Total Protein Digestibility Research Articles

Effect of Restricted Feed Intake of Dams and Heat Stress on Mineral Status of Newborn Calves

To clarify the effects of restricted feed intake, heat stress, and parity on the mineral status of cows and heifers around parturition and on the mineral status of their calves during 1 wk of age, data were collected from 66 Holstein cows and heifers and their calves. In Experiment 1, 36 heifers and mature cows that calved during hot or cool weather were fed to meet requirements for total digestible nutrients (TDN), protein, and minerals. In Experiment 2, 15 mature cows that calved during hot or cool weather were fed to meet maintenance requirements for TDN plus requirements for TDN for the last 2 mo of gestation, and 15 heifers were fed to meet TDN requirements. Heat stress increased rectal temperatures of newborn calves. Blood hematocrit and hemoglobin of heifers around parturition were higher than those of mature cows, but blood hematocrit and hemoglobin of calves born from heifers were lower. The restricted feed intake of dams decreased blood hematocrit and hemoglobin as well as plasma Fe of calves in hot and cool weather. Plasma Ca, inorganic P, and alkaline phosphatase as well as colostral Ca, P, Mg, and Zn of heifers were higher than those of mature cows, but plasma Mg of heifers was lower. Plasma Mg of calves and their dams was lower in hot weather than in cool weather, and restricted feed intake accelerated the reduction in plasma Mg of calves and their dams during hot weather. Plasma Na of calves and their dams was higher in hot weather than in cool weather. Heat stress increased plasma K of heifers and their calves. Heat stress increased Ca concentration in meconium of calves born from cows, and the restricted feed intake increased P concentrations in meconium. These results suggest that the maintenance of optimum erythropoiesis and mineral status in heat-stressed periparturient cows and heifers and their calves must be met by dietary energy and minerals that are fed at maintenance concentrations plus excess requirements necessary during the gestation period.

Comparison of protein digestibility of rumen undegraded protein estimated by an enzymatic and mobile bag method: feeds for ruminants and anaerobic fungus

Crude protein digestibility (CPD) of rumen undegraded protein (RUP) was estimated in vitro with pancreatin method (PM). In parallel, total protein digestibility of rumen undegraded protein in the digestive tract was measured in situ with mobile bag technique (MB). Totally, 55 feed samples including forage, silage, straw and various meals were analyzed. Samples were incubated in the rumen for 16 h and then tested with MB and PM methods. Results obtained from both techniques were compared and equation of linear regression was counted: (CPD PM=7.47+0.95 CPD MB; r 2=0.861). Digestibility of rumen fungal protein was estimated with both techniques. With mobile bag technique the CPD of polycentric fungus Orpinomyces joyonii A4 was 78.08±3.08% and the crude protein digestibility measured with pancreatin method was 79.48±1.66%.

Nutrient utilization and rumen fermentation pattern in crossbred cattle fed different planes of nutrition supplemented with urea molasses mineral block

In order to investigate the effect of the plane of nutrition on intake and nutrient utilization from urea molasses mineral blocks (UMMB) and rumen fermentation pattern, sixteen adult crossbred cattle were divided into four equal groups following a completely randomised design and fed individually for 60 days ad libitum with either wheat straw alone (Group I) or with wheat straw with UMMB (Group II) or with wheat straw and UMMB with 50% of energy requirements provided by crushed barley fortified with mineral mixture and common salt (Group III) or with wheat straw and UMMB with 100% of energy requirements provided by fortified crushed barley (Group IV). At the termination of the feeding trial, a metabolism trial of six days duration was also conducted. A fermentation study was carried out on four rumen fistulated adult cattle following a 4 × 4 latin square design. Results showed that intake (except for ether extract) and digestibility of all the nutrients increased significantly ( P < 0.01) in the block-fed groups which was further enhanced by energy (barley) supplementation except for digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF) which decreased owing to concentrate supplementation. Total digestible nutrients and digestible protein contents of UMMB were 56.6 and 42.5%, respectively. Significantly increased ( P < 0.01) concentrations of total nitrogen and its fractions, except TCA-precipitable-N owing to block feeding were observed. However, it did not influence the TVFA concentration in rumen liquor of fistulated animals. Rumen pH, rumen fluid volume and digesta flow rate were also unaffected. This clearly indicated that supplementing 50% of energy requirements through concentrate on a straw based diet along with UMMB resulted in increased intake of UMMB and better utilization of dietary nutrients in adult crossbred cattle.

Effects of varying dietary levels of total digestible nutrients, protein and fiber on the growth of crossbred Holstein Heifers fed urea-treated rice straw diets under two feeding systems

Effects of varying dietary levels of total digestible nutrients, protein and fiber on the growth of crossbred Holstein Heifers fed urea-treated rice straw diets under two feeding systems

Protein requirements of lactating Beetal goats

Eighteen Beetal does in early lactation were randomly distributed into three groups of six goats. The first group was fed 125% (A), the second 100% (B) and a third 75% (C) of a digestible protein (DP) standard for sheep. Energy (TDN) level was constant in all three groups at 100% of the standard. A randomised block design was followed. Around mid-lactation (from the 7th to the 11th week), a metabolism trial was conducted to measure feed intake, nitrogen balance and milk production. Mean intakes (±s.e.) of dry matter (DM), DP and TDN were 81.5±3.1, 9.3±0.3 and 62.1±2.6 g/kg metabolic body weight (W 0.75) respectively in treatment A, 87.7±3.7, 8.0±0.3 and 66.2±2.8 g/kg W 0.75 in treatment B, and 86.4±5.2, 6.4±0.3 and 65.01±3.9 g/kg W 0.75 in treatment C. There were no significant differences among the three treatments in DM and TDN intake, while DP intake was different ( P<0.01). Requirements of total protein (TP) and DP for maintenance of lactating goats were 6.54 and 3.96 g/day per kg W 0.75 respectively. For 100 g protein (N×6.38) secreted in milk the requirement was 186.97 g TP or 132.13 g DP.

Specific role of endopeptidases in modulating the nature of protein digestion products

The impact of various endopeptidases on the nature of protein digestion products was measured with the digestion cell technique. After a 30 min pepsin pre-digestion, casein and rapeseed concentrates were hydrolyzed with various amounts of pancreatin, trypsin and/or chymotrypsin. This hydrolysis was performed in a dialysis tube (molecular weight cut-off 1000) with continuous collection of the digested material. The addition of pure trypsin or chymotrypsin to pancreatin (Enzyme:Substrate 1:25) did not change the digestibility of casein. Only a higher pancreatin level (Enzyme:Substrate 1:12.5) increased the total protein digestibility without affecting the amino acid spectra. Rapeseed digestibility was markedly increased by the addition of pure trypsin to pancreatin. Lysine and arginine, target amino acids of trypsin, were favored at the expense of chymotrypsin and elastase target amino acids. Supplementation of pancreatin with chymotrypsin enhanced rapeseed digestibility without affecting the relative amino acid digestibility. The impact of a higher pancreatin ratio (Enzyme:Substrate 1:12.5) was similar to that of enriched pancreatin but the rate of amino acid release was modified. The differences between protein sources were mainly attributed to protein structure.

Use of 51-Cr2O3 and TiO2 as markers for the determination of passage rate and protein digestibility in rats

In a tripartite experiment with five rats each the suitability of 51Cr2O3 and TiO2 as markers was tested for estimating the transit time and passage rate as well as the total protein digestibility and the proportion of endogenous nitrogen in the small intestine with very small samples. Both markers are suited for these tests because of their simple analysis, their high recovery rate (94...105% for 51Cr2O3; 98...105% for TiO2) and their quantitative excretion in faeces within 3 days. Depending on the level of crude fibre (5.1 resp. 9.4% of DM) the transit time was found to be 7...8 h for a commercial breeding feed and 5...6 h for this commercial feed +15% straw meal. After the application of a single doses, the marker excretion of 50% appeared within 10 +/- 1 h resp. 8 +/- 1 h, and after the 12th hour there were no significant differences at all. The apparent N-digestibilities estimated by the conventional or the 51Cr2O3 resp. TiO2 indicator method did not show any differences. The proportion of endogenous nitrogen at the end of the small intestine calculated on the basis of the indicator dilution method was 83 +/- 11% for 51Cr2O3 and 83 +/- 12% for TiO2.

INFLUENCE DE LA FERTILISATION AZOTEE ET DE L’ECARTEMENT ENTRE LES RANGS DE CEREALES-ABRI RECOLTEES COMME FOURRAGE SUR L’ETABLISSEMENT DE LA LUZERNE

The effect of companion crop management on the establishment of alfalfa was evaluated. The studied variables included species of cereals, row spacing and seeding rate of companion crop, stage of maturity of the companion crop at harvest, and an additional nitrogen fertilizer application. The cereals were harvested as forage. In the year after the seeding year, the first yield of alfalfa was determined. In seven trials, forage yields of a pure stand of alfalfa were 3350 kg/ha in the first cut of the seeding year. These yields averaged 60% of forage yields obtained from the combination of alfalfa and companion crop. However, cereals substantially reduced the total digestible nutrients, crude protein and calcium contents of the forage as compared to the pure alfalfa. The additional 38 kg/ha of nitrogen at tillering provided an extra yield of 600 kg/ha. Row spacing had little or no effect on forage yield. Even though wider spacings has considerably reduced seeding rates increased spacing from 18 to 54 cm did not affect barley yield while wheat was reduced by 400 kg/ha and oat increased by 300 kg/ha. Also, the average number of stems per meter of row increased by 89% with an average weight gain of 23% for each stem at the 54-cm spacing. At the first cut in the year following establishment, yields of alfalfa established with a companion crop were equal to or lower than those in pure stand. Yield reductions varied from 0 to 13% with barley and wheat but approached 30% when oats were seeded in 18-cm rows. However, the yield reduction was only 14% in the 54-cm row spacing of oats.Key words: Medicago sativa L., nitrogen fertilization, companion crop

Some factors affecting voluntary food intake in buffaloes. 3. Effect of concentrate feeding on intake of roughages fed to lactating buffaloes

SummaryThree experiments, each with six lactating Mehsana-Surti buffaloes, were conducted to investigate the effect of supplementary feeding of concentrates on intake of basal rations of berseem hay, maize silage or wheat straw and on the total intake of feeds in 3 × 3 latin square designs.In the berseem hay experiment, concentrate feeding at 16·8 or 26·1% of hay drymatter intake (DMI) resulted in a decrease of hay DMI by 0·77 and 0·65 kg/kg concentrate D.M., respectively. Intake of total digestible nutrients (TDN) and digestible crude protein (DCP) of buffaloes receiving concentrates in addition to hay were not different from those receiving hay alone. The possibility of some chemical factor limiting feed intake has been indicated for these rations in buffaloes. Supplementary feeding had a little effect on milk production.In the maize silage experiment, concentrate feeding at 14·5 and 27·7% of the silage DMI resulted in a similar increase of total DMI, thereby increasing the TDN intake and DCP intake. Appreciable increases in milk yield and solids-not-fat (SNF) content due to supplementation were noted, although milk-fat content tended to be low.Voluntary intake of rations comprising wheat straw fed free choice with three levels of concentrates at 28·7, 48·0 and 68·8 % of straw DMI was studied in the third experiment. Concentrate supplementation had little effect on straw DMI with the result that intakes of total D.M., TDN and DCP on the medium and high proportions of supplements were higher than those on the low proportion. The milk yield, of buffaloes receiving medium and high proportions of concentrates with wheat straw increased significantly over those receiving the low proportion of concentrates. The SNF and milk-fat contents were similar on all the three treatments. The implication of physical factors limiting intake is discussed in the case of maize silage and wheat straw diets.The lactating buffaloes failed to maintain their weights on either sole berseem hay or sole maize silage rations. Supplementary feeding helped buffaloes to register small weight gains on hay rations and substantial gains on silage rations. The buffaloes on wheat straw fed with three proportions of concentrates tended to put on a little weight. Multiple regression using pooled data of Expts 1 and 3 showed that the partial regression coefficient of metabolic body weight (kgW0·76) on TDN intake was not significant but that of 6% fat-corrected milk on TDN intake was, suggesting a close relationship between milk yield and food intake.

An econometric model of beef production for optimization purposes

The aim of this study was to create a model depicting the growth process of a beef animal to provide means for economic optimization of the slaughter weight and of the length of the rearing period. Using data from Finnish beef rearing experiments, a model with two functions, one for weight gain and the other for feed intake, was estimated. In weight gain functions total energy and digestible crude protein were the main explanatory variables. Intake capacity of the animal was estimated as time needed to consume the dry matter quantity of a given feed input using also protein, crude fibre content and energy content of feed as explanatory variables. The model was estimated separately for Ayrshire bulls and for Friesian-Ayrshire and Charolais-Ayrshire cross-breeds. Functions of Cobb-Douglas or transcendental forms gave the best fits and turned out to be logical. Information given by the regression coefficient estimates was analyzed in detail as background for applications of the model. When dealing with the optimization problem the dynamics of production was discussed and a maximum daily profit was selected as the optimization criterion. An example was then presented to illustrate the profit maximization. Since they were of essential importance in the production economy, the feed composition and its productivity were analyzed and an example was derived to minimize the price of feed mix with maximum productivity.

Influence of Plant Stage at Initial Harvest and Height of Regrowth at Cutting on Forage Yield and Quality of Timothy and Orchardgrass1

AbstractThe need to obtain the best compromise between yield and quality has been recognized for years. The object of this study was to evaluate the influence of initial harvest at various growth stages and height of regrowth (all cuttings after initial harvest) at cutting on forage yield and quality of ‘Climax’ timothy (Phleum pratense L.) and ‘Pennlate’ orchardgrass (Dactylis glomerata L.). First growth of these grasses was harvested at each of the following stages: (a) transition (changing of apical meristem from vegetative to reproductive growth), (b) boot, and (c) anthesis. Following each initial harvest stage, regrowth was removed throughout the growing season at each of the following plant heights: 10 to 15 cm, 20 to 25 cm, 30 to 36 cm, 41 to 46 cm, and 51 to 56 cm. This field investigation was conducted during 1970 and 1971 on a fine, loamy, mixed, mesic Typic Hapludults (Murrill series) at the Agronomy Research Farm near Rock Springs, Penn.Delaying the first harvest of timothy and orchardgrass from the transition to anthesis stage resulted in increased yield and estimated total digestible nutrients (TDN). However, total seasonal regrowth, total TDN of regrowth, total digestible protein, and total digestible protein of regrowth decreased significantly (P≤0.05). Allowing plants of both species to attain heights of 20 to 36 cm, with few exceptions, produced highest total and regrowth forage yield, TDN, and digestible protein. However, frequent removal of regrowth, at a plant height of 10 to 15 cm, resulted in significantly (P≤0.05) lower yields and encouraged weed encroachment. These data indicate first harvest forage removal at the transition stage, followed by regrowth removal each time plants attain a height of 20 to 36 cm results in highest production of quality forage as measured by total seasonal regrowth, total TDN of regrowth and total digestible protein.

Effect on production and carcass quality characteristics of wether lambs of crossing Blackheaded Mutton, Ile de France and Texel rams with Polish Merino ewes

During the period 1972–1974 investigations were made on 120 wethers fattened semi-intensively to a weight of 45 kg liveweight. These lambs originated from commercial crosses of the Polish Merino with rams of the breeds Blackheaded Mutton (B), Ile de France (IF) and Texel (T) as well as pure Merino (M) in the control group. The use of rams of these meat-producing breeds as compared with Merino gave a better growth rate: an increase in the group IF × M of 6.2%, B × M of 7.8% and T × M of 8.8% respectively. The feed consumption, expressed in starch equivalents per kg of weight, decreased in group IF × M by 11.6%, B × M by 15.1% and T × M by 15.6%, and total digestible protein decreased in the group IF × M by 12.1%, B × M by 16.6% and T × M by 16.9%. Crosses with Blackheaded Mutton and Ile de France rams did not fundamentally change the tissue composition of the lamb carcasses. However, the use of Texel rams resulted in carcasses with a higher lean content and less fat as compared with pure Merino (difference 5.7%) as well as with other crosses (differences 4.2–4.8%). Rams of the meat breeds tested did not greatly influence dressing percentage and carcass yield in terms of bone content and the proportion of valuable cuts; nor were dimensions affected, except for a decrease in length of 2–3.5% compared with Merino.

Variability in Mineral and Trace Element Content of Dairy Cattle Feeds

Trace element content of feeds is extremely variable compared to total digestible nutrients or protein. Differences are wide between low and high values for many trace elements within a given type of feed. Coefficients of variation for forages range from 42 to 100%. Summary data are given for both major and trace elements. Problems in supplementation are discussed. Amounts for some elements are skewed with relatively few samples around the mean and over 60% below the mean. Suggested mineral allowances for dairy cows are listed. Under current supplementation, zinc is the trace element most likely to be limiting and manganese the least likely. Iron, copper, cobalt, and iodine may be limiting in some cases. Needs of research and applied nutrition are presented.

Ammonium salts of fatty acids for milk production. 3. The effect of a salt solution containing ammonium acetate on milk yield and composition in Jersey cows fed on a high concentrate diet

SUMMARY1. The experiment involved four pairs of Jersey cows in a double reversal trial with two treatments.2. The control and acetate treatments involved iso-caloric concentrate mixtures together with hay. The concentrates and hay were given in constant ratio of 3 : 1 and total feed intake was regulated according to milk yield. Cows on the acetate treatment received a dilute solution of fatty acids (1·7 % w/w) and an all-cereal concentrate mixture; those on the control diet received water and a concentrate containing 10% groundnut meal. The dilute solution of fatty acids provided approximately 31 % of the total digestible crude protein intake as ammonia-N, and 208 g acetate and 34 g propionate per day.3. The two treatments gave similar dry-matter intakes. The acetate treatment caused a slight and significant depression of milk yield but the fat content of the milk and fat-corrected milk yield were slightly increased by treatment, though not significantly so. The results have been discussed with reference to the end products of digestion in the rumen and role of ammonia-N as a substitute for protein-N.

A Comparison of Blackstrap Molasses Fortified with Soybean Oilmeal and a Conventional Concentrate Mixture as a Supplement for Growing Heifers Fed Fair-Quality Forage

Six Brown Swiss and six Holstein heifers were assigned to one of two experimental rations as they reached 127 days of age, for use in an experiment involving a randomized block design. The 240-day experiment was divided into 8 periods of 30 days each. The heifers were fed individually. Both rations included the same harvested forages, principally sorghum silage or sugarcane silage, the daily allowance of which increased from 5 pounds in period 1 to 28 pounds in period 8. In ration I the forage was supplemented with 5 pounds of a conventional concentrates mixture throughout the experiment. In ration II the daily allowance of concentrates mixture was reduced from 3 pounds in period 1 to 0 in period 4, while the daily allowances of blackstrap molasses and of dehulled soybean oilmeal were increased from 2 to 0.6 pounds, respectively, in period 1 to 5 and to 1.2 pounds, respectively, in period 4, at which level they remained until the end of the experiment. Both experimental rations were expected to supply approximately the amounts of total digestible nutrients and digestible protein needed for normal growth of heifers, according to published feed analyses and published nutrient requirements. Considerable variation in growth rate was found for individual 30-day periods on both rations. During the whole experiment the heifers which consumed ration I gained significantly (P &lt; .05) more than the heifers which consumed ration II (1.01 vs. 0.76 pounds per heifer per day). The former growth rate can be considered barely adequate, while the latter is definitely not adequate. Part of the poor growth rate in the heifers fed ration II can be ascribed to a lower total forage consumption per heifer than in the heifers fed ration I (3,304 vs. 3,045 pounds). Ration II was adversely affected by an overestimation of the digestible protein content of the soybean oilmeal in planning the rations, which was revealed by subsequent chemical analysis. Judging from other published reports, the high levels of molasses employed in ration II may have lowered the amount of net energy for growth contributed per pound of molasses, and decreased the crude-protein digestibility of the whole ration. The following feed costs were calculated under rations I and II: Average costs per heifer per day, $0.26 and $0.23; and cost per pound of live-weight gain $0.26 and $0.30, respectively. The results suggested that the use of a high level of molasses supplemented with a minimal amount of soybean oilmeal as a substitute for all other concentrate feeds in rations based on poor-quality forage for heifers under 12 months of age, is neither nutritionally satisfactory nor economically advantageous.

Energy and Protein Requirements of Milk Production

The currently recommended allowances of total digestible nutrients (TDN) and digestible protein (DP) for milk production and their bases were examined. It was concluded that the uncertainties of estimating the body gain or loss of energy and protein from body weight changes preclude the use of the conventional feeding trial to estimate requirements. As a consequenee, in the present studies the milk production requirements for TDN were estimated by the digestion-trial method and those for DP from published nitrogen-balance data.The TDN values of seven diets ingested at levels of intake ranging from one to five times the maintenance level were determined in 265 individual-cow trials. Per increment of intake equivalent to that of maintenance, the TDN value of the diets declined at rates ranging from 2.1 to 6.2% (average rate, 4.0%). These data indicated that the requirements for TDN (determined at maintenance) increase with increasing feed intakes (or milk outputs). Accordingly, the TDN requirements were computed for the average rate (4%) of depression in the TDN value observed.An examination of nitrogen-balance data indicated that the average rate of utilization of DP for the combined functions of milk production and maintenance of cows in body nitrogen equilibrium is of the order of 65%. This observation suggests that milking cows require an average minimum amount of DP in the diet equivalent to 154% of the quantity of protein in the milk. For usual 4% FCM, the requirement would be 24.4g of DP per pound of milk. Since the DP value declines at about the same rate as the TDN value of the diet with increasing daily inputs of feed, the effect of feeding level was superimposed on the apparent net requirement for DP. This indicated that for cows in nitrogen equilibrium, the requirement would range from 25.3 to 30.0g per pound of 4% FCM for daily yields of 10 and 100lb, respectively. The data also suggest that milk production requires a DP:TDN ratio of 1:5.7.Practical feeding requires a knowledge of a) the dietary needs of the various body functions and b) the nutritive values of feeds. Although nutrient requirements are the basis of practical allowances, a number of conditions need to be taken into account to adapt net requirements to practical feeding situations. Thus, it is necessary to generalize and, in certain instances, to project generalizations, even over gaps in present knowledge.In this report it is the intent a) to summarize the present status of the knowledge of the energy and protein requirements of lactation and b) to extend results of the authors’ recent studies to derive estimates of the energy and protein requirements.

Dry season protein and energy supplements for beef cattle on native pastures at Katherine, N.T

Three experiments planned to gain information on the gross nutritive deficiencies of native pasture as a feed for beef cattle during the dry season were carried out at Katherine, N.T., between 1960 and 1962. Groups of local Shorthorn steers were grazed on native pasture from July to November and fed supplements of crushed sorghum grain and peanut meal at different levels of total digestible nutrients and digestible crude protein. The results suggest that up to the time of early storm rains, prior to the wet season proper, the dry standing native pasture is an adequate source of energy, which can be effectively utilized if cattle are given a small quantity of high-protein supplement. During the period of early rains, the pasture is not an adequate source of energy, and high-protein supplements do not prevent liveweight loss. High spring temperatures before the early rains did not appear to affect adversely the performance of supplemented cattle.

Evaluation of Alfalfa Hay by Chemical Analyses

A method has been proposed for a critical evaluation of alfalfa hay quality by the use of chemical analysis. A modification of the crude fiber method was made so that the remaining ash, which was shown to be largely silica, was included in the crude fiber. A study of regression equations relating total digestible nutrients (TDN) and digestible protein to lignin, crude fiber, “crude fiber plus silica”, and protein revealed that the modified crude fiber was most satisfactory for predicting both TDN and digestible protein. Therefore, determination of dry matter and “crude fiber plus silica” will allow the prediction of TDN and digestible protein content. Studies of hay sampling devices and variation in composition of hay suggest that core samples ⅜-inch by 18-inch from 19 bales of hay in a population will provide a representative sample of that lot of hay for chemical analysis so that 95% of the time the predicted TDN will be within one percentage unit. A table of constants is presented which allows the monetary value of alfalfa hay to be calculated relative to the price of barley and cottonseed meal depending on the crude fiber content of the alfalfa hay.

The nutritive ratio/crude-protein relationships in ruminant and non-ruminant digestion

In both ruminant and non-ruminant digestion, the nutritive ratio of a feed is shown to be very significantly related to the crude-protein content of that feed.This confirms that there is a relationship between the total crude protein and digestible protein in a ruminant feed, and strongly suggests that there should also be a relationship between these two components in non-ruminant feeds.

Antibiotics in Dairy Cattle Nutrition. IV. Comparative Effects of Different Levels of Crystalline Aureomycin and a Crude Aureomycin Fermentation Product (Aurofac 2A) on the Growth and Well-Being of Young Dairy Calves

Summary This experiment was initiated to compare the effects of pure crystalline aureomycin HC1 and a crude aureomycin fermentation product (Aurofac 2A) on the growth and well-being of young dairy calves. Employing a randomized block design, 32 female calves of four breeds were divided into four groups. Calves in one group received Lederle's Aurofac 2A in amounts calculated to supply 45 ing. of aureomycin daily for each 100 lb. of calf weight, and a second group received 45 mg. of pure aureomycin HC1. A third group received 90 mg. of pure aureomycin HC1, and a fourth group received no aureomycin and served as a control. The calves in the three groups receiving aureomycin had a lower incidence of infection than the calves in the control group. No difference in incidence of infection resulting from the difference in antibiotic source was observed. From birth to 12 weeks the growth rates of the three groups of calves receiving aureomycin were significantly greater than that of the control calves. The growth rate of the calves receiving 45 mg. of aureomycin from Aurofac was significantly greater than that of the calves receiving 45 mg. of pure aureomyein and greater, though not significantly, than that of the calves receiving 90 mg. of pure aureomycin. From 13 to 25 weeks the growth rate of the three groups of calves receiving aureomycin was also significantly greater than that of the control calves. The growth rate of the calves receiving 45 mg. of pure aureomycin was significantly (P From birth to 25 weeks of age the growth rate of calves receiving 45 mg. of aureomycin from Aurofac was not significantly different from that of calves receiving 45 mg. of pure aureomycin. Furthermore, there appeared to be no advantage in the use of 90 mg. of pure aureomycin because the growth rate of calves receiving 90 mg. was significantly lower than that of the calves given 45 mg. of pure aureomycin. Feed intakes and efficiency of gains were studied for the first 16 weeks of the experiment. An analysis of variance of the feed consumption data showed that there were no significant differences among the groups in skinimilk, hay, and grain consumption. The three groups of calves receiving aureomycin used significantly less total digestible nutrients and digestible protein per pound of gain than the control calves. The differences among the aureomycin treatments were not significant.