The digestion of perennial ryegrass (Lolium perenne cv. Melle) and white clover (Trifolium repens cv. Blanca) by grazing cattle.

1. Pure swards of perennial ryegrass (Lolium perenne cv. Melle) as a primary growth (May), trimmed primary growth (early June) and regrowth (late June), and white clover (Trifolium repens cv. Blanca) as a mature primary growth (July) and vegetative regrowth (August), were grazed by twelve Friesian steers (mean body-weights throughout experiment 152-231 kg) at daily allocation rates of forage which provided dry matter (DM) intakes ranging from 28 to 36 g/kg body-weight). 2. Total nitrogen contents of the three ryegrasses declined with season (37-20 g/kg DM), but in vitro organic matter (OM) digestibilities were relatively constant (0.76-0.79). The clovers had higher N (average 36.6 g/kg DM) and lower fibre and water-soluble carbohydrate contents than the grasses, and in vitro OM digestibilities of 0.70 and 0.76 respectively. 3. Duodenal digesta samples were obtained, using a portable sampling apparatus from the animals grazing the pasture, and estimates of the flow of nutrients into the small intestine were derived using two indigestible markers which were continuously infused into the rumen using a portable infusion apparatus. Forage intakes were calculated from estimates of faecal output of indigestible OM and the predicted in vivo OM digestibilities of the forages consumed. Coefficients of variation for OM flow to the small intestine and OM intake were 11.8 and 10.9% respectively. 4. The apparent digestion of OM in the rumen ranged from 722 to 741 g/kg digestible OM intake and from 681 to 711 g/kg digestible OM intake for the grass and clover diets respectively. Substantial losses of ingested N before the small intestine were measured on all diets except the regrowth ryegrass. Losses were 0.30 and 0.40 g/g N intake on the primary growth ryegrass and the regrowth clover respectively; N contents were 37 and 39 g/kg DM respectively. 5. Comparison of the values obtained at pasture with that obtained when similar diets were offered to housed cattle (Beever et al. 1985) indicated that combined relations relating duodenal OM and non-ammonia-N (NAN) flows to OM and N intakes respectively could be established for each diet. For two diets (primary-growth grass and regrowth clover) the relations were curvilinear; for the remaining diets, the derived relations were linear.(ABSTRACT TRUNCATED AT 400 WORDS)

The efficiency of energy utilization in growing cattle consuming fresh perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca).

1. Twenty Friesian steers (225 kg live weight) were fed on mid- (M) (June-July) and late- (L) (August-September) season crops of either fresh perennial ryegrass (Lolium perenne cv. Melle) (G) or white clover (Trifolium repens cv. Blanca) (C). Each of the forage diets was offered at three restricted planes of nutrition above maintenance to compare the effect of forage species on the efficiency of energy utilization. All diets were harvested daily from swards of regrowth forage of intended equivalent digestibility. 2. Faecal and urine excretions were measured for 7 and 5 d respectively, followed by two consecutive 24 h measurements of methane, carbon dioxide and oxygen exchange in open-circuit respiration chambers. 3. The apparent digestibility of the energy in perennial ryegrass (0.759) was marginally higher (P less than 0.01) than that in white clover (0.748); the mid- and late-season forages were of similar (P greater than 0.05) digestibilities. Metabolizable energy (ME): digestible energy (DE) in diet G (0.837) was significantly (P less than 0.001) different from that in diet C (0.812). The partition of energy losses when expressed as MJ/GJ gross energy intake (GEI) indicated that energy lost as methane was not significantly different (P greater than 0.05) either between forages (G 62.8, C 63.4) or between seasons (M 63.2, L 63.1). Energy excretion in urine was higher for cattle fed on diet C (77.5) compared with diet G (60.5) (P less than 0.001). Heat production was similar (P greater than 0.05) between forages (G 480, C 478), but lower (P less than 0.01) for L (471) compared with M(486). Energy retention (by difference) was lower (P less than 0.001) for diet C (132) than G (156) and for M (138) than L (149) (P less than 0.05). 4. Parallel-line analysis of unscaled ME intake (MEI) in relation to retained energy (RE; MJ/d) indicated that the efficiency of utilization (kt) was similar (P greater than 0.05) between perennial ryegrass (0.42) and white clover (0.46). Linear extrapolation of the values to zero energy retention indicated that maintenance requirements of ME (Em; MJ/d) were 23.3 for diet G and 28.8 for diet C. The extrapolated Em when expressed in relation to a measured fasting heat production (FHP) of 22.8 (MJ/d) resulted in a derived efficiency of utilization of ME for maintenance (km) of 0.97 (G) and 0.79 (C), suggesting an underestimate of Em for diet G.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of forage species and season on nutrient digestion and supply in grazing cattle.

1. A total of twenty Friesian steers were grazed on pure swards of either perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca) from May to late August to examine the effect of forage species and season on nutrient digestion and supply. Within each forage species, two daily allowances of forage (i.e. 30 and 60 g dry matter (DM)/kg live weight) were given, and nutrient flow into the small intestine was measured on thirteen separate occasions (viz. seven grasses and six clovers). 2. Total nitrogen content of the grasses varied between 28 (early season), 19 (mid-) and 33 (late) g/kg DM, whilst the clovers showed a much narrower range and all values were higher (39-45 g/kg DM). In vitro organic matter (OM) digestibilities of plucked samples ranged from 742 to 809 g/kg OM (grass) and 712 to 790 g/kg OM (clover), the lowest values being noted in late June (grass) and mid-July (clover). 3. OM intakes calculated from estimated faecal OM output (using unlabelled ruthenium) and predicted OM digestibility of the consumed forage indicated mean values of 20.9 (grass) and 26.0 (clover) g/kg live weight (P less than 0.001), whilst the higher forage allowances increased OM intake by approximately 8% on both grass and clover (P less than 0.01) compared with the low allowance. OM intake was significantly (P less than 0.01) lower on the two primary growths of grass examined in May (mean 16.8 g/kg live weight) than the other five grass diets. 4. Rumen molar propionate levels declined with season but were at all times higher on the grass than on the clover diets, whilst acetate levels were unaffected by forage species. Apart from the late-season grass, mean rumen ammonia concentration was less than 100 mg NH3-N/l on all grass diets, whilst values on the clover diets ranged from 200-350 mg/l. 5. Daily duodenal OM flows in relation to animal live weight were approximately 20% higher on the clover than on the grass diets (grass 9.2, clover 11.2 g/kg live weight, P less than 0.001), but estimates of the proportion of digestible OM apparently digested in the rumen were not significantly influenced by forage species (grass 0.69, clover 0.71).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of date of cut and barley substitution on gain and on the efficiency of utilization of grass silage by growing cattle. 2. Nutrient supply and energy partition.

1. The effect of harvesting date of perennial ryegrass (Lolium perenne) on the nutritive value of the resultant silage and the effect of substitution of late-cut silage with barley was examined in growing cattle. The diets comprised early-cut (H) and late-cut (L) silage offered alone or with 280 (LC1) or 560 (LC2) g rolled barley/kg total dry matter (DM) substituted for late-cut silage. 2. Both silages were prepared with the addition of formic acid (850 milligram; 2.4 litres/t fresh weight) to a partially wilted crop, and were judged to be well fermented (pH 3.9, 3.8) with lactic acid contents of 108 and 73 g/kg DM, total nitrogen contents of 24.6 and 18.4 g/kg DM and ammonia-N contents of 121 and 124 g/kg total N (values for early- and late-cut silages respectively). 3. Two experiments were conducted to measure duodenal non-NH3-N (NAN) supply in relation to N intake on the four diets (feeding level 18 g DM/kg live weight (LW] and to examine the partition of the metabolizable energy (ME) supply from the four diets using open-circuit indirect calorimetry (three feeding levels, 14, 17 and 20 g DM/kg LW). The experiments were undertaken with eight and nine Friesian male castrates respectively with a mean starting weight of 300 kg and age 12 months. The animals used in Expt 1 had been previously fitted with cannulas into the dorsal rumen and the proximal duodenum. 4. NAN supply was significantly higher on diet H than all other diets which were similar irrespective of the level of barley inclusion. Mean ME contents (MJ/kg DM) of the two silages differed markedly (H 11.9, L 9.7) and barley addition (LC1 and LC2) restored values to 10.7 and 11.1 MJ/kg DM respectively. Estimated NAN absorption in relation to energy supply was significantly higher for diet H (1.47 g/MJ ME) than for all other diets (mean 1.25 g/MJ ME). 5. Partition of ME supply using conventional linear analysis indicated dietary differences with respect to estimated ME for maintenance (L greater than H, LC1 and LC2) and efficiency of utilization of ME supplied above maintenance (L greater than H, LC1 and LC2), but difficulties in biological interpretation of these findings led to the use of exponential curve analysis. This provided an improved description of the findings, and whilst dietary differences were apparent, none were statistically significant. It was concluded that a single exponential equation could be used satisfactorily to describe all values.(ABSTRACT TRUNCATED AT 400 WORDS)

Examination of energy utilization in cattle offered a forage diet at near- and sub-maintenance levels of feeding.

Eight Friesian calves were reared from birth to the start of the experiment at a predetermined growth rate of 1.0 kg/d. Four calves (group 1) commenced the experiment at 22 weeks of age and the remainder (group 2) at 34 weeks, and feed intake was calculated to provide sufficient metabolizable energy to sustain zero energy balance (Em). Between experimental days 30 and 56 at maintenance levels of feeding, respiratory exchange measurements were made using open-circuit calorimetry to provide indirect estimates of heat production (H) simultaneous with measurements of faecal and urinary excretion of energy and N. A datum point for Em and H was established for each animal giving mean values for Em of 491 and 537 and for H of 476 and 511 kJ/kg live weight (LW)0.75 per d for groups 1 and 2 respectively. Treatment levels calculated as 0.25, 0.5, 0.75 and 1.25 of dry matter intake required to sustain the measured Em, were imposed on individual animals after day 56 and further measurements of H and faecal/urinary balance were made between days 72 and 84 followed by measurements of fasting heat production (FHP) during days 86-90 from the two animals in each group which had received the 0.75 and 1.25 levels of intake. Regression analysis of the treatment levels indicated separate linear models which predicted Em at 419 and 473 kJ/kg LW0.75 per d for groups 1 and 2 respectively. The incorporation of FHP with partitioning of faecal and urinary energy losses measured during fasting altered the relationship but not the predicted Em. Overall predicted Em (days 72-84) from all models were 406 and 478 kJ/kg LW0.75 per d for groups 1 and 2 respectively which were significantly lower (P < 0.05) than Em measured during days 30-56.

The digestion by cattle of grass silage made with formic acid and formic acid-formaldehyde.

1. A primary growth crop of perennial ryegrass (Lolium perenne L., cv. S23) was partially wilted and ensiled after the application of either formic acid-water (1:3, w/v; 7.11 l/t fresh herbage; control diet C) or formic acid-formaldehyde (1:1, w/w; 8.8 l/t fresh herbage; formaldehyde treated diet F) which supplied 50 g HCHO/kg crude protein (nitrogen (N) x 6.25). The two silages were fed separately and a third diet comprising formaldehyde-treated silage, supplemented with urea (20 g/kg dry matter DM) at the time of feeding was also examined (diet FU). 2. The three diets were fed at a level of 16 g DM/kg live weight to six 3- to six-month-old cattle fitted with rumen and re-entrant duodenal cannulas in two 3 x 3 Latin Square experiments, and measurements were made of the digestion of energy, carbohydrate and N. 3. The formaldehyde-treated silage had a lower content of fermentation acids and ammonia-N, and a higher content of water-soluble carbohydrate and total amino acids. The apparent digestibility of organic matter, energy and N were depressed (P less than 0.05, P less than 0.05 and P less than 0.01 respectively) by treatment with formaldehyde, but cellulose and neutral-detergent fibre digestibility were unaffected. 4. Within the rumen the digestion of organic matter, cellulose and neutral-detergent fibre were unaffected by formaldehyde treatment or supplementation with urea. Microbial protein synthesis in the rumen was similar for the three diets (average 131 g/kg apparently digested organic matter in the rumen). 5. The application of formic acid-formaldehyde increased (P less than 0.05) the amount of food protein escaping degradation in the rumen (4.76 diet C, 6.89 diet F; 7.07 diet FU g/kg protein intake). The contribution of amino acids of dietary origin at the duodenum increased (P less than 0.05) from 50 (diet C) to 80 (diet F) and 82 (diet FU) g/kg DM intake, and the flow of total amino acids at the duodenum was 33% higher (P less than 0.001) in cattle fed formic acid-formaldehyde silage diets compared with the control silage due to the reduction in degradation of protein at ensiling and in the rumen.