Browsing by Author "Moolman, Justin"

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    Specialized feeding of lambs for optimized performance during the finishing phase
    (Stellenbosch : Stellenbosch University, 2014-04) Moolman, Justin; Van de Vyver, W. F. J.; Hoffman, Louwrens C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: The aim of this study was to determine whether a lamb finishing ration that is balanced for essential amino acids (EAA), at a specific level of non-structural carbohydrates (NSC) would yield better feedlot performance when compared to a standard commercial finishing ration. Metionine (Met) and Lysine (Lys) were identified as the first limiting amino acids for growing lambs. These two amino acids, as well as Threonine (Thr), Arginine (Arg), Leucine (Leu), Isoleucine (Ile) and Phenylalanine (Phe) were included in an optimized protein (OP) feedlot ration at optimal levels. This ration was formulated to contain 157 g/kg crude protein (CP) and 477 g/kg NSC, with Met, Lys, Arg and Thr at 2.48, 7.45, 8.51 and 8.12 g/kg on dry matter (DM) basis respectively. The second treatment, FIN, was a standard commercial lamb finishing feed without optimized amino acids and contained similar total protein and NSC to OP of 152 g/kg CP and 468 g/kg NSC but with Met, Lys, Arg and Thr at 2.08, 5.49, 7.47 and 4.80 g/kg on DM basis respectively. A third treatment, a low protein (LP) diet served as a positive control and was formulated on lower specifications (139 g/kg CP, 455 g/kg NSC) and was also not optimized for amino acids. This treatment contained Met, Lys, Arg and Thr at 1.93, 4.99, 6.66 and 4.73 g/kg on DM basis respectively. Lambs grazing kikuyu pasture served as the negative control (CON) group. These lambs also received additional supplementary feed at 500 g/day as a production lick to be comparable to a scenario where lambs are finished on grazing. Forty cross-bred Merino x Döhne-Merino lambs with an average weaning weight of 24.35 ± 0.648 kg were finished in a feedlot for 57 days where after they were slaughtered at an average weight of 41.41 ± 1.259 kg. During the feedlot trial lamb performance was measured by monitoring daily growth rates and feed intake. Also, an in vivo digestibility study was carried out on the OP and FIN lambs. During the slaughter process the rumen was removed which was done to collect a sample of the rumen wall from next to the rumino-reticular fold. These rumen samples were mounted onto slides so that the development of the rumen could be examined. The M. longissimus dorsi from both sides of the carcass between the 2nd and 3rd last thoracic vertebra and the 4th and 5th lumbar vertebra were removed. There was no significant difference (P > 0.05) between any of the concentrate feed treatments with regards to the average daily gain (ADG), feed conversion ratio (FCR) or dressing percentage (DP). The CON lambs, as expected, had lower growth rates (P < 0.05) than the concentrate fed lamb and thus showed significant differences (P < 0.05) in terms of ADG. The DP of 45.96 % ± 0.711 for the CON lambs differed significantly (P < 0.05) from the OP (51.44 % ± 0.358), FIN (52.72 % ± 0.653) and LP (51.74 % ± 0.611) treatments. As expected the concentrate feeds were much more effective in maintaining higher growth rates when compared to the CON lambs while the optimizing of EAA in the OP diet did not lead to improved feedlot performance as the FIN and LP treatments were able to achieve similar (P > 0.05) growth rates. Within the feedlot treatments there was no significant difference (P > 0.05) with regard to the papillae length and rumen wall thickness. There was however a numerical increase in the papillae length as the NSC levels in the feed increased. The CON lambs differed from the OP lambs (P < 0.05) in terms of papillae length. This illustrated the importance of having increased levels of NSC in a feedlot diet as it is this fraction that is responsible for the initialisation and maintenance of rumen morphological development. The in vivo digestibility study therefore confirmed that the commercial finishing feed was just as effective as the optimized feed in terms of nitrogen retention as well as in maintaining suitable energy balance. Although the in vivo digestibility for Met and Lys in the OP feed was higher (P < 0.05) than the FIN feed, this did not lead to improved feedlot performance of the OP lambs. The increased digestibility of these amino acids is due to the fact that the OP diet was higher in levels of bypass amino acids than the FIN feed. The in vitro true digestibility (IVTD) of the OP feed was higher (P < 0.05) than that of the FIN feed.