Variation and Heritability of α-Linolenic Acid Content and Rumen Escape Protein Fraction in Fodder Grass and Clover

Abstract

α-Linolenic acid (C18:3) in forages enhances ω-3 fatty acid and conjugated linoleic acid content in milk and meat of ruminants with beneficial effects on human health. An increase of the fraction of rumen escape protein (REP) in grass and clover may reduce nitrogen losses by cattle. To determine the variation of C18:3 and REP, field plot trials under conservation management were set up. The trials included cultivars of perennial ryegrass, Italian ryegrass, meadow fescue, tall fescue, timothy, cocksfoot and red and white clover. For the grasses we found the highest C18:3 content in timothy and the lowest in Italian ryegrass. Tetraploid ryegrass varieties had on average a higher C18:3 content than diploid varieties. The linolenic acid content in white clover was higher than in red clover and the content in both clovers was higher than in the grasses. For all species the C18:3 content was highly positively correlated with the protein content. Among the grasses the REP was highest in cocksfoot and tall fescue and lowest in perennial ryegrass. Diploid ryegrass cultivars had a higher REP fraction than tetraploid cultivars. The REP in red clover was higher than in white clover and the REP in both clovers was lower than in the grasses. REP was highly negatively correlated with dry matter digestibility and the content of digestible protein. For the estimation of the heritability we determined the C18:3 content and REP of 300 single plants of each of the species perennial ryegrass, tall fescue and red and white clover, grown in pots. We carried out positive and negative selections for both parameters in the four species. The results of their offspring suggested a moderate to good heritability of both parameters and opportunities for breeding. Improved grass/clover mixtures may be an important source of C18:3 in ruminant feeding. However because of the negative correlation between REP and the digestible protein content, breeding for improved nitrogen efficiency in cattle by increasing the fraction of rumen escape protein in the forage is not obvious.