Effect of harvest date on the fatty acid composition of different perennial ryegrass cultivars

PALLADINO, R.A., KENNEDY, E., O’ DONOVAN, M.A., MURPHY, J.J., BOLAND T.M., AND KENNY, D.A.

Irlanda

Congreso; Agriculture Research Forum, Ireland; 2008

Irish Grassland and Animal Production Association

Introduction Polyunsaturated fatty acid (PUFA) intake has been positively associated with both human health (Parodi et al., 1999) as well as cow fertility (Ambrose et al., 2006). Linoleic (LA) and Linolenic (LNA) acids are the parent n-6 and n-3 PUFA respectively and are both considered essential dietary fatty acids (FA). In Ireland most milk is produced from pasture fed dairy cows and milk PUFA content will be dictated firstly by respective PUFA concentrations in the diet and secondly by the extent of ruminal hydrogenation. In turn, the content of PUFA in grasses depends on several factors including, soil fertility, regrowth interval, leaf/stem ratio, stage of maturity as well as species and potentially cultivar (Dewhurst et al., 2003). However, despite its economic importance there is little published information on the FA composition of different perennial ryegrass cultivars.  The objective of this work, therefore, was to compare the FA composition of twelve different cultivars of perennial ryegrass (Lolium perenne L.) during the peak growing season. Materials and Methods Twelve perennial ryegrasses (Lolium perenne L.) differing in ploidy (diploid v tetraploid) and heading date (intermediate v late) were sown in triplicate plots on 24th August 2006. Plots were fertilized with P and K in accordance with soil test results and N was added at 60 kg/ha. On 20th January 2007 and after each harvest each plot received 20 kg of N/ha. Three harvest dates were evaluated: 21/05/2007, 11/06/2007 and 29/06/2007. The regrowth interval prior to first harvest was 20 days. Fresh samples (150g) were frozen immediately after cutting and subsequently freeze dried. The FA composition was analyzed by gas chromatography using a one step methylation procedure (Sukhija and Palmquist, 1988). Data were analyzed by ANOVA using PROC MIXED (SAS Institute, 1999). The model included terms for cultivar, cut, and their interaction. Results and Discussion The FA content of the three most predominant FA as well as the total FA content is presented in Table 1. Overall, the recovery of total FA was high which may have been due to the efficient extraction and separation of individual FA (7 FA in total; data not shown). There was a cultivar x cutting date interaction (P<0.05) for total FA. This was manifested through one cultivar (Arrow; diploid, intermediate heading date) having the same total FA concentration across cutting dates while Dunluce and Malone (both tetraploid and intermediate heading date) had higher total concentrations in the last compared with the first and intermediate cutting dates. The total FA concentration of all other cultivars as well as the concentration of both LA and LNA was highest for the last cut and lowest for the intermediate cut.  Overall, Tyrella (diploid, late) had the highest concentration of LA and LNA as well as total FA while Alto (diploid, late) had consistently the lowest values. Conclusion These data suggest that significant variation in FA concentration exists between cultivars of perennial ryegrass and this can be further affected by harvest date even within a relatively narrow window of time. The potential exists therefore to improve the content of dietary essential PUFA in ruminant products through improved grass breeding as well as management strategies.