Recombinantly derived bovine somatotropin (bST) was administered to 25 Friesian cows by 2-weekly injections of a controlled release formulation at a dose rate equivalent to 25 mg/day. Treatment commenced 7 to 11 weeks after calving and continued for 26 weeks. A comparable group of 25 cows treated only with the slow release vehicle served as a control. During the treatment period, administration of bST increased yields of milk (controls 2358 v. bST 2598 (pooled s.e. = 39·8) kg; P < 0·01), fat (107·4 v. 119·3 (pooled s.e. = 1·9) kg; (P < 0·01) and protein (84·7 v. 93·7 (pooled s.e. = 1·2) kg; (P < 0·001). Magnitude of the treatment effect was strongly influenced by season, being greatest in spring/early summer (weeks 1 to 13 of treatment) and autumn (weeks 19 to 25) but not significant during the intervening summer dry period when herbage yield was low. Voluntary intakes, as measured by indigestible marker techniques at weeks 7 to 8 and 12 to 13 of treatment, were not influenced by bST administration. However, the net loss of body condition experienced by bST-treated cows (0·3 condition score units) was not sufficient to explain their responses in yield of milk and milk components, suggesting that some responses in voluntary intake had occurred. Administration of bST had little effect on milk composition, fatty acid composition of milk fat, live weight, reproductive performance or milk yield in the subsequent lactation.

Herbage from the first regrowth of perennial ryegrass based swards was direct-ensiled following treatment with either an inoculant of Lactobacillus plantarum (Ecosyl, Imperial Chemical Industries pic) at 3·0 1/t, formic acid (850 g/kg) at 2·9 1/t, or no additive (control). During harvesting, alternate loads of inoculant material were treated with an absorbent polymer (ammonium polyacrylamide) at the rate of 1 kg/t herbage and ensiled in separate 100-t capacity silos. The mean dry matter (DM) and water soluble carbohydrate concentrations of herbage used for the four treatments was 157 and 120 g/kg respectively. Lactic acid levels post ensiling increased more rapidly in inoculant-treated herbage than with the other treatments. Formic acid and inoculant-treated silages were well preserved whereas control and inoculant-plus-polymer silages were only moderately well preserved. Losses of DM during ensilage were greater with the formic acid treatment with DM recovery values of 0·78, 0·72, 0·76 and 0·73 for the control, formic acid, inoculant and inoculant-plus-polymer silages respectively. Treatment of herbage with an absorbent polymer prior to ensiling resulted in a proportional reduction in effluent volume of 0·2 whereas formic acid treatment increased effluent flow by 0·28. The silages were evaluated in a changeover design experiment with two periods each of 4 weeks duration, using 24 British Friesian dairy cows. Animals were housed in individual stalls and in addition to the treatment silages, received 5 kg/day of supplement containing 193 g crude protein per kg DM. Silage intakes were increased by proportionately 0·10, 0·14 and 0·05 respectively with the formic acid, inoculant and inoculant-plus-polymer treatments compared with the control. The increased silage intakes with the inoculant treatment were reflected in an increased milk yield of 1·1 kg milk per day whereas formic acid and inoculant-plus-polymer treatments had no significant effect, although formic acid treatment did result in a significant increase in milk fat concentration. There were no major differences between treatments in energy or nitrogen digestibility, when determined on a complete ration basis. In conclusion, a large milk yield response was obtained as a result of treatment of herbage with inoculant prior to ensiling and this resulted from increased silage and hence energy intake. Treatment with formic acid increased silage and energy intake but had no effect on milk energy output.

A concentrate containing ground barley, soya-bean meal and fish meal was compared with one containing dried molassed sugar-beet pellets, dried distillers' grains and fish meal, in its influence on lameness in housed dairy cattle. Two groups of 24 cows were offered the diets in a 60:40 concentrate dry matter: grass silage dry matter ratio during weeks 3 to 26 of lactation. The same daily amounts of metabolizable energy and crude protein were offered to the two groups. The barley-based concentrate diet significantly increased locomotion score (indicating poorer locomotion), and the number and duration of clinical cases of lameness, compared with the sugar-beet concentrate diet. Hoof growth, wear, shape and hardness were not significantly affected by the diets. There were 16/24 cows with a locomotion score of 3 or over (1 to 5 scale) for an average of 7·3 weeks on the barley concentrate compared with 10/24 cows for 3·7 weeks on the sugar-beet concentrate. There was no significant difference between treatments in milk production or live-weight gain.

In two experiments, the effects of protected fat and fibre were studied in compound supplements for grazing dairy cows. The protected fat used consisted of calcium salts of long-chain fatty acids. In experiment 1, 17 cows (group S) were given 4 kg/day of a starchy compound and 17 (group F) 4 kg/day of a high-fibre compound containing protected fat for the first 4 weeks after turn-out to grass. No significant difference was found between groups in milk yield, but cows in group F produced milk with a higher fat content (42·6 g/kg) than did those in group S (37·1 g/kg; P < 0·01) and had higher yields of fat (0·88 v. 0·79 kg/day; (P < 0·05). In experiment 2, four groups of five cows were given 4 kg/day of starchy (S) or fibrous (F) compounds, with (P) or without (C) protected fat for the first 4 weeks after turn-out. After 4 weeks, treatments (starchy or fibrous, added fat or none) were reversed for a further period of 4 weeks. There was no significant effect on milk yield, milk protein yield, live-weight change or change in condition score, although cows on treatment SC tended to produce less milk and have greater gains in live weight and condition. For groups SC, FC, SP and FP respectively, milk fat yields (kg/day) were 0·86, 0·98, 0·99 and 1·06 (s.e.d. 0·06); milk protein contents (g/kg) were 34·4, 34·8, 34·2 and 33·0 (s.e.d. 0·68) and calculated milk energy outputs (MJ/day) were 67/2, 74·3, 74·4 and 76·6 (s.e.d. 3·04). It is concluded that substituting fibrous compounds for starchy compounds tends to increase milk fat content and yield; adding calcium salts of fatty acids to either type of compound significantly increases milk fat content and yield but tends to decrease milk protein content.

The effect of recombinantly derived bovine somatotropin (bST) treatment on milk production and pasture intake was examined in 16 New Zealand Friesian cows from low or high genetic merit (breeding index) selection lines. Recombinantly derived bST was administered by 2-weekly injection of a controlled release formulation for a period of 4 weeks (weeks 16 to 19 of lactation) at a dose rate equivalent to 50 mg/day. During this period the animals were housed for 18 days with food intake being measured over the last 8 days. Treatment with bST resulted in significantly higher yields of milk, fat and protein compared with the controls. Cows from the low breeding index (LBI) line were more responsive to exogenous bST than cows of the high breeding index (HBI) line in both milk and fat yield. Milk composition was not affected by bST treatment. There was a significant increase of proportionately 0·108 in intake of freshly cut pasture between bST-treated and untreated animals during days 16 to 23 of treatment. Thus, no significant difference in calculated energy balance was observed between the bSTtreated and untreated cows. This study indicates that the genetic background of cows may be an important determinant of their response to bST treatment and that such treatment rapidly alters voluntary intake in pasture-fed cows.

Two experiments were carried out in the springs of 1986 and 1987 to investigate the effect of energy concentration in complete diets on the performance of heifers and mature cows. In 1986, all animals were on trial for an 8-week indoor period. In 1987, 14 heifers were on trial for 8 weeks, four heifers were on trial for 7 weeks and six heifers were on trial for 4 weeks. Carry-over effects were compared while animals were on pasture. Two diets offered ad libitum were compared. Diet H contained 0·7 concentrates and 0·3 grass silage. Diet L contained 0·5 concentrates and 0·5 grass silage. In 1986, the concentrate portion of diet H had a higher metabolizable energy (ME) content than diet L whereas in 1987 the same concentrate mixture was used in both diets.

Increasing the energy concentration of the diet from 10·66 MJ ME per kg dry matter (DM) to 11·21 MJ ME per kg DM resulted in a significant proportional increase of 0·36 in DM intake for heifers and mature cows in 1986. The proportional increase in DM intake in 1987 for heifers was 0·17. DM intake (kg DM per day) for heifers and mature cows in 1986 and for heifers in 1987 for diets H and L was 11·8, 8·7, 15·0, 11·0, 14·9, 12·7 respectively. The energy concentration of the complete diet did have a significant effect on average milk yield during the treatment period in the 1986 trial for mature cows but not for heifers in either year. Milk yields were 19·1, 17·5, 26·3, 240, 19·8, 18·9 kg/day respectively for heifers and mature cows in 1986 and for heifers only in 1987. In vivo digestibility coefficients in 1986 for energy, DM, organic matter, modified acid-detergent fibre and protein for diet H (0·708, 0·702, 0·724, 0·678, 0·671) were significantly higher than those for diet L (0·677, 0·666, 0·694, 0·653, 0·625).

The total lactation yield for the heifers and mature cows was not significantly influenced by the energy concentration of the diet given in early lactation.

Four concentrate supplements differing in crude protein (CP) and undegradable protein (UDP) content were offered to 16 lactating Friesian cows together with grass silage (dry matter (DM) 196 g/kg, pH 4·38, CP 160 g/kg DM, in vitro DM digestibility 0·68) ad libitum in a Latin-square trial with 3-week periods. The supplement treatments were: (1) barley 122 g CP per kg DM, degradability (dg) 0·77; (2) barley/soya-bean meal 210 g CP per kg DM, dg 0·69; (3) barley/soya-bean meal/fish meal 190 g CP per kg DM, dg 0·61; (4) barley/soya-bean meal/fish meal 219 g CP per kg DM, dg 0·59. Supplements were given at 8 kg/day. Total daily intakes of silage (kg DM), CP and UDP (g) on treatments 1 to 4 were 7·77, 2087, 375; 8·35, 2804, 655; 8·29, 2676, 717; 8·70, 2917, 826, respectively. Milk yield (kg/day) and yields of fat, protein and lactose (g/day) on the four treatments were 21·3, 791, 617, 984; 23·0, 816, 688, 1055; 23·0, 818, 696, 1050; 23·6, 813, 735, 1071 for treatments 1 to 4 respectively. Yield and concentration of protein and lactose were significantly lower on treatment 1 than on the other treatments, while the of blood metabolites indicated treatment effects on blood glucose, non-esterified fatty acids, plasma protein and urea. Digestibility of organic matter and non-ammonia nitrogen (NAN) flow to the abomasum (g/day), measured in sheep given a fixed silage/supplement ratio at maintenance, were 0·81 and 18·4, 0·81 and 20·8, 0·82 and 21·4, 0·82 and 22·4 for treatments 1 to 4 respectively. The NAN flow was significantly greater on treatment 4 than on treatment 1.

Selection of bulls for rate and efficiency of lean gain was studied in a herd of Hereford cattle. There were two selection lines, one selected for lean growth rate (LGR) from birth to 400 days and the other for lean food conversion ratio (LFCR) from 200 to 400 days of age, for a period of 8 years. A control line bred by frozen semen from foundation bulls was also maintained. Generation interval was about 2·4 years and average male selection differentials, per generation were 1·2 and — 1·1 phenotypic standard deviation units for LGR and LFCR respectively.

Genetic parameters and responses to selection were estimated from the deviation of the selected lines from a control line and by restricted maximum likelihood (REML) techniques on the same material. Realized heritabilities were 0·40 (s.e. 0·12) for LGR and 0·40 (s.e. 0·13) for LFCR using the control line. Corresponding estimates from REML were 0·42 (s.e. 0·10) and 0·37 (s.e. 0·14). The estimate of the genetic correlation between LGR and LFCR was about — 0·69 (s.e. 0·12) using REML.

The estimates of direct annual genetic change using deviations from the control were 3·6 (s.e. 1·3) g/day for LGR and — 0·14 (s.e. 0·07) kg food per kg lean gain for LFCR. Corrsponding estimates from REML were similar but more precisely estimated. The correlated responses for LFCR in the LGR line was higher than the direct response for LFCR.

Seventy-eight British Friesian type cows, mean calving date 13 January, were used in a 3 × 2 factorial design experiment to examine the direct and residual responses to replacing 0·8 kg/day of a concentrate containing 184 g/kg crude protein with an equal quantity of fish meal when using three levels of total supplement feeding (0·8, 4·0 and 7·2 kg/day). In addition, all animals had access ad libitum to a high-quality grass silage (in vivo digestible organic matter 750 g/kg dry matter) during the treatment period. Treatments were applied from day 8 post partum until 22 April, when all animals went to pasture, giving a mean treatment period of 91 days. At pasture the animals were rotationally grazed as three groups, based on the three levels of total supplement offered during the treatment period, at the same stocking rate. The effects of treatments in terms of direct effects during the treatment periods, residual effects at pasture and also total lactation were assessed. Also during the treatment period the effects on rumen volatile fatty acid contents and blood composition were monitored. In addition, total diet digestibility and food utilization studies were carried out on six animals per treatment.

Level of supplementation significantly influenced milk output during both the treatment and full lactation periods with the total lactation responses being 2·0 and 1·0 kg milk per kg additional supplement between the food levels of 0·8 to 4·0 and 4·0 to 7·2 kg/day respectively. Level of supplementation also significantly influenced milk fat concentration during the treatment, residual and full lactation periods and milk protein concentration during the treatment period only.

The replacement of 0·8 kg conventional concentrate by 0·8 kg fish meal significantly increased milk yield during the final 21 days on treatment (mean yield per day 20·6 and 21·9 (s.e. 0·44) kg for without and with fish meal treatments respectively) but there were no significant residual or total lactation effects. From the data it was calculated that at low levels of supplementation 0·8 kg fish meal could be used to replace 1·9 kg conventional concentrate but at more moderate levels of nutrition any substitution would be much lower and uneconomic.

The effects of pregnancy status (non-pregnant, early to mid (1 to 5 months) and late (> 6 months)) and month of pregnancy on live weight, carcass weight, dressing proportion, bruising and muscle properties were examined in 237 Shorthorn and Brahman crossbred cows (mean live weight 424 kg, 62% pregnant). The cows were transported 1155 km to an abattoir and given access to food and water until slaughter. Mustering to slaughter periods were 5, 6 or 7 days.

The mean gross hot carcass weights for the 89 non-pregnant, 108 early to mid pregnant and 40 late pregnant cows were 207, 199 and 187 kg (P < 0·05). Their respective dressing proportions were 487, 469 and 443 g/kg (P < 0·05). Among the pregnant cows, carcass weight and dressing proportion decreased by 2·95 kg and 6 g/kg, respectively, for each month of pregnancy (P < 0·05).

Cows in late pregnancy had lower mean initial yield (IY) and peak force (PF) shear values for m.longissimus dorsi (LD) than non-pregnant cows. The late-pregnant cows also had the greatest mean pH 24 h post mortem (pH24) and ultimate pH (pHu) values (P < 0·05). They also had a greater proportion of carcasses with high pHu values than the early to mid-pregnant and non-pregnant cows (0·30 v. 0·157 v. 0·079; (P < 005). Among the pregnant cows, mean pH24 increased by proportionately 0·038 and the proportion of high pH24 carcasses by 0·055 for each month of pregnancy (P < 0·05). Pregnancy status had no significant effect on mean fat depth, bruise score, PF-IY value or cooking loss.

Correlated responses in two lines of Hereford cattle selected for lean growth rate (LGR) from birth to 400 days of age and lean food conversion ratio (LFCR) from 200 to 400 days of age for a period of 8 years were evaluated. Correlated changes were estimated by two methods: deviation of selected lines from a control line and restricted maximum likelihood. Generally, estimates from the two methods were similar but tended to be more precise for the latter. Statistically significant correlated responses occurred in growth rate in the LGR line and in lean proportion and food conversion ratio in both selected lines. Selection for LGR was accompanied by increases in body weight at various ages in both male and female progeny. In the LFCR line there were little or no changes in body weight for male calves but some increases at certain ages for female progeny. There were no adverse correlated responses detected in reproductive traits such as calving difficulty and calving and pre-weaning mortality.

Milk production and food intake records were available on individual animals from a high-yielding Holstein-Friesian herd in which selection had been practised on fat plus protein yield using nationally available artificial insemination sires. The relationship between sires and maternal grandsires' transmitting ability (ICC), expressed as a pedigree index (sire ICC + 0·5 maternal grandsire ICC), and offspring performance for milk production traits, food intake, and gross efficiency (milk energy (MJ)/total energy intake (MJ)) was investigated. The data comprised 475 26-week (data set 1) and 293 38-week (data set 2, a subset of 1) records, and for each data set analyses were conducted on heifers, cows and pooled lactations. Regressions of fat plus protein yield, fat yield, protein yield, and milk yield on their corresponding pedigree index were not far from the theoretical expectation (for a full lactation) of 1, for heifers (0·71 (s.e. 0·20), 0·72 (s.e. 0·20), 0·74 (s.e. 0·21) and 0·75 (s.e. 0·19), respectively), but slightly lower for the pooled lactations (0·57 (s.e. 0·20), 0·55 (s.e. 0·20), 0·67 (s.e. 0·19) and 0·64 (s.e. 0·15)) in data set 1. Regressions of fat plus protein yield, food intake and gross efficiency on pedigree index for fat plus protein yield, each trait expressed as a ratio of herd mean, were 1·31 (s.e. 0·37), 0·38 (s.e. 0·19) and 1·04 (s.e. 0·35) for heifers and 0·89 (s.e. 0·31), 0·48 (s.e. 0·18) and 0·59 (s.e. 0·26) respectively, for pooled lactations, in data set 1. Regressions for cow lactations were lower. Similar results were obtained with data set 2. In this study, a genetic increase of proportionately 0·1 in fat plus protein yield of daughters of sires of high genetic merit for fat plus protein yield, was accompanied by a proportional genetic increase of 0·029 in food intake and a 0·079 proportional genetic increase in efficiency.

The economic values of cattle production traits differ with different production circumstances. This sensitivity implies that (1) production circumstances influence the revenue of breeding programmes, and (2) losses in revenue of breeding programmes occur when circumstances used in defining breeding goals are incorrect with regard to actual production circumstances at the moments of expression of genetic superiorities. In this study, these effects are quantified for a set of genotype and index traits, including milk production traits, food intake capacity and live weight. Twenty-four situations of production circumstances were studied, including alternative output limitations, milk production levels, roughage qualities and product (milk, beef) and production-factor (food) prices.

Results indicate that type of output limitation is the most important factor in determining revenue. Also, incorrect prediction of type of limitation leads to highest losses in revenue found (proportionately 0·01 to 0·06 of revenue). Losses in revenue due to incorrect prediction of production circumstances seem too low to justify complete diversification of cattle breeding goals within a breeding organization, except for different types of output limitations.

Reproductive data of 139 Simmentaler heifers, previously subjected to different levels of winter and summer nutrition, over a 3-year period, were analysed. Pregnancy rates of 77% and 96% were achieved during the first and second seasons for the two groups of heifers, respectively. Winter and summer nutritional levels affected the number of heifers culled, but had little effect on conception. There were no significant differences in the weight at mating between the heifers that conceived and those that failed to conceive. Mean date of conception was within 30 days and 20 days of the commencement of the breeding season for the first and second season, respectively. Post-weaning nutrition played a relatively minor role in affecting the time of conception. Birth weights of the progeny were not affected by treatment. Calf birth weight was however, significantly (P < 0·05) correlated with the weight of the dam at mating. Sixty-three % of the heifers produced three calves in 3 years, 35% produced two calves in 3 years and only two heifers produced one calf in 3 years. The data supported the original hypothesis that the emphasis, when heifers are bred at 2 years of age, should be shifted away from a physiological base to one where management and grazing strategy are more important in rendering the enterprise economically viable.

Three trials were conducted to evaluate the effects of treating soya-bean straw with various alkalis plus ensiling on digestibility of various nutrients and on nitrogen retention in ruminants. Soya-bean straw was treated with sodium hydroxide, calcium hydroxide or ammonium hydroxide and ensiled at 650 g/kg moisture. In trial 1, the effects of level and type of alkali on in vitro digestibility of ensiled soya-bean straw were evaluated. Concentrations of alkalis used were 0 (control), 20, 30, 40 and 50 g/kg dry matter. Both in vitro digestibilities of dry matter and organic matter of soya-bean straw were significantly (P < 0·05) increased with alkali treatment at all levels plus ensiling compared with untreated or treated unensiled straw. The 40 g/kg alkali concentration level in combination with ensiling appeared to be the most effective overall. In trial 2, the effects of type of alkali on nutrient digestibility and nitrogen retention in wether lambs were evaluated. Sixteen wether Suffolk lambs were given untreated or alkali-treated (40 g/kg) ensiled soya-bean straw. Treatments were: (1) water-treated straw; (2) NaOH-treated straw: (3) Ca(OH)1-treated straw; and (4) NH4OH-treated straw. Lambs given NH4OH-treated ensiled straw digested the dry matter, organic matter, and crude protein better than those given water-treated ensiled straw (P < 0·05). NH4OH improved nitrogen intake by proportionately 0·181 but not nitrogen retention. For trial 3, eight Angus steers were used. Chopped soya-bean straw was treated with NH4OH and ensiled in Silopress bags. Treatments were: (1) untreated dry straw; (2) water-treated straw; (3) 30 g/kg NH4OH-treated straw; and (4) 40 g/kg NH4OH-treated straw. The trial consisted of a 7-day collection period which was replicated once. Apparent digestibilities of dry matter, crude protein and various fibre constituents were increased by ensiling or ensiling and NH4 OH treatment combinations (P < 0·05). Alkali treatments in combination with ensiling appeared to improve digestibility of soya-bean straw, but ammoniation did not improve nitrogen utilization. Ensiling appeared to have a more significant effect than alkali treatments per se on the degradability of soya-bean straw.

Two experiments were made to determine the effects on digestion characteristics and live-weight (LW) gain of cattle consuming bermudagrass of supplementing with ground maize, soya-bean meal or a maizegluten— blood meal mix alone or maize plus the protein supplements. Experiment 1 was a Latin-square design with 14-day periods using six beef cows fitted with rumen and duodenal cannulas (490 kg). Cows were given bermudagrass hay at 12·7 g/kg LW alone (control, C) or with 2·4 g/kg LW of ground maize (M), 0·98 g/kg LW of soya-bean meal (S), 0·53 g/kg LW of maize-gluten plus 0·17 g/kg (dry matter basis) of blood meal (GB), M plus S (M + S) or M plus GB (M + GB). Nitrogen (N) intake was 106, 123, 143, 148, 166 and 166 g/day; total N at the duodenum was 101, 124, 117, 126, 140 and 161 (s.e. 5·91) g/day; and post-ruminal N disappearance was 61, 77, 72, 84, 87 and 110 (s.e. 5·6) g/day for C, M, S, GB, M + S and M + GB, respectively. In experiment 2, 96 crossbred beef heifers (203 kg LW) implanted with 200 mg testosterone and 20 mg oestradiol benzoate were allotted to 12 groups by LW (two groups per treatment). Heifers grazed bermudagrass paddocks for 84 days in two 42-day periods and supplement treatments were those in experiment 1. A period × treatment interaction in LW gain was noted (P < 0·05). LW gain was 0·78, 0·81, 0·79, 0·76, 0·70 and 0·95 kg in period 1 and 0·46, 0·51, 0·56, 0·53, 0·64 and 0·61 kg in period 2 for C, M, S, GB, M + S and M + GB, respectively (s.e. 0·049). In conclusion, duodenal flow and post-ruminal disappearance of N were similar for the protein sources when offered singularly, but when given with maize values were greater for the mix of protein meals high in ruminal undegradable protein as compared with soya-bean meal. LW gain by heifer calves grazing bermudagrass was increased only by supplementation with ground maize plus the protein meal mix of low ruminal degradability.

The incidence of twin calvings and double ovulations was studied in two Milking Shorthorn herds and one Friesian herd, each with above-average annual twin calving rates (average 0·031, compared with a national rate of 0·01). The proportions of double ovulations were calculated from records comprising 1237 cow × years (cows over 2·0 years of age); means were 0·08, 0·27 and 0·50, for three groups which had previously produced 0, 1 or >1 sets of twins, respectively. All cows (whether still present or no longer in the herd) were then allocated a twin production status, to indicate the number of twin sets (0, 1 or >1) produced, or produced so far, in their lifetime. There were records from 1559 cows, with sire and dam also known. Twin production status was significantly influenced by dam group (P < 0·01), i.e. the twin production status of the cow's dam. Sires were classified into two groups, according to whether any daughters had produced two or more sets of twins. After allowing for ascertainment, sires in the two groups were found to differ (P < 0·01) by 0·06 in the probability of their daughters producing at least one set of twins in their lifetime (i.e. 0·08 to 0·14). One sire and dam combination in particular had prolific daughters with a probability of 0·39 of producing at least one set of twins in their lifetime (compared with a probability of 0-07 for the other extreme combination). The possibility of these observations being explained by the segregation of a single recessive gene was considered, but the necessary interaction between sire group and dam group was not significant.

A theoretical analysis of the potential benefits of marker-assisted selection (MAS) of candidate bulls prior to entry into a young sire progeny testing programme was carried out. It is assumed that quantitative trait loci (QTL) affecting milk production have been mapped with respect to known genetic markers, and MAS is based on evaluation of elite sires in order to identify marker alleles in coupling to favourable or unfavourable QTL alleles. Candidate bulls, descendants of the elite sire will then be selected, prior to conventional progeny testing, on the basis of the marker alleles derived from the elite-sire ancestor.

The analysis considers recombination between marker and QTL, the difficulty of tracing specific marker alleles from sire to progeny, and the expectation that MAS, in practice, will be implemented in the grandsons, rather than in the sons of elite sires. It is shown that MAS of candidate bulls, based on the use of a single diallelic marker in linkage to a QTL will have only a negligible effect on the rate of genetic progress. Increases of 15 to 20% in the rate of genetic gain, however, can be obtained by the use of single polyallelic markers, and increases of 20 to 30% can be obtained by utilizing haplotypes of diallelic or polyallelic markers.

Forty-nine bulls, 27 Limousin × Friesian and 22 Charolais × Friesian, were evaluated and slaughtered in four batches of about equal size over 4 weeks. Each batch was of one breed. Age, live weight at evaluation and subjective assessments of fatness and conformation were recorded together with fat and muscle measurements by the Delphi, Meritronics, Scanogram, Vetscan, Kaijo Denki, Warren and the Velocity of Sound ultrasonic machines. Experienced operators were used to assess the performance of machine/operator combinations likely to be achieved in bull performance testing in the field. Fat thicknesses and areas, and m. longissimus areas were taken at the 10th rib and 13th rib, and 3rd lumbar regions by most machines. For the Delphi and Meritronics machines, fat thicknesses only were taken; for the Velocity of Sound machine, time interval measurements and anatomical distances were taken at the shoulder, mid back, lumbar and hind limb regions. The left side of each carcass was fully separated into lean, subcutaneous fat, intermuscular fat, bone and waste. All measurements were examined as potential predictors of carcass composition in step-wise regression in a model which included week of evaluation, breed and live weight at evaluation as the first independent variable. On the whole, scanning machines had a higher precision than A-mode machines, with the Velocity of Sound machine achieving the highest precision for carcass lean (g/kg) (residual s.d. = 13·0) and fat (g/kg) (residual s.d. = 14·1). None of the linear and area measurements taken on the carcass achieved the degree of precision of the Velocity of Sound, Scanogram and Vetscan machines.

Three experiments were conducted to determine the metabolizable energy (ME) concentration of dry maize gluten feed (DMGF) in starter (experiment 1), growing (experiment 2) or finishing (experiment 3) diets for steers. Seventy-two weanling Holstein-Friesian steer calves (initially 52 kg live weight); 32 Aberdeen Angus and 24 Shorthorn steer calves (initially 250 kg live weight) and 32 Aberdeen Angus, 24 Shorthorn and 68 crossbred steers (initially 367 kg live weight) were used in experiments 1, 2 and 3, respectively. In experiment 1, calves were given one of three total mixed rations in which energy and protein ingredients on a dry matter (DM) basis were (g/kg): (1) 590 ground maize grain (MG), 260 rolled oats (RO) and 150 soya-bean meal (SBM); (2) 210 DMGF, 400 MG, 260 RO and 130 SBM; or (3) 440 DMGF, 210 MG, 250 RO and 100 SBM. Daily live-weight gains (LWG) and food-to-gain (F/G) ratios were similar across dietary treatments (P > 0·05). Calves given the diet containing 440 g DMGF per kg had higher DM intakes (DMI) than those given no DMGF (P < 0·05). ME concentration of the diet without DMGF was greater than ME concentrations of diets containing DMGF (P < 0·05). In experiment 2, calves were given one of four diets containing, on a DM basis (g/kg): (1) 800 maize silage (MS) and 200 MG; (2) 800 MS and 200 DMGF; (3) 500 MS and 500 DMGF; or (4) 200 MS and 800 DMGF. LWG and DMI of calves given 500 or 800 g DMGF per kg diets were higher than those of calves given 0 or 200 g DMGF per kg diets (P < 0·05). F/G ratios tended to increase and dietary ME concentrations tended to decrease with increasing content of DMGF in diets. In experiment 3, steers were given one of four diets, which on a DM basis were (g/kg): (1) 850 MG and 150 MS; (2) 300 DMGF, 150 MS and 550 MG; (3) 500 DMGF and 500 MG; or (4) 750 DMGF and 250 MG. LWG was not altered when DMGF replaced MG only or MG and MS (diet 2 v. 1 or diets 3 and 4 v. 1, respectively (P > 0·05)) in the diet. Steers given the 300 or 750 g DMGF per kg diets had higher DMI and lower F/G ratios than those fed diets without DMGF (P < 0·05). ME concentration of the diet without DMGF was greater (P < 0·05) than the ME concentration of 300 or 750 g DMGF per kg diets. ME concentration of DMGF, calculated by regression, was proportionately about 0·9 of the value of MG in all experiments and averaged 11·46 MJ/kg DM.