Grazing behaviour of dairy cattle selected for high and average milk yield

Abstract

AbstractThe present study was designed to examine the effects of selection for milk production as well as stage of pregnancy, on the grazing behaviour of dairy cattle. Subjects were 43 Holstein-Friesian cows from the Langhill Dairy Herd in Edinburgh. The herd consists of two genetic lines, one selected for high milk solids yield and a control line of average genetic index for milk solids yield. Animals of both genetic lines were observed as non-lactating heifers in 1992 and as first lactating and dry cows in 1993. Behaviour was recorded using scan-sampling procedures during seven observation periods at day and two periods at night. For analysis animals were grouped by their first lactation 305-day ECM (energy-corrected milk) yield for four observation periods during the day and for both night time observations animals were additionally grouped by stage of pregnancy. The majority of selected animals was in the high yielders’ group. In September 1992 and 1993 herbage intake on pasture was also investigated.No significant influence of 305-day ECM yield on time spent grazing, lying or ruminating was found. The influence of stage of pregnancy was stronger, although results for heifers and cows were contradictory. During the day heifers which were closer to parturition spent less time grazing (P < 0.10 in two of three periods) and more time lying (P < 0.05 in one period) whereas lactating cows in late pregnancy spent more time grazing and less time lying (P < 0.01 and P < 0.10, respectively). High yielders had higher herbage intakes than low yielders but this result was significant for heifers only (P < 0.01).