Effects of stage of maturity and chop length on the release of cell contents of fresh ryegrass (Lolium perenne L.) during ingestive mastication in steers fed indoors

Abstract

-The objective of the trial was to analyse the effects of the mechanical resistance of cell walls and chewing behaviour on the proportion of intracellular constituents (ICs) released during the ingestive mastication of fresh perennial ryegrass (Lolium perenne L.) by steers. The mechanical resistance of cell walls was varied by the stage of maturity (15 vs. 30 days of regrowth). Herbage was offered at two chop lengths (long and short) for each stage of maturity, to influence chewing behaviour. Four steers, each fitted with a large ruminal cannula, were fed indoors with the ryegrass in a 4 × 4 Latin square design. Ingested boli were collected at the cardia and their IC contents were compared with the IC contents of the grass. The average shear energy was lower with the young grass because of a lower proportion of stems and pseudostems. The eating time per unit of dry matter intake was unaffected by the stage of maturity, but was slightly lower with the short herbages. The nature of the ICs had a strong effect on their release with the larger molecules, or the molecules contained in the chloroplasts, being less rapidly released. The ICs released (as a proportion of intake) ranged from 0.166 for the chlorophyll to 0.612 for the nitrates. The treatments had no effect on the rate of release of the small vacuolar or cytoplasmic ICs. The intracellular nitrogenous fractions, partly in the chloroplast, were released faster in the mature grass, because the animals had to masticate more intensively to obtain a 'swallowable'bolus due to it having a higher shear energy. The release of ICs did not seem to be dependent on the duration of chewing but rather on other parameters of mastication like the force exerted by the jaws, the surface-area of the molars, or the quantity of grass eaten per bolus. Résumé -Effet du stade de maturité et de la longueur des brins sur la libération des contenus cellulaires du ray-grass anglais frais (Lolium perenne L.) au cours de la mastication d'ingestion sur des bouvillons nourris à l'auge. L'objectif de cet essai était d'analyser les effets spécifiques de la résistance mécanique des parois et du comportement masticatoire des animaux sur les proportions de constituants intracellulaires (ICs) libérées lors de la mastication d'ingestion chez des bouvillons nourris avec du ray-grass anglais frais (Lolium perenne L.). La résistance mécanique des parois a été modulée par le stade de maturité (15 vs. 30 jours de repousse). Pour chaque stade, le comportement masticatoire a été modulé en offrant l'herbe à deux longueurs de brins (long vs. court). Quatre bouvillons, munis d'une large canule ruminale ont été nourris à l'auge en carré latin 4 × 4. Des bols d'ingestion ont été collectés directement au cardia et leurs teneurs en ICs ont été comparées avec celles de l'herbe offerte. La résistance mécanique de l'offert a été mesurée comme la moyenne des quantités d'énergie nécessaires pour couper chaque type d'organe végétal, pondérée par les proportions pondé-rales de chacun des organes dans l'offert...

Release of cell contents and comminution of particles of perennial ryegrass herbage during ingestion by dairy cows fed indoors or grazing

“…The fate of the ICs contained in the chloroplastic stroma, and more particularly the protein rubisco, remains unclear and may depend on the physical desegregation of the chloroplast during mastication. The proportions of ICs released in the present experiment lay in the same range as the values observed by Acosta et al (2003) and were rather low compared with other studies (Bryant, 1964;Mangan et al, 1976;Boudon and Peyraud, 2001;Boudon et al, 2002b). However, the relative variation in the proportions of ICs released according to the individual ICs studied in this experiment was consistent with previous results (Reid et al, 1962;Mangan et al, 1976;Boudon and Peyraud, 2001;Boudon et al, 2002b).…”

“…It remains difficult to explain between‐forage variability in the proportions of ICs released during ingestion and the average particle size in the ingestive bolus. For instance, the proportions of ICs released increased with increasing stage of maturity of fresh ryegrass offered to cows in the experiment of Boudon et al. (2002b).…”

“…, 1976; Acosta et al. , 2003) or stage of maturity (Bryant, 1964; Boudon and Peyraud, 2001; Boudon et al. , 2002b) could affect the proportions released during mastication after ingestion.…”

“…It remains difficult to explain between-forage variability in the proportions of ICs released during ingestion and the average particle size in the ingestive bolus. For instance, the proportions of ICs released increased with increasing stage of maturity of fresh ryegrass offered to cows in the experiment of Boudon et al (2002b). However, the proportions of ICs released were not affected by the stage of maturity in the experiment of Boudon and Peyraud (2001) where the difference in the stage of maturity was larger.…”

“…As regards the ICs, studies have shown that herbage species (Mangan et al, 1976;Acosta et al, 2003) or stage of maturity (Bryant, 1964;Boudon and Peyraud, 2001;Boudon et al, 2002b) could affect the proportions released during mastication after ingestion. However, in these studies, it was impossible to discriminate the respective roles of chewing behaviour and plant tissue histology in the release of ICs.…”