Masters Degrees (Animal Sciences)

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    The comparative effects of essential oil compounds and monensin in the diet of pre-weaned calves on animal growth, performance and the prevalence of antibiotic resistant Escherichia coli and Salmonella spp.
    (Stellenbosch : Stellenbosch University, 2023-04) Gouws, Michelle; Steyn, Lobke; Van Zyl, J. H. C.; Van den Honert, M. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Ionophores, such as monensin, are used in dairy calf rearing systems to control coccidiosis and aid in growth and health of the calf. However, the need for alternative growth-promoting and disease preventing feed additives to ionophores in calf diets has become a great area of interest. Many European Union (EU) countries have banned the subtherapeutic use of antimicrobial drugs in livestock and increased legislation on therapeutic antibiotic use. The relevant issue of the misuse of antibiotics that may lead to increased antimicrobial resistant pathogens present on farm level, has gained public concern. Since some pathogenic bacteria found in food products stem from the farm, the livestock sector is often viewed as a reservoir for antibiotic resistant pathogens that can easily be transferred to humans through contamination. Essential oil compounds carvacrol, capsaicin, and cinnamaldehyde have shown promising antimicrobial properties and overall health benefits to poultry, pigs, cattle, and pre-weaned calves. The present study investigated the benefit of adding an essential oil blend or monensin to the diet of pre-weaned calves on subsequent growth, health, and rumen development. Furthermore, the abundance of Escherichia coli and Salmonella spp. in the faeces of the calf was investigated to determine if the blend of essential oil compounds or monensin may increase the prevalence of antibiotic resistant bacteria. Two animal trials were conducted in two separate locations. In both trials, the calves were randomly allocated to one of three treatment groups: control (CON), a garlic extract in the liquid diet (0.6 g/calf/day) and a blend of essential oil compounds (150 mg/kg DM) in the starter feed (EOC), and monensin (30 mg/kg DM) in the starter feed (MON). Calves were weaned at 60 days of age. In Trial 1, Jersey bull calves (N = 24; 22.105 ± 1.383 kg birth weight) were raised in an outdoor, sheltered unit to investigate the effect of the treatment groups on rumen development, calf growth and performance, and the prevalence of antibiotic resistant pathogens. In Trial 2, Ayrshire heifer calves (N = 39; 35.5 ± 5.2 kg birth weight) were raised in an intensive indoor rearing unit to assess the effect of the treatment groups on calf health, growth, and performance, as well as the abundance of antibiotic resistant pathogens. No difference in overall growth, health and rumen development was observed between treatment groups, indicating that essential oil compounds can successfully replace monensin in calf diets. However, during Trial 2 an increase in antibiotic administration for treatment of disease was associated with the MON treatment. Furthermore, an increase in multidrug resistant E. coli (71%) was associated with the MON treatment, confirming that monensin contributes to the risk associated with subtherapeutic antimicrobial use in dairy calves. Resistance profiles also differed between farms, with the intensive indoor calf rearing facility having the highest prevalence of multidrug resistance. Similar average daily gain and faecal consistency indexes showed by the CON treatment group, together with an increased abundance of multidrug resistant E. coli associated with the MON treatment, raises the question of the necessity of the supplementation of either monensin or an essential oil compound blend in calf diets. As this study further confirms the association between subtherapeutic antibiotic use and increased multidrug resistant bacteria, the implementation of surveillance programmes for antibiotic use in large, commercial dairy operations is needed. Further research into suitable replacements to subtherapeutic antimicrobial drugs in animal feed are also needed, such as the use of essential oil compounds, and should be prioritized in future endeavors.
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    The effect of pasture biostimulant treatment and decreased concentrate supplementation on pasture production and the production and profitability of pasture fed lactating Jersey cows
    (Stellenbosch : Stellenbosch University, 2023-03) De Beer, Janika; Van Zyl, Johan Hendrik Combrink; Steyn, L.; Kleynhans, T. E.; Swanepoel, P. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: Pasture-based dairy farmers are struggling against rising feed costs and stagnant milk prices. To combat the effect of increasing feed prices on the profitability of a pasture-based dairy farm, levels of concentrate supplementation can be decreased to lower input costs. It is evident that the profitability of a pasture-based dairy farm can be improved through the reduction in concentrate supplementation level while (where possible) the herbage allowance and quality is increased. Profitability studies however failed to include the effect of increase of land use, due to an increased pasture allowance that leads to decreased stocking rate. Plant-biostimulants like fulvic acid and bioflavonoids can increase pasture quantity, thereby improving stocking density. The gap in profitability studies to examine the economic effect of a combined application of reduction of concentration supplementation and the increase in pasture quantity and quality through the application of fulvic acid and bioflavonoids has to the best of the author’s knowledge not been investigated. This study aimed to quantify the effect of reduced concentrate supplementation rates in the production of pasture fed lactating Jersey cows. Simultaneously, the effect of plant-biostimulant treatment, fulvic acid and bioflavonoid, on a mixture of perennial ryegrass and clover pasture was also studied. Lastly, the effect of reduced concentrate feeding and increased pasture allowance on the profitability of Jersey cows was investigated. For the first study, a 3.3 Ha pasture paddock consisting of homogenic one-year old perennial ryegrass and clover pasture were used. A randomized block design with three blocks and two treatment factors (each at two levels) were adopted viz. 12 experimental plots. The first factor was the grazing cycle in two contrasting seasons (summer 2021 and winter 2021). For the second factor an untreated control was compared to a commercial plant-biostimulant cocktail treatment. Two plots per block were treated with the biostimulants. Biostimulant treatment affected pasture botanical composition, resulting in lower ryegrass content in both a winter and summer grazing cycle (P < 0.01). The biostimulant treatment had no effect on the chemical composition nor the total yield of perennial ryegrass/clover pasture within a seasonal grazing cycle. There was however a tendency (P = 0.08) for biostimulant treatment to improve herbage yield in the summer grazing cycle. For the second study twenty-four lactating multiparous Jersey cows for both a winter and summer season were used. A randomized block design was used where cows were randomly assigned to one of two treatments: four kilogram concentrate supplement per day with 12 kg (DM) pasture allowance (LC) and eight kg concentrates supplement per day with 8 kg (DM) pasture allowance (HC). The long-term effects of reduced concentrate supplement feeding were also investigated after the completion of the winter and summer trials. During the long-term evaluation, the cows in both treatment groups grazed pasture ad lib with 4 kg day⁻¹ concentrate supplementation. Milk yield, 4% fat corrected milk yield and energy corrected milk yield remained unchanged regardless of concentrate supplementation rate in both the summer and winter trials. Milk protein yield and milk protein content were not affected by treatment in the winter trial. In the summer trial treatment influenced milk protein yield (P < 0.01) but not milk protein content. Milk protein yield was higher for the HC treatment. Milk fat yield, milk fat content, somatic cell count, body weight and condition score were not affected by treatment in both the winter and summer trials. Milk urea nitrogen levels was affected by concentrate supplementation rate (P < 0.01) in the winter trial but not in the summer trial. Milk urea nitrogen levels were higher for cows in the LC treatment (9.11 mg N dL⁻¹) than cows in the HC treatment (6.56 mg N dL⁻¹) during the winter trial. The cows in the LC and HC treatment groups managed to maintain their body condition score and body weight in both the winter and summer trials up to 150 days after the end of each respective trial. Milk yield after each trial followed the shape of a standard lactation curve and milk yield gradually decreased towards the drying off period. Lastly, the effect of reduced concentrate feeding and increased pasture allowance on the profit margin over feed cost per cow day⁻¹, per cow hectare⁻¹ and per cow month⁻¹ of multiparous lactating Jersey cows in the summer and winter seasons was determined. In the winter trial lowering of concentrate supplementation proved to be profitable when enough good quality pasture is available based on both per cow per day (P = 0.03) and monthly performances (P = 0.04). There was also no negative effect of reduced concentrate supplementation levels on per cow per hectare performance. The only benefit of reduced supplementation levels in the summer trial was based on the profit margin per cow per day. Higher supplementation levels proved more profitable (P < 0.05) on per cow per hectare performance with no difference in profit margin between treatments based on a monthly basis. Although biostimulant application did not improve pasture yield, farmers can still increase farm profitability through reduced supplement rates and increased pasture allowance when good quality pasture is available.
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    A systematic review of the role of genomic copy number variation in cattle (Bos taurus) production and associated genes
    (Stellenbosch : Stellenbosch University, 2023-03) Old, Jessica Anne; Dzama, Kennedy; Molotsi, Annelin; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: With an ever-increasing demand for milk and meat products, and with climate change posing a threat to the productive efficacy of cattle across the globe, there is a need for the application of genomic tools for animal breeding. The valuable genomic variation exhibited in cattle is important for identifying major genes and quantitative trait loci (QTL), to be used as molecular markers in the genomic selection of animals. One of the key steps of selective breeding in cattle is the characterisation of genetic variation responsible for phenotypic differences. Copy number variations (CNVs), such as duplications, deletions, and insertions, are increasingly being shown to be one of the main contributors to genomic diversity and subsequent phenotypic differences observed among animals. Copy number variation can cause major changes in gene expression, phenotypic traits, and evolutionary adaptation, through gene dosage and transcript structure alterations. Several CNV- based studies have identified gene variations that could potentially be responsible for the phenotypic differences, but the sheer number of studies on this topic makes it difficult for one to come to a definite conclusion. This systematic review summarised the relevant findings of cattle CNV research, and identified the important genes involved therewith, to help researchers remain up to date with current and ongoing research in cattle-CNV studies. This review revealed that cattle CNV research has increased considerably since 2008. The extent and distribution of the publications reflect the worldwide growing importance of understanding the cattle genome for genetic improvement of livestock. However, there is a lack of research in developing countries, a lack of emphasis on Bos indicus (12%) and Bos taurus africanus (4%) cattle, and a lack of standardised reporting across cattle CNV studies. Copy number variations can alter the gene expression and consequently influence phenotypic expression. This systematic review identified several important CNV-related genes in the published articles that influence economically important traits in cattle. These genes were related to adaptation and immunity (ABCC4, BOLA gene family, IGLL1, OR family, WC1, ZNF280B, BSP30A, DEFB, ULBP gene family, CATHL gene family, and HSP gene family), milk yield, milk composition and reproduction (DGAT1, IFNT, PAG, PRAME, PRL, AP3B1, IGLL1, SLC27A6, ITFG1, MTHFSD, PRP, and PTK2), meat yield, meat quality and growth (IGF2, PLA2G2D, CAST, IGF1R, APOL3, PTPRC, KCNJ12, CAPN1, AGBL3, CTNNA1, MSTN, ADRA1B, ATRN, LRRC49, MYH3, SORCS2, and TG), feed efficiency (PRKG1, FABP2, and EIF2S1), and coat colour, coat patterns and hair morphology (KIT, AP3B1, MC1R, PRLR, and FGF18). This knowledge is relevant from a molecular perspective to the practical application in animal breeding, and offers breeders the means to consider genomic selection of animals at a younger age. The productive efficacy of cattle is vulnerable, thus, the use of molecular assisted selective breeding is essential for overcoming current and future challenges in cattle productivity.
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    The effect of fenugreek seed cotyledon extract (Trigonella foenum-graecum L.) supplementation on feedlot beef cattle production
    (Stellenbosch : Stellenbosch University, 2022-12) Van Wyk, Daniel John; Van Zyl, Johan H. C.; Cruywagen, C. W.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Globally, beef producers are constantly improving and expanding their production systems to keep up with the demand for beef. Consumer preferences further pressure producers to reduce chemicals as additives in favour of a more natural approach. This natural approach includes the use of effective natural “in-feed” additives to improve parameters like dry matter intake (DMI), feed conversion and manipulating microbe in the rumen to improve the animal productivity and eliminate harmful microorganisms. Consumer concern about the use of growth promoters and “infeed” antibiotics to prevent disease and increased feed efficiency, has propelled animal scientists to research natural alternatives to replace growth promoters and antibiotics. Supplementing animals with fenugreek extract have showed promising improvement in production parameters of dairy cows. A study done by Prof Cruywagen and a student of him, where they included fenugreek extract in the diet of the animals, resulted in increased daily milk yields. This study was conducted to evaluate the effect of dietary fenugreek extract on the production parameters and meat quality of beef feedlot cattle In the first part of the study, the effect of two different diets were evaluated under feedlot conditions and included a control, without fenugreek and a trial, with 120g of NutrifenPLUS® per animal per day which was included in the basal feedlot diet. NutrifenPLUS® is the commercial product used in the study and is a combination of fenugreek cotyledon extract (Trigonella foenum Graecum), fennel seeds (Foeniculum vulgane), saw palmetto berries (Serenoa repens), brown kelp (Laminariales), a natural source of methylsulfonylmethane (MSM) and white distilled vinegar powder. The two diets were fed to 24 Angus bulls (12 bulls per treatment) for 90 experimental days. Starting weight (kg), final weight (kg), DMI (kg/animal/day), total weight gain (kg), average daily gain (kg) and FCR (kg) parameters were determined. The results obtained from the experiment showed no significant differences between the fenugreek and the control treatments in any of the phases for starting weight (kg), final weight (kg), total weight gain (kg), ADG (kg) and FCR. A significant difference (P< 0.04) was however observed during the finisher phase (include Zilmax® - zilpaterol hydrochloride) where the total gain was negatively impacted by the addition of fenugreek. In the second part of the study, the effect of two different diets were evaluated under pasture rearing conditions and consisted of a control group without fenugreek extract and a trial with 120g of NutrifenPLUS® per animal per day in a supplementary basal diet. The two diets were fed to 28 cross-Brahman bulls (14 bulls per treatment) for 90 experimental days. Parameters determined included starting weight (kg), final weight (kg), total weight gain (kg), DMI (kg/animal/day), FCR, feed cost (R), weaner cost (R), carcass income (R) and margin/head (R). The results conducted from the experiment showed no significant differences between the fenugreek and the control treatments for starting weight (kg), final weight (kg), total weight gain (kg), DMI (kg), FCR (kg), feed cost (R), weaner cost (R), carcass income (R) or the margin/head (R) when compared over the total feed period. The results indicate that the addition of fenugreek had no significant effects on the parameters measured. The results found in the study suggest that additional research is required to further investigate the effect of dietary fenugreek extract on the production parameters and meat quality of beef cattle. Different rates of inclusion and different circumstances might however produce different results from that of the current study and should be evaluated in future studies.
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    Studies on the response of lambs and ewes to changes in the ambient climate owing to climate change
    (Stellenbosch : Stellenbosch University, 2022-12) Steyn, Shannong; Cloete, Schalk W. P.; Brand, T. S.; Van Zyl, Johan H. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: This study investigated the impact of climate instability on neonatal lamb behaviour as a proxy for lamb survival in a winter lambing season in the Western Cape, as well as the impact of increased temperatures on heat stress indicator traits in mature ewes in the Western and Eastern Cape. Historic data were used to establish the relationship of neonatal lamb behaviour with cold stress and to derive genetic parameters for early lamb behaviour. Merino lambs of the Elsenburg flock were phenotyped for behaviour latencies from birth to first standing (LTBS) and from standing to first suckling (LTSS). These data were analysed in relation to a cold stress gradient (CSG) derived from a combination of wind, rain, and temperature. The flock consisted of a line selected for number of lambs weaned per ewe mated (NLW; the High or H-Line) and a line selected against NLW (Low or L-Line). H-line lambs progressed faster from standing to first suckling than L-line lambs. Increased CSG-levels resulted in 18% faster progress in LTBS when mild conditions at 800kJm⁻²h⁻¹ were compared to stressful conditions at 1200kJm⁻²h⁻¹. LTSS was compromised by 76.0% as CSG-values increased from 800kJm⁻²h⁻¹ to 1200kJm⁻²h⁻¹. Heritability estimates were 0.22 for LTBS and 0.06 for LTSS. The maternal heritability for LTBS was 0.06 and the dam permanent environment variance ratio 0.09 for LTSS. The traits were not genetically correlated. Further research is required to understand the responses of lambs to cold stress. Average temperatures are likely to increase, resulting in hotter and dryer conditions in South Africa. The impact of these changes on animal production and welfare is not well-defined. Three trials were conducted on 10 to 20 mature, dry ewes at 2 locations to determine the homeothermic response of nine sheep breeds between 2016 and 2022. These breeds were the Dohne, Dormer, Dorper, Ile de France, Meatmaster, Merino, Namaqua Afrikaner, South African Mutton Merino (SAMM) and White Dorper. They were studied in different combinations across trials. On days forecast to be hot at noon, animals were assessed under cool conditions in the morning and hot conditions at noon/afternoon by monitoring individual rectal temperature, eye temperature (thermal imaging), spot temperature, and respiration rate. The increased heat in the afternoon sessions markedly increased all traits across trials. In general, hair breeds (Dorper, White Dorper, Meatmaster, and particularly Namaqua Afrikaner) were able to maintain lower basal respiration rates compared to the wool breeds originating from temperate regions (Dohne, Dormer, Ile de France, Merino, and SAMM). These results suggest that hair sheep and hardy indigenous breeds such as the Namaqua Afrikaner may cope better with the anticipated higher heat load in the future when compared to the breeds originating from temperate regions. Rectal temperature was low- moderately repeatable across trails, while outcomes for respiration rate and spot temperature were more variable and commonly affected by the reranking of ewes across sessions as well. Eye temperature was not repeatable. There is still marked scope for research on ovine adaptation to heat stress conditions in South Africa.