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. <![CDATA[<b>Growth differentiation factor 9 gene variants in Sudanese desert sheep ecotypes</b>]]> Certain variants in the growth differentiation factor 9 (GDF9) gene have major effects on the ovulation rate in sheep. The aim of this study was to analyse GDF9 variability in the Sudanese desert sheep ecotypes Ashgar, Dubasi and Watish, and to test identified variants for association with litter size. For this purpose, ewes of these ecotypes with litter size records for at least two litters were sampled. The complete GDF9 exon 2 was sequenced in a total of 28 ewes. An additional variant in exon 1 (c260G>A) was genotyped by restriction-length polymorphism analysis in 97 ewes. Differences in genotype and allele frequencies of polymorphic positions between two groups differing in litter size (only a single lamb versus more than a single lamb) were tested for significance using Fisher's exact test. GDF9 exon 2 variants c.477G>A and c.721G>A and exon 1 variant c.260G>A were found to be polymorphic in all three sheep ecotypes. Exon 2 variants c.471C>T and c.978 A>G were polymorphic in at least one ecotype. No significant associations were observed between allele and genotype frequencies of identified variants and litter size. This suggests that GDF9 variants influencing ovulation are absent in these Sudanese sheep ecotypes, and therefore cannot be used to increase litter size within this population of sheep. <![CDATA[<b>Effects of various pre-slaughter conditions on pig carcasses and meat quality in a low-input slaughter facility</b>]]> The aim of this study was to determine the effects of gender, slaughter weight, stocking density, lairage time and season on carcass and meat quality parameters in a low-input production system. The study was conducted on 400 slaughter pigs (200 barrows and 200 gilts) with live weight of 115.0 ± 4.70 kg. Barrows had higher slaughter and carcass weights, fat thickness and lower meatiness. Heavier pigs had higher hot and cold carcass weights, fat thickness, lower meatiness, and higher incidences of pale, soft and exudative (PSE) and dark, firm and dry (DFD) meat. Low stocking density during transportation increased skin lesion score, pH45 value and the incidence of DFD meat; while high stocking density decreased pH45 value and increased T45 value and the incidence of PSE meat. Long lairaging reduced slaughter weight, carcass weight, dressing percentage and backfat thickness and increased skin lesion score. After overnight lairaging, pH45 value and the incidence of DFD meat became higher. After short lairaging, the pH45 value was lower, while the incidence of PSE meat increased. Pigs slaughtered in winter had the highest slaughter weight, backfat thickness, pH45 value and incidence of DFD, and the lowest meatiness. Pigs slaughtered in summer had the lowest slaughter and carcass weights and pH45 value, and the highest incidence of PSE meat. In conclusion, gender influenced carcass quality, slaughter weight and lairage time, and season affected carcass and meat quality, while stocking density had an impact on meat quality. <![CDATA[<b>Effects of types and doses of yeast on gas production and in vitro digestibility of diets containing maize (<em>Zea mays</em>) and lucerne (<em>Medicago sativa</em>) or oat hay</b>]]> Two yeast products formulated with Saccharomyces cerevisiae were evaluated at the same colony-forming units (CFUs) per gram of substrate. Samples of maize, lucerne and oat hays were mixed (0.5 kg) to a proportion of 80% forage (lucerne or oat) with 20% maize (DM basis) and combined with each yeast to obtain 1.5 x 10(7) or 3.0 x 10(7) CFU/g DM. There was also a control without yeast. In vitro gas production was measured at 0, 2, 4, 6, 8, 10, 14, 18, 24, 30, 36, 42, 48, 60, and 72 h incubation. There was no forage/yeast interaction. Both yeast products tended to reduce the maximum volume produced quadratically and lag time linearly, while in vitro dry matter digestibility (IVDMD) increased linearly. Ruminal ammonia N and lactic acid were not affected, whereas methane and carbon dioxide tended to be reduced with the intermediate dose of yeast. When the mixture included oat hay, the total volume of gas increased, the lag time decreased, and there was higher IVDMD than in the lucerne-based mixtures, which were associated with lower methane production. Ammonia and lactic acid remained unchanged. The two yeast products showed the same effects on the dynamics of gas production and in vitro digestibility when dosed at the same number of viable cells or CFUs, and there was no interaction with forage quality. <![CDATA[<b>Productivity, chemical composition and ruminal degradability of irrigated Napier grass leaves harvested at three stages of maturity</b>]]> The effect of the stage of maturity on the productivity, chemical composition, and ruminal degradability of Napier grass (Pennisetum purpureum) leaves under irrigation was studied. Samples were collected at three stages of maturity, at intervals of four weeks starting from the fourth week until the twelfth week (April-July) after sprouting and then harvested to determine biomass. The stages of maturity had significant effects on longest leaf length per plant and plant height, but had no effect on number of leaves per plant and number of tillers. Dry matter (DM) increased significantly with maturity, while crude protein (CP) and fat content decreased significantly, with no significant effect on acid detergent lignin (ADL), ash, acid detergent fibre (ADF) and neutral detergent fibre (NDF). Maturity significantly decreased potassium, copper and sodium, while calcium and zinc increased significantly up to the intermediate stage, then declined toward the late stage of maturity. Maturity did not affect the magnesium, phosphorus, manganese and iron contents of the forage. Ruminal degradability of CP at 48, 72, 96 and 120 incubation hour decreased significantly with maturity, with no effect on all other incubation times for DM and CP. Maturity significantly decreased the soluble fraction (a) of DM, with no significant effect on other fractions of DM and CP. Effective degradability (%) of DM and CP decreased with maturity when the rate of passage increased from 2% to 8%. Napier forage should be harvested before maturity to retain its high nutrient content, and the degradability of DM and CP. <![CDATA[<b>Genetic diversity of Hajari and Hajar2 local Saudi chicken lines using mitochondrial DNA D-loop markers</b>]]> This study was conducted to assess genetic diversity of Hajari and Hajar2 local Saudi chicken lines using mitochondrial DNA (mtDNA) D-loop partial sequences. One hundred blood samples were obtained equally from Hajari and Hajar2 Saudi chicken lines as 50 samples from each line. The D-loop region was partially amplified from genomic DNA with a conserved primer set, and the fragments were sequenced. Eight published reference mtDNA sequence data from the GenBank were used for comparisons, and multiple alignments were performed. The most common haplotype was assigned as a basic sequence for comparing within each line. Entropy plot and conserved region analysis were performed. Genetic distances and neighbour-joining (NJ) phylogenetic trees were estimated. The results indicated haplotype variations within and between local Saudi chicken lines, which could explain the phenotypic variation reported earlier. A close genetic relationship was shown between the Saudi local chicken lines. Unique conserved regions and nucleotide substitutions were observed between the two lines. Both lines have a close relationship with the reference Asian local chicken population, especially local Chinese and Indian chicken breeds. The current results are considered the first report of mtDNA sequence diversity for Hajari and Hajar2 lines. Further detailed molecular genetic studies of both lines are indispensable to genetic conservation and development. <![CDATA[<b>Mangosteen peel can reduce methane production and rumen biohydrogenation <i>in vitro</i></b>]]> Mangosteen peel (MP), an agricultural by-product of tropical countries, has been reported to contain condensed tannins and saponins, which can affect rumen microbes to reduce enteric methane emission. In the present study, the effects of mangosteen peel on in vitro ruminal fermentation, gas production, methane production, fatty acid biohydrogenation, and microbial population were investigated. Results showed that MP at medium and high levels (25 % and 50 % replacing alfalfa) were able to reduce (P <0.05) in vitro methane production without affecting volatile fatty acid (VFA) production and the pH of the substrate. The lowering effect of MP on methane production was because of suppression of the rumen microbial populations, especially total protozoa and total methanogens. MP at the higher level (50%) reduced (P <0.05) the amounts of biohydrogenation for linoleic acid (C18:2n-6), α-linolenic acid (C18:3n-3) and the total C18 unsaturated fatty acids (UFA) owing to the reduction of the Butyrivibrio fibrisolvens population, that is, the most important rumen microorganism involved in the biohydrogenation process. In conclusion, mangosteen peel has potential to be used in ruminant livestock feeds, with the advantage of reducing ruminal methane production and biohydrogenation, without adverse effects on ruminal pH and VFA production. <![CDATA[<b>Blood profiles of indigenous Pedi goats fed varying levels of Vachellia karroo leaf meal in Setaria verticillata hay-based diet</b>]]> Vachellia karroo (Acacia karroo) is promising fodder for goats in the critical dry season in communal rangelands. The only limitation to the use of this fodder tree is the presence of phenolic compounds, such as condensed tannins. A study was conducted to investigate the effects of tanniniferous V. karroo leaf meal feeding on blood profiles of indigenous Pedi goats fed a basal diet of Setaria verticillata grass hay. Twenty indigenous Pedi goats, weighing 18 ± 2 kg, were allocated in a completely randomized design to five dietary treatments containing V. karroo leaf meal at 20% (S80A20), 25% (S75A25), 30% (S70A30), 40% (S60A40) and 50% (S50A50) of the total diet in a 22-day trial. Twelve ml of blood were collected from the jugular vein from each goat before and after the experiment for haematological and serum biochemical assays. Daily dry matter intake (DMI) was similar across treatments, ranging from 633 g to 765 g per goat per day. There was no difference in initial and final bodyweights of goats consuming various experimental diets. However, bodyweight gains were significantly higher in goats fed a diet with 50% leaf meal as compared with other treatment groups. There were no differences in haematological indices of Pedi goats except for mean corpuscular haemoglobin (Hb) concentration. Goats fed 50% leaf meal had significantly lower mean corpuscular haemoglobin concentration (MCHC) values as compared with other treatment groups. Similarly, there were no differences in the blood serum chemistry of goats that consumed various inclusion levels of V. karroo, except for serum total protein (TP) and alanine aminotransferase (ALT). Goats fed 50% leaf meal had depressed serum TP, while serum enzyme Alanine aminotransferase (ALT) concentration decreased significantly in goats fed 25% leaf meal as compared with those on the 20% dietary treatment. Tannin concentration of 8.2 g/kg dry matter (DM) had no toxic effect on experimental animals. A 40 % inclusion of V. karroo in a Setaria verticillata hay-based diet may be fed to indigenous Pedi goats without compromising the immunity system and health of the animals. <![CDATA[<b>Geographical influence of heat stress on milk production of Holstein dairy cattle on pasture in South Africa under current and future climatic conditions</b>]]> Heat stress, as a consequence of global warming, can have a profound effect on dairy cattle in South Africa. In this paper, current milk production data of Holstein dairy herds on pasture in South Africa, together with climate variables related to heat stress, were used to model and identify geographical areas for optimal milk production under current and future climatic conditions. To model the influence of heat stress on milk production of Holstein dairy herds on pasture in South Africa, the maximum entropy (Maxent) modelling technique was used in a novel approach to model and map optimal milk-producing areas. Geographical locations of farms with top milk-producing Holstein herds on pasture were used as presence-only data points. Only three of a possible eight climate variables that made significant contributions to the model were included, namely evaporation rate, relative humidity and mean annual temperature. The modelling technique showed good capability to capture the geographical influence of heat stress on milk production of Holstein dairy cattle and to reconstruct this relationship in sites where no data were available. The method performed well with low test omission rates, an area under curve (AUC) value of 0.929, and mean training data predictive rate of 0.66 (SD = 0.13). The modelled map indicated optimal milk production areas in the eastern parts of South Africa, which correlates well with the geographical influence of heat stress as represented by the temperature humidity index for the country. Future climate change projections (2046-2065) were used to predict optimal milk-producing areas for the future, indicating progressive shrinking of currently suitable areas and a geographical shift towards the southern parts of the east coast of South Africa. Possible long-term viable alternatives are suggested, including changes in nutrition and replacing existing breeds with more heat tolerant genotypes. <![CDATA[<b>Effect of taurine and bile acid supplementation and their interaction on performance, serum components, ileal viscosity and carcass characteristics of broiler chickens</b>]]> A 3 x 3 factorial experiment (4 pens/treatment, 10 birds/pen) was conducted with 3 levels of supplemental taurine (Tau) (0.0, 0.25 and 0.50%) and 3 levels of dissected bile acid (DBA): 0.0, 0.25 and 0.50% of the diet were arranged in a completely randomized design. Isocaloric and isonitrogenous starter and grower diets were fed ad libitum to chickens from 7 - 21 and 22 - 42 d, respectively. The measured parameters were body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR), fat digestibility, serum cholesterol (Chol), triglyceride (TG), high-density lipoprotein (HDL), and low-density lipoprotein (HDL). The supplementation of Tau had no effect on FI, BWG and FCR for all periods. Moreover, BWG and FCR were a function of the DBA level in the diet for the finisher and the cumulative periods; birds which received the highest level of DBA (0.50%) had the highest BWG and the best FCR as compared to 0.0 and 0.25%. Fat digestibility was significantly improved by Tau and DBA supplementation. DBA and Tau supplementation had increased serum components at 21 and 42 d of age. The supplementation of Tau or DBA in the diets did not affect carcass parameters at 42 d of age. However, a linear reduction on the small intestinal weight was observed as a result of DBA supplementation. Supplementation of the diets with Tau significantly increased bursa weights. The results of this study indicated that Tau had limited impact on performance, while the supplementation of DBA at 0.50% had the best improvements in performance and blood characteristics and this could be explained in part by its positive effect on fat digestibility.