Effect of Dietary Forage Concentration and Buffer Addition on Duodenal Flow of Trans-C18:1 Fatty Acids and Milk Fat Production in Dairy Cows

Abstract

Milk fat depression in cows fed high grain diets has been shown to be related to increased trans-C18:1 fatty acids in milk. Trans-C18:1 fatty acids are produced as a result of incomplete biohydrogenation of dietary polyunsaturated fatty acids in the rumen. The objective of this study was to determine the effects of varying amounts of dietary concentrate and buffer addition on duodenal flow, apparent absorption, and incorporation of trans-C18:1 fatty acids into milk fat. Four ruminally and duodenally cannulated multiparous Holstein cows in midlactation were fed diets consisting of 60% (high) or 25% (low) forage with or without buffer (1.5% NaHCO3 and 0.5% MgO). Treatments were arranged in a 2 x 2 factorial within a 4 x 4 Latin square design. The diet containing low forage and no buffer increased the flow of trans-C18:1 fatty acids to the duodenum compared with the effects of other diets (120 vs. 57 to 66 g/d). Ruminal pH was lower for cows fed the low forage diets. The addition of buffer increased ruminal pH by 0.19 and 0.02 units for cows fed the low forage and high forage diets, respectively. Cows fed the diet containing low forage and no buffer produced milk with a lower fat percentage. The addition of buffer to the low forage diet partially corrected milk fat depression. Milk trans-C18:1 fatty acids were higher for cows fed the low forage diet without buffer than for cows fed the other diets (5.8% vs. 3.0%). Altered ruminal function resulting from low ruminal pH for cows fed the low forage diet and no buffer may play a role in the increased production of trans-C18:1 fatty acids in the rumen.

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

“…Concentrate level did not significantly affect milk fat percentage, but compared with studies where milk fat depression has been reported [6,7], the concentrate:forage ratio in our study was rather low for both high and low concentrate diets (50:50 and 30:70, respectively). However, the total intake of starch appeared to be a major cause of variation in milk fat percentage (Fig.…”

“…A number of studies have demonstrated that increasing amounts of readily digestible carbohydrates in the diet are associated with increased proportions of trans10,cis12-CLA and trans10-C18:1 in milk fat [4][5][6]16]. The fact that the concentrate level only affected trans10,cis12-CLA and trans10-C18:1 but also the cis9,trans11-CLA and trans11-C18:1 concentration in milk when maize silage was fed, suggests that increased proportions of concentrate (starch) in the diet does not severely affect the ruminal biohydrogenation pattern unless combined with a forage naturally high in starch.…”

“…However, diets that provide large amounts of readily digestible carbohydrates such as starch, with [4,5] or without [6,7] a supplement of vegetable oil often lead to increased proportions of trans10-C18:1 and trans10,cis12-CLA in milk fat. This response is usually caused by a decline in rumen pH [4,6] and shifts in the bacterial populations [8] whereby the biohydrogenation pathway of C18:2n−6 is altered [9]. Since mammals lack ∆ 12 -desaturase enzyme activity in tissues [10], all trans10,cis12-CLA in milk originates from ruminally produced trans10,cis12-CLA with trans10-C18:1 being the subsequent product of hydrogenation.…”

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

“…Trans 18:1 isomers are formed during the penultimate step of rumen biohydrogenation of dietary 18-carbon PUFA to 18:0, with the isomer profile being dependent on the carbohydrate and lipid composition of the diet (Harfoot and Hazlewood, 1997). 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).…”

Effect of grain type and processing method on rumen fermentation and milk rumenic acid production

“…The concentrations of the intermediates in the rumen depends on the extent to which PUFA substrates are metabolized and are influenced by the initial concentration of dietary PUFA (Harfoot et al, 1973), passage rate, and rumen pH (Troegeler-Meynadier et al, 2003;Qiu et al, 2004). Altered rumen function resulting from a low rumen pH has been demonstrated to reduce the extent of PUFA biohydrogenation both in vitro (Martin and Jenkins, 2002) and in vivo (Kalscheur et al, 1997). As rumen pH is mainly influenced by the fermentable carbohydrate in the diet, it is possible that the amount and source of starch and or the rate of ruminal degradation of starch could play a role in altering rumen pH, which in turn could affect biohydrogenation intermediates in the rumen.…”