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Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows
Thesis (MScAgric)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867614121808101376 |
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| access_status_str | Open Access |
| author | Grobbelaar, Theunis Johannes |
| author2 | Van Zyl, J. H. C. |
| author_browse | Grobbelaar, Theunis Johannes Van Zyl, J. H. C. |
| author_facet | Van Zyl, J. H. C. Grobbelaar, Theunis Johannes |
| author_sort | Grobbelaar, Theunis Johannes |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/136046 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:47:00.921Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/136046 Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows Grobbelaar, Theunis Johannes Van Zyl, J. H. C. Cruywagen, C. W. Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science. Thesis (MScAgric)--Stellenbosch University, 2026. Grobbelaar, T. J. 2026. Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/f1a8078c-8b91-4484-90ca-e8721a8d3f90 This thesis investigates whether supplementing dairy cow diets with exogenous α-amylase can offset the performance risks associated with reduced-starch feeding strategies. Rising feed costs and maize price volatility have driven interest in lower-specification diets incorporating fibrous by-products, but these often compromise milk yield and composition. The study combines an in vitro gas production trial with an in vivo lactation experiment to evaluate the enzyme’s efficacy. The literature review highlights maize as the primary energy source in dairy rations, contributing up to 30% dietary starch. While starch is essential for sustaining milk yield, excessive reliance on maize increases costs and can predispose cows to ruminal acidosis. Exogenous α-amylase, such as Ronozyme® RumiStar™, hydrolyses starch into fermentable sugars, potentially improving ruminal fermentation, microbial protein synthesis, and energy availability. Previous research shows inconsistent responses, suggesting enzyme effectiveness depends on starch level and lactation stage. The in vitro trial used a 2 × 2 factorial design comparing high- and low-starch concentrates with or without α-amylase. Results demonstrated that enzyme supplementation significantly increased fermentation rate and reduced lag time in high-starch diets, indicating faster microbial access to starch. However, potential gas production remained unchanged, and low-starch diets showed minimal response. These findings confirm that α-amylase influences fermentation kinetics rather than total substrate degradation, with benefits contingent on starch availability. The in vivo trial, conducted on a commercial Jersey herd, compared a high-spec concentrate with a lower-spec concentrate formulated with α-amylase. Over ten weeks, milk yield and energy-corrected milk were maintained across treatments, despite the lower nutrient density of the enzyme-supplemented diet. Notably, early-lactation cows exhibited a significant ECM increase during the first measurement, suggesting improved energy efficiency during peak metabolic demand. Butterfat concentration and yield improved in early lactation but declined slightly in mid-lactation, while protein and lactose remained largely unaffected. Body weight and condition scores were stable, and milk urea nitrogen showed no differences, indicating adequate nitrogen utilization. Somatic cell count varied inconsistently, likely due to health factors rather than diet. Overall, α-amylase supplementation allowed lower specification diets to sustain performance comparable to high-specification diets, offering a practical strategy to lower feed costs without compromising productivity. The enzyme’s benefits were most evident in early lactation and high-starch contexts, while responses in low-starch diets were limited. Future research should include dry matter intake measurements, rumen health indicators, and economic analyses to refine recommendations and quantify cost-effectiveness. The conclusion is that exogenous α-amylase is a promising tool for improving starch utilization and maintaining milk production under lower-specification feeding systems, particularly during periods of high energy demand and volatile maize markets. Masters 2026-04-21T08:55:35Z 2026-04-21T08:55:35Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/136046 en Stellenbosch University 92 pages : ill. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Grobbelaar, Theunis Johannes Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| title | Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| title_full | Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| title_fullStr | Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| title_full_unstemmed | Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| title_short | Effect of dietary starch and exogenous α-amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| title_sort | effect of dietary starch and exogenous α amylase on in vitro gas production kinetics and lactation performance of lactating dairy cows |
| url | https://scholar.sun.ac.za/handle/10019.1/136046 |
| work_keys_str_mv | AT grobbelaartheunisjohannes effectofdietarystarchandexogenousaamylaseoninvitrogasproductionkineticsandlactationperformanceoflactatingdairycows |