In KwaZulu-Natal the production of beef in summer from veld is a common enterprise. Many techniques are available to optimise the productivity of this enterprise, from improving the quality of the grazing resource (planted pastures) to improving the diet of animals using nutritional supplements. To gain an insight into the production potential and financial returns possible from such improvements a trial was established at the Ukulinga Research Farm during two consecutive summer growing seasons (1997-1998 and 1998-1999). The aim was to determine the optimum beef production system for the area from both veld and kikuyu pastures. To evaluate the benefits of supplying supplementary nutrition, four alternate feed supplements, namely: 1) a Standard commercially available molasses-based protein/mineral/energy supplement; 2) a Brewers grain based protein/mineral/energy supplement, and two supplements consisting of the Brewers grain ration with either; 3) Avoparcin (an additive that improves dietary energy) or 4) Bentonite (an additive that increases the bypass of protein) were compared. As stocking rate has been shown to influence the quality of the diet consumed, the kikuyu pasture was grazed at both the recommended (1.92 LSD ha¯¹) and half the recommended stocking rate for the region. In addition, a commercial hormonal implant was applied to half of the cattle in each treatment. Grazing was monitored using the falling plate disc meter to measure pasture bulk density and laboratory analyses of herbage grab samples for digestibility and crude protein percentage. Cattle were weighed on a weekly basis and their condition was scored prior to slaughter. All enterprise costs and returns were recorded to facilitate financial analyses of the five treatments. Low rainfall and high midsummer temperatures had a detrimental effect on the productivity of the grazing and hence it was difficult to optimise production in either season. In the first season, a midsummer drought decreased the quality and quantity of both veld and kikuyu, limiting mass gain during the latter part of the season. A delay in the onset of rain at the start of the second season limited the available grazing season to 121 days as opposed to 154 days, though fodder production during the season was not limited. Trends in herbage production (quality and quantity) from veld showed moderate quality (Crude protein 7.02%; digestibility 50.2%) with an average available herbage of 1670 kg DM ha¯¹. As anticipated, kikuyu had higher quality (Crude protein 10.84%; digestibility 53.5%) and available herbage (2730 kg DM ha¯¹). These results were similar to regional benchmarks. The variable rainfall highlighted both the drought tolerance of veld and the minimum water requirements of kikuyu pastures. Lighter stocking rates tended to reduce the negative impact of moisture stress on Kikuyu pastures. The best method of producing beef (averaged over two seasons) was from heavily stocked Kikuyu pastures using the Standard supplement (1107.63 kg livemass ha¯¹). Cattle grazing veld and utilising the Avoparcin supplement produced beef at a rate of 95.96 kg ha¯¹. In comparison, the unsupplemented cattle grazing Kikuyu produced 834.87 kg ha¯¹, whilst veld grazing produced 64.43 kg ha¯¹. Hormonal implants significantly (P≤0.05) improved beef production from all sources of grazing. A lack of rain limited grazing time, causing all the cattle to be marketed whilst too lean - this negatively affected live mass gain and, hence, net financial. Although improved biological production is desirable, it is important to ensure that these gains are financially sustainable. Within the trial environment, implanted cattle fed the Standard supplement and grazing Kikuyu pastures at a high stocking rate provided the highest average gross margin of R 859.59 ha¯¹. Changing to this production system from unsupplemented veld improved expected profit by R 632.58 ha¯¹ (averaged over both seasons). Further financial analyses indicated that beef purchase price had the greatest influence on the added profit from switching from the control treatment. From a scientific standpoint these data are conclusive but it is important to remember that consumer pressure and concerns can often limit the introduction of production improvements. Such is the case with both hormonal implants and antibiotic feed additives (Avoparcin) although considering the impact of such limitations is speculative and beyond the scope of this trial. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Three experiments compared ruminal, physiological, and performance responses of beef steers consuming hay ad libitum and receiving grain-based supplements with (CAM) or without (CO) inclusion of camelina meal. In Exp. 1, 9 steers fitted with ruminal cannulas received CAM (2.04 kg of DM/d) or CO (2.20 kg of DM/d). Steers receiving CAM had reduced (P = 0.01) total DMI and tended to have reduced (P = 0.10) forage DMI compared to CO. No treatment effects were detected (P ≥ 0.35) for ruminal hay degradability parameters. In Exp. 2, 14 steers receiving CAM (1.52 kg of DM/d) or CO (1.65 kg of DM/d) were assigned to corticotropin-releasing hormone (CRH; 0.1 μg/kg of BW) and thyrotropin-releasing hormone (TRH; 0.33 μg/kg of BW) challenges. Steers receiving CAM had greater (P < 0.05) serum concentrations of PUFA compared to CO prior to challenges. Upon CRH infusion, mean plasma ceruloplasmin concentrations increased at a lesser rate in CAM compared with CO (P < 0.01). Upon TRH infusion, no treatment effects were detected (P ≥ 0.55) for serum TSH, T₃, and T₄. In Exp. 3, 60 steers were allocated to 20 drylot pens. Pens were randomly assigned to receive CAM (2.04 kg of DM/steer daily) or CO (2.20 kg of DM/steer daily) during preconditioning (PC; d -28 to 0). On the morning of d 0, steers were transported for 24 h. Upon arrival from transport on d 1, pens were randomly assigned to receive, in a 2 x 2 factorial arrangement, CAM or CO during feedlot receiving (FR; d 1 to 29). During PC, CAM had reduced (P < 0.01) forage and total DMI, and tended to have reduced (P = 0.10) ADG compared to CO. Plasma linolenic acid concentrations increased during PC for CAM, but not for CO (P = 0.02). Steers that received CAM during FR had greater (P < 0.05) mean plasma concentrations of PUFA, and reduced mean rectal temperature and concentrations of haptoglobin and ceruloplasmin during FR compared to CO. Therefore, camelina supplementation reduced forage and total DMI, did not alter thyroid gland function, increased PUFA concentrations in blood, and attenuated the acute-phase protein reaction elicited by neuroendocrine stress responses. In conclusion, camelina meal is a feasible ingredient to reduce stress-induced inflammatory reactions and potentially promote cattle welfare and productivity in beef operations. / Graduation date: 2012

Perennial ryegrass (PRG, Lolium perenne) is a hardy cool-season grass that is infected with the endophytic fungus Neotyphodium lolii, which enables the plant to be insect repellant and drought resistant, lowering the use of insecticides and fertilizers. However, this fungus produces the compound lolitrem B (LB, m/z 686.4) which causes the tremorgenic neurotoxicity syndrome 'ryegrass staggers' in livestock consuming forage which contains <2000 ppb LB. Ergovaline (EV, m/z 534) is a vasoconstrictor normally associated with tall fescue (Festuca arudinacea), but has also been found in endophyte-infected PRG. Past research has shown a strong linear correlation between levels of LB and EV in PRG. The purpose of this study was to examine the linear relationship between EV and LB in feces and determine common metabolites. To accomplish this, four groups of steers (n=6/group) consumed endophyte- infected PRG over 70 days consumed the following averages of LB and EV: group I 2254ppb LB/633 ppb EV; group II 1554ppb LB/ 373ppb EV, group III 1011ppb LB/259ppb EV, and group IV 246ppb LB/<100ppb EV. Group I in week 4 was inadvertently given a washout period at which time the steers consumed the amount of LB and EV given to group IV (control). Both feed and feces samples were extracted using difference solid phase extraction methods and quantified by HPLC-fluorescence for LB and EV. Concentrations of EV and LB obtained through HPLC-fluorescence in both PRG and feces showed a linear relationship. Additional screening for metabolites was conducted LC-MS/MS and showed possible oxidation and reduction metabolites for both toxins. / Graduation date: 2013

Made available in DSpace on 2014-06-11T19:23:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-26Bitstream added on 2014-06-13T20:11:42Z : No. of bitstreams: 1 mouraesilva_fc_me_botfmvz.pdf: 536732 bytes, checksum: b483c8eb0344fa45e6c29e1db8477c14 (MD5) / Fundação para o Desenvolvimento da UNESP (FUNDUNESP) / O presente trabalho teve como objetivo determinar os elementos minerais no soro sangüíneo (magnésio, cobre, selênio, zinco, fósforo, cálcio, potássio, ferro) e no tecido hepático (cobalto, cobre, selênio, manganês, molibdênio e zinco) em seis diferentes momentos durante um período de dezesseis meses e verificar se houve variação entre eles. Foram utilizadas 25 novilhas mestiças Nelore, com idade média de 18 meses, que permaneceram durante todo o tempo do experimento no mesmo pasto de Brachiaria brizantha. Os animais ainda receberam mistura mineral comercial em cocho coberto e água à vontade e foram submetidos à coleta de fragmentos hepáticos e sangue para obtenção de soro. Análises da pastagem também foram realizadas nos mesmos momentos em que foram colhidas as amostras de soro e fígado (exceto em fevereiro 2003). A água e o sal mineral também foram analisadas. Os níveis médios dos elementos no tecido hepático foram, respectivamente para as seis diferentes colheitas: Co 0,27;0,27; 0,23;0,21; 0,23 e 0,24 ppm; Mn 9,07; 8,55; 8,67; 8,40; 7,90 e 7,25 ppm; Mo 4,18; 3,85; 3,68; 3,32; 3,54; 3,19 ppm; Zn 113,4; 101,94; 97,91; 92,46; 88,29 e 81,74 ppm; Cu 40,76; 36,33; 24,50; 24,70; 77,75 e 128,03 ppm e Se 0,86; 1,09; 0,72; 1,21; 0,91 e 0,75 ppm. Destes, os níveis de Co, Mn, Mo, Se e Zn foram considerados adequados para bovinos. Os níveis médios dos elementos no soro foram, para as quatro diferentes colheitas: Ca 118,72; 129,36; 125,19; 112,90; 96,76; 85,37 mg/L; P 109,28; 106,30; 117,03; 103,39; 115,78 e 107,75 mg/L; Mg 19,75; 23,62; 26,54; 20,96; 20,80 e 23,12 mg/L; K 139,64; 134,85; 114,19; 131,65; 130,57 e 116,60 mg/L; Cu 0,52; 0,73; 0,41; 0,59; 0,60 e 0,73 mg/L; Zn 1,19; 1,87; 1,38; 1,13;1,28 e 1,37 mg/L; Fe 2,52; 3,44; 2,21; 3,08; 3,00 e 2,89 mg/L e Se 1,19; 1,87; 0,19; 0,44, 0,40 e 0,51 mg/L... / The objective of the present work was to determinate the mineral levels in beef cattle blood serum (magnesium, copper, selenium, zinc, phosphorus, calcium, potassium, iron) and liver (cobalt, copper, selenium, manganese, molibdenium and zinc) at six different moments throughout sixteen months, to verify the occurrence of variation among them. Twenty-five half-breed nelore heifers, all of them about 18 months old, stayed during the experiment in the same Brachiaria brizantha pasture. They also received commercial mineral mixture in appropriate feeders and free acess to water. Pasture were also analised at the same moments we did for serum and liver (except february 2003). Water and mineral mixture were analised as well. The average levels of the elements in the liver, respectively for the six different moments: Co 0.27,0.27, 0.23, 0.21, 0.23 and 0.24 ppm; Mn 9.07, 8.55, 8.67, 8.40, 7.90 and 7.25 ppm; Mo 4.18, 3.85, 3.68, 3.32, 3.54, 3.19 ppm; Zn 113.4, 101.94, 97.91, 92.46, 88.29 and 81.74 ppm; Cu 40.76, 36.33, 24.50, 24.70, 77.75 and 128.03 ppm and Se 0.86, 1.09, 0.72, 1.21, 0.91 and 0.75 ppm. The levels of Co, Mn, Mo, Se and Zn were considered appropriate for cattle. The average levels of the elements in the serum were, for the six different moments: Ca 118.72, 129.36, 125.19, 112.90, 96.76, 85.37 mg/L; P 109.28, 106.30, 117.03, 103.39, 115.78 and 107.75 mg/L; Mg 19.75, 23.62, 26.54, 20.96, 20.80 and 23.12 mg/L; K 139.64, 134.85, 114.19, 131.65, 130.57 and 116.60 mg/L; Cu 0.52, 0.73, 0.41, 0.59, 0.60 and 0,73 mg/L; Fe 2,52; 3,44; 2,21; 3,08; 3,00 and 2,89 mg/L; Se 1.19, 1.87, 0.19, 0.44, 0.40 and 0.51 mg/L and Zn 1.19, 1.87, 1.38, 1.13,1.28 and 1.37 mg/L. In the serum, Ca, P, Mg, Zn, Fe and Se levels were considered appropriate for beef cattle. There was correlation between the hepatic and serum levels of Cu...(Complete abstract, click electronic address below)

CAPES / O trabalho foi desenvolvido na Fazenda Modelo do Instituto Agronômico do Paraná (IAPAR) no município de Ponta Grossa, entre o período de Junho de 2011 a Março de 2012. Com o objetivo de avaliar os sistemas de desmame precoce e da amamentação controlada sobre o desempenho de vacas e bezerros durante o período reprodutivo, foram utilizadas 161 vacas mestiças Purunã e seus respectivos bezerros, distribuídos em três grupos: Desmame precoce (DP), foi realizado através do desmame dos bezerros com média de 75 dias de idade; o grupo Amamentação Controlada (AC), as vacas foram separadas de seus bezerros e colocadas a amamentar apenas uma vez ao dia durante o período da estação de monta; o terceiro grupo era do Desmame convencional (DC), em que as vacas mantiveram seus bezerros em aleitamento durante todo do tempo, sem alguma interferência no manejo durante todo o período de avaliação. As vacas de todos os grupos pariram em condição corporal acima de 3,3 pontos (escala de 1 a 5), não apresentando diferença na taxa de prenhez, sendo 90% para as vacas do DC; 96% para as vacas da AC e 97% para as vacas do DP. Quando em boas condições ao parto a utilização do desmame precoce e da amamentação controlada não trazem benefícios produtivos, podendo o desmame precoce provocar queda na eficiência reprodutiva do plantel de cria devido ao peso do bezerro ser 19,6% menor em relação ao desmame convencional. Os bezerros submetidos ao DP apresentaram menor (P<0,05) ganho de peso diário (0,56 kg) durante o período experimental em relação ao grupo AC e DC (0,95 kg e 0,88 kg, respectivamente) os quais não diferiram entre si (P<0,05). O manejo da amamentação controlada não provoca efeito no desempenho dos bezerros, podendo ser desmamados com peso similar aos bezerros mantidos ao pé da vaca. A categoria das vacas (Jovens, Adultas e Velhas) não apresentou interação com o sistema de desmame. Observou-se que Vacas jovens, são mais leves (P<0,05) ao parto e ao desmame de seus bezerros (383,89 e 399,40 kg, respectivamente) em relação às vacas adultas (444,07 e 451,92 kg) e velhas (452,35 e 470,49 kg). Desta forma as Novilhas acasaladas aos dois anos paridas em boas condições nutricionais apresentam a mesma eficiência reprodutiva que vacas adultas (47,64 e 48,35 kg de bezerro ao desmame/100 kg de vaca, respectivamente), ao passo que vacas velhas apresentam a menor eficiência reprodutiva no plantel de cria (42,99 kg de bezerro/100kg de vaca). O menor peso ao desmame de bezerros filhos de vacas primíparas e velhas é devido ao menor peso desde o nascimento até os 150 dias de idade, não havendo diferença no desempenho a partir deste período. / The study was developed at Fazenda Modelo an Experimental Estation belonged to the Insituto Agronômico do Paraná (IAPAR) in the city of Ponta Grossa, Pr, in the period from June 2011 to March 2012. Aiming to evaluate the systems of early weaning and controlled nursing about the performance of cows and calves during the breeding season, 161 crossbred Purunã cows and their calves were used and the were divided into three groups: Early weaning (DP), which was fulfilled weaning of calves with the average age of 75 days; the group of controlled nursing (AC), the cows were separated from their calves and placed to breastfeed only once a day during the breeding season; and the third group was the conventional weaning (DC), which the cows kept their calves together during the whole time without any interference in the management, with definitive weaning at seven months. Cows from all groups calved in body condition score above 3.7 points (scale from 1 to 5), with no significant difference in the pregnancy rate, 90% for cows in DC, 96% for cows for AC and 97% for cows of early Weaning. When in good condition at calving the use of early weaning or controlled nursing do not bring productive benefitis, early weaning can cause decline in reproductive efficiency of the breeding herd because of the weight of the calf to be 19.6% lower compared to conventional weaning. Calves subjected to the DP showed a lower overage (P <0.05) daily weight gain (0.56 kg) during the experimental period compared to the group at the AC and DC (0.95 kg and 0.88 kg, respectively) which did not differ from each other (P <0.05). The management of controlled nursing causes no effect on the performance of calves, that can be weaned with similar weight to calves maintained together the cow. As the cow category (Young, Adult and Old) showed no interaction with the system weaning, they were discussed independently. It was observed that young cows are lighter (P <0.05) at calving and weaning of their calves (383.89 and 399.40 kg, respectively) compared to mature cows (444.07 and 451.92 kg) and old (452.35 and 470.49 kg). Therefore, the Heifers bred at two years old, that calve in good nutritional conditions have the same reproductive efficiency that adult cows (47.64 and 48.35 kg of weaning calf to 100 kg/cow, respectively), while the old cows show lower reproductive efficiency in a breeding herd (42.99 kg of calf per 100kg/cow). The lower weaning weight of calves born from primiparous and old is because of the lower weight and performance since the birth to 150 days of age, with no difference in performance after this period.

CAPES / O trabalho foi desenvolvido na Fazenda Modelo do Instituto Agronômico do Paraná (IAPAR) no município de Ponta Grossa, entre o período de Junho de 2011 a Março de 2012. Com o objetivo de avaliar os sistemas de desmame precoce e da amamentação controlada sobre o desempenho de vacas e bezerros durante o período reprodutivo, foram utilizadas 161 vacas mestiças Purunã e seus respectivos bezerros, distribuídos em três grupos: Desmame precoce (DP), foi realizado através do desmame dos bezerros com média de 75 dias de idade; o grupo Amamentação Controlada (AC), as vacas foram separadas de seus bezerros e colocadas a amamentar apenas uma vez ao dia durante o período da estação de monta; o terceiro grupo era do Desmame convencional (DC), em que as vacas mantiveram seus bezerros em aleitamento durante todo do tempo, sem alguma interferência no manejo durante todo o período de avaliação. As vacas de todos os grupos pariram em condição corporal acima de 3,3 pontos (escala de 1 a 5), não apresentando diferença na taxa de prenhez, sendo 90% para as vacas do DC; 96% para as vacas da AC e 97% para as vacas do DP. Quando em boas condições ao parto a utilização do desmame precoce e da amamentação controlada não trazem benefícios produtivos, podendo o desmame precoce provocar queda na eficiência reprodutiva do plantel de cria devido ao peso do bezerro ser 19,6% menor em relação ao desmame convencional. Os bezerros submetidos ao DP apresentaram menor (P<0,05) ganho de peso diário (0,56 kg) durante o período experimental em relação ao grupo AC e DC (0,95 kg e 0,88 kg, respectivamente) os quais não diferiram entre si (P<0,05). O manejo da amamentação controlada não provoca efeito no desempenho dos bezerros, podendo ser desmamados com peso similar aos bezerros mantidos ao pé da vaca. A categoria das vacas (Jovens, Adultas e Velhas) não apresentou interação com o sistema de desmame. Observou-se que Vacas jovens, são mais leves (P<0,05) ao parto e ao desmame de seus bezerros (383,89 e 399,40 kg, respectivamente) em relação às vacas adultas (444,07 e 451,92 kg) e velhas (452,35 e 470,49 kg). Desta forma as Novilhas acasaladas aos dois anos paridas em boas condições nutricionais apresentam a mesma eficiência reprodutiva que vacas adultas (47,64 e 48,35 kg de bezerro ao desmame/100 kg de vaca, respectivamente), ao passo que vacas velhas apresentam a menor eficiência reprodutiva no plantel de cria (42,99 kg de bezerro/100kg de vaca). O menor peso ao desmame de bezerros filhos de vacas primíparas e velhas é devido ao menor peso desde o nascimento até os 150 dias de idade, não havendo diferença no desempenho a partir deste período. / The study was developed at Fazenda Modelo an Experimental Estation belonged to the Insituto Agronômico do Paraná (IAPAR) in the city of Ponta Grossa, Pr, in the period from June 2011 to March 2012. Aiming to evaluate the systems of early weaning and controlled nursing about the performance of cows and calves during the breeding season, 161 crossbred Purunã cows and their calves were used and the were divided into three groups: Early weaning (DP), which was fulfilled weaning of calves with the average age of 75 days; the group of controlled nursing (AC), the cows were separated from their calves and placed to breastfeed only once a day during the breeding season; and the third group was the conventional weaning (DC), which the cows kept their calves together during the whole time without any interference in the management, with definitive weaning at seven months. Cows from all groups calved in body condition score above 3.7 points (scale from 1 to 5), with no significant difference in the pregnancy rate, 90% for cows in DC, 96% for cows for AC and 97% for cows of early Weaning. When in good condition at calving the use of early weaning or controlled nursing do not bring productive benefitis, early weaning can cause decline in reproductive efficiency of the breeding herd because of the weight of the calf to be 19.6% lower compared to conventional weaning. Calves subjected to the DP showed a lower overage (P <0.05) daily weight gain (0.56 kg) during the experimental period compared to the group at the AC and DC (0.95 kg and 0.88 kg, respectively) which did not differ from each other (P <0.05). The management of controlled nursing causes no effect on the performance of calves, that can be weaned with similar weight to calves maintained together the cow. As the cow category (Young, Adult and Old) showed no interaction with the system weaning, they were discussed independently. It was observed that young cows are lighter (P <0.05) at calving and weaning of their calves (383.89 and 399.40 kg, respectively) compared to mature cows (444.07 and 451.92 kg) and old (452.35 and 470.49 kg). Therefore, the Heifers bred at two years old, that calve in good nutritional conditions have the same reproductive efficiency that adult cows (47.64 and 48.35 kg of weaning calf to 100 kg/cow, respectively), while the old cows show lower reproductive efficiency in a breeding herd (42.99 kg of calf per 100kg/cow). The lower weaning weight of calves born from primiparous and old is because of the lower weight and performance since the birth to 150 days of age, with no difference in performance after this period.

An experiment was conducted using forty-one Bonsmara steers (age ± 7 months) to determine the effect of zilpaterol hydrochloride (ZH) on the growth performance and carcass characteristics. The trial was structured using a completely randomized design with two treatments, control and ZH group. The steers were fed ZH for 28 consecutive days at the end of the finishing period and ZH was withdrawn from the diet 2 days prior to slaughter of the animals. The steers were placed in individual pens and weighed fortnightly throughout the 4 months trial. Zilpaterol hydrochloride (ZH) was included in the diet at a rate of 8.3 mg/kg of DM. Feeding of ZH increased (P< 0.05) body weight (BW) gain and ADG (1.102 vs. 1.444) and tended to increase (P = 0.067) feed efficiency (F:G) during the last month of the finishing period. There were no significant differences (P> 0.05) in daily dry matter intakes (DMI). For the control group, high treatment weight gains were significantly associated with high initial weight (r = 0.424, P = 0.049) and also high pre-treatment body weight (r = 0.678, P= 0.001). Treatment weight gain increased as the initial and pre-treatment weight gain increased in the control group. For the steers that were fed ZH, there was no significant correlation between the treatment body weight gain with initial weight (r = 0.097, P = 0.694) and also pre- treatment live weight (r = 0.393, P = 0.096). Supplementation of ZH significantly increased (P < 0.0001) the dressing percentage (56.4% vs. 58.4%) and had no significant (P>0.05) effect on the carcass weight. The outcome of the study suggest that supplementation of ZH in the diet during the last month of the finishing period enhances growth performance and shows the repartitioning capacity of the feed additive as a beta- agonist. / Agriculture and  Animal Health / M. Sc. (Agriculture (Animal Science)

Call number: LD2668 .T4 1986 N44 / Master of Science / Agricultural Economics

An experiment was conducted using forty-one Bonsmara steers (age ± 7 months) to determine the effect of zilpaterol hydrochloride (ZH) on the growth performance and carcass characteristics. The trial was structured using a completely randomized design with two treatments, control and ZH group. The steers were fed ZH for 28 consecutive days at the end of the finishing period and ZH was withdrawn from the diet 2 days prior to slaughter of the animals. The steers were placed in individual pens and weighed fortnightly throughout the 4 months trial. Zilpaterol hydrochloride (ZH) was included in the diet at a rate of 8.3 mg/kg of DM. Feeding of ZH increased (P< 0.05) body weight (BW) gain and ADG (1.102 vs. 1.444) and tended to increase (P = 0.067) feed efficiency (F:G) during the last month of the finishing period. There were no significant differences (P> 0.05) in daily dry matter intakes (DMI). For the control group, high treatment weight gains were significantly associated with high initial weight (r = 0.424, P = 0.049) and also high pre-treatment body weight (r = 0.678, P= 0.001). Treatment weight gain increased as the initial and pre-treatment weight gain increased in the control group. For the steers that were fed ZH, there was no significant correlation between the treatment body weight gain with initial weight (r = 0.097, P = 0.694) and also pre- treatment live weight (r = 0.393, P = 0.096). Supplementation of ZH significantly increased (P < 0.0001) the dressing percentage (56.4% vs. 58.4%) and had no significant (P>0.05) effect on the carcass weight. The outcome of the study suggest that supplementation of ZH in the diet during the last month of the finishing period enhances growth performance and shows the repartitioning capacity of the feed additive as a beta- agonist. / Agriculture and  Animal Health / M. Sc. (Agriculture (Animal Science)

Text in English / Cow size influences biological efficiency of individual animals, which influences herd composition and stock flow. This in turn influences the economic efficiency of the herd. This research followed the thread from animal size, to biological efficiency, to economic efficiency for beef cattle production under a typical production system in semi-arid South Africa. Cattle were grouped into three groups namely small, medium and large cattle, with mature weights of 300kg, 450kg and 600kg respectively. The net energy requirements of individual cattle were calculated for maintenance, growth, lactation and foetal production, for each of the three sizes. Growth rates, milk yield, reproduction rates, and management practices were assumed from existing research. Next the stock flow for a herd of small, medium and large cattle were calculated from the above. Income and expenses as commonly used in the research area were calculated from the stock flow. Gross profit above allocated costs were subsequently calculated for the three herds under the above-mentioned conditions. When assuming similar reproduction and growth rates for small, medium and large mature cattle, the following results were obtained: more heads of small cattle could be held on a set resource base, but the total live weight of a herd of large cattle that could be held on the same resource base was greater. This was mostly due to proportionately lower maintenance energy requirements in the herd of large cattle. In the simulation in this study, maintenance energy requirements for the herd of large cattle was 71.2%, compared to 72.0% for the herd of medium cattle and 73.1% for the herd of small cattle. Income from the herd of small cattle was the lowest, as less kilograms of beef were available to sell. Allocated costs for the herd of small cattle were the highest, due to a large number of expenses being charged per head of cattle. As a result, the herd of large cattle were more economically efficient than their smaller counterparts. Income above allocated costs for the herds of large, medium and small cattle were R1,182,865, R1,085,116 and R946,012 respectively. Larger cattle generally have a lower reproduction rate under similar conditions. No equation exists that directly links size to reproduction rates, especially considering the vast number of variables that influences reproduction rates. However, in the form of scenarios, it could be calculated that, given a reproduction rate of 80% for mature small cattle, when reproduction rates of large cattle were 24.7% lower than that of small cattle and the reproduction rates of medium cattle were 15.4% lower than that of small cattle, the large and medium herds became less profitable than the small herd. Smaller cattle mature faster than larger cattle which provides the opportunity for early breeding. When small cattle were bred early, at 15 months, at a calving rate of only 44.5% it was more profitable than when the same cows were bred at 24 months. When medium cattle were bred at 15 months, a calving rate of 37.0% was needed to be more profitable than when they were bred at 24 months. Even when the herd of small cattle were bred at 15 months with a reproduction rate of 100%, it could still not match the profitability of the herd of large cattle bred at 24 months given the reproduction rates of all other classes of animals were similar. When the herd of medium cattle were bred at 15 months, at a calving rate of 53.7%, it matched the profit of the herd of large cattle that were bred at 24 months, when the reproduction rates of other classes were equal. Scenarios were considered were feed intake was limited. When feed was limited to a specific amount, smaller cattle were more biologically efficient and cattle with potential for small mature sizes would grow to a larger size than cattle with potential for medium and large mature sizes. When feed was limited by a factor of the calculated energy requirements of small, medium and large cattle, large cattle were more effective. This is because large cattle use proportionately less energy for maintenance, which allows more energy to be allocated to growth, lactation and foetal production. When energy was limited to an amount per unit of metabolic weight, small cattle were more efficient than medium and larger cattle in the growth and production phases. Small, medium and large cattle were equally efficient (or inefficient) in the maintenance and lactation phases. Energy requirements of cattle in South Africa are commonly calculated using the Large Stock Unit (LSU). The LSU typically overestimates energy requirements for cattle, except in the lactation phase. When using the LSU to match small, medium or large cattle to a resource base, the LSU overestimates energy requirements of large cattle proportionately more than that of small and medium cattle. This is excluding the lactation phase, where energy requirements for all three sizes are underestimated and that of large cattle underestimated proportionately more. There are more considerations when matching cow size to managerial practices. A smaller body size is a natural adaptation to a semi-arid environment and this adaptation can be expressed in different ways. The number of animals on a resource base has implications on management practices. Having more heads of cattle on a resource base increases genetic variation of the herd, allowing for genetic progress to be made faster than in herd of fewer cattle. / Agriculture and  Animal Health / M.Sc. (Agriculture)