Energy and protein nutrition of dairy cows during the dry period and early lactation: Production performance and adaptation from pregnancy to lactation

This thesis consists of studies concerning the effects of dry period energy feeding, and early lactation energy and protein feeding on the metabolic and hormonal status, tissue mobilisation and lactation performance in dairy cows. In all studies, restricted amounts of grass silage were fed during the dry period, and lead feeding with concentrate was applied during the last three weeks of pregnancy. After calving, grass silage was fed ad libitum and the daily concentrate allowance was increased to fixed levels according to preplanned schedules. In experiment I, the effect of two levels of concentrate and glucogenic feed was studied during early lactation. The concentrate levels were 11 and 15 kg/d for multiparous cows and 9 and 12 kg/d for primiparous cows. Glucogenic liquid feed consisted of propylene glycol, polyols, molasses and niacin, and it was fed at 0 or 1 l/d. In multiparous cows, milk production responses to concentrate supplementation differed between the groups with and without glucogenic feed. The high response (1.3 kg ECM/kg concentrate DM) to concentrate supplementation with glucogenic feed was attributed to increased protein intake, since CP contents of silage and glucogenic feed were low. A high substitution rate of concentrate for silage was associated with the lack of milk yield response in multiparous cows without glucogenic feed. Milk yield response of primiparous cows to concentrate supplementation was low. Higher concentrate allowance elevated plasma insulin concentrations and increased live weight gain in primiparous cows after peak yield. Concentrate supplementation and glucogenic feed did not decrease lipid mobilisation, but glucogenic feed decreased concentrations of blood ketone bodies in multiparous cows. In experiment II, the effect of early lactation protein supplementation was examined. A cereal-based concentrate mixture including 0%, 15% or 30% of rapeseed meal was fed to multiparous cows. High milk yield response between 0% and 15% rapeseed meal was attributed to increased lipid mobilisation and more efficient utilisation of metabolizable energy for milk production. The lack of further milk yield response between 15% and 30% levels was associated with the absence of feed intake and diet digestibility responses, and conversion of extra nitrogen to urea. Protein supplementation did not affect concentrations of blood ketone bodies. In experiment III, the effects of concentrate proportion in lead feeding and the increase rate of concentrate after calving were investigated. The concentrate proportions of 20%, 40% or 60% of individual energy requirements during lead feeding had no consistent effect on silage intake after calving. High proportions of concentrate increased plasma insulin and low proportions of concentrate slightly increased plasma concentration of non-esterified fatty acids one week before calving. The increase rate of concentrate after calving did not affect silage intake and fast increase of concentrate did not increase the number of off-feed incidences. The highest milk yields during lactation weeks 1 to 5 were observed in the groups with medium or high concentrate proportion before calving and fast increase rate of concentrate after calving. The combination of low concentrate proportion before calving and slower increase rate of concentrate after calving elevated blood concentration of ketone bodies one week after calving. In experiment IV the effects of body fatness at calving and glucogenic supplementation during the transition period and early lactation were studied. Increased mobilisation of lipid and protein reserves was observed in fatter cows. Increased lipid mobilisation was associated with higher in vitro lipolytic responses to norepinephrine. Glucogenic supplement did not decrease lipid or protein mobilisation, but it prevented the increase of blood ketone body concentration in fatter cows. Plasma leptin started to decrease before calving and the lowest concentrations were measured during the first week of lactation. During early lactation plasma leptin concentrations remained low, but were significantly higher in fatter cows than in