The effects of energy source and level of digestible undegraded protein (DUP) in concentrates on silage intake and performance of lactating dairy cows, offered one of a range of grass silages differing in digestibility and intake characteristics, were evaluated in a partially balanced change-over design experiment involving 48 cows. Four silages were prepared using differing management practices prior to and during ensiling. All silages were treated with an inoculant additive. For silages A, В, С and D, dry matter (DM) concentrations were 199, 320, 313 and 223 (s.e. 4.6) g/kg, pH values 3.82, 4.03, 4·03 and 5·27 (s.e. 0.056), ammonia nitrogen (N) concentrations 58, 122, 66 and 356 (s.e. 13.2) g/kg total N and in vivo DM apparent digestibilities 077, 0.75 , 0.60 and 0.60 (s.e. 0·013) respectively. When offered as the sole diet to 12 dairy cows in a partially balanced change-over design experiment, silage DM intakes were 14.7, 14.7, 12.7 and 10.5 (s.e. 0·36) kg/day respectively for silages А, В, С and D. Six concentrates containing three starch concentrations, each at two levels of DUP, were formulated to have similar concentrations of crude protein, metabolizable energy (ME) and fermentable ME. For the low and high starch concentrates and low and high levels of DUP, starch concentrations were 22·5 and 273 g/kg DM and DUP levels were 44 and 60 g/kg DM respectively. Silages were offered ad libitum supplemented with 10 kg fresh concentrate per head per day. For silages А, В, С and D, DM intakes were 10.8, 11.2, 10·7 and 9·1 (s.e. 0·26) kg/day and milk yields 29.0, 27.6, 27.1 and 25.7 (s.e. 0.69) kg/day respectively. With the exception of milk protein concentration there were no significant (P > 0.05) silage type by concentrate energy source and/or level of DUP interactions on silage intake, milk output or composition. Concentrate energy source had no effect (P > 0.05) on silage DM intake, the yields of milk, fat, protein or fat plus protein or milk fat concentration. However, increasing starch concentration increased milk protein concentration (P < 0·001), urinary allantoin concentration (P < 0·01) and diet apparent digestibility (P < 0·001). Altering concentrate DUP level had no effect (P > 0·05) on silage DM intake, yields of milk, protein, fat or fat plus protein, milk f at concentrations or diet apparent digestibility. Increasing the level of DUP decreased milk protein (P < 0·05) concentration. It is concluded that with silages of varying digestibility, fermentation and intake characteristics, there were no concentrate energy source and/or level of DUP by silage type interactions on silage intake, milk yield or composition, or diet apparent digestibility with the exception of a silage type by concentrate level of DUP interaction on milk protein concentration. With out-of-parlour feeding of concentrates the results of the present study suggest that there is no evidence to justify the formulation of concentrates differing in energy source or level of DUP to complement individual silage types.

The study was carried out on a continuously stocked grass/white clover pasture, which was maintained at two sward heights: 3·5 cm (low; LSH) and 6·5 cm (high; HSH). Three oesophageal-cannulated and three other rumen-cannulated Merino sheep were allocated to each of the plots (LSH and HSH) in order to study the effects of sward height and advancing grazing season on rumen fermentation in grazing sheep. Three grazing periods (13 days) were considered: mid June, late July and early October. During each grazing period and after a preliminary period (7 days), samples of the grazed herbage and of grass hay were incubated in nylon bags in the rumen of each sheep for 0, 3, 6, 12, 24, 48, 72 and 96 h. On days 10 and 12 rumen fluid was sampled at the incubation time (11.00 h) and at 3, 6 and 12 h afterwards and pH, ammonia-nitrogen and volatile fatty acids (VFA) concentrations were determined. Sward height did not affect (P > 0·05) the degradation rate of dry matter (DM) and neutral-detergent fibre (NDF) from grazed herbage in any of the considered periods. Animals grazing LSH presented higher (P < 0·05) DM and NDF effective degradabilities (DMED and NDFED, respectively) during October but no differences were found during June and July. HSH grazing animals presented lower (P < 0·05) degradation rates of DM and NDF from grass hay during June and July than those found for LSH grazing sheep, with no differences (P > 0·05) observed during October. Sward height did not affect (P > 0·05) grass hay DMED and NDFED during July but during June and October HSH grazing sheep presented higher (P < 0·05) values. In general, DMED and NDFED from grazed herbage increased with advancing season, the lowest (P < 0·05) value being observed during June. Rumen ammonia-nitrogen concentrations were higher during October than during June and July for both sward heights but values were higher than 200 mg/l at any sampling time during all grazing seasons. Rumen pH values were within the range considered adequate for maintaining a normal cellulolytic activity at most of the sampling times, with the exception of sheep grazing LSH during October. Rumen VFA concentrations were within the range reported for other grazing studies and only a few differences between sward heights were found. Differences in rumen parameters are discussed in relation to both chemical composition of grazed herbage and pattern of intake.

Four dietary treatments were based on a flat-rate (5 kg/day) of concentrates with ad libitum grass silage. The concentrates were iso-energetic and iso-nitrogenous, based on either barley or unmolassed sugar-beet pulp and either extracted rapeseed meal (RSM) or a 1: 3 mixture of fish and soya-bean meals (F/S). These diets were offered to 61 multiparous Holstein-Friesian cows in a continuous design experiment from lactation weeks 4 to 22. Milk yields tended to he higher with RSM (25·1 v. 23·9 kg/day; s.e.d. = 0·64; P < 0·1), whilst milk fat (38·1 v. 40·0 g/kg; s.e.d. = 0·81) and milk protein (30·4 v. 31·3 g/kg; s.e.d. = 0·41) concentrations were significantly (P < 0·05) lower. There were no significant effects of treatments on the efficiency of conversion of food-nitrogen (N) to milk-N or on N-retention. A lower organic matter apparent digestibility (g/g) was found for RSM-based diets (0·738 v. 0·763; s.e.d. = 0·0096; P < 0·05). The diets were also offered to four fistulated dairy cows in a Latin-square-design experiment. Concentrate energy source had significant effects on rumen pH (P < 0·05) and ammonia-N concentration (P < 0·01), whilst protein sources had no effect; values were always in the optimal range (pH > 6 and ammonia-N > 50 mg/l). There was a significant interaction effect (P < 0·05) such that the N-degradability of the whole diet, estimated in vivo, was unaffected by energy source for RSM-based diets but highly dependent on energy source for FIS diets. Microbial protein yield was reduced on the RSM-based diets (179 v. 220 g/day; s.e.d. = 9·6; P < 0·001).

Comparative studies were performed on the in-situ rumen degradation rate (kd) and the in-situ rumen undegradable residue (U) of dry matter (DM) and crude protein (CP) in sheep and dairy cows. The effect of different treatmentsfor sheep were investigated together with the validity of using cow-based reference protein values of foods for sheep. The effect of different breeds (Texel ewes and crossbred ewes), dietary roughage: concentrate ratio and shearing (mild cold exposure) were investigated for sheep.

The in-situ rumen incubations were performed in accordance with standard operational procedures which were comparable for both species. The foods under consideration were hay and concentrates. Cows displayed lower (DM 0·53 , CP 0·86) Kds than sheep for concentrates.

For hay a clear trend between cows and sheep was not observed but cows displayed 0·40 lower Kds than Texel ewes and 0·30 higher Kds than crossbred ewes. For concentrates U levels did not differ between species but for hay cows had 0·45 higher U values than Texel ewes. Texel ewes showed 0·45 higher Kd and 0·35 lower U for DM and CP than crossbred ewes. Dietary roughage: concentrate ratio in sheep diets did not influence the Kds and Us of the foods under consideration. Shearing of crossbred ewes increased Kd of CP by 0·25 and reduced U for DM and CP by 0·20 and 0.24 .

In conclusion different in situ rumen degradation rates were found between dairy cows and sheep. This probably makes using reference protein values of foods invalid for sheep since they are based on data for cows. Differences (Kd andU) were also found between sheep breeds and between unshorn and shorn crossbred ewes (mild cold exposure). No effect on rumen degradation kinetics could be attributed to dietary roughage: concentrate ratio.

Polyethylene glycol-4000 (PEG) was used to inactivate tannins in Acacia cyanophylla Lindl foliage. In the first of two experiments, four groups of five Barbarine sheep were held in metabolism crates so that intakes, apparent digestibilities, nitrogen balances and urinary excretion of allantoin could be measured. The second experiment involved four groups of three male Queue Fine de l'Ouest sheep fitted with rumen cannulae and housed in individual pens to measure rumen fermentation parameters and dry matter in situ degradation of A. cyanophylla foliage. All animals received fresh A. cyanophylla foliage ad libitum and 330 g concentrate on a daily basis. In each experiment, three groups of sheep received 20 g PEG daily, either mixed with concentrate (PEG-concentrate), dissolved in drinking water (PEG-water) or sprayed as a solution on A. cyanophylla foliage at the point of feeding (PEG-treatment). The fourth group was not supplied with PEG (control). Dry-matter intake of A. cyanophylla was low (28·3 g/kg metabolic live weight (M0·75) per day) and increased in sheep given the PEG-concentrate diet (38·2 g/kg M0·75 per day). PEG-concentrate and PEG-water diets resulted in an improvement in protein utilization as indicated by an increase of crude protein apparent digestibility (2·1 and 1·9 fold, respectively), nitrogen retention (3·2 fold with both dietary treatments) and urinary excretion of allantoin (1·9 and 1·5 fold, respectively). Improvements obtained with PEG-treatment diet were low and in general not significant (P > 0·05). Low neutral-detergent fibre and acid-detergent fibre apparent digestibility coefficients of diets led to the conclusion that conventional detergent extraction techniques are questionable in determining the in vivo digestibility of cell wall constituents for tannin-rich forages. Results from rumen fluid analyses indicated that sheep given PEG-containing diets had higher ammonia-nitrogen and volatile fatty acid (VFA) concentrations (P < 0·05). These results, coupled with the increase of allantoin excretion gave clear evidence that the efficiency of microbial synthesis was improved with PEG addition. The absence of change in ruminal pH and molar proportions of individual VF A suggested similar fermentation patterns among all dietary treatments. PEG supply increased the slowly degradable fraction of A. cyanophylla foliage incubated in the rumen (P < 0·05), thus dry matter potential degradability (a + b) was highest in sheep given PEG-containing diets. It is concluded that the affinity of acacia tannins to PEG, increased the availability of degradable proteins, which resulted in an improvement of the nutritive value of acacia foliage. However, for practical situations, adding PEG to concentrate or to drinking water is recommended for sheep browsing A. cyanophylla trees in the field or fed indoors.

This experiment studied the effects of body condition, long- and short-term levels of nutrition and trypanosomosis infection on the productivity of N’Dama cows using a 2 x 2 × 2 factorial cross-over design. Pre-partum, 23 cows received supplements for 6 months (H), the other group of 20 for 2 months (L). Both groups grazed native pastures. Two days post partum, half the cows from each group were placed on a basal (B) or supplemented (S) plane of nutrition. The diet of concentrate, groundnut hay and andropogon hay was the same, only the quantities differed. Four weeks post partum half the animals in each group were inoculated with T. congolense organisms (I), the others acted as controls (C). The trial continued for a further 6 weeks.

Pre-partum nutrition (H, L had no effect on dry-matter intake (DMI) but pre-partum feeding (H) improved post-partum productivity, evident by higher dam live weights (P < 0·05), body condition (P < 0·001), calf birth weight (P < 0·05) and calf live-weight gain (P < 0·01). Post-partum nutrition had no effect on productivity. Trypanosomosis infection caused a reduction (P < 0·05) in total DMI. The decline in groundnut hay and concentrate intake was proportionally (P < 0·001) greater in the S-I group than in the B-I group. A low plane of nutrition pre-partum depressed milk yield but increased fat concentration (P < 0·05). Infection significantly reduced milk offtake (P < 0·05). The reduction in milk offtake (P < 0·01) and calf live weight (P < 0·05) were proportionally larger in the B-I than in the S-I group. Infection caused a decline in milk protein concentration (P < 0·05) and protein yield (P < 0·01) which was independent of dietary effects. Infection reduced (P < 0·01) the packed-cell volume but there were no interactions with diet. None of the cows was pregnant 150 days post partum but seven were cycling, 3(5) in the H-S-I group, 2(7) in the H-B-I group, 1(5) in the L-B-I group and 1(5) in the L-S-C group. These results suggest that S-I cows attempted to maintain milk yield at the expense of live weight whereas the B-I cows had insufficient live-weight reserves that could be mobilized. This suggests the nutritional balance and changes in weight at the time of infection might be more important than historical planes of nutrition.