Suitability of forage stands with contrasting species richness to improve the nitrogen use efficiency and the milk fatty acid profile of dairy cows

Ineichen, Simon (2018). Suitability of forage stands with contrasting species richness to improve the nitrogen use efficiency and the milk fatty acid profile of dairy cows (Dissertation, ETH Zürich, Umweltsystemwissenschaften, Institut für Argarwissenschaften, Tierernährung)

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Forage from grasslands (in the following referred to as forage) represents the most important feed for ruminants in temperate climates. Intensively managed meadows and pastures are rich in crude protein. The contents of crude protein of forage are often higher than required by ruminants for ideal ruminal conditions. Excess of crude protein increases the excretion of nitrogen and reduces the nitrogen use efficiency. The supply of protein to the animal may however be limited even under conditions of excessive supply of crude protein due to the high ruminal degradability of the forage protein. A high ruminal protein degradability is challenging for the metabolism of the animal and may contribute to environmental pollution. When compared to grasses, herbs often contain higher amounts of phenolic compounds (plant secondary metabolites). A major group of phenolic compounds consists of tannins with its two subclasses of condensed (CT) and hydrolysable tannins (HT). Some condensed tannins can reduce the ruminal degradability of the forage protein, while HT are often related to reduced palatability and forage digestibility. Tannins, both CT and HT may have a beneficial impact on the milk fatty acid profile. In this dissertation, specific herbs or grassland swards rich in herbs were evaluated for their suitability in ruminant nutrition with respect to feed value, nitrogen use efficiency, yield and composition of milk and milk fatty acid profile. In a first experiment (Chapter 2), swards rich in herbs were analyzed for their feed value and the content and composition of phenols. Over a period of two years, forage samples were obtained from swards of three long-term mineral fertilization field experiments. The experimental fields were located in the mountain area of Switzerland: Bremgarten, two cuts per year, 930 m a.s.l., Canton Solothurn, established in 1972; Orsière, 2 cuts per year, 1‘190 m a.s.l., Canton Valais, established in 1984 and Eggenalp, 3 cuts per year, 1‘340 m a.s.l., Canton Berne, established in 1956. At each of the three experimental sites, three different treatments of fertilization were investigated including unfertilized swards, those fertilized with phosphorus and potassium (PK) and swards fertilized with nitrogen, phosphorus and potassium (NPK). A variety of species rich swards have been established due to the differences of the long-term mineral fertilization treatments with respect to geographical location, site, altitude and cutting frequency. Forages samples were analyzed for their chemical and mineral composition. During the first year of sampling (2015), the species composition of each sward was determined, and samples were analyzed for the content and composition of phenolic compounds and the in vitro assessed digestibility, the content of energy (net-energy for lactation, NEL) and protein (utilizable crude protein) with the modified version of the Hohenheim gas test. Based on the investigation of the mountain grassland swards with proportions of herbs between 18.4 to 451. % of the long-term mineral fertilization field experiments, a high forage quality can be achieved depending on fertilization and cutting intensity of the swards. Species rich mountain swards contained elevated contents of phenolic compounds. At site Bremgarten, the content of phenolic compounds and those of HT were particularly elevated due to the high proportion of Geranium sylvaticum L. present in these swards. The proportion of legumes was increased when fertilizing phosphorus and potassium. Legumes species such as those of Lotus corniculatus L. and the one of Lathyrus pratensis L. probably increased the content of CT in the forage, respectively. Based on the experiments conducted with swards obtained from the three long-term mineral fertilizer experiments, effects of swards rich in herbal species obtained from mountain meadows (Chapter 3) or an artificially established sward containing high proportions of plantain (Plantago lanceolata L.), a herb described for its elevated tannin content (Chapter 4) were evaluated in vivo with lactating dairy cows. In two separate feeding experiments with complete collection of feces and urine respectively, the effects of these swards were evaluated with respect to the digestibility, nitrogen turnover, the milk yield and composition as well as the milk fatty acid profile. In each of the two experiments, four distinct diets were created, and each diet was fed to six cows. In the first feeding experiment (Chapter 3), swards conserved as hay were fed to lactating dairy cows with supplementation of concentrates. Two hay swards differing in their proportion of herbs were obtained from mountain meadows and compared to two grass dominated hay swards from the lowland area. A higher proportion of herbs in the swards obtained from mountain meadows was related to higher contents of phenolic compounds and CT. Two reference diets based on ryegrass (Lolium perenne L.) with low contents of phenols and CT were created. While one of the reference diets had a similar content of crude protein as the two diets containing the hay swards from mountain meadows, the other reference diet was characterized by a distinct excess of crude protein. In a second feeding experiment (Chapter 4), the effects of herbs were investigated in intensely managed production systems with the example of plantain. Therefore, three diets with ensiled forage from artificially established swards related to increasing contents of phenolic compounds were designed: Ryegrass; ryegrass and red clover (Trifolium pretense L.) and ryegrass-red clover and plantain. These three diets were fed ad libitum and supplemented with 3 kg of wheat per day and cow each and compared to a reference diet based on corn silage and soybean meal. In both feeding experiments, it could be shown that feeding diets containing herbs increased the intake of phenolic compounds. The contents of CT of swards which were fed within the experiments of this thesis were unable to improve the nitrogen use efficiency in dairy cows. However, in the case of the diet with the sward obtain from the mountain meadow with the highest proportion of herbs; the excretion of nitrogen could be displaced from urine to feces, which was related to the intake of CT. This finding indicates potential to feed swards rich in herbs to reduce the metabolic load of nitrogen for the animal as well as the environmental pollution of nitrogen. The feeding of diets rich in herbs did not result in increased milk yield or excretion of milk fat or protein. The diets containing hay from mountain meadows increased the transfer of α-linolenic acid to the milk fat. Feeding a diet containing plantain resulted in a milk fatty acid profile with increased contents of vaccenic acids, conjugated linoleic acids and overall higher contents of polyunsaturated fatty acids. In this sense, feeding of diets containing herbs increased the content of fatty acids related to potentially beneficial health effects.

Item Type:

Thesis (Dissertation)

Division/Institute:

School of Agricultural, Forest and Food Sciences HAFL > Resource-efficient agricultural production systems
School of Agricultural, Forest and Food Sciences HAFL > Agriculture

Name:

Ineichen, Simon

Subjects:

S Agriculture > S Agriculture (General)
S Agriculture > SB Plant culture
S Agriculture > SF Animal culture

Language:

English

Submitter:

Nadine Werndli

Date Deposited:

23 Mar 2020 12:44

Last Modified:

23 Mar 2020 12:44

Additional Information:

Diss. ETH No. 25’143

URI:

https://arbor.bfh.ch/id/eprint/8437

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