A comparative analysis of nutrient utilisation and meat quality parameters of boer goats and South African mutton merinos

[摘要] ENGLISH ABSTRACT:One of the reasons why meat supply does not meet human demand is that man hasconcentrated on utilising relatively few animal species as a source of meat. Development ofunconventional livestock, such as goats, is advocated as a means of increasing global meatproduction and consumption. Although South Africa possesses large numbers of domesticruminants, meat consumption has been limited mainly to sheep and cattle. Goats are used toa lesser extent. This is partly attributed to a general belief that goat meat is inferior to muttonand beef.Numerous contradictions regarding comparative goat and sheep growth, carcasscharacteristics and meat composition exist in literature. Concepts involved with most of thecontradictions includes average daHy gain (ADG), dressing percentage, carcass weightdistribution and organoleptic characteristics, especially tenderness, juiciness and flavour,particularly as pertaining to animals reared/grown under intensive/feedlot conditions.Therefore this project was undertaken to obtain more information on the growth, carcass andorganoleptic characteristics, as well as meat chemical compositions of Boer goat (BG) kids incomparison with South African Mutton merino (MM) lambs, reared under feedlot conditions.Thirty-two BG kids and 32 MM lambs were used for this investigation. All the animals werecastrated and weaned before entering the feedlot. Two pelleted diets (fed to 16animals/species) with either a low (LE; 8.9 MJ/kg OM) or a high (HE, 10.9 MJ/kg OM)metabolisabie energy level were fed individually, ad lib for either 28 or 56 days. Feed andwater intake, ADG and feed conversion efficiencies (FCE) were monitored. During the lastweek of the feeding trial, 12 BG kids and 12 MM lambs were used to evaluate the digestibilityof the two diets.After either 28 or 56 days, the animals were slaughtered and the carcasses dissected intoSouth African commercial cuts. The m. semimembranosus and 8-9-10-rib cut of each carcasswas dissected for determination of chemical composition, drip loss, cooking loss, shear forcevalues and colour measurement. The m. gracilis was dissected from the hind leg of thecarcass and used for sensory evaluation.MM's had significantly higher AOG's than BG's (e.g. MMHE56: 0.281; BGHE56: 0.162kg/day). Within a diet there was no difference (P>0.05) in FCE between BG's and MM's andonly the MM's FCE differed between the LE and HE diet (e.g. BGLE28: 7.65; BGHE28: 6.37;MMLE28: 8.73; MMHE28: 5.56 kg feed/kg weight gain). BGLE digested dry matter (OM),crude protein (CP) and energy more efficiently and had a higher energy retention than MMLE.The two diets had the same ME-value for the goats, which confirms that goats perform equallywell on a lower quality feed as their contemporaries on a higher quality feed. Neither species,nor diet affected nitrogen retention. The BG had a 49 % lower (P<0.01) water intake per kgweight gain than the MM on both the high and low energy diets. Both species had a lower(P<0.01) water intake on the high than on the low energy diet. Furthermore, the BG had adaily water intake of only 171 ml/kgo.75 compared to the 302 ml/kgo.75 of the MM.The weight of the liver, empty stomach, head and feet (as a percentage of empty body weight)were higher in goats than in sheep. The MM's had significantly heavier skins, probably due towool growth. Both kidney fat and gastro-intestinal tract (GIT) fat increased with age. Theanimals slaughtered after 56 days in the feedlot had significantly longer and deeper carcassesthan their contemporaries slaughtered after 28 days. Within a diet and slaughter age, the MMhad significantly broader and deeper carcasses than the BG's. BG's had significantly lessweight per unit carcass length, and thus more slender carcasses than MM's. Diet had nosignificant influence on the carcass weight distribution of the goats. However, MM's hadheavier carcasses (LE: 19.87 vs. 15.28 kg; HE: 24.01 vs. 17.05 kg) and proportionally heavierribs and buttocks than BG's.Neither diet nor slaughter age influenced the proximate analysis of the m. semimembranosus,but MM's had significantly lower moisture values than BG's. In the 8-9-10-rib cuts BG's hadsignificantly more moisture and protein and lower fat and energy values than MM's. OM, fatand energy values increased with an increase in slaughter age in both species. BG's hadsignificantly higher concentrations of 11 of the 18 measured essential amino acids in their 8-9-10-rib cuts than the MM's. Gaat carcasses had higher Ca, K, Mg, Na and P-Ievels than sheepcarcasses, regardless of the diet fed. There was a tendency for goat's m. semimembranosusto have a lower Fe-content than that of sheep. BG carcasses had a lower carcass cholesterol content than that of lamb (66.77 vs. 99.28mg/100g, respectively). Palmitic (C16:0), stearic (C18:0) and oleic (C18:1 n9) acid comprisedthe greatest proportions of fatty acids in both the m. semimembranosus and 8-9-10-rib cut forboth species. On a LE-diet there was no significant difference between the saturated fattyacid (SFA) to unsaturated fatty acid (UFA) ratio of goat meat and lamb. However, on the HEdiet,lamb had a significantly higher SFA:UFA ratio than chevon (m. semimembranosus: 0.842vs. 0.689; 8-9-10-rib cut: 1.407 vs. 0.892). Organoleptically, a difference was noted betweenchevon and lamb. Each has a specific species flavour, which was not influenced by energylevel of the diet. BG meat was perceived to be stringier than that of the MM, but there was nosignificant difference in Warner-Bratzler shear force values. Tenderness declined with age inboth species and there was also a tendency for goat meat to be less juicy than lamb. Chevonhad a more pronounced aftertaste than lamb. No objective differences could be distinguishedbetween the colour of the cooked chevon and lamb. There was a tendency for fresh lamb tohave a higher a*-value (redness) than chevon. Although diet did not influence drip loss, driploss increased with an increase in slaughter age. Only after 56 days did the MM's m.semimembranosus have a significantly higher drip loss than the BG's (LE: 4.84 vs. 3.43%;HE: 4.72 vs. 3.32%). In the m. semimembranosus of both species, cooking loss increasedwith an increase in slaughter age.Since diet did not influence the growth, carcass weight distribution, water holding capacity,colour, shear force values or organoleptic qualities of chevon, BG's may be finished on a dietwith a lower ME-value than that usually formulated for sheep, without a reduction inperformance. This may render a direct economic advantage for BG feedlot finishing. Meatfrom young feedlot goats is not inferior to that of lamb and it has a higher protein percentageand lower fat percentage. Therefore, it can be considered as a healthy food commodity,especially among low-income groups or people wishing to consume a low calorie diet.

[发布机构] Stellenbosch University