Effect of forage:concentrate ratio on ruminal digestion and duodenal flow of fatty acids in ewes.

Abstract

The objective of this study was to determine the forage:concentrate ratio that would provide the greatest duodenal flow of unsaturated fatty acids in ewes supplemented with soybean oil and to determine how diets differing in forage content affect flow of conjugated linoleic acid (CLA) and trans-vaccenic acid (18:1(trans-11)). Five mature ewes (66.5 +/- 12.8 kg) fitted with ruminal and duodenal cannulas were used in a 5 x 5 Latin square experiment. Diets were isonitrogenous and included bromegrass hay, cracked corn, corn gluten meal, urea, and limestone. Dietary fat was adjusted to 6% with soybean oil. Five ratios of forage:concentrate (18.4:81.6, 32.2:67.8, 45.8:54.2, 59.4:40.6, and 72.9:27.1) were fed at 1.3% of BW daily in equal allotments at 0630 and 1830. After 14 d, Cr2O3 (2.5 g) was dosed at each feeding for 7 d and ruminal, duodenal, and fecal collections were taken for the next 3 d. Duodenal flow of 18:0 increased linearly (P < 0.01) with dietary forage. Duodenal flow of 18:1(cis-9) and 18:2(cis-9,12) decreased (P < 0.001) but duodenal flow of 18:3(cis-9,12,15) increased (P < 0.01) with increased dietary forage. Biohydrogenation of dietary unsaturated fatty acids increased (P < 0.001) as dietary forage increased, which was concomitant with increased ruminal pH. Duodenal flow of 18:2(cis-9,trans-11) increased linearly (P < 0.01) with increased dietary forage but increased abruptly when forage was fed at 45.8%. Duodenal flow of the trans-10, cis-12 and cis-10, cis-12 CLA isomers decreased as dietary forage increased, but flow tended to increase on the highest-forage diet, resulting in both linear (P < 0.01) and quadratic (P < 0.01) effects. Duodenal flow of 18:1(trans-11) decreased from 8.28 g/d on the 18.4% forage diet to 5.47 g/d on the 59.4% forage diet then increased to 7.29 g/d on the highest-forage diet (quadratic, P < 0.1). Duodenal flow of 18:1(trans-11) was 27- to 69-fold greater than flow of CLA. We conclude that when ewes were fed a 6% crude fat diet duodenal flows of dietary fatty acids changed incrementally as dietary forage was increased, whereas changes in flows of CLA isomers seemed to be more abrupt. Biohydrogenation changes were gradual with diet, suggesting a gradual shift in ruminal microbial populations with increasing forage. Finally, the highest-concentrate diet supported the greatest duodenal flows of dietary unsaturated fatty acids, as well as the highest flow of 18:1(trans-11).

Biohydrogenation and digestion of long chain fatty acids in steers fed on Lolium perenne bred for elevated levels of water-soluble carbohydrate

“…Duodenal flows of 18:1 trans isomers in this study are in the same range noted by Lee et al [15]. In studies using sheep, Kucuk et al [11] and Sasaki et al [27] noted an increase in 18:1 trans (vaccenic acid) and a reduction in biohydrogenation with increasing amounts of concentrate and decreasing amounts of forage in the diet. They also found a greater flow of cis 9 trans 11 CLA with increasing forage in the diet.…”

Profile of ingested fatty acids and in the duodenal digest of steers fed different diets

“…The effect of the diet on absortion of CLA also differs depending on the isomer. For example, Kucuk et al (2001) found that the cis-9, trans-11, the main isomer of CLA present in fat tissue, decreased, while trans-10, cis-12 increased with the addition of concentrate in the diet of the animals. In this study, even though the consumption of polyunsaturated fatty acids was higher in animals that received the conventional diet, duodenal flow of CLA was almost nil in this treatment.…”

“…It was expected that biohydrogenation would be inhibited in the presence of concentrate in the diet (Kucuk et al, 2001, Loor et al, 2004, which usually causes a decrease in ruminal pH and a decreased lipolysis (Doreau & Ferlay, 1994), which is a prerequisite for biohydrogenation (Latham et al, 1972). Moreover, Loor et al (2004) suggested that changes in microbial population induced by the presence of starch could also adversely affect the ruminal biohydrogenation.…”

Digestion of fatty acids in ruminants: a meta-analysis of flows and variation factors: 2. C18 fatty acids

“…We selected the 14 experiments with within-experiment differences in ruminal pH higher than 0.2 units, from which we excluded treatments containing fish oil. There was a concomitant variation of forage : concentrate ratio in three of these 14 experiments (Kalscheur et al, 1997;Kucuk et al, 2001;Harvatine et al, 2002). In this subset, mean pH values varied between 5.5 and 6.6.…”