Amino acid contents and intestinal digestibility of lucerne in ruminants as influenced by growth stage

Abstract

Lucerne (<I>Medicago sativa</I> L. var. Palava), harvested at four successive dates over a 30-day period, was evaluated for chemical composition (dry matter, organic matter, crude protein, ether extract, crude fibre, nitrogen-free extract, neutral detergent fibre, acid detergent fibre, acid detergent lignin), amino acid contents and intestinal digestibility in dairy cows. Dry matter (<I>r</I> = 0.78), organic matter (<I>r</I> = 0.95), crude fibre (<I>r</I> = 0.91), neutral detergent fibre (<I>r</I> = 0.94), acid detergent fibre (<I>r</I> = 0.79) and acid detergent lignin (<I>r</I> = 0.48) presented positive linear correlation coefficients (<I>r</I>) with growth stage, whereas crude protein (<I>r</I> = –0.96), ether extract (<I>r</I> = –0.86) and nitrogen-free extract (<I>r</I> = –0.70) showed negative relationships. Total essential amino acid content decreased (<I>r</I> = –0.94) from 84.1 to 55.3 g/kg of dry matter with maturity, with <I>r</I>-values higher than –0.90 obtained between growth stage and contents of lysine, methionine, threonine and valine. With the exception of tyrosine (<I>r</I> = –0.68), r-values between growth stage and individual non-essential amino acids were all higher than –0.90. Total amino acid (<I>r</I> = –0.98) and nitrogen (<I>r</I> = –0.99) contents presented comparable tendencies with successive sampling times. Whereas no definite trends were detected for the amino acid composition of rumen incubated (16 hours) lucerne samples, the intestinal digestibility of total essential (<I>r</I> = –0.78), total non-essential (<I>r</I> = –0.58) and total (<I>r</I> = –0.69) amino acids as well as nitrogen (<I>r</I> = –0.99) decreased with growth. However, due to a small sample size (<I>n</I> = 4), most linear relationships between constituents and growth stage were insignificant. It can be concluded that, although limited in the sample size, this report presents information on the decrease in amino acid contents and intestinal amino acid digestibility as growth proceeds in lucerne (var. Palava) produced in the Czech Republic, which could be utilized in the feeding of ruminants.