Gorniak, Tobias: Silage maize variety and heat stress : effects on nutritive value of maize silage and on digestion events and performance of ruminants. - Bonn, 2015. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-39831
@phdthesis{handle:20.500.11811/6238,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-39831,
author = {{Tobias Gorniak}},
title = {Silage maize variety and heat stress : effects on nutritive value of maize silage and on digestion events and performance of ruminants},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2015,
month = may,

note = {The present thesis addresses two topics; brown-midrib (Bm) silage maize and heat stress in ruminants. The first part of this thesis focused on an experimental Bm silage maize hybrid with regard to dry matter (DM) intake (DMI), performance and digestibility in comparison to a commercial (Con) non-Bm hybrid. For the trials, 64 intact and 6 ruminally and duodenally cannulated German Holstein cows were used. They were fed rations based on silage of the Con or the Bm hybrid. The Bm maize silage-based diets had a lower DMI when fed as total mixed ration but no differences between Con and Bm were observed when silages were fed for ad libitum intake with restricted concentrate feeding. However, utilisation of energy was higher in animals fed Bm maize silage-based diets. Feeding Bm maize silage, furthermore, lowered milk fat content. Ruminal fermentation patterns, especially short chain fatty acid proportions, were not altered. Ruminal, as well as total tract apparent digestibility did not differ between Con and Bm, ruminal particle passage rate, however, was higher for the Bm diet. Microbial crude protein (MCP) synthesis and its efficiency were higher for Bm-fed animals. In part two of the thesis, the Bm and Con silages were tested in digestibility and nitrogen (N) balance trials with sheep. Trials were conducted at 15, 25 and 35°C ambient temperature. Ambient temperature did not affect nutrient digestibility but an interaction of temperature and silage maize variety was found. Results on N utilisation were inconsistent. In animals fed Con urinary N excretion was higher at 15°C compared to 25 and 35°C, whilst urinary N excretion was lower at 25°C compared to 15 and 35°C in animals fed Bm. Finally, the impact of summer temperatures in Lower Saxony, Germany on DMI and performance of mid-lactation dairy cows was evaluated. Feeding trials conducted at the experimental station of the Friedrich-Loeffler-Institute in Braunschweig, Germany between January 2010 and July 2012 were evaluated. Temperature-humidity indices (THI) were calculated for each day and a generalised linear mixed model was used to calculate the impact of THI on DMI, milk yield and milk composition. When THI increased above 60 DMI of the same day was decreased, whereat a decrease in milk yield was observed one day later. With a critical view on the literature on feeding strategies for heat-stressed dairy cows and in consideration of the present results, it can be concluded that Bm maize might reduce negative effects of heat stress. The higher efficiency of nutrient utilisation and the higher rate of ruminal passage of particles of Bm silage might help to maintain DMI during periods of heat stress. Increased efficiency of MCP synthesis may balance protein deficiency due to reduced DMI without the negative effects of increasing dietary crude protein concentration. Further research to characterise the interaction of heat stress and Bm feeding, however, is necessary, both under controlled and field conditions.},
url = {http://hdl.handle.net/20.500.11811/6238}
}

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