated Holstein-Friesian dairy cows were allocated to either a high or low HM (1700 vs 2600 kg DM ha-1) and within herbage mass treatment further allocated to a high or low DHA (20 vs 16 kg of DM cow-1 day-1) in a 4 × 4 Latin square design. Total FA intake and linolenic acid (LNA) intake was higher for cows on high DHA (p<0.05). Ruminal oleic acid, linoleic and LNA were not affected by treatments. Ruminal stearic acid (C18:0) and vaccenic acid (VA) concentrations were higher at low HM (43.6 and 14.8 g/100 gof FA respectively; p<0.01) compared to high HM (42.0 and 12.5 g/100 gof FA respectively for C18:0 and VA). Cows grazing high DHA had higher ruminal concentration of VA (15.3 g/100 gof FA; p<0.01) than low DHA (12.1 g/100 gof FA). Regarding milk FA composition, only some of the milk FA varied across treatments, being the VA and LNA concentrations higher at low HM (p<0.05). These data suggest that low HM and high DHA, at least within the range studied here, promotes the accumulation of ruminal VA which could be available for subsequent conversion within the mammary gland to the human health promoting c9,t11 isomer of conjugated linoleic acid.

Highlights

It is accepted that dietary intake of some polyunsaturated fatty acids (PUFA) can have positive effects on human health
These data suggest that low herbage mass (HM) and high daily herbage allowance (DHA), at least within the range studied here, promotes the accumulation of ruminal vaccenic acid (VA) which could be available for subsequent conversion within the mammary gland to the human health promoting c9,t11 isomer of conjugated linoleic acid
linoleic acid (LA) intake tended to be higher at high DHA (p < 0.10; Table 2)

Summary

Introduction

It is accepted that dietary intake of some polyunsaturated fatty acids (PUFA) can have positive effects on human health. Milk fat from dairy cows is one of the most important sources of c9,t11-CLA in the human diet (Lock & Bauman, 2004; Schroeder et al, 2004) and these beneficial. Pasture is an important source of PUFA, α-linolenic acid (LNA; C18:3 n-3; Palladino et al, 2009a), which is one of the main precursors of c9,t11CLA in milk. The PUFA concentration in milk is dictated by supply of precursors from the diet and by the extent of ruminal biohydrogenation (Dewhurst et al, 2006). Some CLA isomers are synthesized by ruminal bacteria as an intermediary in the biohydrogenation of LNA and linoleic acid (LA; C18:2 n-6). The majority of milk c9,t11-CLA is synthesised de novo in the mammary

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