A study to examine factors that influence dairy cattle fertility was conducted in the United Kingdom (UK) and Malawi. Productivity data from the UK comprising 56,014 records from 574 Holstein cows were retrieved from a database at Scotland’s Rural College Dairy Research Centre in Dumfries. The cows were of either high (select) or average (control) genetic merit and fed total mixed rations with high or low forage. These formed four production systems - high forage select (HFS), low forage select (LFS), high forage control (HFC) and low forage control (LFC). Data from Malawi were obtained through a baseline survey in 67 smallholder farms and monitoring of 28 and 62 dairy cows from smallholder farms and a commercial farm, respectively. The breeds were Holstein-Friesians and Holstein-Friesian x Malawi Zebu crosses predominantly fed forages supplemented with concentrates. Some cows were fitted with accelerometers to enable monitoring of cow activity which was then related to cow fertility and energy balance. The data were analysed using descriptive statistics, mixed models and logistic regression models using SAS 9.3. The UK data showed that production system significantly (p<0.05) influenced milk yield, body energy content (BEC) and fertility. BEC is a trait that indicates absolute level of energy in the body per day regardless of energy use and intake the previous day. Daily milk yield of LFS cows was 35±0.1 (mean±SEM) litres which was significantly (p<0.05) higher than that of LFC (30.4±0.1 litres), HFS (27.5±0.1 litres) and HFC (24.3±0.1 litres) cows. LFS cows also had the highest milk yield acceleration to peak milk yield (0.51 litres/day/day) than (LFC 0.47±0.02 litres/day/day), HFC (0.47±0.03 litres/day/day) and HFS (0.46±0.03 litres/day/day) cows. The interval from calving to nadir BEC was 68±5, 83±6, 88±5 and 106±6 days for LFC, LFS, HFC and HFS cows, respectively. Days to first high luteal activity (DFHLA) and days to successful service (DSS) were significantly different with production system and genetic merit, respectively. LFC cows had DFHLA of 27±2 days (mean±SEM) which were significantly lower (p<0.05) than those of HFC (30±3 days), HFS (30±2 days) and LFS (35±3 days) cows. Average genetic merit cows had significantly lower (p<0.05) DSS (119±5 days, mean±SEM) than high genetic merit cows (132±5 days). Results from data collected in Malawi showed variations that reflected differences in management and other environmental factors. Average daily milk yield per lactation in Malawi was 13.3±4.9 (mean±SD) litres. Fertility traits in the UK herd were better than those in Malawi herds. The average DFHLA in Malawi was 79±29 days while in the UK it was 31±18 days. Cow activity in both the UK and Malawi farms varied with the feeding system, genetic merit and BEC. Select cows on home grown feeding system were more active (motion index =6250±40), stood longer (13.4±0.04 hours/day) and spent more time eating (5.6±0.32 hours/day, mean±SEM) than select cows on by products feeding system that had motion index, standing and eating time of 5166±37, 11.9±0.04 hours/day and 4.6±0.16 hours/day, respectively. Genetic merit, lactation number, days to first observed oestrus, calving BEC, service BEC and service milk yield were significant predictors of pregnancy to first insemination (p<0.05) while genetic merit, milk yield, percentage BEC between calving and service, service milk yield and service BEC were significant predictors (p<0.05) of pregnancy to the first three inseminations. Validation of models derived showed C-statistics of the receiver operating characteristic (ROC) curve of 0.66 (95% confidence interval (CI): 0.57 to 0.75) and 0.65 (CI: 0.55-0.75), respectively. It is concluded that genetic merit, feeding system, parity, energy status and stage of lactation are the major factors that determine the likelihood of achieving pregnancy following insemination. Models developed have a potential to predict the probability of pregnancy to an insemination at an acceptable level of accuracy.

Made available in DSpace on 2014-07-29T15:07:42Z (GMT). No. of bitstreams: 1 Dissertacao Mariana_2012.pdf: 820506 bytes, checksum: f32ae01c75956548ba6dc7e06b8b57ae (MD5) Previous issue date: 2012-03-02 / Performance testing of young bulls are instruments of great utility in breeding programs and is aimed to evaluate the ability of individual animals regarding weight gain,, earliness, yield and carcass finishing, providing support for selection based on individual information of each animal. The objective of this study was to understand and define the relationships between genetic and quantitative genetic merit of Nellore bulls evaluated and their progenies in Performance Testing of Young Bulls(PTYB). In the present study, we analyzed the characteristics of weight calculated at 210 (W210), 365 (W365) and 450 days of age (W450), pre-weaning and post-weaning average daily gain (PREDG and POSTDG), scrotal circumference at 365 and 450 days of age (SC365 and SC450), ribeye area (REA) and carcass finishing (FIN) that were measured during the Weight Gain Tests (WET). The analyzed data set came from the Nellore participants in the Performance Testing of Young Bulls, which includes weight gain on pasture tests, from integrated crop and livestock production, coordinated by Embrapa Rice and Beans and Embrapa Cerrados. For data statistical analysis, we used statistical procedures available on the Statistical Analysis System (SAS) application and for obtaining (co)variance estimates, we used the Derivative-Free Restricted Maximum Likelihood method (DFREML), using univariate animal models and the Multiple Trait Derivative Free Restricted Maximum Likelihood (MTDFREML) application. Estimates of heritability for all traits showed moderate to high magnitudes. For direct and maternal additive effects, the heritability estimates were 0.37 ± 0.13 and 0.32 ± 0.15 and 0.35 ± 0.12 and 0.36 ± 0.16, for W210 and PREDG, respectively. As for W365, W450, POSTDG, SC365, SC450, REA and FIN, the additive heritability estimates were 0.33 ± 0.12, 0.53 ± 0.14, 0.54 ± 0.13, 0.36 ± 0.12, 0.54 ± 0.13, 0.26 ± 0.13 and 0.28 ± 0.14, respectively. Therefore, these results indicate the possibility of improving these characteristics by the use of breeding animals with superior genotype. Over the years there has been a significant entry of new bulls in evidence of weight gain on pasture, resulting in marked variation in predictions of genetic breeding values. However, there was positive and growing relationship between genetic value of bulls and their progeny. Thus, the results show that the selection of the best bulls based on genetic evaluations was efficient in terms of genetic progress. / Os testes de desempenho de touros jovens são instrumentos de grande utilidade em programas de melhoramento e tem como finalidade avaliar a capacidade individual dos animais para ganho em peso, precocidade, rendimento e acabamento de carcaça, fornecendo subsídios para seleção com base na informação individual de cada animal. Objetivou-se com esse estudo, conhecer e definir as relações genéticoquantitativas entre o mérito genético dos touros da raça Nelore avaliados e de suas respectivas progênies em Teste de Desempenho de Touros Jovens (TDTJ). No presente trabalho, foram estudadas as características de peso calculado aos 210 dias (P210), aos 365 dias (P365) e aos 450 dias de idade (P450), ganho médio diário pré desmame e pós desmame (GPPRE e GPPOS), perímetro escrotal aos 365 dias e 450 dias de idade (PE365 e PE450), área de olho de lombo (AOL) e acabamento de carcaça (ACAB) que foram mensuradas durante as Provas de Ganho em Peso (PGP). O conjunto de dados analisados foi proveniente dos animais da raça Nelore participantes do Teste de Desempenho de Touros Jovens que engloba as prova de ganho em peso a pasto, oriundos de sistemas de integração lavoura e pecuária, coordenado, pela Embrapa Arroz e Feijão e Embrapa Cerrados. Para analise estatística dos dados foram utilizados os procedimentos estatísticos disponibilizados no aplicativo Statistical Analysis System (SAS) e na obtenção das estimativas de (co)variâncias, empregou-se a metodologia da Máxima Verossimilhança Restrita Livre de Derivada (DFREML), por meio de modelos animal unicaráter, usando o aplicativo Multiple Trait Derivative Free Restricted Maximum Likelihood (MTDFREML). As estimativas de herdabilidade para todas as características apresentaram magnitudes moderada a alta. Para os efeitos aditivos diretos e maternais, as estimativas de herdabilidade foram 0,37±0,13 e 0,32±0,15 e 0,35±0,12 e 0,36±0,16, para P210 e GPPRE, respectivamente. Já para P365, P450, GPPOS, PE365, PE450, AOL e ACAB, as estimativas de herdabilidade aditiva foram 0,33±0,12, 0,53±0,14, 0,54±0,13, 0,36±0,12, 0,54±0,13, 0,26±0,13 e 0,28±0,14, respectivamente. Portanto, estes resultados indicam a possibilidade de melhoramento destas características por meio da utilização de reprodutores com genótipo superior. Ao longo dos anos houve expressiva entrada de novos touros em provas de ganho em peso a pasto, resultando na marcante variação das predições dos valores genéticos dos animais. Entretanto, houve relação positiva e crescente entre valor genético dos touros e de suas respectivas progênies. Sendo assim, os resultados demonstram que a seleção dos melhores touros baseados nas avaliações genéticas, tem sido eficiente em termos de progresso genético.

Les performances de reproduction des vaches laitières se sont dégradées parallèlement à l’augmentation de leurs performances de production. L’intense sélection réalisée sur la production laitière est tenue responsable de cela. Chaque étape du processus de reproduction a été affectée : les anomalies de cyclicité ovarienne sont plus fréquentes dans la population actuelle, la durée et l’intensité des chaleurs ont diminué drastiquement, et les échecs de gestation sont plus fréquents. La littérature s’accorde sur le fait que la reproduction est affectée parce que la majeure partie des ressources est investie dans la production laitière. L’objectif de cette thèse de doctorat est d’étudier l’intérêt d’une stratégie de sélection alternative basée sur un fort potentiel génétique de taux butyreux et protéique sur la robustesse des vaches laitières.Les hypothèses testées étaient que par rapport aux vaches à fort potentiel de production laitière, celles à fort potentiel de taux butyreux et protéique (i) exportent moins d’énergie dans le lait et donc préservent leur réserves corporelles, (ii) ont de meilleures aptitudes à se reproduire. Nos résultats montrent que les vaches à fort potentiel de taux butyreux et protéique ont un retour de cyclicité plus précoce, une expression des chaleurs similaire mais plus d’échecs de gestation que celles à fort potentiel de production laitière. Ces résultats intrigants suggèrent que les étapes de la reproduction sont partiellement découplées sur le plan génétique. Sélectionner les vaches laitières sur les taux butyreux et protéique dans le but d’amé / Reproductive performance of dairy cows has been declining while their milk production was improving. The strong genetic selection that was applied on milk production is considered to be responsible for this. Each step of the reproductive process has been impacted: abnormal ovarian activity is more common in the current population, the duration and intensity of oestrus has dramatically decreased and the occurrence of pregnancy failures has increased. The consensus in the literature is that reproduction is impaired because dairy cows are investing most of their resources in milk production. The aim of this Ph.D. thesis is to explore the effect of alternative selection strategies based on milk fat and protein content on robustness of dairy cows. Our hypotheses were that at similar genetic merit for milk solids yield, compared to cows with high genetic merit for milk yield,dairy cows with high genetic merit for fat and protein contents (i) are exporting less energy in milk and are consequently safeguarding their body reserve; (ii) have better reproductive performance (earlier resumption of ovarian activity, more intense oestrus, better ability to ensure pregnancy). Our results suggest that cows selected for production through high fat and protein content instead of high milk yield would resume ovarian activity earlier, have similar oestrus intensity but more pregnancy failures. These intriguing results suggest that the steps of the reproductive process are genetically partly disentangled. Selecting dairy cows for fat and protein content is not a promising way to improve repro