The goal of this research was to document the influence of Line 1 Hereford cattle, developed by the United States Department of Agriculture at its research facility in Miles City, Montana, on Hereford populations in the United States, South Africa, Canada, Australia, Great Britain, and Uruguay. Line 1 Hereford cattle were line-bred at the USDA-Agricultural Research Service station of Fort Keogh in Miles City, Montana since 1934. The dissemination of germplasm from Fort Keogh began with the earliest recorded sales in 1948. Analytical approaches made use of both recorded pedigree and genomic markers. Pedigree records numbering nearly 14 million from the American Hereford Association, and 3 million from the Canadian Hereford Association were randomly sampled five times for each year from 1980-2008. Sampled animals were pseudo-mated to Line 1 sires, inbreeding coefficients of the resulting progeny were calculated and relationships of the sampled individuals to Line 1 were estimated as twice the maximum inbreeding coefficient. The Line 1 Hereford population was found to be ancestral to 82% of the current population of purebred Hereford cattle in the United States. The number of Hereford cattle in the Unites States that were related to Line 1 has increased by more than 2% per year. The greatest concentrations of Line 1 genetics were found in the central and Midwestern regions of the country, but Line 1 genetics were found in 48 of the 50 states. Proportion of Hereford cattle registered in Canada that were related to Line 1 increased from 26% to 68% between 1980 and 2007. Animals recorded in the Canadian Herdbook that had ancestors in the American Herdbook were found in 8 of the 9 provinces and of these, animals related to Line 1 Hereford were found in 6 provinces. Two hundred forty animals sampled from the Line 1 herd at Fort Keogh and 311 sires representative of the Hereford breed in the U.S. were genotyped for 50K SNP. Resulting genotypes were used to assess the probability that the animals sampled from the U.S. population were members of Line 1 Hereford. The average probability of membership was 0.20 and the regression of pedigree relationship on genomic probability of membership was 1.73 ± 0.11 (r = 0.65). A similar analysis of the relationship between Line 1 and a sample of the South African Hereford (n = 36) population was conducted using 34 microsatellite loci. It was found that the probability that South African Hereford cattle were descendants of the Line 1 Hereford population was 0.38 ± 0.08. Pedigree relationship of Hereford cattle registered in South Africa with Line 1 was 24%. Obtaining complete herdbooks from other countries proved infeasible. Therefore, pedigrees of highly used sires were used as inferred from the accuracy of their genetic evaluation for direct effects on weaning weight from Hereford populations in the United Kingdom, Australia, and Uruguay with that of Line 1 Hereford. Those estimated relationships were 0.22, 0.30, and 0.23, respectively. The apparent presence the Line 1 Hereford cattle maintain in Hereford cattle around the world is highly important. The observed relationship of Line 1 Hereford with other Hereford populations is indicative of the far-reaching and profound impact of a long-term research program.

A study was conducted to investigate the influence of antioxidant source and fatty acid saturation in a standard finishing diet on apparent digestibility, production performance, fatty acid composition and oxidative stability of lamb. The four dietary treatments consisted of the same basal diet (187 g CP- and 355 g NDF/kg DM) differing in the lipid source (30 g/kg of either saturated beef tallow or unsaturated soyabean oil) and type of antioxidant included (125 g/ton of either a synthetic or natural antioxidant). Eighty-four S.A. Mutton Merino lambs (27.64 ± 1.72 kg) were randomly allocated to the four dietary treatments (n=21 lambs per treatment) and subdivided into seven replicates per treatment (n=3 lambs per replicate). After dietary adaptation of 8 days all lambs received the experimental diets for the remaining period (41 days). A digestibility study was conducted over a 12-day period (4-day adaptation to the faecal bags followed by an 8-day collection period). Seven lambs per treatment were randomly selected and slaughtered at completion of the production study. Physical carcass characteristics, muscle pH, muscle- and subcutaneous fatty acid composition, as well as meat oxidative- (malonaldehyde content) and colour stability was measured. The apparent NDF digestibility was reduced (P =0.0548) with the inclusion of unsaturated soyabean oil in the diet compared to saturated beef tallow. This was associated with a significant (P <0.05) lower digestible NDF and ME content in the experimental diet. No significant (P >0.05) differences in dry matter intake, daily gain and feed efficiency of lambs occurred. The addition of unsaturated soyabean oil significantly increased (P =0.0003) the efficiency of ME utilisation in the diet. Lipid saturation level in finishing diets for lambs did not influence (P >0.05) the physical carcass characteristics and meat pH of lambs. Saturated beef tallow increased (P <0.05) the monounsaturated palmitoleic- and oleic acid content of lamb subcutaneous and/or muscle tissue, whereas the more unsaturated soyabean oil increased (P <0.05) the polyunsaturated linoleic acid, α-linolenic acid and CLA content of both muscle fat and subcutaneous lipid tissue. Monounsaturated vaccenic acid was increased in lamb meat when unsaturated soyabean oil was included in combination with the natural antioxidant. The total PUFA, total n-6 fatty acid and PUFA:SFA ratio of lamb meat increased (P <0.05) with the inclusion of the more unsaturated soyabean oil in the diet. A higher (P <0.0001) n-6:n-3 ratio occurred in the intramuscular fat of lambs fed the unsaturated soyabean oil diet. Unsaturated soyabean oil negatively influenced (P <0.05) the oxidative stability of lamb meat on days 0 (fresh) and 90 (frozen), compared to saturated tallow. The inclusion of a synthetic compared to a natural antioxidant in the diet decreased (P =0.0672) the apparent digestibility of NDF, which was also associated with a significantly (P =0.0159) lower digestible NDF content of the experimental diet. The meat pH measured 45 minutes after slaughter was significantly (P =0.009) decreased when a synthetic antioxidant was added to the diet. Meat pH measured at 24 hours post slaughter was lower (P =0.0433) when a natural antioxidant was added to the diet. With the exception of the natural antioxidant that increased (P <0.05) the saturated palmitic- and monounsaturated palmitoleic acid content of subcutaneous and/or muscle fat, and decreased (P <0.05) the monounsaturated stearic acid content of intramuscular fat, dietary antioxidant type did not to effect (P >0.05) the fatty acid composition of lamb meat, neither the colour- nor oxidative stability. These results suggest that the fatty acid profile of lamb can be manipulated by the saturation level of the lipid source included in the diet. However, the replacement of saturated tallow with unsaturated soyabean oil did not result, from a human health point of view, in the desirable PUFA:SFA and n-6:n-3 ratios in muscle fat and subcutaneous lipid tissue. Therefore, the manipulation of the fatty acid content of finishing diets to achieve the desirable ratios within lamb meat, as well as the optimal inclusion level of a bioflavonoid antioxidant warrants further research.

Up to the 1980âs marginal soils were successfully ploughed for crop production, but unfortunately those soils soon proved to be marginal. Due to high input costs, the Department of Agriculture soon implemented the âsoil conversion schemeâ to promote the conversion of those ploughed marginal soils to permanent pastures. It was especially the low maize prices that triggered the conversion scheme in the 1980âs. Regardless the implementation of the soil conversion scheme, many farmers unfortunately just abandoned some of these marginal fields which resulted in many hectares of unproductive previously cultivated fields, being referred to as abandoned fields. The aim of this study was to investigate a few abandoned fields at a single location in the semi-arid central Free State in an attempt to gather information on the dynamics of such disturbed ecosystems and identify their restoration potential. The study investigated the interaction between plant and soil variables to quantify the impact of different soil physical and chemical characteristics on vegetation dynamics (species composition and density). The species richness, as well as the influence of different soil characteristics were determined to identify which might have the biggest influence on the recovery potential of the disturbed area. The soil seed bank was also investigated to quantify the survival potential of climax grass species on abandoned fields, and why these species do not establish voluntarily on these disturbed areas. The main aim of the study was to quantify the influence of soil characteristics on the vegetation dynamics of abandoned fields. The results clearly showed that marginal soils, withdrawn from cash-crop cultivation, are among the most seriously degraded areas with low soil fertility (N and C content). It is creating a more favourable habitat for pioneer grass species. This study sheds more light on the poor natural rehabilitation rate of abandoned fields in the semi-arid Free State Province of South Africa. It was proven that the establishment of climax vegetation might be largely influenced by phosphorus (P), cation exchange capacity (CEC), nitrogen (N), carbon (C), soil compaction and the composition of the soil seed bank. It was note worthy that some of the abandoned fields still showed very slow progress in natural restoration after 20 years. The areas that showed least recovery needed to be cultivated and established with a cultivated pasture like Digitaria eriantha sub. eriantha. On the other hand, other areas recovered to such an extent that oversowing or the placement of Themeda triandra sheafs might improve restoration. The best recovered areas can only be upgraded in productivity by scientific management strategies which include long resting periods. Drastic human interference is an absolute necessity to speed up the process of plant succession (rehabilitation). Future investigation might include long-term trials to monitor the reaction of vegetation and soil characteristics to the introduction of organic matter as well as the seed of climax grass species.

Bush encroachment is currently of great concern in Marakele Park. The main motivation for this study, conducted during the 2003/2004 and 2004/2005 seasons, was to determine whether mechanical bush thinning, executed with a mechanical mulc her, namely the Barko Tractor, was successful in solving the bush encroachment problem in the areas where it was applied. The specific objectives of this study were to identify, describe and interpret the plant communities of a section of Marakele Park, and to establish the influences of the thinning treatments on the dynamics of the ecosystem, more specifically the regrowth and browse production of the woody plants, the species composition and dry matter (DM) yield of the herbaceous layer and the short term changes in the soil. Eight experimental plots (3 treatments, 3 controls, 2 coppice) were selected in three veld types (Acacia mellifera â Grewia flava, Combretum apiculatum â Grewia flava and Acacia erubescens â Dichrostachys cinerea), in which tree thinning was applied during 2002 and 2003. Each plot was 100 m x 200 m (20 000 m2 = 2 ha) in size. The vegetation of the plots was phytosociologically studied during the 2003/2004 season with the aid of the Braun-Blanquet vegetation sampling method. A total of 80 relevés were surveyed and upon analysis 3 major communities, 7 communities, 6 sub-communities and 3 variants were identified. The woody layer was quantified with a quantitative description technique, which is incorporated in the BECVOL-model. A step point-method and the Ecological Index Method were used to determine the species composition and veld condition of the herbaceous layer, respectively, and a harvesting method was used to determine the DM yield and the associated grazing capacity. The thinning treatments resulted in an initial decreased number of woody plants, but since no follow-up treatments were applied, a large number of new seedlings have since established and the majority of cut-plants coppiced vigorously. However, approximately three years after the thinning treatments the leaf biomass (ETTE ha-1) of the woody layer increased due to regrowth and re-encroachment to a point where negative interactions between the woody and herbaceous plants, as a result of competition for soil water and nutrients, were evident again. The species diversity of the herbaceous layer increased after the thinning treatments, but species normally associated with disturbed and overgrazed veld still dominated. It was concluded that the herbaceous layer of Marakele Park is in a poor ecological state and indications are that it is still deteriorating. The herbaceous DM yield did not respond to the thinning treatments as expected, except in areas protected from grazing herbivores. As a result, the grazing capacity of the Park was comparatively low. It is clear that Marakele Park is currently overstocked with various game species, especially of high density, selective short grass grazers. Thinning treatments will therefore not be successful unless the herbivore game numbers are reduced. Few soil variables changed significantly as a result of the thinning treatments, but in view of the fact that soil enrichment is a slow process, monitoring of the soil variables is recommended. The specific soil propertie s did, however, have a decisive influence on the vegetation type. The Combretum apiculatum â Grewia flava plots occurred on relatively shallow, gravelly soil, while the Acacia dominated plots occurred on deeper, more fertile soil. It was also concluded that the Barko Tractor, due to its size and weight, had a negative impact on the soil, mainly in the form of soil compaction. Subhabitat differentiation, rainfall and herbivory played an important role in the study area and indicated that the vegetation of Marakele Park displays both equilibrial and non-equilibrial trends. The high grazing pressure, together with the high incidence of coppice and re-encroachment of woody plants after the initial thinning treatments, as well as the lack of follow-up treatments, effectively neutralised the success of the mechanical bush thinning treatments. In order to restore these thinned areas from re-encroachment it will be necessary to cut the plants again and combine this effort with a cut-stump treatment (chemical herbicide). Due to the negative impact of the Barko Tractor, it should not be used again during any follow-up operation.

Not available

A study was conducted to evaluate the effects of different dietary energy levels on the productive (ADG, FCR, body weight, carcass) and reproductive (scrotum, testes, semen) characteristics of young Dorper rams. The study was carried out in two phases at the University of the Free State campus in Bloemfont ein, South Africa. Out of a group of 60 rams, 36 animals that were successfully trained for semen collection with the aid of an artificial vagina (AV), were selected to be part of this study and housed in individual metabolic cages. During phase 1 of this study, 36 (11 to 12 months old) Dorper rams with a mean initial body weight of 42.0 ± 0.52kg were randomly allocated to 3 groups (n=12 per group). Each group was randomly assigned to one of 3 experimental diets (treatments), formulated on a crude protein, degradable protein, calcium and phosphorus equivalent basis. A medium energy (Me) diet was formulated according to the National Research Council standards (NRC) for young growing rams to serve as the control diet. The metabolisable energy (ME) content of this diet (Me) was increased by 15 % for the high energy (He) and decreased by 15% for the low energy (Le) diets respectively. The actual ME levels for the Le, Me, He: were 6.52, 8.09 and 9.39 MJ/kg, respectively. The rams received the diets and fresh water ad libitum during a 127 day trial period and were weighed once a week. Their ADG, FCR and ME/kg weight gain calculated and compared amongst groups. During this trial, a digestibility trial was conducted for 7 days (during week 14 of the trial), using 5 randomly selected animals from each treatment group. The amount of feed offered and consumed by each animal as well as the feaces excreted daily were recorded. The chemical composition of the diets and the feaces (dry matter, energy, crude and degradable protein) were determined. Semen was collected from each ram, every forthnight for 3 consecutive days, with the aid of an AV and evaluated for volume, overall sperm motility, forward progression, sperm concentration, % live sperm and % normal sperm. The semen samples were then diluted (using a one-step dilution method with a cryodiluent containing 5% glycerol), packed in 0.25ml plastic straws, equilibrated for 4 hours and cryoperserved (frozen) in liquid nitrogen vapour (-70 ºC). One week after freezing, the semen was thawed (38 ºC for 30 seconds) and evaluated for the same qualitative parameters as the fresh semen. The results were compared amongst groups for each collection time, using ANOVA for repeated measures analysis procedures of SAS. The energy level of the diet and the collection week as well as their interaction was used as independent variables, while the different semen parameters cons idered were the dependent variables in the model. When means differed significantly, the Tukey method was used to compare means. At the end of this trial period, 6 rams per group were randomly selected and slaughtered at a commercial abbatoir. After slaughtering the carcass characteristics (cold carcass weight, dressing percentage, carcass grade, shoulder circumference, buttock circumference, backfat thickness, eye muscle area, marbeling and kidney fat) were recorded and compared amongst groups. The scrotum (total weight, skin weight, fat and circumference), testes (volume and weight) and epid ydimis (weight and volume) characteristics were also recorded and compared between groups, using ANOVA procedures of SAS. When means differed significantly the Tukey method was used to compare means. From the independent variables considered in the model, only the diet (ME level) had a significant effect on the parameters considered. In general, an increase in dietary energy level resulted in higher growth rates, better feed conversion rates, heavier carcasses, higher dressing percentages and greater fat deposition, both in the carcass, around the kid neys and in the scrotum (particularly in the neck region, over the testicular vascular cone). It seems that the energy requirements recommended by the NRC (1985) are not applicable for early mature Dorper replacement ram lambs, as those in the He group, (real ME level similar to NRC recommendations) deposited excessive fat in their body. Despite the significant differences induced by the He on the growth performance, carcass characteristics as well as on the scrotal and testicular characteristics of Dorper rams, no detrimental effects were recorded in their semen quantity, quality and cryotole rance. During the following 90 days (phase 2), the remaining rams (n=6 per group) were further maintained on the Le diet for 90 days. This was done to simulate the situation when overconditioned (fat) rams bought at auctions are placed on low energy diets (veld). Other objectives of this trial phase were to evaluate if the fat deposits accumulated in the scrota of rams fed on high energy diets are mobilized during subsequent periods of moderate nutritional restriction and if these nutritional restrictions induce any changes on the semen characteristics of rams. During this phase of the trial, semen was collected, with the aid of an AV, every 3 weeks during 2 consecutive days. The semen was evaluated using the same procedures described for phase 1 of this study. The rams were slaughtered at the end of this trial period (90 days) at a commercial abattoir. After slaughtering, the carcass characteristics (cold carcass weight, dressing percentage, carcass grade, shoulder circumference, buttock circumference, backfat thickness, eye muscle area, marbeling and kidney fat), the testicular (volume and weight), the scrotal (weight, circumference, skin weight and fat) and the epididymis characteristics (weight and volume) were also recorded and compared amongst groups. Data was analysed statistically using the same procedures as described for phase 1. The results of this trial clearly indicated that the scrotal fat deposits of rams previously fed on the He diet are mobilized (at least partially) during subsequent periods of moderate dietary energy restrictions without adverse effects on semen quantity and qua lity. This is the first time that such finding is reported. Further research on the effect of high energy diets on subsequent ram fertility (short and long terms), as well as their reversibility are warranted. Different age groups, feeding regimes and other management practices must also be associated to high energy diets in order to fully evaluate the effect of these common practices on subsequent ram fertility.

Genetic (co)variances for yearling body weight (BW), clean fleece weight (CFW) and mean fibre diameter (MFD) in the SA Dohne Merino population were estimated using records of 107 389 animals recorded between 1992 and 2004. The data include records of 1 530 sires and 45 178 dams. An animal model with direct and maternal additive, maternal permanent and temporary environmental effects was fitted for all traits. Sire-flock (SF) and sire-flock-year-season (SFYS) was included as additional random effects. Fixed effects were (FYSSM) (1594 classes), type of birth (singles, multiples), age of dam (2 to 7+ years) and average age (± SD) at measurement fitted as a linear covariate (385 ± 12 days). Estimates obtained by single -trait analyses were used as starting values in three-trait analyses. The direct genetic heritability estimates for FD, CFW and BW obtained from the three-trait analysis were 0.447 (0.009), 0.216 (0.008) and 0.277 (0.008) respectively. The genetic correlations were 0.050 between BW and CFW, 0.100 between BW and FD and 0.139 between FD and CFW. The phenotypic correlations were 0.318 between BW and CFW, 0.129 between BW and FD and 0.180 between FD and CFW. Direct genetic correlations of BW, CFW and MFD were positive, which suggest that selection for bigger and heavier sheep would generally lead to a stronger MFD and higher CFW. Because these values are very low the subsequent effect of this phenomenon would be that the effect of selection for body traits on fleece traits would be very small and vice versa. Genetic trends were calculated using the annual average breeding value estimates (EBV) for each trait. According to the genetic trends derived, the selection policy followed did cause genetic change in the traits studied, even though it was slow. The level of inbreeding (F) in the South African Dohne Merino sheep population is very low. The proportion of animals that was inbred to some extent increased from 0% (average F=0) in 1980 to 38% in 2003 (average F=1.22%). No significant inbreeding depression on BW, CFW and MFD could be found. In general the results suggest that inbreeding at present is not a serious problem in the South African Dohne Merino breed.

Incremental levels of sun-dried and coarsely ground cactus pear (Opuntia ficus-indica var. Algerian) cladodes were used to substitute part of the lucerne hay in balanced diets and fed to 28 Dorper wethers. The extent to which sun-dried and coarsely ground Opuntia cladodes can be incorporated in balanced sheep diets without effecting sheep performance was investigated over a period of 70 days. The three treatment diets (T0, T24 and T36) used in this study comprised respectively (air-dry basis) 0, 240 and 360 g/kg sun-dried, coarsely ground Opuntia; 660, 410 and 285 g/kg coarsely ground lucerne hay; 300 g/kg yellow maize meal; 0, 10 and 15 g/kg feed grade urea; and 40 g/kg molasses meal. The dry matter intake (DMI) varied little between diets but the apparent digestibility increased [P<0.05; 71.4% (T0) vs. 75.6% (T36)]. The average daily gain (ADG) of the wethers decreased slightly as Opuntia inclusion increased. This suggests that the overall effects of the diets on the performance of the wethers were small. As the inclusion level of Opuntia increased in the diets, the water intake of the wethers also increased (P<0.05; T0 vs. T36), while urine excretion showed little increase (P>0.05). The faeces DM excreted remained the same for all diets, but with the higher levels of Opuntia inclusion the DM content of the faeces excreted visibly decreased considerably. It is suggested that the mucilage ingested via the Opuntia and present in the digestive tract of the wethers may have interacted with the water fraction in the digesta, rendering some of the water unavailable for absorption. Hence, the wethers were compelled to drink more water to compensate for this extra water loss via the faeces. The wetter faeces were assumed to be the result of diarrhoea by some researchers, but the wet faeces lacked the customary foul smell associated with diarrhoea. Opuntia inclusion in the diets had no effect on carcass characteristics of the wethers (weight, fat thickness, surface area of musculus longissimus dorsi and relative tissue coefficients). This suggests that the effect of Opuntia in the treatment diets on the carcass weight and quality of the wethers were small. From these results, it seems that, irrespective of the dietary treatment, adequate nutrients for sheep maintenance and production was supplied by the diets. Sun-dried and ground Opuntia cladodes can be seen as an alternative feed supplement in semi-arid and arid regions of most countries that can be included in sheep maintenance or production diets without any detrimental effects on animal performance or carcass quality. It is recommended that research should focus on the formulation of Opuntia-based production diets with a high energy content, to be used in feedlots. The effect of mucilage on the wetter faeces excreted by sheep on Opuntia-based diets and what happens in the alimentary canal also needs further investigation.

Merino sheep are an important resource for South Afric an farmers, providing meat and wool and thus an important income source. Indigenous and locally developed breeds are an important asset for many reasons, but particularly because, over time, they have developed unique combinations of adaptive traits to respond to the pressures of the local environment. To be able to distinguish between breeds for conservation and utilization purposes, the genetic variability, population structure and phylogenetic relationships were determined. Seven different Merino genotypes were sampled. These included the Dormer, SA Merino, SA Mutton Merino, Landsheep, Letelle, Dohne and Afrino. The indigenous and locally developed breeds comprised of the Damara, Pedi, Blinkhaar Ronderib Afrikaner, Blackhead Persian, Blackhead Speckled Persian, Redhead Persian, Redhead Speckled Persian, Zulu, Namaqua Afrikaner, Karakul, Swazi, Van Rooy and Dorper. The Merino, indigenous and locally developed breeds were assessed for genetic diversity using 24 microsatellites. Different statistical analyses were performed to determine the genetic variation, genetic relationships and genetic differentiation of the breeds. The SA Merino showed a high number of very distinct alleles. This study confirmed a higher variability of the SA Merino when compared with the other breeds. The genetic distance between the SA Merino and SA Mutton Merino, both fine wool breeds, was high indicating that these two breeds are relatively distant from each other. The Afrino known to have 25% SA Merino, 25% Ronderib Afrikaner and 50% SA Mutton Merino, indicated a closer relationship with the SA Mutton Merino. This result confirmed the development of the breed. From the phylogenetic analysis between the seven Merino genotypes, when compared to the other estimates obtained in the study, it was evident that the Merino genotypes in South Africa have more within breed variation than between breed variation. The genetic distance estimates observed for the indigenous fat-tailed breeds were relatively high indicating that even between these breeds genetic differences exist. As expected, a smaller genetic distance between the Persian varieties was observed. Genetic distances between the developed breeds supported their ancestral development. The results of the indigenous and locally developed breeds present the first study of the genetic characterization of these breeds using microsatellite markers in South Africa. Southern Africa is hosting a very large sheep (Merino, indigenous and locally developed) genetic resource. Adapted to the agricultural production systems of the continent, it represents a unique resource that has great potential for further development of its productivity.

A line x environment interaction study with grade Afrikaner cattle was established at Matopos Research Station, Zimbabwe, in 1956. From a grade pool of 200 cows, two selection lines of 100 cows were reared in different management environments. The non-supplemented (NS) line relied on the range throughout the year and was mated to calve with the onset of the rains (December to February). The supplemented (S) line was offered protein-rich supplements during the dry season and mated to calve prior to the onset of the rains (October to December). Bull selection based on weight at weaning was to develop lines adapted to their respective environments. After approximately 2 generations of selection, lines were sub-divided into 4 sub-lines, consisting of 75 cows each. One sub-line remained within each environment as a control; the remaining sub-lines were interchanged between environments. Bulls were selected within control lines, while replacement heifers were generated within sub-line. Heifers were selected on weight at mating and replacement rates were dictated by the sub-line with the least number of suitable animals (>265kg). Data collected over a 40-year period representing 6 generations of selection were analyzed to determine a) genetic and environmental factors influencing calf growth and survival and cow fertility, b) direct and correlated responses to selection and c) presence and importance of genotype x environment interactions. Productivity in the S environment, in terms of calf growth and cow fertility, was superior compared with the NS environment. While there were no differences in birth weight, calves born early in the S environment were estimated to be 90kg (33%) heavier at 18 months than calves born late in the NS environment. The performance of calf growth from birth to 18 months in this study has emphasized the importanc e of matching animal physiological status with seasonal changes in the sub-tropics. Given the significant and consistent detrimental effects of previous lactation status of the cow on fertility and calf growth, it is recommended that this effect be considered in routine evaluations. The high generation intervals (6.7 and 5.5 years pre- and post-crossover) reflect the cow age at first calving (4 and 3 years respectively for the two periods). Direct cumulative selection differentials for weaning weight were very low (0.08 and 0.05 standard deviation units/generation for the S and NS lines respectively). The correlated cumulative selection differentials for pre-weaning weight gain were negative for the pre -crossover period and positive for the post-crossove r period, and together with the low direct cumulative selection differentials suggest that significant attention was paid to secondary characteristics. Consequently, selection responses were low (2.35+0.045 and 2.22+0.047kg/generation for weaning weight for the S and NS lines respectively). All correlated direct genetic trends were positive and linear, while maternal genetic trends were very low and negative for the S line. Direct and maternal (in parenthesis) heritability estimates for weights at birth, weaning and 18-months were 0.39+0.03 (0.14+0.02), 0.19+0.03 (0.21+0.04) and 0.36+0.06 (0.15+0.04) respectively. Apart from the non-significant direct-maternal genetic correlation for birth weight, other correlations were all moderately negative (-0.35 to â0.57). With the exception of correlations with birth weight which were variable and often close to zero, direct and maternal genetic correlations among traits were high, particularly for traits measured at ages close to each other The average incidence of calving success (CS: including abortions at term and stillbirths) was 68%. Heritability and repeatability (in parenthesis) estimates for CS and calving date (CD: with a 21 day penalty for censored records) were 0.08+0.02 (0.10+0.02) and 0.09+0.02 (0.17+0.02) respectively. Service sire was important for both traits, but only accounted for <2% of the total phenotypic variation. Favourable genetic trends were shown for both traits (1.2+0.14% and 0.8+0.13%/generation for CS for the S and NS lines respectively, and -0.8+0.09 days/generation for both lines for CD). The genetic correlation between CS and CD was high (-0.95) and the correlation of siresâ estimated breeding values (EBV) indicated that a one-day improvement in CD EBV is associated with a 1% increase in CS EBV. However, correlation estimates of siresâ EBV between measures of fertility and growth were all unfavourable, but not-significantly different from zero. There were no indications of line x environment interaction for all the growth traits. A significant interaction was, however, manifested for CS and was due to the markedly poorer performance of the S line cows in the NS environment. While no sire x environment interactions were manifested, significant sire x year interactions were found for all the growth traits and for CS, which serves to highlight the tremendous seasonal differences experienced in the sub-tropics. Therefore there is a need to consider selection for genotypic stability, particularly for the more extensive farming environments. This study revealed that concomitant genetic improvements in both growth and fertility were attainable. It is recommended that fertility and calf survival be included in routine breed evaluations. There is however an urgent need to implement data collection strategies to ensure that all calving activities are comprehensively recorded, not least the adequate definition of contemporary groups.