Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 80-87). Also available via World Wide Web.

Pigs can consume a wide range of feeds to meet their nutritional needs and there is a renewed interest in the use of cheaper nutrient resources for animal feeding. Forages have been proved to be a substantial source of nutrients for pigs, however, the bulk of the existing work has focused on sows and grower-finisher pigs above 50 kg. This study was conducted during May-June 2009 at the Agricultural Research Council (Irene, Pretoria) to determine the voluntary forage intake and nutrient digestibility in growing pigs fed a mixed diet (concentrate + Kikuyu grass). Twenty five 8 weeks old Large White x Landrace crossbred pigs (27 ± 3.8 kg) were blocked by weight into 5 groups of 5 pigs each. One of 5 treatments (A, B, C, D and E), corresponding to 100, 90, 80, 70 and 80 % of a basal concentrate ration, respectively, was randomly assigned to a pig within each block. Indoor treatments were either fed the concentrate only (A) or also received freshly cut Kikuyu grass (Pennissetum clandestinum) ad libitum (B, C and D). Only treatment E animals were housed outdoors in Kikuyu grass paddocks while all other treatments were housed indoors. Forage intake was recorded daily and also estimated using a pair of n-alkanes as markers. Nutrient and diet digestibility were calculated using acid-insoluble ash (AIA) and dotriacontane (C32) as markers. The results showed that the concentrate intake (CI) in treatments A, B and C was significantly different from treatments C and E (P < 0.05) and there was positive correlation between the concentrate level and its intake (P < 0.01). The recorded intake of Kikuyu grass (RKI) and the animal’s average daily gain (ADG) were similar between treatments (P > 0.05). The estimated (EKI) and recorded (RKI) Kikuyu grass intakes were not influenced by CI or the level of concentrate allowance (CL) and RKI was higher (P < 0.05) than EKI. Digestibility estimates with AIA were higher than C32 Keywords: Dotriacontane; Kikuyu; growth performance; forage; monogastrics estimates (P < 0.05). It was concluded that Kikuyu grass intake was not affected by the reduction of the concentrate level allowance. It was proposed that forage intake in a mixed diet (forage + concentrate) was more dependant on its own characteristics than the concentrate’s nutritional value. / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)

Pigs can consume a wide range of feeds to meet their nutritional needs and there is a renewed interest in the use of cheaper nutrient resources for animal feeding. Forages have been proved to be a substantial source of nutrients for pigs, however, the bulk of the existing work has focused on sows and grower-finisher pigs above 50 kg. This study was conducted during May-June 2009 at the Agricultural Research Council (Irene, Pretoria) to determine the voluntary forage intake and nutrient digestibility in growing pigs fed a mixed diet (concentrate + Kikuyu grass). Twenty five 8 weeks old Large White x Landrace crossbred pigs (27 ± 3.8 kg) were blocked by weight into 5 groups of 5 pigs each. One of 5 treatments (A, B, C, D and E), corresponding to 100, 90, 80, 70 and 80 % of a basal concentrate ration, respectively, was randomly assigned to a pig within each block. Indoor treatments were either fed the concentrate only (A) or also received freshly cut Kikuyu grass (Pennissetum clandestinum) ad libitum (B, C and D). Only treatment E animals were housed outdoors in Kikuyu grass paddocks while all other treatments were housed indoors. Forage intake was recorded daily and also estimated using a pair of n-alkanes as markers. Nutrient and diet digestibility were calculated using acid-insoluble ash (AIA) and dotriacontane (C32) as markers. The results showed that the concentrate intake (CI) in treatments A, B and C was significantly different from treatments C and E (P < 0.05) and there was positive correlation between the concentrate level and its intake (P < 0.01). The recorded intake of Kikuyu grass (RKI) and the animal’s average daily gain (ADG) were similar between treatments (P > 0.05). The estimated (EKI) and recorded (RKI) Kikuyu grass intakes were not influenced by CI or the level of concentrate allowance (CL) and RKI was higher (P < 0.05) than EKI. Digestibility estimates with AIA were higher than C32 Keywords: Dotriacontane; Kikuyu; growth performance; forage; monogastrics estimates (P < 0.05). It was concluded that Kikuyu grass intake was not affected by the reduction of the concentrate level allowance. It was proposed that forage intake in a mixed diet (forage + concentrate) was more dependant on its own characteristics than the concentrate’s nutritional value. / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)

Kikuyu pasture was fertilized at low and high levels of nitrogen (N), namely 50 and 200 kg N/ha, after mowing and clearing the plots, to induce low and high levels of N in the herbage. The subsequent growth was harvested at 20-, 30- and 40-d re-growth. These treatments were conducted in spring, summer and autumn. Treatments included level of N, stage of re-growth and season as variables in digestion trials using sheep and voluntary feed intake (VFI) trials using long yearling heifers in pens equipped with Calan gates. Nitrogen fertilization level had no impact on herbage dry matter digestibility (DMD). Stage of re-growth influenced digestibility in the spring and summer, the highest values recorded in the 30-d treatment. However, in the autumn, the 20-d re-growth recorded the greatest digestibility. Digestibility declined as the season progressed. Digestibility was not correlated to any of the chemical fractions measured in the herbage, including in vitro DM digestibility (IVDMD). Voluntary feed intake (VFI) followed a similar trend to digestibility, with peak values recorded for the 30-d treatment in the spring and summer, while the 20-d material induced the greatest intake in the autumn. Nitrogen fertilization had a negative impact on VFI over all seasons. Similarly to digestibility, VFI was not correlated to any of the chemical fractions measured, but was correlated to digestibility and moisture concentration of the herbage. Nitrogen degradability was determined using the in situ bag technique. Differences (p<0.05) were recorded for the quickly degradable N (a) and potentially degradable N (b) fractions within season, but not for the degradation rate of the slowly degraded fraction (c) per hour. The effective degradability (dg) was not influenced by N fertilization level in the spring, while N fertilization increased the dg values in the summer and autumn. Stage of re-growth exerted a positive effect (P<0.05) on the dg values. Rumen pH, rumen ammonia and blood urea nitrogen (BUN) levels were measured in rumen fistulated sheep. Rumen pH increased also with increasing level of N fertilization and declined with advancing stage of herbage re-growth in the autumn. Rumen ammonia increased with time of sampling post feeding to 4 hrs and then tended to decline by 6 hrs. Nitrogen fertilization level influenced rumen ammonia levels (p<0.05), with the low N level producing the lowest rumen ammonia levels. Rumen ammonia levels were highest at 20-d re-growth stage in summer and at the 40-d re-growth stage in autumn. DM concentration of the herbage had an inverse relationship with rumen ammonia. BUN levels were increased by high N fertilization and were positively correlated to rumen ammonia levels. Five years of digestibility data (82 digestion trials) and three years of intake trials (38 trials) data was pooled. These data, chemical composition of the herbage and the daily maximum temperatures, rainfall and evaporation recorded at and prior to the digestion and intake trials at Cedara were analysed using multiple regression techniques. Rainfall and temperature in the period of cutting and fertilization had a negative effect on digestibility, irrespective of the stage of re-growth at harvesting, 20, 30 or 40 days later, and a combination of the two proved significant, accounting for the most variance in DDM. Temperature depressed DMD by 11.4 g/kg DM per degree rise in temperature (Degrees C). Temperatures recorded during the cutting and fertilization phase were highly negatively correlated to VFI, irrespective of stage of re-growth. The DM concentration of the herbage as fed accounting for 32% of the variance in DMD, the NPN content of the herbage accounting for only 12.2% of the variance and the ash concentration of the herbage accounting for 15.9% of the variance in digestibility. Non-protein nitrogen was negatively correlated to VFI. Both DMD and VFI were highly negatively influenced by the moisture concentration of the herbage. Overall, the results of these trials demonstrated that environmental factors such as rainfall and temperature had a far greater impact on the digestibility of kikuyu herbage than the chemical composition, which had a minimal effect. Nitrogen fertilization did not influence herbage digestibility overall, but exerted a highly negative impact on voluntary intake. / Thesis (Ph.D.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Four grazing trials to characterise cultivated pastures, in terms of beef production, were conducted in Bioclimate 3 of Natal. Dual purpose and British beef type cows were run on kikuyu at stocking rates from 2,81 to 7,30 cows plus calves per ha. During the eight seasons of the trial the seasonal rainfall varied from 580 to 933 mm. There was a positive linear relationship between rainfall and pasture yield with maximum yield of kikuyu being recorded during February - March. Stocking rate affected pasture yields only during favourable rainfall seasons. Crude protein (CP) and crude fibre (CF) of kikuyu fluctuated markedly within and between seasons. However, CP increased and CF decreased as stocking rate increased. There were significant relationships between stocking rate and (a) calf performance, (b) calf livemass gain, (c) period required to attain maximum mass, (d) period on pasture for the cows, and (e) cow mass change: Weaners were run on irrigated Italian ryegrass at 5, 7 and 9 weaners per ha for four seasons. Stocking rate had little effect on the growth pattern of the pasture but affected dry matter yields. Reducing the stocking rate resulted in increased pasture yields and CF content but reduced CP levels of material on offer. Steers exhibited higher gains than heifers but lower carcass grades and stocking rates for maximum gain per ha (SRmax). Livemass gains of 1315 and 1224 kg per ha can be expected at SRmax of 6,85 and 9,54 for steers and heifers respectively. Yearling heifers run at four stocking rates on kikuyu for one season showed a negative linear relationship between stocking rate and gain and a positive linear relationship between pasture height and gain. A SRmax of 8,85 allows for a livemass gain of 1 040 kg per ha. The effect of feeding concentrates on foggaged kikuyu was evaluated. Foggaged kikuyu can be used as a source of roughage for fattening steers. However, as the steers became adapted to the concentrate the intake of kikuyu declined from 39 to 19% of their daily intake. Regressions derived from the characterisation trials allow for developing beef systems for different situations. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1985.

South African dairy farmers have generally used kikuyu pasture to tide them over from one ryegrass season to the next, and as a result of its resilient nature, have assumed careful management of it to be unnecessary. This has resulted in its mismanagement which is unaffordable in current times where the profitability of dairy farming is increasingly dependent on low input, pasture-based systems. Kikuyu pasture may play a larger role in supplying nutrients to dairy cattle over the summer months in future as the alternative home produced feed sources such as silage and perennial ryegrass become increasingly unaffordable. Improving animal production from kikuyu is difficult as there is little information relating kikuyu pasture management to dairy cow performance. Efficient utilization and quality of temperate pasture have been more comprehensibly researched. The relations discovered between the chemical compounds in temperate grass species have been applied to tropical pastures such as kikuyu with limited success and often confusing results. For example, crude fibre in kikuyu was found to be positively related to digestibility. In South Africa, much research has been done on the use of kikuyu in beef production systems. This information has been applied to dairy farming systems with limited success, owing to the higher metabolic demands of dairy animals. Pasture farming needs to become more precise to improve pasture quality and hence milk yields as research trials focussing on stocking rate and grazing system comparisons have yielded results that are too general with little application at the farming level. A need for integrated and flexible management of animals and pastures has been recognised. The grazing interval is a key aspect in improving pasture and animal performance and fixed rotation lengths and stocking rates have been identified as being detrimental to performance. The relation between growth stage and pasture quality has lead researchers to identify plant growth characteristics, such as pasture height and leaf stage, as signs of grazing readiness. At the four and a half leaves per tiller stage of regrowth, the chemical composition ofthe kikuyu plant is more in line with the requirements ofthe dairy cow, with the leaf to stem ratio at its highest. The primary limitation of kikuyu pasture is a lack of energy, particularly readily fermentable carbohydrate, which makes the fermentation of structural carbohydrates difficult and dry matter intakes are reduced. Other limitations to animal performance include high cell wall constituents, low calcium, magnesium and sodium content and antinutritional factors such as nitrate and insoluble oxalate. These deficiencies and antinutritional factors are in some cases unique to 5 kikuyu pasture, meaning that kikuyu specific supplementation may be the key to improving performance from dairy cattle grazing kikuyu pasture. The objectives are to evaluate current kikuyu management systems in South Africa and their impact on dairy cow performance and to evaluate the use of pasture height and burning as quality control tools. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Thesis (M. Sc.)(Animal Science)--University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.

The factors affecting the accumulation of nitrate in kikuyu grass pastures and the effect of elevated nitrate levels upon digestion in the ruminant were investigated. A high potassium level in the soil seems to be the major factor stimulating the accumulation of excessive amounts of nitrate in kikuyu grass, when the nitrate content of the soil is also high. The continuous elongation of kikuyu grass tillers allows constant exposure of high nitrate containing stem tissue to the grazing ruminant. Digestibility studies in vitro showed that nitrite, formed during the assimilatory reduction of nitrate to ammonia, reduces cellulose digestion, but the degree of reduction also depends upon the presence of readily available carbohydrates and protein in the digest. Studies in vivo showed that the microbial population can adapt to metabolise high concentrations of nitrate (500 mg% N, m/m) in fresh kikuyu grass, without the accumulation of nitrite in the rumen. However, introduction into the rumen of nitrite in excess of the capacity of the nitrite reducing microbes, causes nitrite accumulation. Nitrite has no direct effect upon rumen cellulase activity. Due to the affinity of rumen carbohydrases for the substrate, attempts to isolate these enzymes by means of isoelectric focusing and other separation techniques met with limited success. Nitrite strongly reduces the xylanolytic, total and cellulolytic microbial numbers with a concomitant decrease in xylanase and cellulase activity of the digest. Decreased microbial numbers could not be .attributed to a less negative redox potential of the digest in the presence of nitrite, nor could the effect upon the cellulolytic microbes be attributed to an effect of nitrite on branched chain fatty acid synthesis required for cellulolytic microbial growth. A study of the effect of nitrite upon the specific growth rate of pure cultures of the major cellulolytic bacteria, Ruminococcus flavefaciens strain FDI, Butyrivibrio fibrisolvens strain Ce 51, Bacteroides succinogenes strain S 85 and Ruminococcus albus strain 22.08.6A and the non-cellulolytic bacterium Selenomonas ruminantium strain ATCC 19205 revealed the extreme sensitivity to nitrite of some of these bacteria and the relative insensitivity of others. Growth inhibition seems to depend primarily upon the extent to which these microbes derive their energy from electron transport-mediated processes. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1985.

The work reported in this thesis was designed to develop a better understanding of the fate of fertiliser nitrogen applied to a tropical pasture under field conditions, with the eventual objective of improving the economy of livestock production off such pastures. This involved an examination of the concentrations of soil total nitrogen, ammonium nitrogen and nitrate nitrogen at different depths within the soil profile following the application of different levels of fertiliser nitrogen to a grazed kikuyu (Pennisetum clandestinum) pasture, as well as the influence of such applications on pasture yield and some elements of pasture quality. The trial was conducted over a two year period at Broadacres in the Natal Mistbelt. A labelled [15]NH[4]N0[3] fertiliser experiment was also conducted to ascertain how the labelled ammonium ion moved through the soil, roots and herbage after being applied in spring onto a kikuyu pasture. In the absence of fertiliser N, a total of 15.45 t/ha of soil N was recorded at an average concentration of 0.15%. More than 30% of the soil total N was, however, situated within the top 10cm of soil. organic matter (OM) content in the top 0-10cm of the profile was high (4.75%), reflecting an accumulation of organic matter in this zone. However, as organic C (and thus c: N ratios) declined with depth, so too did soil total N concentration. Not surprisingly, fertiliser measurably increase soil total N, N applications did not but indirectly may have affected soil N dynamics by increasing net mineralisation (due to its "priming" effect) thereby stimulating plant growth and thus increasing the size of the organic N pool through greater plant decay. Total soil N concentration did not change significantly from the first to the second season. This could be attributed to the fact that N gains and losses on the pastures, being over 15 years old, were probably in equilibrium. Generally similar trends in soil total N down the profile over both seasons was further confirmation of this. Before the application of any fertiliser, 331.9 kg NH[4]-N was measured in the soil to a depth of 1m, on average, over both seasons. This amount represented only 2.1% of the soil total N in the profile. The concentration of NH[4]-N followed a quadratic trend down the soil profile, irrespective of the amount of fertiliser N applied, with the largest concentrations accumulating, on average, in the 0-10cm and 75-100cm depth classes and lowest concentrations in the 50-75cm depth class. Laboratory wetting/drying experiments on soil samples collected from a depth of 75-100cm showed that NH[4]-N concentrations declined only marginally from their original concentrations. A high organic C content of 1.44% at this depth was also probable evidence of nitrification inhibition. Analysis of a similar Inanda soil form under a maize crop did not exhibit the properties eluded to above, suggesting that annual turn-over of the soil was causing mineralisation-immobilisation reactions to proceed normally. Addition of fertiliser N to the pasture significantly increased the amount of NH[4]-N over that of the control camps. Furthermore, the higher the application rate, the greater the increase in NH[4]-N accumulation within the soil profile. As N application rates increased, so the NH[4]-N:N0[3]-N ratio narrowed in the soil complex. This was probably due to NH[4]-N being applied ln excess of plant requirements at the high N application rates. On average, 66.7 kg more NH[4]-N was present in the soil in the first season than in the second after fertilisation. Although this amount did not differ significantly from spring through to autumn, during early spring and late summer/autumn concentrations were higher than in mid-summer. Observed soil NH4-N trends were also very similar to the soil total N trends within both seasons, suggesting that soil total N concentrations might well play an important role in determining soil NH4-N concentrations. Before fertilisation, only 45.6 kg N0[3]-N, representing 0.29% of the soil total N, was on average, found in the profile to a depth of 1m. The highest concentration of N0[3]-N was lodged in the top 10cm of the soil. Nitrate-N declined, on average, with depth down the profile. However, during the second season, even though the concentration of N03-N declined down the profile, it increased with depth during relative to that of the first season, suggesting the movement of N0[3]-N down the profile during this period. Fertilisation significantly increased the concentration of N0[3]-N above that of the control camps. Concentrations increased as fertiliser application rates increased, as did N0[3]-N concentrations with depth. This has important implications regarding potential leaching of N03-N into the groundwater, suggesting that once applications reach levels of 300 kg N/ha/season or more, applications should become smaller and more frequent over the season in order to remove this pollution potential. On average, 94.3 kg N0[3]-N/ha was present down to a depth of 1m over both seasons. However, significantly more N0[3]-N was present in the second season than in the first. This result is in contrast to that of the NH[4]-N, wherein lower concentrations were found in the second season than in the first. No specific trends in N0[3]-N concentration were observed within each season. Rather, N0[3]-N concentrations tended to vary inconsistently at each sampling period. Nitrate N and ammonium N concentrations within each month followed a near mirror image. A DM yield of 12.7 t/ha, averaged over all treatments, was measured over the two seasons. A progressive increase in DM yield was obtained with successive increments of N fertiliser. The response of the kikuyu to the N applied did, however, decline as N applications increased. A higher yield of 1.8 t DM/ha in the first season over that of the second was difficult to explain since rainfall amount and distribution was similar over both seasons. On average, 2.84% protein N was measured in the herbage over both seasons. In general, protein N concentrations increased as N application rates increased. On average, higher concentrations of protein-N were measured within the upper (>5cm) than in the lower <5cm) herbage stratum, irrespective of the amount of N applied. Similar bi-modal trends over time in protein-N concentration were measured for all N treatments and within both herbage strata over both seasons, with concentrations tending to be highest during early summer (Dec), and in early autumn (Feb), and lowest during spring (Oct), mid-summer (Jan) and autumn (March). spring and autumn peaks seemed to correspond with periods of slower growth, whilst low mid-summer concentrations coincided with periods of high DM yields and TNC concentrations. The range of N0[3]-N observed in the DM on the Broadacres trial was 0.12% to 0.43%. As applications of fertiliser N to the pasture increased, N0[3]-N concentrations within the herbage increased in a near-linear fashion. On average, higher concentrations of N0[3]-N, irrespective of the amount of fertiliser N applied, were measured wi thin the upper (>5cm) than the lower <5cm) herbage stratum. A similar bi-modal trend to that measured with protein-N concentrations was observed in both seasons for N0[3]-N in the herbage. High concentrations of N0[3]-N were measured during spring (Nov) and autumn (Feb), and lower concentrations in midsummer (Dec & Jan), very early spring (Oct) and early autumn (March). During summer, declining N0[3]-N concentrations were associated with a corresponding increase in herbage DM yields. A lack of any distinctive trend emerged on these trials in the response of TNC to increased fertilisation with N suggests that, in kikuyu, applied N alone would not materially alter TNC concentrations. Higher concentrations of TNC were determined in the lower <5cm) height stratum, on average, than in the corresponding upper (>5cm) stratum. This may be ascribed to the fact that TNCs tend to be found in higher concentrations where plant protein-N and N0[3]-N concentrations are low. A P concentration of 0.248% before N fertilisation, is such that it should preclude any necessity for P supplementation, at least to beef animals. Herbage P concentrations did, however, drop as N fertiliser application rates were increased on the pasture, but were still high enough to preclude supplementation. Even though no significant difference in P concentration was measured between the two herbage strata, a higher P content prevailed within the lower <5cm) herbage stratum. On average, 2.96% K was present within the herbage material in this trial. The norm for pastures ranges between 0.7 and 4.0%. On these trials, applications of fertiliser N to the camps did not significantly affect K concentrations within the herbage. The lower <5cm) herbage stratum, comprising most of the older herbage fraction, was found to contain the highest K concentration in the pasture. The presence of significantly (although probably biologically non-significantly) less K within the herbage in the second season than in the first may be linked to depletion of reserves of · this element in the soil by the plant and/ or elemental interactions between K and other macro-nutrients. An average Ca content of 0.35% within the herbage falls within the range of 0.14 to 1.5% specified by the NRC (1976) as being adequate for all except high-producing dairy animals. Increasing N application rates to the pasture increased the Ca content within the herbage . No significant differences in Ca concentration were found between the upper (>5cm) and lower <5cm) herbage strata over both seasons, even though the lower stratum had a slightly higher Ca concentration, on average, than the upper stratum. Calcium concentrations did not vary between seasons, probably because concentrations tend rather to vary according to stage of plant maturity, season or soil condition. However, higher concentrations of the element were measured in the second season than in the first. The reason for this is unknown. On average, 0.377% Mg was present within the herbage over both seasons. This compares favourably with published data wherein Mg concentrations varied from 0 . 04 to 0.9% in the DM, with a mean of 0.36%. All camps with N applied to them contained significantly more Mg in their herbage than did the material of the control camps. On these trials, the Ca :Mg ratio is 0.92: 1, which 1S considered to be near the optimum for livestock and thus the potential for tetany to arise is minimal. Magnesium concentrations remained essentially similar within both herbage strata, regardless of the rate of fertiliser N applied. As in the case of Ca, Mg concentrations within the herbage were significantly higher in the second season than in the first. Calcium:phosphate ratios increased, on average in the herbage, as N application rates increased. This ratio was high in spring, dropped off in summer and increased again into autumn, suggesting that the two ions were following the growth pattern of the kikuyu over the season. The K/Mg+Ca ratios were nearly double that of the norm, suggesting that the pasture was experiencing luxury K uptake which may be conducive to tetany in animals grazing the pasture. This ratio narrowed as N application rates were increased, probably as a result of ion dilution as the herbage yields increased in response to these N applications. The ratio was low in spring (October), but increased to a peak in December, before declining again to a low in March. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Kikuyu pasture (Pennisetum clandestinum) is potentially the most important source of roughage used to feed dairy heifers in summer in KwaZulu-Natal. It is commonly believed that on kikuyu pasture beef breed females grow at a faster rate than those from dairy breeds when no supplementation is given. Little conclusive evidence is, however, available to support this. Explanations as to why such differences may exist are also limited. Eight Hereford and eight Holstein heifers of similar age and maturity stage were used in a trial. The trial was run over a twenty week period. For the first ten weeks all the animals in the trial grazed ad libitum kikuyu pasture with no supplementation except for a mineral lick. Over this (grass only) period the two breed groups formed the two treatments. During the second ten week period of the trial all of the Holsteins and four of the Herefords were fed a restricted but equivalent amount (1 .7 kg) of a maize meal based concentrate. The use of a computerized, mobile feeding system allowed concentrate intake of individual animals to be measured. Animal height, weight and condition score readings were taken weekly over the grass only and the concentrate (final seven weeks) periods of the trial. Herbage intake and digestibility were estimated using n-alkanes as indigestible markers in two experiments conducted during the grass only and concentrate periods. The Herefords had a significantly higher ADG than the Holsteins (0.82 vs. 0.04 kg/day; P < 0.01) over the grass only period. During the concentrate period the rate of mass gain of the Holstein treatment did not differ significantly (P >0.05) from the Hereford treatment receiving concentrate. The Herefords receiving concentrate were also not significantly different (P > 0.05) in rate of mass gain from the Herefords not receiving concentrate. Rate of height gain was not significantly different (P> 0.05) between treatments over either the concentrate or the grass only periods. During the grass only period the Holsteins lost condition (0.07 condition score units per week) whilst the Herefords gained condition at an equivalent rate. The voluntary intake of concentrates was not significantly different (P > 0.05) between the Herefords and Holsteins (19.19 vs. 16.40 g/kg/L.W(liveweight) (0.75)). Regression coefficients relating level of concentrate intake to rate of mass gain were also not significant (P > 0.05) for either of the treatments receiving concentrate. The use of n-alkanes as indigestible markers showed the intake of the Holstein treatment to have an intake 55% (P < 0.0 1) higher than the Herefords (185.4 vs. 120.5 g/kg L.W(0.75)) over the first experiment where both treatments were grazing ad lib. kikuyu alone (grass only period). During the concentrate period intake of the Herefords receiving concentrate exceeded that of the Holsteins (P < 0.01) by 23% (139.1 vs. 113.1 g/kg L.W(0.75)). Review of the literature, suggests that the double alkanes technique greatly over-estimated intake. Errors in herbage sampling (accentuated by pasture rotation in the first experiment), a low daily dose of the synthetic alkane (C(32)) and incorrect estimation of the C(32) content in the daily doses are identified as possible causes of the over-estimation of intake. Faecal recoveries of the herbage n-alkanes were demonstrated to increase with increasing chain length and hence C(35) was proposed as the most reliable herbage alkane for dry matter digestibility determination. Digestibility differences between treatments estimated using the C(35) alkane were not significantly different (P > 0.05) in either the first or second experiments. The mean digestibility estimates (using the C(35) alkane) for the first and second experiments were 64.9 and 56.61 %, respectively. In conclusion, higher growth rates of Herefords on kikuyu pasture would seem to be primarily due to differences in the dry matter intake of the grazed herbage. Further work using other breeds of dairy and beef animals is required. The underlying cause of differences in dry matter intake between breeds also requires investigation. / Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 1995.