Browsing by Person "Gerster, Elisabeth Katharina"

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    Langfristige Beurteilung der Energieversorgung von Milchkühen bei unterschiedlichem Kraftfuttereinsatz
    (2020) Gerster, Elisabeth Katharina; Rodehutscord, Markus
    The first objective of the present study was to compile the current knowledge concerning the effect of the amount of CON on dry matter (DM) intake and milk yield of dairy cows, by regression analysis. For this purpose, a dataset was compiled containing 46 studies with feeding trials and graded inclusion levels of CON. When offering the roughage ad libitum, a quadratic relation was found between CON intake and roughage intake. Taking into account the substitution of roughage, the observed increase of milk yield was less than expected. The second objective was to verify the response of Simmental dairy cows to a long-term reduction of the CON input, in terms of dry matter intake, milk yield, and energy supply. During a feeding trial conducted over a two-year period at the experimental station LAZBW in Aulendorf (cooperative research project „optiKuh“) each 24 Simmental dairy cow was fed either 250 (group 250) or 150 (group 150) g CON per kg energy-corrected milk yield (ECM) throughout lactation. Grass and maize silage as well as straw and hay were combined in the total mixed rations to ensure an energy concentration of 6.6 MJ NEL per kg DM of the roughage in both groups throughout lactation. The CON contained a mixture produced on-site (winter wheat, winter barley, faba bean) and rapeseed meal. At 165 days in milk, each cow in both groups was switched individually to a ration containing less CON. Data were gathered also during the dry period. Feed was offered for ad libitum consumption. Statistical analyses were done separately for the lactation and dry period. As fixed effects the calendar week, the group, the parity, and the interaction group*parity entered the model, respectively. Additionally, the days in milk were included as a covariate during lactation. During lactation the mean daily DM intake did not differ significantly between group 250 (21.6 kg DM) and group 150 (21.0 kg DM). The calculated substitution of roughage amounted to 0.75 kg DM per kg CON DM during the mentioned trial period. As lactation progressed, more roughage was substituted. The group 250 had a higher milk yield during the first half of lactation, but a lower milk yield during the second half. The mean milk yield was equal in both groups (28.7 kg ECM per day). The examined blood characteristics (8, 28, 100 days p. p., at drying off, 14 days a. p.) and the milk fatty acids analysis by gas chromatography (5, 28, 100, 200 days p. p.) reflected the different progressions of the energy balance of the two groups. On average the group 250 reached a positive energy balance already at 37 days in milk. Probably owing to a better glucose supply after calving, the serum insulin concentration increased faster and supported the replenishing of body reserves at the expense of milk yield. On the contrary, the group 150 achieved a positive energy balance only after 72 days in milk on average. Indicating the mobilization of body reserves, the blood of group 150 showed a significantly higher D-ß-hydroxybutyrate concentration, and the milk fat a significantly higher concentration of long-chain fatty acids 28 days p.p.. However, the values were within the physiological range. The reduction of CON did not increase the likelihood of illness. During the dry period, despite equal feeding of both groups in this period, the group 150 had an increased DM intake of 0.9 kg DM per day (p=0,026). Thus, they restored body energy reserves. Over time both groups succeeded in balancing the energy deficit of the beginning of lactation. The proposal of SUSENBETH (2018) for the calculation of the energy requirement of dairy cows improved the plausibility of the calculated energy balances compared with the factors according to GfE (2001). The third objective was to develop a model for the estimation of energy balance in the first third of lactation based on characteristics of production with focus on concentration of milk fatty acids. For this purpose, the milk fatty acids analyses 5, 28 and 100 days p. p. of the feeding trial were used (n=200). The model was derived from the regularized linear regression method „elastic net“. The variables milk yield on sampling day, milk fat content, concentrations of the milk fatty acid C12:0 and the milk fatty acid C18:0, as well as the relations n-6/n-3, C15/C17 and oleic acid/C15 were selected. An estimation error of 13.1 MJ NEL per day was determined by leave-one-out cross-validation. Potentially, the model seems to be applicable for the detection of a severe negative energy balance at the beginning of lactation. But first a validation with an independent dataset is required.