**2. Ration design: critical points and opportunities for failures**

In the following, the general aspects of ration design for high-yielding cows and the problems that arise in practice will be discussed. Data from the service area, in which cases of damage caused by nutritive factors will be presented. In addition, results from ongoing scientific studies will be included accordingly.

### **2.1 Selection of suitable feed**

Feed rations for dairy cows consist of roughage (basic feed) as well as concentrates and mineral feeds. The quality of the roughage already has a significant influence on the amount of feed consumed [6, 7]. When checking the hygiene status of grass silage (n = 109), 41% of the samples showed an increased yeast contamination, which is associated with poorer acceptance of the feed [8] and thus lower feed intake quantities (see **Table 1**).

Therefore, it is evident that yeasts are not only found in corn silage, but that in the case of corresponding clinical disorders, the grass silages in the ration should also be considered. In this study, slightly more than 40% of the samples examined had yeast contents that were higher than the usual recommended limit values.

In general, in the case of reduced performance or illnesses in the dairy herd, special attention should be paid to the basic feedstuffs (in addition to corn silage, especially grass silage) and these should be analysed accordingly.

In most cases of clinical disorders in cattle a causal relationship could be established between microbiological findings and pre-reported disorders (see **Table 2**).

Thus, deviations in the hygiene status could be found in every 5th sample examined (22–25%). On average, 25% of the samples already showed deviations in the sensory test. Therefore, it makes sense to take a critical look at the basic feed from time to time.


### **Table 1**

*Microbiological quality of grass silages (n = 109) from practical farms in Germany.*


*\*Analyses due to clinical disorders, no control analyses.*

### **Table 2.**

*Quality of grass silages sent in to the institute (2017–2020).*

In addition to the hygiene status, attention should also be paid to the botanical composition of the green fodder. The presence of velvet grass leads to a poorer acceptance of the forage and to a reduced regurgitation. While the number of chews per bolus averaged 250 ± 57 when hay is offered, the chewing frequency is significantly lower (146 ± 91 chews per bolus) due to the proportion of velvet grass (*H. lanatus*). On the one hand, this means that a smaller quantity of basic feed is consumed, which can lead to a loss of performance. At the same time, chewing and ruminating is reduced and less saliva is produced, so that the buffering effect is reduced.

Due to the more intensive nitrogen (N) fertilisation and the partly developing resistance to common herbicides, there has been an increasing trend in recent years towards the infestation of monocultures with poisonous plants [9]. Examples are the occurrence of black nightshade (*S. nigrum*) in maize crops [7, 9] or the dispersal of dog's mercury (*M. annua*) in intensively cultivated beet fields [10]. Whereas in past years illnesses of dairy cows as a result of ingestion of poisonous plants or plants with poisonous ingredients were rather the exception, recently more questions have been asked about this problem and there have been an increasing number of cases of poisoning.

This development can be explained, among other things, by altered management of agricultural land, such as the trend towards extensification (migration of poisonous plants from fallow land into cropland, restrictions of fertilisers, ban on herbicides). Renaturation measures (e.g. raising the groundwater level) can also promote the spread of certain poisonous plants (e.g. marsh horsetail). In addition, there are neophytes, i.e. plants that are not endemic to the respective area but are spreading more and more over time and as a result of climate change. For example, golden oat grass (Vit. D efficacy!), whose distribution was previously limited to the Alpine regions and southern Germany [11], is now also increasingly found in northern Germany. On the outskirts of cities, ruminants also come into contact with ornamental plants containing toxic substances that are not usually part of their food spectrum (e.g. planting hedges for privacy protection). In this context, the improper "recreational horticultural disposal" of ornamental plants with toxic ingredients on adjacent pastures should be mentioned [12].

Sometimes, under the assumption that detoxification processes generally take place in the rumen, feeds with a reduced hygiene status are used in ruminants, which is obsolete in other species (e.g. horses). The same applies to contamination of the feed with poisonous plants, although some can be quite lethal, these are used in ruminants under the assumption that they are detoxified in the rumen.

While in the years 2000 to 2005 only about 5 to 10 cases per year were sent in, in which feed was to be checked for the presence of poisonous plants or plants with poisonous ingredients, in the past two years there were already 87 (2019) and 117 cases (2020) in which the suspicion of possible contamination with poisonous plants was expressed in the preliminary report.

Offering a feed contaminated with dog's mercury resulted in severe clinical signs. This toxic plant contains mercurialin (= methylamine), trimethylamine, hermidine, saponin (1% in the herb, highest content at fruit ripeness) and essential oils. The main ingredient mercurialin, which belongs to the saponins, leads to liver damage and haemolysis in cattle (typical clinical sign: icterus). The animals typically show apathy, salivation, reduced rumen motility and are often laying in autoscultatory posture. Corresponding laboratory analyses show a high degree of haemolytic anaemia as well as haemoglobinuria [10].

The effect of mercurialin is also present in dried plant material, whereas no information is available on a possible influence of ensiling on the toxic ingredients. In order to clarify the extent to which the ensiling process leads to a degradation of the toxic ingredients, heifers (n = 6) were offered beet leaf silage contaminated with 20% dog's mercury in a feeding trial. Compared to the control group (n = 6), there was a significantly reduced basal feed intake (see **Figure 1**).

The presence of marsh horsetail in a total mixed ration TMR for dairy cows also leads to a significantly reduced feed intake (see **Figure 2**) and thus poorer milk production even at levels of only 1.25%.

In addition to the roughage, the composition of the milk performance feed is also significantly responsible for the performance of the dairy cow. Macroscopically noticeable deviations (also in comparison to the previous batch) upon delivery of the feed should be a reason to have not only the chemical but also the botanical composition of the feed checked. A check revealed considerable discrepancies between declared and actually found feed materials in almost 35%. In one clinical case report (reduced milk yield), a high proportion of rapeseed cake instead of rapeseed extraction meal led to a fat content in the milk performance feed of 7.5% (instead of the declared 3.5%). The use of this feed led to a fat content of over 1500 g/animal/d (tolerated limit: 800 g crude fat/cow/d) and thus to fermentation disorders in the rumen.

*Nutrition of the High-Yielding Dairy Cow DOI: http://dx.doi.org/10.5772/intechopen.99438*

**Figure 1.** *Roughage intake of heifers feeding beet leaf silage with and without dog's mercury.*

**Figure 2.** *DM intake of dairy cows when offered a TMR with different contents of marsh horsetail.*
