Etude comparée des quantités ingérées et du comportement alimentaire et mérycique d'ovins et de bovins recevant des ensilages d'herbe réalisés selon différentes techniques

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Abstract
Twenty silages were given to sheep and heifers: 10 silages harvested with a precision-chop machine and treated with formic acid, 6 silages harvested with a flail-machine and treated with formic acid, 4 silages harvested with a precision-chop machine without preservative. These silages were made from 10 fresh forages, 8 of them were fed to comparable animals during the harvest. Comparisons concerning feed intake, feeding and ruminating behavior were made for a better understanding of the variations in feed intake with animal species and method of silage. All the forages were ingested more by heifers than by sheep and the best silages (short particles, formic acid) were consumed to the same level than fresh forages by the former, but in smaller quantity (86/100) by the latter. Heifers were less affected by the length of silage-particles, which decreased silage intake, than sheep (-16/100 vs. -41/100), but more by the absence of formic acid, which decreased preservation quality and thus silage intake (-19/100 vs. 13/100). Heifers ingested during a longer time than sheep, but the parameters leading to the best understanding of the intake variations between the 2 species and their modifications with the silage method were the unitary eating time (mn/g/kg W0.75) and the quantity of dry matter consumed during the 2 main meals immediately after silage feeding. Sheep ingested the silages with short particles and well preserved as rapidly as fresh forages, but were quickly satieted during the main meals and were not able to compensate during the small meals. For these silages this phenomenon of satiety did not appear in heifers. When the length of silage particles increased the unitary eating time strongly increased in sheep and rumination was disturbed. These phenomena were reduced in heifers. The decrease in silage preservation quality increased the unitary eating time and clearly decreased the feed intake during the main meals in heifers. These phenomena were also observed in sheep, but to a lesser extent. Number of meals per day, characteristics of the small meals, latency time between the end of the main meals and the beginning of rumination, time spent ruminating were also examined. The time spent searching for feed was shorter in heifers than in sheep, and in the latter the number of jaw-movements per g of ingested forage was low. In sheep the behavior parameters of the animals fed silages were closely related to those of animals fed fresh forages. This was not true in heifers which reacted more to preservation quality. When the animals were fed the short well preserved silages, only some parametes were closely related between sheep and heifers: daily dry matter intake, unitary eating, ruminating times and duration of the main meals. The growth stage of the ensiled forage did not affect the observations and conclusions, nor did the weight of the sheep. The reuslts are discussed in connection with the problem of regulation of silage intake by ruminants.