Scielo RSS <![CDATA[South African Journal of Animal Science]]> vol. 46 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Exercise-induced maximum metabolic rate scaled to body mass by the fractal dimension of the vascular distribution network</b>]]> The central postulation of the present approach to metabolic rate scaling is that exercise-induced maximum aerobic metabolic rate (MMR) is proportional to the fractal extent (V) of an animal. Total fractal extent can be calculated from the sum of the fractal extents of the capillary service units, as specified by the formula V <x NL?, where <x means „proportional to'. Here N1is the number of capillaries and L1is capillary length, with D the fractal dimension of the vascular distribution network and with L? the fractal extent of a capillary service unit. D can be any real number in the interval 2 < D < 3. From dimensional considerations V scales with body mass (M) with power exponent D / 3, or V ∞ M D/3. Then ΜΜ R ∞μb with b = D/3 follows from the postulate ΜΜ R ∞ V. The utility of the relationship b = D / 3 depends on the feasibility of estimating D. There are two possibilities. The first is to estimate D from the scaling of aorta cross-section area with body mass. The second is from morphometric observations on various body organs. Both give estimates of b in remarkable agreement with estimates obtained by exercise induction or oxygen half-saturation pressure scaling with body mass. The predicted range 2 / 3 < b < 1 is experimentally observed. Likely causes of notable particular instances of the symmorphosis b = D/3 with 2 < D < 3 include optimal movementrequirements, muscle stress limitation, and maximized oxygen delivery and metabolic rates. Lastly, it is shown that the scaling exponent of basal metabolic rate with body mass can be obtained by taking body composition into account in the product of the scaling exponents of MMR and visceral mass. <![CDATA[<b>Comparison of shear force tenderness, drip and cooking loss, and ultimate muscle pH of the loin muscle among grass-fed steers of four major beef crosses slaughtered in Namibia</b>]]> The authors investigated the effects of breed (Brahman, Bonsmara, Simbrah and Simmental crosses) and post-mortem ageing on meat tenderness, purge, cooking loss and ultimate pH of the longissimus muscle under commercial production and slaughter conditions of the Namibian beef export industry. Fifty steers of each breed cross, at an average age of 2½ years and with an average subcutaneous fat cover of 2 mm over the 9th-10th thoracic vertebrae, were included in this study. The Brahman (BRX) differed significantly (P < 0.05) from all other breed crosses in all ageing treatments, recording higher Warner-Bratzler shear force values. The Bonsmara (BNX) steers showed the highest rate of tenderization and maintained this advantage up to day 30 post mortem. Purge and cooking loss increased initially and then tapered off over ageing time. BNX steers recorded the highest cooking loss. <![CDATA[<b>Effects of <i>Prosopis</i><i> laevigata </i>pods on growth performance, ruminal fermentation and blood metabolites in finishing lambs</b>]]> Twenty-one non-castrated male Rambouillet lambs (21 ±1.44 kg body weight) were used to evaluate the effects of increasing dietary levels of Prosopis laevigata pods (PLP) in a 72 d growth performance trial. Three dietary treatments defined as PLP0 (control, 0 g PLP/kg DM), PLP250 (250 g PLP/kg DM), and PLP500 (500 g PLP/kg DM) were evaluated. Animals fed PLP250 and PLP500 had higher daily weight gain (P<0.05) and feed intake (P<0.01) than lambs fed PLP0. Feed conversion was improved by PLP addition in the diets. Feeding cost decreased linearly as the level of PLP in the diet increased. Blood urea-N concentration increased linearly as PLP increased in the diet. Lambs fed PLP500 had higher (P<0.05) blood uric acid concentrations than lambs fed PLP0 and PLP250. Ruminal total volatile fatty acid (VFA) increased linearly with increasing dietary PLP. Lambs fed PLP250 and PLP500 had higher ruminal ammonia N concentrations (P<0.05) than lambs fed PLP0. Dietary inclusion of PLP did not affect health status of lambs. Prosopis laevigata pods can be used safely in finishing lambs' diets at 500 g/kg. <![CDATA[<b>Identification of genetic variation in the major histocompatibility complex gene region in Turkish sheep breeds</b>]]> The major histocompatibility complex (MHC) in sheep, Ovar-Mhc, remains poorly characterized relative to other domestic animals. However, its basic structure is similar to that of other mammals, comprising class I, II and III regions. In this study, the Ovine MHC class II DRB1 and DRB3 genes were amplified by polymerase chain reaction in eight sheep breeds reared in Turkey. Informative restriction fragment length polymorphisms (RFLPs) were obtained with five restriction enzymes for DRB1 and with two restriction enzymes for DRB3. The digestion of DRB1 exon 2 with NciI, SacI, SacII, Hin1I each produced three genotypes and two alleles (viz., a and b) with frequencies of 0.69 and 0.31; 0.65 and 0.35; 0.91 and 0.09; 0.57 and 0.43, respectively. The digestion of DRB1 exon 2 with DcCeI produced four genotypes and three alleles (viz., a, b and c) with frequencies of 0.62, 0.28 and 0.10, respectively. On the other hand, the digestion of DRB3 exon 2 with NcteII and BsaI each produced three genotypes and two alleles (viz., a and b) with frequencies of 0.72 and 0.28; 0.96 and 0.04, respectively. This study presents the genetic profiles of the exon 2 region of the MHC DRB1 and DRB3 genes in native Turkish sheep breeds.