Dietary factors affecting fatty acid digestion and metabolism in lactating dairy cows

Abstract Text: Our research examined the effects of different dietary factors on fatty acid (FA) digestion, metabolism, and energy partitioning in lactating dairy cattle. Digestibility estimates of individual FA from previous studies were analyzed using meta-analysis and meta-regression. Meta-analysis results indicated that there were minor differences in the digestibility of individual FA. However, using meta-regression, C18:0 digestibility was reduced as the amount of C18:0 reaching the duodenum increased (P<0.001), while the digestibility of other FA were unaffected by their respective flow through the duodenum. The amount of C18:0 reaching the duodenum negatively impacted the digestibility of all 18-carbon FA (all P<0.05). We determined the effects of increasing dietary supplementation of C18:0 on production parameters, digestibility, and incorporation of FA into milk fat. C18:0 was supplemented at 0.8, 1.5, and 2.3% of diet DM compared to a non-supplemented diet. DMI was linearly increased by C18:0 supplementation (P<0.05). However, we observed no effect of C18:0 supplementation on yields of milk or milk components (all P>0.25). C18:0 supplementation resulted in reduced digestibility of total FA (P<0.001) and 18-carbon FA (P<0.001), with no effect on the yield of preformed milk FA (P=0.69). Based on the aforementioned results and our recent work with C16:0 supplementation, we examined the effects of partly replacing dietary starch with fiber and fat to provide a diet with similar NE_L density on yields of milk and milk components and on energy partitioning in mid-lactation cattle. A high fiber and FA diet (HFF) containing 2.5% C16:0-enriched FA supplement was compared to a high starch diet (HS) containing 33% corn grain. DMI (P=0.10) and energy intake (P=0.60) were similar between treatments. Compared with HS, the HFF treatment reduced milk yield, milk protein concentration, and milk protein yield (all P<0.05), but increased milk fat concentration, milk fat yield, milk energy output, and milk to feed ratio (ECM/DMI; all P<0.001). The HFF diet partitioned fewer nutrients towards body reserves as evident by reduced body weight gain, body condition score, and subcutaneous fat thickness (all P<0.05). Using calculated energy values, the HFF diet allocated less energy towards body gain and more towards milk production (both P<0.01). Our results indicate that C18:0 digestibility was negatively impacted by increasing duodenal flow of C18:0, increasing C18:0 in the diet did not impact yields of milk or components, and feeding diets higher fiber and FA to mid-lactation cows may partition less energy to body tissue gain and more to milk. 

Keywords: fatty acids, digestibility, energy partitioning