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A digestibility trial was conducted using yearling wethers to determine the nutrient availability, digestible energy (DE) and metabolizable energy (ME) of five varieties of alfalfa hay (Anchor, Saranac, Thor, Vernal and Washoe) developed for specific pathogen or pest resistance. Crude protein, crude fiber, ash, ether extract and nitrogen-free extract contents were different among the varieties of alfalfa hay; lignin and calcium contents were not different. Total digestible nutrients, digestible energy, metabolizable energy and digestion coefficients of the nutrients, except ether extract, were not influenced by variety of alfalfa hay. However, when digestible crude protein (DCP) and digestible energy were calculated on a yield per hectare basis, differences were found among varieties which were accounted for only partially by crop yield alone.

The energy and nitrogen availability from softwood and softwood-hardwood blend ammonium sulfite liquor (ASL) were compared to urea-sulfur and urea-sulfur-molasses by in vitrotechniques. Fluid collected from rumen fistulated sheep, previously adapted to a high energy ration containing 4% softwood-hardwood blend ASL (dry matter basis) was incubated with test substrates, in triplicate, for a 12-hr period. In vitrorumen microbial metabolism and growth were evaluated by gas, protein and volatile fatty acid (VFA) production. Gas production was insufficient as a criterion to evaluate in vitromicrobial metabolism of the various substrates, as there were no differences in the rates or total gas production. However, total VFA production increased with softwood, and softwood-hardwood blend ASL's at the 4, 8 and 12% levels when compared to substrates with urea-sulfur and urea-sulfur-molasses. Acetate and butyrate production was higher but propionate production was lower with the ASL's than with urea-sulfur and urea-sulfur-molasses diets. Nitrogen from low levels of ASL (4%) was not as well utilized as that from urea containing diets. High levels (20 to 100%) of ASL had an inhibitory effect on gas production and protein synthesis. Softwood ASL, at low levels, appeared to be more beneficial to microbial metabolism than the softwood-hardwood blends of ASL.

The digestible energy (DE), metabolizable energy (ME) and net energy for maintenance and production (NEm+p) values of dehydrated alfalfa and corn were determined in a metabolic and energy retention study with lambs. Twenty-one diets consisting of varying proportions (5% increments from 0% to 100% for each ingredient) of dehydrated alfalfa and corn were used. Crude protein, ether extract and nitrogen-free extract digestibility curvilinearly increased, and crude fiber curvilinearly decreased with increased levels of corn in the ration. There were no interactional (non-linear, non-additive, curvilinear or associative) effects for DE, ME and NEm+pvalues with the various ratios of concentrate to roughage. A linear relationship between energy (DE, ME and NEm+p) and ration composition indicated that the energy values of corn and dehydrated alfalfa were additive and that no interactional effects were evident with the change in ration composition. The caloric value (DE, ME and NEm+p) of the diet increased with increased levels of corn in the diet; and likewise, energy retention increased with increased levels of corn in the diet.

One hundred thirteen wether feeder lambs were individually fed to study the effects of ration and location of fat in the carcass upon fatty acid composition. The rations consisted of dehydrated alfalfa (17% protein) and corn. The proportions of alfalfa and corn varied from 0% to 100% in the 21 different rations by 5% increments. A urea-mineral supplement was added to rations containing 50% corn or more. The lambs were slaughtered after a feeding period of 105 days. Loin, dock and kidney fat samples were obtained from chilled (48 hr) carcasses. Fat samples were extracted, esterified and analyzed by gas-liquid chromatography. Data were statistically analyzed by analysis of variance and orthogonal polynomial regression.Depot fat contents of unsaturated acids (myristoleic, palmitoleic, oleic, linoleic, and linolenic) were affected by rations. Myristoleic, palmitoleic and linoleic significantly increased curvilinearly, oleic increased linearly and linoleic decreased linearly as level of corn increased. Linoleic acid contents were confounded by saturation of dietary linolenic, and oleic contents were confounded by saturation of dietary linoleic.

Metabolic and growth studies were conducted with wether and ewe lambs to determine nutrient digestibility, digestible energy (DE), metabolizable energy (ME), and net energy for maintenance and production (NEm + p) of pea scalpings (i.e., chaff, pea pods, pea hulls, split peas, weed seeds and dirt) and wheat straw. Four pelleted diets consisting of varying proportions (20, 80%; 40, 60%; 60, 40%; an; 80, 20%) of pea scalpings and wheat straw, respectively, were used. Dry matter, CP, EE and NFE digestibilities as well as TDN increased as the percent of pea scalpings increased in the diet. Crude fiber digestibility was not influenced by the various levels of each ingredient in the diet. DE and ME increased as the percentage of pea scalpings increased in the diet; however, there were no differences in the DE and ME values of the 40 and 60% pea scalpings diets. There were no differences in NEm+p among the various rations. The mean DE, ME and NEm+p values, in kcal/g, for pea scalpings and wheat straw were 2.85, 2.58, 1.15, and 1.65, 1.42, .82, respectively. Live-weight and energy gain increased as the percent pea scalpings increased in the diet as a result of increased dietary intake. Ration or sex had no significant effect on the percent of carcass fat or protein.

Metabolism and growth experiments were conducted with barrows to determine the digestible, metabolizable and net energy for maintenance and production of barley and wheat diets in which each of the two grains varied inversely in 10% increments from 0 to 100% of the total grain component of the diet. There was a linear relationship between the ration DE and MEnvalues and the wheat and barley content of the diet. The dietary DE and MEnvalues (kcal/g) of wheat were 3.51 and 3.34; those of barley were 3.12 and 2.95. There was a trend which suggested an interactional effect of barley and wheat as components of the ration on the DE and MEnvalues. Animals fed the barley-wheat rations during the fall season consumed more feed and had a greater daily live weight gain than those fed during the summer. There was a linear relationship between the net energy value and the wheat component of the rations for those animals fed during the fall; the NEm+pvalue of barley and wheat was 2.06 and 2.40 kcal/g, respectively. However, in the summer growth study there was a curvilinear relationship (third order) between the net energy value and the amount of each grain in the rations. The NEm+pof barley varied from 1.75 to 2.64 kcal/g and that of wheat ranged from 1.85 to 2.65 kcal/gram. The NEm+pvalue of barley and wheat fed as 100% of the grain portion of the diet was 2.11 and 2.22 kcal/g, respectively; the same variety of wheat was more efficiently utilized in the fall than in the summer trial. The interactional effect of dietary wheat and barley was observed to be in the utilization of ME for NEm+p. The animals' growth response and carcass characteristics were indicative of the net energy value of the rations and feed intake. The implications of a possible interactional phenomenon of dietary ingredients should not be ignored when evaluating feedstuffs and efficiency of swine production.

The influence of rumen metabolism of interactions among the rations' energy content, physical form and buffers were studied in a randomized complete block trial with rumen fistulated sheep. The productions of total VFA and acetate, propionate and butyrate were estimated at various times after feeding by in vitro techniques and presented on a gram DM basis. Rumen dry matter and pH were also determined on the rumen samples. The concentrations of the total and individual VFA responded to the various factors under study. However, there were few differences in the production of these acids. Acetate production was not affected by the source of energy. There was a greater production of propionate and butyrate with the high than low energy diets. Sodium bicarbonate increased acetate, propionate and butyrate production. Propionate production was the only acid significantly influenced by hours after feeding with the greatest rate of production occurring at 1 hour. The concentration of the total and individual VFA concentration in the rumen had little or no significance as a criteria of evaluating rumen metabolism of feeds as affected by the factors studied. The lambs fed the concentrate energy source had a more severe parakeratotic rumen than lambs fed the roughage energy source. The pelleted rations were more detrimental than the milled rations. Sodium bicarbonate alleviated the severity of rumen parakeratosis for both levels of energy and physical forms. It appears that rumen buffering capacity in relation to energy intake and rumen metabolism is a major contributing factor towards predisposition of parakeratosis.

The chemical similarity and closely related physiological roles of sodium and potassium have prompted several experiments to investigate their nutritional relationships primarily in rats and chickens (Grunert, Meyer and Phillips, 1950; Meyer et al., 1950; Burns, Cravens and Phillips, 1953). It was concluded that the ratio of sodium to potassium in the diets of these species was not critical if there were adequate amounts but no excess of each element. In vitrostudies on sheep rumen micro-organisms revealed that potassium and not sodium was essential for the rumen micro-bial population (Hubbert, Cheng and Burroughs, 1958). However, sodium stimulated microbial activity at low potassium levels while depressing activity at higher levels of potassium.High levels of sodium bicarbonate (Kromann and Meyer, 1966) and sodium chloride (Kromann and Ray, 1967) fed to lambs caused a greater depression in growth and energy retention than could be attributed to a depression in food intake.

A study was made of grazing intensity effects by imposing on irrigated pasture stocking rates of 1.35, 2.25, 3.06, 3.93 and 4.68 steers per acre. A group of steers fed soilage from the same pastures served as a positive control similar to what might be expected from pasturing forage without the superimposed animal influence. To increase the precision of the comparisons, body composition, intake and digestibility of the forage were added to the usual measurements of weight gains, clipping yields and chemical composition of the forage. Increased stocking rate decreased yield of the forage as the season progressed. No carry-over influence, however, was found the following season. Yield of forage from the soilage treatment was greater during the latter part of the season than from pasture treatments. The digestible energy content of the forage consumed by the soilage steers was 126 meal, per 100 lb. For pasturing, a light stocking rate allowed the steers freedom to select a more nutritious forage, 130 to 132 meal., whereas heavy stocking forced the steers to consume a less nutritious forage, 122 meal, per 100 lb.As grazing intensity increased from 1.35 to 4.68 steers per acre, feed and energy intake decreased, weight gain decreased and the energy content of the carcass decreased. In this pasture experiment maximum production per animal was not the proper measure. Production per acre was more realistic. As stocking rate increased the animals harvested and consumed more of the forage and digestible energy per acre even though consumption decreased per animal. A most important animal-plant interaction was present because liveweight gain and corrected carcass production per acre increased to a point, about four animals per acre, and then rapidly decreased. Increasing the stocking rate increased consumption of forage per acre, but here also consumption per animal was low enough so that too much forage was used for maintenance rather than gain and per-acre production decreased as a consequence.A wide range in grazing intensity, 2.25 to 4 steers per acre, allowed close to maximum corrected carcass production per acre. This seems to indicate that a pasture operator has a wide latitude in stocking rate. A highly significant correlation (0.85) was found between digestible energy intake and forage available per animal as determined by pregrazing clipping.Soilage compared to pasturing at the same stocking rate resulted in greater per-acre consumption of digestible energy and a 32% increase in corrected carcass production.

Urea toxicity, as influenced by various nutritional and physiological factors, was investigated with 160 sheep. The variables (energy levels, protein levels, age, period of fasting and urea levels) were studied in a 25factorial design. The two energy levels were a low-energy (15% concentrate) and a high-energy (85% concentrate) ration; and the two digestible protein levels were 3.8 and 8.8%. Lambs, 5 months of age, and ewes, approximately 5 years of age, were the two age groups. The sheep were administered either 44 or 176 g urea per 100 kg live weight at 1 or 24 hr. after feeding. The effect of these various factors was determined by blood NH3-N levels at 0, 30, 60, 90 and 120 min. after treatment and by mortality. The animal survival and blood NH3-N levels were influenced by all factors studied. The highest mortalities and highest blood NH3-N levels occurred with animals fed the high-energy, low-protein diet; thus, the ratio of energy to protein was most important. The lambs were more susceptible to the toxicity of urea than the ewes. The period of fasting, per se, had very little effect on the toxicity of urea. The mortality and blood NH3-N levels were directly related to the urea dose level.The LD50of urea was determined with 50 wether feeder lambs using a “multiple sample up-and-down method” bioassay technique. The mean LD50for urea was 1.45 log dose (g/100 kg body weight).

FEEDERS have commonly observed that rate of gain of fattening lambs decreases as they grow or fatten. Although information has accumulated on the effects of sex and length of the feeding period on live-weight gain and carcass traits, little is known concerning the combined effects of the feeding period and the age of the lamb on body composition and energy metabolism in lambs. Sex of the animal has a pronounced effect upon growth and carcass traits. Kromann, Ray and Nelson (1966) found no significant difference in weight gain and carcass data for lambs of both sexes fed rations supplemented with protein at 1-, 7-, 14- or 21-day intervals; however, wethers gained significantly more than ewe lambs and utilized the energy of the ration more efficiently. Ray and Mandigo (1963) found no difference in loin-eye areas from ram and ewe lambs; however, Bradford and Spurlock (1964) found rams had larger loin-eye areas than wethers.

Variation in lamb growth experiments was studied with 24 individually-fed and 48 group-fed wether lambs ( 16 groups of three). The variables ( method of feeding, energy level and environment) were studied in a 23factorial experiment. The two methods of feeding were individual and groups of three. The two energy levels were a high-energy and a low-energy ration. The two environments consisted of an open and a semi-closed barn. The group-fed lambs had a greater rate of gain and energy gain than those fed individually. The greater energy gain was due to a greater growth response and a heavier final weight, since there were no differences in percent body protein or fat. The group-fed lambs consumed more dry matter than the individually-fed lambs; however, there were no differences in the NEM+Pof the ration. The lambs fed the high-energy ration had a greater growth response, energy gain and NEM+Pof the ration than those fed the low-energy ration. The Iambs fed the high-energy ration in the semi-closed barn had a greater carcass fat content than those fed in the open barn whereas the lambs fed the low-energy ration in the open barn had a greater carcass fat content than those fed in the closed barn. The advantages of using individually-fed lambs in nutritional and biological research were discussed.

One-hundred-eight wether and ram feeder lambs were used in a factorially designed experiment to study the effect of the levels of energy, levels of sodium chloride, treatments for prevention of enterotoxemia, lines of breeding and sexes on energy metabolism in lambs. Lambs gained more rapidly on the 60% and 90% concentrate energy levels than on the 0% and 30% levels. The proportion of carcass fat, the ratio of fat: protein and the net energy for maintenance and production (NEM + P) of the ration increased as the level of concentrate in the ration increased. Sodium chloride reduced weight gain and energy gain. However, the detrimental effect of sodium chloride decreased as the levels of concentrate in the ration increased. Sodium chloride appeared to increase the NEM+Pof the 90% concentrate energy levels. The D line of breeding gained more and had a higher proportion of carcass fat and a greater energy gain than the L line of breeding. The ram lambs gained more than the wethers. The NEM+Pof alfalfa hay as fed in the ration decreased as the milo in the ration increased, and the NEM+Pof milo in the ration increased as alfalfa hay decreased.

A method was described to determine the energy values of foods as components of a ration by using simultaneous equations. NEM+Pand DE were determined by this method from two experiments reported in the literature. The NEM+Pand DE of the basal ration increased as molasses was increased in the ration, and the NEM+Pand DE of the molasses decreased. The NEM+Pof alfalfa hay decreased as milo was added to the ration: also, the NEM+Pof milo decreased as alfalfa was added to the ration.

Experiments were designed to study the DE, ME and NEM+Pmetabolism in sheep, as influenced by source of energy, physical form and buffers and interactions thereof. The concentrate energy source ration had a significantly higher DE, ME and NEM+Pthan the roughage energy source. Nutrient digestibility and DE decreased when the roughage energy source was pelleted, but did not materially change when the concentrate energy source ration was pelleted. Increased feed intake from pelleting the roughage energy source occurred and thus increased growth and energy gain of growing fattening lambs, because of the greater intake of feed above that required for maintenance. Sodium bicarbonate fed at 5 and 12% of the ration decreased feed intake and growth, particularly when the roughage energy source ration was fed and decreased percent carcass fat to a greater extent than expected from the decreased feed intake. ME and NEM+Pwas not affected by pelleting the rations or adding 5 and 12% sodium bicarbonate to the ration.

A factorially-designed experiment using 80 crossbred lambs was used to study the growth response (weight gains), carcass data and NEM+Pof the ration as influenced by source of protein, frequency of protein supplementation and sex. There was no significant difference between the protein sources (dehydrated alfalfa and cottonseed meal) in growth response or carcass data. Lambs fed the control rations (no protein supplement) gained significantly less than lambs fed protein supplement. There was no significant difference in weight gain and carcass data for lambs fed rations supplemented with protein at 1-, 7-, 14- or 21-day intervals. Wethers gained significantly more than ewe lambs and utilized the energy of the ration more efficiently. The rations supplemented with cottonseed meal had a greater NEM+Pvalue than rations supplemented with dehydrated alfalfa; however, there were no significant differences due to frequency of protein supplementation.

An experiment was designed to study the requirements of steers grazing irrigated pasture. Various degrees of grazing intensity produced variations in energy gain and digestible energy intake. Included was a non-grazing control fed the same forage as soilage in a small drylot. A behavior study revealed that from 2.2 to 4.2 more hours were spent by steers grazing forage than eating soilage. No difference, however, was found in the maintenance requirement for digestible energy between steers fed soilage in a small drylot and those grazing the pasture. Furthermore, comparisons between regression equations on digestible energy requirements of these pasture steers and steers fed in drylot showed no significant difference. It is suggested by these data that the extra activity involved in grazing on irrigated pasture does not result in a measurable increase in digestible energy requirements.

ENERGY metabolism is influenced by environmental, digestive and metabolic factors of which the chemical composition of the diet, associative effects of feeds and nutrients, level of feed intake, heat increment and maintenance are probably the most important. It appears that maintenance requirement increases with an increase in production. Since the animal has only one metabolism which varies with level of energy intake and production, NE should not be separated into two theoretical fractions, NEmand NEp. The California, German and British systems of determining NE were evaluated on the basis of the number of metabolic factors which they consider as variables in predicting NE. The German and British NE systems take into account more variables than the California system, which regards all of the factors to be constant under different environmental conditions. Nevertheless, these methods have made important contributions to the promotion of the net energy system in evaluating feeds and rations and in describing the energy requirement of animals. However, further research is needed to determine the magnitude of the factors which may influence NE and to determine the conditions under which these influences are exerted.