Effects of mountain grassland maturity stage and grazing management on carotenoids in sward and cow's milk

Abstract

Carotenoids are involved in the sensorial and nutritional values of dairy products. In grazing systems, both herbage maturity stage and grazing management may affect the amount of carotenoid ingested, thus these factors may affect carotenoid concentrations in milk. Two homoge- nous plots of mountain grassland (1.4 and 2.0 ha) were grazed during two cycles of growth by 6 dairy cows in mid lactation, in strip (SG) and rotational grazing (RG), respectively. We monitored the changes in carotenoid concentrations in sward and milk, measured by HPLC twice a week. Seven carotenoids were identified in the sward: violaxanthin, antheraxanthin, epilutein, lutein, zeax- anthin, s-carotene and 13-cis s-carotene. Forage quality decreased throughout the course of the first growth stage, but carotenoid concentration in sward did not significantly change. In early regrowth, forage quality was high and the concentration of s-carotene and xanthophylls also tended to be higher. Carotenoid concentrations in sward were not affected by grazing management, averaging 350 µg per g DM. The carotenoids identified in milk were β-carotene (75%) and lutein (25%). A significant decrease in s-carotene concentration in milk was observed throughout the course of the first growth stage, from 5.37 to 3.87 µg per g fat, whereas it increased to 4.91 µg per g fat in early regrowth. β-carotene concentration in milk was not affected by grazing management, averaging 4.72 and 5.03 µg per g fat for RG and SG, respectively. However, lutein concentration was slightly lower for RG than for SG, averaging 1.39 and 1.74 µg per g fat, respectively. It is concluded that carotenoids in milk were only slightly affected by herbage maturity stage, and to a lesser extent by grazing management. carotenoids / cow's milk / mountain grassland / maturity stage / grazing management