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.

Guidelines for poultry production enterprises to increase the efficiency of broiler production and optimize the nutritional value of poultry litter and manure for use in ruminant nutrition is urgently needed. Therefore a study was conducted to investigate the effect of wood shaving (SA), wheat straw (WS), peanut hulls (PH) and sunflower hulls (SH) as bedding materials on the performance of broilers in conventional floor systems. In a second study the effect of different types of bedding materials and collecting periods on the feeding value of respectively broiler and layer hen manure for ruminants were investigated. Six hundred, day old Ross -1-broilers were randomly divided into 30 groups of 20 each. Six groups (replications) were then randomly allocated to one of the following five treatments: 1. Wood shavings and saw dust (Byproduct Development Services, 0.5 to 5 cm) 2. Peanut hulls 3. Sunflower hulls 4. Wheat straw (ground through a 30 mm sieve) 5. Control group (cement floor) Commercial broiler diets were fed ad lib. to all experimental groups. On the basis of weight of water absorbed per weight of bedding material, WS absorbed significantly more water than PH, SA or SH. No significant (P>0.05) differences in the percentage moisture release of different bedding materials occurred. Accordingly no significant differences in ammonia production, feed intake, weight gain, efficiency of feed conversion, carcass weight and dressing percentage of broilers were detected among the various treatments. The highest production number (weighted sum of average weight, percent livability, period and feed conversion) was calculated for broilers on peanut hulls, followed by no bedding material (control), wood shavings, sunflower hulls and lastly wheat straw. It was calculated that a broiler excreted approximately 878g dry matter in a 42 day period. The highest (P<0.05) crude protein content occurred in the manure of broilers raised on no bedding material followed by the peanut hulls treatment. No significant differences (P>0.05) occurred in the crude protein content of manure from the wood shavings and wheat straw treatments. Bedding materials in broiler litter did not influence effective degradability of crude protein statistically significant. The highest (P<0.05) acid detergent fibre content was recorded for wood shavings and the lowest for the control treatment, while the rest showed no significant differences. No significant differences occurred in the neutral detergent fibre (NDF) content of broiler litter gathered on the different bedding materials. The lowest (P<0.05) NDF content was again found where no bedding material was supplied. No significant differences occurred in the fat content of broiler litter originating from the different treatments. The highest (P<0.05) ash content and in vitro digestibility was in the pure excretion and the lowest in broiler litter containing wood shavings. There were no significant differences amongst the remaining treatments. Bedding material had no significant (P>0.05) influence on the mineral content of broiler litter. In an effort to investigate the effect of composting time (collecting period) on the feeding value of layer hen manure, ninety, 20 week old White Plymouth Rock layer hens were then randomly divided into 30 groups of 3 each. The 30 groups were then randomly allocated to 5 treatments. The manure of each treatment was respectively collected daily and after 14, 28, 42 and 56 days. All the layers received a commercial layer diet ad lib. The collection of layer manure after 56 days resulted in a significant (P<0.05) reduction in crude protein content, degradability and in vitro digestibility. No clear trend or influence of composting time on the ADF and NDF content of layer manure could be detected. Composting time had no influence on the fat content of layer manure. The ash content of layer manure increased significantly (P<0.05) with a delaying collecting period. Delaying of collecting time resulted in an increase in the percentage of Na, Ca, K, Mg, P and Cu of layer manure. No significant (P>0.05) influence of composting time on the concentrations of Fe, Zn and Mn was observed. It was concluded from the performance of the broilers on the different bedding materials and the nutritive value of the broiler litter that peanut hulls should be preferred as bedding material. SH should be the second choice followed by WS. Lastly it seems that layer manure should be collected on a regular basis and that the composting time should not exceed 42 days.

The study was conducted in the Somali region of eastern Ethiopia, with an arid to semiarid climate. The study aimed at the characterization of the rangeland resources, assessing the current condition of the rangeland, understanding pastoral perceptions on rangeland degradation and developing drought feeding strategies for livestock. Three experimental sites, representative of the three predominant vegetation types of eastern Ethiopia were selected. They were the arid Asbuli grassland (used as grazing area for large and small ruminants), the arid Aydora open savanna (bush-grassland: entirely used for grazing/browsing by all types of livestock), and the semi-arid Hurso closed savanna (bushland: selected for its importance as browsing for camels and goats). A degradation gradient was identified in each of the three vegetation types, where the botanical composition was surveyed and the rangeland condition assessed. The perceptions of the pastoralist on rangeland degradation were also quantified. The dry matter production of both the herbaceous and woody layer was determined, while the grazing and browsing capacity calculated. Key forage species were identified and the grazing pattern of various livestock species along the degradation gradient studied. The soil seed bank regeneration potential was assessed in a greenhouse experiment and the response of cattle, sheep and goats to a simulated drought, in terms of reduced fodder, was conducted under controlled conditions. The results of the study confirmed the existence of severe rangeland degradation that occurred since 1944 and which was aggravated after the 1974 drought. This contributed to an increase in the number of poor households. The average livestock holding per household declined from 809 Tropical Livestock Units (TLU) before 1974 to 483 TLU after 1974. Livestock holding shifted from a predominance of cattle to small ruminants, which are able to utilize the degraded rangeland more effectively. Camels are now the most important livestock species in terms of milk and meat production, mainly due to their ability to tolerate drought. The abundance of herbaceous plants, basal cover, dry matter production and grazing capacity was found to be higher in the benchmark sites compared to the other rangeland conditions. There was also a corresponding increase in percentage bare ground, soil compaction and soil erosion along the degradation gradients. Over-grazing and overutilization through continuous grazing of the herbaceous layer were identified as the main causes of these differences. Rangeland condition was observed to significantly influence the grazing behaviour of livestock in terms of plant species selection, grazing intensity and intake per animal. When forage sources were adequately available, animals selected fever plant species. As forage resources declined the animals spend more time grazing and more species selected, including less palatable species. The number of bites, intake per bite and intake as a percentage of the animalâs body mass also increased as the rangeland become more degraded. Acacia nubica and A. mellifera were identified as aggressive encroaching species in the Aydora open savanna and Hurso close savanna. The Aydora open savanna experienced extensive encroachment by woody plants with increasing plant densities across the degradation gradient. The Hurso closed savanna experienced an opposite trend where severe deforestation and a loss of valuable browse species occurred, mainly as a results of over cutting of the woody plants for firewood, charcoal making, construction and the clearing of the land for planted crops. The study on the soil seed bank of soil collected along the various degradation gradients showed a high abundance of plant seed present in the soil, confirming the potential of the area for rangeland restoration. As expected the body weight losses of all livestock species in the controlled feeding trial were highly correlated with the reduction in daily dry matter feed. More than 50% of the animals showed pronounced emaciation and physical weakness and 25% of the cattle and goats collapsed and died within ten weeks after the trial started. This explained the large scale mortalities of livestock during prolonged droughts. Drought must be accepted as part of the pastoral life and there should be an adequate early warning system regarding livestock feed availability and strategies of appropriate mitigation strategies. More realistic stocking rates is the obvious solution to the avoidance of stock losses during droughts, but in view of the well established culture of the pastoralists it is highly doubtful if they will be willing to reduce their animal numbers. In conclusion, the experimental results indicated the existence of genetic variability among the various Somali livestock breeds regarding the tolerance to feed shortages and in rates of compensatory growth. This demonstrates the opportunity for improving the genetic composition of the Somali herds through selection.

Genetic evaluation systems require accurate estimates of genetic parameters. The genetic, phenotypic and environmental parameters for objectively measured wool, subjectively assessed wool and conformation traits as well as 16-month live weight were estimated for South African Merino sheep. Records of the Tygerhoek Merino resource flock were used to estimate these parameters. The database consisted of records of 4 495 animals, the progeny of 449 sires and 1 831 dams born in the period 1989 to 2004. The pedigree records used have been collected between 1969 and 2004. In this data, four lines were represented, namely a line selected on clean fleece weight, a line selected against rearing failure, a fine wool line, as well as an unselected control line. Single trait linear mixed models were used. Fixed effects that were assessed included birth status (single/multiple), sex (male/female), age of the dam in years (2-6+years), year of birth (1989-2004) selection line (1-4) and the sex*birth year interaction. Preliminary analysis showed that all the fixed effects had significant (P<0.05) effects on all the traits studied. The random effects included a combination of direct additive, maternal additive and maternal permanent environmental effects as well as the covariance between direct and maternal additive effects. The direct heritability estimates (h²a) for objectively measured traits were 0.38 for 16- month live weight (LW), 0.36 for greasy fleece weight (GFW), 0.40 for clean fleece weight (CFW), 0.65 for clean yield (CY), 0.37 for staple length (SL), 0.20 for staple strength (SS), 0.68 for fibre diameter (FD), 0.61 for coefficient of variation of fibre diameter (CVFD) and 0.61 for standard deviation of fibre diameter (SDFD). The maternal heritability estimates were 0.05 for LW, 0.09 for GFW, 0.10 for CFW and 0.05 for FD. The proportion of the total phenotypic variance due to the maternal permanent environment (c²pe) amounted to 5% for fleece weights. The correlation between direct and maternal genetic effects for LW, GFW and CFW were -0.28, -0.65 and -0.70 respectively. These results suggested that worthwhile responses to selection for objectively measured traits would result from directed selection. Estimates of h²a for subjectively assessed wool traits were 0.49 for wool quality (QUAL), 0.28 for regularity of crimp (ROC), 0.33 for wool colour (COL), 0.23 for wool oil (OIL), 0.21 staple formation (STAPL), 0.22 belly and points (BANDP), 0.50 for woolly face score (WFS), 0.15 for face cover score (FCS), and 0.45 for pigmentation (PIGM). Maternal genetic effects were significant for QUAL, ROC and COL amounting to 0.06, 0.03 and 0.07 respectively. The correlation between direct and maternal genetic effects for QUAL, ROC and COL were -0.62, -0.70 and -0.45 respectively. The h²a estimates for subjectively assessed conformation traits were 0.13 for topline (TOPL), 0.39 for total fold score (TOT), 0.15 for front quarters (FQ), 0.16 for pastern score (PS), 0.32 for hocks (HOCKS) and 0.37 for the general conformation score of the head (GEN). Among the subjectively assessed conformation traits the maternal genetic effects were significant only for PS at 0.05 while GEN was affected by c²pe at 5%. The correlation between direct and maternal genetic effects was -0.71 for PS. The improvement of subjectively assessed wool and conformation traits by selection seems possible from the results of present study. Genetic correlations (rg) among objectively assessed traits general agreed with literature values. Among the subjectively assessed traits favourable rg estimates were estimated between ROC and COL (0.31), for QUAL with ROC (0.49) and COL (0.26) and between STAPL and BANDP (0.58). The relationships between ROC and STAPL (-0.49) and for QUAL with STAPL (-0.45) and BANDP (-0.20) were unfavourable. Estimates of rg among subjective conformation traits were generally low, variable in sign and not significant. The only exceptions were rgâs between HOCKS and FQ (0.71) and of GEN and TOPL with TOT (-0.31 and -0.47 respectively). Phenotypic and environmental correlations among objective, subjective wool and conformation traits were low to moderate. Maternal relationships of respectively 0.86 and 0.19 were found between GFW and CFW and between CFW and FD. The rg of LW with subjective wool traits were not significant, with the exception of moderate and favourable rg for LW with ROC (0.20) and for LW with WFS (0.20). These results suggested that heavier sheep are likely to have more even fleeces and higher scores for WFS. The rg were favourable with COL (-0.19), STAPL (0.35) and BANDP (0.42). CFW and CY were also favourably related to COL, STAPL, BANDP and QUAL where sheep with higher fleece weights and yield had wool with higher quality and better scores for COL, STAPL as well as BANDP. SL was favourably related to COL, BANDP and WFS and negatively related to OIL. These results indicated that sheep with longer staples had better scores for COL, BANDP and WFS as well as lower scores for OIL. Among the subjective wool traits only ROC was significantly related to SS at 0.33. Moderate and unfavourable genetic correlations were estimated for FD with QUAL, ROC and FCS, where sheep with a good quality wool that have more even fleeces and softer wool covering the face had reduced FD. The corresponding relationship with STAPL and BAND were unfavourable. Genetic correlations of CVFD and SDFD with QUAL and ROC were favourable and while these traits were unfavourably related to a number with STAPL. Phenotypic and environmental relationships between objectively measured traits and subjectively assessed wool traits were low to high and variable in sign. On the genetic level LW was favourably related to all the subjectively assessed conformation traits studied. Heavier sheep were generally plainer, had better scores for GEN, HOCKS, and FQ as well as for TOPL. Estimates of rg were favourable for CY with GEN (0.25), HOCKS (0.19), TOT (-0.26) and FQ (0.18), for FD with PS (-0.16) and TOPL (-0.18), for CVFD with HOCKS (-0.17), FQ (-0.33) and TOPL (-0.25), between CFW and GEN (0.23), and between SS and FQ (0.39). The relationships of SDFD with FQ and TOPL were negative. Unfavourable correlations occurred between SS and TOT (0.25), between FD and HOCKS and FD and TOT at 0.13, for fleece weights with TOT (GFW 0.48 and CFW 0.28) and TOPL (GFW 0.34 and CFW 0.29) and between CY and TOT at -0.26. Phenotypic and environmental relationships between objectively measured traits and subjectively assessed wool traits were low to high in magnitude and variable in sign. The results showed that selection for LW and objective wool traits will thus not seriously compromise subjective wool and conformation traits. The exception is FD, CVFD and SDFD, where unfavourable genetic relationships with STAPL and BANDP were found. Furthermore, from these results, it was clear that unrestrained discrimination against wrinkles in Merino sheep would adversely affect economically important objectively measured wool traits such as SS, FD and wool weight. Selection against wrinkles should be carefully monitored to minimise the risk of animals producing reduced fleece weights with broader fibres. It is therefore, proposed that animals with excessive wrinkles be culled from the breeding stock.