Records on 18 939 Friesian-Holstein cows classified for 16 linear-type traits and total score in first lactation by the British Friesian Cattle Society and similarly on 13 192 cows in second lactation were analysed to estimate heritabilities and genetic correlations among the linear traits. These comprised progeny of 542 and 477 young sires, respectively, together with older sires included to increase connections. Correlations of type with milk production traits and correlations between type in first and second lactations were estimated from subsets (of about one-half) of the data. Effects due to proportion of Holstein in the sires were removed.

Heritabilities of the linear traits were similar in first and second lactations, ranging from under 0·15 for one of the leg traits to about 0·5 for stature. Genetic correlations between traits in first and second lactation were generally over 0·75, whereas phenotypic correlations for most traits ranged from 0·3 to 0·6. Genetic and phenotypic correlations among the linear traits were generally low, except for those involving size.

Phenotypic correlations between linear traits and milk yield and composition were all small, none exceeding 0·3. Genetic correlations were generally almost as small: taking first and second lactations together, the only consistent non-negligible correlations with yield were for angularity (+0·3), fore-udder attachment (–0·2) and udder depth (–0·4). The linear traits are not useful predictors of yield.

In two experiments, 165 dairy cows were allotted to groups given post-partum diets ad libitum containing either 150 g (LP) or 190 to 200 g (HP) crude protein (CP) per kg dry matter (DM).

In experiment 1, which lasted 21 weeks after calving, cows were given pre-partum two amounts of energy (National Research Council (NRC) recommended amount v. 1·4 × NRC recommended amount). Pre-partum amounts of energy did not affect DM intake, milk yield or milk composition. Protein intake, including that for maintenance, was 84 and 116 g CP per kg milk in the LP and HP groups, respectively.

During 2 to 6 weeks after calving the HP concentration in a diet containing 850 g concentrates and 150 g hay per kg, decreased DM intake, whereas in a diet containing 650 g concentrates and 350 g hay per kg, the HP concentration increased DM intake. During weeks 12 to 21 after calving, the HP concentration decreased milk yield from 33·0 to 28·7 kg and increased milk fat concentration from 24·1 to 29·3 g/kg. Rumen fluid ammonia-N concentrations were 135 and 200 mg/1 in cows given the LP and HP diet, respectively. Plasma urea-N concentrations were 114 and 172 mg/1 in the same groups, respectively.

In experiment 2, three groups of cows were given, during 15 weeks after calving, diets LP, HP and HP containing soya-bean meal treated with formaldehyde (HPSP). Protein intake, including that for maintenance, was 71, 82 and 86 g CP per kg milk in the three groups, respectively. Mean daily milk yields during 15 weeks after calving were 37·5, 39·2 and 39·3 kg in groups LP, HP and HPSP, respectively. Cows given the LP and HP diets lost, after parturition, 22·5 kg body weight, whereas cows given the HPSP diet lost only 6·0 kg. Rumen fluid ammonia-N concentrations were 95, 175 and 81 mg/1 and plasma urea-N concentrations were 80, 200 and 143 mg/1 in cows given the LP, HP and HPSP diets, respectively. It is concluded that on certain diets high-yielding dairy cows can be given, in addition to that for maintenance, as little as 60 g CP per kg milk. Formaldehyde-treated soya-bean meal may increase milk yield during the first 3 weeks after calving, and reduce body weight loss.

Changes in blood metabolite and insulin concentrations in response to metabolic stimuli were evaluated as potential predictors of dairy merit. Calves of high or low genetic merit for milk production were subjected to the stress of: simulated feeds by injection of sodium propionate (0·5 mmol/kg body weight), a short fast and short-term cold exposure. Responses of insulin, free fatty acids, urea, glucose and D-β-hydroxybutyrate were determined by serial blood sampling.

Injections of sodium propionate did not greatly affect blood metabolite concentrations but did sharply increase insulin concentrations; no difference in response between high and low lines was observed. During fasting serum free fatty acid and D-β-hydroxybutyrate concentrations were greatly increased but no variation due to line was observed. Urea concentrations were also greatly increased during fasting and in this case animals of high dairy merit showed a considerably smaller increase than animals of low dairy merit. Heart rates decreased by one-third during the fast but no variation due to line was apparent;during refeeding high dairy-merit animals had lower heart rates than low-merit animals.

Short-term cold exposure did not significantly alter plasma insulin or metabolite concentrations.

These results are discussed in relation to previous findings and it is concluded that serum urea concentrations during a fast may provide the basis for a useful and robust predictor of dairy merit in young animals.

Three experiments were conducted in the early grazing seasons of 1982–84 inclusive. Autumn-calved lactating British Friesian cows grazed a perennial ryegrass pasture either by strip grazing to leave 80 mm residual herbage (SG) or by rotationally grazing six paddocks on a fixed pre-determined cycle (PG). They were offered grazing only or grazing and average quality grass silage (S) or a 1: 1 mix of silage and ensiled brewers' grains (SB) given individually overnight in a cubicle house.

In experiment 1, cows received treatments SG or SGS. The intake of silage dry matter (DM) was 4·3 kg/day and the estimated intakes of herbage DM from measured animal performance were 15·2 and 8·9 kg/day respectively. Milk yields were 18·4 and 15·3 kg/day, the concentrations of fat and protein in the milk were 38·0, 41·8 and 33·3, 30·8 g/kg and live-weight change was +679 and +348 g/day for treatments SG and SGS respectively.

For experiment 2, cows received treatments SG, PG or PGS and grazing stocking rates were 5·2, 5·5 and 11·0 cows per ha respectively. Silage intake was 6·1 kg/day DM and the estimated intakes of herbage DM were 14·2, 15·3 and 7·7 kg/day respectively. Milk yields were 18·2, 18·2 and 16·1 kg/day, the concentrations of fat and protein were 41·6, 39·8, 42·3 and 33·3, 33·0, 30·4 g/kg and live-weight change was +325, +540 and +161 g/day for treatments SG, PG and PGS respectively.

For experiment 3, cows received treatments PG, PGS or PGSB and grazing stocking rates were 5·8, 11·6 and 11·6 cows per ha respectively. The intakes of silage and silage plus brewers' grains DM were 6·5 and 8·5 kg/day. The estimated intakes of herbage DM were 14·2, 7·2 and 7·3 kg/day, milk yields were 18·7, 14·6 and 18·9 kg/day, the concentration of fat and protein in the milk were 37·3, 42·1, 40·3 and 33·4, 32·6, 32·9 g/kg and live-weight change was +425, +415 and +441 g/day for treatments PG, PGS and PGSB respectively.

The results show that offering silage overnight allowed grazing stocking rates to be doubled, raised the concentration of fat in the milk and depressed the yields of milk and protein. When brewers' grains were given with the silage, yields of milk fat and protein were greater compared with when silage was offered alone and the yield of fat was greater than for herbage alone.

Four groups of 12 cows were fed from between 12 and 18 weeks before calving to achieve condition scores at calving of 2·0 (T) or 3·5 (F). For 20 weeks after calving all cows were offered 10 kg/day of a dairy concentrate (metabolizable energy (ME) 13 MJ/kg dry matter (DM)) containing 74 g undegradable dietary protein (UDP) per kg DM (groups TH and FH) or 45 g/kg DM UDP (groups TL and FL), 2 kg/day sugar-beet pulp, 5 kg/day brewers' grains and hay ad libitum.

Milk yields were similar for all groups over the first 20 weeks of lactation, but slightly lower for cows in group FL than for other cows. Cows in group FH lost condition over the first 15 weeks and cows in group FL lost proportionally more condition over the first 12 weeks of lactation. Cows in groups TH and TL increased in condition slightly over the first 20 weeks of lactation. After calving, cows in groups TH and TL had significantly higher intakes of DM, digestible DM and ME than did cows in groups FH and FL (P < 0·001). Cows in group TL had higher intakes than did cows in group TH.

Groups TH and FH were in negative energy balance until weeks 10 and 11 respectively. Group FL was in negative energy balance between weeks 4 and 7 and group TL was only in negative energy balance in week 5. The biological efficiency of milk production (energy output in milk/energy intake) was 0·37, 0·35, 0·40 and 0·38 for groups FH, FL, TH and TL respectively.

It was concluded that cows which are thin at calving produce more milk directly from food than cows which are fat and are biologically more efficient; higher UDP levels in the diet led to increased negative energy balances but in thin cows this was due to lower food intakes whereas in fat cows this was due to higher milk yields which led to greater losses of condition.

Differences between Friesians and Jerseys and between progeny of high and low contemporary comparison (CC) sires were sought by examining nine blood constituent concentrations around first and second calvings and during lactation. A total of 1359 samples from animals at first lactation and 1148 samples at second lactation were collected. All animals were individually fed a complete pelleted diet ad libitum. Blood constituents analysed were free fatty acids (FFA), ketones, glucose, calcium, magnesium, copper, phosphorus, albumin and globulin. All nine constituents showed marked changes around parturition and early lactation and several constituents showed changes with age. Jerseys had higher average copper and albumin levels and lower globulin levels than Friesians at both lactations and higher FFA concentrations at second lactation. Changes in plasma concentrations of FFA, ketones and glucose around calving were consistent in suggesting that Jerseys and progeny of high CC sires had a substantially greater energy deficit in early lactation than Friesians and progeny of low CC sires at the first but not the second lactation. Predicted requirements v. recorded intakes suggested that the Jerseys and high CC progeny had the greater energy deficit at both lactations. Although the incidence of hypocalcaemia was nearly zero, changes of calcium and magnesium concentrations were consistent with reports of Jerseys being more susceptible to hypocalcaemia in later life.

Despite large differences in milk yield, differences in plasma concentrations between animals classified as either high or low achieved yielders within their genetic class were generally smaller than differences between progeny of high and low CC sires.

The effects of long-term administration of exogenous growth hormone (GH) on growth and carcass composition of pasture-fed, pre-pubertal dairy heifers were examined. Purified bovine GH (specific activity, 0·78 i.u. per mg) was administered daily for 21 weeks (0·6 mg GH per kg M0·75) to one member of each of 12 sets of twins. GH administration resulted in a significantly higher growth rate (0·58 kg/ day) compared with the control group (0·54 kg/day) and produced a heavier carcass (75·6 kg v. 69·5 kg). However, this production gain did not persist when GH treatment ceased. Plasma metabolite concentrations and carcass composition were not affected by GH treatment. GH tended to increase slightly the voluntary intake of freshly cut herbage dry matter (3·5 kg/day v. 3·7 kg/day; P < 0·05), but had no effect on food conversion efficiency. Serum somatomedin levels were not significantly increased by GH during week 13 of treatment. This experiment indicates that pre-pubertal heifers chronically treated with GH will increase their food intake to sustain an increased rate of growth. However, the production gains made over the treatment period were transient and within 5 weeks of the cessation of GH treatment there was no difference in the live weight of the two groups.

The fat plus protein yield of 70 011 records of pedigree British Friesian/Holstein cows was regressed on various components of their dam's Cow Genetic Index (CGI) in order to obtain the regression coefficients for comparison with the index weights currently used in the calculation of the CGI. For the first and later (2 to 5) lactation components of the CGI, the regression coefficients obtained by analysis were consistent with the tabulated index weights, but the coefficients for the sire component tended in some cases to be lower than the table values. The analysis was repeated using only dams that had widely used sires. The partial regression coefficients for the first and later lactation components were again consistent with the tabulated weights, and the coefficient for the sire component lay within one s.d. of the table values. In all cases, a cow's CGI is shown to take full account of her first and later lactation information and her sire's and dam's transmitting abilities.

In the breeding of dairy cattle the selection of bulls to breed young bulls for progeny testing is a crucial process. This paper compares several policies for making this selection based on the criteria-selection response, inbreeding depression, loss of genetic variance and variability of response. A number called the ‘effective number of new bulls to breed bulls selected each year’ (NBBe) is defined which is closely related to the last three of these criteria. Past studies of the design of dairy cattle breeding programmes have assumed that selection is within a group of bulls progeny tested in the same year (policy I). However, modern sire evaluation methods allow comparison of sires tested in different years. To evaluate the effect of selecting bulls to breed bulls from all available bulls (policy II) a computer simulation program was used. Policy II results in an increase in the response to selection but a substantial decrease in NBBe. When compared at the same NBBe, policy II results in a smaller selection response than policy I. A policy which allows the best bulls to be used for more than 1 year but which limits the maximum number of years for which they can be used, results in the best compromise. If bulls are to be used for several years there is little advantage to be gained from making more matings within each year to more high-rated bulls or to older, more reliably evaluated bulls.

Records on birth weight and pre-weaning growth of 3959 Boran calves, which were progeny of 51 sires and 979 dams, were analysed by least-squares analysis of variance. The variance components for sires, dams and maternal grandsires were estimated from the data. On the basis of assumed genetic correlations −0·44 and −0·55 between direct and maternal effects on birth weight and weaning weight, respectively, the maternal genetic component and the genetic covariance between direct and maternal effects were estimated. The heritabilities for direct effects on birth weight and weaning weight were 0·11 and 0·22, respectively, while the heritabilities of maternal effects were estimated as 0·02 and 0·11, respectively for the same traits. Selection indices for direct and maternal genetic components of weaning weight were constructed for practical use. These selection indices combined information on the individual, the parents and sibs.

Groups of 12 spring-calving cows and their calves were allocated to each of three continuous grazing treatments: cows and calves grazed a 4- to 5-cm sward (LI), cows grazed a 4- to 5-cm sward and their calves grazed an 8- to 10-cm sward (Lh) and cows and calves grazed an 8- to 10-cm sward (Hh). In each case cows and calves grazed separately. Sward height had a large effect on both cow and calf performance and intake. The short swards reduced cow herbage intake proportionately by 0·2 compared with that of the taller sward. Cow live-weight gains were −0·60, −0·59 and 0·42 (s.e.d. 0·103) kg/day on treatments LI, Lh and Hh respectively while calf live-weight gains were 0·80, 0·95 and 1·14 (s.e.d. 0·040) kg/day. Calf milk intakes were 7·05, 5·78 and 9·34 (s.e.d. 0·508) kg/day respectively while daily herbage intakes were 17·2, 22·0 and 19·8 (s.e.d. 1·35) g organic matter per kg live weight for treatments LI, Lh and Hh. There was a negative association between calf herbage and milk organic matter intakes in the treatments where the calves had access to a more generous sward height (treatments Lh and Hh), the regression coefficient being −0·89 (s.e. 0·381), indicating the calves' ability to increase herbage intake in response to a reduction in milk intake. On the LI treatment there was no significant relationship between milk and herbage intakes. The ability of grazing suckled calves to compensate for a reduction in milk intake is thus dependent on sward conditions, and may also depend on herbage digestibility. The increase in herbage intake cannot however compensate fully for a restriction in milk supply.

A simple dynamic model of metabolism in growing beef cattle is described; the scheme is based on carbon and nitrogen fluxes. There are six state variables, three relating to blood metabolite levels and three to body composition. The blood metabolite variables are acetyl-coenzyme A equivalents, glucose equivalents and amino acids, and the body composition ones are ash, lipid and protein. The fluxes in the model are based on nine biochemical transactions, six of which are catabolic and three biosynthetic. The model simulates changes in carcass composition in response to changing nutrient input and gives a measure of agreement with comparative slaughter data. It also highlights the need for more complete data on profiles of nutrient absorption in association with comparative slaughter experiments.

Four groups of calves (10 bulls, 10 steers, 10 heifers and 10 ovariectomized heifers) of Simmental- Hereford breeding were individually given a high-energy diet from 10 to 16 months of age. At the end of the experiment, the 9-10-11th rib section was dissected into fat, lean and bone and chemical analysis was performed on the dissected soft tissue. For each group, the relationship between food intake and change in body weight was examined by a method designed to separate intake into its simultaneous maintenance and gain components: least-squares estimates for the maintenance coefficient (βm, kg/day per kg body weight) and the gain coefficient (βg, kg food per kg gain) were obtained for each animal. Conventional measures of food conversion ratio (kg food per kg gain) were examined on both common age and common weight-gain bases. Bulls, followed by steers, accumulated the most lean and least fat while heifers and ovariectomized heifers accumulated the least lean and most fat. Maintenance coefficients (βm) were lower in males than in females but did not differ within gender. Gain coefficients (βg) did not differ among the groups, although the coefficients appeared to be similar within gender. Food conversion ratio computed over a common age interval did not differ among groups. Food conversion ratio computed over common weight intervals was lowest in bulls followed in increasing order by steers then the two female groups. It is concluded that males grow more efficiently than females while accumulating more lean and less adipose tisue and that this greater efficiency is achieved by consuming less food per unit of body weight for maintenance, leaving proportionately more of the total intake available for gain.

Experimental designs with optimal allocation of animals within and between breeds are given for investigating inter-breed relationships between different traits. Optimal designs are given for estimating the following between-breed parameters: the genetic regression with breeds random, the genetic correlation, the ratio of genetic standard deviations for two traits and also the comparison of regressions within and between breeds. As in the case of between-breed variation, these turn out to be multibreed designs with a few animals per breed and usually as many different breeds as possible. Formulae are given for obtaining optimal numbers and estimation errors for traits with intra- and inter-breed correlations lying within restricted ranges.

If an exepriment with a multibreed design is to be effective, the optimum number of animals (or sires) per breed would normally lie between two and 10. If the optimum number per breed is much greater than 10, the experiment is unlikely to be worthwhile unless the total number of animals is large (at least several thousand).

Eighteen bulls each of double-muscled (DM), Beef Synthetic (SY) and Hereford (HE) breed types, serially slaughtered from about 250 to 800 kg live weight, were used to examine muscle-bone relationships in double-muscled and normal cattle.

Relative to total side bone, DM animals differed significantly from the other breed types in relative growth rate of muscles in all regions which exhibited gross muscular hypertrophy. They showed generalized and regionally differentiated muscular hypertrophy. At equal bone weight in the given anatomical region, DM/HE and DM/SY muscle:bone ratios were respectively: proximal hindlimb 1·35 and 1·24; proximal forelimb 1·25 and 117; back and loin 1·20 and 1·10; and the expensive regions 1·30 and 1·20. In the limbs of DM animals, muscular hypertrophy in the proximal region was associated with bone hypotrophy while minimal muscular hypertrophy in the distal parts was associated with relatively heavier bones. Consequently, increased muscle:bone ratios were most pronounced in the proximal region, which suggests that muscles in these animals had increased in weight without proportionate increase of bones, i.e. muscle and bone growth were to some extent independent. Bone response in the distal limbs may have been influenced by a relative increase in weight support function.

The inter-breed relationship of birth weight and maternal and paternal weight in cattle was examined using published data on over 200 different breeds from a total of over 500 experiments. This collection of data was far from optimal for estimating genetic between-breed regressions and should have contained fewer breeds and more experiments on the same breed. Nevertheless, it was established that the mean mature weights of bulls and cows maintained a constant ratio throughout the range of breed size but mean calf weight declined relative to mean sire and mean dam weight as breed size increased.

When considered in conjunction with other results on litter weight at birth, the best relationship to use appeared to be that of proportionality to dam weight to the power 0·83, which could uniformly be applied to both breeds and species. The constant of proportionality found for cattle was 0·197 which can be compared with estimates of 0·183 for sheep, 0·185 for dogs and 0·165 on average for mammalian species.

In eight experiments, ewes nursing one or two lambs were offered restricted amounts of concentrate in the range 285 to 605 g dry matter (DM) per day and hay ad libitum, from lambing until day 42 of lactation.

Hay intake increased sharply during the first 2 weeks and reached its maximum during the 5th or the 6th week. Ewes' body weight at lambing, ewes' body-weight change, and milk production (estimated by litter growth rate) were significantly related to hay intake which depended also on breed (Romanov × Limousine ewes eating more than pure Limousine, P < 0·001) and age (mature ewes eating more than old ewes, P < 0·001) but not on number of suckled lambs.

Replacement rate of concentrates for forage increased as lactation progressed (0·53 to 0·86 from first to third fortnight) and varied with hay neutral detergent fibre (NDF) concentration (0·42 or 0·89 for hays with 700 or 500 g NDF per kg DM). Daily hay DM intake decreased by 1·28 g for each gram of hay NDF content increment. The NDF effect was increasingly more important as lactation progressed.

Utilization of present results in formulating diets for lactating ewes is discussed.

In three experiments the effects of replacing barley with citrus or unmolassed beet pulp in starter diets for calves was examined. In experiment 1, 40 Friesian bull calves were offered to appetite from 14 to 91 days of age one of four complete pelleted diets, each of which contained 200 g ground straw per kg and n i which the ratio of barley to pulp (citrus and beet pulp in the ratio 1:1) was 100:0 (A); 67:33 (B); 33:67 (C) and 0:100 (D). All diets contained 12·1 MJ metabolizable energy and 187 g crude protein per kg dry matter (DM). Milk replacer containing 200 g fat per kg was offered once daily (0·44 kg/day) until day 49 when the calves were abruptly weaned. Up to weaning (days 14 to 49) and after weaning (days 50 to 91) intake of DM was significantly increased by replacing barley with pulp (P < 0·05). Intakes (kg DM per day) of diets A, B, C and D were 0·31, 0·44, 0·51 and 0·50 before weaning and 2·07, 2·08, 2·23 and 2·38 after weaning. Weight gains (kg/day) of calves given pulp tended to be higher before weaning (0·44 v. 0·58 for A v. mean of B, C and D) but lower after weaning (0·73 v. 0·68) than of calves given the cereal-based diet. In experiment 2, 65 calves were given diets similar to A and C except that the pulp was supplied totally by unmolassed beet pulp, they were given only 0·35 kg milk replacer per day and weaned on day 35. The results were similar to those obtained in experiment 1; between days 14 to 84 intake was higher (P < 0·05) and there was a tendency for weight gain to be higher in calves given the diet containing pulp. The DM digestibility of the diets decreased significantly with inclusion of pulp (P < 0·05); digestibility of nitrogen was severely depressed but there was an increase in digestibility of acid-detergent fibre. Growth rate was possibly restricted by the availability of nitrogen in diets containing pulp.

Four experiments were carried out on individually penned Finn Dorset and Suffolk × Finn Dorset ewes receiving complete diets of milled hay and concentrates and rationed at various levels below voluntary intake. In the first experiment, 20 non-pregnant non-lactating ewes were each given daily 1·6 kg food and injected intramuscularly with either isotonic saline (control), progesterone plus oestrogen (20 mg + 80 ng per 24 h) to mimic hormone status in pregnancy, bromocriptine (1 mg per 12 h) to suppress plasma prolactin, or thyrotrophin releasing factor (TRF) to elevate plasma concentrations of prolactin and the iodothyronines. Fractional outflow rates of chromium-mordanted fish meal from the rumen were estimated from the rate of excretion of chromium in faeces and were proportionately 0·25 higher for ewes given TRF than for controls (P < 0·025). None of the other treatments had a significant effect on outflow rate.

In experiment 2, fractional outflow rates from the rumen were determined during July (long daylength) and again during December (short daylength) in 12 ewes that had their seasonal pattern of plasma prolactin modified by removal of their anterior cervical sympathetic ganglia. Another 12 sham-operated ewes were used as controls. Neither the seasonal changes in prolactin nor their modification by cervical ganglionectomy significantly affected outflow rate.

Twelve non-pregnant non-lactating ewes were used in the third experiment to test the effects of mid-winter shearing (mean ambient temperature −4°C) on fractional outflow rates from the rumen and on the plasma concentrations of prolactin, thyroxine (T4) and cortisol. Shearing caused a drop in plasma prolactin, gave proportional increases (P < 0·05) of 0·47 and 0·16 in T4 and cortisol respectively and gave a 0·12 increase (P < 0·01) in the outflow rate of chromium-mordanted fish meal from the rumen. The increases in T4, and outflow rate were sustained for at least 2 weeks.

For experiment 4, 22 ewes each suckling two lambs were used in three trials to see if variation between ewes in milk production and in lamb growth rate was correlated with variation in outflow rate from the rumen. The only significant correlation (r = 0·68, P < 0·01) was between outflow rate and lamb growth rate for the eight ewes in trial 1. The results of all four experiments are discussed in relation to the mechanisms by which non-dietary factors, via their effect on the rate of outflow of digesta from the rumen, may alter the quantity of protein reaching the abomasum and the likely significance of this alteration on animal performance.