A large data set derived from total diet digestibility assessments on lactating dairy cows (535 Holstein-Friesian and 29 Norwegian) was used to examine effects of dietary and animal factors on manure (feces and urine) nitrogen (N) output and to develop mitigation strategies and prediction equations for manure N output in lactating dairy cows. Manure N output was positively and significantly related to live weight, milk yield, dietary crude protein (CP) concentration, dry matter intake, and N intake. Reducing the dietary CP concentration or increasing the milk yield decreased manure N output per kilogram of milk yield. Prediction equations for manure N output using live weight and milk yield, either alone or combined, had relatively low R2 (0.227 to 0.474) and large standard error (70.6 to 85.6) values. Addition of dietary CP concentration to these relationships considerably increased R2 to 0.754 and reduced the standard error to 48.2. Relating manure N output to N intake produced a very high r2 (0.901) and a very low standard error (30.6). The addition of live weight and milk yield to this relationship as supporting predictors only marginally increased R2 to 0.910 and reduced the standard error to 29.3. The internal validation of these equations revealed that use of N intake as the primary predictor produced a very accurate prediction of manure N output. In situations in which data on N intake are not available, prediction equations based on dietary CP concentration, live weight, and milk yield together can produce a relatively accurate assessment of manure N output.

Three cutting heights, 1, 3 and 5 in. (2-5, 7-6 and 12-7 cm), and three cutting frequencies, 3, 6 and 10 weeks, were imposed on a pure sward of Italian ryegrass {Lolium multifloruni) cv. Irish. Lowering the cutting height increased tbe yield of DM, digestible DM, crude protein and crude fibre. Increasing tbe interval between cuts increased tbe yield of DM, digestible DM and crude fibre. Tbe results are discussed in relation to otber researcb findings and to tbe management of sbort-term leys of Italian ryegrass.

Two experiments were conducted to examine the effect of two winter feeding systems on the performance of dairy cows in early lactation. Experiments 1 (144 d duration) and 2 (146 d duration) involved sixty-four (primiparous) and eighty-six (primiparous and multiparous) Holstein Friesian dairy cows respectively. Rations offered comprised grass silage, maize silage [0AE26-0AE29 of forage dry matter (DM)] and concentrates (10-12 kg d )1 ). With the complete diet (treatment CD), the forage and concentrate components were mixed using a complete diet mixer wagon, and offered daily in the form of a 'complete diet'. With the easy feed (treatment EF), the dairy cows were offered the forage component of the ration twice weekly in whole blocks, in quantities sufficient for the following 3-or 4-d period, while the concentrate component of the diet was offered via electronic out-of-parlour feeding stations. Total DM intakes were similar, namely 17AE6 and 17AE0 kg d )1 (Experiment 1) and 18AE7 and 18AE5 kg d )1 (Experiment 2), for treatments CD and EF respectively. Feeding system had no significant effect on milk yield, milk fat or milk protein content, or on end of study indices of body tissue reserves in either experiment (P > 0AE05). Similarly, feeding system had no significant effect on the digestibility of the ration measured in Experiment 2 (P > 0AE05). Feeding times associated with each component of the two feeding systems were measured, and these were then used to calculate total feeding time for a 97-cow dairy herd. Calculated feeding times for this herd were 209AE3 and 156AE0 min week )1 for treatments CD and EF respectively.

The effects of continuous stocking by sheep at sward surface heights (SSH) of 3, 5, 7 and 9 cm in grass/clover (GC) and nitrogen‐fertilized grass (GN) swards were examined in relation to herbage mass and quality, clover content, tiller density and rates of herbage production and senescence in two periods in each of three grazing seasons (1987‐89). The GN swards received a total of 300 kg N ha−1 each year in six equal dressings from March; GC swards received a single dressing of 50 kg N ha−1 in March each year. Herbage mass measured from ground level increased linearly with SSH with overall mean herbage masses of 0·89, 1·38, 1·78 and 2·12 t OM ha−1 (s.e.m.0·024, P < 0·001) at SSH of 3, 5, 7 and 9 cm respectively. GN and GC swards had mean herbage masses of 1·58 and 1·51 t OM ha−1 (s.e.m. 0·051, NS) respectively. Mean N content of herbage on GN swards was greater than that on GC swards and declined with increasing SSH. Crude, fibre (CF) content of herbage was similar for both sward types and increased with increasing SSH. Clover content of GC swards remained low throughout the experiment, ranging from 0·002 to 0·074 of herbage mass. However, from tissue turnover rates it was estimated that its contribution to herbage production was in the range of 0·049–0·219 of net herbage growth. Total growth increased with increasing SSH in both sward types, with maximum growth rates in GN swards of 143 and 130 kg DM ha−1 d−1 and in GC swards of 88·2 and 85·4 kg DM ha−1 d−1 in Periods 1 (up to early July) and 2 (after July) respectively. Senescence rates ranged between 13·3 and 50·1 kg DM ha−1 d−1 and tended to be higher in Period 2 than in Period 1. Net production increased with increasing SSH in Period 1, while in Period 2 net production declined at SSH above 6·5 cm. The increased net herbage production in taller swards was not associated with greater utilized metabolizable energy production at sward heights above 5 cm.

Over three grazing seasons (1984)(1985)(1986)) a sward of perennial ryegrass, cv. Talbot, which received a total of 336 kg N ha" ' each season, was cut or grazed with ewes at 3-or 4-week intervals on a rotational basis.Sward productivity was higher under cutting than under grazing irrespective of the interval between defoliations. Under cutting, mean herbage organic matter (OM) yields over both intervals were 8-66, 9-62 and 8-17 t ha" ' in 1984, 1985 and 1986 respectively while under grazing the corresponding yields were 7-65, 8 • 63 and 7 • 501 ha " '. The mean annual yield of herbage defoliated at 3-week intervals was 7-50, 8 • 64 and 7 • 201 OM ha "' compared with 8-80. 9-60 and 8 461 OM ha"' for swards defoliated at 4-week intervals in the three years respectively.The nitrogen (N) content of both the available and the residual herbage was consistently higher under grazing than under cutting. Available herbage contained 31-3 and 27-7 g N kg OM "' and residual herbage 26-1 and 22-7 g N kg OM "' under grazing and cutting respectively.The mean yield of N under cutting was 284 kg ha"' compared with 304 kg ha"' under grazing. Defoliation interval had no effect on N yield, the overall mean yield being 294 kg ha "' under both 3-and 4-week defoliation intervals. The effect of the treatments on tiller population was slight and inconclusive.