Effect of silage type and concentrate level on conjugated linoleic acids, trans-C18:1 isomers and fat content in milk from dairy cows

Abstract

-The objective of the study was to examine how the fatty acid composition of milk especially concentrations of conjugated linoleic acids (CLA) and trans-C18:1 isomers and milk fat percentage were affected by silage type and concentrate level. Forty dairy cows were blocked and randomly assigned to one of four diets in a 2 × 2 factorial arrangement of treatments and a six week experimental period. Treatments were total mixed rations with maize (M) or grass (G) silage differing in polyunsaturated fatty acid (PUFA) profile and starch content, combined with a high (H) or a low (L) level of concentrate (with or without grain). Treatments had no significant effect on milk, protein and lactose yield, but energy corrected milk yield, milk fat percentage and fat yield was lower and protein percentage higher for maize compared with grass silage diets. Overall, maize silage diets resulted in higher concentrations of CLA isomers compared with grass silage diets, but there was a significant interaction between silage type and concentrate level for concentrations of cis9,trans11-CLA; trans10,cis12-CLA; trans11-C18:1 and trans10-C18:1. A high level of concentrate increased trans10"cis12-CLA and trans10-C18:1 and reduced cis9,trans11-CLA and trans11-C18:1 when maize but not grass silage was provided. The results suggest that high levels of concentrate (grain) do not significantly alter the pattern of PUFA biohydrogenation in the rumen, the concentration of CLA and trans-C18:1 isomers in milk or cause milk fat depression unless combined with forage naturally high in starch and C18:2n-6 such as maize silage.CLA / trans-C18:1 isomers / milk fat / silage type / concentrate level

Effect of replacing grass silage with maize silage in the diet on bovine milk fatty acid composition

“…Inclusion of MS in the diet had no effect on milk fat content. Typically, increases in starch intake coupled with decreases in NDF ingestion are associated with a reduction in milk fat (Lock and Shingfield, 2004;Nielsen et al, 2006). A lack of effect on milk fat concentrations in this experiment may reflect a higher intake of NDF on MS-containing diets, in spite of this forage containing lower amounts of this constituent than GS.…”

“…Kalscheur et al (1997) found that increasing the amount of dietary readily digestible carbohydrates caused an increase in certain milk trans 18:1. More specifically, studies have also found that complete replacement of GS with MS in the diet increases milk trans-10 18:1 concentrations (Shingfield et al, 2005;Ferlay et al, 2006;Nielsen et al, 2006). The effects of ruminant-derived trans FA on human health have yet to be fully clarified -the isomer profile of ruminant products is different from that of industrial trans FA.…”

“…It is well established that relative to GS, diets based on MS increase the milk yield and milk protein content (Phipps et al, 1995). Recent studies have reported that these forages also alter milk FA composition Nielsen et al, 2006). Effects on milk FA may, at least in part, reflect inherent variations in the amount and composition of carbohydrate and lipid between GS and MS (Givens et al, 2001;Nielsen et al, 2006), which will influence both the rumen environment and biohydrogenation.…”

“…Recent studies have reported that these forages also alter milk FA composition Nielsen et al, 2006). Effects on milk FA may, at least in part, reflect inherent variations in the amount and composition of carbohydrate and lipid between GS and MS (Givens et al, 2001;Nielsen et al, 2006), which will influence both the rumen environment and biohydrogenation. Chilliard et al (2001) concluded that milk from cows fed either MS or GS does not tend to have a significantly different total polyunsaturated fatty acid (PUFA) content.…”

“…Even though several studies have -E-mail: k.e.kliem@reading.ac.uk directly compared the effects of GS and MS on milk FA composition Nielsen et al, 2006), the impact of feeding diets containing variable proportions of these forages as part of a TMR is unclear. The current study was designed to examine changes in milk FA composition following the replacement of GS with incremental amounts of MS in diets containing a constant proportion of forage, typical of rations fed on farms in Europe.…”