The effects of out-wintering replacement dairy heifers on deferred grazing, kale or fodder beet, without or with a trace mineral bolus on first lactation performance in commercial spring calving herds

There is little effect of out-wintering forage source on subsequent lactation performance, but the provision of a mineral bolus may improve performance and reproduction in early lactation particularly when out-wintered on kale.
Out-wintering replacement dairy heifers on grass, kale or fodder beet, is most common amongst low input spring calving systems (Atkins et al, 2014). Farmers out-wintering heifers generally consider performance in first lactation, equal to that of housed animals (Atkins et al, 2014). Indeed, past research has reported comparable lactation performance in dairy cows out-wintered on forage brassicas or grass compared with housing (Keogh et al, 2009). Trace mineral nutrition, particularly when grazing kale, may also affect the subsequent lactation performance due to the low trace mineral concentration in forages and anti-nutritional factors. The objective of the study was to compare the effects out-wintering on deferred grazing, kale or fodder beet, without and with additional trace minerals during the out-wintering period, on first lactation performance.