The potential of milk allantoin as an index ofmicrobial protein supply was evaluated in two experiments conducted with 12 multiparous Holstein-Friesian dairy cows that examined the effects of altering the supply of metabolizable energy (ME) and fermentable metabolizable energy (FME). In the first experiment, late lactation cows received a 14·3 kg dry matter (DM) per day basal diet consisting of (g/kg DM) chopped barley straw (415), soya-bean meal (322), molassed sugar-beet pulp (197), molasses (33), urea (17) and a vitamin and mineral supplement (17) for a 21-day co-variance period. During four 16-day periods, six treatments were allocated randomly to cows, consisting of potato starch (1, 2 or 3 kg DM per day) or fat supplements (0·64, 1·27 or 1·91 kg DM per day). In the second experiment, early lactation cows received 40 kg/day (fresh weight, (FW)) of silage (307 g/kg toluene-corrected dry matter, 149 g/kg DM crude protein and 11·6 MJ/kg ME). During three 21-day periods, four treatments were evaluated consisting of supplements of either 4·1 (LI) or 8·1 (12) kg fresh weight per day of a low fat concentrate (acid hydrolysis ether extract (AHEE) 45 g/kg DM) or 3·8 (HI) or 7·5 (H2) kg fresh weight per day of a high fat concentrate (AHEE 110 g/kg DM). Both experiments showed individual cow milk allantoin concentration or excretion to be poorly correlated with urinary purine derivative excretion or calculated microbial protein supply. Use of treatment mean (TM) values dramatically improved these relationships. For pooled TM (no. = 10) values from both experiments, close relationships existed between milk allantoin excretion and concentration with milk yield (r values 0·991 and 0·883, respectively). Auto-correlation with milk yield appeared to account for milk allantoin excretion and concentration being highly correlated with urinary purine derivative excretion (r values 0·908 and 0·934, respectively) and calculated microbial protein supply (r values 0·938 and 0·945, respectively). Current experimental data indicates that measurement of milk allantoin is not a reliable indicator of microbial protein supply for individual cows.

The objective of this study was to evaluate the influence of calving season on the interactions among reproductive disorders prior to conception and their effect on subsequent reproductive performance in dairy cows. Data from 3170 lactations of Holstein-Friesian cows that subsequently conceived were analysed by means of path analysis techniques. The cows were from nine commercial dairy herds in north-eastern Spain. Lactation incidence rates for retained placenta, metritis, ovarian cysts and repeat breeding (more than four artificial inseminations per conception) were 6·4, 3·7, 5·4 and 7·9%, respectively, and there were no differences between warm (May to September) and cool (October to April) calving seasons. However, our data show that calving season influenced the interrelationships among reproductive traits. Lactation number was not related to any of the path model variables for cows calving in cool seasons and retained placenta did not directly influence ovarian cysts or repeat breeding. In contrast, older cows that calved during warm seasons showed an increased risk of experiencing retained placenta, ovarian cysts and more days open; retained placenta was a direct risk factor for ovarian cysts and repeat breeding. Our data indicated that a cool season decreased interactions among reproductive disorders of dairy cows. Cows that calved in a cool environment could more effectively cope with reproductive disorders prior to conception and this fact was mainly observed in older cows.

Two experiments were carried out with Holstein Friesian early lactation cows of high genetic merit to evaluate the effects on intake and milk production when the animals were offered a concentrate supplement either within a complete diet (CD) or separately from grass silage (separate feeding, SF) through a computerized out-of-parlour feeder system. This system offered the daily allowance of concentrates in four × 6h time windows and the cows could choose to have several accesses to concentrate within each time window. In experiment 1 22 first lactation cows were used in a two-treatment change-over design with 10-week periods, while in experiment 2 48 animals (28 in lactation 1 and 20 in lactation 2 or over) were used in a continuous design with an average of 80 days on experiment. In both experiments the diets on the CD treatment were offered ad libitum with a concentrate proportion of 0·61 in total dry-matter (DM) intake while on the SF treatment grass silage was offered ad libitum and the allowance of concentrate was made equal to the mean concentrate intake of the CD treatment during the previous week. All the animals in experiment 2 were turned out to pasture on 5 April for 120 days to examine the residual treatment effects. Twelve mid to late lactation cows and eight rumen-fistulated beef steers were also used to evaluate the effects of the two feeding methods on nutrient utilization and rumen fermentation, respectively. In the latter two trials, the concentrate on the SF treatment was also offered four times daily but in a conventional trough-feeding arrangement.

In experiment 1 both silage and total DM intakes were similar between the two treatments. However, in experiment 2 silage DM intake was significantly increased fP < 0·002) and total DM intake tended to be higher (P > 0·05) with the SF treatment. Feeding the complete diet tended to increase milk yield in both experiments (P = 0·057 in experiment 1), but significantly reduced both the concentration and yield of fat in experiment 2 (P < 0·05). There were no significant treatment effects on the concentration of protein in either experiment, nevertheless in experiment 1 the yield of protein was significantly increased (P < 0·05) with the CD treatment. When the animals in experiment 2 were turned out to pasture, there were no significant residual effects of the indoor feeding treatment on milk production, or yield of fat or protein. However, the concentrations of fat and protein in milk, obtained during the first 60 days on pasture, were significantly higher for the cows offered the concentrate separate from silage during the indoor feeding treatment. The nutrient utilization and rumen fermentation trials indicated no significant difference between the CD and SF treatments in either whole tract apparent digestibility of nutrients (DM, organic matter, energy or nitrogen (N)) or rumen fermentation characteristics (pH, ammonia-N concentration, total volatile fatty acids (VFAs), or molar proportion of each individual VFA in the rumen liquor). It is concluded that feeding the concentrate within a complete diet rather than separately from the silage had no significant effects on total DM intake, milk production, nutrient digestion or rumen fermentation.

Data comprised information on herd life from two different sources: actual lifespan and type data. The optimum way of predicting breeding values (BVs) for herd life from both these sources is a multivariate best linear unbiased predictor (BLUP) analysis of lifespan and the linear type traits most closely related to it. To reduce computing requirements, we suggest a bivariate BLUP analysis, where the direct information is lifespan, measured in lactations and the indirect information is a phenotypic index of type traits weighted by their economic values. Such an index is shown to be almost as efficient as using the individual traits.

Genetic correlations between functional lifespan and the linear type traits were estimated, and based on these foot angle (rg = 0·22) udder depth (rg = 0·24) and teat length (rg = -0·44) were chosen to predict herd life. Breeding values for herd life were predicted in a BLUP analysis for around 500 000 heifers. The traits were lifespan and the phenotype index offoot angle, udder depth and teat length. For bulls with a minimum of 10 daughters BVs ranged from -0·9 lactations to +1·0 lactations, indicating a difference of approximately one lactation between the daughters of extreme bulls. For sires with at least 50 daughter records for lifespan, type information contributed little to the accuracy of herd life BVs.

The effect of pregnancy on the fat and protein contents of milk was studied on a 414-lactation sample. One hundred and forty-nine lactations of non-pregnant cows managed under identical conditions served as controls. The difference between individual fat or protein contents of each pregnant animal and the mean corresponding values in controls was computed weekly from the week of conception. The effect of pregnancy on fat and protein concentrations began to be significant from the 20th week of pregnancy, regardless of the week of conception. It was higher in the Friesian breed than in Holstein or Montbeliarde cows. In Holstein and Montbeliarde cows, the effect of pregnancy was higher in high producing multiparous cows (+2·8 and +2·9 g/kg for fat and protein concentrations, respectively, at the 29th pregnancy week) than in primiparous or low producing multiparous cows (+2·0 and +1·4 g/kg, for fat and protein concentration, respectively). In each of these three lactation groups (Friesian, high producing multiparous Holstein and Montbeliarde cows, other Holstein and Montbeliarde cows) the following linear model

was fitted, where Y is the difference between fat or protein concentration of pregnant and non pregnant cows at a given stage (week), Pw is the pregnancy week, and a and b are parameters. This increase in milk fat and protein concentrations in late pregnancy cannot compensate the concomitant decrease in milk yield, so that fat and protein yield decreased in the same manner as milk yield during pregnancy (-77 glday and -68 glday at the 29th week of pregnancy, for fat and protein yield, respectively).

Bovine blood neutrophil oxidative burst activity, the total leukocyte count and its differentiation, as well as progesterone, glucose and cortisol levels were studied on 10 cows from 1 week prior to calving until 8 weeks after parturition.

From day –7 before parturition a decrease in the metabolic oxidative burst activity of neutrophils was observed, reaching the lowest value 3 days after calving (0·28 (s.e. 0·06) nmol/l H2O2 per min 106 neutrophils) (P <0·01). Thereafter, values increased with a maximum of activity 26 days after parturition (0·57 (s.e. 0·05) nmol/H202 per min per 106 neutrophils). At the end of the experiment the neutrophils H2O2-productionwas comparable to values observed on day–7.

The maximum total leukocyte count was observed on the day of parturition (8, 108 (s.e. 370) leukocytes per /A blood) (P <0·01) returning to normal levels about 3 weeks after calving. Lymphocytes and neutrophils showed a trend analogous to that of the total leukocytes. Eosinophils and monocytes did not change during the entire period. With the rapid increase of circulating neutrophils observed on the calving day, a marked left shift was observed with a maximum number of immature neutrophils (48·6%) observed on day +3 (1477 (s.e. 242) immature neutrophils per fjl blood) (P <0·01), reaching normal values about 4 weeks after parturition.

A significant increase (F < 0·01) of plasma glucose was found on the day of parturition (91·4 (s.e. 6·8) mg per 100 ml plasma), while the levels of cortisol reached their maximum 3 days after calving (22·05 (s.e. 8·46) nglml plasma).

Progesterone levels averaged 4·07 (s.e. 1·21) jigll 7 days before calving, declining precipitously to 0·06 (s.e. 0·45) Hg/l 3 days after calving (F < 0·01), remaining very low for a period of about 3 weeks. Minimum and maximum anoestrus post-partum were 22 and 57 days, respectively.

Despite great hormonal variation observed in the peripartum period, no significant correlation was found between measured hormones and the oxidative burst activity of neutrophils.

A comparison was made between fattening systems with Belgian Blue bulls of the double-muscle type, in order to assess the reponse in terms of compensatory growth when the bulls were grazed at a high stocking rate. Two groups of eight bulls were grazed on Lolium perenne and Trifolium repens pasture during an initial period of 135 days (period I). One group grazed at a stocking rate of six animals per ha allowing for normal growth at pasture (NGP); the other group grazed at stocking rate of 10 animals per ha (low growth at pasture, LGP). Both groups were then finished indoors (period II) with a concentrate based on dried sugar-beet pulp. Eight control bulls were also fattened indoors on the concentrate diet during periods I and II (CG). The bulls were slaughtered according to similar finishing fattening state. Live-weight gains were 1·47, 1·10 and 0·52 kg/day (P < 0·002) during period I in CG, NGP and LGP groups respectively. Corresponding live-weight gains during period II were 1·22, 1·37 and 1·50 kg/day (P > 0·05). The LGP group had lower food conversion ratios, slaughter weights (P < 0·05) and dressing proportions (P < 0·01). The meat from the grazed bulls had lower cooking losses (P < 0·05) and tended to have lower drip losses (P > 0·05) and higher tenderness (P > 0·05). It also had a higher cholesterol (P < 0·05) content. Large differences were observed in the fatty acid composition according to fat location (subcutaneous, intermuscular or intramuscular). The proportions of mono and polyunsaturated acids were increased in the fats of the animals previously grazed (P > 0·05, P < 0·05).

Five ruminallyfistulatedAngus steers (360 (s.e. 15·4) kg) were givenfood to maintain body weight constant: maize silage (TO) at 0·6 kg dry matter (DM) per 100 kg body weight twice a day. After a 15-day adaptation period they were infused continuously (I) for 96 h, with a solution of NaH14CO3 at a rate of 7 to 8 micro Curies (μCi) per h. On the last 2 days of infusion 30 g (Tl) and 60 g (T2) urea, respectively, were placed in the rumen at the end of the morning meal. Spot samples of urine (250 ml) were taken before and 5 h after the morning meal and after at least 24 h of infusion. Thereafter, animals continued with TO for one additional week, in which they were prepared with catheters inserted in salivary ducts and infused for 48 h, as previously described. Eighteen pairs of spot samples of urine and saliva were takenfrom three of thefive steers (369 (s.e. 20·7) kg), over a period of 5 h, after at least 24 h infusion (six per animal). Rate of carbon dioxide (CO2) production was estimated as the ratio USA (specific activity of CO2)from which energy expenditure was calculated (22 kj/l CO2). Silage composition, in situ degradability and ruminal ammonia and pH were measured. In situ degradability in thefirst 6 h was 200 g/kg and ruminal ammonia was in the range of 20·6 to 39·6 mg/l. Ammonia increased rapidly to 394·2 (T1) and 673·9 mg/l (T2) 1 h after addition of urea into the rumen but in 6 h in situ degradability was unchanged. Ruminal ammonia decreased linearly at rates (mgll per h) of89·3 in Tl (R2 = 0·57, s.d. = 21·5) and 151·6 in T2 (R2 = 0·81, s.d. = 23·3). Animal energy expenditure rates were not affected (P > 0·05) by treatment (TO = 15·6, Tl = 15·6 and T2 = 15·8 kj/h per M075). There was no difference (P > 0·05) in CO2 production rate (mllh per kg M0·75) determined from the SA of CO2 from urine (604) or saliva (630) samples. It was concluded that the energy cost associated with detoxification of the excess of ruminal ammonia was of minor importance in terms of total animal energy expenditure and that estimations ofC02 ratesfromsamples ofurine or saliva are comparable.

A selection index which incorporates estimated breeding values of traits recorded in the United Kingdom pedigree beef cattle breeds is described. The breeding objective is made up of commercial carcass, calving difficulty and gestation length traits. Economic values for these breeding objective traits are summarized from related studies, while partial genetic regression estimates of breeding objective traits on recorded traits are derived mainly from the literature.

The selection index is described in terms of the reduction in expected genetic response from selection on the index when individual recorded traits are omitted and the expected genetic responses in breeding objective traits with selection on the index under the assumption of mass selection. Failure to record all calving traits (birth weight, calving difficulty and gestation length) resulted in a reduction in expected economic response to selection of 8% from the situation where both calving traits and production traits (400-day weight, ultrasonic fat and muscle depths, and muscling score) are recorded. With a few stated exceptions, the index is relatively robust to errors in estimates of individual parameters.

It is suggested that the total index be used to assist commercial bull and semen buyers in their selection decisions but that two sub-indices for calving and production traits also be published to allow buyers to adjust emphasis on the two groups of traits depending on their individual production circumstances.

With the objective of studying the response patterns of two biotypes of different body (structural) size to stocking rate (SR) in terms of individual growth rate (ADG), meat production per ha (PROD) and backfat thickness (BFT) under grazing conditions, 64 steers of two biotypes of the Angus breed of different body size were used: small-sized (SB: frame score of 1·3 (s.d. 0·7)) and medium-sized (MB: 2·9 (s.d. 0·6)). Four levels of SR were applied (1·8, 2·3, 2·8 and 3·3 steers per ha). The experiment lasted 241 days (April to December). Animals were weighed every 14 days, forage availability (FA) was estimated on four occasions and BFT was recorded at the end of the experiment (between 12th and 13th ribs). There were no differences between biotypes in ADG. SB tended to be earlier maturing showing higher BFT (4·39 v. 3·97 mm; P = 0·22). ADG was affected by SR and was higher at lower SR (0·612, 0·529, 0·414 and 0·375 kg/day, for 1·8, 2·3, 2·8 and 3·3 steers per ha, respectively). Individual average daily gain of the MB was more variable across the seasons of the year. None of the variables showed effects of the biotype × SR interaction but differences in ADG between biotypes as a function of the SR were observed as a trend (P = 0·29). Despite the difference in frame score between biotypes it was not possible to associate it with consistent differences in the response variables. Individual productivity (potential) of MB was not reflected in a greater productivity per surface unit. The data from this experiment do not allow the choice of a particular biotype in order to optimize the productivity of the pastoral production systems.

At an experimental farm, five camels and five cows were each given a similar basal diet for 6 months. They received oral trace element supplementation for 3 months (day 22 to 112) which included zinc, copper, selenium, manganese, iodine and cobalt and corresponded to twice the daily requirement generally recommended for cows. Plasma selenium concentrations were significantly lower in the camels (20 (s.e. 2) mg/l) compared with the cows (33 (s.e. 2) μg/l). The mineral supplementation induced a large increase in the plasma selenium concentration in the camels which reached 200 (s.e. 35) fig/l. In the cows, the increase was much smaller and did not go beyond 65 (s.e. 8) μg/l. Before supplementation the red blood cell glutathione peroxidase activity was similar in the camel and the cow varying between 4000 and 6000 IU per 100 g haemoglobin. In both species, this activity increased with mineral supplementation and remained very high even when mineral supplementation was stopped. The results suggested that selenium metabolism in camels is different from that in the cows.

During three journeys of 15 h in a lorry and two sets of experiments in a trailer, the relative importance of ambient noise and vehicular motion were assessed by measurements of salivary cortisol concentration, heart rate and behaviour. Mean sound levels in the lorry were approximately 96 dbA with occasional episodes at 103 dbA. Vehicular motion was assessed in terms of numbers and magnitude of acceleration events registered by a triaxial accelerometer. The three lorry journeys showed, respectively, that heart rate was correlated with vehicular motion when sheep were loosely stocked (0·41 m2 per sheep) but not when they were tightly stocked (0·28 m2 per sheep); that heart rate sometimes tended to increase when ambient sound was greater and that the effect of sound was not as consistent as that of vehicular motion. In the first trailer experiment, salivary cortisol response was the same whether sheep confined in a quiet stationary trailer (60 dbA) were or were not exposed to extra noise (90 dbA) while heart rate was higher in the former condition. In the second trailer experiment when the trailer was being towed on public roads with or without extra noise (92·3 and 100·5 dbA respectively), heart rate and salivary cortisol concentration were both elevated compared with control sheep in a pen but the extra noise had no consistent effect. The sheep showed no orientation away from the noise source, nor was there any difference in their expression of a behaviour (standing with the head below the level of the shoulders) which could indicate discomfort. Hence vehicular motion can result in poor welfare in sheep, especially at loose stocking density but ambient noise was not found to have a consistent effect.

Three experiments investigated differences between sheep breeds in response to supplementary feeding and very close confinement with familiar and unfamiliar sheep; and differences between individuals in response to a taming procedure prior to transport in a trailer. The first two experiments were with a mixed flock of Clun Forest lambs and crossbred lambs from Orkney. An initial tendency to feed with others of the same breed diminished over 3 weeks. Responses of heart rate and salivary cortisol concentration when one sheep (the visitor) was penned in an enclosure of 1 m2 with three other sheep of the same or the other breed (the trio group), did not depend on whether the visitor and the trio group were of the same or different breed. Clun Forest sheep showed little response while Orkney sheep showed increased heart rate and some elevation of salivary cortisol concentration. In the third experiment, 34 Beulah Speckled Face ewes were divided into two groups one of which was subjected to a taming procedure over a period of 3 weeks. Response of salivary cortisol concentration to subsequent journeys of 2h in a livestock trailer did not differ between tamed and untamed sheep. There were individual differences in the response to taming and this was correlated with the cortisol response during transport, in that those sheep which responded most to taming showed the least elevation during transport.

The dry-matter (DM) intake and growth rate in male lambs were predicted from rumen degradability characteristics, rumen DM losses at different times, neutral- or acid-detergent fibre (NDF or ADF) contents and DM apparent digestibility of roughages. Four different straws consisting of wheat, barley, oat and rice were each offered ad libitum to 24 Merino male lambs with 200 glday concentrate for 4 weeks to determine DM intake and growth rate. Apparent digestibilities of the straws were measured with three Merino male sheep. Measurements were made during the last 10 days of each 20-day period. The degradation characteristics of the straws were measured by incubating samples in nylon bags for 8, 16, 24, 48, 72 and 96 h in the rumens of three Merino male sheep fitted with rumen cannulae. The exponential model p = a + b(l - er^) was fitted to the data. Potential degradabilities of DM (defined as a + b) and apparent digestibilities of DM ranged from 530 to 679 and 440 to 560 g/kg, respectively. The mean DM intake of the straws varied from 543 to 745 glday, the digestible DM intake from 236 to 417 glday and growth rate from 17 to 95 glday. Using the degradation characteristics A, B and c in a multiple regression analysis, the correlation coefficients with DM intake and growth rate were 0·79 and 0·70, respectively. NDF and ADF were related to DM intake (i = 0·65; r = 0·64) and growth rate (r = 0·55; r = 0·56). The correlation coefficient between DM apparent digestibility and DM intake was 0·76. It is concluded that the rumen degradation characteristics have potential for predicting intake of straws and growth rate in sheep.

The study was designed to measure (i) dry-matter intake (DMT) of sheep when diets including different tannins were offered and (ii) the effect of administration of polyethylene glycol (PEG), a tannin-binding agent, on DMI of tannin-rich diets. Acacia saligna phyllodes, a potential food for sheep, quebracho powder or tannic acid were added to a concentrate diet that served as a control and were offered to 16 ewe lambs (34·6 (s.d. 3·3) kg) that is, four lambs per diet. A. saligna has high levels of tannins; quebracho is a complex mixture of phenolic compounds in which condensed tannins predominate while tannic acid is a relatively pure example of a hydrolysable tannin. Intake was measured during four periods (I to IV) of 10 days each in which PEG was offered during periods II and IV. Food and water were available ad libitum. The DMI of the concentrate diet ranged between 925 glday and 1050 glday which was higher than for the other three diets (P < 0·05). The lambs consumed approximately 600 g dry matter (DM) of the diet that included 400 g A. saligna phyllodes per kg, and 500 g DM of the diets that included 100 glkg quebracho or 150 glkg tannic acid. With the quebracho and tannic acid diets, there was a distinct increase in intake when PEG was added and a decrease without PEG. This was not so with the Acacia diet when the intake remained high in period III without PEG and increased again in period IV with PEG. Body mass of control lambs increased in all periods and the increase was greater than in the other diets (P < 0·05). With the quebracho and tannic acid diets, there was an increase in body mass when PEG was added and a decrease without PEG. With the Acacia diet, there was a decrease in body mass in period I and an increase thereafter, even without PEG in period III.

An experiment was carried out to estimate the concentration of sodium, potassium, whey albumin and total protein of normal and experimentally infected milk from meat breed ewes. Intramammary infection significantly (P > 0·0001) increased the concentration of sodium, albumin and total protein and decreased that of potassium. The potassium decrease was not statistically significant fP = 0·08). The increase in whey albumin and total protein was followed by a significant decrease in the albumin and total protein of blood serum. The increases and decreases of sodium, potassium, albumin and total protein were significantly correlated to the rise in somatic cell count and subsided 3 to 4 days after failure to isolate the infecting micro-organisms from the milk of ewes. Changes in the concentration of albumin could be used in identifying infected mammary glands or to evaluate the virulence of the infecting micro-organism.

Two experiments involving 213 finishing lambs were carried out to examine the responses in growth rate and carcass composition to the addition ofmetabolizable energy (ME) to a mixed diet in theform ofeither grass silage concentrate. In the second experiment the performance of lambs offered silage only was also compared at equal intake with the performance of lambs given mixed diets. On average the silages contained 224 g dry matter (DM) per kg; 148 g crude protein (CP) per kg DM; 86 g ammonia-nitrogen per kg total nitrogen and 723 g digestible organic matter per kg DM. Concentrates were based on barley and soya-bean meal and contained 181 g CP per DM. Responses in carcass weight gain when additional ME was added to mixed silagelconcentrate diets in theform ofgrass silage and concentrates were 9·2 and 10·2 (s.e. 0·90) gIM] respectively in experiment 1 and 9·8 and 10-(s.e. 0·33) g/MJ respectively in experiment 2, and responses in energy retention in experiment 2 were 0·34 and 0-(s.e. 0·012) MJ/M] respectively. However carcass gain and energy retention sustained by a silage only diet were only 0·67 and 0·70 respectively of those sustained by a high-concentrate diet at the same ME intake. The diet did not significantly affect body or carcass composition.

The effect of intake level during the milk-feeding period and dietary protein content during the post-weaning period on performance, weight of components of the digestive tract and carcass and non-carcass chemical composition was investigated in 28 Churra lambs. A 2 × 2 factorial design was used with two intake levels during the milk-feeding period (Lmilk: 0·9 and Hmilk: 1·5 MJ gross energy per kg M0·75 daily) and two concentrate supplements (Lprotein:barley grain and Hprotein: barley grain plus 200 g/kg fish meal) during the post-weaningperiod. After selecting an initial slaughter group of four 2-day-old lambs, 12 lambs were assigned randomly to each of two intake levels during a 4-week milk-feeding period and given food individually. Four lambs from each intake level were slaughtered at weaning (30 days old) and the remaining 16 were weaned between 30 and 49 days old (weaning period). Eight lambs from each nutritional regimen during the milk-feeding period were further divided into two equal groups and given food individually ad libitum with hay and the post-weaning concentrate, according to the experimental design until thefinal slaughter weight (20 kg) (post-weaning period). Lmitk lambs showed a capacity to grow as well as the Hmilk during the weaning and post-weaning period and there were no differences (P > 0·05) in dry-matter intake and food conversion ratio among treatments. Before weaning, the weight of the reticulo-rumen was not affected by the intake level during the milk-feeding period. The most affected component of the gastrointestinal tract was the small intestine as proportion of the digestive tract which was lower in Lmilk lambs (P < 0·05). At 20 kg live weight, the relative size of the reticulo-rumen was greater (P < 0·01) and the abomasum (P < 0·05) and large intestine (P < 0·01) were smaller in lambs which were given the Hprotein concentrate after weaning. The organic matter apparent digestibility (OMD, P < 0·05) and crude protein apparent digestibility (CPD, P < 0·05) of the post-weaning diets was greater in Lmilk lambs and the Hprotein post-weaning diet was associated with a greater dry-matter apparent digestibility, OMD and CPD when lambs were close to final slaughter weight. At 20 kg live weight, the proportion of protein in the carcass of Lmilk lambs was greater (P < 0·05) than in Hmilk lambs. The greater growth of the reticulo-rumen of the Lmilk lambs might have increased solid food intake after the milk-feeding period, led to greater CPD of post-weaning diets and had consequences in terms of carcass composition.

The rôle of nutrition in the periparturient breakdown of resistance to gastrointestinal parasitism in mature ewes was investigated. Host resistance around this period, as measured by faecal egg concentration and worm burden, was sensitive to protein supply and to a lesser extent energy supply and body condition. Resistance was significantly less in ewes bearing and suckling twin lambs than those with singles. Differences in larval intakes spanning the range likely to be experienced in practice did not appear to be important. In dual infection with Teladorsagia circumcincta and Trichostrongylus colubriformis, the breakdown of resistance occurred almost exclusively with T. circumcincta confirming previous evidence of parasite species specificity in the periparturient breakdown of resistance.

The voluntary intake and apparent digestibility of kleingrass (Panicum coloratum cv. Verde) were measured in seven periods, comprising one full year. The forage was offered twice a day ad libitum to seven rams, fitted with faeces collection bags; each experimental period was composed of 8 days for adaptation and 8 days for collection of data. The dry-matter (DM) intake (DMI) varied from 36·1 to 64·9 glkg M075, the digestible dry-matter intake (DDMI), from 17·4 to 41·9 glkg M0·75 and the in vivo dry matter apparent digestibility (DMD), from 0·471 to 0·667.

Daily samples of offered forage were taken and pooled subsamples from each of the seven periods were incubated in nylon bags in the rumen of three Hereford steers. The data were fitted to the exponential equation: p = a + b (1-e-ct) to estimate p (the proportionate loss of DM at time t of incubation); effective degradability (ED) and lag time (L) were also estimated.

The parameters obtained in situ were related to the in vivo results by simple and multiple regression. The correlation coefficients of the rate of degradation (c) and ED with DMI, DDMI and DMD were, respectively, 096 and 0·97; 0·97 and 0·96; 0·86 and 0·88. By including a, b, c and L into a multiple regression analysis, the coefficients of determination (R2) were: DMI: 0·99; DDMI: 0·99 and DMD: 0·91. Within the conditions of this study, the parameters obtained in situ were reasonable estimators of voluntary intake and apparent digestibility.