The effect of changes in the mating system on the rates of genetic progress and rates of inbreeding are considered for MOET nucleus breeding schemes. Methods are derived to calculate best linear unbiased predictors of breeding value in MOET schemes and the rate of inbreeding under selection. These are applied to different mating systems in which the numbers of sires and dams, and the number of offspring per sire and offspring per dam, remain constant.

Results showed that compared with nested mating systems, factorial mating systems in which the maternal half-sibs are produced instead of full-sibs, could increase genetic progress by 1·12-fold with no additional inbreeding. The increased progress arose through an increase in the selection intensity applied. The rates of inbreeding derived were found to be approximately double those estimated by the formula of Wright (1931) in the absence of selection.

In practice, even if a complete factorial system were to increase the generation interval and consequently reduce progress below that predicted, changes in the mating system avoiding this problem could be implemented that would be of immediate benefit.

Thirteen dairy cows between 7 and 20 days post partum were fitted with catheters in both the jugular vein and caudal vena cava, the latter with the tips anterior to the junction with the ovarian veins. Blood samples were taken from nine control cows from both sites at 15-min intervals for periods of between 8 and 16 h. Four more cows were sampled for 13 h and given 4 × 2·5 ug GnRH intravenously at 3-h intervals starting 1 h after sampling began. Plasma oestradiol-17(3 concentrations were significantly higher in the vena cava than in the jugular vein in the two cows in which they were compared. Twenty-eight LH pulses occurred in the nine control cows during the sampling periods. These were followed within 1 h by increases in caval oestradiol-17β concentrations in 26 cases. LH pulses occurred after 14 of the 16 GnRH injections and with one exception were associated with oestradiol pulses in the vena cava. Oestradiol concentrations generally peaked 15 to 45 min after each LH peak. It is concluded that ovarian follicles are responsive to LH pulses by releasing oestradiol pulses early in the post-partum period.

Six alternative lactation curves were derived by considering the proportional rates of change in milk yield during lactation. Experimental data showed that rates of change do not necessarily fall to a constant value in mid and late lactation. This accounts for the systematic lack of fit reported by several authors using the derivative of the incomplete gamma function, whose second derivative has a horizontal asymptote. Curves whose derivatives are not restricted in this way described patterns of milk yield in first to third lactation animals more closely. Some statistical properties of their parameters have been examined. The curve loge (y) = a - bt'(1 + kt') + ct'2 + d/t, where t is days since calving, t' = t – 150, A: is a constnat and a, b, c and d are parameters to be estimated, is recommended. This curve was also fitted to yields of milk fat, protein and lactose.

During weeks 3 to 26 of lactation, two groups of 24 cows were offered either a 60:40 (high) or a 40:60 (low) ratio of concentrate dry matter:silage dry matter. The 40:60 diet was restricted to give the same daily metabolizable energy and crude protein intake. The hooves of half the cows on each diet were trimmed prior to the experiment, the other half remaining untrimmed. The high concentrate ratio significantly increased locomotion score (high scores indicating poorer locomotion), and the number and duration of clinical cases of lameness. Trimming of hooves significantly reduced the number and diiration of clinical cases. Hoof growth was significantly increased by trimming. Hoof hardness was significantly reduced by the high concentrate ratio. The low concentrate ratio had 8/24 cows lame for an average of 3·3 weeks compared with 11 cows for 3·9 weeks on the high ratio. There were 7/24 trimmed cows lame for 3·1 weeks compared with 12 untrimmed cows lame for 4·2 weeks. The main hoof lesions were solar ulcers and heel erosion. There was no significant effect on milk yield, but milk protein was signficantly increased by the high concentrate ratio. Condition score was significantly negatively correlated with locomotion score.

Repeated cloning of bovine embryos by nuclear transfer, producing large clones of monozygous animals, may be possible in the future. Initially, clones could be tested and the best one selected and spread over the commercial population by embryo transfer. Further genetic improvement could be obtained by rebreeding a number of the best clones to produce a new set of clones. However, the testing and selection systems to pick the best clone (for short-term clonal response) and to pick clones with the best breeding values (for long-term genetic response) are different. The objective of this study was to derive a system which achieves both high clonal and high genetic responses. An adult MOET (multiple ovulation and embryo transfer) scheme with 40 breeding males and 40 breeding females per generation (cycle) was used to maintain adequate genetic variation for continued genetic response. For a fixed set of testing facilities and a given family structure initial clonal response is maximized by testing several members per clone. Long-term genetic response is usually greatest when testing one member per clone. Compromises to obtain both high clonal response and high genetic responses were from 95 to 100% efficient.

The influence of season and management system on the productivity of Friesian cows in a Mediterranean climate was assessed. Intakes of food and water and milk yields were measured in 154 cows over 2·5 years while intensively managed in yards giving access to shelter (free stalls) or that were fully exposed to solar radiation (open lots). Food quality was also monitored to permit estimates of the efficiency of utilization of metabolizable energy for milk production over fortnightly periods.

The highest milk yields and energetic efficiencies were recorded during spring. Energy intakes were highest but energetic efficiencies were lowest during winter. Cows consumed the least food during summer and autumn and drank the most water during summer. The only significant effect of management system was for water intake, which was higher in the open lots than in the free stalls. There was evidence of heat stress in summer and cold stress in winter, but there appeared to be little benefit with milk yields through the provision of shelter.

The work done, distance travelled and body temperature of five teams of oxen ploughing land for winter crops was measured continuously over a 5-h working day. On terraces in East Nepal the cattle worked at slow speeds (about 0·3 m/s). Daily work output was variable and depended on ground and soil conditions and on the man working the team. Estimated daily energy expenditure on working days in October and November was 1·25 to 1·46 × maintenance. Differences between teams were small. No noticeable change in performance occurred over the 5-h work, with the exception of one team which usually worked erratically over the last 2 h. Only one animal showed signs of heat stress during work, when its body temperature increased by 1·8 to 2°C, otherwise body temperature varied little (< 1°C) during work.

The generation of profit in dairy production can be approximated by a generalized profit equation, which is a function of the genotype of the animals used. In the absence of legislated quotas on production, the economic weights for traits contributing to profit, for use in a selection index, have been shown to be simple functions of the partial derivatives of profit with respect to output of the traits. These functions reflect the fact that output in most agricultural industries will already be maximized, either because of saturated markets or limitations on total inputs. When a single quota applies, different functions result, which reflect the downward rescaling of enterprise size as output per animal of a trait under quota is increased. Difficulties arise when multiple non-independent quotas apply, such as in the United Kingdom (UK) milk market where quotas are triggered by both milk volume and fat concentration. The functions describing the economic weights are then dependent on the form of the dependency between the quota criteria and on the genetic change resulting from the applied selection index. Economic weights for milk volume, fat, protein and lactose yield applicable to Holstein'Friesian cattle in the UK were found to be –1·6 p/1, 76·6 p/kg, 170·0 p/kg and 7·0 p/kg, scaled to 1986 prices. These weights would not change much if the quota were changed to fat yield only. Use of appropriate selection indexes should result in genetic increases of milk volume, fat, protein and lactose yield, with gradual increases in fat and protein concentrations and the fat to protein ratio. In most situations, selecting on the combined evaluation for fat plus protein yield would be a simple procedure with high efficiency (0·995 of maximum efficiency).

Data were collected on 19 high-producing Holstein dairy cows from day 20 post partum until they were either determined pregnant or reached 150 days post partum. Blood metabolites (progesterone (P4), glucose, beta-hydroxybutyrate (BHBA) and free fatty acids (FFA)) were related to the interval from parturition to first luteal phase, first visual oestrus and conception. Prior to data analysis, cows were divided into two groups based on their 120-day milk production and designated as below herd average (BHA; no. = 9) or above herd average (AHA; no. = 10). Average 120-day milk productions for BHA, AHA and herdmates (no. = 56) were 3932 (s.e. 157), 4841 (s.e. 60) and 4353 (s.e. 96) kg, respectively. Days from parturition to first luteal phase were not different between the BHA and AHA groups (31·7 (s.e. 1·7) and 31·5 (s.e. 6·9), respectively). In contrast, days from parturition to first visual oestrus and to conception oestrus were less for the BHA group than for the AHA group (46·8 (s.e. 4·6) and 76·9 (s.e. 7·5) v. 67·7 (s.e. 5·2) and 102·5 (s.e. 9·2) days, respectively (P < 0·05)). Further, average glucose concentration from day 20 to first luteal phase was higher (P < 0·05) for the BHA group than for the AHA group (64·1 (s.e. 1·6) v. 58·4 (s.e. 1·6) mg/dl). From day 20 to first visual oestrus, plasma glucose concentration increased while BHBA and FFA declined; all three metabolites then remained relatively constant until conception. These data suggest that as the amount of milk a dairy cow produces increases, the interval from parturition to first visual oestrus and conception increases. These data are consistent with a suppression of oestrus behaviour rather than with a delayed interval to ovarian cyclicity.

Dry-matter (DM) intake and water consumption were recorded in Borana cattle (Bos indicus) which were subjected to infrequent watering regimes, prolonged walking and night-enclosure. DM intake and water intake were depressed in cows watered every 2nd day (0·04 and 0·16 respectively) and in cows watered every 3rd day (0·1 and 0·3 respectively) as proportions of the food and water intake of daily watered cows. DM intake was further reduced by proportionately 0·05 as a result of a 40-km walk every 3rd day throughout the dry season and by 0·05 as a result of night-enclosure. Digestibility of food was unaffected by treatments. Water intake increased in some months as a result of walking but not as a result of night-enclosure. It is thought that DM intake was depressed with decreasing frequency of watering owing to the physiological effects of dehydration resulting in inappetence. Water consumption fell owing to the constraint imposed by rumen volume at drinking. Walking and night-enclosure independently reduced DM intake as a result of the greatly decreased time available for grazing.

Four groups of six cows were fed from 12 weeks before calving to achieve condition scores at calving of 3·23 (F) and 1·98 (T). For the first 20 weeks of lactation all cows were given 10 kg/day of isonitrogenous (180 g crude protein per kg dry matter (DM)) compounds containing either a high (13·0 MJ/kg DM; HE) or a low (9·8 MJ/kg DM; LE) concentration of metabolizable energy, together with 3 kg/day molassed sugar-beet pulp and hay offered ad libitum.

The mean milk yield of cows receiving compound HE (27·7 kg/day) was higher (P > 0·05) than that of cows receiving compound LE (25·6 kg/day). Cows in group FHE yielded 27·0 kg/day, compared with 25·5 kg/day for FLE (P > 0·05); cows in group THE yielded 28·4 kg/day compared with 25·17 kg/day for TLE (P <0·05). After peak lactation, milk yields were maintained better in group THE but declined at a faster rate in group TLE than in groups FHE and FLE. Neither dietary energy concentration nor condition score at calving significantly affected milk composition (butterfat 43·5, protein 29·1, lactose 50·2 g/kg). Cows receiving compound HE consumed significantly (P < 0·001) more energy (208 MJ/day) than cows receiving compound LE (188 MJ/day). Over the first 10 weeks of lactation, changes in condition were –0·83, –0·88 +0·08 and –0·25 (s.e.d. 0·22, P < 0·05) condition score units for cows in groups FHE, FLE, THE and TLE respectively.

It is concluded that with diets of high energy concentration intake is mainly limited by physiological mechanisms so that thin cows eat more than fat cows and produce similar amounts of milk. With diets of lower energy concentration, intake is limited by rumen capacity and thin cows eat the same as fat cows. This results in increased fat mobilization and a slight decrease in milk yield by cows which are fat at calving but the limited fat reserves of cows which are thin at calving are insufficient to compensate for reduced energy intake so large reductions in milk yield are observed.

Two pairs of cattle and two pairs of buffaloes carted loads, in wooden wheeled local carts, 16 to 17 km over the same flat route on village tracks. One team worked each day in temperatures of 24 to 37°C for a total of 6 days per team.

Body temperature, respiration rate and stepping rate in one animal from each pair and work done and distance travelled were monitored.

Buffaloes and cattle started work at speeds of 1 m/s or more. Cattle kept this up for most of the day whereas the buffaloes showed a steady decrease in speed over the day to speeds of less than 0·9 m/s in the last hour. Body temperature of the buffaloes increased during work. By 3-5 h, increases of up to 3·5°C in starting values could be seen. It was necessary to stop and let the buffaloes wallow for at least 20 min to allow them to cool off before they would continue to work. During wallowing body temperature decreased to or below values seen at the start of the day's work. Unlike the buffaloes, the cattle showed changes of less than 1°C in body temperature during work. Respiration rates of buffaloes increased at least two-fold as they began panting usually after 1·5 to 2·5 h. Respiration rates of the cattle could also increase up to three-fold during work. The results have shown that in well fed animals there is little to choose between buffaloes and oxen in daily work output. Estimated daily energy expenditures by the buffaloes and cattle on working days were similar, 1·75 to 1·79 and 1·74 to 1·78 × maintenance, respectively. However, buffaloes usually took longer to achieve the work, as time had to be allowed for wallowing. This is seen as the main disadvantage of using buffaloes for carting on longer routes.

A deterministic model was developed to examine the optimization of open nucleus breeding schemes in order to maximize the rate of genetic response in dairy cattle. By changing the parameters, the model was able to simulate both a closed nucleus and a progeny testing scheme. The model implicitly optimized the generation interval and the selection across tiers by means of truncation across age classes and tiers respectively. The effects of size of the progeny test group and the nucleus size were assessed by comparing alternative plans. It is possible to optimize a breeding plan given the reproduction rates of the animals, the availability of different sources of information, the age distribution of the animals (survival rates) and the phenotypic and genetic parameters of the trait.

The steady state selection response was assessed by calculating the genetic progress year after year until it stabilized. The genetic gain was corrected for the effects of reduced variances due to previous selections and increased variances due to genetic differences between parental age classes.

In an example, the model was used to predict the improvement in milk yield in a closed artificial insemination breeding scheme. The genetic gain of a conventional progeny testing scheme was about one-third lower than the genetic gain of the optimized breeding plan. The variance reduction due to selection decreased the steady state genetic gain by a factor 0·3

A sequential procedure for the development of breeding objectives for beef cattle improvement is presented. The procedure is general, and could be used for other types of domestic livestock. The development proceeds in four phases: (1) specification of the breeding, production and marketing system; (2) identification of sources of income and expenses; (3) determination of biological traits influencing income and expense; (4) derivation of the economic value of each trait, based on discounted gene flow methods. As an example, a breeding objective is developed for a pure breeding herd from which male calves are marketed at 9 months of age and surplus heifers are sold at 15 months of age. Situations examined included: (1) the effect of discounting on the breeding objective (income and expense per year v. discounting at 0, 5 and 10%); (2) the effect of ignoring the economic value for food intake in the objective; (3) the effect of inclusion of yearling weight or the deletion of calving date from the selection index. In general, correlations between objectives for discounting and income and expense per year were greater than 0·95, whereas correlations between indices were greater than 0·85. Setting food costs equal to zero shifted emphasis from reproduction to growth traits, with a consequent increase in food intake. The addition of yearling weight to the index caused a small increase in the accuracy of the index, whereas the deletion of calving date had a large effect, halving the accuracy of the index. The practical implications of the results are discussed.

To determine effects of photoperiod and ovaries and their interactions on live-weight (LW) gain, carcass composition, growth hormone (GH), insulin (INS) and prolactin (PRL), crossbred beef heifers were utilized. Heifers (no. = 70) were blocked by LW and assigned to a pre-treatment slaughter group for estimation of initial carcass composition or to treatments in a 2 × 2 factorial experiment (no. = 14 per treatment). Main effects were: photoperiod (8 h light (L): 16 h dark (D) v. 16L: 8D) and ovaries (intact (INT) v. ovariectomized (OVX)). Heifers were given a maize-based mixed diet (115 g protein and 11·5 MJ metabolizable energy per kg dry matter) ad libitum once per day at 07.30 h. On days 64 and 138, blood samples were taken every 30 min for 10 h from five heifers in each treatment. On day 144 treated heifers were slaughtered. Relative to OVX heifers, INT heifers had greater (P < 0·01) average LW gain (1·03 v. 1·17 kg/day), carcass weight (252 v. 270 kg) and carcass protein accretion rates (68 v. 82 g/day) but carcass fat accretion was not affected (P < 0·l; 381 v. 399 g/day). Compared with 8L: 16D, exposure to 16L: 8D non-significantly increased LW gain more in OVX heifers (16 kg) than in INT heifers (3 kg). Photoperiod did not significantly influence weight or composition of the carcass. There was no significant interaction between photoperiod and ovaries on carcass composition. Across all heifers GH declined (P < 0·05) and INS and PRL increased (P < 0·05) from day 64 to 138. Compared with 8L: 16D, exposure to 16L: 8D increased PRL on day 64 (P < 0·05; 13·4 v. 28·5 u.g/1) and decreased INS averaged across days 64 and 138 (P = 0·l; 0·71 v. 0·55 u/l) but had no effect on GH. GH, INS and PRL did not differ between INT and OVX heifers. It is concluded that ovariectomy of heifers reduces LW gains, carcass weights and accretion of protein, and that exposure to 16L: 8D partially prevents the loss in LW gain.

The effective degradability (Dg) of dry matter (DM), nitrogen (N) and amino acids (AA) in soya-bean meal (SBM), fish meal (FM), dried brewers' grains (DBG) and ensiled lucerne (EL) was measured using polyester bags suspended in the rumens of six cows given a basal diet of maize silage, hay and concentrate. Rumen outflow rate was measured using chromium-mordanted SBM.

AA were grouped into essential (EAA), non-essential (NEAA) or branched chain (BrAA). The AA concentration in DM varied from 88 g/kg DM for EL to 566 g/kg for FM. The proportion of determined AA in crude protein (CP) was similar for SBM, FM and DBG and always higher than 0·85. EL had the lowest A A concentration in CP, partly due to the presence of ammonia N (170 g/kg total N).

Methionine always had a higher, and threonine a lower Dg than total AA in all foods. Dg of other AA was generally food dependent.

SBM always had the highest EAA, BrAA, NEAA, mean AA and total N degradability, whilst FM always had the lowest Dg for EAA, BrAA, mean AA and total N, and these values were significantly different in comparison with SBM. The effective Dg of BrAA in DBG was significantly lower than in SBM and significantly higher than in FM. In EL, NEAA and mean AA Dg were significantly lower compared with SBM.

Effective Dg of total AA in SBM and EL was significantly lower than the CP Dg; this difference was not apparent in DBG or FM.

The undegraded fraction of FM and EL had a significantly higher proportion of EAA whilst DBG and EL had a higher proportion of BrAA when compared with the unexposed food. Isoleucine concentration, highest in EL, and lysine and methionine contents, highest in FM, differed significantly between the four protein source residues.

The first limiting AA after rumen incubation, in relation to casein and meat, was always methionine. The essential amino acid index of the food residues post incubation, relative to casein and meat, was lower in SBM, DBG and EL but higher in FM.

Cloning of cattle from embryos has been achieved by nuclear transfer. Repeated cloning to produce large clones of genetically identical individuals for commercial use may soon become possible. The main advantage in breeding will come from identifying and using superior clones, selected to fit particular husbandry and marketing niches. Two types of cattle clones will be required, terminal clones chosen for economic merit in production traits, such as growth and carcass traits, and maternal clones chosen for reproduction and maternal traits, such as short calving interval, ease of calving, milking and mothering ability and small mature size. Clonal selection and use will provide several steps of improvement. An initial gain will come by recruiting clones from elite stocks and further responses by selecting the best clones for commercial use. This will reverse the normal improvement lag between breeding and commercial stocks. Heterosis will also be exploited by using crossline clones. For continuous genetic improvement, genetic variation will be maintained by breeding the next generation from a number of selected male and female clones and testing and selecting their progeny, the new set of clones, as before. For maximum improvement rates, both male and female clones will need to be tested. In the short term (5 to 10 years), benefits will come from testing a large number of clones by which gains in economic merit of proportionately 0·15 to 0·30 of the mean can be achieved. Further improvements will come by rebreeding the best clones and testing and selecting the new set of clones from which annual genetic response rates of proportionately 0·02 to 0·03 per year are possible. Cloning thus offers considerable advantages in the improvement of beef cattle.

Two alternative ways of estimating cumulative selection differentials are compared. An alternative method is developed that includes the advantages of both methods. This alternative method is shown to give rise to less biased estimates of realized heritability

The study aimed to determine the effect of the growth promotant avoparcin on the digestion and absorption of nitrogen and amino acids from pre-ruminant milk-fed calves. Eighteen male Friesian calves, 45 kg live weight, were allocated to three diets: a commercial high-quality milk replacer compound (control); control with 100 mg zinc bacitracin per kg (positive control) and control with 40 mg avoparcin per kg. The diets were given once-daily at a set rate of intake during a 14-day metabolic study. On the 15th day the calves were fed at 2-h intervals and ileal digesta were sampled (8 h after the start of feeding) from the euthanazed animal. Estimates of apparent ileal digestibility were determined by reference to an indigestible marker, with the comparable faecal estimates determined following the total collection of faeces.

There was no significant effect of avoparcin or zinc bacitracin addition on faecal apparent digestibility of dry matter, nitrogen, gross energy and amino acids or on ileal apparent digestibility of nitrogen and amino acids. Neither was there a significant effect of either additive on nitrogen retention, daily urinary urea and total nitrogen excretions or portal and peripheral plasma urea concentrations. Ileal apparent digestibility coefficients determined on the control diet ranged from 0-82 for glycine to 0-96 for phenylalanine, tyrosine and methionine. The ileal measures of apparent digestibility were more variable than the comparable values determined over the entire digestive tract. Measurements on the faeces compared with measurements on digesta at the terminal ileum gave higher values (P < 0·05) of apparent digestibility for nitrogen and 10 of the 16 amino acids.

This paper evaluates the consequences of using the wrong genetic model when predicting the merit of previously untested crossbred genotypes. Eight models are considered, seven including different biological interpretations of two-locus epistatic interaction, plus one excluding epistatic effects. Published results from 13 genotypes generated from Hereford and Angus parental breeds were analysed, and predictions of a further seven genotypes made using different models. Under a dominance model, the predicted superiority in pregnancy rate (%) of a ¾ Hereford: ¼ Angus composite over a two-breed rotation was +1·2%, yet under all other models this was a negative value ranging from –1·9% to –3·7%. However, few such cases were found in which significant decision errors could conceivably be made. It is concluded that decisions on the choice of crossbred genotypes are generally quite robust to differences in the genetic model of the type studied here