Gerlach, Katrin: The aerobic deterioration of silages as estimated from chemical composition and dietary choice by goats. - Bonn, 2013. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Katrin Gerlach}},
title = {The aerobic deterioration of silages as estimated from chemical composition and dietary choice by goats},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2013,
month = jun,

note = {Conserved forage as silage provides an important source of energy and nutrients for livestock in many countries of the world. After opening the silo for the feed-out phase or due to damages of the covering, oxygen ingresses into the silage and abolishes anaerobic conditions. The activity of aerobic spoilage organisms can cause dry matter (DM) and nutrient losses as well as negatively affect fermentation and hygienic quality of the silage. There is a lack of information regarding the changes taking place after opening and especially their impact on feed intake by ruminants. Furthermore, it is difficult to objectively assess silage quality once aerobic deterioration has started. This study focuses on characterizing chemical and microbiological changes caused by aerobic exposure and evaluating the effect on short-time DM intake and preference behaviour by goats. For these purposes, a 2 x 2 x 2 x 2-factorial design was used to evaluate 16 silages differing in substrate (maize and grass), DM, chopping/cut length and compaction pressure at ensiling. After anaerobic storage, silages were exposed to air for 8 days (d). In 2-d intervals, silages were sampled for chemical analyses, and the microbiological status was determined by enumeration of yeasts, moulds and aerobic mesophilic bacteria. Furthermore, silage from these days was stored anaerobically in vacuum-sealed plastic bags for use in preference trials. After aerobic exposure, for each silage a preference trial was done with Saanen-type goats, each one lasting 21 d. During the experimental phase, each possible two-way combination of the five silages and one standard lucerne hay was offered as free choice for 3 h. At opening, maize silages had a high fermentation quality, but during aerobic exposure, strong changes concerning fermentation products and microbiological quality occurred. Lactic and acetic acids were degraded, resulting in an increase of the mean pH of the experimental silages from 3.9 (d0) to 5.8 (d8). Counts of yeasts rose drastically during the first 4 d of aerobic exposure causing an increase of mean silage temperature of 29 °C above ambient. In the preference trials, a significant decline occurred in DM intake (DMI) after 4 d of aerobic exposure with a mean decrease in DMI of 53% at d8 in comparison to the fresh silages. The DMI was negatively correlated to silage temperature (as difference to ambient) and the concentrations of ethanol and ethyl lactate. All grass silages were aerobically stable during the examination time showing neither an increase in temperature (> 3.0 K above ambient) nor changes in the composition of fermentation products. The DMI of 33% DM-silages decreased after 4 or 6 d of aerobic exposure and silage that had been exposed to air for 8 d was avoided in each case with a mean reduction of 50% in comparison to d0-silages. Low-DM silages showed signs of malfermentation with higher concentrations of butyric acid and ammonia-N. The DMI was lower and fewer differences between silages with different lengths of aerobic exposure occurred. Mean decrease in DMI after 8 d of storage was 20%. Especially products from protein and amino acid degradation (ammonia-N, iso- and n-butyric acid) were negatively correlated to DMI. It was concluded that, in well-fermented silages, aerobic exposure for a length of time that is of practical relevance negatively impacts short-time DMI and preference by goats, even if silages are at an apparently low stage of deterioration. Still unidentified degradation products might therefore have an impact on feeding behaviour of goats. The results highlight the importance of fermentation quality and aerobic stability in the preference behaviour of ruminants, but identifying single silage characteristics being responsible for preference or avoidance was difficult. At the moment measurement of silage temperature seems to be the best suitable single indicator for predicting preference behaviour and DMI at farm level},
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