The effect of increasing the interval between recordings from 1 month to 2 months was studied by analysis of milk, fat and protein yield records obtained in alternate monthly herd visits. The data comprised records on over 34 000 daughters of 40 proven and 705 young sires which were analysed by multivariate restricted maximum likelihood.

Heritability estimates of bimonthly test day records were similar to the average of the estimates for the two corresponding monthly test day records, as were genetic and phenotypic correlations between bimonthly test day and lactation records. A quartic regression removed most of the additional variance due to the wide range of days to first test and therefore the variance-covariance structure of bimonthly test day records could be predicted from that of monthly test day records.

The accuracies of prediction of breeding value for 305-day yields of milk, fat and protein using the sum of five bimonthly test day records and the sum of seven 6-weekly tests were estimated to be at least 0·97 and 0·99, respectively, of the accuracy of using 10 monthly test day records.

If milk yield were recorded daily, prediction of lactation fat or protein yield from the product of the sum of daily milk yields and the average fat or protein content would be more accurate than using yield and content records solely from test days.

Two groups of eight N'Dama calves were fed different quantities of milk from birth to 10 months of age to compare efficiencies of converting milk to live-weight gain, and to assess the economic efficiencies of the two feeding regimes. Group 1 received an average of 347 (s.e. 2·4) kg per calf, with a daily and seasonal pattern of feeding designed to simulate a village production system where calves have access to only part of the milk produced by their dams, the rest being extracted for human consumption. Group 2 received an average of 617 (s.e. 5·1) kg per calf, and simulated situations where no milk is extracted such as in a ranch or station-type of operation.

During the first 6 months, when growth was certainly mediated only by milk, and live-weight gains were consistently positive at 151 and 262 g/day in groups 1 and 2 respectively, the biological conversion of milk to live weight did not differ between groups (8·7 v. 8·8 kg milk per kg live-weight gain). When the two groups were compared over the same weight range to remove possible effects of variable maintenance requirements, the conversion efficiencies again did not differ significantly. Over the whole 10-month period the biological conversion factors were slightly less favourable but still not different between groups (9·5 v. 9·4 kg/kg). When monetary values of milk and live weight at farmgate prices were applied to quantities of milk consumed and calf live-weight increases, the cost efficiency of group 1 was superior to that of group 2.

Based on these findings and results from other on-farm experiments in The Gambia, it was concluded that the current practice of partial milk extraction as occurs in the village production system is a logical approach for profit maximization.

Two studies were conducted to examine the effects of selection for milk-fat yield on pancreatic responses to exogenous glucose, as measured by circulating insulin concentrations following an intravenous glucose load, in heifer calves. The first study involved 6-month-old Friesian heifers, eight each from the Massey University high breeding index (HBI) and low breeding index (LBI) lines. Average breeding indices (BI) for milk-fat yield of the calves based on ancestry BI were 136 (s.d. 2) and 112 (s.d. 2), respectively. Oestrous cycling of the heifers was controlled by intravaginal insertion of progesterone-impregnated controlled internal drug-releasing devices (CIDRs). Challenges of glucose (0, 75, 150 and 300 mg/kg live weight) and insulin (0, 0·1, 1, and 10 fig/kg live weight) were administered via indwelling jugular cannulas and were followed by serial blood sampling to measure responses. Plasma insulin concentrations immediately following the glucose challenge were significantly (P < 0·05) greater in HBI than in LBI heifers, peak insulin concentrations (above baseline) in the HBI group being approximately twice those in the LBI group. Plasma glucose concentrations were marginally lower in HBI heifers, probably due to the secondary effect of the relatively greater hyperinsulinaemia in this group. Although the exogenous insulin challenge significantly reduced circulating glucose concentrations in all heifers, there was no difference between the lines in the magnitude of insulin-induced hypoglycaemia.

The second study was designed to determine whether insulin responses to an exogenous glucose load were influenced by stage of the oestrous cycle in heifers of the two lines. In this study, eight yearling HBI heifers and eight LBI heifers (with BI of 135 (s.d. 4) and 111 (s.d. 1) respectively) were administered an intravenous glucose load (150 mg/kg live weight) on tivo occasions, the first being after 17 days of CIDR treatment (simulating the luteal phase of the oestrous cycle) and the second 46 h after withdrawal of the CIDRs (when the heifers were expected to be in oestrus). HBI heifers again showed significantly greater circulating insulin concentrations than LBI heifers following the glucose challenge but the magnitude of this effect was not influenced by time relative to CIDR withdrawal. It is concluded that heifers selected for high milk-fat yield have an increased pancreatic response to exogenous glucose which is apparently independent of the stage of the oestrous cycle. This difference may provide a useful means of identifying heifers of superior genetic merit for milk-fat production prior to their first lactation.

Selection decisions in breeding schemes can involve choices between candidates evaluated to different accuracies. A Bayesian framework is put forward for choosing among candidates, and it is shown that attaching loss functions for estimation errors makes this process different from selecting upon best linear unbiased predictions alone. Examples are given using both linear and quadratic loss to show that when estimation errors are penalized, the selection process tends to select more unrelated and more accurately evaluated individuals. In a dairy cattle breeding scheme response was only slightly lower than that from selection on expected breeding values but with a much reduced coefficient of variation. However, if prediction errors are preferred, with the hope of selecting individuals whose breeding value are higher than expected, extra genetic progress could be obtained by favouring the selection of individuals with low accuracy. This requires consideration of more than a single generation.

With discrete generations and equal measurements on candidates the decision framework was shown to be equivalent to a single quadratic restriction on the selection scores of parents in the previous generation.

A framework based on Bayes decision theory could be simply applied to produce a flexible means for producers to select according to their individual risk preferences.

The records of 1397 cows calving in the spring were collected in the years 1979 to 1984. They were from 638 Angus and 759 Hereford × Friesian cows, and were used to examine the dependencies of post-partum anoestrous interval (ppai), length of oestrous cycle after calving, and conception rate to each oestrus after calving.

Two-year-old cows had longer ppai (P < 0·05) than older cows (76 v. 72 days), and Hereford × Friesian cows had shorter (P < 0·05) ppai than Angus cows (68 v. 72 days). Cows due to begin calving on 8 August (early calving) had longer (P < 0·01) ppai than cows due to begin calving on 19 September (71 v. 55 days).

The linear regression between ppai and calving date (−0·60) did not differ between years, nor between early and late calving. Non-parametric regressions showed that the dependence between ppai and calving date was linear between plus or minus 20 days of the mean ppai in both early- and late-calving herds. Outside these limits variability of ppai increased and there was no relationship with calving date.

The length of the first oestrous cycle after calving was 22 days in 2-year-old cows and 24 days in older cows. Second and third oestrous cycles after calving were 20 days for all breeds and age classes. There was a correlation of −0·41 between the ppai and the length of the first oestrous cycle after anoestrum. There was no significant deviation from normality of ppai or the succeeding post-partum oestrous cycle lengths.

The conception rate to the first oestrus after calving was significantly lower (P < 0·01) than for later oestrous periods. The conception rate to first post-partum oestrus showed dependence on the ppai, logit regressions showing a 0·005 to 0·01 proportional improvement in conception at first oestrus per day increase in ppai.

The significance of these results to the construction of mathematical models of reproduction in the beef cow is discussed.

Mature cows of nine breeds were fed (four cows per level within breed) at either 0·55, 0·71, 0·88 or 1·05 MJ metabolizable energy (ME) per kg initial body weight0·75 per day during non-lactational periods for an average of 4 years. During lactation, energy allowances were increased by 0·17 MJ ME per kg body weight0·75 per day. Breeds represented four biological types: moderate genetic potential for milk yield and growth (Angus, Hereford, Red Poll), moderate milk and high growth (Charolais, Eimousin), high milk and moderate growth (Braunvieh, Pinzgauer) and high milk and growth (Gelbvieh, Simmental). The objective was to test the effects of biological type and nutritional environment on length of post-partum interval as determined from serum progesterone levels. The potential of serum insulin-like growth factor-1 (IGF-1) level at 3 weeks post partum for predicting the length of the post-partum interval was also evaluated. Non-parametric statistical analyses appropriate for right-censored survival data were used to test effects on post-partum interval because collection of serum was terminated prior to ovulation in some cows.

Energy availability × biological type effects on post-partum interval were significant. Increased energy availability tended to decrease post-partum interval in all biological types with high potential growth types exhibiting the greatest positive response to increased food. Post-partum interval for types with high growth potential was shorter within food level when associated with high rather than moderate potential for milk yield. Serum IGF-1 was related to post-partum interval at lower energy availability but appeared to have limited usefulness for identifying cows with extended intervals. Inherent direct and maternal production potential interact with available food resources to influence the post-partum interval of mature beef cows.

Over 3 years a total of 204 bucket-reared calves (from Holstein/Friesian dams) and 187 suckled calves (from Hereford × Friesian dams) were monitored during the first 9 or 6 months of life respectively. Within each rearing system there were approximately equal numbers of calves sired by Charolais and Hereford bulls and also about equal numbers of heifer and steer calves. All breeds and sexes within each rearing system were managed as a single group.

Differences in daily live-weight gain from arrival (January) for the bucket-reared calves and from birth (April) for the suckled calves through to the autumn were significantly different at 0·66 and 1·01 kg/day respectively (P < 0·001). By comparison, differences in growth rate between sex and breed within each rearing system were small. Hereford cross calves from both systems however carried significantly more condition in the autumn compared with Charolais crosses (P < 0·01).

The results suggest that when animals are reared on the same plane of nutrition and given similar management, differences in initial growth rate between early and late maturing breeds and sexes may be less than those perceived by commercial producers the views of whom are influenced by the fact that the types are often managed differently in practice.

An experiment was designed to determine whether combining a single injection of 125 μg prostaglandin F2α analogue (PGF) with a 5-day progestagen pessary treatment (PPT) would obviate the problem with refractory animals that occurs when randomly cycling ewes are synchronized with PGF alone. The efficacy of the combined treatment, in comparison with single and double dose PGF regimes, was also assessed.

A total of 210 ewes were used in this investigation conducted during the 1989 and 1990 breeding seasons. In both breeding seasons, 100% of the ewes treated with PGF combined with PPT were mated by fertile rams within a 3-day period, compared with 52·9% of ewes treated with a single injection PGF or 100% of ewes treated with two injections of PGF, 11-days apart. Returns to service for the three groups were 14·2%, 16·2% and 17·4%, respectively. There was no effect of treatment on lambing performance in 1989. However, in 1990 there were differences between groups in gestation length and birth weight, but these were attributable to enzootic abortion. The results demonstrate that PGF combined with PPT will produce levels of oestrous synchronization and fertility comparable with other methods.

Telemetric techniques for the monitoring of physiological parameters during housing, handling and transport may help producers to reduce mortality and improve meat quality. In order to know the reliability of electrocardiogram parameters as stress indicators, piglets (12 to 23 kg) being different with respect to the halothane gene (homozygous halothane sensitive (nn) and non-sensitive (NN), heterozygotes (nN)), and thus different with respect to stress susceptibility, were monitored with an ambulatory ECG device during housing, handling and transport. Skeletal muscularity of all animals was measured with an ultrasound device.

Heterozygotes and homozygote halothane sensitive piglets had a higher muscularity, but only the homozygotes had a higher ST-elevation from the isoelectric line of the QRST-complex of the electrocardiogram when measured within housing conditions. This means a different propagation of the electric current related to the activation of the ventricle. Halothane gene carriers (Nn and nn piglets) had a statistically significant higher mean maximal heart rate during housing conditions. During handling heart rate rose by 14·8%, 0·61% and 42·9% respectively for NN, nN and nn piglets, with nn piglets having the highest values. During transport these measurements were respectively 6·88%, 3·66% and 9·7% higher for lines NN, nN and nn as compared with those in housing conditions. Heart arrhythmicity parameters were not different between housing and transport, but during handling up to a 23-fold increase could be observed.

Heart rate and arrhythmicity parameters may generate reliable information to monitor stress during housing, handling and transport of piglets through genotypes and skeletal muscularity.

Heat production, energy and nitrogen balances of artificially reared piglets from specific pathogen free sows, housed in a respiratory chamber, were measured over five successive periods of 7 days each from 4 to 39 days of age. The experiment was carried out at an environmental temperature decreasing from 33 to 27°C. The mean weight increased from 1·5 (at day 4) to 11·9 kg (at day 39). Daily rate of gain increased from about 100 g in periods 1 and 2 to 502 g per piglet in the fifth period.

Daily protein deposition, as measured via nitrogen balance, increased from 17 to 96 g; fat deposition increased from about 0 to 100 g. Body composition at the start and end was determined by a comparative slaughter technique. Protein and fat content had a high correlation coefficient with body weight (R2 = 0·69 and 0·89, respectively). At birth these values were much lower, 0·24 and 0·01 for protein and fat, respectively.

Nitrogen balance compared with slaughter technique led to an overestimation for protein deposition of proportionately 0·07. Fat gain measured from slaughter was proportionately 0·08 lower than that calculated from energy balance.

Ratio of gain estimated from protein and fat gain with the balance technique relative to that measured ranged between 0·93 to 1·15 in various periods.

Data on 3783 Yorkshire, 2842 Landrace and 937 Duroc littermate pairs of boars, station tested between 1976 and 1989, were used to measure genetic parameters of average daily gain (ADG) from 30 to 90 kg, live backfat at 90 kg (BF), estimated lean growth rate (LGR), average daily food intake, food conversion ratio (FCR) and lean food conversion ratio (LFCR), as well as measures of residual daily food intakes over and above requirements for growth and lean growth. A method was developed to obtain restricted maximum likelihood estimates of genetic variances and covariances under an animal model when observations are on the means of sib pairs. Heritabilities of ADG, BF, LGR, FCR and LFCR were 0·43, 0·59, 0·39, 0·28 and 0·34, respectively. Heritability of daily food intake was 0·45, and heritability of measures of residual daily food intake ranged from 0·30 to 0·38. About half of the variation in daily food intake was residual (0·48 to 0·56). Genetic correlations of ADG with daily food intake, FCR and LFCR were 0·80, −0·28 and −0·09, respectively, and were small and positive (0·18 to 0·34) with measures of residual daily food intake. Backfat had genetic correlations of 0·42, 0·24 and 0·52 with daily food intake, FCR and LFCR, respectively, and genetic correlations between backfat and measures of residual daily food intake ranged from 0·15 to 0·61. Selection against residual food intake may be a useful means of improving efficiency of food utilization.

Predicting the performance of animals is a general problem in animal production, the solution to the problem depending, in part, on being able to describe the animals adequately. Numerous approaches have been made to model the growth of pigs, with different methods being employed to describe the genotype. A simple approach is to describe the potential rate of growth of body protein using a Gompertz equation, and to predict the growth of the other chemical components of the body using allometry. These components are added to determine the body weight of the animal.

In this paper an experimental procedure is proposed that will predict values for the parameters of the Gompertz growth equation under non-limiting conditions. These parameters include the rate of maturing of the animal and the mature protein weight. The lipid-to-protein ratio at maturity is required to describe the allometry between protein and lipid. With these few parameter estimates the potential growth rate of animals can be described. It is then possible to use this information to predict the growth rate of animals under conditions constrained by the food or the environment.

An experiment was designed to quantify the specific genetic parameters which will describe the growth potential of a pig. The experiment was conducted in two stages. In the early stage, 11 unimproved crossbred pigs were serially slaughtered at 2, 13 and 23 days of age. In the later phase, 16 pigs were serially slaughtered at 80, 90 and 100 kg live weight. The chemical composition of each of the entire empty bodies was determined. Linear regression analyses were performed on body protein and lipid weights to determine the Gompertz growth parameter (B), mature body protein weight (Pm) and the lipid: protein ratio at maturity (LPRm) The B value for boars was 0-0107 (s.e. 0·00060) per day and for females 0·0120 (s.e. 0·00044) per day. Pm estimates were 38·7 kg and 28·4 kg whilst the LPRm ratios were 2·60 and 3·89 for boars and gilts respectively.

Responses of gross energy intake and body weight of mice from weaning to maturity to dietary composition of energy-yielding nutrients were studied. Twenty-four groups of ddY male mice were fed for 70 days purified diets with a range of 0·08 to 0·75 protein, 0 to 0·92 fat and 0 to 0·92 carbohydrate concentration, calculated on a gross energy basis. Food intake and body weight data in each group were analysed by non-linear regression to obtain values of the parameters in the feeding and growth equation of Parks (1982). Prediction equations for these parameters were obtained with mixture model forms as a function of dietary protein, fat and carbohydrate. These equations for the parameters were then used to construct the response surfaces of body weight and growth rate at a given time on a triangular graph. The response surfaces of body weight at any time were convex, peak positions of which shifted from 043 protein and 0·29 fat at 10 days to 0·36 protein and 0·52 fat at 70 days. The configuration of response surfaces of growth rate (dW/dt) to the three components depends on feeding periods and at the longer periods of feeding the convex configuration of the surfaces became planar. The response surfaces of food efficiency (dW/dF) at any age were almost parallel to those of dW/dt, whereas a parallelism was observed between response surfaces of dW/dt and dF/dt only in young animals. These results suggested that the responses of body weight in young animals to dietary composition of energy-yielding nutrients depended on those of daily energy intake as well as food efficiency, but that those in older animals were affected by food efficiency only.

The apparent and true amino acid (AA) digestibility from soya-bean meal (SBM), vetch meal (VM), field pea meal (FPM) and bitter vetch meal (BVM) were determined in the lower ileum of growing chickens force-fed on semisynthetic diets (120 g crude protein and 13·1 MJ metabolizable energy per kg dry matter) based on each meal as the sole source of protein. The average apparent and true digestibility values were 0·82, 0·73, 0·76 and 0·60 and 0·90, 0·91, 0·87 and 0·74 for diets SBM, VM, FPM and BVM, respectively. Marked differences in AA digestibility among diets were found. The apparent digestibility of methionine, the most limiting essential AA in poultry diets, was significantly higher in diet SBM than in diets FPM and BVM (P < 0·05). It is concluded that the seeds of vetch and field pea may be suitable for inclusion in poultry diets as partial substitutes for soya bean. The use of bitter vetch is not recommended.

Straw-Flow is a novel housing system for growing pigs which simplifies the handling of bedding and manure by allowing pigs to take unchopped straw from dispensers. Three groups of 50, 50 and 60 Large-White × Landrace pigs were housed in Straw-Flow pens from 5 to 90 kg. They were supplied daily with 50 to 100 g unchopped straw per pig and given food ad libitum. From 30 to 90 kg, mean growth rate was 863 g/day and food conversion ratio was 2·56 kg food per kg growth. The pigs' behaviour was divided approximately into: 0·820 lying, 0·100 active, 0·075 feeding and 0·005 drinking (on a proportional basis). There were no differences (P > 0·05) between groups or different weights for any of the behaviour categories. The pigs were less active before noon than after noon (P < 0·05). The daily number of visits to the drinker between weights 5 and 25 kg fell from 23·7 to 11·0 (P < 0·05). A single drinker, of new design, appeared to be adequate for a group of 50 to 60 pigs.

Two experiments were carried out from April to September 1990 at Zaragoza, Spain. Fifty-three Rasa Aragonesa (RA) ewes, weaned in April, were studied in experiment 1, whilst 33 Salz (Sz) ewes, weaned in June, were studied in experiment 2. From weaning onwards, the animals were allocated to two groups receiving two planes of nutrition: high (H) and low (L). Mean time between weaning and the first detected oestrus was 113 (s.e. 2·7) and 52 (s.e. 3·0) days for RA and Sz ewes, without any significant effect of the plane of nutrition. Ewes of the H group showed a constantly higher ovulation rate than those of the L group with a significant effect of the plane of nutrition in the second fortnight of August (P < 0·05) and of September (P < 0·001) in RA ewes (1·68 v. 1·29 and 1·89 v. 1·38 corpora lutea for H and L groups, respectively) and in September (P < 0·01) in Sz ewes (2·53 v. 2·00 corpora lutea for H and L groups).

In conclusion, a slightly higher plane of nutrition after weaning in these sheep breeds, lambing in spring, cannot advance either the reproductive resumption or increase the ovulation rate of the first cycle. The high plane of nutrition after weaning exerts a significant effect on the ovulation rate in the medium term, in the early breeding season.

Thirty-two Blackface female mature sheep weighing 45 kg on average were blocked by weight and randomly allocated 60 days before slaughter to be untreated controls (C) or subcutaneously implanted with 20 (TA1), 40 (TA2) or 60 (TA3) mg trenbolone acetate (TBA). Samples of blood were collected throughout the study and post-mortem samples of selected body tissues were analysed residues.

Concentrations in blood of 17β-hydroxy-trenbolone (TBOH) peaked within 1 to 2 weeks of implantation and declined thereafter. Concentrations in blood of oestradiol-17β (OE) were elevated and generally increased with increasing dose levels of TBA. The highest concentrations of solvent extractable residues (TBOH for group TA3) ranged from 613 ng/kg in kidney to 130 ng/kg for rib muscle. Trenbolone-17β- glucuronide was detected in liver and kidney at maximum concentrations of 157 ng/kg and 94 ng/kg respectively. Implantation with TBA had no effect on concentrations of OE in any of the post-mortem tissues examined.

The relationships between body composition, live weight (LW) and subjective condition score (CS) were examined in an experiment in which 54, second to fourth parity, lactating autumn-calving Holstein-Friesian dairy cows were slaughtered at 0, 2, 5, 8, 11, 14, 19, 24 and 29 weeks post partum. Multiple regression analyses showed the weight of fat and the quantity of energy within the body were significantly correlated with both LW and CS. The weight of crude protein showed a linear correlation with LW. These results are discussed and compared with previously published investigations with non-lactating dairy cows.