When comparing progeny-testing schemes with individual performance selection, one should use equivalent selection intensities and population structures in the two systems. Adapting formulae from open-nucleus theory, the relative efficiency of progeny testing has been tested for a range of heritabilities, fertility levels, upward gene-transfer rates, mating ratios and numbers of sires selected. In sheep and beef cattle breeding, the heritability of the trait under consideration has usually to be very low to make progeny testing worth-while. High fertility increases genetic gains but does not change the relative efficiency of progeny testing. Opening the nucleus to females from the base increases genetic gains and reduces relative efficiency of progeny testing, both effects being of small magnitude. For fixed mating ratios, only a small fraction of females should be in the nucleus, but for fixed sire numbers approximately one-third of the population should be mated to proven sires. In these analyses, variances were adjusted for the effects of repeated selection and for the effects due to mixing groups with different means. This adjustment did reduce absolute genetic gains, but did not change conclusions on progeny testing efficiency and optimum design.

Over a 2-year period, 80 dairy cows were used to investigate the relationship between nutrition and fertility. The plane of nutrition of half the cows was raised for a 9-week period around the expected time of artificial insemination in both breeding seasons. The net effect was that the high-plane cows received 15% extra metabolizable energy during the 9-week period. This was achieved by giving these cows a high-energy concentrate (calculated value 13·1 MJ metabolizable energy per kg dry matter), whereas the control cows received a concentrate with a calculated energy density of 12·5 MJ metabolizable energy per kg dry matter. All cows received a basal ration that supplied an average of 75 and 80 MJ metabolizable energy per cow per day in the 2 years, respectively. Control cows received their calculated amount of dry matter using the control concentrate, whereas the high-plane cows received their calculated dry matter using the high-energy concentrate. The high-plane cows also received an additional 0·5 kg dry matter per head per day of their concentrate. They also received additional concentrates (2 kg per head per day) for 8 weeks, commencing 12 weeks before the second calving.

There was no effect of dietary treatment on the reproductive performance of the cows, although some measures of milk yield, live weight and body condition were affected significantly.

Analysis of data from all cows, regardless of treatment group, showed that the probability of pregnancy to an insemination was most strongly associated with milk yield on day 21 of lactation. Only the cumulative yield to day 21 was related to the probability of pregnancy after accounting for the trend with yield on day 21. The chance of pregnancy was lower in cows whose milk yields on day 21 were high but, among cows with similar yields on day 21, those with the higher cumulative yields at that time tended to become pregnant more readily. Thus both yield per se and rate of increase in yield in early lactation were associated with subsequent reproductive performance.

A field study involving 1087 cows and 191 heifers on nine carefully selected English dairy farms was conducted to evaluate the effect of nematocidal treatment on subsequent milk production. As many of the cattle as possible were allocated to pairs according to specific criteria and dosed with either levamisole and oxyclozanide, or oxyclozanide alone, soon after calving. The remaining unpaired animals were assigned alternately to the two treatment groups according to calving date. The milk production and health status of all the cattle in the study were closely monitored.

Analysis of pooled milk production data over a 2-year period failed to show a statistically significant response to nematocidal treatment. When individual herd data were analysed, a significant response to treatment was recorded on one farm. It was noted that the apparent value of the response varied according to method of analysis.

Factors considered likely to account for differences in response between farms and also between trials are considered.

Body condition score, assessed subjectively on the live animal, was related to the directly determined body composition of 73 mature, non-pregnant, non-lactating cows of Hereford × Friesian, Blue-Grey, Galloway, Luing and British Friesian genotypes. Relationships between condition score and chemically determined body fat were all very highly significant, and considered to be of value for predictive purposes. Differences between genotypes in the proportion of fat stored in the main depots of the body resulted in differences in the relationship between condition score and body fat. British Friesian cows had a higher proportion of their fat in the intra-abdominal depots and the lowest proportion of subcutaneous fat, resulting in their being fatter at any given condition score. Hereford × Friesian cows had the highest proportion of subcutaneous fat and were thus the least fat at any condition score. One unit change in condition score was associated with a change of 2242 (s.e. 103) MJ of body tissue energy in Hereford × Friesian, Blue-Grey, Galloway and Luing cows and 3478 (s.e. 392) MJ in British Friesian cows. These figures may be used to bring a greater degree of precision to the nutritional management of beef and dairy cows.

A number of possible indices of body composition (live weight, skeletal size, total body water as estimated by deuterium oxide dilution, blood and red cell volumes as estimated by Evans Blue dilution, ultrasonic measurements of subcutaneous fat depth and eye-muscle area, and body condition scoring) was examined using 73 non-pregnant, non-lactating, mature cows of Hereford × Friesian, Blue-Grey, British Friesian, Galloway and Luing genotypes, ranging in body condition score from 0·75 to 4·5. Direct measurements of body composition in terms of water, fat, protein and ash were made following slaughter.

Live weight, deuterium oxide dilution, ultrasonic measurements of subcutaneous fat depth and eyemuscle area, and body condition score were all considered to be potentially useful predictors of body composition. Combinations of techniques offered better predictions than did any single index. Using a combination of measurements it was possible to predict body fat and protein with a residual s.d. of 13·1 kg and 3·15 kg respectively. Breed differences in the partition of fat among the main adipose tissue depots necessitated the development of specific prediction equations for body fat based on condition score and subcutaneous fat depth for different breeds. Equations remain to be developed for predicting body composition in cows in different physiological states.

1. Two experiments were conducted with four sheep and four lactating Friesian cows to investigate the effect of food intake on the outflow of protein supplements from the rumen. Protein supplements treated with sodium dichromate were used.

2. Dichromate treatment had little or no effect on particle size distribution or density of the protein supplements. The dichromate-treated proteins were rendered completely undegradable in the rumen and the rate of outflow of chromium-treated protein from the rumen was estimated from the concentrations of chromium recovered in the faeces.

3. There were highly significant linear effects of feeding level on fractional outflow rate per h of chromium-treated protein supplements from the rumen of sheep and cows. Fractional outflow rates of chromium-treated fish meal and soya-bean meal, respectively, from the rumen of sheep were 0·0080 and 0·0076; 0·0182 and 0·0259; 0·0319 and 0·0335; and 0·0383 and 0·0385 per h at 0·2, 1·0, 1·5 and 2·0 times the energy requirements for maintenance, respectively. There were no significant differences between the two tested chromium-treated protein supplements in fractional outflow rates per h when the particle size was similar, nor any difference in particle size or density. Soya-bean meal was ground to achieve a particle size distribution similar to that of fish meal. For the dairy cows, the fractional outflow rates of fish meal from the rumen were 0·065, 0·072, 0·091 and 0·088 per h, at 1·5, 2·0, 2·5 and 3·0 times the energy requirements for maintenance.

4. There were significant differences between sheep in fractional outflow rates per h of protein supplements from the rumen due to the considerably higher values obtained for one animal.

1. Energy costs of eating were determined from the increased rates of oxygen uptake by five steers aged 18 to 20 months and weighing 298 to 407 kg.

2. Five diets were tested: pelleted concentrate (500 g barley grain per kg, 400 g lucerne meal per kg, 90 g soya bean meal per kg, and 10 g NaCl, trace mineral and vitamin supplement per kg); pelleted lucerne; lucerne hay; chopped-grass hay (700 g brome per kg, 300 g fescue per kg); and chopped fresh turnips. The dry-matter concentration of the pellets and hays was approximately 900 g per kg while the turnips contained only 140 g per kg.

3. The rates of ingestion differed markedly between diets during the (15 to 50 min) twice-daily (morning and evening) feeding periods. On a dry-matter basis, the pellets were consumed most rapidly at a rate of 130 to 138 g per min, while the hays were consumed at approximately 38 g per min and the turnips at 30 g per min.

4. The energy costs per min spent eating were similar for all rations (27·6 to 35·6 J/ kg live weight). However, because of different rates of ingestion, the energy costs per kg DM ingested were different: 222 to 238 J/kg live weight for the pelleted foods, 1029 J/kg live weight for the hays and 1427 J/kg live weight for the turnips.

5. The energy cost of eating is more a function of time spent eating than a function of the amount of food ingested. Thus, rate of ingestion and duration of the meal are key factors in determining the energy cost of eating in cattle.

One hundred and five Hereford heifers were reared on varying amounts of the same diet of grain and hay to grow at either high (H: 0·91 kg/day), medium (M: 0·67 kg/day) or low (L: 0·55 kg/day) rates between 2 and 8 months of age. Between 8 and 14 months, intake was restricted for half of the H heifers (HL: 0·14 kg gain per day), ad libitum for half of the L heifers (LH: 0·97 kg gain per day) and moderate for all other heifers (HM: 0·57; MM: 0·58; LM: 0·55 kg gain per day). These treatments resulted in a range of live weights at 8 (weaning) and 14 (premating) months commonly seen in commercial production. Heifers were mated with Hereford bulls at 14 months of age and subsequently grazed at pasture. Milk yields (I/day) at 30 days post partum and the 240·day sex-adjusted calf weaning weights (kg) for HM, HL, MM, LH and LM heifers in the first lactation were 4·1, 218; 4·9, 236; 4·3, 221; 5·7, 241; and 6·3, 259 respectively (P < 0·01). Calves from HM and MM cows were significantly smaller and leaner than those weaned by LM cows. Milk yields 30 days post partum and 200·day sex-adjusted calf weaning weights for the second lactation averaged: HM, 5·2 and 202; HL, 6·8 and 217; MM, 7·0 and 222; LH, 6·6 and 219; and LM, 7·0 and 229, respectively; and for the third lactation: 5·1 and 211; 6·5 and 225; 7·2 and 223; 7·4 and 230; and 7·6 and 237, respectively. The continued lower milk yield of HM cows (P < 0·05) was offset by a trend (NS) to higher fertility and lower calfmortality, particularly in the 1st and 2nd years of production. Over the three lactations studied, the number of calves weaned per opportunity and the total actual weight (kg) of calves weaned per cow kept averaged: HM, 0·86 and 573; HL, 0·66 and 465; MM, 0·68 and 466; LH, 0·70 and 512; and LM, 0·67 and 507, respectively.

The high growth rates commonly achieved by autumn-born Hereford heifers under commercial grazing conditions may reduce their subsequent milk-yield potential. This potential appears to be more sensitive to level of nutrition before 8 months of age than between 8 and 14 months.

Barley straw was treated with anhydrous ammonia, sodium hydroxide, ammonia plus sodium hydroxide, sulphuric acid or ammonia plus sulphuric acid to study the effect on the digestibility of straw and the degradability of the straw in the rumen of sheep.

In experiment 1 four wethers fitted with rumen cannulae were given ammonia-treated straw to appetite and were used for measuring the dry- and organic-matter degradability of straw in the rumen after different in sacco incubation times. The organic-matter degradability (g/kg) after 48 h in sacco incubation was 459, 603, 576 and 660 for control, ammonia, sodium hydroxide and ammonia plus sodium hydroxide-treated straw respectively. Each treatment improved the degradability significantly (P < 0·01). The effect of ammonia plus sodium hydroxide treatment on rumen degradability of straw was additive (P < 0·05).

In experiment 2 the treated straws studied in experiment 1 were given to four wethers in a 4 × 4 Latin-square design, to measure the voluntary intake, digestibility, water consumption and urine excretion. The digestibility (g/kg) and daily intake of digestible organic matter (g/kg M0·75 per day) were 554, 12·5; 628, 24·7; 653, 19·7; and 668, 24·3 for the control, ammonia, sodium hydroxide and ammonia plus sodium hydroxide-treated straws, respectively. Intake of ammonia-treated straw was significantly greater than for sodium hydroxide-treated straw (P < 0·01). The water consumption and urine excretion by sheep were increased significantly by sodium hydroxide and ammonia plus sodium hydroxide treatments (P < 0·01).

In experiment 3, either straw or ammonia-treated straw were treated with 20, 40 and 60 g sulphuric acid (200 ml/1 solution per kg). The degradability of the acid-treated straws was measured using three wethers fitted with cannulae and given ammonia-treated straw to appetite. The dry-matter degradabilities (g/kg) after 48 h in sacco incubation were 52·0, 53·9, 58·7 and 67·4 for the control, and 20, 40 and 60 g acid per kg treatments, whereas the values were 61·3, 60·4, 68·4 and 69·4 for the ammonia-treated straw, and 20, 40 and 60 g acid per kg treatments respectively. There was a significant effect of acid treatment and ammonia treatment on dry-matter degradability.

Four experiments with sheep fitted with rumen cannulae were conducted to investigate whether the rate of digestion of ammonia-treated straw, estimated as disappearance of dry matter from nylon bags in the rumen, might be increased by supplements of either soya bean meal, sucrose or sugar beet pulp at a level of 0·1, or by increasing the concentrations of dietary soluble micro and macro minerals.

There were no differences among treatments in rate and extent of digestion of straw due to supplementations.

In another experiment, the effect of increasing the proportion of molassed sugar beet pulp or rolled barley on rate of digestion of ammonia-treated straw was investigated. A greater proportion of sugar beet pulp (0·45) could be included in the diet before the rate of digestion was decreased in comparison with rolled barley (0·35).

Assuming that the digestibility of the sugar beet pulp and the rolled barley was not changed by the increasing proportion in the diet, it could be calculated that the digestibility of straw was reduced from 0·538 with straw alone to 0·403 with the sugar beet pulp and to 0·218 with the rolled barley supplement when the supplements were included at a level of 0·70.

Thirty-six British Saanen female kids, born between either 20 March and 6 April (E) or 10 April and 16 June (L), were reared under three different patterns of lighting — a constant 18-h light: 6-h dark (C); or a weekly step-wise reduction from 18-h to 10-h light: 14-h dark over 10 weeks, commencing at either 6 (R6) or 10 (R10) weeks of age. Vasectomized males were used to test for oestrus; blood samples were collected to determine plasma progesterone concentration. Thirty-three goats attained puberty; all but two kids showed oestrus at first ovulation. The mean ( ± s.d.) age and live weight at puberty were 174·6 (± 4·1) and 141·7 (± 4·3) days (P < 0·001), and 28·6 (± 0·9) and 22·8 (± 1·0) kg (P < 0·001), for E and L treatments, respectively. For R6, R10 and C treatments, the ages and weights wer e 151·6 (± 4·7), 160·4 (± 5·2) and 164·7 (± 4·9) days (NS), respectively, and 24·5 (± 1·1), 25·3 (± 1·2) and 27·8 (± 1·1) kg (NS), respectively. A significant date of birth × lighting-pattern treatment interaction was found for date at puberty (P < 0·001), with puberty occurring earlier for E than L kids only when a reduction in daylength occurred. Puberty occurred earlier on R6 than R10 treatments only for L kids.

Data on 1542 Damascus kids, collected from 1977 to 1981, were used to study environmental and genetic factors influencing pre-weaning and post-weaning growth traits of kids. Season of birth, type of birth, sex of kid and dam lactation number were the environmental factors investigated. Phenotypic and genetic parameters were estimated from paternal half-sib correlations. The average sire family size was 17·2 kids. Single kids were heavier at birth, at weaning and at 140 days of age than twins or other multiples (P < 0·01). Male kids were heavier (P < 0·01) and grew faster (P < 0·01) than female kids from birth to 140 days of age (4·7 and 4·2 at birth, and 29·2 and 24·6 kg at 140 days, respectively). Dam lactation number significantly affected pre-weaning growth, but had no effect on the post-weaning growth rate of kids.

Heritabilities for birth, weaning and 140-day weights, and pre-weaning and post-weaning growth rate, were 0·31 (s.e. 0·08), 0·27 (s.e. 0·07), 0·21 (s.e. 0·07), 0·16 (s.e. 0·06) and 0·22 (s.e. 0·07), respectively. Genetic correlations were mostly high and all positive, especially between weaning weight and 140-day weight (0·82 (s.e. 0·08)), and pre-weaning growth rate and 140-day weight (0·80 (s.e. 0·10)). The corresponding phenotypic correlations were also high and positive (0·71 and 0·67, respectively). No genetic antagonisms were found among the characters studied. Response to selection for post-weaning growth should be effective.

Data on 1474 lactation records obtained from 1972 to 1978 were used to study environmental and genetic influences on production characters in the Damascus goat. Year and month of kidding had a significant effect on 90- and 150-day milk production after weaning, lactation length and litter weight at weaning (P < 0·01), but no influence on litter weight at birth. Milk production after weaning was not related to litter weight at birth or at weaning. Age of goat at kidding had a significant quadratic effect on milk production, and litter weight at birth and at weaning. No such effects were found for lactation length.

Estimates of heritability, from paternal half-sib correlations, for 90- and 150-day milk production were similar (0·29 (s.e. 0·14)). The genetic correlation between 90- and 150-day milk yield (0·92 (s.e. 0·03)) was high, indicating that part and whole lactation yields are influenced by the same genes. The phenotypic correlations among milk yield traits and lactation length were also high and positive.

Mortality, efficiency of food utilization and carcass value of growing pigs were investigated in relation to engineering and control of the house environment. Data originated from contract farms and were made available by the Belgian Farmers' Association. The following parameters were investigated by means of analysis of variance and covariance: food conversion ratio, mortality, emergency slaughter rate and carcass values. Data were classified according to characteristics of the heating, air inlet and air outlet systems of the pig houses.

Within the limitations of our project, the expected favourable effect of heating on mortality and efficiency of food utilization of growing pigs depended on the construction and the functioning of the air inlet and outlet systems. Pigs fattened in houses with mechanical ventilation had a higher proportion of carcasses in the higher carcass grades. Seasonal effects were observed with respect to mortality rate, emergency slaughter rate and efficiency of food utilization. Differences between food conversion ratio with respect to heating and no-heating were comparable with those between summer and winter conditions. Hence the seasonal influence was not completely buffered by the housing conditions.

Thirty-three Landrace × Large White multiparous sows were allocated randomly to one of three treatment groups, and were weaned after a 10-day (treatment A), 21-day (treatment B) or 42-day lactation (treatment C). All sows were bled regularly from weaning through to day 24 post coitum, at which time the sows were slaughtered and their reproductive tracts recovered and dissected.

Ovulation rates were similar for all groups. Embryo survival for treatments A, B and C respectively was 0·638, 0·728 and 0·777 but this difference was not significant. Oestradiol 17-β concentrations were significantly higher in sows weaned after 10-day lactations throughout the whole period from weaning to day 10 post coitum compared with the other two treatment groups (P < 0·001).

The efficacy of a single injection of oestradiol benzoate, or a combination of pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG), for the induction of a fertile oestrus and ovulation in the prepubertal pig was investigated in two experiments.

In the first experiment, 1·2 mg of oestradiol benzoate induced 21/23 gilts to ovulate, and 22/23 gilts showed oestrus and were inseminated on day 4 or 5 after treatment. At 28 days after insemination, 12 gilts were pregnant and carrying a mean of 7·1 (s.d. 3·3) live embryos, giving an embryonic survival rate of 0·703. All the 22 gilts treated with 400 international units PMSG plus 200 international units HCG as a single injection ovulated but only 10 showed oestrus and were inseminated. At 28 days after insemination, six gilts were pregnant with a mean of 13·0 (s.d. 5·8) live embryos, giving an embryonic survival rate of 0·583.

In the second experiment, 9/11 oestradiol benzoate and 10/10 PMSG/HCG gilts ovulated in response to treatment. Oestrous detection and insemination were delayed until the expected time of the second oestrus, 20 to 30 days after treatment. Nine gilts (3 oestradiol benzoate, 6 PMSG/HCG) showed oestrus in this period and eight were inseminated. Five gilts were pregnant 28 days after insemination with a mean of 11·4 (s.d. 1·1) live embryos, giving an embryonic survival rate of 0·860.

Twenty-four 1-year-old boars of proven fertility were assigned randomly to one of two temperature-controlled trailers. A control group in each trial was held at 17 ± 0·5°C while the other group was exposed to a diurnal ambient temperature cycle. Cycles followed a sine-wave pattern with minimum and maximum temperatures occurring at 04.00 and 16.00 h respectively. Cycling temperature ranges were 17 to 33 ± 0·5°C (low-temperature stress), 19·5 to 35·5 ± 0·5°C (medium-temperature stress), and 22 to 38 ± 0·5°C (high-temperature stress). Semen samples were collected every 3 or 4 days over an experimental period of 42 days.

Low-temperature stress and medium-temperature stress boars were not affected significantly in the five parameters of semen quality observed. The difference between controls and high-temperature stress boars was highly significant for motility, abnormal spermatozoa, gel-free volume, and total spermatozoa per ejaculate. Concentration of spermatozoa was not affected by treatment. Significant time effects were observed for motility, abnormal spermatozoa and total spermotozoa per ejaculate. Significant differences began to appear after 2 or 3 weeks and changes still appeared to be occurring at 6 weeks.

By studying the behaviour of the time series of the difference between the observed values of milk yield and the fitted lactation curve, a stochastic model for milk yield is derived. The model is used to improve the fit of the lactation curve, to forecast milk yield and to generate simulated values of milk yield.

In pigs growing from 20 to 70 kg live weight, the addition of 40 g sodium bentonite to each kg diet was without significant effect on growth performance under ad libitum and restricted feeding regimes. Sodium bentonite appeared to be indigestible and inert, as dry-matter digestibilities were reduced from 0·87 to 0·85 and 0·83 by the addition of 20 and 40 g sodium bentonite per kg diet respectively.

Twelve British Saanen female kids were exposed to male goats for 1 h daily on 29 July (Ml), 12 on 12 August (M2) and 12 on 27 October (M3), when the kids were, on average, (± s.d.) 136·4 (± 12·2), 150·2 (± 12·8) and 225·4 (± 3·5) days of age, respectively. Blood samples were collected to determine plasma progesterone concentrations from 17 July onwards. By 27 October, 11 and 12 kids from treatments Ml and M2 had attained puberty, compared with no kids from treatment M3. Ten kids from treatment M3 attained puberty after male introduction. The mean ages and dates at puberty for treatments Ml, M2 and M3, respectively, were as follows: 205·5, 215·3 and 233·0 days (P < 0·001); and 7 October, 17 October and 3 November (P < 0·001). The mean reaction interval to male introduction for treatments Ml, M2 and M3 was 69, 66 and 7 days (P < 0·001), respectively. The variances for the date of attainment of puberty showed differences in the degree of synchronization of the event between all three treatments.