The use of a Latin square change-over design with dairy cows to detect differences in the quality of tropical pastures

Abstract

The value was investigated of a latin square change-over design for detecting differences in herbage quality in terms of milk production and milk composition from Jersey cows grazing pure stands of three tropical grass pastures, Digitaria decumbens, Setaria sphacelata cv. Kazungula, and Chloris gayana CV. Pioneer. Relatively small differences in milk production could be measured using limited resources of land and cows, and estimates were calculated of the number of cows required to detect true differences in milk yield. A 9-day standardization period was shown to be more desirable than a 4-day standardization period. Residual effects of previous treatments, although small, were significant. Suggestions are made for improving the efficiency of change over experiments using cyclic designs to estimate residual effects. The overall level of milk production from these pastures was low (8-10 kg/cow/day). Cows grazing Digitaria decumbens produced significantly more milk than those on Chloris gayana and Setaria sphacelata, most probably due to a higher consumption of herbage. Similar milk production was obtained from cows grazing Chloris gayana and Setaria sphacelata although milk from the latter tended to contain a lower percentage butterfat.