Effects of continuous and rotational grazing of different forage species on ewe milk production

Abstract

The aim of this research was to evaluate the effects of continuous and rotational grazing of different forage species on milk production in ewes. The forage species were chicory (Cichorium intybus L.), a mixture of oat (Avena sativa L.) and berseem clover (Trifolium alexandrinum L.), and sulla (Hedysarum coronarium L.). Forty ewes were divided into 5 groups, and subjected to one of the following treatments: continuous grazing on chicory, continuous grazing on the mixture, continuous grazing on sulla, rotational grazing on the mixture, or rotational grazing on sulla. Among the species continuously grazed, chicory showed a lower biomass than the mixture, or sulla. Ewes grazing chicory produced more milk than ewes grazing the mixture (1243 vs. 1003 g/d; P ≤ 0.01), whereas ewes grazing the sulla showed an intermediate milk yield (1136 g/d). During the experiment there was a gradual decrease in milk yield which was less pronounced for chicory, than for the other species. The fat, protein, and casein contents in the milk increased as the milk yield decreased. Compared with continuous grazing, rotational grazing produced a greater forage biomass. Moreover, ewes on continuous grazing produced a higher milk yield than those under rotational conditions (1070 vs. 951 g/d; P ≤ 0.05). The grazing period also influenced milk production: in the first period (April), when more forage was available, the ewes produced more milk than during the second period (May). Furthermore, the ewes grazing sulla recorded a higher milk yield in the first period, compared to those grazing the mixture (1377 vs. 1159 g/d; P ≤ 0.05), but this difference was not evident during the second period. These results highlight the productivity of sulla, and the potential of chicory in providing a lasting good-quality herbage, and therefore the positive effect of these species on dairy performance in grazing ewes. Although rotational grazing produced more forage biomass, the results indicate that it does not always lead to increased milk production in animals, because of the lower nutritional value of forage grazed in an advanced phenological stage.