Sixteen varied grass silages metabolizable energy (ME): 9·76 to 11·99 MJ/kg ethanol-corrected toluene dry matter (TDM); crude protein (CP: 149 to 211 g/kg TDM; lactic acid: 3·5 to 134·7 g/kg TDM; butyric acid 0·4 to 46·7 g/kg TDM) were offered ad libitum to early-lactation dairy cows (12 per experiment) along with a fixed allocation of 7 kg/day of a standard concentrate. Four silages were offered in each of four incomplete change-over design experiments with three 21-day periods. This design meant that each cow was allocated to receive three of the four silages evaluated in that experiment. ME intake ranged from 108 to 262 MJ/day (mean 177 (s.d. 30·2)). Similar variation was obtained with milk yields (mean 26·5 (s.d. 4·36) kg/day), fat content (mean 37·7 (s.d. 5·60) g/kg) and protein content (mean 29·0 (s.d. 2·36) g/kg). Urinary purine derivative/creatinine ratio (PD/C), an index of microbial protein measured in spot samples (two per day) averaged 2·92 (s.d. 0·757) mol/mol. Allantoin made up an almost constant molar proportion of PD excretion (mean 0·876 (s.d. 0·0377)), with a small but significant (P < 0·001) decline of 0·0132 (s.d. 0·003) per unit increase in PD/C.Maximal utilization of silage nitrogen occurred with silages having higher ME and lower CP concentrations. Urinary PD/C suggested that microbial protein yield varied in a way which would not be predicted in current schemes and that it was a major source of variation in milk protein yield under the conditions of the present experiment. Principal components regression confirmed independent effects of ME supply and MP supply (indexed by urinary PD/C) on milk protein yield. Further work should pursue the possibility of using the urinary PD/C technique to refine protein feeding at the farm level.

1.A primary growth of perennial ryegrass (Lolium perenne) was cut early or late to produce silages of high and low digestibility. The crops were wilted for 2 4 h and preserved with formic acid at 2.4 litres/t fresh weight. The resulting silages were well preserved with a pH of 3.9 and 3.8, lactic acid content of 108 and 73 g/kg dry matter (DM) and total nitrogen content of 24.6 and 18.4 g/kg DM for early-and late-cut silage respectively.2. Forty-two British Friesian male castrates (steers) initially 12 months of age and 305 kg live weight (LW) were used, of which ten were slaughtered at the start of the experiment. The remaining steers were divided into four groups of eight animals and were given the early-cut silage alone (H) or the late-cut silage alone (L) or with barley at either 280 (LCl) or 560 (LC2) g DM/kg total DM. The intake of total DM was restricted to a daily allowance of 18 g DM/kg LW and the steers were slaughtered in two groups after 119 and 140 d on experiment.3. Both earlier cutting of herbage and substitution of late-cut silage with barley significantly (P < 0.001) increased the apparent digestibility of gross energy (H0748, L0619, LClO.668, LC20.705), whereas earlier cutting increased the digestibility of acid-detergent fibre from 0.638 (L) to 0777 (H) and substitution with barley resulted in a significant (P < 0001) depression to 0.595 (LCI) and 0.519 (LC2). Substitution of late-cut silage with barley significantly (P < 0,001) increased metabolizable energy (ME) intake from 58.9 (L) to 69.5 MJ/d (LC2) and crude protein (N x 6-25; CP) intake from 688 (L) to 779 g/d (LC2), but the highest intakes of ME and CP (73.5 MJ/d and 952 g/d respectively) were achieved with the early-cut silage. 4.Earlier cutting resulted in significant (P < 0.001) increases in body-weight gain from 292 to 696 g/d, fat gain from I21 to 260 g/d, protein gain from 31.1 to 86.9 g/d and energy retention from 5.5 to 12.2 MJ/d for silages L and H respectively. However, substitution of the late-cut silage with barley increased gains to a greater extent. Thus, empty-body gain was increased to 552 and 800 g/d, fat gain to 189 and 302 g/d, protein gain to 76 and 116 g/d and energy retention to 9.2 and 14.6 MJ/d for diets LC1 and LC2 respectively. The difference in gains between diets H and LC2 achieved significance (P i 0.05) for all components except fat.5. It is concluded that although earlier cutting of herbage for silage results in increased gains of protein and energy, the amounts retained are less than those from a similar increment of ME and CP achieved by substituting a late-cut silage with barley.

Ninety-four silages were made over 5 years from predominantly perennial ryegrass swards using a range of cutting dates (19 May to 18 September), wilting periods (0 to 48 h) and additives (none, acids, inoculants, sugar, sugar + acids, sugar + inoculants). A wide range of silage composition was achieved (CV for dry matter (DM), crude protein (CP), digestible organic matter (DOMD), lactic acid, total volatile fatty acids (VFA) and sugar were 0-22, 0-19, 0-07, 0A3, 0-84 and 0-69 respectively). Silage dry-matter intake (SDMI) was measured for 88 silages using lambs (mean live weight (M) 28 kg) given silage as their sole diet in four incomplete block design experiments using four lambs per silage and a standard hay given every third period for covariance correction. Thirty-four of the silages were also evaluated using early lactation cows (M, 561 kg and milk yield 27 kg/day) with 7 kg/day of concentrate in eight incomplete block change-over experiments each using 12 cows. Intakes (SDMI mean, range, s.d. glkg M 075 ) were 56, 25 to 84, 13-7 for lambs and 90, 64 to 119, 13-4 for cows. Scaling lamb SDMI by M 1 ' 47 accounted best for the effect of lamb weight on intake (mean, range 5-07, 2-43 to 7-68). (NIRSdry) or fresh samples (NIRSwetl using a vertical transport mechanism and NIRSwet2 using a rotating cup). The most useful predictors within each group were firstly identified by step-wise multiple linear regression and models were then derived by partial least squares. Standard errors of cross validation (SECV) obtained by the 'leave one out' method were for lamb SDMI (g/M 1 ' 47 ) BASAL + HPLC, BASAL + ET, NIRSdry,[5][6][7][8][9][2][3][4][5]. Inclusion of fermentation measurements made by ET, but not by HPLC, improved SDMI prediction over that obtained from the BASAL set. However, NIRSdry and NIRSwet2 were the most accurate methods giving values for s.d. (reference population) I SECV of 2-27 and 2-13 for lambs and 2-65 and 5-28 for dairy cows. Use of these methods in advisory silage evaluation should substantially reduce the errors of predicting the intake potential of grass silages. Silage predictors were grouped as follows: traditional values (BASAL) -DM, CP, organic matter (OM), DOMD, neutral-detergent fibre (NDF), acid-detergent fibre (ADF), ammonia nitrogen (NH 3 N), pH, acid hydrolysed ether extract (AHEE); silage fermentation values obtained by high-performance liquid chromatography (HPLC); or by electrometric titration (ET); and near infra-red reflectance spectra (NIRS) obtained on either 100°C dried

High digestibility ryegrass was ensiled using either good methods including formic acid application (HDG) or poor methods without formic acid (HDP). Low digestibility ryegrass (LDG) and lucerne (LUC) were ensiled using similar methods to HDG. Digestible organic matter in the dry matter (DM) in vivo (DOMD) for HDG, HDP, LDG and LUC were 0-756, 0-774, 0-645 and 0-562 respectively. Silages were offered ad libitum to 40 Holstein-Friesian cows in two Latin-square design experiments during weeks 8 to 22 of lactation either alone (experiment 1) or with 3, 6, 9 or 12 kg concentrate DM per day (experiment 2). Relative intakes of silage given alone were respectively 1-00, 0-44, 0-98 and 0-79. Low intake of HDP could not be predicted from silage analysis. In experiment 2, DM intake increased by 0-11 kg and milk yield by 0-24 kg for each 0-010 change in grass silage DOMD. Intake of HDG, LDG and LUC declined linearly with increasing concentrate, on HDP the effect was nonlinear and intake increased up to the 6 kg level. In experiment 1, milk and protein yields were greatest on HDG, protein yield was higher on LDG than LUC and fat concentration higher on HDP and LUC. With supplementation milk yield was greatest on HDG up to the 6 kg level, at higher levels differences between silages were not significant. Fat concentration was highest on LDG and protein highest on HDG and lowest on LUC. On all silages giving the highest concentrate level reduced the concentration and yield of fat. Protein concentration increased up to the 9 kg level. Fat plus protein yields reached a maximum on HDG with 6 kg concentrate DM per day and with 9 kg on the remaining silages.

A sward of perennial ryegrass was either directly ensiled at 181 g dry matter (DM) per kg fresh weight with formic acid applied at 3-6 1/t fresh material or wilted for 65 h to achieve a DM concentration of 407 g DM per kg. Physical and respiration loss were measured in the field and losses during ensiling were estimated from buried bags. The silages were offered to 58 British Friesian steers, initially 3 months of age and 101 kg live weight (LW). Ten steers were allocated to an initial slaughter group and the remainder were offered the two silages either ad libitum or at two restricted levels of feeding. These animals were slaughtered after a mean period of 112 days to estimate the increments in the components of the body.Loss of DM in the field increased from 4-3 to 86-6 g/kg on wilting and proportionately 0-75 of this additional loss was due to respiration. The fermentation characteristics of the silages were broadly similar except that the concentration of ethanol was higher in the unwilted than in the wilted silage (57-6 v. 5-6 g/kg DM). Losses of DM during ensiling were slightly higher with the unwilted (104-4 g/kg ensiled) than with the wilted (80-1 g/kg) material. Losses of nitrogen were relatively higher and energy losses lower than was the loss of DM.Wilting significantly depressed the digestibility of gross energy from 0-651 to 0-631 (P < 0-001) and at the ad libitum level steers ate proportionately 006 more wilted silage (P > 0-05) resulting in similar intakes of digestible energy. At the ad libitum level of feeding steers given wilted silage gained more LW (+55 g/day) and empty-body weight (+64 g/day) than those given unwilted silage (P < 0-05). However, steers given wilted silage contained less fat and energy in the empty body at slaughter ^than those given unwilted silage. Thus, wilting did not influence the efficiency of utilization of digestible energy for energy retention nor the efficiency of utilization of dietary protein for protein gain. Since efficiencies by the animal were similar and also the increased field loss on wilting was partly compensated for by a reduced silo loss, it is concluded that the proportion of energy and protein in the standing crop retained by the steers is unaffected by wilting (65 and 64 kJ/MJ and 125 and 138 g/kg N for unwilted and wilted systems respectively). Further work is needed to establish the effect of wilting for a shorter period than in the current trial by increasing the drying rate of herbage.