The effect of air exposure before and after ensiling on maize silage quality and dietary choice by goats
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Beschreibung
The effect of air exposure before and after ensiling on maize silage quality and dietary choice by goats
Management factors that affect the time to achieve anaerobic conditions in the silo are of utmost importance for production of high-quality silages. These factors include high compaction and rapid sealing. If this can only be achieved inadequately, a loss of dry matter (DM), nutrients and feed value threatens. The growth of microorganisms, in particular of yeasts, can be seen as particularly critical, since they can survive the anaerobic phase of conservation. This results in an increased risk of aerobic instability after opening the silo. In addition, yeasts are able to form ethanol from available water-soluble carbohydrates (WSC), from which, in turn, further volatile organic compounds (VOC), such as ethyl ester, can be formed during the anaerobic phase. These have been found in silages on farms and may have led to reduced feed intake of dairy cows and goats under experimental conditions. In extensive studies, a strong correlation was found between ethanol and the contents of ethyl esters, which were reported as indicator substances for other volatile organic compounds and which were considered together with the other VOC for the decrease in feed intake. When silage is exposed to air after opening, aerobic deterioration may occur as a result of undesirable microbial activity. Aerobically deteriorated silage is undesirable for feeding due to lower nutritive value and risk of negative effects on animal performance and health.
The overall aim of the thesis was to determine the effect of air exposure before and after ensiling on quality of whole-crop maize silages and to determine the influence of the resulting changes on dietary choice by goats. Therefore, an ensiling experiment and preference trials were conducted in which three fixed factors (compaction, sealing and aerobic exposure post-opening) were varied in order to ensure ingress of air in different stages of the conservation process and afterwards.
The aim of the ensiling experiment was to determine the effect of compaction and sealing on maize silage quality regarding chemical and microbial composition and fermentation pattern before sealing and at silo opening. Additionally, it should be determined how an aerobic exposure of 6 days affects the quality of silage after opening and what changes take place. Subsequently, the differently treated silages were offered to goats in preference trials. The specific aim was to study the effects of the changes caused by treatments on forage choice and short-term feed intake. It should also be determined, which silage characteristics impact on preference or avoidance.
For this purpose, whole-crop maize (277 g kg-1 DM) was chopped, mixed, sampled and ensiled in 120-L plastic silos (6 replicates per treatment), which were either compacted to low (194 kg DM m-3) or high (234 kg DM m-3) density and sealed either immediately or with a delay at day 2 or at day 4 post-filling. One of the six silos of each treatment that were sealed with a delay was sampled immediately before sealing to determine the changes in chemical and microbial composition. After sealing, all silos were stored at ambient temperature of 12 ± 2.9°C for at least
175 days and then opened. After silo opening, the silages were removed, mixed, sampled and exposed to air for 6 days in form of a quadratic single heap. During aerobic exposure, samples were taken from the silages at 2-day intervals to determine chemical and microbial composition and fermentation pattern, as well as aerobic stability and sensory properties. Silage was removed from heaps at the respective days of exposure (day 0, 2, 4 and day 6) for subsequent preference trials and was then vacuum-stored in polyethylene bags for further use as feed. A 15-day preference trial consisting of an adaptation and an experimental phase was carried out with goats (German Improved White Goat, n = 5) for each of the six treatments (2 compaction x 3 sealing times). During the 10-day experimental phase, each possible two-way combination (n = 10) of the exposed silages (day 0, 2, 4 and day 6) and of a lucerne hay, which served as standard feed, was offered for 3 hr. During this time, each goat could freely choose between the two feeds present in combination. The amount of each feed, which was eaten, was determined after 30 min and after
3 hr. In addition, goats were offered grass hay in the afternoon for 2 hr and the intake was also determined.
Delayed sealing of the silos after 2 and 4 days caused changes in both chemical and microbial composition, which was particularly evident in the increase in yeast counts as well as in a decline of up to 65% in WSC before sealing. Sealing the silos after
4 days caused high DM losses of up to 11%. At silo opening, higher contents of ethyl acetate and ethyl lactate were found in silages sealed with a delay than in immediately sealed silages. A 4-day delay resulted in a shorter aerobic stability compared with immediate sealing (65 vs. 50 hr). Aerobic exposure after opening led to considerable changes in silage composition, to a drastic loss in feed value and, finally, spoilage. This was mainly reflected in the increase in yeast counts, the strong rise in pH, the worsening of the sensory properties and the rapid heating. Neither the different compaction nor the delay significantly influenced forage choice and short-term feed intake. On the other hand, prolonged aerobic exposure of more than
4 days had a detrimental effect. Exposing silages to air for 6 days resulted in strong avoidance and, across all treatments, a mean decrease in DMI of 71% compared with silages at opening. Increasing fibre fractions, a deteriorating microbial status and poor silage sensory properties, probably caused by a combination of different fermentation products can be considered for decrease in preference.
The ensiling experiment shows that even in the instance of a silo with a small surface-to-volume ratio, detrimental effects of low compaction and delayed sealing on maize silage quality can occur before sealing and at silo opening. Furthermore, both factors can adversely impact on silage quality during aerobic exposure post-opening (feed-out). Under the conditions of the ensiling experiment, the overall effects of sealing had a greater impact on silage quality than that of compaction. The longer the silo remains unsealed, the greater the silage quality deterioration. Under the conditions of the preference trials, aerobic exposure after ensiling had a more pronounced effect on silage preference and short-time DMI than compaction and delayed sealing.
In conclusion, all measures should be taken to ensure a high degree of compaction and particularly an immediate seal in order to minimize losses in feed value. Aerobic exposure after opening the silo (feed-out) should be limited as much as possible to prevent steady deterioration of silage and reduction in feed intake.
Finally, it appears imperative to prevent ingress of air from harvesting to feed-out to ensure both high feed value and high feed intake.
Autor*in
Dave Brüning