Strategies to Improve Reproductive Efficiency in Cattle with Dietary Intervention
| dc.contributor.author | Davis, Ty Chapman | en |
| dc.contributor.committeechair | White, Robin R. | en |
| dc.contributor.committeemember | Wilson, Thomas Bain | en |
| dc.contributor.committeemember | Ealy, Alan Dale | en |
| dc.contributor.committeemember | Mercadante, Vitor R. G. | en |
| dc.contributor.department | Animal and Poultry Sciences | en |
| dc.date.accessioned | 2021-07-15T08:00:08Z | en |
| dc.date.available | 2021-07-15T08:00:08Z | en |
| dc.date.issued | 2021-07-14 | en |
| dc.description.abstract | This dissertation examines how reproductive efficiency can be improved through dietary intervention. The use of diet to enhance reproduction is theoretically a low-cost and low-input method that will co-align with reproductive technologies' beneficiary effects. Ideally, with improved nutrition intervention, these technologies will become more feasible and practical to producers. The first study examines the diet nutrient composition and its relative interactions on days to ovulation postpartum, overall pregnancy rates, and pregnancy at first AI in cattle. Most notably, the highest predicted overall pregnancy rate for multiparous cows was observed at high crude protein (CP), moderate non-structural carbohydrates (NSC), Low neutral detergent fiber (NDF) and high ether extract (EE). Additionally, the highest predicted pregnancy at first AI rate was when CP was high, moderate NSC, high NDF, and low EE. The second study examines the impact that a high starch diet may have on reproductive hormones, follicular growth, and pregnancy rates. The high starch diet tended to have a greater placental associated glycoprotein concentration, a greater number of large follicles on the day of breeding and a 20% numerically greater overall conception rate. The high fat diet did exhibit a greater number of medium sized follicles on the day of breeding. There were no observed differences in progesterone concentrations between the two treatment groups. The final study examines the effect that a higher starch diet might have on follicular development, CL growth and size, reproductive hormones, and insulin like growth factor binding proteins -2, -3, -4, -5, and pregnancy associated plasma protein A gene expression in granulosa cells. The experimental group that received the diet greater in starch exhibited a greater concentration of plasma IGF-1, greater number of large follicles on the dates that insemination would occur in a TAI situation, and a lower amount of days to reach a dominant follicle at the diameter of ≥ 10mm. Additionally, the high fat diet did exhibit a greater concentration of progesterone. Although, no statistical differences were observed in the granulosa cell gene expression and corpus luteum size. The feeding technique here may provide producers insight into non-expensive and straightforward ways to improve their reproductive efficiency and, ideally, adopt reproductive technologies in harmony with dietary intervention. | en |
| dc.description.abstractgeneral | Improving reproductive efficiency in both beef and dairy cows is essential to continually improve meat and milk production to meet the growing global demand for animal food products. In both beef and dairy operations, the goal is to produce one healthy calf per cow per year. However, each operation type faces unique challenges which, at present, often preclude achieving this goal. Intensive genetic selection for milk production has resulted in inadvertent selection against reproductive efficiency in the dairy industry. In the beef industry, the production conditions and tight profit margins mean that producers are often hesitant to use assisted reproductive technologies like estrus synchronization or artificial insemination, which may help improve reproductive efficiencies. On account of these challenges, there is a clear need for supportive tools and technologies which can be applied within the beef and dairy industries to improve the reproductive efficiencies of these production systems. One possible strategy that could be employed to improve reproductive efficiency within the beef and dairy industries is nutritional manipulation. Although there are mixed results within the literature regarding how dietary manipulation can be leveraged to affect reproductive outcomes, feed supplementation is typically a strategy readily leveraged by beef and dairy producers for various production outcomes. As such, dietary manipulation may be a promising method to improve reproductive efficiency, assuming discrepancies among studies within the literature can be reconciled to provide feeding recommendations to improve reproduction. One strategy to evaluate commonalities among literature data is the use of meta-analysis. Our first study leveraged meta-analysis to evaluate how diet composition and its interactions with parity, genetics, and housing situation affect reproductive outcomes. This study found that reproduction is affected by complex interactions among diet, management, genetics, and time. Thus, leveraging nutrition to improve reproductive efficiency will require precise identification of the correct supplement for the correct animals, based on their age and management conditions. Experimental work to confirm the efficacy of different nutritional modulation strategies will be essential to confirm such strategies before widespread use. Rather than experimentally evaluating an exhaustive listing of strategies to improve reproductive efficiency, confirmation experiments will be more efficient if they evaluate dietary approaches that appeared successful under most conditions simulated in the meta-analysis. In our meta-analysis, supplementation of non-structural carbohydrates (NSC) and ether extract (EE) fairly consistently improved reproductive outcomes when compared with crude protein (CP) and neutral detergent fiber (NDF) supplementation, which had more mixed results. Current literature on these feed supplements is often confounded with energy intake, meaning that it is difficult to discern whether the consistency in response reflects consistent benefit of added energy or unique benefits of these energy-providing substrates. As such, we designed an experiment to evaluate the effect of isoenergetic supplementation of EE and NSC within the diets of grazing Angus crossbred beef heifers to evaluate the effects on reproductive outcomes. Responses of interest included progesterone concentrations, pregnancy rates, placental-associated glycoprotein concentrations, and follicle size and number. Supplementation of NSC resulted in lower plasma progesterone and a significantly lower number of medium follicles on the day of breeding, relative to supplementation with fat. However, heifers supplemented with NSC also had elevated placental-associated glycoprotein concentrations, numerically increased conception rates, and a greater number of large follicles on the day of breeding when compared with the heifers supplemented with fat. As such, the data suggest the NSC diet promoted the maturation of large follicles, which may support improved conception rates. The EE diet promoted elevated progesterone concentrations, but did not appear to support the maturation of medium to large follicles, likely accounting for the numerically lower conception rates. Because heifers are well acknowledged to differ from cows due to their energy requirements, it is useful to also evaluate the efficacy of these dietary treatments in mature cows to assess the consistency of responses. Toward that goal, the objective of our second study was to compare supplementation of high NSC or high EE feeds to mixed-breed, non-pregnant, multiparous beef cows when evaluating reproductive outcomes. The results of these supplementation strategies were similar to those identified within the heifer trial. The group consuming the high EE supplement had elevated plasma progesterone concentrations. The group consuming the high NSC supplement had a greater number of large follicles on the days of GnRH administration. There were no differences in gene expression of aspirated granulosa cells between the two groups. The consistency of results between the heifer and cow studies suggest that supplementation with high NSC or high fat supplements may consistently affect cows, irrespective of physiological stage. As such, further work to titrate the minimum required supplementation levels to assess the possible economic returns of this approach to optimizing reproductive efficiency. Our studies concluded that reproductive efficiency can be enhanced through dietary manipulation in a manner independent of dietary energy intake. Additionally, the utilization of a propiogenic precursor such as a high NSC diet appears to support the maturation of follicles in cattle utilizing a timed artificial insemination estrus synchronization protocol, likely leading to improved pregnancy rates. As such, assessment of NSC supplementation for reproductive modulation may be a productive line of future work. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:31441 | en |
| dc.identifier.uri | http://hdl.handle.net/10919/104172 | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Cattle | en |
| dc.subject | Reproduction | en |
| dc.subject | Nutrition | en |
| dc.title | Strategies to Improve Reproductive Efficiency in Cattle with Dietary Intervention | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Animal and Poultry Sciences | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
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