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

Grass is a rich source of alpha-linolenic acid (18: 3n-3) and in this study the effects on ruminal fatty acid metabolism of feeding beef steers zero-grazed Lolium perenne containing elevated levels of water-soluble carbohydrate (WSC) were investigated. Eight Hereford x Friesian steers were offered ad libitum access to one of two varieties of Lolium perenne, Ba11353, high WSC (HS) or AberElan, intermediate WSC ( experimental control) harvested at different times of the day ( 14: 00 and 10: 00 h, respectively) to accentuate WSC differentials. The grass was zero-grazed and fed for 21 days, after which the animals were offered ad libitum grass silage for 14 days to provide a covariate intake. The dry matter ( 202 vs. 167 g per kg fresh weight), WSC( 243 vs. 161 g per kg DM), total fatty acids (21.4 vs. 17.9 g per kg DM) and proportion of 18: 3n-3 (0.54 vs. 0.43) were greater and fibre content was lower ( 251 vs. 296 g ADF per kg DM) for HS compared with the control. DM intake and intake of total fatty acids and 18: 3n-3 was higher for HS (9.3 vs. 6.7 kg per d; 201 vs. 117 and 108.5 vs. 51.3 g per d, respectively). There was a trend ( P <0.1) for the flow of 18: 3n-3 at the duodenal to be higher on HS (8.5 vs. 5.7 g per d) but surprisingly there was no significant difference in the flows of 18: 0 or 18: 1 trans (58.5 vs. 48.8 and 11.1 vs. 9.1 g per d, respectively). This may be attributed to the net flows of fatty acids across the rumen ( duodenal flow - intake) which were positive on the control and negative on the HS. Biohydrogenation of 18: 2n-6 and 18: 3n-3 was not different between treatments and averaged 79.9 and 90.5%, respectively. Intestinal absorption as a proportion of duodenal flow of all the fatty acids were high ranging from 0.70 for 12: 0 to 0.96 for 18: 1 trans. In conclusion, treatment HS a Lolium perenne bred for elevated levels of WSC had higher total fatty acids and a higher proportion of the beneficial fatty acid 18: 3n-3 compared to a control. The higher DM intakes achieved when feeding the treatment HS along with the greater content of 18: 3n-3 resulted in a trend for greater intakes of this fatty acid and flow to and absorption from the small intestine.