African Journals Online
South African Journal of Animal Science

Volume 33, Issue 1, 2003
ABSTRACTS

Genetic markers and their application in livestock breeding in South Africa: a review: review article

Van Marle-Koster, E.; Nel, L.H.

Abstract: The development of molecular biological techniques has created new possibilities for the selection and genetic improvement of livestock. The discovery of the PCR had a major impact on the research of eukaryotic genomes and contributed to the development and application of various DNA markers. DNA markers have already found wide application in parentage verification, individual identification and control of genetic disorders. The ultimate use of DNA markers would be to identify quantitative trait loci (QTL) in order to practice genotypic selection. This paper reviews DNA markers (RAPD, DFP, RFLP AFLP, minisatellites, microsatellites, SNP) and provides a brief overview of the current application of these markers in animal breeding.

Evaluation of the growth parameters of six commercial crossbred pig genotypes 1. Under commercial housing conditions in individual pens

Ferguson, N.S.; Kyriazis, S.T.

Abstract: Simulation modelling is an active part of animal nutrition, which relies on mathematical functions to predict the performance of an animal. The Gompertz equation is one such function that is simple, but fits animal growth data well and when used in conjunction with allometry, can accurately predict the potential growth of an animal. When using this approach only three parameters are needed to sufficiently describe a genotype, viz. an estimate of mature size (protein weight at maturity - P_m), a rate of maturing (B) and an estimate of fatness (lipid:protein ratio at maturity - LPR_m). The objective of this study was to estimate these parameters in South African commercial crossbred pigs under commercial environmental conditions. Thirty pigs each from six commercial genotypes were analysed using a serial slaughter method in which pigs were slaughtered at four and 14 days of age, and at 30, 40, 70, 80, 90 and 100 kg live weight. The animals were fed a choice between a high and low protein food and were housed in individual pens in two conventional open-sided housing facilities. The results indicated that there were no significant differences in mature weights or B of the various body chemical components between genotypes. This would support the use of a common set of growth parameters (B, P_m and LPR_m of 0.0114±0.0005 /d, 40.0±1.86 kg, and 1.77±0.213 kg lipid/kg protein, respectively), inclusive of all commercial crossbred male pigs. However, the rate body lipid matures was significantly lower than the rate of other components within two genotypes. Evidence for the use of common allometric coefficients to define growth was inconclusive.

Evaluation of the growth parameters of six commercial crossbred pig genotypes 2. Under ideal temperature conditions in chambers

Ferguson, N.S.; Kyriazis, S.T.

Abstract: To test whether animals grown under ideal temperature conditions would have different growth parameters to animals grown in more conventional housing, 60 Large White x Landrace male pigs from three genotypes were housed in six temperature-controlled chambers. The results were compared with data from a similar trial, with the same three genotypes, conducted in an open-sided house. Estimates of mature size (as measured by mature protein weight (P_m)), rate of maturing (B) and levels of inherent fatness (LPR_m) were obtained from serial slaughtering four pigs per genotype at 30, 40, 70, 80 and 90 kg live weight. The results indicate that for commercial crossbred male pigs there were no significant differences in the growth parameters between genotypes grown under ideal temperature conditions (Controlled), nor were there any differences between similar genotypes grown in Controlled vs. commercial conditions (Uncontrolled). The rate of maturing was also similar for all three genotypes and for all components. Mean estimates of P_m, B and LPR_m determined from both Controlled and Uncontrolled conditions can be combined to give values of 40.4±1.62 kg, 0.0114±0.0005 per day, and 1.67±0.153 kg/kg, respectively. Furthermore, controlling temperature had minimal effect on the allometric relationships between protein and the remaining body components for different genotypes. The determination of growth parameters for commercial crossbred pig genotypes can, therefore, be accomplished when the animals are grown individually in an open-sided house.

Kikuyu (Pennisetum clandestinum) intake determined by alkanes administered in a xantham gum suspension

Mann, J.; Stewart, P.G.

Abstract: The alkane method of measuring herbage intake in ruminants was compared with actual intake determined by transponder-controlled feed gates (Calan gates). Kikuyu (Pennisetum clandestinum) intakes of yearling bulls (Holstein-Friesland and Hereford) were measured for a period of seven days. No significant effect of breed on intake was found. Herbage intake calculated from the alkane technique (mean of morning and afternoon faecal sampling times) compared favourably with actual intake with an average intake of 6.25 kg DM/day (93 g DM/kg W^0.75/day) (CV 22%). However, a significant effect in the faecal sampling times on intake was observed. Herbage intake determined from alkane concentrations in the faecal samples that were collected in the morning underestimated actual intake by 11%, while intake calculated from faecal alkane concentrations of samples that were collected in the afternoon overestimated actual intake by 8%. It is hypothesised from this study that the dosing of the alkane (dotriacontane) should be every 12 hours when administered in a xantham gum suspension

The persistence to slaughter age of scars resulting from damage inflicted to ostrich skins during the grow-out phase

Meyer, A.; Cloete, S.W.P.; Brown, C.R.; Van Schalkwyk, S.J.

Abstract: Damage to ostrich skins in the form of cuts and scratches obtained during the grow-out phase results in lower quality skins that fetch lower prices. This represents major financial losses to the ostrich industry. The stage at which such damage occurs and its persistence to slaughter age, when it affects skin grading, is not known. In this study we assessed the persistence through to slaughter age of wounds inflicted on the skins of ostrich chicks at ages 1, 4, 7, 10 and 13 months. Superficial and deep wounds were investigated by either scratching the skin with a nail, or by cutting through the skin with a scalpel blade. Experimental animals were slaughtered at either 11 or 14 months of age and visible scars were assessed on the processed skins. The length and surface area of each scar were measured to obtain an adjusted scar size. Orientation of lacerations (dorso-ventral or anterior-posterior) proved to be unimportant. Cut wounds were persistent to slaughter as were scratch marks, with only a small percentage of scratch wounds incurred at a young age not persisting to slaughter age. Mean scar size at slaughter became smaller with an increase in age at which the wounds were inflicted, except at 13 months of age where it was assumed that the wounds had not had sufficient time to heal properly. Deep cut wounds caused larger scars at slaughter age than superficial scratch damage. It seems that both superficial (scratches) and deep (cuts) wounds will result in lower skin grading, irrespective of age of infliction. This indicates that changes in chick rearing practices are necessary to reduce the incidence of skin damage if skin quality is to be improved.

The effects of storage temperature and position on embryonic mortality of ostrich (Struthio camelus) eggs

Sahan, U.; Ipek, A.; Yilmaz, B.

Abstract: The present study was carried out with the aim of determining the effects of storage temperature and storage position on embryonic mortalities in ostrich eggs. A total of 229 ostrich eggs was collected from two commercial ostrich farms. The effects of storage temperature on embryonic mortality differed. Embryonic deaths (totalled for early, medium and late incubation) were determined at respectively 28.6, 32.0, 42.9% in groups of eggs from stored immediately after collection for seven days at 16 °C, 21 °C and 25 °C. Embryonic mortality was not affected by storing eggs for one week at 16 °C in either the vertical position (with the aircell at the top, or the aircell at the bottom) or the horizontal position. The percentage of embryonic mortalities was 25.8, 26.7, 24.1 for the different storage positions, respectively. These results indicate that ostrich eggs must be stored at 21 °C or less after collection to maximise hatchability and that embryonic survival is not affected by storing position.

Age trends in economically important traits of Merino ewes subjected to 10 years of divergent selection for multiple rearing ability

Cloete, S.W.P.; Gilmour, A.R.; Olivier, J.J.; Van Wyk, J.B.

Abstract: Data were recorded for annual reproduction, wool traits and pre-joining live weight of between 992 (for staple strength) to approximately 1200 production records of Merino ewes over the period from 1997 to 2002. The resource population has been divergently selected from the same base since 1986, either for (H line) or against (L line) maternal multiple rearing ability. When expressed relative to mean L line performance, the advantage in reproduction for the H line amounted to 34% for number of lambs born per ewe, 49% for number of lambs weaned per ewe and 56% for weight of lamb weaned per ewe. Overall trends in reproduction with an increase in age from 2 - 7+ years were consistent with corresponding trends in the literature. The shape of these curves did not differ between selection lines, i.e. no significant interaction between selection line and ewe age was found. Maiden H line ewes were heavier than L line contemporaries. Ewe joining weight increased with age in both lines. Line differences were reduced to a tendency in 3-year old ewes, and no subsequent line differences were found. The random non-linear component of the spline for ewe age also interacted with selection line for clean fleece weight. Conclusive advantages in favour of L line ewes were obtained at 3 - 6 years of age. In maiden ewes the line difference was restricted to a tendency in favour of the L line while no line difference occurred in 7-year old ewes. Ewes in the L line outperformed H line contemporaries for staple strength at four years of age, but no line difference was found at other ages. Coefficient of variation of fibre diameter and mean fibre diameter did not differ between lines. Coefficient of variation of fibre diameter generally declined curvi-linearly with an increase in ewe age, while fibre diameter showed a near linear increase. Estimates of h² for reproduction traits were 0.09±0.05 for number of lambs born per ewe, 0.05±0.05 for number of lambs weaned per ewe, and 0.05±0.05 for weight of lamb weaned per ewe. Corresponding h² estimates for wool traits were 0.34±0.08 for clean fleece weight, 0.05±0.05 for staple strength, 0.74±0.02 for coefficient of variation and 0.76±0.02 for fibre diameter. A h² estimate of 0.37±0.09 was obtained for ewe live weight at joining. Ewe permanent environment (c²_ewe) for the reproduction traits were 0.15±0.05 for number of lambs born per ewe, 0.19±0.05 for number of lambs weaned per ewe and 0.19±0.05 for weight of lamb weaned per ewe. The corresponding c²_ewe estimate for ewe joining weight was 0.40±0.09, while those for annual wool production traits were 0.31±0.08 for clean fleece weight and 0.12±0.05 for staple strength. Coefficient of variation and mean fibre diameter were not influenced by the ewe permanent environment. Line differences in age trends for wool traits and ewe joining weight were attributed to the drainage by reproduction on the reserves of H line ewes.

Sensory and objective mutton quality characteristics of SA Merino sheep selected for and against reproductive fitness

Hoffman, L.C.; Schmidt, D.; Muller, M.M.; Cloete, J.J.E.; Cloete, S.W.P.

Abstract: The effect of divergent selection for ewe multiple-rearing ability over a 15-year period on mutton quality was examined on the M. longissimus dorsi and M. semimembranosus of entire rams (R) and ewes (E) derived from two Merino lines. The selection of these two lines was based on maternal ranking values for multiple-rearing ability in a positive (P) and negative (N) line. In the negative line the replacements were based on the progeny of ewes that rear less than one lamb per joining or lambing opportunity (i.e. failed to lamb or lost all progeny born at least once). Progeny of ewes that reared more than one lamb per joining (i.e. reared twins at least once) were selected for the positive line. Ratings of sensory quality characteristics on the M. semimembranosus of the different genotype lines were obtained from a trained taste panel and related to data on physical and chemical characteristics. The moisture, total lipids, protein, ash, mineral concentrations and fatty acid composition of the M. semimembranosus were obtained. Physical parameters measured on the M. longissimus dorsi were: ultimate pH (pH₄₈), drip loss, cooking loss and Warner-Bratzler shear force (WBS). The influence of selection line on the sensory characteristics of the mutton was generally negligible, with the exception of the sensory attribute of first bite, where meat derived from the positive line was rated to be less tender than that of the negative line contemporaries. Chemically, the meat derived from the four different groups differed significantly in moisture and lipid content. The Positive Ram (PR) group had the highest moisture (ca. 76%) and the lowest lipid (ca. 7%) concentrations, whereas the Negative Ewe (NE) group had the lowest moisture (ca. 70%) and the highest lipid (ca. 10%) concentration. No significant differences were detected in the proximate chemical composition between the P and N lines. The pH₄₈ and WBS values showed significant differences between the four groups. The Negative Ram (NR) group had the highest pH₄₈ and the lowest WBS values. Results indicated a line effect on WBS tenderness. Meat derived from the positive line was less tender compared to the meat from the negative line. Differences between the reproductive lines pertaining to the mineral and fatty acid composition were also noted. A general tendency found, was for the Positive Ewes (PE) to have the highest and the NE to have the lowest mineral concentration. Significant differences were detected between the four groups in the individual fatty acids arachidic acid (C20:0), lignoceric acid (C24:0), eicosenoic acid (C20:1n-9), linoleic acid (C18:2n-6), homo-g-linolenic acid (C20:3n-6), arachidonic acid (C20:4n-6), eicosapentaenoic acid (C20:5n-3), docosadienoic acid (C22:2n-6), docosapentaenoic acid (C22:5n-3) and docosahexaenoic acid (C22:6n-3) concentrations. The PR group had the highest total PUFA (polyunsaturated fatty acids) content (ca. 8%) and the NR the lowest PUFA content (ca. 6%). The positive group had significantly higher C18:2n-6, C20:3n-6, C20:4n-6, C20:5n-3, C22:5n-3 and C22:6n-3 concentrations in comparison with the negative line. Significant difference in the total PUFA composition was also detected between lines, with the positive line showing a higher concentration (ca. 7%) compared to the negative line (ca. 6%).

The chemical composition, energy and amino acid digestibility of cowpeas used in poultry nutrition

Tshovhote, N.J.; Nesamvuni, A.E.; Raphulu, T.; Gous, R.M.

Abstract: The aim of this study was to determine the chemical composition and digestibility of cowpeas for use in poultry diets. Three cowpea cultivars, Glenda, Agrinawa and Indigenous were evaluated. The cultivars showed a relatively narrow range of protein concentrations (253.5 to 264.3 g/kg). The concentrations of amino acids (AA) varied among the cultivars. Dietary crude fibre levels varied from 51.5 to 58.1 g/kg. The cultivars were almost devoid of lipid and calcium, but were relatively high in phosphorus. The apparent and true metabolisable energy (AME_n and TME_n) values ranged from 9.88 to 10.02 and 10.29 to 10.78 MJ/kg DM, respectively. The mean digestibilities of the AA's ranged from 72.8 to 81.0%, with methionine having the highest digestibility and lysine the lowest. Cowpeas appear to be suitable for use in poultry feeds, their composition being equivalent to plant protein sources such as lupins and field peas, but lower in most nutrients compared with soybeans and canola.