The effect of feed processing and nutrient density level on the growth rate, feed conversion, rumen fermentation parameters and economy of finishing lambs

Uys, Pieter Hendrik Schalk (2022-04)

Thesis (MScAgric)--Stellenbosch University, 2022.

Thesis

ENGLISH ABSTRACT: The primary objective of this study was to investigate the influence of feed processing on lamb performance, feedlot profitability and rumen fermentation parameters and the interaction of feed pelleting effects with nutrient density in the diet. In the first trial a total of 64 S.A. Mutton Merino male lambs were randomly allocated to 8 pens. The pens were randomly assigned to 2 treatment blocks of either high nutrient density (HD) or low nutrient density (LD). Within each treatment block, the control group was offered a total mixed ration (TMR) containing coarse grain, protein, additives and chopped roughage (Groups L0 and H0). Three treatment groups within each block were offered a complete pelleted ration (CPR) with pellet sizes of 4mm (L4 and H4), 6mm (L6 and H6) and 8mm (L8 and H8) diameter. Over an experimental period of 7 to 8 weeks, the dry matter intake (DMI), average daily gain (ADG), feed efficiency (FCR) and feedlot economy were measured for the different groups. The average DMI of the H4 group was significantly (P < 0.05) lower than the average DMI of all the other groups except for the L0 group. The ADG of lambs that received the L0 diet was significantly lower (P < 0.05) than the ADG of all the other groups. The lambs receiving the H6 diet achieved the highest ADG (0.305 kg/d ± 0.04). The ADG of the H6 group was significantly higher (P < 0.05) than the ADG of lambs on the H4 diet. Pelleting increased ADG in the low- density diets by an average of 44% (195g/d versus 281g/d; P < 0.01), while no significant ADG response of pelleting was observed in lambs fed the high-density diets. The least effective feed conversion rate (FCR) was achieved by the L0 group (6.9 kg ± 0.90), which also differed significantly (P < 0.05) from all the other groups. Although not significant, the FCR of the high- density groups was numerically better than the FCR of the low-density groups. Within the LD and the HD groups, a tendency (P < 0.10) towards a better FCR with an increase in pellet size were established. The average dressing percentage (DP) of the lambs that received HD diets were significantly (P < 0.05) higher than the lambs on LD diets. The highest average gross profit (GP) was obtained by the H8 (R310/lamb) and the H0 (R283/lamb) groups and differed significantly (P < 0.05). At an average of R76/lamb, the L0 group returned the lowest GP of all the groups. The pelleting of the complete LD diet improves growth and economic performance of fattening lambs mainly due to an increase (P < 0.05) in DMI and a better FCR, while pelleting of a complete HD diet did not show any effect on lamb performance. The use of larger diameter pellets in a HD diet seems to be more beneficial to lamb performance than the use of smaller pellets. The aim of the second study was to evaluate the effects of feed pelleting and feed nutrient density on the rumen fermentation parameters of sheep. A total of 8 mature S.A. Mutton Merino ewes were used in a change-over design with a repeated observation experiment. The main treatment blocks were either high nutrient density (HD) or low nutrient density (LD) rations. Within each treatment block, the control group was offered a total mixed ration (TMR) containing coarse grain, protein, additives and chopped roughage (Groups L0 and H0). Three treatment groups within each block were offered a complete pelleted ration (CPR) with pellet sizes of 4mm (L4 and H4), 6mm (L6 and H6) and 8mm (L8 and H8) diameter. The animals fed the LD diets resulted in significantly (P < 0.05) higher daily dry matter intake (DMI) compared to the HD diets. The average ruminal pH of the sheep dropped to a minimum at approximately 4 hours after feeding, after which the pH slowly returned to the initial values. The sheep that received both the L8 and L6 diets had the lowest average ruminal pH reading at 4 hours after feeding, while group H0 had the lowest reduction in ruminal pH (P < 0.01). The ruminal pH of sheep on all three of the LD pelleted diets, experienced a lower ruminal pH for a longer time after the meals than what was observed in the HD pelleted rations and was attributed to higher DMI. Sheep that was fed unprocessed feeds (H0 and L0), had a less significant drop and a slower recovery rate to the initial ruminal pH compared to the sheep on processed feeds. Concentrations of volatile fatty acids were higher in the LD groups than in the HD groups. Rumen ammonia nitrogen (RAN) measurements and methylene blue reduction (MBR) test results did not indicate to any association between nutrient density and level of processing of the diet. The faecal pH of the sheep at 6 hours after feeding followed the general trend of the ruminal pH findings, but no definite association with either feed nutrient density or level of processing could be established. The same was observed with the MBR test on the ruminal fluid at 6 hours after feeding. The observed differences in rumen fermentation parameters in sheep on high and low nutrient density diets, could be explained by higher DMI as well as rate of starch intake.

AFRIKAANSE OPSOMMING: Die primêre doel van hierdie studie was om die invloed van voerprosessering deur verpilling en voerdigtheid op lamprestasie, voerkraalwinsgewendheid en rumenfermentasie parameters te ondersoek. In die eerste studie is 64 S.A. Vleis Merino ramlammers met 'n aanvangsmassa van 30-32 kg ewekansig aan 8 groepe toegeken. Die groepe is ook ewekansig aan twee behandelings blokke toegeken, naamlik ‘n hoë voedingsdigtheid (HD) voer en ‘n lae voedingsdigtheid (LD) voer. Binne elke behandelingsblok was die kontrolegroep 'n volledige rantsoen bestaande uit growwe graan, proteïen, bymiddels en gekerfde ruvoer (Groepe L0 en H0). Drie behandelingsgroepe binne elke blok het 'n volledige verpilde rantsoen ontvang met pil groottes van 4 mm (L4 en H4), 6 mm (L6 en H6) en 8 mm (L8 en H8). Gedurende die eksperimentele periode van 7 tot 8 weke is die droë materiaal inname (DMI), gemiddelde daaglikse toename (ADG), voeromsetdoeltreffendheid (FCR) en ekonomie vir die verskillende groepe gemeet. Betekenisvol hoër (P < 0.05) daaglikse DMI is waargeneem by diere wat LD diete teenoor HD diete gevoer is. Die gemiddelde DMI van die H4-groep was betekenisvol (P < 0.01) laer as die gemiddelde DMI van al die ander groepe, met die uitsondering van die L0- groep. Die ADG van lammers wat die L0-dieet ontvang het (0,195 kg/d ± 0,03) was aansienlik laer (P < 0.05) as die ADG van al die ander groepe. Die lammers wat die H6-dieet ontvang het, het die hoogste ADG behaal en was was aansienlik (P < 0.05) hoër as die ADG van die lammers op die H4-dieet. Verpilling het die ADG van die lammers wat die LD diete ontvang het, met gemiddeld 44% verhoog (195 g/d teenoor 281 g/d; P < 0,01), terwyl geen noemenswaardige ADG-respons weens verpilling by lammers op die HD diete waargeneem is nie. Die swakste voeromsetdoeltreffendheid (FCR) is deur die L0-groep (6,9 kg ± 0,90) behaal, wat ook betekenisvol (P < 0.05) verskil het van al die ander groepe. Alhoewel nie- betekenisvol, was die FCR van die groepe wat die HD dieet ontvang het, numeries beter as die FCR van die groepe wat die LD diete ontvang het. Binne die LD- en die HD-groepe was daar 'n neiging (P < 0.10) na 'n beter FCR met 'n toename in pil grootte. Die gemiddelde uitslag persentasie (DP) van die lammers wat HD-diëte ontvang het, was betekenisvol (P < 0.05) hoër as die lammers op LD-diëte. Die H8 (R310/lam) en H0 (R283/lam) groepe het die hoogste bruto marge (GP) van alle groepe gerealiseer en was ook aansienlik beter (P < 0.05) as die GP van al die LD-groepe. Die L0-groep het die laagste GP van al die groepe gerealiseer, met ‘n gemiddeld van R76/lam. Die beter GP van die HD-groepe was hoofsaaklik toegeskryf aan die beter karkas opbrengs. Die gevolgtrekking van die proef is dat verpilling van die LD-diete die groei en ekonomiese prestasie van lamafronddiete verbeter hoofsaaklik weens verhoogde DMI en 'n verbeterde FCR. Verpilling van 'n volledige HD-diete het nie 'n beduidende uitwerking op lamprestasie gelewer nie. Die gebruik van voerpille met ‘n groter deursnit in 'n HD-dieet is meer voordelig vir lamprestasie as die gebruik van kleiner pille. Die doel van die tweede studie was om die effek van voerverpilling en voerdigtheid op die rumen fermentasie parameters van skape te evalueer. Altesaam 8 volwasse S.A. Vleis Merino-ooie is gebruik in 'n omskakelontwerp met 'n herhaalde waarnemings eksperiment. Die belangrikste behandelingsblokke was of die hoë voerdigtheid (HD) of lae voerdigtheid (LD) diete. Binne elke behandelingsblok het die kontrolegroep 'n volledige dieet ontvang wat growwe graan, proteïen, bymiddels en gekerfde ruvoer bevat (Groepe L0 en H0) het. Drie behandelingsgroepe binne elke blok het 'n volledige verpilde dieet ontvang met 4 mm (L4 en H4), 6 mm (L6 en H6) en 8 mm (L8 en H8) deursnit respektiewelik. Die gemiddelde ruminale pH van die skape het ongeveer 4 uur na voeding tot 'n minimum gedaal, waarna die ruminale pH stadig na die aanvanklike waardes teruggekeer het. Die skape wat beide die L8- en L6- diete ontvang het, het die laagste gemiddelde pH-lesing op 4 uur na voeding gehad, terwyl H0 groep die laagste (P < 0 .05) daling in ruminale pH getoon het. Die ruminale pH van skape op al drie die LD-korrel-diete, het 'n laer pH vir 'n langer tyd na die maaltye getoon as wat in die HD-korrel-diete waargeneem is. Skape wat die ongeprosesseerde voere (H0 en L0) ontvang het, het 'n minder beduidende daling en 'n stadiger hersteltempo tot die aanvanklike ruminale pH ervaar as wat die geval met die skape wat die verpilde voer ontvang het was. Konsentrasies van vlugtige vetsure was hoër in die LD-groepe as in die HD-groepe. Rumen- ammoniak stikstof (RAN) metings en metileenblou reduksie (MBR) -toetsresultate het geen verband met voedingsdigtheid of die vlak van prosessering van die dieet getoon nie. Die fekale pH van die skape op 6 uur na voeding het ‘n soortgelyke tendens as die algemene neiging van die ruminale pH-bevindings getoon, maar daar kon geen definitiewe verband met voerdigtheid of vlak van prosessering bepaal word nie. Dieselfde is waargeneem met die MBR-toets op die ruminale vloeistof 6 uur na voeding. Die waargeneemde verskille in rumen fermentasie parameters by skape op hoë en lae voerdigthede, kan verklaar word deur hoër DMI en hoër tempos van styselinnames.

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