Feed intake, milk yield and metabolic status of early-lactation Swedish Holstein and Swedish Red dairy cows of different parities fed grass silage and two levels of byproduct-based concentrate

Dairy cows can produce highly nutritive food products (milk, meat etc.) from fibrous feed e.g. grass and different byproducts from the food and fuel industry, that cannot be consumed directly by humans. However, as there are limited amounts of byproducts available, decreasing the amount of byproduct-based concentrate in the diet could be a strategy for improving sustainability within dairy production if high milk production should be maintained. In this study, 26 multiparous (n = 14) and primiparous (n = 12) dairy cows of the breeds Swedish Red (n = 14) and Swedish Holstein (n = 12) were followed between lactation weeks 1 and 6. They were fed either a low-concentrate (n = 13; LC) or high-concentrate (n = 13; HC) byproduct-based (sugar beet pulp, rapeseed meal, distiller's grain, wheat bran) ration, in combination with highly digestible grass-clover silage ad libitum. To achieve similar concentrate intake per kg body weight in primiparous and multiparous cows, multiparous cows were offered 5 kg concentrate on the LC diet and 15 kg concentrate on the HC diet, while primiparous cows were offered 4 kg concentrate on the LC diet and 14 kg concentrate on the HC diet as target concentrate rations. We found no overall differences in dry matter intake, energy-corrected milk yield, energy balance, blood plasma metabolites, blood hormones or milk fatty acids between cows on the LC and HC diets. However, HC cows had a higher yield of ECM in lactation week 6 and gained body weight compared with LC cows. As expected, multiparous cows had higher dry matter intake and energy-corrected milk yield, but we found no difference in energy balance between parities. However, multiparous cows lost more body condition and had higher blood plasma concentrations of non-esterified fatty acids, indicating that they used more body tissue to support milk production. In conclusion, both multiparous and primiparous Swedish Red and Swedish Holstein dairy cows seem able to adapt to low-concentrate diets in early lactation when the diets are based on byproducts and grass-clover silage, providing the potential to increase sustainability in dairy production