Scielo RSS <![CDATA[South African Journal of Animal Science]]> vol. 47 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Basal metabolic rate scaled to body mass between species by the fractal dimension of the vascular system and body composition</b>]]> Exercise-induced maximum aerobic metabolic rate (MMR) is related to the fractal dimension (D) of the self-similar vascular blood transport system by a whole body mass (Mw) power with exponent b of the form b = D/3. The principle of self-similarity of the vascular system is in agreement with each organ in the body having a major artery supplying it with blood from the heart and a major vein returning it. This implies that the whole body fractal vascular dimension D is also applicable to all organs or collections of organs such as the viscera and skeletal muscle. The principal reason that basal metabolic rate (BMR) and MMR scale with different power exponents to whole body mass is that MMR is due mainly to respiration in skeletal muscle during exercise and BMR to respiration in the viscera during rest. It follows, therefore, from the self-similarity of the vascular system that BMR is related to viscera mass (Mv)in the same way that MMR is related to muscle mass. Hence, BMR scales to Mv with exponent b and, additionally, if Mv scales to Mw with exponent d, then BMR will scale with Mw with exponent bd, where bd = b²for b = d. Here this approach is justified by an assessment of the scaling of viscera and its components with total body mass. The applicability of fractal vascular scaling to the sum of visceral organ metabolic rate contributions is confirmed from organ tissue slices, mitochondrial surface areas, and blood oxygen transport. Estimates obtained from oxygen halfsaturation partial pressure scaling exponents show that BMR scaling with b²is of general occurrence between species. <![CDATA[<b>Effect of post-slaughter handling during distribution on microbiological quality and safety of meat in the formal and informal sectors of South Africa</b><b>: </b><b>A review</b>]]> Global reports on illnesses and deaths related to food consumption continue to raise concern in most countries. This has led to diligent efforts to improve the manner in which food is handled. Hygienic handling of carcasses after slaughter is critical in preventing contamination and ensuring meat safety in both formal and informal meat trading sectors. However, in the informal sector, regulations as prescribed in the Meat Safety Act No. 40 of 2000, which have been set to protect consumer health, are not always adhered to. Although these regulations are put into practice in the formal sector, meat safety challenges associated with meat handling during distribution continue to raise concern. The distribution stage is the most critical period, during which the quality of meat can easily be compromised. Furthermore, meat inspection at the abattoir covers only visual assessment, without considering microbiological tests. Meeting food safety requirements set by government regulations remains a challenge to almost all food processors. This paper reviews the impact of post-slaughter handling on carcass quality and its implications for meat safety during the distribution stage in the formal and informal sectors in South Africa. It also details how meat handling in the informal meat trade exposes consumers to high health risks and recommends that governments create legislation that would be applicable to carcasses produced in the informal sector to align this sector with the regulations governing food production. <![CDATA[<b>Methane, nitrous oxide emissions and mitigation strategies for livestock in developing countries: A review</b>]]> Methane (CH4) and nitrous oxide (N2O) are two important greenhouse gases (GHGs) that are emitted into the atmosphere by livestock during the process of enteric fermentation and manure management. Developing countries produce a large quantity of those emissions, caused mainly by inefficient animal rearing systems, feed production and manure management. This paper outlines the CH4 and N2O emitted from livestock in developing countries and the mitigation actions that could be put in place to reduce atmospheric emissions and increase animal productivity. Emission intensity expresses emission (CO2 equivalents) per unit of product and describes it in relation to the capacity of local animals to produce from local resources. Developing countries are characterized by low production per animal and, consequently, high emission intensity. The emission intensity of dairy cattle in developing countries ranges from 2 to 9 kg CO2-eq/kg fat and protein corrected milk (FPCM) and in only a few cases is below 2 kg CO2-eq/kg FPCM. In sub-Saharan Africa, the average emission intensity is 7.5 kg CO2-eq/kg FPCM for dairy cattle, 71 kg CO2-eq/kg of carcass weight for beef cattle, 6.9 kg CO2-eq/kg FPCM for sheep and goats, and 5 kg CO2-eq/kg eggs for chickens. Taking into account the limited economic and technical resources in most developing countries, the application of appropriate mitigation tools is recommended to reduce the emissions of CH4 and N2O gases in the atmosphere. Increasing livestock productivity through selection and feeding is the most effective tool to reduce emission intensity. <![CDATA[<b>Oxidative stress biomarkers in West African Dwarf goats reared under intensive and semi-intensive production systems</b>]]> This study explored the variation in physiological oxidative status of West African Dwarf (WAD) goats as the rainy season progressed in a humid climate in south-west Nigeria. A total of 24 growing WAD bucks, averaging 10.5 kg + 0.78 liveweight, were reared under intensive and semi-intensive management systems during the rainy season. Twelve (12) bucks were used for each management system. Animals raised intensively were fed Megathyrsus maximus hay ad libitum, while those reared semi-intensively were allowed to graze freely in a fenced paddock. Their diets were supplemented with a maize grain-based concentrate. Blood samples were collected at the onset of the experiment and fortnightly throughout the 16-week experimental period. Oxidative stress biomarkers in blood were measured and analysed separately for each rearing system using repeated measures analysis. Means of oxidative stress biomarkers measured at the beginning and end of the rainy season were compared using a T-test. Results showed that intensively managed goats had significantly higher levels of bilirubin and uric acid in the early season than in the late rainy season. In semi-intensively managed goats, bilirubin, uric acid, and glutathione (GSH) levels were significantly higher at the start compared with the end of the rainy season. It could be concluded that the antioxidant capacity of WAD goats was greater early in the rainy season compared with the late rainy season under both management systems. Thus, during the early raining season WAD goats tend to have higher antioxidant capacity and, consequently, better immune responses, while the opposite is true during the late rainy season. <![CDATA[<b>Effects of mannan-oligosaccharides-supplemented diets on production performance of four close-bred flocks of Japanese quail breeders</b>]]> The present study was conducted to find out the dietary effects of mannan-oligosaccharides (MOS) supplemented diets on the production performance of four close-bred flocks (CBFs) of Japanese quail (Coturnix coturnix japonica) breeders. A total of 960 twelve-week-old birds of four CBFs were randomly divided into four groups (n = 240) with 12 replicates (n = 20). Birds were fed a corn-based basal diet or the same diet supplemented with 0.25%, 0.50%, and 1.0% MOS for 15 weeks. The authors analysed the data by two-way ANOVA techniques using SAS (Statistical Analysis System). Birds fed MOS-supplemented diets had significantly higher body and egg weight, egg mass, and egg number than the control group. Similarly, the feed conversion ratio (FCR)/dozen eggs, FCR/kg egg mass, and mortality were significantly lower in MOS supplemented groups. However, no significant effect of MOS supplementation was recorded on feed intake and egg production of birds. None of the parameters differed significantly among CBFs. The results showed that feeding MOS as a replacement for antibiotic growth factor may positively influence the production performance and health of Japanese quail breeders. <![CDATA[<b>The influence of polyethylene glycol inclusion in <i>Vachellia tortilis </i>leaf meal on nitrogen balance in growing pigs</b>]]> The incorporation of polyethylene glycol (PEG), a tannin binding agent, in high tannin feedstuff is known to prevent tannin-protein complexes. Environmental contamination with nitrogen-containing products in manure is a topical issue in the tropics. The objective of the study was to determine the extent to which the incorporation of PEG in Vachellia tortilis leaf meal improved nitrogen balance, serum iron, and phosphorus in growing pigs. Forty-eight clinically healthy male PIC pigs (31.3 ± 1.28 kg; Landrace x Large White) were allotted to individual pens in a completely randomized design, with eight pigs per treatment. They were offered a diet that contained 150 g V. tortilis/kg dry matter (DM). The diets were treated with 0, 5, 10, 15, 20, and 25 g PEG/kg. As PEG inclusion increased, serum iron concentration also rose until it reached a plateau. Nitrogen (N) utilisation and retention significantly increased linearly with PEG inclusion. Nitrogen excretion through faeces and urine significantly decreased linearly when increasing the amount of PEG in V. tortilis leaf meal in feed offered to pigs. Nitrogen utilization significantly increased linearly as the inclusion of PEG rose. It can be concluded that the inclusion of PEG increased N balance. <![CDATA[<b>Phenotypic and genetic parameters for selected production and reproduction traits of Mpwapwa cattle in low-input production systems</b>]]> The objective of this study was to assess the genetic improvement programme of the Mpwapwa dairy cattle breed over the past four decades, based on on-station selection and breeding. Estimates of genetic parameters and genetic trends for total lactation milk yield (LMY), 305-day lactation milk yield (305LMY), lactation length (LL), age at first calving (AFC), and calving interval (CI) were derived. The study used 1,003 lactation records from 385 cows and 78 sires collected from 1967 to 2012. Genetic parameters were estimated using an animal model procedure with ASReml software. The heritability for LMY and 305LMY were moderately high (0.33 ± 0.11-0.44 ± 0.04) and low for LL (0.13 ± 0.17.0). Repeatability for LMY and 305LMY was high (0.62 ± 0.04-0.70 ± 0.03) and moderate for LL (0.27 ± 0.06). The heritability for AFC (0.13 ± 0.11) and CI (0.10 ± 0.05) were low. The repeatability for CI was low (0.10 ± 0.05). Genetic correlation of 305LMY with LMY and CI were 0.87 ± 0.02 and -0.06 ± 0.009, respectively, while the corresponding phenotypic correlation estimates were 0.82 ± 0.01 and -0.01 ± 0.001. Variation among animal estimated breeding values (EBV) was significant, suggesting that selection to improve these traits is feasible. Thirty seven out of 78 sires had favourable EBV (0-900 kg) for milk yield, which suggests that selection for specific sires could result in increased LMY. Annual rates of sires EBV change for 305LMY, LL, CI, and AFC were -0.05, 0.15, and -0.14 days, respectively. All these traits showed that a decline in genetic progress for Mpwapwa dairy cattle in the on-station breeding programme. <![CDATA[<b>Changes in the composition and fatty acid profile of Najdi ewes' milk before and after weaning</b>]]> This trial aimed to study the changes in the yield, composition, and fatty acid (FA) profile of ewes' milk during suckling and milking periods. Nineteen multiparous Najdi ewes were kept under identical management and feeding conditions during a 12-week trial that was divided into two periods. Milk samples were collected on each sampling day from the total yield during the suckling (3rd, 6th, and 9th week) and milking (12th week) periods. The milk yield and the total solids, fat, protein, and lactose contents of the milk remained constant throughout the suckling weeks, but the protein content increased and milk yield and lactose content decreased after weaning. There were no differences in milk saturated FA (SFA), unsaturated FA (UFA), and monounsaturated FA (MUFA) contents during the suckling and milking periods, whereas the polyunsaturated FA content increased during the milking period. There were no differences in the individual milk SFA during the weeks of suckling, but the contents of caproic acid (C6:0), caprylic acid (C8:0), margaric acid (C17:0), and stearic acid (C18:0) decreased. However, myristic acid (C14:0), lauric acid (C12:0), and isomers of pentadecanoic (C15:0) acid increased during the milking period. The percentage of vaccenic acid (C18:1A11t), rumenic acid (C18:2A9c,11t; conjugated linoleic acid (CLA)), ω-3 FA group, and the atherogenicity index did not differ during the suckling period, but increased after weaning in the 12th week of lactation. This study demonstrated that weaning lambs in Najdi ewes is probably a factor that strongly affects milk traits by changing yield, composition, and FA profile. <![CDATA[<b>Preliminary genome-wide association study for wet-dry phenotype in smallholder ovine populations in South Africa</b>]]> The aim of this study was to identify single nucleotide polymorphisms (SNPs) associated with genomic region underlying variation in the binomial reproductive trait 'wet-dry' in sheep. The wet-dry phenotype was used to represent the reproductive status of the ewes, divided into two categories, dry (ewes that did not lamb or that lost a lamb) and wet (ewes that had lambed and had at least one suckling lamb). Wet-dry records were obtained from smallholder farmers (n = 176) and Nortier Research Farm (n = 131) for the 2014 breeding season. Ages of the ewes ranged from 1 year to 6+ years. Data from 307 individuals were analysed, of which 172 Dorpers and 4 White Dorpers were from smallholder sheep flocks and 48 Dorpers, 46 Namaqua Afrikaners, 26 South African Mutton Merinos, 4 South African Mutton Merino x Dorper and 7 Dorper x South African Mutton Merino crossbreds were from the research farm. A logistic regression model was fitted to adjust the data for the fixed effects of farm, breed, and age of the ewe and weight at mating as a covariate. Linkage disequilibrium (LD) and inbreeding coefficient were estimated using PLINK. Association analysis was performed using the genome-wide efficient mixed-model association package (GEMMA) to determine whether any significant SNPs were associated with the wet-dry reproductive trait. The wet-dry phenotype differed significantly between the smallholder (0.63 ± 0.04) and research farm flocks (0.79 ± 0.04). Genome-wide LD across all populations was r² = 0.36. Dorpers from the smallholder flock exhibited rapid LD decay versus the resource ovine populations. Inbreeding levels were also lower for the smallholder flock (4 ± 0.003%) versus the research flock (13 ± 0.008%). No significant SNPs were identified after correction for false discovery rate. The heritability estimate for wet-dry using SNP information was 0.24. This estimate concurs with the literature and indicates the possibility of using genomic selection to improve reproduction in smallholder sheep flocks. <![CDATA[<b>Effects of chromium supplementation on growth, nutrient digestibility and meat quality of growing pigs</b>]]> The aim of the study was to evaluate the effects of chromium picolinate (CrPic) on growth performance, nutrient digestibility, and protein and lipid quality of five anatomical parts in growing pigs. The 30-day study was conducted on eight castrated Topigs growing male pigs, with an initial bodyweight of 17.16 ± 0.62 kg. The pigs were assigned to two groups (C, E), housed in individual metabolic cages, and fed on conventional diets with 17.80% crude protein (CP) and 3078 kcal/kg metabolizable energy (ME). The diet of E was supplemented with 200 ppm CrPic. Samples of ingesta and faeces were collected in three balance periods of five days each. At the end of the experiment, blood samples were collected, all pigs were slaughtered, and meat (tenderloin, loin, ham, shoulder, and belly) samples were collected. No significant differences of productive or plasma parameters were noticed. The results of the balance study showed that CrPic did not influence the digestibility of nitrogen, but the digestibility of fat was significantly decreased for group E. The nutritional quality of the collected samples was evaluated for proximate analysis. The tenderloin and ham samples had increased protein concentrations compared with C group. For belly and ham, the fat concentrations decreased significantly. As a result of this observation, amino acids and fatty acid profiles were analysed and a significant improvement were determined for E regarding essential amino acids. The conclusion of the study was that CrPic had positive effects on protein and fat metabolism and the meat had functional food attributes. <![CDATA[<b>Chewing activity, metabolic profile and performance of high-producing dairy cows fed conventional forages, wheat straw or rice straw</b>]]> In this study, production and physiological responses of high-producing dairy cows fed wheat (WS) or rice (RS) straw, as a partial forage replacement for the conventional forages lucerne hay (LH) and maize silage (MS), were investigated. The straws were treated under dry alkaline conditions, adjusted pH (pH ~12), and then ensiled. Twelve lactating Holstein cows were used in a replicated (n = 4) 3 χ 3 Latin square design experiment with three periods of 21 days. Cows were offered one of three diets that differed in their forage sources: 1) 20% LH and 20% MS (control); 2) 12.8% LH, 12.8% MS; and 12.8% WS; and 3) 12.8% LH, 12.8% MS and 12.8% RS. Diet 1 had 60% concentrate, and diets 2 and 3 had 61.6% concentrate. Diets were iso-nitrogenous and iso-energetic. Supplemental buffer (NaHCO3) was omitted from the straw diets. However, straw diets contained greater sodium and dietary cation-anion difference (DCAD) compared with the control diet. Cows fed the WS had significantly greater apparent dry matter (DM) (69.7 versus 63.9%) and neutral detergent fibre (NDF) (55.4 versus 42.4%) digestibility than cows fed the control. Additionally, feeding either WS or RS significantly increased dry matter intake (DMI) (27.5 versus 25.6 kg/d) and milk production (48.4 versus 45.6 kg/d) compared with control, but milk components were unaffected by treatments. Plasma minerals and metabolites concentrations and ruminal, urinary and faecal pH were similar across treatments. Feeding WS and RS resulted in lower time spent chewing per kg DMI compared with the control (P = 0.01). Although there were no significant differences in performance between WS and RS, nutrient digestibility (DM, OM, and CP) was significantly higher while total chewing was lower for the WS diet than the RS diet. Partial inclusion of dry treated straw in lactating diets (12.8% DM basis) led to increases in sodium and DCAD levels and improved digestibility, DMI and milk yield without negative effects. <![CDATA[<b>Genetic parameters for test-day milk yield in tropical Holstein Friesian cattle fitting a multiple-lactation random regression animal model</b>]]> Accurate estimates of genetic parameters are essential for genetic improvement of milk yield in dairy cattle and for setting up breeding programmes. Estimates of genetic parameters from test-day models, particularly for Holstein Friesian cattle maintained in tropical environments, are scant in the literature. The objective of this study was therefore to estimate genetic parameters for milk yield by fitting a multiple-lactation random regression animal model (RRM) based on data from Ethiopian Holstein Friesian herds. Data were used from the first three lactations of cows that calved between 1997 and 2013. The data comprised 13 421 test-day milk yield records from 800 cows from two large dairy herds. Variance components were estimated using the average information restricted maximum likelihood method fitting an RRM. Heritability estimates for first, second, and third lactations ranged from 0.20 to 0.26, 0.15 to 0.27, and 0.17 to 0.28, respectively. Heritability estimates ranging from 0.15 to 0.28 indicate that effective genetic improvement should be accompanied by a corresponding improvement of the production environment. Across-lactation genetic correlations between first and second, second and third, and first and third lactations, expressed on a 305-day yield basis, were 0.88, 0.83, and 0.70, respectively. These genetic correlations, less than or equal to 0.88, indicate that different lactations are different traits. For an accurate evaluation of the genetic merit of animals for milk yield, lactations should be treated as different, but correlated traits in a multiple-lactation analysis. <![CDATA[<b>Modelling of digesta passage rates in grazing and browsing domestic and wild ruminant herbivores</b>]]> Ruminant utilization of poor-quality feeds is governed by rates of digestion and of passage through the rumen. The passage rate of feed material determines the quantity of bypass nutrients and the efficiency of synthesis of microbial protein in the rumen, making modelling of passage rate important. Artificial neural networks were used to develop models of liquid and solid passage rates. Studies that reported fractional passage rates, along with class and body mass of ruminants, were included in the dataset. Factors that affect rates of passage in all the studies were identified, which included animal and feed factors. The dataset was composed of observations of domestic and wild ruminants of variable body mass (1.5 to 1238 kg) from 74 studies and 17 ruminant species from various climatic regions. Observations were randomly divided into two data subsets: 75% for training and 25% for validation. Developed models accounted for 66 and 82% of the variation in prediction of passage rates for solid and liquid, respectively. On validation with an independent dataset, these models attained 42 and 64% of precision in predicting passage rates for solid and liquid, respectively. Liquid and solid prediction passage rate models had no linear and mean bias in prediction. This study developed better prediction models for solid and liquid passage rates for ruminants fed on a variety of diets and/or feeds from different climatic regions. <![CDATA[<b>Growth performance, immune status and organ morphometry in broilers fed<i> </i></b><b><i>Bacillus subtilis</i></b><b>-supplemented diet</b>]]> The present research aimed to investigate the effects of Bacillus subtilis (B. subtilis) on performance, immune system, gut, and lymphoid organs' microarchitecture in broilers. A total of 120 day-old broiler chicks were randomly distributed into four groups. The birds were fed a corn-soy-based basal diet (BD) (control) or the same BD supplemented with 10% zinc bacitracin (ZnB), 0.05 g/kg or 0.1 g/kg of B. subtilis (BS). The broilers fed 0.1 g/kg of B. subtilis had superior mean bodyweight and lower feed conversion ratio compared with the non-supplemented or ZnB-fed groups. The BS-0.1 group registered higher antibody titer against the Newcastle disease (ND) virus. Cell-mediated immune response post Phytohaemagglutinin-P (PHA-P) injection was attained by both BS-0.1 and BS-0.05 groups. Histomorphological study revealed increased thymus cortical width, and cortex/medulla ratio in BS-0.1 group compared with control. Area of bursal follicles and germinal centres of spleen also improved in BS-0.1 group. Compared to ZnB and control, higher villus height (VH) and villus crypt ratio of the duodenum and jejunum were recorded on day 21, and higher VH of duodenum and ileum was noted on day 35 in BS-0.1 and BS-0.05 groups. In conclusion, B. subtilis-type probiotics contributed positively to better growth performance, improved immune system and modulated morphology of lymphoid organs and gut mucosa in broilers. <![CDATA[<b>Effects of restricted feeding and re-alimentation of dietary protein or energy on compensatory growth of sheep</b>]]> The study investigated the effects of re-alimenting dietary protein or energy on growth, carcass characteristics and meat eating quality parameters of sheep. Twenty-seven intact rams (~9 months; 11.3 ± 0.5 kg) were randomly divided into three groups. Each group was fed a maintenance diet (MT) containing, on dry matter (DM) basis, 105 g/kg crude protein (CP) and 8.4 MJ/kg DM metabolizable energy (ME) for 30 days. Thereafter, they were continually fed the same MT or re-alimented with a high protein diet (HP) containing 169 g/kg DM CP and 9.3 MJ/kg ME or a high energy diet (HE) containing 123 g/kg DM CP and 10.6 MJ/kg ME for an additional 30 days to determine the effects of re-alimentation of protein or energy on their growth performance and carcass characteristics. During the initial 30-day period, DM intake (DMI) and growth performance were similar among the three groups. However, upon re-alimentation, average daily gain (ADG) and feed efficiency of sheep re-alimented with HP were greater than those maintained continually on MT or re-alimented with HE. Sheep on HP had higher feed efficiency, ADG and heavier carcasses than those fed MT or re-alimented with HE during the whole 60-day period. Growth of most viscera was less responsive to the restriction-re-alimentation feeding regimen except for the weights of the lungs, heart and intestines. Meat from sheep re-alimented with HE had a more intense 'sheepy' flavour than those fed MT or re-alimented with HP, but juiciness and tenderness were not affected. The higher ADG of sheep re-alimented with protein may be related more to enhanced efficiency of feed utilization than to higher DMI. <![CDATA[<b>Growth performance, body measurements, carcass composition and some internal organ characteristics in young Pekin ducks</b>]]> The aim of the study was to compare the bodyweight and body measurements, carcass composition, and characteristics of major visceral organs in male and female Pekin ducks. A total of 80 hybrid SM3 Heavy ducks were kept in a conventional building and fed complete commercial diets ad libitum. The male and female were weighed individually at one day old and their bodyweight and body measurements were determined at 21, 35 and 49 days of rearing. On day 49, 20 males and 20 females were chosen for slaughter. After slaughter, the carcasses and visceral organs were collected. No significant differences were observed between males and females in bodyweight (1 d, 58.6 vs 56.3 g to 49 d, 3518 vs 3433 g) and feed conversion ratio (FCR) (0-49 d, 2.44 vs 2.49 kg/kg gain). At 35 days old males demonstrated a significantly longer body and shanks and, at 49 days old a significantly longer body than females. The sex of ducks had no significant effect on the percentage of wings, muscles from breast and legs, skin with subcutaneous fat, abdominal fat and carcass remainder. The neck content was significantly greater in male carcasses than female ones. The contents of proventriculus, liver, and spleen in the bodies of males and females were similar. Gizzard percentage was significantly greater in males, and heart percentage was significantly greater in females. Due to their high bodyweight, good FCR, and favourable carcass composition, SM3 Heavy male ducks are more useful as broiler duck than females.