There is increasing interest in how the raw material make-up of concentrates can influence the milk performance of dairy cows. Thus, over two consecutive winters, 54 dairy cows were used to investigate the effects on dry matter (DM) intake, milk yield and its composition of feeding concentrates of diverse energy source (LNDF — 131 g neutral-detergent fibre per kg DM, 492 g starch plus sugars per kg DM; HNDF — 244 g neutral-detergent fibre per kg DM, 293 g starch plus sugar per kg DM) at two formulated crude protein (CP) levels (157 v. 187 g/kg DM) and three levels of concentrate allowance (9, 11, 13 kg DM). The concentrates were formulated to be of equivalent metabolizable energy concentration (MJ/kg DM) and were offered with silage ad libitum for a 10-week period (weeks 4 to 13 of lactation).

Silage intakes were variable but not significantly influenced by concentrate energy source or formulated CP level, except in the 1st year where animals consuming the high CP concentrate ate more silage. Silage DM intake decreased as concentrate allowance was increased with the substitution rate (kg silage DM per kg concentrate DM) increasing as concentrate allowance was increased.

Increasing the concentrate allowance effected the expected increases in milk yield. Concentrate energy source did not influence milk yield but the higher CP levels effected a 2-kg increase in milk yield. Feeding of LNDF concentrates depressed milk fat concentration and its yield, the depression being accentuated with each increase in concentrate allowance. The depression in milk fat concentration was negatively correlated with the forage: concentrate ratio of the diet consumed. Furthermore, dietary NDF proportion was shown to account for greater than half of the variation in milk fat concentration. In contrast to the observations made for milk fat, feeding the LNDF concentrates effected an increase in milk protein concentration but only at the lower CP level of the concentrate.

The value of indicator traits (7), such as physiological or biochemical traits in the genetic improvement of dairy cattle for milk yield (M) was studied. First, some corrections were made to the base rates of genetic change possible by improvement systems based on progeny testing and on multiple ovulation and embryo transfer (MOET), and on combinations of these. Efficient field progeny-testing systems can be competitive with current adult MOET nucleus herd schemes but juvenile MOET nucleus herd schemes offer substantial increases in rates of response. With high co-heritability, selection for the T alone may allow greater rates of response than those currently considered feasible using progeny testing. However, faster rates are obtained with combined selection. When breeding values are accurately measured by pedigree and performance records on M, as in the progeny test, the extra rates of response with combined selection may be small. Where breeding values are less accurately assessed, as in juvenile MOET nucleus schemes, the extra rates of response can be appreciable. For T with co-heritability (hMrGhT) of 0·27 and the CV for M from 0·15 to 0·20, response rates of 2·0 to 2·7% of the mean per year possible by traditional methods could be increased to 2·2 to 2·9% in progeny testing schemes, 2·3 to 3·1% and to 4·3 to 5·7% for adult and juvenile MOET nucleus schemes respectively.

A possible useful indicator trait is blood urea nitrogen (BUN) measured in young animals after a short fast. Results from four experiments with calves having high or low genetic merit for M were summarized. The pooled co-heritability estimate was —0·27 (s.e. 0·05). With this, or even a more modest effect, BUN would be a useful indicator trait in selection for milk production. Its use in practice in high and low selection lines or in a section of the industry, would allow assessment of the merit of the method.

Two varieties of rice straw, long variety — no. 370 Basmati traditional (L) and short variety — no. PR106 hybrid (S) were separated into botanical fractions giving the proportion of leaf plus leaf sheath, internode, node and chaff (g/kg dry matter) as 633, 247, 83 and 37 for L and 680, 156, 76 and 88 for S, respectively. Samples of whole plants, leaves plus leaf sheaths and internodes were subjected to ammonia treatment. The chemical composition and the rumen degradability of dry matter and organic matter determined by the nylon bag technique were ascertained for treated and untreated samples of whole plants and botanical fractions of plants from both varieties. The ash and silica content were higher in leaf plus leaf sheath, 211 and 102 g/kg for the L and 190 and 67 g/kg for the S, than in internodes, 160 and 29 g/kg for L and 184 and 29 g/kg S, respectively.

The potential degradability (a + b) value from the formula p = a + b(−e−ct) for dry-matter loss (DML), organic-matter loss (OML) and degradability of organic matter in dry matter (DOMD) were significantly higher for the S being 622, 659 and 544 g/kg, than for the L being 561, 586 and 500 g/kg, respectively (P < 0·01). The degradation rate too was significantly higher for the S than for the L for DML, OML and DOMD (P < 0·01). The ammonia treatment significantly improved the potential degradability for DML, OML and DOMD for both the varieties and their fractions (P < 0·01).

The live-weight gain (LWG) and efficiency of food utilization of purebred British Friesian and Canadian Holstein steers and of crossbred steers out of British Friesian dams by Charolais, Hereford, Limousin, Lincoln Red, Simmental, South Devon and Sussex sires were examined in two beef production systems. One was similar to the commercial 18-month grass/cereal system (16-month) and the other to a commercial 2-year system (24-month). The cattle were serially slaughtered at three levels of fatness covering the commercial range and determined by the use of the Scanogram ultrasonic machine. The trial extended over 4 years and involved a total of 650 cattle. Data for the two production systems were analysed separately. Changes in growth performance were examined relative to estimated carcass subcutaneous fat content (g/kg; SFC) and sire breed crosses compared at the mean fatness level within system: 65 g/kg SFe for 16-month and 74 g/kg SFe for 24-month.

Sire breed differences were not detected (P > 0·05) in the regressions on SFe of age and live weight at slaughter, overall daily LWG and overall efficiency of weight gain. Pooled within sire breed, live at slaughter and age at slaughter increased by 2·5 kg and 2·8 days (16-month) and 2·2 kg and 2·1 days (24-month) for each g/kg increase in SFe.

Charolais crosses and Canadian Holsteins were heaviest at equal SFC in both systems, but the latter were 63 days older (16-month) and 42 days older (24-month): Hereford, Lincoln Red and Sussex crosses were lightest and among the youngest in both systems.

Sire breed crosses differed significantly in daily LWG: Charolais crosses grew fastest in both systems; the relative growth rate of other sire breed crosses was less consistent between the two although the Hereford crosses and British Friesians grew slowly in both systems. Overall efficiency of LWG (g gain per kg digestible organic matter intake) ranged from 164 to 205 (16-month) and 146 to 171 (24-month). Canadian Holsteins and British Friesians had the lowest efficiency of LWG in both systems of production; differences between the other breeds were not statistically significant (P > 0·05).

Carcass characteristics, and the rate and efficiency of lean gain of purebred British Friesian and Canadian Holstein steers and of crossbred steers out of British Friesian dams by Charolais, Hereford, Limousin, Lincoln Red, Simmental, South Devon and Sussex sires were examined in two beef production systems. One was similar to the commercial 18-month grass/cereal system (16-month) and the other to a commercial 2-year system (24-month). The cattle were serially slaughtered at three pre-determined fatness levels, estimated by the Scanogram ultrasonic machine. The trial extended over 4 years and involved a total of 650 cattle, 398 of which had their left sides separated into tissues. Breeds were compared at equal carcass subcutaneous fat proportion determined by visual carcass assessment (SFe). Data for the two production systems were analysed separately.

Sire breed differences were not detected in the regression on SFe for most characteristics (P > 0·05). Sire breeds differed in killing out and visual conformation score in both production systems (P < 0·001): Charolais and Limousin crosses had the highest values and purebred Canadian Holsteins the lowest. The overall range between sire breeds was 30 g carcass weight per kg live weight and five points on a 15-point conformation scale.

Breeds with the higher conformation scores generally had higher carcass lean proportions and higher lean: bone ratios. Canadian Holsteins had a 20 g/kg lower carcass lean proportion than the British Friesians (P < 0·05).

Breed crosses with larger adult body size tended to have higher lean tissue growth rates: the difference between mean values for Charolais crosses and Hereford crosses was 49 g/day (16-month) and 38 g/day (24-month). The lean tissue growth rates of the British Friesians and especially the Canadian Holsteins were low in relation to their adult body size.

Limousin and Charolais crosses had the highest efficiency of lean gain (g lean per kg digestible organic matter intake). These and the other crosses were significantly more efficient than the purebred Canadian Holsteins (P < 0·05). The overall range between breeds was 20 g/kg.

A series of experiments was conducted to examine the potential of using ammonia released from the hydrolysis of urea for alkali treatment of straw.

In an initial experiment (1) the effect on urea hydrolysis of adding either hydrochloric acid (HC1) or the surfactant alkyl phenyl ethylene oxide to straw of differing dry matter (DM) concentration was examined. The inclusion of HC1 or surfactant failed to improve the proportion of urea hydrolysed at straw DM concentrations of 450, 600 or 750 g/kg.

In experiment 2, straw was prepared and treated with urea, at a level of 20 (U2), 50 (U5), 70 (U7) g/kg straw DM and ammonia 40 (A4) g/kg straw DM to compare with untreated straw (S). Samples of the straws were milled and degradability at 60 h was estimated using the nylon bag technique. DM loss was significantly higher for all treated straws compared with untreated straw (P < 0·001). However, the proportion of added nitrogen retained from all urea treatments was less than 0·33 but U7 and U5 were approximately double that obtained from A4.

In experiment 3, 3-t batches of straw equivalent to treatments U2, U7, A4 and S were treated during September and later offered to steers in digestibility and food intake trials. Straws were ground through a 40-mm screen and offered to steers in digestibility stalls, in a balanced incomplete-block design. There were increases in the digestibility of DM (+0·08 g/kg), organic matter (+0·08 g/kg), and acid-detergent fibre (+0·09) of U7 and A4 straw compared with values for untreated straw (P < 0·01).

In a subsequent food intake trial treatment of long straw, with 20 g urea per kg straw DM (U2) failed to prevent moulding, however digestible organic matter intake (DOMI) of U7 and A4 straws increased by 0·42 and 0·27 kg/day respectively compared with intakes of untreated straw (P < 0·01). The application of 70 g urea per kg straw DM gave results comparable with treatment with 40 g ammonia per kg straw DM in improving digestibility of ground straw and the DOMI and preservation of long straw.

The effect of castration on the cellular characteristics of dissected fat partitions was examined in 20 Dorset Horn rams and 20 Dorset Horn wethers. Cellular characteristics of dissected carcass (subcutaneous and intermuscular partitions) and non-carcass (kidney fat, omental and mesenteric partitions) fat partitions were examined in 13 mature animals, and the rate of change in adipocyte volume relative to the change in chemical-fat weight in that partition, examined in 27 immature animals.

Mature wethers had a greater concentration of chemical fat in the subcutaneous fat partition than mature rams (917 v. 885 g/kg, respectively). This, in combination with a greater weight of dissected subcutaneous fat, resulted in a greater weight of chemical fat in the subcutaneous partition of wethers compared with rams. Mature wethers had larger adipocytes than mature rams in all dissected fat partitions, with the largest increase in the subcutaneous and omental fat partitions. The increased adipocyte volume in the dissected fat partitions in mature wethers resulted in a smaller total estimated number of adipocytes in all carcass and non-carcass fat partitions compared with mature rams.

Standardized allometric coefficients for adipocyte volume relative to chemical-fat weight in that partition showed that increases in chemical-fat weight were due to a combination of hypertrophy and hyperplasia. In the omental and kidney fat partitions, hypertrophy contributed more to the increase in chemical-fat weight in wethers compared with rams.

The cellular characteristics of dissected carcass (subcutaneous and intermuscular fat) and non-carcass (kidney fat, omental and mesenteric fat) fat partitions were examined at maturity in a total of 34 rams and ewes from flocks of Peppin Merino sheep selected for high (weight-plus) or low (weight-minus) weaning weight and from a randomly bred control flock. Strain and sex effects on the rate of change in adipocyte volume in each fat partition relative to the change in chemical-fat weight in that partition, were examined in 60 immature animals.

Selection for high or low weaning weight had no effect on adipocyte volume in the mature animals, with the increased weight of fat in the weight-plus animals due to an increased number of adipocytes in the dissected fat partitions. Consequently, hyperplasia had a greater contribution to increases in chemical-fat weight in the weight-plus, compared with the weight-minus animals.

Mature ewes had larger and fewer adipocytes in the subcutaneous and intermuscular partitions than the mature rams, whereas there was no difference between the sexes in adipocyte volume in the kidney, omental and mesenteric fat partitions. Mature ewes had fewer adipocytes than the mature rams in the subcutaneous, intermuscular, omental and mesenteric fat partitions. With the exception of the kidney fat partition, there was no sex effect on the relative contribution of hypertrophy to increases in chemical-fat weight of the dissected carcass and non-carcass fat partitions.

The responses to supplements differing in protein concentration and degradability were measured in lactating ewes and their twin lambs when offered fresh ryegrass either cut or grazed. Housed Scottish Halfbred ewes, offered fresh-cut grass ad libitum received no supplement (N) or supplements with barley and maize starch (B); barley and soya-bean meal (S); barley, soya-bean meal and fish meal (SF) or barley and fish meal (F) in weeks 2 to 7 of lactation. By feeding supplements, herbage organic-matter (OM) intake was depressed (2·00 v. 1·74 kg/day). Mean daily milk yield was increased when protein supplements were given and, because milk protein concentration was higher for supplement F and similar for all other diets, mean daily milk protein output increased with increasing fish meal in the diet. Milk yields were N 2·55, B 2·59, S 3·17, SF 3·15 and F 3·17 kg/day. Total milk solids and fat concentrations were also higher for S, SF and F than N or B. Lambs from ewes supplemented with protein grew faster and the ewes generally lost less weight and body condition compared with unsupplemented ewes.

At pasture, Masham ewes grazed at herbage allowances of either 4 (L) or 10 (H) kg OM per day and received no supplement (N) or supplements B or F, for the first 6 weeks of lactation and then, in weeks 7 to 12, grazed without supplements. For NL, BL, FL, NH, BH and FH respectively lamb growth rates from birth to 6 weeks were 235, 242, 274, 267, 286 and 302 g/day; from birth to 12 weeks were 210, 209, 249, 255, 275 and 287 g/day and losses in ewe body-condition score from birth to 12 weeks were 1·28, 1·22, 1·06, 0·97, 0·62 and 0·76.

It is concluded that protein supplements increased milk yield and lamb growth rates and that the response tended to be greater with fish meal.

In a 2 × 2 × 2 × 2 factorial experiment, the effects on reproductive performance of active immunization against androstenedione and of two sward heights in two periods, August to October (period 1) and October to November (period 2), were investigated in 144 Beulah Speckled-face and 146 Brecknock Cheviot ewes. Sward heights of either 5 to 6 cm (2200 kg dry matter (DM) per ha) (high) or 2 to 3 cm (650 kg DM per ha) (low) were achieved by adjustment of stocking rate during period 1. Two groups of ewes were balanced for body condition score across breed and sward height and the ewes of one group were actively immunized against androstenedione by injection with Fecundin® at 8 and 5 weeks before mating at the second synchronized oestrus after progestagen pessary withdrawal. Ewes were reallocated to the high (at 15 ewes per ha) and low (at 20 ewes per ha) swards at the start of period 2 by breed and immunization treatment, balanced for live weight, body condition score and sward height in period 1. After mating in mid November, all ewes were run at 19 ewes per ha on the residual pasture of the high sward until slaughtered either at return to service or at 4 weeks after first mating when corpora lutea and embryos were counted.

There were no effects or interactions due to sward height in period 1 on the reproductive responses to sward height in period 2. Ovulation and potential lambing rates were greater in the Beulah breed than in the Cheviot, and on the high sward than on the low in period 2. Ovulation rates were higher in immunized ewes than in control ewes but the effects of immunization and sward height on potential lambing rate were not independent. Potential lambing rates were higher in immunized ewes than in control ewes at the low sward height but not at the high sward height.

Adjustment of stocking rate during period 1 served to increase the range in ewe body condition at the start of period 2 in mid October. Reproductive response to body condition at this time differed between the breeds, the relationship being strongly positive in the more prolific Beulah control ewes but less so in the less prolific Cheviot control ewes. The response to immunization in both breeds was relatively greater at lower levels of body condition, thereby reducing the effect of body condition in immunized ewes.

The use of Fecundin® is therefore unlikely to produce much advantage when pre-mating nutrition or body condition are high but there may be some advantage in using it when nutritional resources are limited in the autumn, particularly in ewes in poorer body condition.

An experiment involving 320 gilts was conducted to investigate the effects of age and growth traits on puberty attainment and reproductive performance in gilts given boar stimulation with or without exogenous gonadotropins. Following ad libitum feeding during rearing, groups of gilts were stimulated for puberty at one of four ages, namely 130, 150, 170 or 190 days. Within each age group, gilts were selected to maximize the variation in live weight, relocated, mixed and allocated to two treatments in a randomized-block design: (a) mature boar contact (boars only) and (b) boar contact plus an intramuscular injection of 400 i.u. pregnant mare's serum gonadotropin + 200 i.u. human chorionic gonadotropin (boars + PG600). Gilts were mated at puberty and slaughtered at 35 days post coitum.

For the gilts on the boars-only treatment, the interval from stimulation to puberty decreased significantly (P < 0·05) and became less variable with ascending age at stimulation. Increasing live weight at a given age also reduced the interval from stimulation to puberty. Multiple regression equations involving age, live weight and backfat thickness at stimulation and growth rate from birth to stimulation were calculated to obtain a prediction equation for the interval from stimulation to puberty. The effects of age and live weight at mating on ovulation rate, embryo survival and number of live embryos 35 days post coitum were not significant.

For the gilts on the boars + PG600 treatment, 92% attained puberty within 6 days of treatment, with a non-significant trend to improve with increasing age. Mating rates were similar to those on the boars-only treatment (90%). Ovulation rates were higher (P < 0·001) but embryo survival rates were lower (P < 0·001) in the boars + PG600 group, resulting in similar litter size at 35 days post coitum in the boars-only and boars + PG600 treatments. There was a non-significant trend for litter size to increase with age in the boars + PG600 treatment. Thirty-eight of the gilts treated with hormones failed to conceive and 53% were found by ovarian morphology at slaughter to be cycling normally with a tendency for this proportion to increase with age.

Estimates were made of total body protein in 45 unimproved crossbred pigs slaughtered serially between 20 and 200 kg live weight. Allometric functions were used to estimate protein weight at any given body weight and the Gompertz function was used to express live-weight changes in relation to time and to predict weight at maturity. Predicted values for daily protein retention increased rapidly from 20 kg to attain, at around 75 kg live weight, maxima of 130 g for entire males, 120 g for females and 105 g for castrated males. Between 45 and 110 kg live weight rates of protein retention were maintained within 10 g of the maximum rate. Mature live weights were estimated to be 240, 215 and 225 kg for entire males, females and castrated males. The allometric exponents for whole body protein as a function of body weight were 0·963 (s.e. 0·025), 0·927 (s.e. 0·021) and 0·850 (s.e. 0·049) for entire males, females and castrated males respectively.

Two trials involving young pigs (total numbers 288 and 400, respectively) were performed to compare the biological activity of Dl- and L-tryptophan under restricted (trial 1) and ad libitum (trial 2) feeding conditions. In trial 1, three additions of Dl-tryptophan (0·3, 0·6 and 0·9 g/kg) and two additions of L-tryptophan (0·3 and 0·6 g/kg) to a basal diet containing 0·9 g natural tryptophan per kg were tested. In trial 2, the treatments were additions of 0·4, 0·8 and 1·2 g Dl- or L-tryptophan per kg to a basal diet having 1·3 g natural tryptophan per kg. Both trials were of 6 weeks duration. In trial 1, almost equal performance was achieved with both tryptophan sources at a dietary level of 0·3 g/kg, whereas at a level of 0·6 g/kg, Dl-tryptophan produced slightly better performance in weight gain, food intake and food conversion efficiency than did L-tryptophan. In trial 2, the supplemental level of 0·4 g L-tryptophan per kg produced weight gain and food intake results which were significantly superior to those of Dl-tryptophan. However, at supplemental levels of 0·8 and 1·2 g/kg, diets with Dl-tryptophan produced somewhat better performance than did L-tryptophan. Based on the results of trial 2, it was estimated that the pig's need for total tryptophan over the weight range of 10 to 35 kg is at least 2·3 g/kg in a diet having 10·3 MJ net energy per kg.

The experiment compared four different space allowances for growing pigs housed on fully slatted floors. Space allowance (A m2) was defined in relation to live weight (M kg) of the pigs according to the equation A = kM0·67, using values for the constant (it) of 0·024, 0·027, 0·030 and 0·034. Six replicate pens of 12 pigs were housed on each treatment in a controlled environment building. Food was given ad libitum and from 34 kg until slaughter at 85 kg pigs were individually weighed each week and the pen size was adjusted according to the appropriate equation. Increasing space allowance increased live-weight gain (844, 862, 883, 897 (s.e.d. 14·4) g/day). Differences in killing-out proportion reduced the effect on final carcass weight (63·3, 63·9, 64·1, 64·5 (s.e.d 0·82) kg). Daily food intake was unaffected by treatment but food conversion ratio was significantly poorer at the lowest space allowance (2·70, 2·56, 2·60, 2·59 (s.e.d. 0·043) kg/kg). Economic analyses of the results indicated an adverse effect on profitability of space allowance less than that defined by the equation A(m2) = 0·027 M0·67 (kg). A minimum allowance defined by the equation A (m2) = 0·030 M0·67 is recommended in commercial practice for pigs in fully slatted housing.

Relative growth of length and thickness of femur, tibia, humerus and radius-ulna was studied using data from 320 rabbits from both sexes of two lines (New Zealand White and California). A cross-sectional design was used with slaughter points fixed at weekly intervals from 1 to 20 weeks of age. Carcass length was chosen as independent variable and two models were fitted to the data. Model 1 assumed the existence of one allometric change at some moment of the post-natal development and model 2 of a continuous change of the allometric coefficient throughout the experimental period.

Most of the bone measurement showed allometric changes and in all the cases they were not abrupt but continuous. The theoretical and practical implications of the existence of these changes are discussed. The allometric coefficients of all the bone measurements showed a decreasing rate of change except radius-ulna thickness. While the coefficients for bone lengths were positive tending to isometry, for bone thickness they were always negative.

Body weight and food intake were measured at different ages up to 30 weeks in males and 21 weeks in females in lean, fat and commercial lines of broiler chickens given diets of different crude protein content. The lean and fat lines showed no differences in rates of body-weight gain or final body weights but the lean line had consistently lower food intakes. Dietary protein concentration within the ranges studied did not influence final body weights.

Equations derived from a theory of feeding and growth were used along with the data up to 21 weeks of age to calculate mature body weights and various feeding characteristics. These values were compared with those obtained by application of the theory to another set of broiler data. The theory was found to be sufficiently robust to give some consistent interpretations of data from experiments involving considerable differences in time, breed and diet.

In ruminants a dynamic state of protein turn-over has been poorly understood although the methodology of measuring the rate of protein turn-over has recently been advanced to a great extent (Waterlow, Garlick and Millward, 1978). Available evidence suggests that ruminants such as sheep and cows are no exception among various mammalian species when whole-body protein synthesis of adult animals is compared on a metabolic body-weight basis (Waterlow et al., 1978; Reeds and Lobley, 1980).