Understanding the relationships between food intake, milk output and body condition in high-yielding dairy cows is crucial in determining suitable management strategies. During two winter feeding periods 38 and 37 cows were individually fed, to appetite, complete diets which on average contained 11-7 MJ metabolizable energy per kg dry matter and comprised grass silage, concentrate meal and brewers' grains (draff). The groups' mean 305-day yield was 7 240 kg (s.d. 1 281) with 42 g (s.d. 4-3) fat per kg. Regression analysis was carried out to describe dry-matter intake both for 26 weeks post calving and for four successive 6-week periods from calving. The final equations, which had a residual s.d. of 0-07 to 0-10 of the observed intake, included milk yield, cow size and a measure of body-condition change. The cows were divided into three groups (high, medium and low) on two criteria: (1) mean milk yield (MJ/day) during the first 26 weeks of lactation and (2) post-calving backfat index determined ultrasonically. Differences were found between milk-yield groups from gross efficiency (milk yield (MJ)/ energy intake (MJ metabolizable energy)) (P < 0-001), mean metabolizable energy intake (MJ/day) (P < 0-01), dry-matter intake as a proportion of live weight (P < 0-05), and post calving live weight (kg) (P < 0-05). Differences were found between backfat-index groups for maximum backfat loss, and loss to day 42 (P < 0-001); also for mean live weight during the 26 weeks and post calving live weight (P < 0-001), dry-matter intake as a proportion of live weight (P < 0-05) and lactation number (P < 0-05). Interactions were found between the milk yield groups and backfat groups for milk yield (P < 0-01) and gross efficiency (F < 0-05) with the fattest group containing the highest and lowest yields and efficiencies.

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Twenty-two Friesian and Friesian cross Ayrshire cows and 16 first lactation heifers were paired. Twenty were injected subcutaneously with 500 mg recombinant bovine somatotropin (sometribove) and 18 with a placebo at fortnightly intervals, starting 80 (+/- 7) days after calving, through the winter of 1986-87. The cows' weights and changes in condition, milk yields, milk solids, health and fertility were recorded regularly. Compound cake was fed at a fixed stepped rate according to the number of days since the cow calved. Silage was available on an easy-feed basis. Ten cows had their daily silage intake measured. Sometribove treated cows produced on average 27.7 kg of milk per day, 4.5 kg more than the controls. Treated heifers produced 23.5 kg per day, 2.5 kg more than the controls. Milk quality was unchanged. Treated cows gained weight during the trial, but not by as much as the controls. Control heifers also gained weight but the treated heifers lost, on average, 3 kg. Local reactions at the injection site were not felt to be of welfare concern, nor was the general effect of the extra milk production. A small number of treated animals experienced mastitis and had poorer fertility but the differences were mostly not statistically significant. If bovine somatotropin should become licensed for use in Britain it is recommended that clear guidelines should be issued on the management practices necessary for economic success and for the welfare of the treated animals.

In a rotational grazing system for dairy cows, to achieve maximum yield/cow, optimum post grazing stubble height of between 8-10 cm is recommended. At this mean height, however, selective patchy grazing and excessive stem production occurs, particularly around dung patches. Sward deterioration gets progressively worse as the grazing season progresses, resulting in a decline in pasture utilisation and output. An alternative to topping to improve sward structure is a leader-follower system with sheep, as tested In Ireland (O'Riordan, 1989). A pilot investigation was carried out in 1989 and a more detailed evaluation of the technique was made in 1990. Results for 1990 are reported in this paper.A high yielding herd of 114 Holstein/Friesians (herd average 7200 l), in a genetic selection programme at the University of Edinburgh's Langhill Farm, were turned out on 3 May 1990. The cows rotationally grazed 2-3 ha paddocks for 3-4 days. Speed of rotation was determined by herbage availability and daily milk production, every effort being made to ensure that herbage intake to the dairy cows was never limiting.