1,720,966 research outputs found
Genetic prediction of feed efficiency in South African Holstein cattle.
No full textDoctoral Degree. University of KwaZulu-Natal, Durban.Feed efficiency is a trait of outstanding importance in dairy cattle; however, it is difficult and expensive to measure and, therefore, not easy to improve through selection. The current study investigated the possibility of predicting the genetic merit for feed efficiency, in South African Holstein cattle, using routinely recorded easy-to-measure traits. The first two objectives were mainly to develop and validate models to predict dry matter intake (DMI) and gross feed efficiency (GFE) using milk production traits and live weight (LW). Data consisted of 30 daily measurements of DMI, milk yield (MY), energy-corrected milk (ECM), butterfat yield (BFY), protein yield (PROY), lactose yield (LACY), butterfat percent (BFP), protein percent (PROP), lactose percent (LACP), and 25 daily LW records of a group of 100 first-parity Holstein cows, fed a total mixed ration. Similar measurements were also collected from a group of 110 multiparous Holstein cows, in lactations 2 to 6. Gross feed efficiency was calculated as kg ECM divided by kg DMI. Forward stepwise regression analyses were performed to develop the models, using the PROC REG procedure of the Statistical Analysis System (SAS) software. Within-herd validation of the models for robustness and accuracy, was subsequently conducted by performing regression analyses between actual and predicted DMI and GFE records. The developed models reliably predicted daily DMI (kg/day) and GFE from milk, butterfat yield and/or live weight, with accuracies ranging from 66 to 98%. Validation of the best model to predict DMI, for first-parity cows, yielded a fairly moderate R2 value (0.49) and a low root mean square error (RMSE) (1.46 kg/day), while the best prediction model for GFE yielded a fairly high R2 value (0.64) and a low RMSE (0.13). The best prediction model for GFE, for multiparous cows, had a fairly moderate R2 value (0.54) and a low RMSE (0.06), upon validation, suggesting reasonable robustness and accuracy. The developed models, therefore, present an opportunity to easily generate large quantities of phenotypic data on individual cow DMI and GFE, at a relatively low cost, which can be used to achieve accurate selection for feed efficiency.
The third objective was, essentially, to assess the extent of genetic variability for the predicted traits, in order to evaluate their utility as selection criteria for feed efficiency. First, repeatability animal models were used to estimate genetic parameters for predicted gross feed efficiency (pGFE) and its relationship with energy-corrected milk (ECM) in the first three parities, using the ASReml software. Data of 11,068 test-day milk production records on 1,575 Holstein cows that calved between 2009 and 2019, were used. Predicted gross feed efficiency was calculated using the models developed in the first two objectives. Heritability estimates for pGFE ranged from 0.09 ± 0.04 in mid lactation to 0.18 ± 0.05 in late lactation. Estimates were moderate for primiparous (0.21 ± 0.05) and low for multiparous (0.10 ± 0.04) cows. Repeatability and heritability estimates across all lactations were 0.37 ± 0.03 and 0.14 ± 0.03, respectively. Genetic correlations between pGFE in different stages of lactation ranged from 0.87 ± 0.24 (early and mid) to 0.97 ± 0.28 (early and late), whereas a strong genetic correlation (0.90 ± 0.03) was obtained between pGFE and ECM, across all lactations. The average genetic merit for pGFE, across all lactations, increased at a marginal rate of 0.0058 per year, for cows born during the period 2007 to 2017. The low to moderate heritability estimates for pGFE suggest potential for genetic improvement of the trait through selection, albeit with a modest accuracy of selection. The high genetic correlation of pGFE with ECM may, however, assist to improve accuracy of selection for feed efficiency by including both traits in multi-trait analyses.
Due to the scarcity of information on the genetic variation exhibited by predicted dry matter intake (pDMI) from milk components, further genetic analyses were undertaken. Such analyses were important to determine whether pDMI could be a useful selection criterion for feed efficiency in dairy cattle. These analyses under the third objective involved estimation of heritabilities, repeatabilities and genetic correlations among predicted dry matter intake and gross feed efficiency, by repeatability animal models. Data consisted of 440,062 test-day records of 62,695 cows, in the first three parities, that calved between 2009 and 2019. Predicted dry matter intake was generated from milk yield data, using the developed prediction model, and pGFE was derived as kg ECM divided by kg pDMI. Heritability estimates ranged from 0.05 ± 0.02 for pGFE in mid lactation to 0.13 ± 0.03 for pDMI in late lactation. Estimates of heritability across parities were 0.08 ± 0.02 and 0.13 ± 0.02 for pGFE and pDMI, respectively. Corresponding estimates of repeatability across parities were 0.26 ± 0.01 and 0.41 ± 0.01 for pGFE and pDMI, respectively. Genetic correlations between pDMI and pGFE were moderate and negative in early (-0.42 ± 0.24) and mid lactation (-0.20 ± 0.24), and low and positive in late lactation (0.05 ± 0.17). The genetic correlation between pDMI and pGFE decreased with increase in parity, from 0.26 ± 0.16 to -0.09 ± 0.17. The low heritability estimates for pDMI and pGFE indicate low accuracy of selection for these traits in South African Holstein cattle. This can, however, be improved through multi-trait analyses including traits with which they are correlated.
Results of the current research pave the way for achieving genetic improvement in feed efficiency in the South African Holstein cattle population. This can go a long way towards the development of a more profitable and environmentally sustainable dairy industry. Higher rates of genetic change can be attained through genomic selection, by using the predicted phenotypes to identify genes or markers associated with feed efficiency
A deterministic evaluation of alternative management options for the smallholder dairy cattle production system in South Africa
No full textThesis (PhD (Animal Science))--University of Pretoria, 2020.The aim of this thesis was to evaluate alternative management options for the smallholder dairy cattle production system in South Africa (SA). Specific objectives included, were to benchmark cow performance in the smallholder (SH) against their counterparts in a high-input system (H), to develop a SH herd model, and to evaluate alternative management options for the improvement of smallholder dairy herd profitability. Data on production (305 day yields of milk, fat and protein), lactation length, somatic cell count (SCC), and reproductive traits (age at first calving (AFC), and calving interval (CI) obtained from the South African National Dairy Animal Improvement scheme (NDAIS) were used in a benchmarking study. Least squares means per trait were compared between the two systems, and lactation curves for production traits and SCC were plotted. Results revealed that mean yields of milk, fat and protein were significantly (P<0.05) lower in the SH (4 097±165, 174±5.1 and 141±4.5 respectively) compared to the H system (6 921±141, 298±4.7, and 245±4.1, respectively). Mean lactation length was significantly (P<0.05) shorter for the SH (308±15.1) compared to the H system (346±12.8). Log-transformed SCC was significantly (P<0.05) higher in the SH (2.41±0.01) relative to the H system (2.27±0.01). Cows in H herds exhibited typical lactation curves, in contrast to flat and low-peaking curves obtained for the SH system. SH cows had significantly (P<0.05) older AFC (30±0.5) than those in the H system (27±0.5). There was no significant difference (P<0.05) in CI between the two systems. A bio-economic SH herd model was developed by adapting a previously developed model for the H system in SA. Parameters used were obtained from NDAIS, survey data, personal communications, and literature. The model integrated herd dynamics, outputs, nutrient energy requirements, management, and their associated economics. Nutrient energy requirements were estimated for maintenance, growth, reproduction, and lactation. The developed SH herd model was used to evaluate alternative herd management options, using the partial budget approach. Milk yield (MY), live weight (LW), AFC, and CI were used as indicators of cow performance. Herd management practices studied were herd size (HS), replacement rate (RR), feeding system (FS), breeding methods (natural service vs artificial insemination), and source of replacement heifers (raising vs. buying in). Improvements in profitability were attained by increasing MY or increasing herd size, using small to medium sized cows, or reducing AFC, CI or RR. Break-even points were 3 687.4l/year, 500 kg, 29 months, 420 days and 25% for MY, LW, AFC, CI, and RR, respectively. Profitability was mostly sensitive to the prices of milk and feed. A drop in the price of milk below R4.50/l or increase in the cost of feed above R5.60/kg DM generally resulted in nonprofitability. Relying on pasture only for feed was non-viable, and supplementation of pasture with concentrate was the most profitable feeding system. Feeding systems based on supplementation of pasture with concentrate, and silage were resilient to fluctuations in the price of milk, remaining profitable even when the price dropped to R4.10/l. Using artificial insemination or buying-in replacement heifers are additional management strategies that increase SH dairy farming profitability. These recommended management options should be used in combination for achieving maximum herd profitability. Keywords: Benchmarking, Bio-economic model, high-input, production, reproduction, simulation, smallholder, somatic cell countAnimal and Wildlife SciencesPhD (Animal Science)Unrestricte
Comparative performance of KiwiCross™, Holstein and Jersey dairy cattle on pasture herds in KwaZulu-Natal
No full textDissertation (MScAgric (Livestock Production))--University of Pretoria, 2022.Crossbreeding is found in almost all sectors of agriculture, including maize cultivars, poultry, pigs, small and large livestock breeds. Dairy has traditionally been one of the last strong holds of pure breeding strategies for Holstein, Jersey and Ayrshire. New Zealand was one of the first countries to adopt crossbreeding on a commercial scale by supplying semen from crossbred bulls for artificial insemination. Interest in crossbreeding is often due to concern with the depreciation of secondary, or management traits and is a relatively simple method to reduce inbreeding depression, introduce favourable traits from complementary breeds and take advantage of heterotic effect in several traits. Many South African dairy farmers have adopted the pasture-based and seasonal farming system, practicing criss-cross breeding between Holstein-Friesian and Jersey sires. Crossbred KiwiCross™ semen from New Zealand became available to these farmers, however, a Biological Impact Assessment study was requested by Government as a prerequisite to importing KiwiCross™ semen into South Africa. Individual cow performance data were recorded from six dairy farms in KwaZulu-Natal that were using KiwiCross™ sires alongside Holstein-Friesian and Jersey sires from LIC New Zealand. There were official milk (INTERGIS) records on 148 Holstein-Friesian, 80 Jersey, 476 KiwiCross™ and 287 non-descript sired heifers, and all were born in 2014. Records comprised of milk production, somatic cell count, inseminations, calving and visual inspection data. Mean lactation milk yield was not significantly different (P>0.05) between KiwiCross™, Holstein and non-descript breeds. The three sire breed groups, however, produced significantly higher (P0.05) in somatic cell score among the four sire breed groups. Lactation yields of milk, fat and lactose were significantly lower (P<0.05) for the Jersey compared to Holstein, KiwiCross™ and non-descript breeds. For protein yield, a significant difference (P<0.05) was only observed between the KiwiCross™ and non-descript, with the KiwiCross™ having the highest and non-descript the lowest lactation yield. Age at First Calving was significantly higher (P<0.05) for the KiwiCross™ compared to Jersey, Holstein and non-descript breeds. Services per conception were significantly higher (P<0.05) for the non-descript than the KiwiCross™, Holstein and Jersey. Analysis of the production and fertility data, along with linear visual inspection yielded results similar to what is seen in other international studies, i.e. crossbred animals raised in pastural systems produce production figures comparable with Holstein-Friesian and significantly higher (P<0.05) than Jersey pure breeds while showing slightly higher values in reproduction, health and welfare traits.Animal and Wildlife SciencesMScAgric (Livestock Production)Unrestricte
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Phenotypic and whole-genome single nucleotide polymorphisms (SNP) characterization of Mozambican indigenous cattle breeds
No full textThesis (PhD (Animal Science))--University of Pretoria, 2022.Mozambican (MZ) indigenous cattle are generally reared in resource-poor management systems and are well adapted to harsh environments. Despite their significance in food security and improved livelihoods, a limited number of studies have attempted to investigate the genetic variation of these genetic resources or their genetic relationships with other cattle breeds and ecotypes in the region. The current study aimed to characterize three Mozambican indigenous cattle breeds on both phenotypic and genomic levels, in four provinces of Mozambique, namely Maputo, Gaza, Inhambane, and Tete. Firstly, a total of 614 cattle from three indigenous populations including Angone (n=140), Landim (n=292), and Tete (n=182), were sampled in twenty-three villages in four provinces to collect body measurements and qualitative data. Findings showed significant morphological differentiation between the populations. Landim males and females were significantly (p<0.05) heavier than their Tete and Angone counterparts. A combination of six morphometric traits (Body length, horn length, rump width, height at withers, height at the rump, and top-line length) could be used for an individual assignment using discriminant function analysis of SPSS, with a success rate exceeding 70% for both Angone and Landim cattle. Tail hair samples from 228 animals (consisting of the three indigenous populations) were genotyped using the International Dairy and Beef SNP BeadChip array (IDBV3). Population genetic parameters showed a moderate level of variation, with estimates of expected heterozygosities ranging between 0.304 ± 0.166 (Angone) to 0.329 ± 0.148 (Tete). The three indigenous populations all had low positive (across-population average of 0.065±0.109) inbreeding rates. Both principal component (PCA) and admixture analyses indicated poor between-breed differentiation. A downward trend was observed in the effective population sizes of all three populations over time, indicating a narrowing genetic pool for the genetic resources. South African genotypes which included SA Nguni (n=150), SA Tuli (n=150), and SA Boran (n=150) were included in a between-population analysis. These genotypes were generated using the GeneSeek Genomic Profiler (GGP) 80K panel and compared with the Mozambican Nguni (MZ Nguni) cattle. Medium levels of genetic diversity, measured as expected heterozygosity, were observed, ranging from 0.284±0.158 (SA Boran) to 0.324±0.153 (SA Tuli). Runs of homozygosity (ROH) analysis revealed low inbreeding rates with the average FROH ranging from 0.003 (SA Nguni) to 0.006 (SA Tuli). A high frequency of short (ROH ≤ 5Mb) ROH segments suggested ancient inbreeding in all populations. PCA and Admixture analyses revealed a tight cluster of the two Nguni populations, while SA Tuli and SA Boran diverged, as expected, into two distinct clusters. Genome-wide FST and Rsb analyses identified 229 differentiated SNP potentially under selection in the MZ Nguni cattle breed compared to SA cattle populations. These regions were enriched with genes implicated in several metabolic processes essential for adaptation and production traits. This study indicate that Mozambican indigenous cattle populations have a high level of genetic diversity; and Mozambican Nguni and South African Nguni have similar genetic ancestry. A joint regional strategy for the preservation and sustainable use of indigenous animal resources will improve regional food security and the livelihood of farming communities.Animal and Wildlife SciencesPhD (Animal Science)Unrestricte
Factors affecting milk urea nitrogen and its relationships with production traits in South African Holstein cattle
No full textDissertation (MSc Agric)--University of Pretoria, 2013.The efficiency of utilization of dietary nitrogen can be monitored using milk urea nitrogen (MUN). Overfeeding or underfeeding of protein can be identified through the observation of deviations from target MUN concentrations. This will assist in lowering feed costs of dairy farms, and improving nutrition management of herds. Higher efficiency of utilization of dietary nitrogen might result in a reduction in environmental pollution. Non-genetic factors affecting variation in MUN were herd-test-day (HTD), lactation stage and year of calving. The contribution of HTD was the highest, ranging from 58.56% to 63.18% in parity 1 to 3. Lactation stage had the second largest contribution to the MUN variation. Differences in least squares means for MUN in various years of calving were observed. The heritability estimate for MUN was 0.09±0.01 in the first parity, and remained constant at 0.11±0.01 in the second and third parity. Heritability estimates for milk, fat and protein yield ranged from 0.40±0.01 to 0.43±0.01, 0.21±0.01 to 0.26±0.01, and 0.32±0.01 to 0.38±0.01, respectively. These estimates were within acceptable ranges for South African Holstein cattle. Genetic correlations between MUN and milk production traits were low and positive, ranging from 0.01±0.003 to 0.10±0.004 across parities. Phenotypic correlations ranged from 0.02±0.11 to 0.16±0.07, being generally higher than the genetic correlations. The positive associations between MUN and milk production traits are undesirable as the dairy cows would be less efficient in utilizing dietary protein and may result in increased environmental pollution. The genetic trend for MUN was 0.44, 0.007 and 0.049 mg/dl in the first, second and third parity, respectively. Results of the current study indicate that MUN has potential as a management tool in South African Holstein dairy herds. It might be a good indicator of the efficiency of dietary protein utilization of dairy herds, and has practical advantage as it is currently collected by the national dairy herd recording and improvement scheme.gm2014Animal and Wildlife Sciencesunrestricte
A deterministic evaluation of alternative management options for the smallholder dairy cattle production system in South Africa
No full textThesis (PhD (Animal Science))--University of Pretoria, 2020.The aim of this thesis was to evaluate alternative management options for the smallholder dairy cattle production system in South Africa (SA). Specific objectives included, were to benchmark cow performance in the smallholder (SH) against their counterparts in a high-input system (H), to develop a SH herd model, and to evaluate alternative management options for the improvement of smallholder dairy herd profitability. Data on production (305-day yields of milk, fat and protein), lactation length, somatic cell count (SCC), and reproductive traits (age at first calving (AFC), and calving interval (CI) obtained from the South African National Dairy Animal Improvement scheme (NDAIS) were used in a benchmarking study. Least squares means per trait were compared between the two systems, and lactation curves for roduction traits and SCC were plotted. Results revealed that mean yields of milk, fat and protein were significantly (P<0.05) lower in the SH (4 097±165, 174±5.1 and 141±4.5 respectively) compared to the H system (6 921±141, 298±4.7, and 245±4.1, espectively). Mean lactation length was significantly (P<0.05) shorter for the SH
(308±15.1) compared to the H system (346±12.8). Log-transformed SCC was significantly (P<0.05) higher in the SH (2.41±0.01) relative to the H system (2.27±0.01). Cows in H herds exhibited typical lactation curves, in contrast to flat and low-peaking curves obtained for the SH system. SH cows had significantly (P<0.05) older AFC (30±0.5) than those in the H system (27±0.5). There was no significant difference (P<0.05) in CI between the two systems. A bio-economic SH herd model was developed by adapting a previously developed model for the H system in SA. Parameters used were obtained from NDAIS, survey data, personal communications, and literature. The model integrated herd dynamics, outputs, nutrient energy requirements, management, and their associated economics. Nutrient energy requirements were estimated for maintenance, growth, reproduction, and lactation. The developed SH herd model was used to evaluate alternative herd management options, using the partial budget approach. Milk yield (MY), live weight (LW), AFC, and CI were used as indicators of cow performance. Herd management practices studied were herd size (HS), replacement rate (RR), feeding system (FS), breeding methods (natural service vs artificial insemination), and source of replacement heifers (raising vs. buying in). Improvements in profitability were attained by increasing MY or increasing herd size, using small to medium sized cows, or reducing AFC, CI or RR. Break-even points were 3 687.4 l/year, 500 kg, 29 months, 420 days and 25% for MY, LW, AFC, CI, and RR, respectively. Profitability was mostly sensitive to the prices of milk and feed. A drop in the price of milk below R4.50/l or increase in the cost of feed above R5.60/kg DM generally resulted in non-profitability. Relying on pasture only for feed was non-viable, and supplementation of pasture with concentrate was the most profitable feeding system. Feeding systems based on supplementation of pasture with concentrate, and silage were resilient to fluctuations in the price of milk, remaining profitable even when the price dropped to R4.10/l. Using artificial insemination or buying-in replacement heifers are additional management strategies that increase SH dairy farming profitability. These recommended management options should be used in combination for achieving maximum herd profitability.UP Postgraduate/Doctoral Research BursaryAnimal and Wildlife SciencesPhD (Animal Science)Unrestricte
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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