The impact of internal and external parasitism on productivity of farm animals is considered for cattle, sheep, pigs and poultry. The parasitic challenge experienced and the outcome of that challenge is a dynamic one in which environment, management practices, including housing or grazing management, nutritional status, the host's ability to develop effective immunity and the speed with which this can occur, play a significant role. Much of our assessment of the impact of infection comes from pathophysiological and nutritional studies with contrived infestations. A common feature of all infestations is reduced efficiency of food utilization through reduction in food intake, though in some cases increases in nutrient requirement are induced as a result of damage to or loss of host tissue. Assessment of the impact on productivity in the field is technically very difficult and must take account of fluctuating challenge, determined by environmental and management decisions, and the manager's objectives for the performance of a particular category of livestock. This review attempts to integrate the assessment of losses in productivity based on pathophysiological studies with those based on protection of groups of livestock in production systems by regular pesticide use. Throughout the review the limitations inherent in both approaches and in our knowledge of how parasites impair productivity of the host are emphasised.

Three groups of 16 cattle each comprising three multiparous Jersey cross Holstein-Friesian cows, seven primiparous and six multiparous Holstein-Friesian cattle were offered, ad libitum, a silage-based complete diet with different concentrate ingredients following an initial 3-week covariate period. The relationship between these three diets and other parameters with lesions of the weight-bearing surface of the hoof was studied by scoring mobility weekly (locomotion score) and examining all the feet of all cows for visual lesions particularly those involving the horn of the foot. In addition hoof angle, hardness and growth and wear were also recorded. The mean locomotion score during the initial 3-week covariate period was a significant covariate for the subsequent locomotion score, milk yield, and live weight (P < 0·001). Furthermore weekly locomotion score also proved a significant covariate for weekly milk yield (P < 0·05). There were no significant differences between dietary treatment groups for locomotion score, overall lesion score (despite significantly fewer ulcers of the sole in one dietary group: P < 0·001) but a significant (P < 0·05) difference between cow ‘type’ and there was also a significant (P < 0·05) diet × breed interaction for locomotion score and milk yield. It was concluded first that initial mobility was an important factor in subsequent mobility of the cow and so experimental design; secondly that while nutrition and genotype interacted to influence mobility, visual lesions of the hoof and lameness, the mechanisms involved were far from clear; and thirdly that the simple lesion score used required some adjustment or correction factor(s) to ensure that more severe lesions were given a greater weight than a simple unitary increase.

First lactation production and linear type records of 72 559Holstein-Friesian cows, calving from 1982 to 1989, were analysed by multivariate restricted maximum likelihood, using a sire model. The data comprised offspring of 1066 randomly used sires, and 91 proven i.e. widely used bulls. All phenotypic correlations between the type traits and the yield traits were small, but moderate genetic correlations were obtained between milk, fat and protein yield and angularity (~—0·43) and between the yield traits and udder depth (~0·44), indicating that higher yielding heifers are more angular and have deeper udders. The heritabilities of the type traits were in line with previous analyses, but those for milk, fat and protein yield were rather high at 0·47, 0·52 and 0·45 respectively

Growth-promoters are banned by the European Community, but different hormonal cocktails are still illegally used. This experiment was therefore conducted to evaluate the effects of one of the most currently used cocktails on some hormonal parameters and spermatogenesis in finishing bulls in an attempt to provide a suitable screening technique for their illegal use. Sixteen double-muscled Belgian White Blue finishing bulls (mean ivcight: 535 (s.d. 37) kg) were blocked into control (C; no. = 7) and treated (Dex; no. = 9) groups. Animals were treated i.m. with the hormonal preparation (dexamethasone isonicotinate and phosphate, chlormadinone acetate and ethinyl oestradiol) on day 0, day 15 and day 30. Animals were slaughtered on day 45. Three h before each treatment and just prior to slaughter, jugular blood samples were collected to monitor the testosterone (T) response to an i.v. injection of gonadotropin releasing hormone (GnRH) (0·5 fig GnRH per kg body weight). Testicular tissue was also collected at slaughter. Plasma T and insulin-like growth factor-1 (IGF-1) concentrations were measured by radioimmunoassay. IGF-binding proteins (IGFBPs) were evaluated using Western ligand blotting. Daily weight gains were lower in the control group (1·29 (s.d. 0·13) kg for C v. 1·60 (s.d. 0·39) kg for Dex) but the difference ivas not significant. After treatment, spermatogonia, spermatocytes, spermatids and spermatozoa disappeared from the testis and seminiferous tubules consisted only of Sertoli cells; these observations suggest that treated animals were sterile. Moreover, plasma T concentrations in response to GnRH stimulation were suppressed fP < 0·001) in the Dex group between day 15 and day 45 (mean maximal responses: 5·4 to 7·9 μg/l in C group v. < 0·2 μg/l in Dex group at day 15, 30 and 45). Treatment did not show any prominent effect on plasma IGF-1 levels but increased IGFBPS band intensity. In conclusion, treatment with a cocktail containing dexamethasone esters, chlormadinone acetate and ethinyl oestradiol for a short period induced a number of changes in finishing bulls luhich might be possible to develop as a screening method for the identification of illegally treated animals.

One hundred and twenty spring-born steers, comprising 40 Friesians (FR), 40 Meuse-Rhine-lssel (MRI) × Friesians (MR), and 40 Belgian Blue × Friesians (BB) were reared together from 3 weeks of age to the start of their second winter. During the second winter there was a 3 (FR, MR and BB breed types) × 2 (3 kg and 6 kg supplementary concentrates per head daily with grass silage ad libitum) × 2 (96- and 220-day finishing periods) factorial arrangement of treatments (10 animals per subgroup). Carcass weights and grades were recorded after slaughter at the end of the second winter, and one side from each of 96 carcasses (eight per subgroup) was dissected into bone, muscle, intermuscular fat and subcutaneous fat. A sample of m. longissimus from the 10th rib was chemically analysed. Slaughter weights and carcass weights per day from arrival to slaughter were 796, 813 and 828 (s.e.d. 11·7) g and 419, 440 and 457 (s.e.d. 7·1) g for FR, MR and BB, respectively. Corresponding carcass weights were 314, 329 and 342 (s.e.d. 4·5) kg. BB had better conformation than both FR and MR. BB also had a lower carcass fat score, lower proportions of bone, intermuscular fat and subcutaneous fat, a higher proportion of muscle and muscle with higher proportion of moisture and a lower proportion of lipid than FR and MR. The higher level of concentrates increased side iveight by 8 kg, but the overall effects on carcass composition were small. The longer finishing period increased side weight by 25 kg and was associated with significantly reduced proportions of bone and muscle and an increased proportion of fat. Allometric regression coefficients for carcass weight on slaughter weight, and for bone, muscle and fat weights on side weight were 1·19, 0·39, 0·80 and 2·16, respectively. It is concluded that despite the better carcass conformation of MR, there was little difference in carcass and muscle composition between FR and MR. BB, in addition to having a higher growth rate and better carcass conformation than FR, also had more muscle in the carcass, more of the total muscle in the higher value joints and a lower proportion of lipid in the muscle. It was calculated that FR, MR and BB would have similar proportions of separable fat in the carcass at approximate carcass weights of 300, 320 and 400 kg, respectively.

The effect of inclusion of live yeast culture (YC, Saccharomyces cerevisiae plus growth medium) in a high concentrate diet given to buffalo (Bubalus bubalis) calves on the rumen microbial population and fermentation pattern and in sacco dry matter disappearance of dietary constituents was examined. Six rumen-fistulated buffalo calves of about 120 kg live iveight were divided into two equal groups. The control group was given a diet consisting of, on a dry-matter basis, 0·90 kg ivheat straw, 1 kg berseem (Trifolium alexandrinum) and ISO kg concentrate per day per calf and the yeast group the above diet plus 5 g YC which was put directly into the rumen via the fistula. After feeding this diet for 6 weeks (supplementation period), inclusion of YC was stopped and both groups were given the control diet for a period of 3 weeks to examine the performance of the YC group after withdrawal of YC. At week 4 of YC supplementation the pH was significantly increased (P < 0·01) and lactate concentration was decreased (P < 0·01) in the rumen fluid for up to 6 h post feeding. The number of total bacteria, total viable bacteria, cellulolytic bacteria, amylolytic bacteria and protozoa were increased proportionately by 0·554 (P < 002), 0·482 (P<0·01), 0·670 (P <0·01), 0·077 (P > 0·05) and 0·079 (P>0·05), respectively. The concentrations of total volatile fatty acids, particularly at 4 h post feeding (P < 0·01), acetate fP < 0·01) and propionate and the acetate to propionate ratio were higher in the YC compared with the control group. On YC inclusion, the concentration of ammonia-nitrogen was decreased while that of trichloracetic acid insoluble protein was marginally increased. All these differences in rumen variables started to disappear on YC withdrawal and values returned to control levels by the 3rd week after YC withdrawal. YC supplementation increased the in sacco dry-matter disappearance of various dietary components particularly after 3, 6 and 22 h incubation.

Effects of time of supplementation on forage intake, nutrient apparent digestibility and rumen fermentation were studied with 12 mature castrated male sheep (wethers) offered grass hay from 16.30 h to 09.30 h and supplemented with a cereal-based concentrate given at either 09.30 or 16.00 h. Voluntary intake of hay organic matter (OM) was decreased by feeding the concentrate (P < 0·01). Offering concentrate at 09.30 h after hay was available, increased intake of hay and total OM compared with offering it at 16.00 h before hay was available (P < 0·05). Daily pattern of hay intake was not changed when concentrate was offered at 09.30 h compared with feeding hay alone, but concentrate given at 16.00 h resulted in a lower hay intake between 16.30 and 18.00 h. Sheep offered concentrate at 09.30 h had higher rumen ammonia levels than those offered concentrate at 16.00 h, but there were no differences in the apparent digestibility of the nutrients, rumen pH and molar proportions of the main volatile fatty acids. There were also no differences between groups in the blood plasma concentrations of 3-hydroxybutyrate (30HB), nonesterified fatty acids (NEFA) and glucose. It is concluded that feeding supplement after rather than before a period of intake of forage or a bout of grazing may offer a means of minimizing reduction of forage intake as a consequence of feeding concentrate.

Thirty-four Dorset and 34 Suffolk rams were slaughtered in pairs within breed at birth, weaning, at monthly intervals to 420 days and then at bimonthly intervals until 600 days to compare factors used to estimate mature size and to determine how genetic size-scaling affects the comparison of body composition between breeds. At equal empty body weights there were no detectable differences between the breeds in amounts of water, protein or ash but Dorsets contained more lipid. Dorset and Suffolk asymptotic values of water (40 and 61 kg), water-plus-protein-plus-ash (51 and 77 kg), metacarpal bone length (127 and 147 mm) and metacarpal bone weight (59 and 101 g) were used to estimate mature size. Regardless of the estimator of mature size, there were no significant differences between breeds in degree of maturity at a given metabolic age. At the same degree of maturity within the estimators of mature size, there were no differences between breeds in the degree of maturity of water, protein or ash, with the exception of small differences in protein for two of the mature size indicators. Because lipid appeared to accumulate without limit in these sheep, the mature body was assumed to contain 300 g lipid per kg. Using this proportion to estimate amount of mature lipid, there was a higher degree of maturity of lipid for Suffolk than for Dorset rams at equal degrees of maturity of water, water-plus-protein-plus-ash or metacarpal bone weight. Thus, Dorsets with greater lipid content at equivalent empty body weights were leaner than Suffolks when adjusted for mature size.

Two experiments were conducted to investigate the effect of supplementation with fodder tree leaves on the utilization of teff straw. This ivas aimed at testing the hypothesis that forage supplements (e.g. sesbania) that disappear faster from the rumen compared with those that disappear slowly (eg. leucaena) may elicit higher intakes of the basal diet. Experiment 1 investigated the effect of level (i.e. 0,200,300 and 400 g/kg dry matter (DM) intake) of leaves of Sesbania sesban or Leucaena leucocephala on the utilization of teff straw fed ad libitum. Seven sheep were given the seven diets in four periods following a partially balanced (7 × 4) cross-over design. In experiment 2, teff straw alone or supplemented with graded levels of sesbania (250, 350 and 450 g/kg DM intake), were fed to 16 sheep in a completely randomized block design. Intake, degradability, nitrogen (N) utilization, particulate and liquid passage rates were estimated.

In experiment 1, protein source × protein level interaction was not significant. Supplementation increased intakes of total DM (P < 0-05), organic matter (P < 0·01) and N retention (P < 0·01) but had no effect on the intake of teff straw. Supplementation with sesbania, but not with leucaena, increased (P < 0·05) the apparent digestibility of DM. Both supplements increased (P < 0·05) the fractional rate of passage from the rumen. In experiment 2, graded levels of sesbania increased DM intake (P < 0·05), fractional rate of liquid outflow (P< 0·05) and tended to increase the rate of degradation. It was concluded that the effect of fodder tree leaves on roughage intake is a function of their disappearance rate from the rumen.

The effects of inbreeding on the gross financial returns from ezues have been studied in a flock of sheep comprising three hill breeds and Ihe crosses among them. Each of these groups mis represented In non-inbred sheep (purebred and crossbred, designated O2, and F2, respectively) and four classes of inbreeding (inbreeding coefficients (F): 0·25, 0·375, 0·50 and 0·59). A second non-inbred class ums represented by crosses of inbred lines.

Gross lifetime income per eive derived from the sale of lamps for slaughter, cast ezves and wool was reduced by inbreeding in an almost linear fashion (between the O2/F2 and the F 0·50 class) at a rate of £1·27 (at 1992 prices) for ench 0·01 (percentage point) increase in the level of inbreeding — an overall reduction to 0·35 of the O2/F2 level. Line crosses gave a better return than the other non-inbred sheep. When expressed in terms of ewe metabolic body weight (M0·73) the decline with inbreeding was less —an overall reduction to 0·4 of the O2/F, income. Inbreeding of Ihe lamb caused a further decline in output independent of the inbreeding of the ezve.

Responses to four generations of divergent selection for lean groivth rate with ad-libitum feeding (LGA), for lean food conversion (LFC) and for daily food intake (DFI) in Large White pigs were studied. The LGA (LFC) selection criterion was designed to obtain equal correlated responses in growth rate (food conversion ratio) and carcass lean content, measured in phenotypic s.d. The selection criteria had phenotypic s.d. of 27, 29 and 253 units, respectively, and results are presented in s.d. units. There was a total of 3537 pigs, with an average of 40 boars and 40 gilts performance tested in each of the high, low and control lines per generation and the lines consisted of 10 sires and 20 dams. The generation interval was equal to 13·5 months. Animals were performance tested in individual pens with mean starting and finishing weights of 30 kg and 85 kg respectively.

Cumulative selection differentials in the three selection groups were 5·8, 3·6 and 3·3 phenotypic s.d. for LGA, LFC and DFI respectively. Direct responses to divergent selection were 1·7, 1·3 and 1·2 (s.e. 0·17) for LGA, LFC and DFI. The correlated response in LFC (1·6 (s.e. 0·18)) with selection on LGA was greater than the direct response in LFC. Conversely, the direct response in LGA was greater than the correlated response (1·1 (s.e. 0·18)) with selection on LFC. The response in LFC (–1·1 (s.e. 0·17)) with selection on DFI was similar in size but opposite in sign to the direct response in LFC. Responses were asymmetric about the control, as the high LGA and LFC responses were proportionately smaller (0·74 and 0·58) than low line responses. In contrast, the difference between the high DFI and control was four times greater than the difference between low line and control.

Heritabilities of LGA, LFC and DFI were 0·38, 0·35 and 0·29 (s.e. 0·03), when estimated by residual maximum likelihood, with common environmental effects of 0·09 (s.e. 0·02). Genetic correlations for LGA with LFC and DFI were positive, 0·76 (s.e. 0·03) and 0·23 (s.e. 0·07), but the genetic correlation between DFI and LFC was negative, –0·45 (s.e. 0·06). The experiment demonstrated that substantial responses to selection can be achieved in LGA, LFC and DFI. Selection on LGA resulted in larger direct and correlated responses than selection on LFC.

Responses to divergent selection for lean growth rate with ad-libitum feeding (LGA), for lean food conversion (LFC) and for daily food intake (DFI) in Landrace pigs were studied. Selection was practised for four generations with a generation interval ofl year. A total of 2642 pigs were performance tested in the high, low and control lines, with an average of 37 boars and 39 gilts performance tested per selection line in each generation. The average within-line inbreeding coefficient at generation four was equal to 0·04. There was one control line for the DFI and LFC selection groups and another control line for the LGA selection group. Animals were performance tested in individual pens with mean starting and finishing weights of 30 kg and 85 kg respectively with ad-libitum feeding. The selection criteria had phenotypic s.d. of 32, 29 and 274 units, for LGA, LFC and DFI, respectively, and results are presented in phenotypic s.d.

Cumulative selection differentials (CSD) were 5·1, 4·5 and 5·5 phenotypic s.d. for LGA, LFC and DFI, respectively. Direct responses to selection were 1·4,1·1 and 0·9 (s.e. 0·20) for LGA, LFC and DFI. In each of the three selection groups, the CSD and direct responses to selection were symmetric about the control lines. The correlated response in LFC (1·1, s.e. 0·19) with selection on LGA was equal to the direct response in LFC. In contrast, the direct response in LGA was greater than the correlated response (0·7, s.e. 0·18) with selection on LFC. There was a negative correlated response in DFI (-0·6, s.e. 0·18) with selection on LFC, but the response with selection on LGA was not significant (0·2, s.e. 0·16).

Heritabilities for LGA, LFC and DFI ivere 0·25, 0·25 and 0·18 (s.e. 0·03), when estimated by residual maximum likelihood, with common environmental effects of 0·12 (s.e. 0·02). Genetic correlations for LFC with LGA and DFI were respectively positive (0·87, s.e. 0·02) and negative (-0·36, s.e. 0·09), while the genetic correlation between DFI and LGA was not statistically different from zero, 0·13 (s.e. 0·10). Selection on components of efficient lean growth has identified LGA as an effective selection objective for improving both LGA and LFC, without a reduction in DFI.

Responses to four generations of divergent selection in pigs for lean growth rate (LGS) with restricted feeding were studied. The selection criterion was designed to obtain equal correlated responses in growth rate and carcass lean content, measured in phenotypic s.d. Animals were to be performance tested in individual pens with a mean starting weight of 30 kg for a period of 84 days. Daily food intake was equal to 0·75 gig of the daily food intake for pigs offered food ad-libitum. In the high, low and control lines, there ivere 1250 Large White-Edinburgh (LW) pigs and 875 British Landrace-Wye (LR) pigs. Each selection line consisted of 10 sires and 20 dams, with a generation interval ofl year.

After four generations of selection, cumulative selection differentials were 5·9 and 4·8 phenotypic s.d. for LW and LR populations, with similar responses, 1·8 (s.e. 0·17) phenotypic s.d. Mean weight at the end of test, growth rate and backfat depths at the shoulder, mid back and loin were 89 kg, 712 g/day, 26,13 and 13 mm for LW and for LR pigs were 87 kg, 683 g/day, 28,10 and 10 mm. High line pigs were heavier at the end of test (4·3 (s.e.d. 1·4) kg and 4·0 (s.e.d. 1·6) kg) for LW and LR populations, with corresponding responses in growth rate (54 (s.e.d. 16) g/day and 47 (s.e.d. 18) g/day). Responses in the three backfat depths were −4·1 (s.e.d. 1·2) mm, −2·6 (s.e.d. 0·7) mm and −2·9 (s.e.d. 0·7) mm for LW and −2·2 (s.e.d. 0·05) mm, −2·2 (s.e.d. 0·4) mm and −2·4 (s.e.d. 0·5) mm for LR populations. Responses in weight off test and backfat depths were symmetric about the control lines.

Heritabilities for LGS were 0·34 and 0·28 (s.e.d. 0·5) for the LW and LR populations, when estimated by residual maximum likelihood. Common environmental effects for LGS were 0·11 (s.e. 0·03) for LW and 0·17 (s.e. 0·04) for LR. Heritabilities for growth rate and average backfat depth were similar for LW and LR populations (0·17 and 0·29, s.e. 0·05), as were common environmental effects (0·10 s.e. 0·04). Average phenotypic and genetic correlations between growth rate and backfat, for LW and LR populations, were small (0·15 (s.e. 0·03) and −0·06 (s.e. 0·16), respectively).

Responses to selection and genetic parameter estimates demonstrate that there is substantial genetic variation in growth and fat deposition when pigs are performance tested on restricted feeding.

Genetic and phenotypic parameters and correlated responses in performance test traits were estimated for populations of Large White (LW) and British Landrace (LR) pigs tested in Edinburgh and Wye respectively, to four generations of divergent selection for lean growth rate (LGA), lean food conversion (LFC) and daily food intake (DFI) with ad-libitum feeding.

There were differences between the two populations in genetic parameters, as LW heritabilities for growth rate, daily food intake and backfat depths were higher and the correlation between growth rate and backfat was positive for LW, but negative for LR. However, heritabilities, genetic and phenotypic correlations were generally comparable between selection groups, within each population. Genetic and phenotypic correlations indicated that animals with high daily food intakes were faster growing, had positive residual food intakes (RFI), were fatter with higher food conversion ratios. RFI was highly correlated with daily food intake and food conversion ratio, but phenotypically independent of growth rate and backfat, as expected.

Selection for LGA, in LW and LR populations, increased growth rate (54 and 101 g/day), but reduced backfat (−3·9 and −2·0 mm), food conversion ratio (−0·23 and −0·25) and total food intake (−11·8 and −12·6 kg). There was no change in daily food intake in LW pigs (−19 g/day), but daily food intake increased in the LR pigs (69 g/day). With selection for LFC in LW and LR populations, there was no response in groivth rate (9 and 9 g/day), but backfat (−4·1 and −2·1 mm), total (−6·6 and −11·8 kg) and daily food intake (−90 and −172 g) were reduced, as animals had lower food conversion ratios (−0·13 and −0·22). LW and LR pigs selected for DFI ate more food in total (6·8 and 5·9 kg) and on a daily basis (314 and 230 g), grew faster (94 and 51 g/day) and had higher food conversion ratios (0·12 and 0·13). Backfat was increased in LW pigs (3·7 mm), but not in the LR population.

In general, efficiency of lean growth was improved by increasing groivth rate, with little change in daily food intake from selection for LGA, but was primarily due to reduced daily food intake with selection on LFC.

To reduce nitrogen excretion (NEx) the effect of nitrogen supply on nitrogen retention (NR) and NEx was studied in pregnant sows during three parities. A nitrogen supply of 40 g/day (treatment L) was compared with 62 g/day (treatment C) during day 0 to 85 of pregnancy. In the last month of pregnancy nitrogen supply on treatment L was 50 g/day and on treatment C 74 g/day. Faecal digestible lysine supply followed the same pattern as nitrogen. Nitrogen and energy balances were measured during mid pregnancy (day 50 to 60; no. = 22) and late pregnancy (day 105 to 112; no. = 60). During mid pregnancy treatments had a minor affect on NR and energy metabolism. NEx on treatment L was proportionately about 0·40 lower than on treatment C. During late pregnancy NR was lower on treatment L than on treatment C. NEx on treatment L was proportionately reduced by 0·35 compared with treatment C. In parity 1 the lower NR on treatment L was compensated by a higher fat gain. Results indicate that nitrogen and faecal digestible lysine supply on treatment L were close to minimal requirement in late pregnancy. Assumed values for maintenance requirement of nitrogen (0·45 g N per kg M0·75) and efficiency of ingested nitrogen to NR (0·6) were in line with the results of the balance trials. The observed nitrogen retention of sows, especially during mid pregnancy, permits a reduced nitrogen supply to reduce NEx.

We propose a new method for determining age in mullet fishes taking the thoracic spines as material of analysis. The relations length-age and tueight-age were evaluated by von Bertalanffy and logarithmic regressions. Both methods closely agreed with the observed data but the von Bertalanffy's model showed the best R2 values in both species. Two parameters related to growth speed; the K coefficient of von Bertalanffy's model and the slope of logarithmic regression, were higher in Liza ramada than in Liza saliens. However, our results show that mullet have both high rates of size-growth and weight-production, in comparison with other marine fishes.

In an experiment involving 30 roosters and 15 mature male ostriches the apparent metabolizable energy (ME) values, corrected for zero nitrogen retention (AMEn), were determined by balance method for maize and lucerne meal. A group of 10 roosters received maize as the sole dietary component. For the second group of 10 roosters a blend of 750 g/kg maize and 250 g/kg lucerne was prepared. The diet of the third group consisted of 500 g/kg maize and 500 g/kg lucerne meal. The ostrich basal diet consisted of 1000 g/kg lucerne, and was blended in the ratios 50 lucerne: 50 maize and 25 lucerne: 75 maize. Each dietary treatment was given to five ostriches, individually housed in metabolism crates. Food intake and excreta collection was carried out over a period of 5 days after the ostriches had been accustomed to the diets for 7 days. For roosters food intake and excreta collection lasted for 72 h after an adaptation period of 24 h.

The AMEn value for maize was 14·49 (s.e. 0·046) MJ/kg in roosters while in ostriches AME,, values of 14·3 (s.e. 1·81) and 14·5 (s.e. 0·845) MJ/kg for the 500 g/kg inclusion and 250 g/kg inclusion respectively were found.

In roosters lucerne meal yielded AME,, values of 4·49 (s.e. 0·506) and 4·05 (s.e. 0·321) at 250 g/kg and 500 g/kg inclusion levels respectively. For the ostriches a value of 8·9 (s.e. 0·755) Mj/kg was found for lucerne.

True ME, corrected for zero nitrogen retention, (TMEJ was computed by regressing gross energy output on gross energy input over all feeding levels. Maize yielded values of 14·65 (s.e. 0·0455) and 14·9 (s.e. 0·351) for roosters and ostriches respectively while corresponding values for lucerne were 4·03 (s.e. 0·118) and 8·6 (s.e. 0·296) MJ/kg.

It was concluded that the ostriches were capable of digesting a high starch diet such as maize to the same extent as adult roosters but ostriches were capable of digesting a high fibre ingredient such as lucerne meal much more efficiently.

Eight sets of identical twin heifers and their first three calf crops were used to determine effects of single-trait selection for blood serum insulin-like growth factor 1 (IGF-1). Twin heifers were offspring of Simmental sires and Hereford × Simmental or Hereford × Angus dams. All 16 heifers were mated with the same Simmental bull in each year of the study to produce calves born in 1989, 1990 and 1991 (no. = 16, 13 and 10, respectively). Although differences were noted in performance of progeny from the four twins with the highest v. the four with the lowest IGF-1 concentrations, they zoere not large enough to recommend single-trait selection for blood serum IGF-1 in beef heifers.