Effects of feeding ryegrass of varying maturity on the metabolism and composition of lipids in the rumen of sheep

Abstract

Two experiments were carried out to test the effects of ryegrass maturity on rumen lipid metabolism. In the first experiment the effect of stage of maturity of perennial ryegrass on lipid metabolism in the rumen was studied with grazing sheep fitted with rumen cannulae. The pasture was either immature (13-8% crude protein), mature (8-1% crude protein) or senescent (5-5% crude protein).The rates in vitro of triacyl glycerol lipolysis and linoleic acid (18: 2w6) hydrogenation were found to decrease with increasing age of the ryegrass.In the second experiment the sheep were dosed with emulsified linseed oil (30 g) via rumen cannulae while grazing immature or senescent ryegrass and the rumen digesta and blood plasma sampled at 0, 4 and 8 h after dosing.The proportions of linseed oil retained in the rumen were greater and blood plasma linoleic (18:2w6) and linolenic (18:3w3) acid concentrations higher when senescent ryegrass was fed.It was concluded that the rates of rumen lipolysis and hydrogenation decreased with the age of pasture and that after dosing with linseed oil the polyunsaturated fatty acid concentrations in blood plasma increased. INTRODUCTIONacids in the rumen and their appearance in blood plasma. Previous work has established that diet affects lipid metabolism in the rumen. Thus concentrate MATERIALS AND METHODS diets reduced the rates of lipolysis and hydrogenation by rumen digesta (Gerson, John & King, Animals 1985) and enhanced the unsaturation of tissue Romney wethers aged 2 years and weighing lipids (Leat, 1977), plasma lipids (Moore, Noble & between 45 and 52 kg, fitted with 85 mm (i.d.) Steele, 1968) and milk fat (Latham, Storry & rubber rumen cannulae were used. For Expt 2 the Sharpe, 1972). Diets low in N resulted in low rates cannulae were fitted with probes for dosing and of lipolysis and hydrogenation of unsaturated fatty sampling. These consisted of 2 cm diameter, 10 cm acids (Gerson, John & Sinclair, 1983) and increased long perforated metal cylinders, covered with 1 mm unsaturation of fatty acids in rumen digesta, plasma nylon mesh placed at the end of 20 cm polythene and perirenal fat (Gerson et al. 1982).tubing. In the present work the objective of the first experiment (Expt 1) was to study the effect of rye-Diets grass of varying maturity on the rates in vitro of The ryegrass pasture {Lolium perenne L. var. lipolysis and hydrogenation by sheep rumen di-Grasslands Nui) was strip grazed at a high stocking gesta.density (about 300 sheep/ha) in order to minimize The purpose of the second experiment (Expt 2) pasture selection. Dry matter (D.M.) density of was to examine the effects of dosing sheep fed pastures cut to ground level were: immature (preimmature or senescent ryegrass with linseed oil and bloom) 2-2 t/ha, mature (after seed head formation) to compare the retention of polyunsaturated fatty 2-6 t/ha and senescent (mostly dead) 4'2 t/ha.

Effect of forage conservation method, concentrate level and propylene glycol on the fatty acid composition and vitamin content of cows' milk

“…Lipolysis is believed to be rate-limiting for biohydrogenation (Harfoot & Hazlewood, 1988), but lipids in grass are also hydrolysed to a varying extent during ensiling (Elgersma et al 2003). Incubations in vitro show that the rate and extent of 18 : 2 n-6 and 18 : 3 n-3 biohydrogenation is higher for ensiled than for dried grass (Boufaïed et al 2003b), while lipolysis and biohydrogenation of PUFA in ryegrass are reduced by advances in maturity (Gerson et al 1986). Particle size is also known to affect bacterial colonization and lipolysis of lipids in dried grass (Gerson et al 1988).…”

Lipid metabolism in the rumen: New insights on lipolysis and biohydrogenation with an emphasis on the role of endogenous plant factors

“…Other dietary factors which diminish LP and rumen BH are advanced maturity of forage and/or forage which has been ground into extremely fine particles (Gerson et al, 1986(Gerson et al, , 1988. In the latter case the adherence of bacteria to feed particle surfaces is poor and the transit rate through the rumen is increased, thereby reducing time of exposure to microbial activity.…”

Frequent moving of grazing dairy cows to new paddocks increases the variability of milk fatty acid composition

“…Different phenological stages induce variations in the herbage chemical composition (i.e. CP and fibre contents), influencing the ruminal biohydrogenation of polyunsaturated fatty acid (PUFA; Gerson et al, 1986). The effect of the botanical composition of upland pasture is due to specific secondary plant ingredients abundant in dicotyledons, inhibiting ruminal bacteria implied in the ruminal biohydrogenation of PUFA (Willems et al, 2014), resulting in larger amounts of PUFA available in the duodenum and then in milk (Leiber et al, 2005).…”