Growth performance and meat characteristics of hair lambs grazing stargrass pasture without supplementation or supplemented with concentrate containing different levels of crude protein

Abstract

Forty crossbreed hair lambs (19.1 kg body weight; 8 months of age) grazing on a Cynodon plestoctachyus pasture without supplementation or supplemented with 300 g of concentrate containing different levels of crude protein (CP) were randomly assigned to treatments defined as follows: control (without supplementation); CP130 (concentrate 130 g CP/kg), CP150 (concentrate 150 g/kg), CP170 (concentrate 170 g/kg), and CP190 (concentrate 190 g CP/kg). Lambs fed supplements had higher final body weight (BW), total gain, average daily gain (ADG), total dry matter intake (DMI), total tract digestion, and carcass dressing than lambs in control treatment. Final BW, total gain, ADG, total DMI, feed conversion, and total tract digestion were improved linearly as protein level in concentrate increased. Meat of lambs fed supplements was lighter, redder, and less yellow than meat of lambs in control treatment. It is concluded that supplementation improved ADG, feed conversion, carcass dressing, and meat color.     

Studies on the effect of lysine and methionine supplementation of a high‐protein maize‐soyabean diet and of a low‐protein barley‐white fish meal diet on the performance of caged layers

Selected literature relating to the amino acid supplementation of layers’ diets is reviewed and the results of two experiments are presented.

In the first experiment a basal soyabean meal diet (14.3 per cent crude protein) was supplemented with L‐lysine and DL‐methionine, singly and together. Supplementation of the basal soyabean diet with the amino acids caused no significant effects on egg production, mean and total egg weight or food conversion efficiency. None of the soyabean diets proved as satisfactory for egg production or food conversion efficiency as a fish meal control diet (16.9 per cent crude protein).

In the second experiment the effect of adding 0.1 per cent each of L‐lysine and DL‐methionine or 0.2 per cent each of l‐lysine and DL‐methionine to a low fish meal diet (2.5 per cent fish meal) was examined. The addition of 0.2 per cent of each amino acid caused an increase in egg production.

Mean egg weight was improved by the addition of amino acids at both levels although this effect was not statistically significant. Comparison of the low fish meal diets with a fishmeal control diet (10 per cent fishmeal) showed that at the 0.2 per cent addition of amino acids, egg production, total egg weight and food conversion efficiency were better than on the 10 per cent fish meal control diet.

Two breeds, light and medium hybrids were used in both experiments.

The results are discussed with reference to their practical significance.     

低蛋白质日粮补充赖氨酸、蛋氨酸对离乳期梅花鹿氮代谢的影响

为研究低蛋白质日粮添加赖氨酸和蛋氨酸对仔鹿氮代谢的影响,采用4×4完全拉丁方试验,选取3月龄、健康、离乳梅花鹿仔鹿4只,体重为(30±0.12)kg(X?±SD),进行消化代谢试验。对照组(Ⅰ组)饲喂16.28%粗蛋白质的高蛋白质日粮,试验组饲喂13.40%粗蛋白质,添加0.23%赖氨酸,并分别添加0(Ⅱ组)、0.06%(Ⅲ组)、0.12%(Ⅳ组)蛋氨酸的低蛋白质日粮。结果表明:1)对照组蛋白质消化率显著高于Ⅱ组(P<0.01)、Ⅲ组和Ⅳ组(P<0.05),脂肪消化率显著低于Ⅱ组(P<0.01),其他营养物质消化率差异不显著(P>0.05)。2)对照组和Ⅳ组蛋氨酸消化率显著高于Ⅱ组和Ⅲ组(P<0.05),对照组其余氨基酸消化率(赖氨酸、胱氨酸除外)显著高于各试验组(P<0.05)。3)对照组吸收氮显著高于Ⅱ组(P<0.01)、Ⅲ组和Ⅳ组(P<0.05),尿氮排放量显著高于各试验组(P<0.05),氮利用率及氮生物学效价低于各试验组(P>0.05)。4)对照组尿嘌呤衍生物总排放量显著大于Ⅱ组(P<0.01)和Ⅲ组(P<0.05),尿囊素显著大于Ⅱ组(P<0.01)、Ⅲ组和Ⅳ组(P<0.05),对照组、Ⅲ组和Ⅳ组黄嘌呤和次黄嘌呤显著高于Ⅱ组(P<0.01)。补充赖氨酸、蛋氨酸可改善低蛋白质日粮仔鹿营养物质消化率利用率,除粗蛋白外其他营养物质消化率与常规蛋白质水平相近,甚至更好,提高氮沉积、氮利用率和生物学效价,改善氮平衡,减少氮排放,降低环境污染。     

Effect of dietary crude protein level on the reproductive performance and growth of New Zealand white rabbits

An experiment utilizing 391 preweaning and 187 postweaning litter records from 145 does was conducted for 12 mo to determine the effect of dietary crude protein level on performance of commercial New Zealand White rabbits. Does and their litters were fed alfalfa-based pelleted diets containing either 17.5, 19 or 20.5% crude protein (CP). In a separate experiment, the 17.5 and 20.5% CP diets were fed during lactation to 10 does to determine nitrogen (N) digestibility and retention. Body weights of does fed 17.5% CP were lower (P less than .01) than for the other treatments after 21 and 28 d of lactation. No differences (P greater than .10) were observed for doe weight at kindling, percentage fertility, litter size, preweaning litter mortality, 1- to 21-d consumption, preweaning feed efficiency and 28- to 56-d average daily consumption, average daily gain and average weight. Total born tended to be higher (P = .07) on higher protein levels but percentage born alive was greatest (P less than .01) on the 17.5% CP diet. Does fed 19% CP tended to have a greater number of parities (P = .06). Other significant differences observed for preweaning litter traits were between 17.5 and 19% CP groups. Does fed 19% CP had heavier litters at birth (P less than .01), at 21 d (P = .05) and 28 d (P = .06) and had greater 1- to 21-d litter gains and 21- to 28-d consumption (P = .05) than those fed 17.5% CP. For postweaning performance, feed efficiency values were lowest and mortality was highest for litters fed 20.5% CP. When litters were switched to different diets after weaning, mortality tended to be higher (P = .07) for animals that were fed 20.5% CP before weaning. The month of experiment effect did not influence any of the characters studied (P greater than .05). Parity number was important for percentage fertility, percentage born alive, litter birth weight and doe weight at 21 and 28 d (P less than .05). Does at first parity showed the poorest performance for all traits (except percentage fertility). Fertility fluctuated throughout the first four parities and then steadily declined. Does fed 20.5% CP had greater apparent dry matter and acid detergent fiber digestibilities and N intakes (P less than .05) and retained 90% more N during lactation (P = .22) than does fed 17.5% CP. Milk production and CP digestibility did not differ between the two diets tested.(ABSTRACT TRUNCATED AT 400 WORDS)     

Role of caeca in the nitrogen nutrition of the chicken fed on a moderate protein diet or a low rotein diet plus urea

1. A study was carried out to investigate whether the back‐flow of urine into the caeca benefits the nitrogen economy of adult cockerels fed on a diet containing 100 g protein/kg and when dietary urea is absorbed, excreted into urine and utilised.

2. No significant effects of colostomy on nitrogen utilisation were observed in chickens fed on 100 g/kg protein diet, whereas colostomy was highly effective in decreasing it in chickens on a diet containing 50 g protein/kg plus urea (P< 0.05).

3. Nitrogen utilisation in conventional birds was significantly less when a diet of moderate protein content was fed than when a low protein diet plus urea was fed, but the opposite effect was seen with colostomised birds (P <0.05).

4. Colostomy increased urea excretion (nitrogen/kg body weight/day) from 4 to 9 mg in chickens fed on the moderate protein diet, but greatly, from 45 to 182 mg, in those fed on the low protein diet plus urea (P<0.05).

5. Blood urea concentration increased by about 20 mg per 100 ml in 3 h, a value which was maintained up to 6 h but which returned to the prefeeding concentration at 24 h; both control and colostomised chickens on the low protein diet plus urea responded similarly.

6. After feeding urea, half the daily excretion of urea was observed to occur within 6 and 9 h, respectively, in control and colostomised chickens. The excretion rate of urea (the peak occurred during 3.6 h in the colostomised and during 1.3 h in the control) was at least twice as high in colostomised as in normal birds 3 h postfeeding.

7. It is concluded that the caeca play a useful role in nitrogen economy of the protein‐depleted chicken, but not in the protein‐adequate chicken and that dietary urea degradation in the caeca occurs from 3 h after feeding.     

棕榈粕对肉兔生长性能及养分利用率的影响

文章旨在研究日粮添加棕榈粕对肉兔生长性能及养分利用率的影响。本研究开展了两个试验。试验1选择20只50 d的肉兔,平均体重为(1.55±0.18)kg,随机分为两组,每组10只用于代谢试验。试验2选择35 d断奶肉兔96只,随机分为两组,每组4个重复,每个重复12只,对照组饲喂基础日粮,试验组用20%的棕榈粕等量替代基础日粮,试验由断奶当天到63 d。结果显示:试验日粮较基础日粮显著提高了干物质、有机物和粗蛋白质的表观消化系数(P <0.05),显著提高了粗脂肪、中性洗涤纤维和酸性洗涤纤维的表观消化系数(P <0.05)。日粮添加棕榈粕显著提高了半纤维素和纤维素的表观消化系数(P <0.05),对酸不溶蛋白的表观消化系数无显著影响(P> 0.05)。与基础日粮组相比,棕榈粕组日增重显著降低了4.8%(P <0.05)。日粮添加20%棕榈粕对粪中产气荚膜杆菌的数量无显著影响(P> 0.05),但自由采食条件下,基础日粮组和棕榈粕组均显著提高了粪中产气荚膜杆菌的含量(P <0.05)。结论 :棕榈粕对肉兔是一种较好的纤维、蛋白质和脂肪来源,可以代替部分日粮中的部分苜蓿草粉。日粮添加20%棕榈粕可以提高肉兔的生长性能,对饲料消化率无负面影响。     

Effects of rumen-protected methionine in a low protein ration on metabolic traits and performance of early lactating cows as opposed to rations with elevated crude protein content

A 5‐week experiment with 24 multiparous early lactating Brown Swiss cows was conducted to investigate the effects of supplementary rumen‐protected methionine in conjunction with dietary protein reduction on metabolism and performance after 1 week of control measurement. Three rations containing 175, 150 and 125 g of crude protein/kg feed dry matter were supplemented with methionine. The fourth ration, also only containing 125 g of crude protein/kg dry matter, remained unsupplemented. The four treatment groups had a similar metabolic supply of other essential amino acids, protein and energy, as calculated by various approaches. The two low protein rations were, however, slightly deficient in ruminally degraded protein. Treatment effects remained low on feed intake, forage meal pattern, milk yield and fat as well as lactose content. In contrast, the content and yield of milk protein significantly declined only in the unsupplemented low protein ration relative to the initial value. Compared with this ration, the decline in milk protein yield was clearly delayed in the supplemented low protein ration. Blood plasma methionine tended to be reduced without supplementation and to be increased with additional methionine. Supplementation of methionine reduced other plasma amino acids. Plasma insulin, glucose, lactate, ketone bodies and aspartate amino transferase activity indicated a certain liver stress and a somewhat elevated energy requirement with high and particularly with low protein content (when unsupplemented). Methionine improved metabolic protein utilization, followed by the lowest plasma, urine and milk urea levels in the supplemented low protein diet. In conclusion, no major adverse effects were assessed under the conditions tested. Supplementation of methionine may nevertheless be useful in rations with particularly low protein content fed to early lactating cows in order to prevent negative long‐term effects which were only visible here as trends.     

猪不同生长阶段连续使用赖氨酸强化低蛋白日粮的效果研究

选取40头25kg左右的仔猪,随机分为2组,探讨在其25～50kg、50～80kg和80～100kg3 个生长阶段连续使用低蛋白日粮,并添加赖氨酸对其各阶段生长性能的影响。结果表明,将日粮粗蛋白含量降低2个百分点,补加适量的赖氨酸,其第一阶段和第二阶段的日增重均低于对照组,料重比均高于对照组。但差异不显著(P>0.05)。第三阶段的日增重与对照组接近,料重比略高于对照组,但差异仍不显著(P>0.05)。     

Effect of supplementation with urea,blood meal,and rumen-protected methionine on growth performance of Holstein heifers grazing kikuyu pasture

Supplements with corn grain, molasses cane, and different nitrogen sources were evaluated in 16 growing Hosltein heifers [227 ± 33 kg body weight (BW)] grazing kikuyu (Pennisetum clandestinum) pasture in a 10-ha sward (rotational grazing with electric fences) during 90 days in the summer season. The nitrogen sources were urea (U); urea and blood meal (U + BM); and urea, blood meal, and rumen-protected methionine (U + BM + RPM). Heifers were randomly assigned to four experimental supplements defined as follows: control (no supplementation), U, U + BM, and U + BM + RPM. Two kilograms (as fed) of supplement was offered daily. The final BW of heifers fed U + BM + RPM was higher (P < 0.05) than heifers not supplemented. The total and average daily weight gain of heifers supplemented with U + BM + RPM were higher than heifers not supplemented or supplemented with U and U + BM (P < 0.05). The average daily gain of heifers supplemented with U and U + BM were higher than heifers not supplemented (P < 0.05). Grass intake was not affected by supplementation, but total dry matter intake was increased by supplements with U, U + BM, and U + BM + RPM (P < 0.05). Feed conversion was improved by U + BM + RPM (P < 0.05). Total tract digestion was not affected by supplements. Blood urea nitrogen concentrations of heifers supplemented with U, U + BM, and U + BM + RPM were higher than heifers not supplemented (P < 0.05). It is concluded that supplements with U + BM + RPM improved growth performance and feed conversion in heifers grazing kikuyu pasture.     

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 performance responses to increased tryptophan supplementation in growing barrows fed three different very low crude protein corn and soybean meal-based diets fortified with essential amino acids

Seventy-five individually fed barrows averaging 35 kg were used in a series of three experiments for 6-week growth assays (25 barrows each) to determine the effects of l -tryptophan (Trp) supplementation on growth performance and to establish the lower limits of dietary crude protein (CP) levels. Corn and soybean meal (SBM)-based diets containing 9% (Experiment 1), 10% (Experiment 2), and 11% CP (Experiment 3) fortified with deficient essential amino acids (AAs) except Trp were used as basal diets for each experiment. The experimental diets were supplemented with 0.00%, 0.02%, 0.04%, or 0.06% Trp. A 16% CP corn–SBM-based diet was set as a positive control in each experiment, and feed and water were provided ad libitum. Average daily gain and gain-to-feed ratio improved quadratically (P < 0.05) as supplemented Trp increased in the 9% and 10% CP group, although these positive effects were not observed in the 11% CP group. Because the maximum performance parameters in 9%, 10%, and 11% CP groups were not different from that of the 16% CP positive control group, the marginally reduced level of dietary CP without growth performance being affected appears to be around 9% at most. A potential reduction of nitrogen intake was clearly indicated.     

Intestinal metabolism of weaned piglets fed a typical United States or European diet with or without supplementation of tributyrin and lactitol

The aim of the study was to investigate the effects of supplementation of a microencapsulated blend of tributyrin and lactitol (TL) to a standard European (EU) diet without antibiotic growth promoters on intestinal metabolism and mucosa development of weaned piglets and to compare it with a standard US diet containing animal proteins, zinc oxide, copper sulfate, and carbadox. Ninety piglets weaned at 21 d were divided into 3 dietary groups consisting of 5 replicates each: 1) US diet supplemented with 55 mg/kg of carbadox, and 2.5% each of plasma proteins and spray-dried blood cells in the first phase, 3,055 mg/kg of Zn in the first and second phases, and 180 mg/kg of Cu in the third phase; 2) EU diet based on vegetable proteins and no antibiotics; and 3) the same EU diet supplemented with 3,000 mg/kg of microencapsulated TL. The study was divided into 3 phases: 0 to 7, 8 to 21, and 22 to 35 d. On d 7, 21, and 35, animals were weighed, and feed consumption and efficiency were determined. On d 14 and 35, one pig per pen was killed, and the intestinal contents and mucosa from the proximal, middle, distal jejunum and the ileum were sampled. Intestinal wall sections were fixed for histological analysis, and intestinal content was used for VFA, ammonia, and polyamine analysis. Throughout the study (d 0 to 35), the US diet had greater ADG and ADFI than the EU diet (P < 0.05). The EU diet supplemented with TL tended to have 11% greater ADG (P = 0.17). Feeding the EU diet caused a reduction in proximal and middle jejunum villi length by 10% (P < 0.05) and an increase in crypt size in proximal jejunum (P < 0.05) compared with the US diet, probably due to an increased rate of cell loss and crypt cell production. The TL supplementation resulted in longer villi along the jejunum and less deep crypts in the proximal jejunum (+15.9 and -8.9%, respectively; P < 0.05) than the unsupplemented EU diet. The TL diet increased the concentrations of cadaverine and putrescine in the small intestine (P < 0.05) and seemed to increase cadaverine, histamine, putrescine, and spermine in the large intestine by 1.5- to 10-fold compared with the US or EU diet. In conclusion, although the US diet had a greater effect on growth performance and mucosal trophic status than the EU diets, the supplementation with slowly released TL seemed to be an effective tool to partially overcome the adverse effects of vegetable protein diets.     

蛋氨酸形式和饲粮蛋白质水平对黄羽肉鸡生产性能的影响

选用1日龄快长型岭南黄羽肉鸡公雏1500只,随机分为5个处理,每处理6个重复,每重复50只鸡,分别饲喂以下5种饲粮:正常蛋白质加Alimet饲粮(处理1)、正常蛋白质加DLM饲粮(处理2)、低蛋白质(比正常水平降低约1.5个百分点)加Alimet饲粮(处理3)、低蛋白质加DLM组饲粮(处理4)、正常蛋白质未加蛋氨酸饲粮(处理5)。结果表明,在等摩尔量有效成分添加基础上,Alimet比DLM更有利于提高黄羽肉鸡生长性能,降低饲料成本和死亡率;饲粮蛋白质水平和蛋氨酸形式对43～63日龄和0～63日龄黄羽肉鸡生长性能的影响存在互作效应,表现为在正常蛋白质水平时添加Alimet对黄羽肉鸡生长性能的改善效果优于DLM,且更有利于降低饲料成本,而在低蛋白质水平时添加Alimet和DLM则无显著差异;在本试验条件下,降低饲粮蛋白质水平会对黄羽肉鸡的生长性能、饲料成本和成活率产生不利影响。     

Effect of protein level and flushing method on the reproductive performance of rabbits

Fifty‐five New Zealand white × California cross‐bred female rabbits were used to study the effect of protein level and flushing method on the reproductive performance of rabbits. The treatments consisted of three protein diets (18, 20 and 24% crude protein (CP)) and three flushing methods in a 3 × 3 factorial design. The flushing methods consisted of (i) flushing multiparous does and feeding a 16% CP diet during pregnancy; (ii) flushing multiparous does and feeding an 18% CP diet during pregnancy; and (iii) flushing nulliparous does and feeding an 18% CP diet during pregnancy. Flushing rabbits with different levels of protein did not significantly affect gestation length, litter size and mortality of kits. The trend showed an increase in litter weight with the increase in protein level from 18 to 24%. However, kits from does flushed with 24% CP had a higher individual kit weight gain than those on 20 and 18% CP. Gestation length, total litter size at birth, number of kits dead at birth and number of kits dead at 21 days post‐partum were not affected by flushing methods. There was, however, a significant effect of the flushing method on the number of kits alive at birth, and 7, 14 and 21 days post‐partum. Nulliparous does flushed and maintained on 18% CP during pregnancy had a significantly higher number of kits alive at birth, and 7, 14 and 21 days post‐partum. Litter weight was significantly higher for nulliparous does at 7, 14 and 21 days compared with that of multiparous does flushed and placed on a 16 or 18% CP diet during pregnancy. Protein intake during pregnancy had a significant effect on litter birthweight. Nulliparous and multiparous does flushed and placed on an 18% CP diet during pregnancy had a significantly higher litter birthweight than multiparous does flushed and placed on a 16% CP diet during pregnancy. The effect of protein level during pregnancy on the number of kits alive at birth was not significant. There was no interaction between protein level and flushing method on the reproductive performance of rabbits.     

Effects of feed and water restriction and receiving diet crude protein on feeder pig performance

Two experiments were conducted to determine the effects of feed and water restriction and receiving diet crude protein level on feeder pig performance. In Exp. 1, a total of 239 commingled feeder pigs transported over 1,000 km were used in two trials. Pigs given access to feed and water (FW) at the market weighed more (P less than .0001) following marketing and transport than pigs given no feed and water (N) for the comparable 25-h market period (20.7 vs 19.6 kg). While FW pigs weighed less (P less than .02) than N pigs at the conclusion of the trials (93.9 vs 96.6 kg), there was no effect (P greater than .1) on overall average daily gain (.32 vs .35). There were no effects of receiving diets containing 12, 16 or 20% crude protein on daily gain, daily feed intake or feed efficiency for the overall growing-finishing period. Scour scores on d 8, 9, 10, 11, 13 and 14 post-arrival increased (P less than .01) with increased levels of protein in the receiving diets. In Exp. 2, a total of 360 crossbred feeder pigs was mixed and moved from a nursery to grower-finisher facilities in three trials, given feed and water access immediately (FWG) or denied access for 44 h (NG). At the end of the 44-h period, FWG pigs were heavier than NG pigs (P less than .0001; 18.3 vs 16.7 kg). There was no treatment effect on overall pig weight, daily gain or feed efficiency.     

在生长獭兔日粮中添加尿素的试验研究

选用生长獭兔２７只，随机分为３组，分别饲喂加入０％、１．０％和２．０％尿素的日粮，研究对试兔增重、饲料转化率、屠宰率及肉和毛皮品质的影响。试验结果表明：１０％、２０％尿素组的试兔增重分别比对照组提高２．８３～９．２１％，随尿素添加量的增加，每天每只兔的采食量稍增加，蛋白效率比以１．０％尿素组最好。日粮中添加１．０％、２．０％的尿素对生长獭兔的屠宰率、肉及毛皮质量均无不良影响，１．０％尿素组的单位增重成本比对照组降低１．１９％。因此，生长獭兔日粮中添加１．０％尿素是可行的     

Effects of amino acids supplementation in low crude protein diets on growth performance,carcass traits and serum parameters in finishing gilts

This study investigated the effects of amino acids (AA) supplementation in low crude protein (CP) diets on growth performance and carcass characteristics in finishing gilts. One hundred and eighty gilts (59.1 ± 5.1 kg) were randomly allotted to one of five diets which consisted of a high CP (15.6%) diet or four low CP (11.6%) diets for 50 days. The low CP diets were supplemented with lysine + threonine + methionine (LCM), LCM + tryptophan (LCT), LCT + valine (LCV) or LCV + isoleucine (LCI), respectively. Gilts were housed at six pigs per pen with six pens per treatment. At the end of the 50‐day experiment, 30 gilts (one pig per pen) with average body weight (BW) of 98 kg were killed to evaluate carcass traits. The pigs fed the diet supplemented with LCV obtained the highest average daily gain (ADG), which was higher than those of pigs fed the diet supplemented with LCM (P < 0.05). Dietary supplementation with tryptophan, valine and isoleucine in low CP diets increased ADG (linear and quadratic effect, P < 0.05), serum levels of valine (quadratic effect, P < 0.05) and isoleucine (linear and quadratic effect, P < 0.05) and immunoglobulin G (IgG) and IgA (linear and quadratic effect, P < 0.05) in finishing gilts. © 2016 Japanese Society of Animal Science     

Inhibitory effect of penicillin on caecal urease activity in chickens fed on a low protein diet plus urea

1. The effects of dietary penicillin on the urease activities of small intestine, large intestine, caecum and their contents, liver and kidney in chickens fed a diet containing 5 g/kg protein plus urea were examined.

2. About 0.88 of the total urease activity determined was observed in intestinal contents, of which 0.95 of the activity was accounted for by caecal contents, 0.05 by colo‐rectal contents and none by small intestinal contents. Intestinal tissues (caecum included), liver and kidney accounted for 0.03, 0.06 and 0.02, respectively, of the total urease activity.

3. Dietary penicillin decreased urease activity to 0.17 in caecal contents and to 0.05 in colo‐rectal contents of the corresponding control values (P< 0.01). The urease activity of caecal tissue was lowered by penicillin to half that of control activity (P < 0.05) but none of the activities of other tissues were affected.

4. It is concluded that, even when the urease activity is stimulated by dietary urea, 20 mg/kg dietary penicillin can strikingly lower it in the caecum, where most of the urease activity in the chicken body is to be found.