Effect of energy supplementation on intake and digestion of early and mid-season ryegrass and Panicum / Smuts finger hay, and on <i>in sacco</i> disappearance of various forage species

Abstract

Supplementation of early and mid-season Italian ryegrass (Lolium multiflorum cv. Midmar) with maize meal, maize meal with NaHC0₃ buffer, or maize meal plus combinations of slowly degradable protein was studied. Supplements were administered via a rumen fistula. The effect on intake and digestion of ryegrass was measured. In another experiment, the effect of maize meal supplementation on in sacco degradation of some typical South African forages was investigated. Maize meal depressed intake and digestibility of early season ryegrass, but not of mid-season ryegrass. Additions of the buffer did not alleviate the depression, but additions of a slowly degradable protein source did. In other forages, maize meal depressed in in sacco degradation of lucerne and kikuyu (Pennisetum clandestinum), but not of Panicum maximum, Smuts finger (Digitaria eriantha spp. eriantha), mature Midmar ryegrass and Eragrostis curvula. In general, energy supplementation markedly depressed cell wall degradation below forage NDF levels of 55-60%, but not above these levels, whether examined within or between forage species. Also, degradation in the absence of supplements was markedly slower in forages containing more than 55-60% NDF than in forages with lower NDF values. The present results support the literature in suggesting that energy intake on forages with more than 55-60% NDF is unlikely to be sufficient to sustain satisfactory animal production, because of slow fermentation and long rumen retention times. Such forages may, however, be supplemented with energy without interfering much with fibre digestion.

Supplementering van Italiaanse raaigras (Lolium multiflorum cv. Midmar) met mieliemeel, mieliemeel plus NaHC0₃- buffer en mieliemeel plus kombinasies van stadig-degradeerbare proteïenbronne is bestudeer. Die supplemente is per rumenfistel toegedien. Die invloed op inname en vertering van raaigras is gemeet. In 'n verdere eksperiment is die invloed van mieliemeelsupplementering op in sacco-degradering van sekere tipies Suid-Afrikaanse weidings bestudeer. Mieliemeel het inname en verteerbaarheid van die jong raaigras onderdruk, maar nie dié van die ouer raaigras nie. Byvoeging van die buffer het nie die onderdrukking opgehef nie, maar byvoeging van die stadig-degradeerbare proteïenbron het wel. By die ander gewasse het mieliemeel die in sacco-degradering van lusern en kikoejoe (Pennisetum clandestinum) onderdruk, maar nie die van Panicum maximum, Smutsvinger (Digitaria eriantha spp. eriantha), volwasse Midmar-raaigras en Eragrostis curvula nie. In die algemeen, in studies binne en tussen gewasse, het energiesupplementering die selwanddegradering aansienlik benadeel by gewas-NBV -peile van minder as 55-60%, maar nie by hoër peile nie. Voorts was degradasie, in die afwesigheid van supplemente, aansienlik stadiger by gewasse met meer as 55-60% NBV as by dié met minder as 55-60% NBV. Die huidige resultate en ondersteunende resultate vanuit die literatuur suggereer dat energie-inname op gewasse wat meer as 55-60% NBV bevat, onvoldoende vir bevredigende diereproduksie sal wees as gevolg van stadige  fermentasie en lang rumenretensietye. Aan die ander kant kan sodanige gewasse met energie gesupplementeer word sonder veel (negatiewe) inmenging met veselvertering.

Keywords: Forage species, in sacco disappearance, intake, sheep, supplementation.