Kristin Erdmann
Investigations on the influence of ration formulation and linseed oil supple-ments on rumen fermentation, the quantity of ingredients, especially trans-fatty acids and CLA in the duodenal chyme and in the milk of dairy cows.
An experiment with eight “German-Holstein” dairy cows, which were fitted with ru-minal and duodenal cannulae, was designed to study the following questions:
o How does the roughage:concentrate ratio and the supplements of linseed oil affect ruminal transformentation, and the flow of nutrients and fatty acids to the duodenum?
o How does the roughage:concentrate ratio and the linseed oil supplements af-fect the milk fat content and the tC18:1 and the CLA contents in milk fat?
o Exists a relationship between the tC18:1- and the CLA-isomers in the intesti-nal chyme, and in milk fat?
The rations, which were fed, consisted of meadows hay and a concentrate mixture given in a ratio of 70:30 (H 70 and HLO 70) or 30:70 (H 30 and HLO 30) on a dry matter basis. The supply amounted in the treatments H 70 and HLO 70 13,1 kg DM per day and in the treatments H 30 and HLO 30 12,8 kg DM per day. The cows of treatments HLO 70 and HLO 30 were additionally fed 200 g linseed oil, which was given on the ration to increase the PUFA-intake. The nXP- and NEL-supply met the mean requirements. The experiment was arranged applying an incomplete latin square design and was submitted into 4 periods of 4 weeks each. After 3 weeks of adaptation to the respective experimental ration samples from the rumen fluid were taken to characterise the ruminal fermentation conditions, blood samples to study the fatty acid distribution in the plasma and in the erythrocytes. Additionally, milk samples were analysed for their ingredients and milk fat composition. Milk yield was registered
daily. In experimental week 4, samples from the duodenal chyme were taken to study the flow of dry matter and nutrients as well as the fatty acid distribution.
The results are summarized as follows:
o The pH-value, the NH3-N concentration and the content of short-chain fatty ac-ids in the rumen was not significantly affected by linseed oil supplements.
However, low portions of hay in the ration reduced significantly the pH-value and increased the NH3-N concentration. An influence of the rough-age:concentrate ratio on the C2:C3 ratio failed to reach significance due to large differences between individuals.
o A significant effect of linseed oil on “apparent ruminal digestibility” of OM and NDF was not detected. However, the efficiency of microbial protein synthesis seemed to be increased (P < 0,1). Increased hay portion (H 70/HLO 70) in the ration resulted in an increased NDF-degradation in the rumen as compared to the rations high in concentrate (H 30/HLO 30). Due to an increased flow of mi-crobial OM after high concentrate feeding (H 30 and HLO 30) the “apparent ruminal digestibility” of OM was calculated to decrease although the quantity of FOM (fermented organic matter) increased. Feeding the rations poor in hay (H 30 and HLO 30) increased the flow of NAN and nXP significantly due to the significantly increased microbial protein synthesis (g MP/d) and a significantly improved efficiency of microbial protein synthesis (g MP/kg FOM) as well.
o The linseed oil supplements increased the daily duodenal flow of MUFA, SFA, tC18:1, and total CLA significantly. The daily amount of MUFA, SFA, tC18:1, and total CLA reaching the duodenum increased significantly with feeding higher concentrate portions in the ration. In detail the flow of tC18:1 was re-markably higher compared to that of CLA. The t10-, and the t11-isomers formed the major portion of the total tC18:1 isomers. Among the tC18:1-isomers, t10- and t11-C18:1 were found predominantly. Whereas, the flow rate of t10-C18:1 was higher than of t11-C18:1, feeding H 30 or HLO 30 rations. In contrast, the flow rate of t11-C18:1 was higher than of t10-C18:1, feeding H 70 or HLO 70 rations.The t9,t11-CLA formed the highest and the
c9,t11/t8,c10-CLA the second-highest portion of the c9,t11/t8,c10-CLA-isomers. The t10,c12-c9,t11/t8,c10-CLA-isomer was found more frequent after HLO 30-intake than after HLO 70-intake, but their quantity was subordinate in total. Significant interactions between the die-tary portion of hay and the amount of linseed oil have been verified with regard to the tC18:1 concentration, their isomers and the CLA-isomers.
o The tC18:1- and CLA-isomers in blood plasma, as well as the fatty acid profile in the erythrocytes were not affected by the linseed oil supplement or by the rhoughage:concentrate ratio.
o As the milk yield of the cows varied considerably, they probably effected the daily excretion of milk fat, and fatty acids. For this reason the results were only subjected to discussion on contents of milk fat and milk fatty acids.
o Linseed oil supplements increased MUFA content in milk fat (mg/g MF) signifi-cantly, while the SFA content decreased significantly. The PUFA content was positively affected by an increased concentrate supply. Although linseed oil supplements resulted in a significant increase of total CLA, the absolute amounts proved to be small only (1,8 mg/g MF feeding treatment HLO 70, and 2,8 mg/g MF feeding treatment HLO 30). However, the tC18:1 in milk fat (8,9 mg/g MF feeding treatment HLO 70, and 37,2 mg/g MF feeding treatment HLO 30) increased, considerably. The principal isomers were analysed to be t10- and t11-C18:1. A differentiation according to feeding treatments showed the highest t10-C18:1 values after feeding H 30 and HLO 30 (P <0,1), whereas the t11-C18:1 content was highest, with feeding treatment HLO 70 and HLO 30 (P < 0,001). Not dependent from all treatments, the c9,t11-CLA was found as the predominant isomer in milk fat in contrast to the t10,c12-isomer, which was only found in low concentration. The c9,t11-CLA content was increased (P < 0,015) by linseed oil supplements, whereas the t10,c12-CLA content was increased (P <0,025) by the feeding treatments H 30 and HLO 30.
o The definite higher CLA content in milk fat as compared to that in the digesta confirms the endogenous synthesis of CLA in the udder tissue through ∆ 9-desaturase. An increased ∆9-desaturase activity due to the linseed oil
applica-tion using the C14:0/C14:1 ratio in milk fat as parameter failed to reach signifi-cance. The similar distribution of the tC18:1-isomers in intestinal digesta or in milk fat seem to support the thesis of direct transfer of tC18:1 into the milk fat.
o The significant decrease of amount and percentage of milk fat after linseed oil application supports the already described effect of t10,c12-CLA and t10-C18:1 on the desaturase activity, additionally the inhibitory effect of long-chain fatty acids on the acetyl-CoA-carboxylase. However, the state of lactation and the constitution of the animal might have an influence as well.
Linseed oil application and ration type have proved to influence significantly fatty acid distribution in the digesta and also the fatty acid composition in milk fat. To improve the knowledge on the relationship between ruminal parameters, PUFA supplements and bio-hydrogenation as well as the content of tC18:1 and CLA in the milk fat addi-tional studies with graded oil supplements seem necessary with higher performing dairy cows.