In 1979/80, 390 cows of black and white breeds produced more than 750 kg fat plus protein in a 305-day lactation, compared with a mean of 390 kg for all recorded black and white cows. The cows were distributed in 207 herds and were the daughters of 177 sires whose breeding values (with population means in brackets) were +220 kg milk ( + 100), +8 kg fat (+5) and +6 kg protein (+2). The farms on which they were kept were not markedly different from average holdings in England and Wales. Management was characterized by high labour input, with high intakes of diets containing a high energy and protein concentration, and care was taken to ensure that food was on offer at all times. Grassland management tended towards conservation by silage rather than hay. Calving intervals were slightly longer than average (393 days v. 386 days for all recorded cows of a similar age).

The most obvious characteristic of management was the close attention given to ways of persuading the animals to eat enough food to satisfy their nutritional requirements.

Plasma hormone concentrations and metabolite responses to changes in energy equilibrium were measured in experiments designed to compare a) Hereford × Friesian with Friesian calves and b) Friesian calves sired by bulls with a high level of Improved Contemporary Comparison with those sired by bulls of a low level. The concentration of thyroxine and triiodothyronine tended to be greater in calves of higher dairy merit. The concentration of growth hormone was largely unrelated to dairy merit in the circumstances studied. The concentration of insulin was greater in Hereford × Friesian than in Friesian calves following feeding and following the injection of propionate. Responses to the injection of insulin and of growth hormone (as measured by changes in the plasma concentration of urea nitrogen, free fatty acids, glucose or the other hormone) were little affected by the level of Improved Contemporary Comparison of a calfs sire.

It was concluded that the thyroid system and the response of insulin to perturbation of energy balance may provide criteria of genetic merit for milk production which are neither age- nor sex-limited.

Lifetime maternal performance records of 113 Angus cows born over a 12-year period were used to estimate the relationship between cow size characters, mature size (A) and maturation rate (K), and lifetime maternal performance characters, years in the herd (YH), number of calves (NC), total calf weight (TW), average calf weight at weaning (AW) and calf weight per year in herd (kg/year). Pertinent reproductive management of the herd was: heifers were mated to calve as 2-year-olds; any heifer failing to calve or any cow failing to wean a calf a second time was culled; all matings were to purebred Angus sires. Mean cow mature size was 487 ± 5 kg with a maturation rate of 0·058 ± 0·001. Means for maternal characters were: YH, 7·4 ± 0·4; NC, 6·4 ± 0·3; TW, 1283 ± 71; AW, 200 + 1·8; and kg/year, 173 ±5·1. The correlations between maternal characters and A and K, respectively, were: YH, −0·21, 0·15; NC, −0·21, 0·15; TW, −0·16, 0·12; AW, 0·20, −0·15; and kg/year, 0·05, −004. The regression of maternal characters on mature size was quadratic in every instance with optimal cow size for each character being: YH, 468; NC, 465; TW, 471; AW, 493; and kg/year, 475. The optimal cow size for average weight of calf weaned was 18 to 25 kg heavier than the optimal size for those characters associated with fertility. Relationships between maturation rate and maternal performance were not statistically significant.

Two experiments examined the effects of including sodium bicarbonate in the diet of dairy cows in early lactation for two different feeding systems. In experiment 1, 28 Friesian cows were allocated to two groups according to parity, calving date and their milk yield in days 5 to 14. Cows were given either a standard home-mixed concentrate or a similar concentrate with sodium bicarbonate included at 25 kg/t. Concentrates were given to individual cows twice daily at a flat rate determined by their 5- to 14-day yield, and hay was group-fed to appetite. Milk yield in days 15 to 100 post-calving did not differ significantly between treatments, but cows given concentrate containing bicarbonate ate more hay and had a higher milk fat concentration (36·0 v. 32·5 g/kg, P < 0·01). In experiment 2, 80 cows were allocated to two treatments according to parity, calving date and previous lactation yield. There were two replicates of each treatment. All groups were given silage and concentrates as a complete diet for 8 weeks from calving, and 20 g sodium bicarbonate per kg total dry matter was included in the diet of half the animals. Cows given the diet containing bicarbonate had higher food intakes (14·9 v. 13·9 kg dry matter per head per day) and lower live-weight losses (13 v. 44 kg, P < 0·001). Milk yield and milk quality did not differ between treatments. Conception tended to be better in cows given the bicarbonate diet.

The nylon bag technique was used to determine the effects of offering to steers an allowance of turnips in a diet based on straw on the degradation of dry matter and acid-detergent fibre of the straw. Rumen-cannulated steers were offered basal diets of (a) sodium hydroxide (NaOH)-treated straw ad libitum, (b) NaOH-treated straw plus turnips (50 g dry matter per kg W0·73) offered once daily or (c) turnips ad libitum. Samples of straw, treated with NaOH, anhydrous ammonia (NH3,) or untreated straw were incubated in nylon bags in the rumen along with each of the basal diets. Additionally molasses (66 g dry matter per kg W0·75) was infused into the rumen of the steers offered the NaOH-treated straw. Dry matter and fibre losses of straw from nylon bags were in the order NaOH-treated > NH3,-treated > untreated; there was no interaction (P > 0·05) between method of straw treatment and effect of basal diet on 40-h or 72-h dry matter or fibre degradability. Supplementation of the basal straw diet with either turnips or molasses depressed (P < 0·01) degradability of both dry matter and fibre of the incubated straw at 40 and 72 h, molasses infusion producing a greater depression (P < 0·05) than offering turnips. There was a fall in rumen fluid pH shortly after steers consumed their turnip allowance or molasses was infused into the rumen, minimum pH values were 6·09 ± 0·241 and 5·75 ± 0·205 respectively. The pH of rumen fluid and degradability of dry matter and fibre of barley straw were depressed by the presence of carbohydrates in turnips and molasses. A reduction in the activity of cellulolytic bacteria may have been the cause of the depression in straw degradability.

1. The primary growth of perennial ryegrass was cut between 7 and 9 June and ensiled with formic acid at 2·5 1/t. The regrowth was cut on 24 July; part was dried at high temperature (dried grass), the remainder was left to dry in the field (hay). The dried grass (DG) and part of the hay were ground and pelleted, the hay being pelleted alone (PH) or with the addition of formaldehyde at 20 g/kg crude protein (PHF). The remainder of the hay was offered in the chopped form (CH). The four supplements (CH, PH, PHF, DG) were offered at two levels, 6·5 (L) and 130 (H) g dry matter per kg live weight to 54 British Friesian steers (initial live weight, 110 kg) receiving the silage ad libitum.

2. The silage had a high pH and a high proportion of the total nitrogen was in the form of ammonia, indicating poor fermentation. The solubility of nitrogen in the supplements was highest (262 g/kg total nitrogen) in CH, progressively less in PH and PHF and lowest (122 g/kg total nitrogen) in DG.

3. Total dry-matter intake was highest with DG at the higher level of inclusion. Dry-matter intake was significantly higher for PH and PHF than for CH (P < 0·001). However, intake of digestible energy did not differ between hays. Live-weight gain was increased from a low level of 0·24 kg/day (silage alone) by all supplements, but this effect was greater with DG than with the hays (P < 0·001). Level of supplementation increased live-weight gain from 0·54 to 0·74 kg/day.

4. Supplements of dried grass gave higher live-weight gains than did hay made from the same sward. However, the results indicate that supplementation of badly preserved silage with grass hay of good quality can produce acceptable levels of performance of up to 0·70 kg/day in 4-month-old steers. Processing of the hay had little effect on animal performance.

Three concentrate mixtures were compared in a replicated 3 × 3 Latin square feeding trial with cows in early lactation to evaluate the effect of inclusion of tallow. The concentrates were based on barley and soya bean meal (223 g crude protein per kg dry matter) with either no tallow addition (control group) or with the addition of a protected tallow premix (0·75 spray-dried formaldehyde-treated tallow, 0·25 casein) or an unprotected tallow premix (0·75 spray-dried tallow, 0·25 casein), both added at 138 g/kg. Each concentrate was given at a rate of 8 kg per cow per day and silage was offered ad libitum. The inclusion of unprotected tallow in the concentrate did not significantly change milk yield, fat concentration, lactose concentration or live weight compared with those in the control group. The inclusion of the protected tallow supplement resulted in significantly higher yields of milk (22·9 kg/day), fat (0·95 kg/day) and lactose (1·05 kg/day) compared with those of the control group (21·3 kg/day, 0·79 kg/day, 0·95 kg/day), whilst milk protein concentration was significantly reduced. A digestibility trial with steers showed that, when hay was given with the diets, inclusion of tallow in the concentrate significantly increased the digestible and metabolizable energy concentration of the diets compared with the control diet, but dry matter, energy and fibre digestibility was reduced.

The value of several live animal measurements for predicting carcass lean content was assessed on 97 Hereford bulls. The bulls were from a series of performance tests extending over a period of 4 years. The measurements made were live weight, ‘Weighband’ estimate of live weight, skin-fold thickness at the 13th rib, anal-fold thickness and Danscanner and Scanogram ultrasonic fat area. All measurements, except anal-fold thickness, showed satisfactory repeatability from one day to the next (0·45 to 1·00). Ultrasonic measurements showed the highest correlations with carcass lean content (0·22 to 0·66; corresponding residual s.d.'s, 13·87 and 26·46 g/kg). The most precise prediction of lean content was achieved with live weight and ultrasonic measurements in a multiple regression. The precision achieved and best anatomical sites for ultrasonic measurement varied with the group of bulls (highest R2 values 0·61 to 0·77; corresponding residual s.d. 's, 25·75 and 22·47 g/kg). The Scanogram machine produced more repeatable results than the Danscanner. When compared on the same animals Scanogram measurements gave slightly more precise prediction of carcass lean content than Danscanner measurements. Over all groups of bulls the two machines produced results of similar accuracy. Accounting for precision of estimating carcass lean content, response to selection for leanness was estimated to be 0·0034 to 0·0049 of the mean per annum for bulls of about 400 or 500 days of age.

One hundred Friesian heifers were tail-painted between 14 and 21 days after calving. Once a week the paint strip was renewed if any paint had been removed. Over the whole period of observation the ovulation detection rate by definite signs of oestrus was high (0·79), whilst the proportion of silent ovulations detected by tail paint removal was low (0·10). In addition, tail paint was not removed on 0·28 of the occasions when definite oestrus with ovulation occurred and on 0·26 of the occasions when all the paint was removed it was not associated with any reproductive event. In practice, the critical time for tail paint to be effective is during the service period. Again, tail paint identified fewer (P < 0·001) ovulations than definite signs of oestrus (0·66) and had a significantly higher false positive rate (P < 0·001). Month of calving did not affect these results but the accuracy of tail paint declined as the season progressed (P < 0·001). False positive indications were not associated with individual animal characteristics. In a second trial 43 cows were tail-painted and 43 were not. There was no significant difference in the mean number of days from calving to first insemination or successful pregnancy between the two groups. It is concluded that in these trials tail paint was not an effective or reliable aid or alternative to oestrus detection.

In three experiments 250 high-yielding dairy cows were fed for 18 weeks after parturition either a low-protein (LP) diet containing 150 to 160 g crude protein per kg or a high-protein (HP) diet containing 190 to 200 g crude protein per kg. In all three experiments cows were fed an average of 2·6 to 2·9 kg crude protein per day on the LP diet and 3·3 to 3·7 kg crude protein per day on the HP diet. Inclusive of maintenance, crude protein intake was, on average, 71 to 83 g crude protein per kg milk on the LP diet and 84 to 112 g crude protein per kg milk on the HP diet.

Protein intake did not affect the post-partum decrease in body weight; however, cows in their 4th and later lactations lost significantly more weight than cows in their 2nd and 3rd lactations (P < 0·01). Number of lactation did not affect the levels of rumen fluid ammonia or plasma urea, but older cows had significantly higher milk yields than younger ones. In all the experiments the first oestrus was observed, on average, between 38 and 43 days after parturition. The first insemination was carried out, on average, between 69 and 75 days after calving. Protein intake or age did not affect the intervals between parturition and the first observed oestrus or insemination. Proportional conception rates of cows fed the LP and HP diets were 0·566 and 0·431, respectively (P < 0·05). Conception rates of cows in their 2nd and 3rd lactations were 0·582 and 0·515 for cows on the LP and HP diets, respectively, whereas conception rates of cows in their 4th and later lactations were 0·526 and 0·288, respectively (P < 0·02). Within the HP-fed group the difference in conception rate between cows in their 2nd and 3rd lactations and those in their 4th and later lactations was also significant (P < 0·01). The proportion of cows pregnant 126 days after parturition was 0·786 and 0·645 for cows fed the LP and HP diets, respectively (P < 0·05). The proportion of cows in their 2nd and 3rd lactations which were pregnant, was 0·792 and 0·702 for cows of the LP and HP groups, respectively. Pregnancy rates for cows in their 4th and later lactations were 0·769 and 0·515 in the LP and HP groups, respectively (P < 0·05).

Post-partum changes in the concentration of progesterone, oestradiol-17β and prolactin were measured by radioimmunoassay in the blood plasma and milk of 28 buffaloes. The mean concentration of progesterone in the plasma of normal animals was 0·24 ± 0·04 μ.g/1 on the day of calving and decreased linearly during the post-partum period, until the complete regression of the residual corpus luteum of pregnancy occurred, when the plasma concentration was recorded as 0μ05 to 0μ08 μg/l. The concentration at a silent oestrus was 0μ17 ± 0·02 μ.g/1. The milk progesterone profile was parallel to that of plasma but the level was 2 to 4 times higher.

The mean concentration of oestradiol-17β in plasma was 41·0 ± 2·34 ng/1 on the day of calving; it declined significantly by day 1 post partum (P < 0·001) and fluctuated between 8 and 16 ng/1 until oestrus, when the concentration was approximately 25 ng/1. The oestradiol-17β concentration in milk was significantly higher than that of plasma on the day of calving. During the first 20 days post partum, a similar concentration of oestradiol-17β was maintained in both fluids but thereafter the concentration in milk was 2 to 3 times that of plasma.

The mean concentration of prolactin in plasma was 212·6± 19·08 μg/1 on the day of calving and then declined and fluctuated between 70 and 270 μg/1 during the rest of the period. A minor elevation occurred around oestrus. The prolactin concentration for the first 2 days post partum in milk was significantly higher than that in plasma but during the rest of the period it was similar to that in plasma.

The progesterone concentrations were slightly lower in anoestrous animals than in those cycling. The concentration of prolactin was significantly higher in multiparous animals (P < 0·001), whilst the progesterone and oestradiol values were similar in primiparous and multiparous animals.

The performance of 200 F1 Friesian ♂ × zebu ♀ and 90 zebu heifers on 14 dairy cooperative farms near Addis Ababa was compared over a 2-year period. The farms varied in management and feeding but in general the standards were low. Each farm had zebu and Friesian × zebu cows given the same management and feeding. Measurements were made of milk production traits of economic importance, including physiological and behavioural factors important for management purposes.

The Friesian ♂ × zebu ♀ crossbred heifers showed an advantage in having an earlier age at puberty and at first calving, higher milk production, longer lactations, better disposition at milking and better reproductive performance. The calves from these crossbred heifers were larger at birth but there were more problems at calving. The zebu heifers withstood better the two periods of drought that occurred during the study. No significant differences were found in disease incidence, parasitic resistance, mastitis incidence or mortality. The interval between oestrus was normal in the F1 heifers but longer in the zebus. The duration of gestation was much longer in the zebus (mean 291 days). The duration of oestrus was 4·5 h for the zebu and 10·0 h for the F1 heifers, the latter being-much longer than the mean of 7·4 h reported in the literature. The F1 heifers showed the first oestrus after calving much sooner than did the zebus.

Growth performance and body composition differences between Large White control (C) and index-selected (S) pigs were evaluated on feeding scales calculated to give very low, low and medium daily growth rates of approximately 450 g, 550 g and 650 g respectively. Starting at 30·3 (s.e. 0·32) kg, 72 boars were penned in groups of six, and one C and one S boar was fed on each of the three feeding scales for 84 days. The feeding scales started at 1·1, 1·2 and 1·3 kg per pig per day for the intended very low, low and medium growth rates with weekly increments of 0·025, 0·050 and 0·075 kg per pig per day. The 34 C and 35 S boars which completed the trial were slaughtered, their carcasses dissected and the whole empty bodies minced and chemically analysed. In no case was the interaction between line of pig and feeding treatment significant. S boars grew faster than C boars on all three levels of feeding. S boars also grew lean tissue faster, deposited less total fat, and had smaller backfat depths than C boars. Similar differences between lines in chemical composition were also apparent for whole body crude protein and lipid. Although the index selection at Newcastle was based on ad libitum performance tests, improvements in the lean content and lean tissue growth rates of the selection line were apparent even at very low levels of feeding.

1. A trial was carried out with 96 purebred Large White and Landrace pigs to assess the optimum content of skimmed milk in diets given from 20 to 90 kg.

2. Pigs on treatment 1 (control) received a barley and soya bean diet providing 12·9 MJ digestible energy per kg and 161 g crude protein per kg until they reached 54 kg and 144 g crude protein per kg thereafter. Those on treatments 2 to 4 received 3·5, 4·5 and 5·75 1 skimmed milk per day, respectively, from 28 kg live weight, after a gradual increase from 2·0 I/day at 20 kg; this was given with a basal barley diet which provided 12·9 MJ digestible energy per kg and 111 g crude protein per kg. All diets were given according to scales to permit all pigs equal daily intakes of digestible energy. Treatments 1 and 2 were approximately isonitrogenous.

3. In order of treatment, average daily gains (g) were 658, 712, 743 and 737 (s.e. of difference, 15) and food: gain ratios were 3·06, 2·73, 2·63 and 2·60 (s.e. of difference, 0·05). There were no important treatment effects on linear carcass measurements.

4. It appeared that lysine supply was a major determinant of the results obtained.

5. The greatest daily gains were achieved when a minimum of 4·5 1 of skimmed milk was given daily with the basal diet; this approximates to an average skimmed milk: meal ratio of 2·8 I/kg.

The response of the growing female pig (25 to 55 kg live weight) to increasing dietary methionine plus cystine concentrations was assessed by measurement of growth rate, food utilization, ham dissection and changes in blood metabolite concentrations. A range of 13 methionine plus cystine concentrations from 3·5 to 5·79 g/kg resulting from combinations of three basal diets and synthetic methionine, was studied. The diets were formulated using barley, a yeast protein, tapioca and synthetic amino acids to contain similar energy concentrations, 9·5 g lysine per kg diet, and adequate concentrations of other essential amino acids and non-essential nitrogen. They were offered once daily according to a restricted feeding scale.

Responses were interpreted by broken line functions which indicated, from the growth performance experiment, a requirement between 4·5 and 4·8 g/kg of the diet, when the complete range of methionine plus cystine concentrations was studied. The influence of a range of dietary methionine plus cystine concentrations from 4·1 to 5·3 g/kg diet on changes in plasma urea, methionine, lysine and threonine concentrations indicated a requirement for methionine plus cystine of 4·5 g/kg of the diet.

Eighteen male and 18 female weaned rabbits were randomly allocated to two diets formulated to give energy concentrations of 8 (LE) and 10 (HE) MJ metabolizable energy per kg dry matter and three target slaughter weights (1·5, 2·25 and 3·0 kg live weight) to give a 2 × 2 × 3 factorial design with three replicates. Voluntary food intake and live-weight gain were monitored and the carcasses chemically analysed. The metabolizable energy concentrations of the diets were determined by balance and found to be 9·87 and 6·84 MJ/kg dry matter for diets HE and LE respectively.

Rabbits fed the LE diet consumed more dry matter (P < 0·001) and metabolizable energy (P < 0·01) in total, but grew more slowly than those fed the HE diet (P < 0·001). A diet × slaughter weight interaction occurred (P < 0·01); rabbits of the LE–3 kg treatment took longer to reach target weight as a result of a flattening of their growth curve.

Rabbits fed the LE diet had lower killing-out proportions (P < 0·05), heavier gut weights (P < 0·05) and gut contents (P < 0·05), but lighter livers than those fed the HE diet. Killing-out proportion progressively increased with increasing slaughter weight. External offal weight as a proportion of live weight tended to increase while internal offal weight as a proportion of live weight tended to decrease as slaughter weight increased. The carcasses of rabbits slaughtered at 3 kg had lower moisture contents (P < 0·001), greater fat contents (P < 0·001) and lower ash contents (P < 0·05) than other slaughter treatments. A significant diet × slaughter weight interaction occurred in fat content, with rabbits of the LE–3 kg treatment having proportionally more fat. With age at slaughter as a covariate, rabbits fed the HE diet had proportionally more fat (P < 0·05).

Scottish Blackface (BF) and East Friesland × Scottish Blackface (EFX) ewes rearing single or twin lambs grazed for 14 weeks of lactation on two different pasture types in two consecutive years. Mean daily milk production, live-weight change and herbage intake of the ewes and live-weight gain of the lambs were measured each week.

In the first year the ewes grazed a ryegrass/clover sward. There were significant differences in milk production associated with breed of ewe and number of lambs reared. Peak yields, achieved in the 3rd or 4th week, reached 2·25, 2·5 and 3·25 kg/day for BF ewes with a single lamb and EFX ewes with single or twin lambs, respectively. Corresponding yields in the 14th week were 0·5, 1·35 and 1·15 kg/day. Live weight of ewes in all groups declined during the first 2 weeks but recovered by week 6. Herbage intake increased in all groups until the 8th week and then declined much more rapidly in the BF than in the EFX ewes. Lamb growth was related to milk intake to give weaning weights of 31·5, 39·0 and 29·0 kg, respectively.

In the second year, when ewes grazed a hill pasture dominated by an AgrostislFestuca community, differences in milk production, though significant, were smaller than in the previous year. Peak yields were 2·1, 2·25, 2·25 and 3·1 kg/day, respectively, for BF ewes with single or twin lambs and EFX ewes with single or twin lambs. At 14 weeks, yields had fallen to between 0·6 and 1·0 kg/day. The patterns of live-weight change and food intake were similar to those in the previous year. The EFX ewes consumed more food than BF ewes throughout lactation, particularly in the second half. Lamb growth rate was again related to milk supply and was lower than in the previous year. Weaning weights were 31·0, 25·5, 34·5 and 27·0 kg for single or twin lambs reared by BF or EFX ewes, respectively.

Lamb mortality in a Scottish Blackface hill sheep flock subjected to long term selection for cannon bone length and fleece medullation score was investigated, using maximum likelihood analyses. The selection for cannon bone length and for medullation score had no significant effect on lamb mortality.

Sixty-nine rams of three crossing-ram breeds were mated on 11 farms over 3 years to produce crossbred ewes for a large field trial. Scottish Blackface and Welsh Mountain ewes mated to Bluefaced Leicester rams had larger litters at weaning than those mated to Border Leicester and the Animal Breeding Research Organisation's Damline rams. The crossbred Bluefaced Leicester lambs were heavier than the other crossbred lambs at both birth and weaning.

Suckling post-partum cows treated for oestrous synchronization exhibited oestrus and became pregnant earlier in the mating period than untreated cows. Combined treatment with a progesterone-releasing device and prostaglandin F2α synchronized oestrus in a greater proportion of the cows than treatment with prostaglandin Fα alone (P < 0·01). The combined treatment appeared to induce ovarian activity in post-partum anoestrous cows that were approaching their first ovulation.