The long-term genetic contributions were calculated for 219 Finnish Ayrshire bulls born between 1958 and 1964 to 707 Finnish Ayrshire bulls made available for artificial insemination and born between 1986 and 1988. Three strategies were employed:(i) using all known pedigree information; (ii) ignoring information on the dam of females; (iii) only using information on sires. Expected contributions were calculated using gene flow matrices.

The contributions from strategies 1, 2 and 3 were only 0.6 (1 and 2) or 0.7 (strategy 3) of those expected. The causes of this shortfall for strategies 2 and 3 were identified as (i) the use of an imported sire and (ii) generation skipping. For strategy 1, 0.2 of the expected pathways remained unaccounted for and were ascribed to missing pedigree information.

Of the 219 ancestors, only 86 made positive contributions to the descendants. Only 10 ancestors made contributions more than the average, and one bull accounted for 0.3 of all pathways traced on strategy 2. There was general agreement in the relative contributions of individual bulls when assessed using the three strategies.

The rate of inbreeding (ΔF) estimated by regression from 1974 to 1988 and using known pedigrees was 0.0018 per year and the average coefficients of additive genetic relationship among cohorts was increasing by 0.0030 per year. AF was estimated using the contributions calculated by strategies 1, 2 and 3 to be 0.0147, 0.0151 and 0.0125 per generation respectively. These were converted into rates per year by assuming a generation interval of 6.5 years taken from both published and new information on generation intervals in the Finnish Ayrshire population. This gave annual rates of 0.0023, 0.0023 and 0.0019. The estimates from strategy 3 were obtained without the use of any pedigree information pertaining to dams.

This paper presents an approach for ethical evaluation of biotechnology, which is illustrated by cloning in dairy cattle breeding. The approach for ethical decision-making that was followed, the so-called network model, started with determining fundamental moral principles that together constitute a framework for the detection of ethical issues in a given situation. In terms of human ethics, four fundamental principles have been defined: beneficence, non-maleficence, justice and autonomy. In the context of animal biotechnology, the same four fundamental moral principles as in humans are considered, except that autonomy is replaced by respect for the integrity of the animal. Based on a Dutch advisory committee concerning animal biotechnology, two additional principles were considered: irreversibility and veriflability. For each individual case, moral decision-making means balancing of moral intuitions, moral principles and morally relevant facts. The final outcome on moral acceptability of an action, therefore, will differ among people. The latter is demonstrated using three types of people (the ruler, the steward and the partner/participant). For each type of person, the fundamental attitude toward animals and nature is defined and a possible decision on the application of cloning in dairy cattle breeding is given. The authors' opinion, however, is that the benefits of cloning are relatively small, especially in the long term, whereas the moral drawbacks of cloning are considerable. The authors conclude that other ways of furthering animal husbandry should have priority.

‘Sustainability” has been defined in so many different ways that it no longer has an accepted (or acceptable) meaning. Nevertheless, it is being used as a label to confer respectability on corporate plans and research proposals, practical projects, attitudes and intellectual positions. The weaknesses of current definitions are examined with a view to clarifying the physical, biological and socio-economic objectives, covered by the term ‘sustainable’.

Since it is no longer feasible to abandon the term or to restrict its scope, it is worth considering what useful meaning can be attached to the concept. An attempt is made to spell out the tvays in which it could sensibly be used in relation to animal production systems. It is suggested that this would have to take the form of a package of expressions covering the essential attributes offuture animal production systems.

Direct genetic evaluation of profit was investigated as an alternative to a selection index. PROFk was defined as (net income)/(food requirement) until the start of the kth lactation, for k = 2 to 6. Genetic parameters such as heritabilities and genetic correlations were estimated for profit traits for Australian Holstein-Friesian and jersey dairy cattle. Heritabilities for profit until the start of a given lactation were moderate, ranging from 0·12 (for profit until the start of the second lactation in Holsteins) to 0·31 (profit until the start of the third lactation in Jerseys). Genetic correlations between profit traits were very high, and approached unity for most pairs of traits, so that profit early and late in herd life were nearly the same trait. Genetic correlations between profit traits and stayabilities until a given lactation were high, ranging from 0·71 to 0·97. Genetic correlations between profit traits and first lactation milk yield traits were approximately 0·80 for Holsteins and 0·90 for Jerseys. A single analysis urns carried out for lifetime profit using all data, including cows that were still in the herd at the time of data collection. Heritabilities were 0·13 for Holsteins and 0·19 for Jerseys. Genetic correlations between lifetime profit and first lactation yields were high. For the selection of dairy bulls, a multivariate analysis on a milk yield trait (e.g. protein yield) and profit until the last known lactation of bulls' progeny was suggested.

A dynamic programming model was used to derive economic values for the goal traits milk, fat and protein yield and longevity. The economic values derived were £3.37 per % cows surviving to complete lactation four (conditional on having a milk record in the first lactation) and £-0.03, £0.60 and £4.04 per kg for milk, fat and protein yield respectively. In terms of genetic standard deviations the weight for protein, fat, milk and longevity were 1.0, 0.21, —0.25 and 0.55, respectively. Using economic values and genetic (co) variances, weights were derived for milk fat, protein and four linear type traits (chosen out of fifteen on the basis of the genetic correlation with longevity): angularity (angular), foot angle (steeper), udder depth (shallower) and teat length (shorter). Three additive indices were derived, assuming that the breeding goal was for: (i) yield only (PIN), (ii) longevity only (LIN) or (ii) yield and longevity, hence economic merit (ITEM). Selection on ITEM is expected to give a 2% higher annual rate of genetic progress compared with selection on PIN. Efficiency of using ITEM was larger than 0.97 compared with the optimum index, when the real individual economic values increased or decreased by a factor 1.5 or 2.0. Weights for ITEM were calculated assuming that predicted transmitting abilities (PTAs) from complete multivariate analysis were used as index measurements. In the practical situation that index measurements came from (i) separate univariate best linear unbiased prediction (BLUP) evaluations or (ii) two multivariate BLUP evaluations (one for type and one for yield), efficiency of ITEM (compared with the optimum index) decreased with decreasing accuracy of the PTAs and with increasing ratio between number of records for type and yield, or vice versa, but remained close to 100%. Only in the (not practical) situation where accurate PTAs for type and inaccurate information for yield were combined, did the efficiency of ITEM drop as low as 0.44, due to a change of sign for udder depth in the optimal index.

To investigate strategies for concentrate allocation, 155 multiparous Holstein-Friesian cows received grass silage ad libitum during lactation weeks 4 to 22 in two experiments. A standard concentrate (196 g crude protein (CP) per kg dry matter (DM)) was offered at the same average amount across the lactation period either at aflat rate or as two rates with a change of 6 kg in week 13. Treatments, described as kg concentrate DM per day in the first and second periods of lactation, were 3: 3, 6: 0, 3: 9 (experiment 1), 6: 6, 9: 3, 9: 9 and 12: 6 (experiments 1 and 2). In experiment 2, two additional treatments maintained CP supply from concentrate after a change from 9 and 12 kg DM by giving 3 and 6 kg high-protein concentrate (HP) DM per day (575 and 383 g CP per kg respectively).

Generally as concentrate intake increased silage intake fell, DM intake rose and yields of milk and all milk solids increased linearly. However, in experiment 1 from a base of 3 kg DM, as concentrate intake increased so did fat yield overall and protein yield in mid-lactation but at a declining rate. Fat concentration was depressed at the lowest and highest concentrate levels. Protein concentration rose as concentrate allowance increased particularly at low levels. Increasing concentrate in mid lactation improved protein but not fat concentration. Additional concentrate either spared weight loss or increased weight gain. Distributing more of a fixed allowance of concentrate to early lactation did not affect cow performance overall.

Silage intake, milk, protein and lactose yields and protein concentration increased and fat concentration was reduced by giving HP concentrates, effects being greater with 3 than with 6 kg DM per day. Reducing concentrate level while maintaining CP intake did not influence milk and solids yields. The ratios of responses to concentrate CP (3 kg DM per day HP v. 3 kg DM per day standard) compared with concentrate energy (9 kg DM per day standard v. 3 kg DM per day HP) were 2·1, 2·2, 7·4 and 1·9 for milk, fat, protein and lactose yields respectively. The results suggest feeding strategies for manipulating the production and quality of milk from grass silage diets.

Twenty-four Holstein Friesian cows in experiment 1 and 40 cows in experiment 2 were used over 12 weeks in continuous designs, to evaluate winter wheat as a forage for dairy cows. In experiment 1, whole-crop wheat was ensiled at 350 g dry matter (DM) per kg (EW) or harvested later and stored at 550 g DM per kg following treatment with 40 g urea per kg DM (40W). In addition to these treatments in experiment 2, whole-crop wheat of 550 g DM per kg treated with 20 g urea per kg DM (20W), and combine harvested wheat grain plus wheat straw (40: 60 ratio) treated with sodium hydroxide (SG) were also included. These whole-crop wheat forages were incorporated into the diet at a level of 400 g/kg of the forage DM in experiment 1, and 330 g/kg in experiment 2, with the remainder of the forage being grass silage. A control treatment of grass silage (GS) offered as the sole forage was also included. The forages were mixed in a mixer wagon and offered ad libitum. A fixed level of 8 kg/day of concentrates was offered in experiment 1 and 7 kg/day in experiment 2. Total DM intake was significantly greater for EW and 40W than for GS in experiment 1, but not in experiment 2. Milk yield was not significantly affected by diets (mean 28·8 kg/day in experiment 1 and 29·6 kg/day in experiment 2). Milk fat, protein and lactose contents and yields were also not significantly affected by diets. The additional total metabolizable energy (ME) intake of the whole-crop diets compared with GS was partitioned to live weight. There was no evidence of ME intakes being substantially greater than ME requirements as found in previous studies. A 5 × 5 Latin square digestibility experiment was carried out with Holstein-Friesian heifers offered the individual forages used in experiment 2. Intake was significantly greater for the urea-treated whole-crop wheat forages than for grass silage and for sodium hydroxide-treated grain and straw. The digestible organic matter in the dry matter (DOMD) of grass silage was 692 g/kg and the whole-crop wheat diets ranged from 626 g/kg for ensiled whole-crop wheat to 682 g/kg for the sodium hydroxide-treated grain plus straw (40: 60 ratio), with the DOMD of urea-treated whole-crop being intermediate. The results indicated that whole-crop wheat had higher intake characteristics than grass silage in spite of its lower digestibility.

Thirty-six Holstein/Friesian cows were used in a 3 × 2 factorial design randomized-block experiment to evaluate the production and nutrient utilization responses of animals of three genetic indices (cow genetic index 90 (CGI); 950, 650 and 550), each given either a complete diet (CD) or concentrate separate from grass silage through out-ofparlour feeders (OPF). The experiment included days 11 to 160 of lactation. On the CD treatment the diet was offered ad libitum with a concentrate proportion of 0.64 (dry matter (DM) basis), while on the OPF treatment the grass silage urns offered ad libitum and the allowance of concentrate was made equal to the mean concentrate intake of the CD treatment during the previous week. The concentrate was based on barley, maize gluten, molassed sugar-beet pulp, citrus pulp, soya-bean meal, fish meal and protected fat. During the experiment eight blocks each of six animals were used in metabolism studies to determine total ration digestibility, nitrogen balance and energy utilization.

No significant feeding method × genetic index interactions were found in terms of food intake, milk production or nutrient utilization. Although CGI had no significant effect on total DM intake, silage DM intake increased linearly as the cow CGI increased (P < 0.01) across the CD and OPF treatments. The high CGI cows produced respectively 6.60 and 8.25 kg/day more milk fP < 0.001) than the medium and low CGI animals without altering milk concentrations of fat and protein, but with on average a negative live-weight change with the high CGI cows. Although nitrogen digestibility was significantly higher with the low than medium CGI cows (P < 0.05), cow CGI had no significant effects on DM and energy digestibilities, daily methane energy output, heat production or the efficiency of utilization of metabolizable energy for lactation fk,) in the metabolism study. The results indicated that higher milk production with the high CGI cows was mainly attributed to an alteration in nutrient partitioning between milk energy and body energy retention.

Across the three genetic indices, feeding method had no significant effect on total DM intake, although silage DM intake was 0.46 kg/day higher (P < 0-05) on the OPF treatment. However feeding the complete diet resulted in 3.04 kg/day more milk CP < 0.05) than feeding concentrate separate from silage without altering milk concentrations of fat and protein. In the nutrient metabolism study whole tract digestibilities of DM (F < 0.001), nitrogen (P < 0.05) and energy (P < 0.01) were higher on the OPF treatment, but methane energy output and heat production were similar between the two treatments.

Forty-eight culled dairy cows were assigned to one of two treatment groups to investigate the effect of a β-adrenergic agonist in mature cattle. They were finished during a 63-day period on a concentrate diet, containing 0 or 4 mg/kg cimaterol. No food was given in the 20 h prior to slaughter.

Cimaterol had no effect on food intake, but significantly improved food conversion efficiency and increased live-weight gain, carcass weight and dressing proportion (P < 0·05). Cimaterol induced muscle hypertrophy as evidenced by an improved EUROP carcass classification and a higher longissimus thoracis (LT) cross-sectional area (P < 0·001). EUROP fat score and fat content in the carcass and the LT were lowered (P < 0·05). Cimaterol resulted in brighter meat (higher L-value: 37·0 v. 35·6; P<0·05) with a higher shear force value (64·0 v. 46·4 Newton; P<0·01) compared with control animals. It seems likely that mature cattle receiving cimaterol respond similarly to younger growing animals.

Two groups of eight Charolais heifers were used to examine the effect of feeding level during the post-weaning winter on the grazing behaviour and herbage intake over three periods during the first 2 months of grazing. The winter diets (L and H) were given to achieve a mean difference of 50 kg between groups at turn-out. The heifers were set-stocked together on a hill pasture where sward height was maintained at 12 cm.

The winter live-weight gains were 0·31 and 0·70 (s.e. 0·032) kg/day for L and H heifers respectively, and spring gains 1·94 and 1·66 (s.e. 0·082) kg/day respectively. Intakes increased throughout the spring grazing for both groups. Absolute intakes were lower for L than for H heifers only during the first period (P < 0·05). Intake per kg live weight was higher in L than in H heifers (23·0 v. 21·1 (s.e. 0·54) g organic matter (OM) per kg live weight). Bite weights of H heifers were constant throughout (434, (s.e. 12·9) mg OM), while bite weights ofL heifers only reached those of H heifers in the last period. Bite weight was linearly related to live weight. Bite rates were not different between groups, but L heifers compensated for lower bite weight by grazing longer and they increased their grazing time after turn-out faster than H heifers. Grazing time was mainly responsible for higher relative intakes in L heifers, and thus, partly, for compensatory gain observed.

An experiment zoas conducted to assess differing methods of twin pregnancy establishment in Hereford × British Friesian beef cows and heifers. The experiment was 2 × 2 × 2 × 2 factorial design in which the factors were (i) source of embryos (in vivo or in vitro produced); (ii) pregnancy status of recipient (inseminated or non-inseminated); (Hi) method of embryo transfer (surgical or cervical); and (iv) uterine location of a native and transferred embryo, or two transferred embryos (both located in the ipsilateral, or one in each of the ipsi and contralateral uterine horns). Pregnancy and twinning rates for 285 animals used for embryo transfer were initially diagnosed at day 56 after induced oestrus by transrectal ultrasonography. Subsequently, calving rate and birth weiglit at calving were recorded.

Pregnancy rates at day 56 after induced oestrus were similar for both surgical and cervical transfers (58·6% v. 55·2%), as was the case for twinning rate (36·2% v. 30·0%). Similarly, there were no differences between these two methods of transfer (50·0% v. 46·9%) and (26·1% v. 17·7%) for calving and twin calving rates respectively. Recipients which had two embryos located in the ipsilateral uterine horn had higher (P < 0·001) pregnancy rates (66·6% v. 47·3%) but similar twinning rates (32·6% v. 33·4%) at day 56 after induced oestrus to recipients which had one embryo located in each horn. A greater (P < 0·05) percentage of recipients with two embryos originally located in the ipsilateral horn calved (56·0% v. 41·0%) but fewer (P > 0·05) produced twins (17·8% v. 25·7%) than was the case for recipients which originally had one embryo located in each horn. In vivo produced embryos resulted in higher (P < 0·001) pregnancy rates (74·4% v. 39·7%) and twinning rates (48·3% v. 18·0%) at day 56, and higher (P < 0·001) calving rates (64·5% v. 32·7%) and twin calving rates (36·3% v. 7·6%) than did in vitro produced embryos. Inseminated (Al + ET) recipients had slightly greater (P>0·05) pregnancy rates (61·6% v. 51·6%) and twinning rates (36·9% v. 28·7%) than non-pregnant recipients which received two embryos. A greater (P<0·05) percentage of inseminated recipients (Al + ET) calved (54·3% v. 42·0%) than was the case for non-pregnant recipients which received two embryos. The percentage producing twins at calving were similar for these two methods of twin pregnancy establishment.

Embryo survival to day 56 after induced oestrus averaged 45·0% and was found to be non-independent of its co-twin. From day 56 to parturition foetal loss averaged 21·0% and foetal survival was found to be independent of the fate of its co-foetus. Twin foetuses located in the same uterine horn were lighter at birth than twin foetuses located in separate uterine horns (33·0 v. 35·2 kg; P < 0·05).

One hundred and two multiparous Holstein/Friesian dairy coivs were used to examine the effect on food intake and milk production of replacing 330 g/kg dry matter (DM) of first-cut perennial ryegrass silage (GS) with either fermented (FW) or urea (40 g/kg DM) treated (UW) whole-crop wheat, brewers' grains (BG), fodder beet (FB) or maize silage (MS). A forage mixture containing GS and 750 g/kg DM of maize silage (MSH) was also offered. Dietary crude protein (CP) concentrations were equalized by offering all cows 6 kg DM per day of an appropriate concentrate supplement. DM intake and milk yield of cows offered GS (15·3, 23·0 kg/day) were increased (F < 0·01) by the inclusion of BG (16·3, 26·7 kg/day), FB (17·6, 25·9 kg/day), MS (16·6, 26·4 kg/day) and MSH (18·5, 27·6 kg/day). BG, FB and MS all produced similar increases in milk yield. Although the inclusion of FW and UW increased (F < 0·05) DM intake, milk yield was not significantly affected. The differences between the highest and lowest milk fat concentration, produced by FB (42·9 g/kg) and BG (40·1 g/kg) respectively, and the highest and lowest milk protein concentration produced by FB (32·1 g/kg) and GS (29·9 g/kg) respectively, were statistically significant (F < 0·001). Milk fat and protein yields of cows offered GS (0·97, 0·71 kg/day) were increased (F < 0·01) by BG (1·07, 0·82 kg/day), FB (1·11, 0·83 kg/day), MS (1·11, 0·83 kg/day) and MSH (1·12, 0·88 kg/day). Intermediate values were recorded for FW (1·01, 0·72 kg/day) or UW (1·00, 0·73 kg/day). Results show that farmers should consider replacing a major part of the grass silage component with an alternative forage or forage substitute.

Data from two experiments are reported which test the hypothesis that nutrient and/or dry-matter intake and body condition may interact to modify hypothalamic opioidergic activity and thus influence the pulsatile release of LH during the early post-partum period and during the oestrous cycle. Experiment 1 involved 16 multiparous, twin-suckling beef cows, and was a 2 × 2 × 2 factorial design in which the factors were level of post-partum energy intake (80 v. 130 M) metabolizable energy (ME) per day), the digestible undegradable protein (DUP) content of the post-partum diet (14 v. 31 g/kg dry matter), and treatment with either 200 mg or 400 mg naloxone hydrochloride. Blood samples were collected at 15-min intervals for 4h at weeks 4 and 7 post partum. Naloxone was administered intravenously after the eighth sample. Experiment 2 involved 16 cyclic maiden heifers and was also arranged in a factorial manner, with two levels of body condition at the start of the experimental period (2·50 and 3·16 units) and two levels of energy intake thereafter (40 and 80 MJ ME per day). Seven blood samples were collected at 15-min intervals on 4 days consecutively during the mid-luteal phase of the oestrous cycle. On the first 2 of these 4 days naloxone was administered, whilst on the last 2 days a gonadotropin-releasing hormone agonist (buserelin; GnRH) was administered, both after the fourth sample. Plasma from both experiments was assayed for LH and prolactin (Prl).

In experiment 1, cows on 130 MJ ME per day returned to oestrus and ovulated earlier than cows on 80 MJ ME per day (44·5 v. 55·0 days; s.e.d. = 3·93; P < 0·05). At week 4 post partum the proportional increase in plasma LH following naloxone challenge was greater for cows on 130 MJ ME per day than cows on 80 MJ ME per day (1·38 v. 1·12; P < 0·05), but the converse was true at week 7 (1·15 v. 1·68; P < 0·05). Cows on the high DUP diet required a higher dose of naloxone to elicit an LH response. Few heifers in experiment 2 exhibited an LH response to naloxone. In contrast, there were significant dietary treatment effects on the LH response to GnRH (P < 0·01). Relatively thin heifers on 40 MJ ME per day exhibited the lowest proportional increases in plasma LH to GnRH challenge, whereas heifers on 80 MJ ME per day and given the higher dose of GnRH produced the greatest plasma LH responses. Mean Prl concentrations before and after feeding in experiment 2 were respectively 13·2 and 10·2 ng/l (P < 0·01).

Suckled cows given a high energy diet during the early post-partum period can overcome the opioid mediated block on LH release and resume oestrous cycles earlier than cows given a low energy diet. LH would appear to be inhibited by a non-opioid mechanism in mid-luteal phase heifers. Total pituitary reserves ofLH may be influenced by the animals nutritional status.

Foods produced from two cereal-legume cropping systems were evaluated in a 250-day growth trial using Friesian × Boran crossbred steers. Crops and crop combinations in cropping system 1 were oat-vetch (Avena sativa-Vicia dasycarpa; OV), wheat-trifolium (Triticum aestivum-Trifolium steudneri; WT), teff (Eragrostis tef) and chickpea (Pisum sp). Cropping system 2 differed from 1 in that maize-lablab (Zea mays-Lablab purpureus; ML) replaced ivheat-trifolium. Twenty-four steers (mean initial live weight 157 (s.d. = 4·5) kg were assigned randomly within weight group to four treatments. Treatments comprised ad libitum teff straw (TS) given alone (Tl), TS plus wheat middlings (WM) given at 0·01 M (body weight) (Tl), forages from system 1 fed in the order OV, WT and TS plus chickpea for 135, 48 and 67 days respectively (T3) or forages from system 2 fed in the order OV, ML and TS plus chickpea for 73, 147 and 30 days respectively (T4). The feeding period for each crop ofT3 and T4 was based on its contribution to the total dry matter (DM) yield of the cropping system. Apparent digestibility of DM measured by the acid-insoluble ash method was higher (P < 0·05) for T3 and T4 than for T2. DM intake was higher (V < 0·01) for steers on T2 resulting in 1 kg higher daily intake of digestible DM than for T3 and T4. Steers on T4 gained (average daily gain, ADG) more (P < 0·01) weight than steers on T3 (149 v. 85 g per head per day) but less (P · 0·01) than those on T2 (528 g per head per day). Steers on Tl lost 94 g per head per day. Food efficiency (kg yain per kg food) followed a similar trend as ADG. At the end of the trial, two steers from each treatment were slaughtered for carcass assessment and the remaining steers used in a realimentation study of 120 days and then slaughtered for carcass assessment. Steers which gained poorly during the 250-day trial (Tl, T3 and T4) exhibited compensatory gains of 497, 550 and 565 g per head per day respectively compared with 398 g per head per day for steers on T2. Carcasses from T2 yielded significantly more (P < 0·05) lean and fat than carcasses from T3 and T4. The results suggest that growing food crops in association with legumes has the potential of increasing cattle performance.

Mature dry cows, 18-month-old heifers and 7-month-old female calves of the Charolais breed (eight animals of each age) were strip-grazed on moderate (15cm) or tall (52 and 32cm) cocksfoot swards over two 15-day experimental periods. The swards were leafy regrowths of 2 (short) and 8 (tall) weeks of age. Herbage intake was estimated by the alkane method, and grazing behaviour was visually recorded.

Bite weight was lower, grazing time and biting rate greater, and organic matter in take of grass (OMIG) higher on shorter swards, the latter being related to a higher in vitro digestibility and nitrogen concentration. Average OMIG per kg live weight (M) was 15·2, 19·1 and 17·0 (s.e.d. 0·49)g in cows, heifers and calves respectively. The average allometric coefficient between OMIG and M was 0·88 (similar between swards), and close to that obtained with hay after the grazing trial.

Faecal markers suggested a greater selectivity of calves compared with older cattle. Average bite weights (BW) were 310 (s.e. 40), 467 (s.e. 112) and 718 (s.e. 144)mg OM in calves, heifers and cows respectively. The allometric coefficient between BW and M was higher in short swards than in tall ones. Biting rates increased and grazing times tended to decrease with age of cattle.

Alternative closed breeding schemes for beef cattle are analysed using stochastic computer simulation. Multiple ovulation and embryo transfer (MOET) schemes are compared with conventional schemes (schemes without MOET) with an equal expected number of progeny born per year. Schemes are compared for genetic gain and inbreeding obtained after 25 years of selection. The trait considered, evaluated in both sexes, has an initial heritability of 0·35. Different population sizes and numbers of sires selected are evaluated. Current realistic parameters for embryo production are assumed in MOET schemes.

After 25 years of selection, and with no control on inbreeding, cumulative genetic gains are about 50% higher in MOET schemes compared with conventional schemes. The benefit from MOET is mostly due to increased selection intensities in females. The rate of inbreeding increases by up to nearly 300% when MOET is used. This maximum percentage increase in inbreeding following the use of MOET can be reduced to about 100% when selection and mating strategies for controlling inbreeding are used. The effect of the number of sires used on the inbreeding obtained is more important than the effect of the size of the herd. In MOET schemes, increasing the number of sires selected by a factor of three, leads to reductions in inbreeding rates of 40%. When schemes of the same size are compared at similar acceptable inbreeding levels, MOET schemes give around 30% higher genetic progress than conventional schemes.

The relationship between puberty and the cessation of luteal activity after nutritional restriction was evaluated in 15 Angus × Hereford heifers. Heifers attained puberty at a body weight of 297 (s.e. 6) kg and a body condition score (BCS) of 5·5 (s.e. 0·1) on a scale of 1 (emaciated) to 9 (obese). After 154 (s.e. 16) days of nutritional restriction, heifers became anoestrus at a weight of 273 (s.e. 8) kg and a BCS of 3·0 (s.e. 0·2). The Spearman's rank correlation coefficient between date of-puberty and date of cessation of luteal activity was (r = –0·49; P < 0·06). This indicates that the heifers that attained puberty first were the last to cease luteal activity during nutritional restriction.

Crossbred wethers (34 (s.e. 0·9) kg), with catheters in a hepatic vein, the portal vein and a mesenteric vein and artery, were offered ad libitum alfalfa (A), bermudagrass (B) or ryegrass-wheat (RW) hay and approximately 0, 200 or 400 g/kg maize (dry matter) to determine influences of maize level on net flux of oxygen and nutrients across the portal-drained viscera (PDV) and liver with different forage sources. Digestible energy intake (MJ/day) was 8·5, 12·0 and 12·8 (s.e. VIS) for A; 4·5, 5·5 and 9·0 (s.e. 0·93) for B; and 9·4, 8·8 and 12·2 (s.e. 0·93) for RW with 0, 200 and 400 g/kg maize, respectively. Splanchnic bed oxygen consumption (mmol/h) was 301, 304 and 322 (s.e. 27·2) for A; 178, 187 and 217 (s.e. 30·0) for B; and 226, 133 and 233 (s.e. 19·0) for RW with 0, 200 and 400 g/kg maize, respectively. Increasing dietary maize level linearly increased (P < 0·05) PDV release of alpha-amino nitrogen with B (5, 9 and 14 mmol/h) but not with A or RW. Dietary maize level did not consistently alter PDV or hepatic net flux of urea or ammonia nitrogen, suggesting that changes in ruminally fermentable organic matter from diets offered ad libitum, presumably induced by varying dietary concentrate level, may not alter nitrogen recycling when forage is 86 g/kg or greater in crude protein. Propionate release by the PDV and hepatic uptake increased linearly (P < 0·08) as maize level in A and B diets increased, although increasing dietary maize level did not significantly alter PDV, hepatic or splanchnic bed net flux of glucose regardless of forage source. Nevertheless, glucose concentration in arterial blood with A and RW increased linearly fP < 0·05) with increasing maize level, suggesting increased peripheral glucose availability. In conclusion, the potential to decrease energy consumption by splanchnic tissues relative to digestible energy intake by dietary inclusion of maize, thereby increasing the proportion of absorbed energy available to extra-splanchnic tissues, may be greater for low-quality forage than for forage of moderate or high quality and for moderate v. low dietary levels of maize with low-quality forage.

Reproductive performance of purebred Angus (A) and Criollo (C) cows and crossbred CA and AC cows in the temperate area of Buenos Aires, Argentina, was assessed through the study of reproductive rates, calving date, first insemination date, number of inseminations and weight related variables. The herd was grazed on pastures all year round. Matings were by artificial insemination with visual oestrus detection, from October to December. Heifers first calving was at 3 years of age. All traits were analysed with general linear models including, as corresponded, fixed effects of dam and calf genetic groups, calving year and month, dam physiological status, calving age and first order interactions. Female genetic group adjusted means were used to estimate direct (gl) and maternal (gM) breed differences and heterosis (hl) effects on reproductive traits. Weaning rate was mostly determined by oestrons detection rate. Due to the inhibitory effects of nursing on reproduction, female genetic group effects were significant for suckling cows only: mean oestrous detection rate was higher (P < 0·05) for crossbred cows (AC: 91·2 (s.e. 5-1) %; CA: 88·4 (s.e. 2·9) %) than for A (76·3 (s.e. 2·0) %) and C (49·9 (s.e. 3·3) %); direct breed effects favoured A (glA - g1c = 26·4 (s.e. 3·7) %; P < 0·001) and h1 was 26·7 (s.e. 3·4) % (P < 0·001). When only oestrous-detected cows were considered, direct breed effects were significant only for pregnancy rate fg1A —g1c = 8·5 (s.e. 4·4) %) whereas h1 was significant for pregnancy (8·3 (s.e. 3·8) %), calving (9·3 (s.e. 4·1) %) and weaning (10·1 (s.e. 4·1) %) rates (P < 0·05). Criollo cows calved later than crossbred (≍19 days) and A (≍15 days) cows mainly due to longer post-partum anoestrous. For calving date, direct breed effects favoured A (g1A — g1c = 20·8 (s.e. 5·9) days; P <0·0·001) and h1 was 11·4 (s.e. 2·8) days (P < 0·001). Low reproductive performance in C was not associated with live iveight at the beginning of mating. This genetic group was the latest in showing oestrous behaviour, even when not suckling. Number of inseminations was similar for the four genetic groups. These results sustain the principle of utilizing Fl Criollo-Angus cows to improve beef herd productivity, whereas they do not support the recommendation of using purebred Criollo females under this type of production system.

Mature non-lactating cows, 18-month-old heifersand7-month-oldfemale calves of the Charolais breed (eight animals of each age) were strip-grazedon short (S, sward surface height: 7·5 cm), medium (M,10·2 cm) and tall (T, 21·1 cm) cocksfoot (Dactylis glomerata) swards at a daily herbage allowance of 40 g dry matter per kg live weight over three 15-day experimental periods. The swards were leafy regrowths of 1 (S), 2 (M)and 3·5 (T)weeks of age. Herbage intake was estimated by the n-alkane method, and grazing behaviour was recorded visually.

Intakes per kg live weight of calves and heifers were higher than those of cows on all swards(P < 0·01). Calves tended to maintain intake, whereas cows and heifers reduced their intake as sward height decreased. Bite weight decreased linearly with sward height, this decrease being greater for larger animals (P < 0·001). As sward height decreased, the scaling factor of bite weight to live weight decreased. Biting rates increased as sward height decreased (P < 0·001) and were lower in calves than in older cattle (P < 0·001). Calves had lower intake rates per kg live weight than cows in T swards, and the reverse was true in S swards (P < 0·001). Younger cattle always grazed longer than cows, but differences were reduced as sward height decreased (P < 0·01). Cows and heifers wereunable to increase their grazing time sufficiently to compensate for lower intake rates in S and M swards, resulting in reduced herbage intakes. Faecal markers and grazing behaviour suggested a greater selectivity by calves compared with older cattle.