Artificially dried grass of 2 tropical species (Setaria spacelata and Digitaria decurnbens) from which most of the stem had been removed, and a temperate grass (Loliurn perenne) grown under the same subtropical conditions, were compared for energy and protein value. Data for a temperate clover hay (Trifolium resupinatum) that was tested concurrently are included because they provide useful contrasts. Each was evaluated by measuring energy, nitrogen (N) and carbon balances in 4 adult sheep at 2 levels of intake (ad libitum and near energy maintenance) and during fasting. The 3 grasses had similar leaf content (76-83%) and the clover much less (60%). The tropical forages had similar chemical composition but they contained less crude protein (10%) than the ryegrass (L. perenne) (1 5%) and more cell wall constituents (63-66% v. 58%). The clover had the most crude protein (19%) and the least cell walls (38%); it also was highest in carbohydrates, pectin and heat of combustion. Voluntary intakes of the setaria, pangola (D. decumbens) and ryegrass were similar and 20-30% lower than the intake of clover. Digestibilities of dry matter (DM), organic matter (OM) and energy were similar for the grasses and 8 percentage units lower than for the clover whereas digestibility of crude protein differed between the tropical and temperate species, the latter having digestibilities 12-15 units greater. Digestibility of cell walls did not vary. The metabolisable energy (ME) values of the grasses at maintenance were 8.3-8.5 MJ/kg DM while that of clover was 10.1; at maximum intakes, corresponding ME values were 7.9 and 10.0 MJ/kg DM. Net availability of ME for gain was 0.42 for the tropical grasses and the persian clover and 0.36 for the ryegrass. By contrast, the tropical forages supported higher gains of N relative to N supply than did the temperate forages because urinary N loss was not affected by intake of the tropicals; these differences in N gain were drastically reduced when gain was expressed in relation to ME. These results do not support the contention that forages of tropical species have a lower energy value per kg than temperate forages of similar composition. Indeed, the tropical species tested here appear to have had an ideal balance of energy and protein insofar as efficiency of use of digestible N was close to 100% and their energy values were commensurate with their chemical composition.
Four combinations of maize silage and artificially dried red clover were fed consecutively to adult wether sheep ad libitum and at a level designed to maintain liveweight. On a dry matter (DM) basis, the diets contained silage and clover at ratios 1 :0, 2: 1, 1:2, and 0:1. A fifth diet contained maize silage plus urea (as 1% of the silage DM). Energy, nitrogen (N), and carbon balances were measured at both feeding levels and while fasting. The maize silage contained 11 g N and 41 1 g cell wall organic matter/kg DM; corresponding values for red clover hay were 37 and 290 g. Energy and protein metabolisms were monitored on the 5 diets and were related to dietary N content. Feed intake and digestibility increased with the proportion of clover in the diet and, hence, with increasing dietary N content. Energy losses from methane and heat production did not differ among diets, whereas urine energy losses were smallest, and therefore, efficiencies of utilisation of metabolisable energy (ME) greatest, on the silage-only and silage + urea diets. Greater urinary N losses on the diets of 1 : 2 silage: clover and clover-only led to lower N balances at the same apparently digested N intake on these 2 diets. There were positive associative effects between the silage and clover for voluntary feed consumption; digestibilities of energy, N, and cell wall organic matter; and energy and N balances. A ratio of ME to digestible energy of 0.81 underestimated the content of ME in silage by 0.5 MJ/kg DM, yet overestimated it in clover by 0.4 MJ/kg DM. The ME value of the silage + urea diet (11.6 MJ/kg DM) was one of the highest reported in sheep for maize silage using indirect calorimetry.
Lupin seed was evaluated as a supplement to cereal hay and as the sole component of a production ration, by measuring energy, nitrogen (N), and carbon balances in 4-6 adult wether sheep. Seven diets of different combinations of lupin seed and chaffed wheaten hay were fed in sequence to 4 sheep. The hay was offered as a restricted ration of 800 g/day with and without 100 g lupin seed/day, and ad libitum with and without 2 levels of lupin seed (100, 400 g/day). In addition, lupin seed alone was offered at near maintenance and ad libitum to 6 sheep. The dry matter (DM) content of the wheaten hay contained 7.7 g N/kg DM and 572 g cell wall organic matter (CWOM), and its gross energy (GE) value was 18.1 MJ/kg DM. The GE was 49% digestible, and its metabolisable energy (ME) value was estimated at 6.4 MJ/kg DM at ad libitum intake levels. Corresponding values for the lupin seed fed alone were 49 g N, 199 g CWOM, 20.1 MJ GE, 86% digestible energy, and 15.7 MJ ME/kg. Ad libitum intakes of wheaten hay were below that required to sustain energy maintenance, but total DM intake was increased substantially with 100 g/day of lupin seed supplement. At higher levels of supplementation some substitution did occur, although the response was variable. Methane production was reduced by increasing the level of lupin seed in the ration, but ME and heat (both expressed in relation to DE) and energy balance (expressed in relation to ME) could each be effectively described by single rectilinear relationships, suggesting that the energy value of lupin seed was similar if used as a production ration or as a supplement. Energy values of lupin seed fed alone compared favourably with published values for other leguminous seeds and some cereal grains. Net availability of ME for gain was estimated to be 61%. Urinary N loss, in terms of apparently digested N or available energy, was very high when lupin seed was fed alone, indicating that protein retention was low compared with legume forages of similar N and cereal grain (e.g. oats). Therefore, although leguminous seeds have rely high levels of protein and obvious potential as energy and N supplements, it may not be valid to presume they are ipso facto important sources of amino acids for ruminants. High energy availability and a low potential for protein deposition would imply a significant diversion of energy into fat with such diets.
Various parameters relating to digestion of a clover diet in the stomach and intestines were measured by marker techniques in the same weaner lambs at 15, 24 and 40 weeks of age when body weights averaged 18, 29 and 44 kg respectively. Significant small changes were observed with increasing age and body size in the values of several of the parameters measured. Thus at 40 weeks relative to 15 weeks values were higher for (i) crude protein digested in the intestines per unit feed intake (+ 10%), (ii) sodium content of rumen liquor and sodium flow from the rumen per unit feed intake (+ 9%, + 14%), (iii) potassium and chloride contents of abomasal liquor (+ 9%, + 7%) and (iv) pH of abomasal digesta (+ 0.3 pH unit). Values were lower for (v) digestibility of organic matter and cell wall constituents in the whole alimentary tract (c. – 1.8%), (vi) ammonia content of rumen liquor and ammonia flow from the rumen and abomasum per unit feed intake (– 15% to – 20%) and (vii) potassium content of rumen liquor (– 9%). No changes attributable to age or body size were observed with several paramefers, including (i) rate of production of volatile fatty acids in the rumen per unit feed intake, (ii) rate of absorption of volatile fatty acids from the rumen, (iii) rate of flow of digesta through the stomach per unit feed intake, and (iv) mean residence time of water-soluble marker in the rumen. The results indicate that care needs to be exercised in applying digestion data obtained with adult sheep to the nutrition of the growing weaner lamb.
Some aspects of digestion were studied in small groups of fistulated wether lambs from two breeds, Dorset Horn and Corriedale. The Iambs were given a ground and pelleted diet of equal parts hay and concentrates once daily at two levels of intake. At the same liveweight (25 kg), the higher intake was associated with reduced digestion of organic matter (OM) and fibre in the whole gastro-intestinal tract; rumen mean retention times were also reduced, as was the proportion of OM digestion which occurred in the rumen. An increase in the amount of protein entering the intestines appeared to be composed of both undegraded dietary protein and microbial protein. Despite a reduction in the digestibility of non-ammonia nitrogen in the intestines, more crude protein was digested there per unit of digestible OM intake (25.9 v..23.6%; P < 0.05). Differences between the breed groups were smaller than those associated with level of feeding. Nevertheless, particularly at lower relative intakes, rumen mean retention times were longer, rumen digesta content was greater, and rumen OM and fibre digestion tended to be greater in the Dorset Horn lambs; crude protein digestion in the intestines per unit of digestible OM intake also tended to be less at the low intakes. More than three-quarters of the cellulose digestion but less than half the hemicellulose digestion occurred in the rumen. The proportion of the urea synthesized that was degraded in the gastrointestinal tract (0.24-0.30) was consistently lower in these lambs than has been reported for adult sheep.
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