Scielo RSS <![CDATA[South African Journal of Animal Science]]> vol. 38 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Genetic diversity and population structure of locally adapted South African chicken lines</b>: <b>implications for conservation</b>]]> In this study microsatellite markers were applied to investigate the genetic diversity and population structure of the six local chicken lines kept in the "Fowls for Africa" program, for better clarification of parameters for breed differentiation and genetic conservation of this valuable resource. The lines included the Black Australorp, Potchefstroom Koekoek, New Hampshire, Ovambo, Lebova- Venda and a Naked Neck line. Unbiased estimates for heterozygosity ranged from 50% in the Potchefstroom Koekoek to as high as 65% in the Naked Neck chickens. F IS values varied from as low as 0.16 for the Black Australorp line to as high as 0.35 for the Ovambo chickens. The FST values indicated moderate to high genetic differentiation between the Naked Neck and New Hampshire (0.11); Ovambo and Naked Neck lines (0.12), and Naked Neck and Lebowa- Venda (0.14). A total of 13% of the total genetic variation observed was between the chicken lines and 87% within the lines, supporting moderate genetic differentiation. Population structure was assessed using STRUCTURE where the Black Australorp was genetically best defined. Although six clusters for the different populations could be distinguished, the other lines were not as clearly defined, with individual birds tending to share more than one cluster. Results support a broad classification of these lines and further investigation of unique alleles is recommended for conservation of the lines within the program. <![CDATA[<b>Estimation of carcass composition and fat depots by means of subcutaneous adipocyte area and body and tail measurements in fat-tailed Akkaraman lambs</b>]]> This study was conducted to establish prediction equations for subcutaneous adipocyte area and body and tail measurements to estimate carcass composition and fat depots of indigenous Akkaraman lambs. As a major carcass tissue, body fat depots play an important role in deciding the optimum slaughter weight and grading of the carcass and meat quality. In this respect, forty male Akkaraman lambs were slaughtered and dissected to define the partitioning of fat among body depots after recording the body and tail measurements and taking adipose tissue samples. Mean cold carcass weight was 19.8 kg with a composition of 48.9% muscle, 30.3% fat, 19.6% bone and 1.2% waste. The dressing percentage was 48.4 %. Tail fat, subcutaneous fat and intermuscular fat were the major fat depots with overall means of 15.3%, 10.2% and 4.9%, respectively. Heart girth had the highest correlation (r = 0.91) with total body fat, while tail circumference had the highest correlation (: r = 0.72) with total body fat among the tail measurements. Correlation coefficients were also high between the adipocyte area and cold carcass (r = 0.84), total body fat (r = 0.84) and carcass fat (: r = 0.86) values. The established regression equations showed that tail fat (R² = 0.81), carcass fat (R² = 0.89) and total body fat (R² = 0.93) weights could be predicted with a high accuracy. It is concluded that carcass composition and body fat depots could be estimated with a high degree of accuracy by establishing the regression equations based on the adipocyte area and external measurements of the body and tail in Akkaraman lambs. <![CDATA[<b>Effect of dietary protein content on growth, uniformity and mortality of two commercial broiler strains</b>]]> Two experiments were conducted to determine the response in performance, including uniformity and mortality, of two broiler strains to dietary protein content. In Experiment 1, 480 Cobb 500 and 480 Ross 788 day-old sexed broiler chickens were housed in cages to 21 d with 10 chickens per cage, and in Experiment 2, lasting 42 d, 1680 sexed broiler chickens of each of these two strains were placed in 48 floor pens with 70 chickens per pen. Males and females were reared separately in both experiments. Six levels of dietary protein were fed for 21 d in both experiments, the composition changing for the period 22 to 42 d in Experiment 2. Body weight of each bird was measured at weekly intervals up to 21 d in Experiment 1, and of 20 randomly selected birds from each pen on days 1, 21 and 42 in the second experiment. Broilers in the latter trial were group-weighed by pen at weekly intervals. Mortality was monitored daily. The highest body weight gains and feed conversion efficiencies (FCE, g gain/ kg food) were recorded in Cobb, with a correspondingly higher food intake for the starter feed in both experiments. In the finisher period Ross birds consumed significantly more than Cobb broilers (9 g/d) but in this case there was no difference in growth rate between the two strains, resulting in a significantly poorer FCE for Ross (487 vs. 522 g gain/kg feed). The pattern of food intake in the finisher period also differed between the two strains: the Cobb birds increased their food intake as the dietary protein content was decreased, but food intake decreased with protein content in the Ross. Uniformity was greatest in both strains when they were fed the highest protein feeds in both experiments, the variation in live weight increasing as the protein content decreased. There was no nutritional effect on mortality, although mean overall mortality was twice as high in Cobb broilers. <![CDATA[<b>The performance and meat quality of Bonsmara steers raised in a feedlot, on conventional pastures or on organic pastures</b>]]> The effects of production system (feeding regime and time on feed) on growth performance, yield and economics and the effects of feeding regime, pre-slaughter treatment and electrical stimulation on meat quality were evaluated. Sixty Bonsmara steers were divided into three treatment groups, viz. feedlot, organic pasture and conventional pasture feeding. The feedlot and conventional pasture groups received a diet consisting of the same components, while the organic group received a diet with approved organic components. Initial weight, final live weight, warm carcass weight, cold carcass weight, warm and cold dressing percentage, average daily gain (ADG), pH at one and 24 hours post mortem, intramuscular fat content of the loin and subcutaneous back fat thickness were measured. The effects of electrical stimulation, feeding regime and pre-slaughter rest (recovery days at the abattoir) on meat tenderness were also investigated. Feedlot cattle had significantly higher final weights, warm and cold carcass weights, warm and cold dressing percentage, ADG, intramuscular fat content and back fat thickness measurements than organic and conventional pasture cattle. Pre-slaughter resting of animals for a week at the abattoir had no effect on meat tenderness, but electrical stimulation showed a significant positive response. Growth and carcass results were used to calculate price and feed margin for the different production systems. Feedlot cattle showed a higher profit than conventional and organic pasture groups, mainly due to faster and more efficient growth. The organic pasture cattle showed higher profit than the conventional pasture cattle as a result of the premium paid for the organically produced meat. <![CDATA[<b>Systematic factors that affect ostrich egg incubation traits</b>]]> Data obtained from a pair-mated ostrich flock maintained at Oudtshoorn, South Africa, were used to estimate environmental and genetic parameters for egg weight (EWT), water loss of incubated eggs up to 21 days (WL21), water loss up to 35 days (WL35), pipping time (PT) and weight of day-old chicks (CWT). Between 13806 and 19913 artificially incubated ostrich eggs during the 2003 to 2006 production years were used. Systematic factors affecting these traits such as production year, breeding season, female age, incubator type, storage time and ostrich breed, were initially assessed in single-trait-analyses, using ASREML. Eggs and chicks produced by Zimbabwean Blue (ZB) females were 5 and 7% heavier, respectively, than those produced by South African Black (SAB) females. WL21 and WL35 were not significantly different between ZB and SAB birds. There were trends for within-season effects on EWT and CWT, but no general, robust trend applicable to all years could be discerned. Season had a significant effect on WL21, WL35 and PT. An increase was apparent in EWT, CWT and PT with an increase in female age. There was a linear increase in pipping time as egg storage time prior to incubation increased. Incubator type had an effect on WL21 and WL35. Systematic factors affect traits such as WL21, WL35 and PT and should be accounted for before the estimation of genetic parameters. These factors should be considered when planning commercial ostrich husbandry and artificial incubation operations. <![CDATA[<b>Fish meal supplementation to early lactation Jersey cows grazing ryegrass pasture</b>]]> This trial was conducted to test the hypothesis that early lactation cows grazing ryegrass pasture and receiving maize and mineral supplementation could respond to additional supplementation with a protein source such as fish meal. Multiparous Jersey cows in early to mid lactation that grazed annual ryegrass pasture in spring were used in a randomised complete block design experiment. In addition to the pasture, cows received 6 kg (as is) of a maize-based supplement, including minerals, fed in two equal portions in the milking parlour. Three groups of 15 cows received a control, a low fish meal or a high fish meal treatment (0, 4 or 8% fish meal replacing maize). Milk yield was measured and milk samples taken fortnightly. A simultaneous study on rumen fermentation was conducted using eight rumen cannulated cows receiving the control and high fish meal treatments in a cross-over design experiment. Ruminal pH and ammonia-N and volatile fatty acid concentrations were measured. Milk yield, 4% fat-corrected milk yield and milk fat and protein percentages of cows on the low and high fish meal treatments (21.9 and 22.1 kg milk/d, 24.1 and 24.2 kg 4% fat corrected milk/d, 4.73 and 4.67% fat and 3.49 and 3.45% protein) were higher than the control (20.5 kg milk/d, 20.4 kg 4% fat corrected milk/d, 3.97% fat and 3.25% protein). The ruminal ammonia-N concentration was higher in the cows on the high fish meal treatment than the control (16.7 vs. 14.2 mg/dL). Fish meal supplementation to cows on ryegrass proved to be profitable. <![CDATA[<b>Changes in nutrient composition of kikuyu foggage as winter progressed</b>]]> Samples of kikuyu foggage (standing hay) were collected in northern KwaZulu-Natal from five adjoining paddocks to measure the changes in nutrient composition of the foggage as winter progressed. Leaves and stems were separated. The first samples collected on the 18th of May contained green to dry material at a ratio of 3 : 1 and that was reduced to practically no green material in July. Although the proportion of leaf decreased from 64.6% to 56.8% as winter progressed, differences were not significant. Crude protein (CP) levels and effective dry matter degradation decreased significantly with time while neutral and acid detergent fibre levels increased. The calcium (Ca) and phosphorus (P) concentrations in the leaves decreased significantly between the first collection and later collections, while these changes were less pronounced in the stems. At all stages the stems contained significantly lower concentrations of Ca than the leaves, while P concentrations between leaves and stems did not differ. Consequently, the Ca : P ratios in the leaves varied between 2.08 and 1.60 and that of the stems between 0.74 and 1.10. These results suggest that the significantly lower Ca levels in kikuyu stems compared to leaves could make a significant contribution to the variation in Ca : P ratios reported for kikuyu. The concentrations of the other elements measured did not differ between the leaves and stems. Concentrations of CP, potassium, magnesium, copper and selenium in the kikuyu foggage decreased rapidly from the first collection that contained a relatively high proportion of green material to later collections when the foggage was dry. <![CDATA[<b>Carcass characteristics and meat quality of progeny of five merino dam lines, crossed with dormer and suffolk sires</b>]]> This study details the slaughter traits of lambs born from a terminal crossbreeding experiment that involved five Merino type dam lines crossed with Dormer and Suffolk sires. Dam lines included dual purpose types; South African Mutton Merino (SAMM), Dohne Merino, SAMM rams crossed to commercial Merino ewes (SAMM cross) and specialist Merino lines selected either for clean fleece weight (FW+) or for an increased fertility (Rep+). Data include between 228 and 483 individual records, depending on the trait. The unadjusted fat depth 25 mm from the midline at the 13th rib of lambs from dual-purpose ewes was between 22 and 32% greater than that of lambs from FW+ Merino ewes. Progeny from Rep+ Merino ewes showed a closer resemblance to the progeny of dual-purpose breeds than to those of FW+ Merino ewes in this instance. Adjustment for slaughter weight eliminated these differences. The initial pH of meat from progeny of FW+ Merino ewes was lower than that from progeny of dual-purpose ewes, and Rep+ Merino ewes. No differences in Warner-Bratzler shear values of the meat were found between the different crosses. Crossbred progeny of the Merino lines performed satisfactorily for all the traits considered, and will not be discriminated against in the market. No conclusive differences in favour of either sire breed were found. <![CDATA[<b>Structural assessment of backcrossing using microsatellite markers</b>]]> Backcrossing, coupled with marker or gene assisted selection, can be used to introgress a specific gene or chromosomal region from one population into another. The objective of this study was to assess the genomic structure of cattle produced by backcrossing for loci that are unlinked to a locus that was being introgressed. Genotypes of the two parental populations, their F1 progeny, and two subsequent backcross generations of animals were determined at 34 microsatellite loci that were not linked to a locus being introgressed. There was little evidence to suggest any systematic genome-wide departure from pedigree derived expectation as a result of the breeding system. These data validate the desired intention of a backcrossing program that progressive generations migrate genotypically toward one of the parental type. <![CDATA[<b>Physical impact of grazing by sheep in the Nama Karoo subshrub/grass rangeland of South Africa on litter and dung distribution</b>]]> The direct short-term impact of three rates of stocking (4, 8 and 16 Small Stock Units/ha) on arid Nama Karoo vegetation (shrub/grass) was quantified in terms of dung distribution and trampling. Grazing, by mature Merino wethers took place for one month at a time over a period of two years (1995 and 1996). As expected, the quantity of litter and dung significantly increased with an increase in stocking rate. When litter and dung are expressed in terms of loss and excretion per animal, both decreased with increased stocking rate. On average 80% of the dung was excreted on only 10% of the camp area, which mostly took place at the watering and sleeping places. These findings demonstrate the complex interaction between grazing and soil parameters. <![CDATA[<b>The drying rate and chemical composition of field and artificially dried lucerne hay</b>]]> The drying rate and chemical composition of lucerne hay that was field dried (sun cured) or artificially dried in a forced air bulk drier (FABD) were compared during summer (which is the dry season in the Western Cape Province). On six hay cutting occasions, plant material was left in the field for 24 hours after which some material was transferred to a FABD while the rest was left in the field for sun curing. The drying rate of lucerne hay in the FABD was significantly higher than in the field. The chemical composition of sun cured and lucerne hay dried in the FABD did not differ significantly. The study showed that, under good hay making conditions, sun cured lucerne hay is just as good as artificially dried lucerne hay, although the drying rate in the FABD was higher than field drying.