A study was carried out to compare the fermentation parameters and kinetics of digestion of a range of different foods in the rumen of two breeds of sheep (Churra and Merino). Ten mature sheep (five Churra and five Merino), each fitted with a rumen cannula, were used in this study. In situ rumen degradability of both dry matter (DM) and cell wall was greater in Churra than in Merino sheep, the breed differences being significant for most of the foods used in the study (P < 0·05). These differences were greater when the foods had a higher cell wall concentration and this could be related to differences in the ruminal environment. However, when the foods were incubated with rumen fluid their in vitro organic matter (OM) degradability was similar in both breeds. Rumen pH was higher (P < 0·05) and ammonia concentrations were lower (P < 0·05) in Churra than in Merino sheep. Rumen volatile fatty acid concentrations tended to be higher in Merino than in Churra sheep, though differences were only significant just before feeding (P < 0·05). The ratio acetate: propionate was higher in the Churra than Merino breed before and 12 h after feeding (P < 0·05). Protozoa numbers in rumen liquid were similar for both genotypes. The greater degradation of forages in the rumen of Churra sheep is discussed in relation to the possible higher activity of fibre-degrading micro-organisms and the greater buffering capacity of the rumen contents against fermentation acids, which could result in more favourable conditions for the microbial degradation of foods in the rumen.

Milk temperature was measured automatically during milking with a view to detecting silent oestrus in dairy cows. A total of 38 silent oestrous periods were studied, based mainly on ovulation and milk progesterone levels together with visual observation.

In 78·9% of silent oestrous periods, a significant increase in milk temperature amounting to a mean of 0·6 (s.e. 0·07)°C was found, and this was highly correlated (r = 0·90) with an increased body temperature. In most silent oestrous periods increases in milk and body temperatures and ovulation with milk progesterone levels below 2 μg/l were found, the oestrous cycles being characterized by typical progesterone profiles. In some cows increases in milk and body temperatures and ovulation during a silent oestrous period were associated with non-typical progesterone profiles although most of these occurred shortly after parturition.

The aim of the current study was to investigate the effects of level of feeding and level offish-meal supplementation on the carcass composition of young steers and in doing so, to assess the potential for employing near infrared reflectance spectroscopy (NIRS) in such studies. In addition to wet chemical techniques, NIRS was used to examine carcass samples from animals offered silage-based diets at one of four levels of feeding ranging from near maintenance to ad libitum and with one of four levels offish meal (0, 50,100 or 150 g/kg silage dry matter).

Wet chemical data indicated an increase in fat concentration (P < 0·001) and decrease in crude protein concentration (P < 0·05) in the fresh carcass in response to increasing level of feeding but no statistically significant effect of level of fish meal. Ash concentration was not affected significantly by either level of feeding or level of fish-meal supplementation. Ground, freeze-dried samples were scanned in the wavelength range 1100 to 2498 nm. Calibration equations for ash, fat and crude protein concentration (g/kg carcass) were derived using a modified partial least-squares regression technique. Equations were found to be superior for fat compared with those for crude protein and ash. Standard errors of calibration (g/kg carcass) and multiple correlation coefficients of 6·96 and 0·42, 6·61 and 0·95 and 4·36 and 0·61 were obtained for ash, fat and crude protein respectively with corresponding standard errors of cross validation of 7·71, 7·82 and 4·96 g/kg carcass respectively. Qualitative analysis of spectral information using multivariate techniques and difference spectra clearly showed differences in carcass composition resulting from the different levels of feeding and less so the different levels offish-meal supplementation.

It is shown, that NIRS can be used both quantitatively and qualitatively to study the effects of nutrition on carcass composition.

Shearing ewes during pregnancy frequently increases the birth weight of lambs. In housed ewes, the birth weight responses are greatest when shearing occurs relatively early in pregnancy. This study examined the effects of the timing and method of shearing on foetal growth, as measured by birth weight, in ewes at pasture. Border Leicester × Romney ewes were allocated at day 50 of pregnancy to: four ‘time of shearing’ treatments — pregnancy day 70 (P70), P100, P130 (no. = 60 for each treatment) and unshorn (no. = 34); two methods of shearing (by standard comb or cover comb); and two levels of pregnancy/rearing rank All ewes had been mated over a 14-day period and grazed pasture together throughout the trial The mid-point of lambing was 17 August.

At no time during pregnancy or lactation did ewe live weight differences between the groups exceed 4 kg. Ewes shorn by cover comb were heavier prior to lambing and during lactation than standard comb-shorn ewes. Time of shearing, method of shearing and ewe rearing rank had no effect on ewe annual greasy fleece production. There was a highly significant (P < 0·001) interaction between the effects of birth rank and time of shearing on lamb birth weight. Time of shearing did not affect birth weight of single-born lambs but birth weight of twin lambs increased with earlier maternal shearing to a maximum of 0·7 kg (per lamb) in those born to ewes shorn on P70. These results imply that shearing reduced the greater extent of maternal constraint which applies to the growth of twin v. single foetuses in utero. This selective increase in birth weights of twins achieved by early pregnancy shearing may have advantages in reducing lamb mortality.

Feeding behaviour of six sows receiving a diet with a high inclusion (500 g/kg) of sugar-beet pulp (SBP) was compared with that of six sows receiving a conventional cereal-based diet (control). The feeding rate was determined for both the rate of consumption of the daily food allowance (SBP or control diet) and of a test portion (of control diet) offered at different intervals after the daily food allowance. SBP sows consumed their daily food allowance more slowly than control sows, SBP sows also consumed the test portion more slowly than control sows, when this was offered immediately after the daily food allowance. Prolonging the time taken to eat the control diet, by presenting it in meal form, did not change the feeding rate of the test diet. Offering the test portion 2 h after the daily food allowance, increased the feeding rate of the test portion for both control and SBP sows, with a smaller but still significant treatment difference. Gastric distension appeared to be a major factor in regulating intake when feeding a diet containing SBP. The extent to which feeding rate could be used as an index of feeding motivation and the welfare consequences of using bulky diets for sows are discussed.

Employing practical-type diets containing graded levels of all-rac-α-tocopheryl acetate (0, 5, 15, 30, 45, 60, 75 or 100 mg/kg), the quantitative requirement for a-tocopherol by juvenile African catfish (Clarias gariepinus Burchell) was investigated. Diets, defined with respect to selenium, fatty acid and ascorbate inclusion, were offered for 12 weeks during which catfish grew from 10 g to 120 g. Dietary regime had no significant effect on growth (P > 0·05), although haematocrit values increased with increasing tocopherol dose above 15 mg/kg (assayed) (R2 = 0·71, P < 0·05). Tissue accretion of the vitamin increased concomitant with dietary dose (P < 0·001). Employing a colorimetric assay for thiobarbituric acid reactive substances (TBARS) it was evident that concentration ofTBARS in muscle and liver reflected tissue oxidation status, in that elevated dietary vitamin E resulted in decreased assayed TBARS (P < 0·05). By broken-line analysis the requirement for this species to suppress lipid peroxidation was estimated as 30 to 40 mg all-rac-a-tocopheryl acetate per kg dry diet and this agrees with published requirements of many fish species.

According to animal breeding theory, profit after, say, 10 generations of selection is maximized when the usually non-linear profit function is approximated by a linear breeding goal where the linearization is at the population mean in generation 10 and the linear breeding goal is subsequently predicted by a linear index for which the animals are selected. The prediction of the population mean at generation 10 requires linear relationships among the traits that constitute the non-linear profit, because otherwise this prediction becomes very complicated.

A non-linear index is proposed that simply estimates the non-linear goal H =f(u) by Ĥ =f(û), where u = vector of genetic values for the traits and u is its (BLUP) estimate. This non-linear index does not require predictions of (future) population means and does not require linearly related traits.

To test these indices a simple meat production example was constructed where the non-linearity between the traits was due to the competition between weight and probability of survival for the same resources from food intake. In the model selection for weight and, in particular, for weight over costs (mainly food) led to reduced profits due to large reductions of survival rates. Although, the example was oversimplified, this should provide a warning for the use of oversimplified breeding goals, e.g. fitness traits may reduce by more than expected from base population genetic parameters.

When probability of survival and weight were measured, a non-linear index of these non-linear traits gave the greatest genetic gains. Failure to update genetic parameters each generation severely reduced genetic gain and, if linear indices were used, it was also important to update the economic weights. When probability of survival was measured, profit could be calculated on each animal and included as a trait in the calculation of estimated breeding value. This yielded high genetic gain and did not require updating of genetic parameters or economic weights.

Forty-five Bos indicus (zebu) cows were blocked by body condition (BC) score at calving and allocated by body weight (BW) to three treatments: untreated controls (CON), and progesterone-releasing intra-vaginal device (PRID)-treated at either 45 (T45) or 60 days (T60) post partum. Cows were given food individually and blood-sampled three times a week for progesterone. Calves sucked twice a day and were weighed weekly. PRIDs resulted in only 21% of cows responding at 60 days and they did not reduce anoestrus (PPI) or calving interval (CI) (P > 0·05). Dry matter (DM) and metabolizable energy (ME) intake were 7·1 (s.e. 0·6) kg and 54·3 (s.e. 4·6) MJ/day, respectively. BC score and BW at calving, and ME intake influenced cow and calf average daily gain ranging from −580 to 625 and 331 to 868 g/day, respectively. Milk yield during the first 4 months was 507 (s.e. 97) l. Cows gained 25 kg per unit increase in condition but lost 50 kg for a unit decline. CI (mean 14·2, range 10 to 24 months) was inversely related to BC score at calving (r = −0·31) and was delayed by a long PPI (r = 0·51), ranging from 38 to 297 days. Most (95%) cows experienced one or more ‘silent ovulations’ before first oestrus, the number extending PPI length (r = 0·49, P < 0·001). Efficiency of ME utilization was higher for smaller cows of 240 (s.e. 28) kg at calving. It is concluded that: (1) PRID treatment before 60 days post partum is unlikely to reduce anoestrus in Boran zebu cattle; (2) given adequate energy intake zebu cattle in thin condition at calving initially replenish body reserves at the cost of lactation and experience more ‘silent’ ovarian activity before returning to oestrus; (3) cows in good condition at calving express maximum lactation potential, mobilizing their own body reserves to support milk production, yet resume oestrous activity earlier despite weight losses to support higher milk yields.

A selection experiment was established in Coopworth sheep in 1981 to breed for increased or reduced ultrasonic backfat depth (scan C). Foundation females came from four flocks recorded for scan C and live weight, with weight-adjusted scan C data within flock being used for initial screening and subsequent selection. Three groups of animals per source flock, comprising proportionally the fattest 0·12, a random sample, and the leanest 0·12, were used to establish the F, control and L lines, respectively. Ewe flock numbers from 1981 to 1992 averaged 51 per line. Foundation rams were selected in the same manner from four different farms (two sources each in 1981 and 1982) to provide F line (proportionally the fattest 0·04), control line and L line (leanest 0·04) rams for use in 1981 and 1982, with four mated per line per year. Thereafter homebred rams were selected, with 41 or 42 homebred rams being used per line until 1992. Average generation intervals were 2·13 years and annual inbreeding rates per line 0·004. Bivariate heritability estimates for log scan C and log live weight, and a univariate estimate for log scan C using restricted maximum likelihood with an animal model, were 0·28, 0·22 and 0·38, respectively (all with s.e. 0·03). There was a suggestion of lower heritabilities in the L line for log scan C after adjustment for live weight. Realized heritabilities in the F and L lines were 0·34 (s.e. 0·07) and 0·26 (s.e. 0·03), respectively. Deviations of back-transformed weight-adjusted scan C in the last 2 years ofF and L data analysed (1991 and 1992 birth years) from the control flocks were 2·08 and −0·85 mm, which corresponded to responses of +2·50 and −1·03 phenotypic standard deviations, respectively. In addition there were relatively large responses in live weight taken at scanning, with F and L lines averaging 34·0 and 40·2 kg, compared with 38·0 kg for controls in the 1991 and 1992 birth years. The genetic and phenotypic correlations between log scan C and log live weight at scanning were 0·16 (s.e. 0·07) and 0·46 (s.e. 0·01) respectively.

The effect of ammonia treatment of straw on both the rumen environment and the extent of its microbial fermentation was studied. Four rumen cannulated sheep were randomly given 700 g/day of untreated straw plus urea (US), ammonia-treated straw (TS) and alfalfa hay (AH) in a change-over design with three periods. Rumen pH was lower and ammonia-nitrogen and total volatile fatty acid (VFA) concentrations were higher (P < 0·001) with AH than with US or TS. With the straw diets, TS promoted a lower pH than US (P < 0·05), but differences were less than 0·3 units and the mean pH was never below 6·5. There were no differences between the straw diets in ammonia-nitrogen or VFA concentration (P > 0·05). When untreated barley straw (BS) and treated straw (TS) were incubated in situ disappearance of dry matter (dDM) at 12, 24 and 48 h (P < 0·01) and neutral-detergent fibre (dNDF) at 48 h (P < 0·001) were higher with TS. In vitro incubation showed a higher gas production with TS only after 36 h (P < 0·05) whereas gas from BS fermentation was higher up to 14 h (P < 0·05). Among diets, dDM, dNDF and gas production with US were numerically higher than with TS or AH throughout, although few significant differences were observed, except for a higher dDM at 12 (P < 0·01) and 24 (P < 0·10) h and a higher dNDF at 12 h (P < 0·10). Particle-associated enzymes were extracted from BS and TS incubated in the rumen for 4, 8, 22 and 24 h. Results ofxylanase and cellulase activities support those of straw incubation, with a drop between 4 and 8 h in TS diet. The concentration of residual phenolics per unit of incubated straws after 12 and 24 h show that phenolics release to the media was higher with the TS diet. Daily changes of phenolic concentration into rumen liquid was also higher with TS than with US (P < 0·001). The increased release of straw phenolics by ammoniation reduced the potential for rumen degradation of straw, mainly in the first hours of the fermentation period.

Thirty-five mature Churra ewes, ranging in live weight from 30·3 to 52·6 kg and in body condition score from 1·25 to 4·00 were used to study the relationship between body condition score (BCS), live weight (LW) and body composition and fat distribution in ewes of this breed, which is one of the major sheep breeds of northern Spain. The procedure at slaughter and at subsequent dissection was designed to partition each body into two components, carcass and ‘non-carcass’. Right side carcasses and ‘non-carcass’ components were used to analyse the chemical composition. From the left side of the lumbar region a joint was cut and dissected into muscle, bone, subcutaneous and intermuscular fat. According to the results obtained, omental fat represented the highest proportion of total internal fat regardless of the level of fatness. Distribution of internal fat was similar to that observed in other milk production breeds. Regressions on LW explained more of the variation than those on BCS for individual internal fat depots and chemically determined ‘non-carcass’ fat. The prediction of total body fat afforded by LW was better than that provided by BCS. The subcutaneous and intermuscular fat depots in the lumbar joint were well correlated with BCS, carcass fat and total fat in the body, validating the use of this region for assessing BCS in Churra ewes. Nevertheless, the correlation coefficient with the omental depot was not statistically significant. The results of this study suggest that BCS was not as accurate for estimating body composition and fat depots in mature Churra ewes as has been shown previously in other breeds. The single most effective prediction index was LW. However, the utilization of both BCS and LW together provided more accurate estimations.

Three hundred and eight cattle, comprising steers and heifers from continental and British crosses were finished on an 18-month beef production system at Warren Farm, Lambourn, Berkshire and slaughtered across a range of fatness levels. The eating quality of roasting joints (semimembranosus.) and sirloin steaks (longissimus thoracis et lumborumj was evaluated and the chemical composition of the lean tissue was taken on a subset of the samples. Results suggested that the greatest differences between the breeds was in the joints. There were significant (P < 0·01) differences in the lipid, moisture and collagen contents of the lean tissue of the joints from the different sire breeds. The Belgian Blue sire progeny had significantly lower lipid content than the Charolais or Aberdeen Angus crosses, and significantly lower collagen content than the Aberdeen Angus cross. In addition joints from Belgian Blue crosses were more tender than joints from other breed crosses. Although the lipid and moisture contents of the steaks from different sire crosses were significantly different there was no evidence of differences in eating quality. Perhaps surprisingly there were no significant relationships between the eating quality and chemical composition between or within breed. Irrespective of breed, carcass fatness influenced the juiciness of both the joints and the steaks although the response was different for continental crosses and British crosses and depended on carcass sex. Over and above this response, steer meat was generally more juicy than heifer meat.

Variance components were estimated from an animal model using a restricted maximum likelihood procedure which allowed for unequal design matrices and missing observations (VCE). Data sets containing: (i) 15 275 records of linear type classifications on heifers, (ii) 3399 live weight and condition scores measured at calving and (iii) 1157 records of yield, dry-matter intake, average live weight and condition score during the first 26 weeks of lactation; were analysed jointly.

Heritability estimates for dry-matter intake, live weight and condition score in the largest data set were 0·44, 0·44 and 0·35 respectively and the genetic correlation between condition score and the yield traits ranged from −0·29 to −0·46. The genetic correlation between milk yield and average live weight was negative (−0·09) but after adjusting for the genetic variation in condition score this correlation was positive (0·29). Genetic correlations between live weight and stature, chest width, body depth and rump width were consistently high (0·52 to 0·64; 0·75 to 0·86; 0·59 to 0·81; 0·56 to 0·74, respectively). Chest width and body depth were little to moderately correlated with dry-matter intake (0·25 to 0·28 and 0·20 to 0·34 respectively), and angularity (−0·47 to −0·77) and chest width (0·32 to 0·73) appeared to be good predictors of condition score. These correlations showed that (i) the relative value of live weight compared with food intake capacity determines the optimum direction of selection for stature, chest width, body depth and angularity, and consequently the optimum size of the dairy cow, and that (ii) live weight, condition score and food intake can be predicted from the type traits with little loss in accuracy. A restricted index which maintains condition score at its current level was predicted to reduce overall (economic) genetic gain by 5%.

An experiment was carried out to study the effect of changes in either the quality or the quantity of dietary protein intake on the free essential amino acid profiles in plasma, muscle or liver of growing chickens. Following a randomized paired-feeding design based on metabolic body weight (kg M0·75), White Rock male broilers were allocated to one of three isoenergetic (14·5 kJ metabolizable energy per g dry matter (DM)) semisynthetic diets containing different levels of protein (60, 120, 180 or 240 g/kg DM). All diets were based on soya-bean meal, as the sole source of protein, either unsupplemented (diets S) or supplemented with 20 g/kg L-lysine (diets SL) or 2 g/kg DL-methionine (diets SM). Samples of blood, biceps muscle and liver were taken and amino acid analysis was determined by high performance liquid chromatography. Plasma was only adequate to detect the effect of the supplementation with methionine to balance the dietary amino acid (AA) profile. Plasma concentrations of free methionine significantly increased as a result of the supplementation with methionine (P < 0·001) and remained unaffected by the amount of protein ingested. When lysine was added to diets S to induce an AA imbalance, a significant increase in muscle concentrations of free valine, isoleucine and phenylalanine (P <0·05) and a significant decrease in liver concentrations of free arginine and phenylalanine were observed (P<0·05). The supplementation with DL-methionine gave rise to a significant fall in the concentrations of free histidine, glycine and threonine (P < 0·05) and increased those of isoleucine and methionine in the skeletal muscle (P < 0·05), while in liver it significantly lowered the concentrations of free arginine, valine, leucine, phenylalanine and methionine (P < 0·001 to P < 0·05) and raised that of free glycine (P < 0·001). The ratios lysine: phenylalanine, lysine: valine and methionine: glycine in muscle together with that of methionine: glycine in liver seem to be appropriate indexes of the adequacy of the dietary AA profile to requirements.

Heart size of purebred boars (13 Landrace, 12 Yorkshire, and 14 Duroc) and crossbred (Landrace × Yorkshire × Duroc) boars (no. =18) and gilts (no. = 24) was studied. Purebred boars were raised from 30 kg for 110 days and slaughtered. Crossbred pigs of various body weights (30 to 110 kg) were selected and their plasma and blood volume were measured before sacrifice. The variation of heart size of pigs was studied and its correlation with growth performance or to vascular space was investigated. According to the principal component analysis heart size was best expressed by its weight, followed by the thickness of the anterior ventricle septum or the thickness of the left ventricle (LV) wall. The food/gain ratio of boars during testing period was significantly correlated with some size characteristics of their heart including weight, width, and LV thickness. The back fat thickness at 100 kg was significantly negatively correlated with heart weight, heart/body weight ratio, and LV thickness. Thus, selection for growth performance would result in a bigger heart in domestic pigs. In the crossbred study, an allometry fitting of H = 12·18B0·73 (r = 0·96) was obtained between heart weight (H, g) and body weight (B, kg). The fittings of heart weight to blood/plasma volume generated values of r of between 0·79 and 0·75 in allometry models or between 0·84 and 0·80 in linear models. Thus, vascular space is no better than fractional body weight as the basis to express relative heart weight in pigs. It is suggested that the normal exponent relating heart size to body weight in growing pig is effectively 0·75, similar to the exponent of metabolic size, 0·734 or 0·75. Therefore, the size of the heart of domestic pigs varies in size proportionally with the changes of metabolism seen in terms of growth or maybe even reproduction. The wild boar, the ancestor of domestic pigs, has a heart proportionately about 0·5 bigger than modern pigs when scaled according to M0·75. The attribution of metabolic difference to the bigger heart of wild boar is uncertain and needs further elucidation. The trend to bigger hearts in domestic pigs under current selection pressure for leanness should not necessarily be interpreted as returning to a natural form but may reflect a pathophysiological change.

Eleven maize silages with crude protein (CP) and neutral detergent fibre (NDF) ranging from 77 to 93 and 359 to 542 g/kg dry matter (DM) respectively, were used to study the relationship between ear content, chemical composition, fermentative characteristics, in vitro DM digestibility and ruminal degradation characteristics, on the one hand, and the voluntary DM intake by sheep or in vivo organic matter apparent digestibility (OM digestibility), on the other.

The silages were offered ad libitum to mature ewes given a daily supplement of 85 g of soya-bean meal. DM intake varied from 41·1 to 68·6 g DM per kg M0·75 daily. OM digestibility and NDF apparent digestibility were measured, using the same ewes in a period subsequent to that of voluntary intake measurement. The silages, in this case, were offered at a feeding level of 1·2 maintenance. OM digestibility and NDF apparent digestibility ranged from 0·622 to 0·757 and from 0·377 to 0·605, respectively. Rumen DM disappearance was measured by incubating samples in nylon bags in the rumen of three silage-fed rumen-cannulated wethers for 3, 6, 12, 24, 48 and 72 h and by fitting the exponential model to the results. Potential degradabilities (defined as a + b) for DM ranged from 728 to 815 g/kg.

Accurate prediction of DM intake (r = 0·93; P < 0·01; residual s.d. = 3·9) and OM digestibility (r = 0·86; P < 0·01; residual s.d. = 0·022) was achieved using the soluble fraction (a) and the insoluble but fermentable matter (B) and the insoluble but potentially degradable fraction (b), respectively. However, looking for a compromise between accuracy and simplicity, reliability and inexpensiveness, ear content is proposed as a predictor of OM digestibility (r = 0·85; P < 0·01) and the pH and acetic acid concentration of the silages may be used as a predictor of DM intake (r = 0·80; P < 0·05).

The heart rate (fH) and the energy expenditure (EE) of seven Hintenvaelder (Bos taurus) draught oxen and three zebu (Bos indicusj oxen were measured, while the animals were standing, walking and pulling different loads. Linear regressions for all animals relating EE to fH were highly significant (P < 0·001). The standard errors of the estimate expressed as a percentage of the mean EE (PE) ranged from ±6·7% to ±10·5%. Two animals with PE ±13·7% and ±17·1% were beyond that range. One year later, fH and EE were measured on six of the original seven Hinterwaelder oxen while the animals were standing and walking on a treadmill, on the level and at gradients of 3%, 6% and 9%. In the two experiments mean slope and mean intercept of the regressions of EE on fH were not different (P > 0·05). Irrespective of the kind of work (draught work or lifting work),fH allows a reliable prediction to be made of the EE of working oxen.

At weaning at 3 months of age (week 1), 30 red deer hind calves were housed in six groups of five animals at a stocking density of 1·5 m2 per head and maintained in these groups for 4 weeks. At the start of week 5, all calves were immunized with ovalbumin (OVA). Fifteen calves, from three groups, selected at random, were transferred to individual pens which restricted visual and tactile contact with others (ISO) while the remaining animals were kept in their groups (GP). The behaviour, food intake, live-weight gain, antibody and lymphocyte responses in vitro to OVA and lymphocyte responses in vitro to the non-specific mitogen, concanavalin A (ConA), of all calves were assessed in each of weeks 5 to 9. Isolated calves had a lower mean live-weight gain than GP calves (P < 0·001), although there were no differences in food intake. Significantly more time was spent lying (P < 0·001) but less time feeding (P < 0·05) and self-grooming (P < 0·001) by ISO than by GP calves. There was no significant difference between ISO and GP calves in the cortisol response to an ACTH challenge test (10 i.u.) at week 11. Lymphocyte responses and antibody titres to OVA were lower in GP than in ISO calves at weeks 7 (P < 0·05) and 8 (P < 0·05), respectively. In contrast, GP calves had greater lymphocyte responses to the non-specific mitogen, ConA, in weeks 7 (P < 0·05) and 10 (P < 0·001) but not in week 9 compared with ISO calves. Differences in lymphocyte stimulation were attributed to the non-specific mitogenic nature of ConA. Factors such as agonistic interactions evident in group housing may have compromised the antibody and lymphocyte responses to OVA by GP calves but conversely the lack of social contact may have also suppressed behavioural activity in ISO calves.

This paper describes a general framework which enables responses to selection for resistance to gastro-intestinal parasites in sheep to be stochastically modelled. The model incorporates between-animal variation for pasture intake, the proportion of larvae ingested from the pasture which survive to become adults, the fecundity of the mature worm, along with density-dependent control of this trait and the mortality rate of the worms. The between-animal variation for each component is partitioned into genetic, permanent and temporary environmental components which vary with age. Infection rates are estimated from existing pasture larval contamination and new contamination from infected animals. Using this framework, selection for reduced mean faecal egg count was practised, in silico, for a period of 10 years. Several general patterns emerged. First, a curvilinear response to selection was observed, with responses initially being large then declining over time. Mean faecal egg count declined from approximately 500 to 140 eggs per gin 10 years and worm burdens and pasture larval contamination showed similar patterns of response. The initial responses to selection were approximately 1·7 times that predicted by quantitative genetic theory because the epidemiology of the disease changed as the animals' genetic resistance improved. A method of partitioning selection responses into components due to the altered genotypes of the animals and components due to altered disease epidemiology is outlined. Secondly, the faecal egg count distribution became more aggregated, or skewed, as selection progressed. Thirdly, correlating pasture contamination levels across years (carry-over effects) resulted in even greater apparent responses to selection. Finally, regular anihelmintic treatment reduced mean faecal egg counts but did not alter the patterns of response to selection, indicating that selective breeding should be feasible under a variety of anthelmintic regimes.