Apparent Digestibility Of Crude Fibre Research Articles

Ningxiang Pig-Derived Microbiota Affects the Growth Performance, Gut Microbiota, and Serum Metabolome of Nursery Pigs.

The gut microbiota is crucial for maintaining the host's intestinal homeostasis and metabolism. This study investigated the effects of fecal microbiota transplantation (FMT) from Ningxiang pigs on the growth performance, fecal microbiota, and serum metabolites of the same-old DLY pigs. The results indicated that the average daily gain of FMT pigs was significantly greater than that of the control (CON) group. Compared to the CON group, the FMT group significantly improved the apparent digestibility of crude fiber, crude ash, gross energy, and calcium of the pigs. The analysis of serum antioxidant status revealed that the activities of total superoxide dismutase and catalase in the serum of pigs in the FMT group were significantly elevated, whereas the level of malondialdehyde was significantly reduced. Furthermore, 16S rRNA sequencing analysis revealed that the Ningxiang pig-derived microbiota altered the fecal microbiota structure and modulated the diversity of the gut microbiota in the DLY pigs. Untargeted LC-MS metabolomics demonstrated that pigs in the FMT group exhibited distinct metabolomic profiles compared to those in the CON group. Significant changes were observed in key metabolites involved in amino acid, lipid, and carbohydrate metabolism. Additionally, a correlation analysis between serum differential metabolites and the gut microbiota revealed that the relative abundance of Lachnospiraceae_NK4A136_group and Corynebacterium was highly correlated with lipid compounds. In conclusion, Ningxiang pig-derived microbiota can alleviate oxidative stress and enhance growth performance in DLY pigs by modulating their gut microbiota and metabolic features.

Study on the Characteristics of Coarse Feeding Tolerance of Ding'an Pigs: Phenotypic and Candidate Genes Identification.

Ding'an (DA) pig, a prominent local breed in Hainan Province, exhibits notable advantages in coarse feeding tolerance and high-quality meat. To explore the potential genetic mechanism of coarse feeding tolerance in DA pigs, 60-day-old full sibling pairs of DA and DLY (Duroc-Landrace-Yorkshire) pigs were subjected to fed normal (5%) and high (10%) crude fiber diets for 56 days, respectively. The findings showed that increasing the crude fiber level had no impact on the apparent digestibility of crude fiber, intramuscular fat, and marbling scores in DA pigs, whereas these factors were significantly reduced in DLY pigs (p < 0.05). Through differential expression analysis and Weighted Gene Co-expression Network Analysis (WGCNA) of the colonic mucosal transcriptome data, 65 and 482 candidate genes with coarse feeding tolerance in DA pigs were identified, respectively. Joint analysis screened four key candidate genes, including LDHB, MLC1, LSG1, and ESM1, potentially serving as key regulated genes for coarse feeding tolerance. Functional analysis revealed that the most significant pathway enriched in differential genes associated with coarse feeding tolerance in Ding'an pigs was the signaling receptor binding. The results hold substantial significance for advancing our understanding of the genetic mechanisms governing coarse feeding tolerance in Ding'an pigs.

Benefits of heat-killed Lactobacillus acidophilus on growth performance, nutrient digestibility, antioxidant status, immunity, and cecal microbiota of rabbits.

Heat-killed probiotics, as a type of inactivated beneficial microorganisms, possess an extended shelf life and broader adaptability compared to their live counterparts. This study aimed to investigate the impact of heat-killed Lactobacillus acidophilus (L. acidophilus, LA) - a deactivated probiotic on the growth performance, digestibility, antioxidant status, immunity and cecal microbiota of rabbits. Two hundred weaned Hyla rabbits were randomly allocated into five equal groups (CON, L200, L400, L600, and L800). Over a 28-day period, the rabbits were fed basal diets supplemented with 0, 200, 400, 600, and 800 mg/kg of heat-killed LA, respectively. Results revealed a significant reduction in the feed-to-gain ratio (F/G) in the L600 and L800 groups (p < 0.05). Additionally, the L800 group exhibited significantly higher apparent digestibility of crude fiber (CF) and crude protein (CP) (p < 0.05). Regarding digestive enzyme activities, enhanced trypsin and fibrinase activities were observed in the L600 and L800 groups (p < 0.05). Concerning the regulation of the body's antioxidant status, the L800 group demonstrated elevated levels of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in both serum and ileal tissue (p < 0.05). In terms of immune capacity modulation, serum tumor necrosis factor-α (TNF-α) levels were significantly lower in the L600 and L800 groups (p < 0.05), while immunoglobulin A (IgA) and immunoglobulin M (IgM) levels were higher (p < 0.05). Additionally, the L800 group exhibited a substantial increase in secretory immunoglobulin A (SIgA) levels in the intestinal mucosa (p < 0.05). In comparison to the CON group, the L800 group exhibited a significant increase in the relative abundance of Phascolarctobacterium and Alistipes in the cecum (p < 0.05). Phascolarctobacterium demonstrated a positive correlation with SIgA (p < 0.05), IgM (p < 0.01), and Glutathione peroxidase (GSH-Px) (p < 0.05), while displaying a negative correlation with TNF-α levels (p < 0.05). Concurrently, Alistipes exhibited positive correlations with IgA (p < 0.05), IgM (p < 0.05), SIgA (p < 0.01), GSH-Px (p < 0.05), SOD (p < 0.05), and T-AOC (p < 0.01), and a negative correlation with TNF-α (p < 0.05). In conclusion, the dietary incorporation of 600 mg/kg and 800 mg/kg of heat-killed LA positively influenced the growth performance, nutrient digestibility, antioxidant status, immune capacity and cecal microbiota of rabbits. This highlights the potential benefits of utilizing heat-killed probiotics in animal nutrition.

Effects of Saccharomyces cerevisiae cell wall addition on feed digestibility, fecal fermentation and microbiota and immunological parameters in adult cats

BackgroundThis study aimed to evaluate the effects of increasing dosages of a commercial product composed by Saccharomyces cerevisiae yeast (YAM), with active metabolites, which are beta glucans, nucleotides, organic acids, polyphenols, amino acids, vitamins and minerals (Original XPCtm, Diamond V, IOWA, USA) added to a commercially available dry cat food. Apparent digestibility of dietary nutrients, fecal microbiota, fecal fermentation products and immunological parameters were evaluated. Twenty-seven healthy cats of mixed sexes, with a mean body weight of 4.19 ± 0.83 kg and a mean age of 9.44 ± 5.35 years were distributed by age in an unbalanced randomized block design, consisting of three experimental treatments: CD (control diet), YAM 0.3 (control diet with 0.3% yeast with active metabolites) and YAM 0.6 (control diet with 0.6% yeast with active metabolites).ResultsThe inclusion of the additive elevated the apparent digestibility of crude fiber (p = 0.013) and ash (p < 0.001) without interfering feed consumption, fecal production and fecal characteristics. Regarding fermentation products present in the feces, prebiotic inclusion increased lactic acid concentration (p = 0.004) while reducing isovaleric acid (p = 0.014), only in the treatment YAM 0.3. No differences were noticed on biogenic amines (BA), fecal pH, ammonia concentration, total and individuals short-chain fatty acids (SCFA) and total and individuals branched-chain fatty acids (BCFA) (except isovaleric acid in YAM 0.3). As regards to fecal microbiota, prebiotic inclusion has resulted in the reduction of Clostridium perfringens (p = 0.023). No differences were found in the immunological parameters evaluated.ConclusionIt can be concluded that the additive, at the levels of inclusion assessed shows prebiotic potential and it has effects on fecal fermentation products and microbiota without interfering on crude protein and dry matter digestibility. More studies evaluating grater inclusion levels of the prebiotic are necessary to determine optimal concentration.

PENGARUH PEMBERIAN SUMBER SERAT BERBEDA DALAM PAKAN TERHADAP KECERNAAN SEMU SERAT KASAR DAN HEMISELULOSA PADA AYAM PEDAGING STRAIN COBB

THE EFFECT OF DIFFERENT FIBER SOURCES IN THE FEED TO DIGESTIBILITY OF CRUDE FIBER AND HEMICELLULOSE IN COBB STRAIN OF BROILERS. This research was carried out with the aim to determine the effect of providing different sources of fiber in feed on the apparent digestibility of crude fiber and hemicellulose in cobb strain of broilers. This study used 20 cobb strain of broilers 35-day-old. The design used was a Completely Randomized Design (CRD) with the treatment of 4 different fiber sources in the feed which was repeated 5 times. The treatments consisted of: R0 (commercial feed),R1 (commercial feed with coffe skin), R2 (commercial feed with rice bran), R3 (commercial feed with coconut pilp). Variables measured were: apparent digestibility of crude fiber and hemicellulose. Apparent-digestibility measurements using the total collection method. Data were analyzed using general linear model (MINITAB version 16), then differences between treatments were tested with Tukey’s simultaneous test. Apparent digestibility of crude fiber feed has a very different (P&lt;0,01) with treatment R2 and R1. The treatment of R2 was not significantly different (P&gt;0,05) from R1. Apparent digestibility test for hemicellulose shows that R3 is the same as R0, but it is significantly different (P&lt;0,01) with treatment R2 and R1. The treatment od R2 was not significantly different (P&gt;0,05) from the treatment of R1. It was concluded that coconut pilp as a source of fiber in the feed of strain cobb of broilers provides better digestibility of coarse and hemicellulose fibers than coffe huks and coffe branKeywords: Apparent digestion of crude fiber, Apparent digestion of hemicellulose, strain cobb of broiler

Effects of Dietary FOS and CPP on growth performance and serum biochemical parameters for weaned piglets

The present experiment was conducted to study the effects of different levels of oligosaccharide(FOS) and complex CPP preparation(CPP) in diets on growth performance and serum biochemical parameters for weaned piglets. 240 crossbred DLY( Duroc× Landrace× Yorkshire) 21-day-old weaning piglets, about 7.2 kg in initial body weight were selected and randomly divided into 6 groups, with 2 repeats for each group, 20 each repeat(half male and half female.). Group 1, as the control group, was fed base diet(BD), group 2 was fed BD adding 0.10% aureomycin, group 3, 4, 5, 6, respectively, was fed BD adding 0.05% CPP, 0.05% FOS, 0.20% FOS and 0.10% FOS + 0.05% of CPP. Feeding trial was conducted for 35 days. Results: (1) The combination of 0.10%FOS and 0.05%CPP(group 6) were added, the average daily gain of weaned pigs increased by 13.71 % (P &lt; 0.05) and the feed conversion ratio was reduced by 7.41 % (P &lt; 0.05) compared with control. The diarrhea rate of piglets decreased by 94.63 % (P &lt; 0.01) compared with the control (p &lt; 0.05), and decreased by 62.86 % (P &lt;0.05) compared with group 2.(2)There was no significant difference in the apparent digestibility of nutrient, such as ether extract and crude protein, by adding FOS and CPP individually or jointly in diet of weaned piglets, but apparent digestibility of crude fiber increased , to acertain extent, and there was no significant difference with diet adding 0.10 % of antibiotics (group 2)(P &gt;0.05).(3) There was no significant difference in serum biochemical indexes, such as serum total protein, albumin, urea nitrogen, cholesterol, triglycerides, alanine aminotransferase, aspartate aminotransferase and sugar by adding FOS and CPP individually or jointly in diet of weaned piglets (P &gt; 0.05);there was no significant effect in serum immunoglobulin IgG and IgM (P&gt; 0.05), but the serum IgE content was increased in different degrees. Conclusion: Adding FOS and CPP in diet for weaned piglets can improve the growth performance, reduce diarrhea rate of piglets, and promote digestion and absorption of feed nutrients, without significant difference between them and diet adding antibiotics. Among them, the effect of adding 0.10%FOS+0.05%CPP was the best.

Effects of raw material extrusion and steam conditioning on feed pellet quality and nutrient digestibility of growing meat rabbits.

This study was conducted to investigate the effects of raw material extrusion and steam conditioning on feed pellet quality and nutrient digestibility of growing meat rabbits, in order to determine appropriate rabbit feed processing methods and processing parameters. In Exp. 1, an orthogonal design was adopted. Barrel temperature, material moisture content and feed rate were selected as test factors, and acid detergent fiber (ADF) content was selected as an evaluation index to research the optimum extrusion parameters. In Exp. 2, a two-factor design was adopted. Four kinds of rabbit feeds were processed and raw material extrusion adopted optimum extrusion parameters of Exp. 1. A total of 40 healthy and 42-day-old rabbits with similar weight were used in a randomized design, which consisted of 4 groups and 10 replicates in each group (1 rabbits in each replicate). The adaptation period lasted for 7 d, and the digestion trial lasted for 4 d. The results showed as follows: 1) ADF was significantly affected by barrel temperature (P < 0.05); the optimum extrusion parameters were barrel temperature 125 °C, moisture content 16% and feed rate 9 Hz. 2) Raw material extrusion and steam conditioning both significantly decreased powder percentage, pulverization ratio and protein solubility (P < 0.05), significantly improved hardness and starch gelatinization degree of rabbit feed (P < 0.05). They both had significant interaction effects on the processing quality of rabbit feed (P < 0.05). 3) Extrusion significantly improved the apparent digestibility of dry matter and total energy (P < 0.05). Extrusion and steam conditioning both significantly improved the apparent digestibility of crude fiber (CF), ADF and NDF (P < 0.05), but they had no interaction effects on the apparent digestibility of rabbit feed. Thus, using extrusion and steam conditioning technology at the same time in the weaning rabbits feed processing can improve the pellet quality and nutrient apparent digestibility of rabbit feed.

Dynamic distribution of the gut microbiota and the relationship with apparent crude fiber digestibility and growth stages in pigs.

The gut microbiota plays an important role in nutrient digestibility in animals. To examine changes in the pig gut microbiota across growth stages and its effects on nutrient digestion, the gut microbiota population in pigs at 28 days (before weaning), and 60, 90, and 150 days of age was assessed by 16S rDNA gene sequencing. The apparent digestibility of crude fiber (CF), neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP) and ether extract (EE) was also assessed in these pigs. A total of 19,875 operational taxonomic units (OTUs) were identified from all samples. Both bacterial abundance and diversity increased with age. A total of 22 phyla and 249 genera were identified from all fecal samples; Firmicutes and Bacteroidetes were the most dominant phyla in all samples. With increasing age, the proportion of TM7 and Tenericutes increased, whereas the proportion of Lentisphaerae and Synergistetes decreased. The abundance of 36 genera varied with age, and the apparent digestibility of CF increased with age. Three phyla, Proteobacteria, Tenericutes and TM7, and 11 genera, including Anaeroplasma, Campylobacter, and Clostridium, were correlated with apparent CF digestibility.

Neuweltkameliden in der Schweiz. III. Verdaulichkeit der Futtermittel in verschiedenen Betrieben von Neuweltkameliden in der Schweiz

Feces from 15 adult llamas were collected in 4 herds and the exact diet was determined, either of the group or of individual animals, to examine apparent digestibility. A questionnaire was submitted to the animal owners. The questionnaire included questions about the animals in the herd (number, age, gender, origin), management methods, pastures, watering and feeding facilities for the animals, hay supplementation, composition of the ration and fodder additives used. Analysis of the feed revealed an average apparent digestibility for dry matter of 81+/-4%, for the organic matter 77+/-7%, for crude protein 69+/-10%, for nitrogen-free extract 83+/-5%, for calcium 60+/-17%, for phosphorus 54+/-11% and 81+/-9% for crude fiber. All feed components seem to be digested similarly to domestic ruminants whereas the apparent digestibility of crude fiber was high, which indicates that the digesting system seems to be more effective.

Dietary soyabean oil depresses the apparent digestibility of fibre in trotters when substituted for an iso-energetic amount of corn starch or glucose.

The aim of the present study was to establish whether the inhibitory effect of fat feeding on fibre digestion has been underestimated due to the substitution of fat for corn starch. A high fat intake has been shown to lower total intestinal tract apparent digestibility of crude fibre in horses but, since fat was substituted for nonstructural carbohydrates, including starch, the specific effect of fat could not be ascertained. The possibility could not be excluded that starch also inhibits fibre digestibility, so that the fat effect observed earlier would have been underestimated. In this study, the intakes of iso-energetic amounts of soyabean oil, corn starch or glucose were compared as to fibre digestibility. Unlike starch, glucose is fully absorbed by the small intestine and, therefore, is not expected to influence fibre fermentation in the caecum and colon. Six trotters were fed rations high in soyabean oil (158 g/kg dry matter), corn starch (337 g/kg dry matter) or glucose (263 g/kg dry matter) according to a 3 x 3 Latin square design. Apparent crude fibre digestibility was similar for the rations with corn starch (mean +/- s.d., 70.7 +/- 3.06% of intake, n = 6) or glucose (71.0 +/- 1.90%), but was significantly depressed by fat feeding (56.5 +/- 7.65%). Similar observations were made for apparent digestibilities of neutral and acid detergent fibre and of cellulose. It was concluded that the addition of fat to the feed ration of horses has a specific inhibitory effect on fibre utilisation and, therefore, reduces the amount of energy provided by dietary fibre.

Apparent digestibility of crude fibre in ponies fed either a low or high-protein diet.

The question addressed was whether apparent crude fibre digestibility in ponies would change after lowering protein intake from adequate to borderline deficient. Four adult ponies were fed a low- and high-protein diet according to a cross-over design. The diets consisted of grass hay and concentrates and provided either 1.5 or 3.6 g digestible crude protein/kg(0.75) per day. The two whole rations provided 2.4 g crude fibre/kg body weight per day. Apparent crude fibre digestibility was not affected by protein intake (low-protein diet: 42.9 +/- 4.03%; high-protein diet: 38.1 +/- 1.14%, means +/- SE, n=4). The low-protein diet caused a significant increase in the ratio of faecal: urinary nitrogen. It is suggested that, when the low-protein diet was fed, sufficient urea flew from the blood into the intestine and ammonia released in the hindgut was conserved so that microbial growth, and thus fibre fermentation, was maintained.

Growth rate, feed intake and feed utilization of small East African goats supplemented with Leucaena leucocephala

Growth and digestibility studies with grazing indigenous Tanzanian goats used different levels of Leucaena leucocephala. Four treatments were hay only (H), hay and 100 g leucaena (HL 1), hay and 200 g leucaena (HL 2) and hay plus leucaena ad libitum (HL 3) in the growth study; and hay only (H), hay and 100 g leucaena (HL 1), hay and 200 g leucaena (HL 2) and leucaena only (L) in the digestibility study. Supplemented goats had higher growth rates ( P<0.001). Daily gains were 20, 23, 29 and 30 g for animals on treatments H, HL 1, HL 2 and HL 3, respectively. Leucaena leucocephala supplementation increased total dry matter intake from 42.3 g/kg W 0.75 in the control group (H) to 77.9 g/kg W 0.75 in HL 3 ( P<0.001). Crude protein digestibility increased with higher levels of leucaena in the diet ( P<0.001). Apparent digestibility of crude fibre was depressed with increased leucaena supplementation. Digestibility coefficients for treatments H, HL 1, HL 2 and L were 23.1, 55.2, 55.1 and 62.3 in trial 1 and 35.2, 49.3, 58.9 and 62.0 in trial 2 for crude protein; and 61.4, 60.9, 55.9 and 54.7 in trial 1 and 69.5, 59.1, 62.9 and 40.3 in trial 2 for crude fibre, respectively. Water intake and daily nitrogen retention increased with leucaena levels. Supplemented goats in HL 1, HL 2 and L retained 1.8, 3.5 and 9.6 g/day nitrogen compared to goats in H which were in negative nitrogen balance.

A notes on nutrient digestibility and nitrogen retention in ewes fed whole grains of triticale, wheat and maize

ABSTRACTTwo digestion trials were conducted using sheep fed whole grains of triticale, wheat or maize on an equal amount or an isonitrogenous basis. Nine ewes were used in a 10-day collection period for each trial. Both trials consisted of three treatment groups of three animals each. Each ewe received daily either 1200 g of a diet containing 740 g (per kg diet) triticale, wheat or maize (trial 1) or 900 g of a diet containing 650, 650 and 600 g (per kg diet), respectively, of the above grains. Digestibilities of various nutrients, dry matter and organic matter were generally similar among treatments. However, apparent digestibility of crude fibre was significantly higher for ewes fed triticale than for those fed maize or wheat diets.

Studies on the Digestion in the Rabbit

This experiment made clear the effect of the small intestinal fistulae fixation on the excretion pattern of hard feces and soft feces, apparent digestibility of crude fiber, and the recovery rate of manganese dioxide in the experimental pellet diet. The filter stick method for crude fiber determination and the wet-ashing method for manganese were approved to be useful. Radioactivity measurements of both duodenum and ileum digesta, collected after the oral administration of radioactive manganese dioxide prepared by the neutron irradiation method, resulted in a considerably rapid passage rate of manganese dioxide through the small intestinal tract.

THE EFFECT OF AGE, BODY WEIGHT, FEED INTAKE AND ADAPTABILITY OF PIGS ON THE DIGESTIBILITY AND NUTRITIVE VALUE OF CELLULOSE

A total of 88 metabolism trials were conducted with eight 65-kilogram pigs. Four pigs received a control ration and four received the same amount of control ration plus 40 per cent wood cellulose (solka-floc). A 4-week early growing, a 6-week maintenance and a 3-week late growing period were followed by a 2-week changeover period in which all pigs received solka-floc. The reduction of feed intake to a maintenance level caused an increase in the apparent digestibility of crude fiber and crude protein in both groups. This resulted in a higher digestible energy intake, carbon retention and body weight gain in the solka-floc group. The digestibility of crude fiber and crude protein of the solka-floc ration decreased in the late growing period but still remained higher than in the early growing period. The data indicated that digestibility was influenced more by the level of feeding and changes in body weight than by age. Pigs fed solka-floc for 15 weeks were no better adapted to digest it than those which received it for 1 week. Fecal protein was doubled by the addition of solka-floc. The solka-floc was 5.0, 29.1, and 18.3 per cent digested during the early-growing, maintenance and late-growing periods respectively, while the extra fecal protein resulting from feeding the supplemental cellulose was equivalent to 9.0, 6.7 and 8.1 per cent of the solka-floc intake. The relationship of dry matter content of the feces to digestibility and rate of passage is discussed.

Effect of Feeding Different Ratios of Roughage to Concentrate upon Milk Production and Digestibility of the Ration

Summary A randomized block design was used to study the productive and digestive efficiency of cows consuming rations containing 80, 60, and 40% dry matter from roughage and the balance from concentrates. Twelve animals were used and the experimental period was 112 days in length. Digestibility trials, involving total fecal collections, were conducted at about the 10th and 20th wk. of lactation. In addition, eight dry cows were used for obtaining digestibility values on the roughage portion of the ration. As the proportion of concentrate in the ration became larger, the apparent digestibility coefficients of the mixed ration increased for dry matter, crude protein, ether extract, N-free extract, and total carbohydrates (crude fiber plus N-free extract). Total digestible nutrient and dry matter intakes also increased. The apparent digestibility of crude fiber decreased as the proportion of concentrate in the ration increased. There was no significant difference in the average amounts of milk produced by the animals consuming the different rations. Efficiency of milk production, expressed as pounds of total digestible nutrients per pound of 4% fat-corrected milk produced, decreased as the proportion of concentrate in the ration increased. The data support other reports which suggest that present U. S. feeding standards for dairy cattle are not as accurate at high or low levels of production as at medium levels, and that they are more accurate with usual rations than with very high proportions of either concentrates or roughage.

The Effect of Different Levels and Prolonged Supplementation of Chlortetracycline upon Roughage Digestion by Sheep

Three experiments were conducted with 38 wether lambs, that weighed an average of about 65 lb. each, to determine the effect of chlortetracycline on the apparent digestibility of feed constituents of a ration which consisted primarily of low quality roughage. The rations were composed of 80% ground corncobs and 20% concentrate mixture. In Experiment 1 the basal ration was supplemented with 10 mg. of chlortetracycline and chlortetracycline as Aurofac 2A per pound of feed. In Experiment 2 the basal ration was supplemented with chlortetracycline and chlortetracycline as Aurofac 2A, each at the 1 and the 2-mg. levels per pound of feed. Experiment 3 was a repetition of Experiment 2, except the levels of antibiotic fed were increased to 5 and 10 mg. per pound of feed, and the collection period consisted of three consecutive 10-day collection periods. In all experiments the initial supplementation of 5 and 10 mg. of chlortetracycline or Aurofac 2A caused a loss of appetite within 40 to 72 hours. All levels of chlortetracycline supplementation significantly decreased the apparent crude fiber digestibility except the 1 mg.level of chlortetracycline as Aurofac 2A in Experiment 2. This same trend was present for dry matter, organic matter, and nitrogen-free extract. As the level of chlortetracycline was increased from one to two and from 5 to 10 mg. the decrease in apparent digestibility of ration constituents became greater. In Experiment 3 there was a definite period effect in the chlortetracycline supplemented groups with a recovery of apparent digestibility of ration constituents in Period 3. The average apparent digestibility of crude fiber for both sources of chlortetracycline at the 10-mg. level for Periods 1, 2 and 3 in Experiment 3 were reduced by 18.4, 11.5 and 5.4%, respectively. This same trend of recovery was present for dry matter, organic matter and nitrogen-free extract. The implications of these findings are discussed.