1. Eight calves of each of two breed types, Friesian (Fr) and Brahman × Friesian (FB), were fed ad libitum on one of two diets; the digestibility of the dry matter of the diets was 72% and 63%. Eight calves were kept at 34°C and eight at 17°C. In a second experiment six of the calves previously exposed to 34°C were subjected to daily exposures to a radiant heat load at 32°C air temperature, while fed on the diet of lower digestibility.

2. Rectal temperatures and respiratory rates were higher, and food intakes and growth rates were lower, at 34°C than at 17°C. However there was only a small difference in growth rate between the two temperatures after the effect of temperature on food intake had been removed by regression.

3. At 34°C FB calves had lower rectal temperatures and respiratory rates than Fr calves, and when fed on the diet of higher digestibility FB calves ate more and grew faster than Fr calves at both temperatures; however there were only small corresponding differences between the breed types for calves fed on the diet of lower digestibility at both temperatures.

4. At 34°C FB calves had lighter (weight) hair coats than Fr calves and FB calves had lighter coats at 34°C than at 17°C; the latter difference was not apparent for Fr calves. Nevertheless, neither rectal temperature nor respiratory rate was significantly affected for either breed by removal of the hair coat at 34°C.

5. In the second experiment the rectal temperatures of FB calves increased by smaller amounts during exposure to radiant heat than was the case for Fr calves; FB calves had faster sweating rates than Fr calves during these exposures.

Twenty-four Hereford × Friesian cows (HF) and 24 Blue-Grey (Whitebred Shorthorn × Galloway) cows (BG) were housed in individual stalls. For the last 12 weeks of pregnancy they were fed hay to supply 75% of estimated maternal maintenance energy requirements. From calving (11 February to 9 April) until turning out to graze on 15 May they were given hay for maintenance, and a concentrate sufficient for either 2·25 kg (L) or 9·0 kg (H) milk per day, balanced within genotype. From 15 May until the end of the experiment on 7 September the cows and calves grazed as a single herd in a paddock grazing system, at a controlled daily herbage allowance of 50 g dry matter, measured to ground level, per kg total weight of cows and calves.

Cows on Treatment L lost more weight between calving and turnout than those on Treatment H, gave less milk, and their calves grew more slowly and were lighter at turn-out. Milk yields increased substantially after turn-out. Subsequently, milk yields and calf growth rates, and herbage intakes by the cows, did not differ significantly, although all were marginally higher for animals previously on Treatment L. Final calf weights, cow weights and cow body condition scores did not differ significantly.

Calves from HF cows were heavier at all stages than calves from BG cows. HF cows were heavier at calving than BG cows, gave more milk (though the difference was not significant) and lost more weight in early lactation. Final live weights and condition scores did not differ significantly.

The limited evidence suggested that conception to artificial insemination following oestrus synchronization was not affected by plane of nutrition in early lactation.

Striking similarities are known to exist in the growth processes of different mammalian genotypes. Two genetic size-scaling rules formally summarize these well-established similarities. In consequence, experimental results in one breed or species can often provide an excellent quantitative guide to biological relationships in other species. Despite strong genetic similarity, much genetic diversity usually remains.

The use of variation in metabolism to predict genetic merit for milk production was studied using 42 Friesian calves: 11 ♀♀, 10 ♂♂ were the offspring of four bulls with high (H), and 11 ♀♀, 10 ♂♂ of four with low (L) improved contemporary comparison (ICC) values (mean = + 402 kg and − 276 kg respectively). The animals were 14 or 15 weeks of age at the start of the study and treated similarly throughout.

Blood samples were collected: I—in relation to feeding; II—at set intervals; III—during a 44-h fast; and IV—following the sudden introduction of an energy metabolite (sodium propionate), and then refeeding. Plasma concentrations of β-hydroxybutyrate, glucose, urea, free fatty acids, total proteins and albumin were measured in all samples.

Blood characteristics apparently differed among animals, particularly protein and urea (repeatability 0·74 and 0·62 respectively).

The progeny of high ICC bulls had lower levels of urea during fasting (H = 4·70, L = 5·62 P < 0·05) but higher levels of free fatty acids (H = 578, L = 492 μ equivalents/l; P < 0·05). There was a small difference in total protein (H = 69·7, L = 66·8 g/l, P < 0·05) but the other metabolites showed no significant ICC group difference.

In general, sex of the animal did not influence the metabolites.

Results suggest that calves with different potentials for milk production vary in aspects of energy and nitrogen metabolism; the possibility of using these as criteria for genetic selection for milk production is discussed.

Eight pregnant beef cows and four rumen-fistulated cows were given 1·67 kg barley dry matter per day and 5·1 kg chopped oat straw dry matter treated by one of four different methods. The straw treatments (given in a 4 × 4 Latin square design) were (A) nil, (B) sodium hydroxide (25 g/kg straw, dry matter basis), (C) a fully soluble liquid supplement containing urea, calcium, phosphorus, sodium, trace elements and vitamins (40 g/kg straw, dry matter basis), and (D) sodium hydroxide plus liquid supplement. In the absence of liquid supplement 0·3 kg per day of the straw dry matter was not consumed, and with the sodium hydroxide plus liquid supplement treatment the cows would have consumed more straw than was offered. Sodium hydroxide increased the digestibility of the straw organic matter from 0·46 to 0·50 (P <0·05), and this was further increased to 0·53 (P <0·01) for the combined sodium hydroxide plus liquid supplement treatment. The calculated metabolizable energy intakes from straw were increased from 31 (nil) t o 36 by either the sodium hydroxide or liquid supplement treatments (P <0·05) and to 41 by the combined treatments (P <0·001). Sodium hydroxide tended to increase the concentrations of n- and iso-butyric acids in the rumen liquor.

The genetic size-scaling rules recently proposed by the author are used to derive genetically standardized growth equations.

A randomized block experiment, using 30 British Friesian cows, was used to assess the effects of offering supplements containing 172 and 234 g crude protein per kg dry matter in addition to grass silage which had a very high digestible organic matter in the dry matter of 769 g/kg. The animals, which had a mean calving date of 1 February, were blocked according to calving date and lactation number and allocated at random within each block to the two treatments. The treatments were applied from day 8 of lactation until the animals went to pasture on 13 April and both supplements were offered at the same rate of 7·6 kg per day. The total yields of milk produced during the experimental period were 1626 and 1650 ±38·4 kg and the mean daily yields during the final week were 24·8 and 25·6 ± 0·58kg for the medium and high protein supplements respectively. The mean live weights for the two groups were 524 and 544 ± 5·5 kg, and body condition score 2·9 and 3·3 ± 0·34 for the medium and high protein supplements respectively at the end of the treatment period. No significant treatment effects on milk composition were recorded at any stage during the experiment. Analysis of blood samples taken during the final week of the experiment showed plasma urea levels, at 220 and 290± 18 mg/1 for the medium and high protein supplements respectively, to be significantly different.

Progesterone profiles were obtained from 533 dairy cows during the interval from calving to the re-establishment of pregnancy by twiceweekly radioimmunoassay of milk progesterone. The importance of abnormal patterns of ovarian activity on herd fertility was determined. Animals were divided into five categories based on profile analysis: A, normal; B, delayed start to ovarian cycles; C, cessation of cycles; D, prolonged luteal activity; and E, silent oestrus. Animals in categories B to E were subdivided into treatment groups: categories B and C either (i) untreated controls, (ii) single injection 0·5 mg luteinizing hormone-releasing hormone (Hoechst) or (iii) progesterone-releasing intravaginal device (Abbott Laboratories Ltd) inserted for 14 days; categories D and E either (i) untreated controls or (ii) single injection 0-5 mg cloprostenol (Imperial Chemical Industries).

The proportion of cows in each category was: A 77·5%; B 4·9%; C 5·1%; D 1·9%; and E 10·7%. The incidence of ‘normal’ cows was 75% (first lactation), 80% (2nd to 5th lactations) and 69% (5th to 11th lactations). For normal cows (no. = 413) the interval to the start of cyclicity varied significantly with season but was not correlated with either the intervals to first insemination or to conception. In categories B to E the open period, the number of services per conception, and the days from first insemination to conception were greater than in category A, but only in category C were any differences significant. None of the treatments reduced calving-toconception intervals.

A 3 × 2 factorial design experiment using 84 British Friesian cows was conducted to assess the effect of offering three types of grass silage and two levels of concentrate supplementation during early lactation on the total lactation performance of cows which calve during January and February. The three types of silage were early-cut wilted (ECW), early-cut unwilted (ECU) and late-cut unwilted (LCU), and the two levels of concentrate supplementation were 538 kg (LC) and 738 kg (HC) during a mean post-calving period of 71 days. The animals had a mean calving date of 29 January and were blocked according to calving date, and allocated at random to the treatments within each block on day 7 of lactation. The treatments were applied from day 7 of lactation until the animals were turned out to pasture on 18 April. Mean milk yields for the indoor period were: HC treatments 1963 (ECW), 1979 (ECU) and 1830 (LCU); LC treatments 1938 (ECW), 1942 (ECU) and 1731 (LCU) ± 41·3 kg; and for the total lactation were: HC treatments 5375 (ECW), 5438 (ECU) and 5284 (LCU); LC treatments 5509 (ECW), 5529 (ECU) and 5316 (LCU) ± 184·1 kg. There was no significant interaction between silage type and level of concentrate supplementation.

Milk composition, animal live weight and body condition were not significantly affected by either silage type or level of concentrate supplementation.

The effects of three levels of crude protein in the diet, 10, 12 and 14 %, on the performance of entire Israeli Friesian male cattle (bulls) during fattening, was studied in two experiments.

The bulls were 5 months old and 200 kg live weight, and 7·5 months and 250 kg, at the start of Experiments 1 and 2, respectively, and were slaughtered after 178 to 268 days (Experiment 1) or 156 to 166 days (Experiment 2) on trial, at a live weight of 430 to 480 kg.

In Experiment 1 mixed diets of two metabolizable energy concentrations (11·1 and 10·5 MJ metabolizable energy/kg dry matter) were used, each containing concentrates with 10, 12 or 14% crude protein content. In half of the treatments the crude protein content of the concentrate was increased by two percentage units for the first 61 days of the experiment. Daily live-weight gain was significantly higher at 14% and 16% crude protein than at 10% and 12% crude protein during the first 61 days for animals on the high energy diet, but liveweight gain was not affected by crude protein content on the low energy diet over this period, or at either energy concentration from 62 days to slaughter.

In Experiment 2 the diet consisted of concentrate, wheat straw and cotton hulls, giving a metabolizable energy concentration of approximately 10·55 MJ/kg dry matter. Daily live-weight gain did not differ significantly between concentrates containing 10, 12 or 14% crude protein, but carcass weight gain was higher at 12% and 14% crude protein than at 10% crude protein.

It is concluded that in order to ensure the best performance of bulls of the Israeli Friesian breed, diets with a high concentration of energy should contain 14% crude protein when fed to animals with a body weight of 200 to 300 kg, and 12% crude protein for heavier animals.

Forty British Friesian calves aged approximately 90 days, mean initial live weight 107 kg, were divided into five groups and the animals in each group offered, ad libitum for 84 days, one of five diets based on maize silage. The basal diet of maize silage and 20 g urea/kg dry matter (diet 1) was supplemented with fish meal at 47 g/kg dry matter (diet 2) or with legume silage supplements at 310 g silage dry matter/kg dry matter. The silage supplements were red clover ensiled with formic acid (diet 3), red clover ensiled with formic acid plus formaldehyde at 30 g/kg crude protein (diet 4), or sainfoin ensiled with formic acid (diet 5). Diets 1 to 5 contained 23·7, 28·8, 28·3, 28·3, and 27·1 g total nitrogen/kg dry matter respectively.

The proportion of the total nitrogen insoluble in water, an indicator of the protein in the diet that was likely to escape degradation in the rumen, was 273, 356, 377, 413 and 339 g/kg for diets 1 to 5 respectively. Increasing the proportion of insoluble nitrogen in the diet by including fish meal or formaldehyde-treated red clover silage improved rates of live-weight gain and efficiency of feed conversion. Mean daily intakes of 15·2, 16·2, 16·2, 15·4 and 15·8 g digestible organic matter/kg live weight produced daily live-weight gains of 0·79, 1·05, 0·88, 0·93 and 0·83 kg/head by calves on diets 1 to 5 respectively. Diet 2 produced live-weight gains and gains per kg of digestible organic matter intake that were greater than those for diets 1, 3 or 5 (P<0·05), but not significantly greater than those for diet 4 (P<0·05). Calf live-weight gains were similar and satisfactory on the basal diet (maize silage and urea) and the diets with formic acid-preserved silage of red clover or sainfoin, but poorer than on the diet with 47 g fish meal/kg diet dry matter (P<0·05).

A change-over design experiment, comprising four periods each of 4 weeks' duration, was used to evaluate three silage types each fed with two levels of protein in the supplement in a 3×2 factorial arrangement. The three silages were high digestibility unwilted (A), high digestibility wilted (B) and low digestibility unwilted (C). The supplements had crude protein contents of 152 and 240 g/kg dry matter, and were offered at a standard rate of 10 kg undried weight daily. The mean silage intakes were 9·3, 9·5 and 8·6 ±0·19 kg dry matter/day for A, B and C respectively, but protein content of the supplement had no significant effect on the intake of silage. Milk yield was significantly affected by both silage type and protein content of the supplement, with the mean yields being 23·6, 23·9 and 22·0 ± 0·49 kg/day for A, B and C respectively, and 22·4 and 24·0 ±0·40 kg/day for the medium and high protein supplements respectively. Although there was no significant interaction between silage type and protein content of the supplement, the greatest response to increased protein was obtained with B. Neither silage type nor protein content ofthe supplement affected animal live weight or milk composition (other than fat content, which was significantly affected by silage type). Blood plasma urea levels were 281 and 405 ± 28·0 mg/1 for the medium and high protein supplements respectively.

Total ration digestibility and nitrogen balances were carried out on three animals per treatment. The digestibility of dry matter, organic matter and nitrogen was significantly affected by both silage type and level of protein in the supplement. The output of nitrogen in the urine was also significantly affected by both these factors.

A randomized block experiment using 108 British Friesian cows was conducted over a 2-year period to assess the effects of level and pattern of concentrate allocation during early lactation on the performance of cows which calve during January and February. The three concentrate levels were 280 (L1), 405 (L2) and 530 (L3) kg during a 74-day post-calving period, and the two systems of allocation were either a uniform daily allowance (uniform system) or a high input for the first 4 weeks after calving followed by a low input (high/low system). The animals had ad libitum access to medium-quality grass silage during the indoor period and in both years were turned out to pasture on 9 April. At pasture they were grazed rotationally in treatment groups at a stocking rate ranging from 6·4 cows ha-1 in the early-grazing season to 4·9 cows ha-1 in the late-grazing season.

Mean milk outputs for the indoor feeding period were: high/low system 1577 (L1), 1705 (L2) and 1764 (L3), uniform system 1583 (L1), 1676 (L2) and 1783 (L3) ±33·8 kg; and for the total lactation were high/low system 4625 (L1), 4906 (L2) and 5148 (L3), uniform system 4830 (L1), 4933 (L2) an d 5301 (L3) ±118·9 kg.There was no significant interaction between level and system of concentrate allocation. Feed intake, milk composition, animal live weight and body-condition data are also presented.

Measurements of live weight and of ultrasonic (Scanogram) fat depth and m. longissimus cross-sectional area at the 12th/13th rib were taken at 4— to 6-week intervals from 10 to 35 months of age (23 occasions) on 15 Hereford males (bulls), 15 castrate males (steers) and 15 females (heifers) managed under grazing conditions.

Mean rates of live-weight change throughout the measurement period (0·51, 0·47 and 0·39 kg/day for bulls, steers and heifers, respectively) were significantly different. When compared at the same ages, fat depth was similar in the steers and heifers, beginning at about 3 mm and increasing to 11 mm. Fat depth changed little in the bulls, beginning at 1·7 mm and increasing to 3 mm. At the same age, bulls had larger m. longissimus cross-sectional areas than steers and steers had larger muscle cross-sectional areas than heifers.

Absolute variation within sex groups increased throughout the experiment in live weight and fat depth, but not in m. longissimus crosssectional area. Simple correlation coefficients, pooled within sex groups, of relationships between the same measurements at various measuring occasions, indicated that measurements of fat depth and of muscle cross-sectional area at 10 to 12 months of age are poor indicators of these measurements at periods of 6 months or more later in life.

When compared at the same live weights, heifers had the greatest and bulls had the smallest fat depth and, within animals, fat depth was closely related to live weight. At any live weight, m. longissimus cross-sectional area was less in heifers than in steers and bulls, which were not significantly different from each other in this trait. Equations relating fat depth and muscle area to live weight are presented and, under the conditions of this study, indicate that there is no basis for adjustment of fat depth for live weight in bulls subjected to contemporaneous selection.

The milk production of 14 Hereford × British Friesian females in their second lactation (cows) and 36 in their first lactation (heifers) was measured at three levels of nutrition either by machine-milking twice a day, without the use of exogenous oxytocin, or by a calf-suckling technique. Machine-milking significantly increased the number of cows drying-off within 150 days of parturition (i><0·05) and significantly reduced milk yields compared with the calf-suckling technique (P< 0·01).

The 150-day cumulative milk yields of the heifers were not significantly affected by method of milking, but the coefficient of variation of milk yield was significantly greater in the machine-milked group(P< 0·05). One machine-milked heifer dried-off within the first 150 days of lactation.

There was no evidence of an interaction between method of milking and plane of nutrition in either the cows or the heifers.

It was concluded that measuring the milk production of beef cows by machine-milking, without the use of exogenous oxytocin, may be unreliable. Factors influencing the usefulness and reliability of the calf-suckling technique are discussed.

Progeny of younger dams grow more slowly than those of older dams. When the environmental effects of dam age are not allowed for in selection for growth rate, selection differentials and genetic responses to selection are reduced.

In a model herd, with cows aged 2 to 8 years, it was found that neglecting the dam age effects reduced genetic gains by about 15% when selection is for weaning weight, and by 11 to 7 % when selection is at an age of 12 to 20 months. Much of the reduction occurs because of the selection of higher proportions from genetically inferior groups.

If genetic differences among dam age groups are small the reduction is only 7% at weaning and less at older ages. The effect of ignoring calf age was also estimated. It was found that if calves born within a period of 33 days were compared and calf age was neglected, the response to selection for weaning weight would be reduced by about 6%.

A combined nutritional balance and comparative slaughter experiment using 20 animals compared entire male and castrate male cattle when pair-fed at high and medium levels of feeding and slaughtered at a constant 400 kg live weight. The carcasses were dissected into lean meat, separable fat, and bone, and the edible portion of the carcass was further analysed for crude protein, fat and water.

There were no significant differences between entire and castrate animals in their ability to digest energy, nitrogen or modified acid detergent fibre. The mean metabolizable energy values (MJ/kg dry matter) of the diets were 10·6 for castrates and 10·9 for entire animals. Live-weight and carcass gains (kg/day) for each treatment were respectively: entire high feeding level, 1·10, 0·69; entire medium feeding level, 0·91, 0·57; castrate high feeding level, 0·92, 0·57; castrate medium feeding level, 0·79, 0·48. Castrate carcasses contained significantly (P < 005) less lean meat and more separable fat. The edible portion of these carcasses also contained significantly (P < 0·05) more total fat but less protein and water than entire carcasses. Daily carcass protein gain was significantly higher for entire animals (P < 0·001) but daily energy gain was not significantly different. The most efficient conversion of dietary metabolizable energy and crude protein to either live weight or carcass meat production was obtained by the use of entire animals and the high level of feeding.

1. An experiment was undertaken with 44 finishing steers (initially of more than 400 kg live weight) into the effects of copper and cobalt treatments.

2. Significant responses to copper treatment of up to 0·41 kg per head per day of live-weight gain were obtained.

3. A different response to copper treatment between Friesian and beef-type (Hereford or Devon) steers reflected not a true breed effect but a difference in initial copper status.

4. Cobalt bullet therapy proved to be ineffective in maintaining normal plasma vitamin B12 concentrations over the course of the experiment although liver cobalt levels were generally adequate.

Factors influencing reproductive performance and calf and dam live weights were examined for two indigenous breeds, Angoni and Barotse, and an introduced breed, Boran, under ranching conditions in Zambia.

Over 5 years, 675 Angoni, 731 Barotse and 815 Boran records gave calving percentages of 82·5, 78·1 and 75·4 respectively. Year was an important influence on calving and weaning percentages in all breeds; age of dam had little effect and status at mating was only important in the Angoni breed, in which lactating dams produced more calves than dry dams.

Mean calf weaning weights were 147·3, 167·0 and 169·5 kg for the Angoni, Barotse and Boran dam breeds respectively. Hereford, Friesian and Boran bulls sired heavier progeny than Angoni and Barotse. Dam age and status did not influence calf weights, which were positively correlated with dam weights and negatively correlated with dam weight change during lactation.

Dam live weights at the beginning of the breeding season were 313, 357 and 348 kg for the Angoni, Barotse and Boran breeds respectively. Angoni and Boran dams reached maximum live weight at 7 years and Barotses at 9 years. Subsequent calving rate was not influenced by live weight at the beginning of the breeding season nor, in lactating dams, by live-weight change between the autumn peak and mid breeding season.

The sweating rate of N'Dama cattle was found to show a significant stepwise increase from 10.00 h to 14.00 h (P ><0·01).

Among breeds, the sweating rates (mg/10 cm2 per 5 min) in White Fulani and N'Dama cattle were similar (100·8 to 118·3), but were significantly higher than for N'Dama × German Brown (74·4), German Brown (62·6) and Friesian (56·7) cattle (P<0·10).

Sweating rate was significantly higher for the neck and midside (90·0 to 93·3) than for other sites (75·1 to 80·0) (P<0·05).