Browsing by Author "Jordaan G.F."

Now showing 1 - 11 of 11
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    Epistaxis related to exercise-induced pulmonary haemorrhage in South African Thoroughbreds
    (2003) Weideman H.; Schoeman S.J.; Jordaan G.F.; Kidd M.
    This study investigated if environmental factors had an effect on the incidence of epistaxis related to exercise-induced pulmonary haemorrhage (EIPH) among racehorses in southern Africa. Data covering the period 1986-2001 and involving 778 532 race runs were analysed. This included the following information: date of race, age, sex, name of breeder, trainer, distance, jockey, state of going, weight carried, racing centre and altitude. Veterinarians employed by the Jockey Club suspended officially entered horses that presented with epistaxis (frank bleeding from the nostrils) after racing. On-course endoscopy is not performed as a standard practice at any southern African racetrack. Epistaxis was identified in 1287 horses (0.165 %). More horses presented with EIPH-related epistaxis (a) at sea level, (b) from May to October, (c) when older (>3 years), (d) after 1995, (e) on Fridays and Sundays, and (f) more in geldings than in mares or entire males. No association could be established between epistaxis and breeder, trainer, distance run, jockey, state of going and weight carried. It is concluded that the frequency of EIPH-related epistaxis is associated with altitude, winter and spring, sex and age. It is suggested that racing at lower altitudes may increase the probability of exercise-induced pulmonary haemorrhage.
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    Estimates of crossbreeding parameters in a multibreed beef cattle crossbreeding project
    (2000) Skrypzeck H.; Schoeman S.J.; Jordaan G.F.; Neser F.W.C.
    Data from purebred and crossbred cattle, consisting of the Afrikaner (A), Simmentaler (S) and Hereford (H) breeds managed in a relatively intensive but high stocking rate environment, were analysed to estimate breed direct effects, individual heterotic effects, breed maternal and maternal heterotic effects for birth weight (BW) and weaning weight (WW). Simmentaler breed direct effects, expressed as deviation from the general mean, were positive (P ≤ 0.01) for both traits. Hereford and Afrikaner breed direct effects were negative (P ≤ 0.01) for both traits while the Afrikaner breed direct effects exceeded those of the Hereford. Afrikaner direct maternal effects were positive (P ≤ 0.01) for both traits. The Hereford direct maternal effect was negative (P ≤ 0.05) (-2.9%) for WW. Simmentaler maternal effect was negative (P ≤ 0.01) for BW but non-significant (P ≥ 0.05) for WW. Individual heterotic effects for BW were significant (P ≤ 0.01) in H x S (3.5%) and S x A (11.0%) only. Individual heterotic effects were positive (P ≤ 0.01) for WW, with that of the H x A (9.8%) and S x A (6.7%) crosses exceeding the S x H (3.1%) cross. Maternal heterotic effects were non-significant (P ≥ 0.05) for both BW and WW.
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    Genetic and environmental parameters for ewe productivity in Merinos
    (2002) Duguma G.; Schoeman S.J.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Jordaan G.F.
    Data of 3272 lambing records collected on 818 ewes born from 689 dams and sired by 371 rams were used in the evaluation of ewe lifetime productivity (total number born, number weaned and total weight weaned). These records were collected from ewes born from 1969 to 1994 and which gave birth during the period from 1971 to 1999. Year of birth of ewe and ewe two-tooth liveweight affected the ewe productive traits investigated. Multiple born ewes were superior both in total number of lambs born and weaned compared to singles. Heritability estimates of 0.23, 0.17 and 0.20 were obtained for total number of lambs born (TLB), total number of lambs weaned (TLW) and total weight of lamb weaned per ewe over four lambing opportunities (TWW), respectively. For total weight weaned per ewe over the first lambing opportunity (TWW1) a heritability of 0.02 was estimated. Genetic correlation estimates of -0.10, 0.57 and 1.00 were obtained between TWW1 and TLB, TWW1 and TLW and TWW1 and TWW, respectively. High and positive genetic correlations ranging from 0.61 to 0.92 were estimated between ewe lifetime traits. Genetic progress could be expected when selection is applied on these traits. © South African Society for Animal Science.
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    Genetic and phenotypic variation of some reproductive traits in Egyptian buffalo
    (2001) Aziz M.A.; Schoeman S.J.; Jordaan G.F.; El-Chafie O.M.; Mahdy A.T.
    The objectives of this study were to determine the effects of season, year of calving and parity on lactation period, calving interval, number of days open and dry period in Egyptian buffalo, and to estimate genetic and phenotypic parameters for these traits using a multi-trait animal model. Season of calving, year of calving and parity affected the traits studied. Heritability estimates for lactation period, calving interval, dry period and number of days open were 0.09, 0.07, 0.13 and 0.08 respectively and repeatability estimates were 0.27, 0.14, 0.27 and 0.19 respectively. Estimates of the permanent environmental component (c2) were low. Genetic correlations between these traits were low and positive, except for that between lactation period and dry period, which was negative. A similar pattern was observed for phenotypic correlations, but these were higher than those observed for genetic correlations.
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    Genetic parameters for reproductive traits in a beef cattle herd estimated using multitrait analysis
    (2001) Van Der Westhuizen R.R.; Schoeman S.J.; Jordaan G.F.; Van Wyk J.B.
    The object of this study was to estimate heritabilities and genetic correlations for reproductive traits in a composite multibreed beef cattle herd using multitrait analysis. A REML procedure fitting a multitrait animal model was used to analyse data. Heritabilities and genetic correlations for calving interval (CI), calving date (CD), calving date with a penalty score (CDP) and age at first calving (AFC) were estimated as traits of the dam. The estimated heritabilities for CI, CD, CDP and AFC obtained in this study were 0.01, 0.04, 0.06 and 0.40 respectively with a repeatability of 0.07, 0.12 and 0.13 for CI, CD and CDP. Genetic correlations between traits varied from low to moderate, except for high correlations between CD and CDP (0.98), CI and CD (0.75) and between CI and CDP (0.79). Heritabilities, genetic correlations and repeatabilities of CD and CDP obtained in this study suggest that CD and CDP are the same traits and that selection for CDP rather then for CD does not have any additional advantages. Due to the additional advantages of CD over CI and the fact that CD is a less biased measurement of the female reproductive complex, CD and AFC (because of its high heritability) may be considered as selection criteria for improvement of reproduction in beef cattle herds.
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    Heritability estimates derived from threshold analyses for reproduction and stayability traits in a beef cattle herd
    (2001) Van Der Westhuizen R.R.; Schoeman S.J.; Jordaan G.F.; Van Wyk J.B.
    The object of this study was to estimate heritabilities and sire breeding values for stayability and reproductive traits in a composite multibreed beef cattle herd using a threshold model. A GFCAT set of programmes was used to analyse reproductive data. Heritabilities and product-moment correlations between predicted breeding values for stayability at 36, 48, 60, 72 and 84 months of age, calving success and longevity were estimated. The estimated heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08 respectively. Product-moment correlations between breeding values for stayability traits were low. The highest correlation of 0.22 was obtained between the ages of 36 and 48 months. Heritability estimates and correlations between traits appear to be of such a low magnitude that selection for these characteristics would result in limited genetic improvement, and also indicate that sires had little influence on the stayability, longevity or calving success of their daughters.
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    Pre-weaning growth traits of the Hereford breed in a multibreed composite beef cattle population
    (2000) Skrypzeck H.; Schoeman S.J.; Jordaan G.F.; Neser F.W.C.
    Data from a multibreed composite beef cattle population, managed under intensive irrigated grazing conditions, were used to estimate direct additive heritabilities (h2a), maternal heritabilities (h2m) and maternal permanent environmental effects (c2) for birth weight (BW) and weaning weight (WW) of the calf and cow efficiency of the dam (CE: WW/dam weight0.75 x 100). Calves born between 1968 and 1993 (n = 52628) had varying levels of Hereford genes, ranging from 0% to 100%, with an average of 19.3%. Direct heritabilities, fitting unitrait models, were 0.72, 0.54 and 0.19 for BW, WW and CE, respectively, with corresponding estimates of maternal heritabilities being 0.14, 0.21 and 0.42. Genetic correlations between direct and maternal effects (ram) were negative for all three traits, varying from -0.40 to -0.65. Maternal permanent environmental effects were 0.06, 0.12 and 0.11 for BW, WW and CE, respectively. Direct breeding values and maternal breeding values for BW and WW decreased with increasing proportion of Hereford. Direct breeding value for CE increased, while maternal breeding value for CE reached a minimum value at 0.62 proportion of Hereford.
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    The effect of Charolais and Hereford sires and straightbred and crossbred dams on pre-weaning growth of calves
    (2002) Dadi H.; Jordaan G.F.; Schoeman S.J.; Van der Westhuizen J.
    Weaning performance of calves sired by Charolais and Hereford on dams of Angus, Bonsmara and Hereford and various crossbred dam combinations was compared. Charolais sired calves were on average 5 kg heavier at birth and 20 kg heavier at weaning than Hereford sired calves. Among the three straightbred dam breeds, the Bonsmara weaned calves that were approximately 6% heavier than both the Angus and the Hereford calves. The use of crossbred dams having intermediate levels of Charolais composition is suggested in crossbreeding programmes in intensive production systems based on cultivated pastures under irrigation.
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    The influence of Charolais and Angus breeding levels on pre-weaning growth performance traits in crossbred calves
    (2002) Dadi H.; Schoeman S.J.; Jordaan G.F.; Van Der Westhuizen J.
    Data collected on birth and weaning weight traits of beef cattle calves over the period of 1968 to 1992 with varying levels of Angus and Charolais genes, ranging from 0% to 75%, were analysed to determine possible optimum breeding levels for birth weight (BW), weaning weight (WW) and pre-weaning average daily gain (ADG), fitting a unitrait animal model. The estimated heritabilities were used to predict direct (DBV) and maternal breeding values (MBV) for each animal. Best Linear Unbiased Estimates (BLUEs), DBVs and MBVs per genetic group estimated were regressed on proportions of Charolais and Angus breeding. The BLUEs of the traits increased with increasing proportion of Charolais, while they decreased with increasing Angus breeding levels. In general, MBVs increased with increasing the proportions of both breeds. The DBVs of the Charolais increased and reached a maximum at 35, 38, and 45% proportions of Charolais for BW, WW and ADG, respectively. Except for BW, DBVs of WW and ADG decreased as the genetic contribution of the Angus increased. No optimal Angus proportion was found in this herd within the specific environmental condition. It is suggested that increasing the proportion of the Charolais to intermediate levels would tend to improve the performances of pre-weaning traits. © South African Society for Animal Science.
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    The influence of outliers on a model for the estimation of crossbreeding parameters for weaning weight in a beef cattle herd
    (2002) Aziz M.A.; Schoeman S.J.; Jordaan G.F.
    Data on 17348 weaning weight records from a beef cattle crossbreeding operation were used to determine the effect of outliers on regression coefficients. Different criteria were used for detecting potential influential points. Eliminating a small number (932 or 5.4%) influential points resulted in the improvement of the model fitted. The R2 values increased from 41% to 49% while the mean square error was reduced from 672.9 to 500.4. The use of diagnostic statistics for detecting influential observations is recommended before any analysis is performed. © South African Society for Animal Science.
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    The influence of proportion of Simmentaler breeding in a multibreed synthetic beef cattle population on preweaning growth traits
    (2000) Schoeman S.J.; Jordaan G.F.; Skrypzeck H.
    Data from a multibreed composite beef cattle population managed under intensive irrigated grazing conditions were used to estimate direct additive heritabilities (h2a) and maternal heritabilities (h2m) for birth weight (BW) and weaning weight (WW) of the calf and cow efficiency of the dam (CE; WW/dam weight0.75). Calves born between 1968 and 1993 (n = 52 628) had varying levels of Simmentaler genes, ranging from 0% to 97%, with an average of 33.4%. Direct heritabilities fitting unitrait models were 0.66, 0.53 and 0.21 for BW, WW and CE respectively, with corresponding estimates of h2m being 0.22, 0.36 and 0.59. Genetic correlations between direct and maternal effects (ram) were negative for all three traits, varying from -0.32 to -0.63. Direct breeding values for BW and WW decreased and maternal breeding values increased with increasing proportion of Simmentaler. Cow efficiency was unaffected by an increase in the proportion of Simmentaler.