Feedlot performance and essential amino acid growth requirements of Dorper lambs

[摘要] ENGLISH ABSTRACT:The Dorper is numerically the second most abundent of all the sheep breeds inSouth Africa. It is the most numerous sheep breed in the dry arid areas of SouthAfrica which make out a very big portion of the natural grazing in South Africa. In thisstudy the feedlot performance was specifically investigated since so little researchhas been done in this regard. In the first study (Chapter 1), the production efficiency,body components and commercial yield of 13 Dorper and 12 Merino lambs wereinvestigated. A pelleted diet was fed ad lib and the water intake per day wasmeasured. Lambs were slaughtered at 30kg and at 40kg live weight and cut upaccording to the South African commercial cuts. The weights of the organs, head,feet, skin and carcass were also recorded. Results from the first study showed thatDorpers had a lower (P<0.05) water efficiency (285.97 mVkgO75/day) than theMerinos (240.07 mVkg075/day), but had a higher (P<0.05) nitrogen retention. Thehead, feet, skin, heart, lungs, kidneys and diaphragm of Merino lambs were heavier(P<0.05). Merinos had heavier (P<0.05) breast and shank and thick rib (only at40kg live weight) cuts. But the Dorper had a significantly heavier hindquarter(buttock and loin) which is the high-priced cut of any carcass. It seems that theDorper will do well under feedlot conditions, and would possibly make a bettercommercial meat producer than the Merino under all circumstances.In the second study (Chapter 2), the free-ranging Dorper on natural grazing werecompared with 7 Dorper lambs in the feedlot study. The essential amino acids in theduodenal contents were compared. The free-ranging Dorpers were randomlyslaughtered at 40 kg live weight and a duodenal sample was collected. The feedlotDorpers were also slaughtered at 40 kg live weight and a duodenal sample wastaken. The second study indicated no significant differences between the EAAcomposition of the duodenal samples, whether protein quantity was taken intoaccount (gAA/100g crude protein (CP)) or not (expressed as % of lysine). Thechemical scores indicated that the two most limiting amino acids in the duodenaldigesta for whole empty body growth were: arginine and histidine. Excess levels ofamino acids tend to be present in all three duodenal digesta samples (isoleucine,leucine, lusine, methionine, phenylalaline, threonine and valine). The whole emptybody EAA composition (g AA/100 g crude protein) was as follows 7.10 arginine; 2.40histidine; 3.31 isoleucine; 7.22 leucine; 6.61 lysine; 1.62 methionine; 3.91phenylalanine; 3.77 threonine and 4.85 valine. The composition can serve as anexample of the ideal EAA requirements for whole empty body growth between 30and 40 kg live weight of Dorper ram lambs. The duodenal amino acid concentrationsof the free-ranging Dorper compared well with those of the feedlot Dorpers whichsuggests that the microbial organisms have a big influence on the amino acidconcentration which reaches the intestines.

[发布机构] Stellenbosch University