A recursive procedure for the estimation of the lactation curve of a dairy cow, which allows the inclusion of prior information on the curve and which takes account of the correlation between successive observations, is described. The method is based on the Kalman filter. It was found to give accurate estimates of the total milk yield at early stages of lactation.

Multiparous dairy cows were allotted at the beginning of the dry period to two groups, each of about 75 cows. In addition to a basal diet containing a very low concentration of carotene and a normal concentration of retinyl ester, the carotene group was given a daily supplement of 500 mg carotene during the dry period and 750 mg carotene during lactation, and the retinol group was given an equivalent amount of retinyl ester. Plasma carotene concentrations were much higher in the carotene group (ca. 4·2 mg/1 v. ca.. 0·35 mg/1), but plasma retinol did not differ. Neither peripheral plasma progesterone concentration nor the interval between calving and first insemination were affected by carotene supplementation. Conception rate was greatly improved by carotene supplementation in the younger cows (second and third lactation) during the first part of the experiment (cows calving in September to December): conception rates at first insemination were 0·70 v. 0·33 (P < 0·05); for all inseminations, conception rates were 0·71 v. 0·38 (P < 0·01). However during the second part of the experiment (cows calving in January to April) no significant differences were found between the two groups.

Plasma tocopherol concentration in cows given carotene was significantly higher during the dry period and the 1st weeks of lactation, but these differences disappeared in the later stages of lactation. Plasma cholesterol concentration in the carotene group was highly correlated with plasma carotene concentration (r = 0·52 to 0·59, P < 0·001); however even higher correlation coefficients were found between plasma cholesterol and plasma tocopherol in both the carotene and the retinol groups (r = 0·61 to 0·80, P < 0·001). Plasma concentrations of triglycerides, glucose, urea and aspartate aminotransferase were not affected by the treatment.

A high plasma carotene concentration is not a prerequisite for conception; however, under certain conditions which need defining, the carotene concentration appears to be a limiting factor.

In a 20-week experiment beginning at week 3 post partum, autumn-calving dairy cows were offered either a flat rate of concentrates in which all the cows received the same daily amount throughout the experiment (G). or a flat rate based on their individual milk yield at 2 weeks post partum (I). Two amounts of concentrates were compared and grass silage was available ad libitum. The amounts of concentrate were 6 kg/day (6) and 12 kg/day (12). In the I treatments the ranges of individual inputs were 4 to 8 and 9 to 15 kg/day for the 6 and 12 kg/day treatments respectively. For treatments 6G, 61, 12G, and 121 respectively, mean milk yields were 25·5, 25·7, 28·9 and 27·6 kg/day; mean live-weight changes +0·05, +0·04, +0·19 and +0·27 kg/day; and mean silage dry-matter intakes 11·1, 11·2, 8·1 and 7·5 kg/day. The differences between systems of allocation were not significant, but differences between amounts of concentrate offered were significant. The system of allocation had no significant effect on milk composition. In the residual period (2 weeks indoors and 19 weeks grazing) there were no significant effects on performance. The mean 305-day milk yields for 6G, 61, 12G and 121 respectively were 6376, 6422, 6720 and 6597 kg.

An experiment with 25 dairy cows was performed to investigate the effects of different energy intakes on food intake, performance and blood hormone and metabolite levels during the last 70 days of pregnancy and the first 125 days after parturition. Compared with animals fed ad libitum before parturition, cows fed only according to requirements during the same time showed no decrease of food intake at calving. Cows fed at a restricted level also showed a faster increase in food intake, a smaller energy deficiency at the onset of lactation and a smaller weight loss after parturition. Peak milk yield was also lower, but the peak was maintained for a longer period, and during the first 2 months of lactation these cows had higher concentrations of glucose and lactic acid, and lower concentrations of non-esterified fatty acids and ketone bodies in the blood. Weight losses, and decrease of milk production during the 1st weeks of lactation were higher in cows fed only 0·75 of requirements during the first 60 days of lactation than in animals whose energy intake was planned to cover energy requirements, and during the first 2 months of lactation levels of unesterified fatty acids, ketone bodies and urea were higher, whereas levels of insulin, thyroxine and triiodothyronine were lower. Endocrine and metabolic changes seen during early lactation suggested improved glucose homeostasis, diminished fat mobilization and ketogenesis in cows given reduced amounts of energy during the dry period compared to animals fed ad libitum. To prevent the development of acetonaemia an adequate energy supply during the first part of lactation is, however, of greater importance.

A function to describe live-weight changes of dairy cows between two calvings is constructed. The following measurements were used: live-weight level (scale), pregnancy parameter, maximum decrease of live weight during the lactation and the time during lactation at which minimum live weight occurred.

An analysis was carried out for each of 71 dairy cows of two genotypes, Dutch Friesian and Holstein Friesian crossbreds, given a high or a low concentrate diet. Data set 1 contained data of 40 weeks lactation and data set 2 data from calving to calving.

The mean residual standard deviation per genotype-diet group ranged from 11 to 14 kg. The mean R2 ranged over the subgroups in data set 1 from 0·715 to 0·792 and in data set 2 from 0·857 to 0·906. Diet had a significant influence on the magnitude of the decrease in live weight during the lactation (71 v. 46 kg) and the mean time during the lactation at which minimum live weight occurred. The latter time ranged from day 58 to 100 over the four groups and a diet effect existed. The pregnancy parameter could not be estimated accurately based on measurements during the first 40 weeks of lactation. The correlation coefficient between the pregnancy parameter in data sets 1 and 2 ranged from +0·13 to +0·78. The other parameters showed coefficients from +0·82 to +0·99.

The effects of administering bovine growth hormone (bGH) on milk production in cattle were examined in two experiments.

In experiment 1, a Latin-square design, three groups of four Friesian cows were injected daily with one of two doses of bGH (6 ng/kg and 30 ug/kg; 0·82 unit/mg) or with saline (control) throughout three successive 21-day periods in mid-lactation. At 30 ug/kg daily bGH stimulated a significant increase in milk yield (P < 0·001) and this response increased with the duration of treatment. Changes in the yields of milk fat, protein and lactose closely followed the changes in milk production. The concentrations of milk fat (P < 0·05) and protein (P < 0·05) rose and fell respectively during the 1st week of injections.' A daily dose of 6 ug/kg bGH failed to stimulate an increase in milk yield but milk lactose content was reduced (P < 0·05) during the 2nd and 3rd weeks of treatment. The proportion of milk serum samples containing detectable quantities of the hormone was increased by the higher dose of bGH.

In experiment 2 the milk yields of four Friesian cows were measured when bGH (21·0 to 37·9 mg/day) or saline was infused intravenously for 6 days. The infusions produced up to eight-fold increases in plasma bGH. These were within physiological limits, and remained at elevated levels throughout the 24-h period. Three of the cows demonstrated a clear increase in milk production.

Hereford and Charolais x Hereford steer calves were given an all-concentrate diet ad libitum. The Hereford steer calves were marketed at about 400, 440 and 475 kg live weight. The Charolais x Hereford steer calves were marketed at about 525, 570 and 610 kg. For each kg increase in slaughter weight of Hereford steers, the digestible energy required per unit live weight gain increased by 0·024 (s.e. 0·009) MJ, the killing-out proportion increased by 0·22 (s.e. 0·08) g/kg, and the backfat thickness by 0·004 (s.e. 0·002) cm. The area of m. longissimus increased by 0·245 (s.e. 0·037) cm2 and 0·139 (s.e. 0·048) cm2 for Hereford and Charolais X Hereford steers, respectively, for each kg increase in carcass weight. Among Hereford steers, mean backfat thickness as indicated by carcass grade scores (score of 1 to 4 as backfat increases) at the two lowest slaughter weights were similar and lower than scores at the high weight. Among Charolais X Hereford steers, the carcass grade was not influenced by slaughter weight. Slaughtering Hereford and Charolais x Hereford steers at light weights does not ensure that all the carcasses will be lean when the cattle are given a high concentrate diet to appetite from weaning to slaughter.

In an experiment designed to investigate the effects on the growth and voluntary food intake of grass silage by calves, the silage was supplemented with varying levels of fish meal and sucrose. The grass silage had a pH of 3·6, a lactic acid content of 90·0 g/kg dry matter (DM) and total nitrogen content of 15·5 g/kg DM. Supplements of 50, 75 and 100 g fish meal per kg silage DM and 50, 75, 100 and 150 g sucrose per kg silage DM were mixed with the silage just prior to feeding. The eight diets were offered to 32, 4-month-old British Friesian steers for 12, 7-day periods. Intake was recorded daily and live weight weekly.

Digestibility of organic matter (P < 0·05) and N (P < 0·001) were increased by fish-meal supplementation but the effect of level of fish meal was not significant. Sucrose supplementation significantly decreased both N (P < 0·01) and cellulose (P < 0·05) digestibility. The effect on cellulose digestibility increased with level of sucrose (P < 0·01).

The intake of silage DM increased in response to increasing level of fish-meal inclusion when intake was expressed in terms of kg/day (P < 0·01) but not when expressed in g/kg live weight. Total DM intake showed a significant (P < 0·001) linear response when expressed both in terms of kg/day and g/kg live weight. The intake of silage DM declined in response to increased level of sucrose supplementation both in absolute (P < 0·05) and live-weight terms (P < 0·001) but sucrose supplementation had no significant effect on total intake.

Live-weight gain was significantly increased with increasing level of fish-meal supplementation (P < 0·001), but sucrose supplementation had a significant effect on live-weight gain relative to the control treatment at only the 75 g/kg level, where live-weight gain was increased.

Silage cut twice annually (June and August) from a tetraploid red clover/grass sward and three times annually (May, July and September) from a low nitrogen (N) and high N perennial ryegrass/white clover sward was fed in proportion to dry-matter yield from each cut, over a 10-week period, each winter for 3 years to castrated male cattle of initial live weight 401 kg in year 1 and 425 kg in years 2 and 3. The silages were supplemented with 0, 1, 2 and 3 kg concentrate per head daily.

Total dry-matter yield from the red clover/grass sward was similar to that from the perennial ryegrass/white clover sward (high N grass) receiving 360 kg N per ha but the digestibility, particularly of first cut material was much lower. Dry-matter production of the low N grass/white clover sward was 0·73 of high N grass sward and produced silages of similar digestibility and fermentation.

Dry-matter intakes by the cattle were higher on the legume-based silages in years when clover made a worthwhile contribution to total yield, but this did not significantly improve utilization or animal performance compared with high N grass silage. Mean daily carcass gain per head on red clover/grass silage was 0·41 kg which was significantly less than the 0·61 kg on white clover/grass silage and 0·59 on high N grass (P < 0·001). Carcass output from red clover/grass silage was 618 kg/ha and 629 kg/ha from white clover/grass, both of which were significantly less than the 863 kg/ha from the high N grass silage (P < 0·001). Dressing proportion was also significantly poorer in animals fed red clover/grass silage compared with the other silage types.

A study was made of the growth of Holstein Friesian females in an intensive production system in the Venezuelan tropics, using monthly weights from birth (no. = 922) up to 72 months of age (no. = 63). Birth weights were adjusted for age of dam, month and year of birth of heifer, whereas subsequent weights were adjusted for birth weight and month and year of birth. Despite lower weights at birth (mean = 35·9 kg), live weights were comparable to the Beltsville standard for the breed up to 12 months of age. However, at 24, 36, 48 and 72 months of age the weights observed only reached 0·84, 0·77, 0·75, 0·79 and 0·78, respectively, of the Beltsville standard. No effect was observed on birth weight of age of dam, month or year of birth, but birth weight affected subsequent weights (P < 0·001) and the effects of month and year of birth on live weight were significant at most ages. The poor quality of the forage consumed and stress due to high environmental temperatures and humidity appear to be the main reasons for the reduced growth rates. Von Bertalanffy's model gave a higher residual error than a polynomial model when fitted to the data, but resulted in a curve which agreed more closely with the conventional biological growth pattern.

Over a period of 3 years, silages subjected to various mechanical treatments by the use of conventional silage harvesters were offered ad libitum to pregnant ewes and to castrated male lambs and the effects on intake and productivity were measured. The intake of silage made from grass harvested with a precision-chop harvester was substantially greater than the intake of silage made with other types of harvester (especially, a flail harvester), causing a lower degree of comminution.

Mean daily silage dry-matter intake of ewes was 0·99 kg and 1·28 kg in mid-pregnancy, and 0·85 kg and 1·10 kg in late pregnancy with flail-harvested and precision-chop silages respectively. Silage was supplemented with various levels of concentrate in late pregnancy and an increasing level of concentrates did not reduce silage intake. In early lactation, when 800 g concentrate was given daily, ewes consumed 1·00 kg flail-harvested silage and 1·39 kg precision-chop silage. Compared with flail-harvested silage, precision-chop silage increased ewe body weight immediately post lambing by 5·1 kg, lamb birth weight by 0·27 kg and lamb growth rate by 58 g/day. Increases in intake of precision-chop silages by hoggets were on average greater, though more variable, than by ewes and were reflected in increased carcass weight.

The reason for the increased intake of the finely-chopped silage was examined. It would appear that the major factor is the physical size of particle involved though there was some evidence that improved fermentation resulting from finer chopping may have been partly responsible for increased intake.

Two trials were undertaken to investigate the effect of rolling on the digestibility of barley and oat supplements offered to pregnant ewes at 0·43 kg dry matter per day. In the first trial, with ewes given a basal diet of grass silage ad libitum, rolling barley improved the apparent dry matter digestibility of the diet by 0·036 (s.e. 0·0115) and reduced the excretion of whole grains from 0·127 (s.e. 0·0190) of grain fed to almost nil. Method of storage (dried or treated with propionic acid) had no effect on utilization of whole or rolled barley. Grain excretion was lower with whole oats 0·049 (s.e. 0·0147) than with whole barley. In the second experiment, basal diets containing hay or roots ad libitum were supplemented with whole or rolled barley and oats. Excretion of whole grains was very low on the root-based diets and amounted to only 0·047 (s.e. 0·0177) for the whole barley and hay diet. Excretion of whole grains varied between animals and was shown to be a characteristic of the animal. It was concluded that in most situations grain should be given whole to ewes but that it may be advantageous to roll barley when it is given with silage.

The accuracy of six methods to estimate carcass leanness in young rams was studied in 36 Texel-Oxford rams, measured at 5 months of age. The rams were slaughtered and dissected. Plasma non-esterified fatty acid and very low density lipoprotein concentrations, sampled before, during and after fasting, showed no relationship with carcass leanness. The same was true for food conversion efficiency measured from 6 to 16 weeks of age, and for measurements taken with the Scanogram ultrasonic machine. The Vetscan and Danscanner ultrasonic machines gave repeatable measurements of fat depth (0·41 and 0·46 respectively). The Vetscan was the best predictor of carcass leanness by proportionally reducing the residual mean square by about 0·20, corresponding to a correlation of −0·45 between ultrasonic fat depth and carcass leanness. Inclusion of average daily gain and ultrasonic fat depth in a selection index would allow appreciable improvements in both traits.

Four experiments were conducted with lactating dairy cows offered a hay and concentrate diet (0·5:0·5) to investigate the effects of (1) the frequency of feeding a completely mixed diet (experiment 1) compared with feeding the concentrate fraction and the roughage fraction separately (experiment 2), and (2) the addition of sodium chloride to a completely mixed diet (experiment 3), on the fractional rate of outflow (FRO) of chromium (Cr)-treated fish meal from the rumen, and on milk yield and composition. The cows were offered the diet at either twice the maintenance requirement (experiments 1 and 2), or 2-5 x maintenance (experiment 3) in a 4 x 4 Latin-square design. The effect of the particle size of the Cr-treated soya bean meal was investigated in experiment 4.

The frequency of feeding of the completely mixed diet had no significant effect on the rate of outflow of Cr-treated fish meal from the rumen, or on milk yield or composition. FRO per h were 0·070, 0·085, 0·079 and 0·086 when the diet was offered once, twice, four times or 12 times per day respectively. Increasing the frequency of feeding of the concentrate fraction of the diet had no significant effect on FRO. FRO per h were 0·073, 0·078, 0·081 and 0·081 when the concentrate fraction was offered once, twice, four times or 12 times per day respectively.

The addition of NaCl to the diet significantly increased water intake (P < 0·001), but had no significant effects on FRO or milk yield. FRO per h were 0·074, 0·075, 0·076 and 0080 when 50, 265, 529 or 794 g of NaCl were added into the diet respectively. The respective intakes of water were 66·6, 74·1, 88·4 and 101·6 kg/day.

The FRO per h of fine particles of Cr-treated soya bean meal was 0·085 and for coarse particles, 0·096. The difference was not significant.

Performance records for the progeny of matings of Oxford, Texel, Texel-Oxford, Charollais, Charmoise and Meatlinc rams with crossbred ewes were analysed. The lambs, born from 1980 to 1982, were randomly allocated to three slaughter groups: (1) slaughter at fixed weights of 36 and 38 kg for ewe and castrated lambs; (2) slaughter according to estimated fat cover; (3) slaughter at a fixed age of 4·5 or 5·5 months with half-carcass dissection. The analyses were by least squares and effects were fitted for terminal sire breed, breed of maternal grand sire, year of birth, age of dam at lambing, birth-rearing type and sex of lamb and all two-way interactions. The results followed a well-established pattern where weight for age rankings were constant from birth, through weaning, to slaughter. Progeny of Oxford rams were the heaviest, followed by Texel-Oxford, Meatlinc and Charollais, Texel and Charmoise in that order. Lambs sired by rams of low mature weight reached a fixed weight at a later age than those sired by rams of high mature weight. They also reached a similar degree of fat cover at an earlier age and at lighter weights than the larger breeds. The carcass traits indicated that Texel crosses had a higher lean and lower fat proportion than would be expected from their growth and mature weight.

The comparative performance of crossbred lambs from 15 terminal sire breeds was assessed, at the same proportion of carcass subcutaneous fat, by combining the results of three experiments.

The Hennessy Grading Probe (GP) and the SFK Fat-O-Meater (FOM) are instruments capable of automatically measuring fat and muscle thicknesses from the differential light reflectance of tissues. They may offer advantages in the precision and cost of measurement over the simpler optical probe (OP). The GP and FOM were used on the slaughterline at nine abattoirs to measure fat thickness over the m. longissimus dorsi (MLD) and MLD depth at the last rib (LR) and third to fourth from last rib (3/4 LR) positions. The probes were used alternatively on runs of 100 carcasses which were also measured for LR fat thickness by OP in the normal course of carcass classification. In all 4642 (GP) and 5760 (FOM) carcasses were measured. A further 130 carcasses sampled from six of the abattoirs were measured by all three probes and their left sides were dissected into component tissues. The performance of the automatic probes relative to the OP was found to differ between abattoirs. The FOM worked more effectively on the slaughterline, requiring fewer repeat readings to obtain a satisfactory measurement than the GP. Both automatic probes gave more precise results when used at the 3/4 LR position. In the overall sample, residual s.d. for the prediction of OP-measured fat thickness were 2·33 mm (GP) and 2·07 (FOM). Residual s.d.'s for the prediction of carcass lean content from 3/4 LR fat thickness were 30·8 g/kg (OP), 36·6 (GP) and 31·4 (FOM). Addition of MLD depth provided a significant improvement in precision; residual s.d. were 35·9 g/kg (GP) (P < 0·05) and 29 1 g/kg (FOM) (P < 0·001). These results rate the FOM as superior but the differences are not large enough to discount the GP.

The responses of growing pigs to dietary lysine concentration, as influenced by food intake, sex (intact males and females) and live weight were investigated in a 4 x 2 x 2 x 2 factorial experiment involving 128 Large White pigs. Lysine concentrations were 7, 8, 9 and 10 g/kg air-dry food. The basal wheat-soya bean meal diet (14·0 MJ digestible energy per kg) was offered either ad libitum or on a restricted feeding scale to pigs from 20 to 85 kg live weight. During the 50 to 85 kg growth phase, the effects of proportionately reducing the lysine concentrations by 0·2 were investigated. Performance response was assessed in two ways; by analysis of variance for the 20 to 50, 50 to 85 and 20 to 85 kg phases, and by response surface analyses of data from successive 10-kg weight intervals.

An initial analysis of variance indicated that food intake (of pigs fed ad libitum), daily gain and food conversion ratio varied with lysine concentration, but that the responses differed with food intake, sex and phase of growth.

Analysis of the response surfaces delineated by lysine level and phase of growth indicated that for males and females with restricted food and males fed ad libitum, maximum daily gain was produced by feeding at least 10 g lysine per kg, declining to about 8 g/kg at 80 kg. With females fed ad libitum, maximum daily gain was obtained by feeding 9·9 g lysine per kg at 20 kg, declining to less than 5·6 g/kg at 75 kg.

Carcass characteristics were largely unaffected by lysine concentration.

In two experiments 480 and 360 pigs were housed in groups of 10 and given diets containing different proportions of cassava between 35 and 87 kg live weight. The cassava contained 672, 34, 57 and 39 g/kg air dry matter of starch, crude fibre, total ash and insoluble ash respectively. The diets in the first experiment contained 0, 238, 475 or 713 kg cassava per t. In the second experiment the different levels of dietary cassava (0, 150, 300 or 450 kg cassava per t) were combined in a factorial design with different levels of tallow (0, 50 or 100 kg tallow per t). The pigs were given quantities of food calculated to give isoenergy intakes on the assumption that air-dry cassava contained 14·2 MJ digestible energy (DE) per kg. The feeding scale increased with time to give a maximum daily allowance of DE of 31·8 MJ per pig. Relative to each MJ of DE the calculated levels of lysine and of methionine plus cystine in the diets were 0·64 g and 0·39 g respectively.

In both experiments, increasing levels of cassava resulted in significant reductions in growth rate but had no effect on the conversion of food to live weight or on carcass weight. In both experiments, the diets with the highest inclusions of cassava produced pigs with the thickest backfat. The effect was not significant in the second experiment but in the first experiment the differences were significant between diets with the highest and intermediate levels of cassava. There was a significant interaction between cassava and tallow on growth rate with the depression due to high levels of cassava being reduced when 100 kg tallow per t was included in the diet.

The results of these growth experiments suggested that cassava of the type used here was of similar value to barley on an energy basis when used in diets based on barley and soya bean meals.

The effects of susceptibility to halothane anaesthesia on litter productivity were investigated by comparing susceptible and normal females in two sets of data. The first comprised 206 litters from the first five generations of Pietrain/Hampshire synthetic lines selected for and against halothane susceptibility. Susceptible and normal females were mated to boars of their own type. The second data set consisted of 93 litters from the same susceptible and normal females mated to normal boars. Compared with normal contemporaries, litter sizes of susceptible females were reduced by 1·16 (s.e. 0·40) piglets at birth, and 1-76 (s.e. 0·41) at weaning (ca. 1 weeks). Maximum likelihood estimates of the proportions of piglet deaths from birth to weaning as a trait of susceptible v. normal dams were 0·32 v. 014 (P < 0·001). There were no significant differences in piglet weights or perinatal mortality, and no apparent influence of piglet genotype on any trait. The lower litter size of susceptible females at weaning appeared to result from reductions in both numbers born and survival to weaning. The study bears out previous reports of a reduction in litter productivity due to the halothane gene. However, the present differences could have arisen largely from random genetic differentiation between lines, or linkage disequilibrium in the synthetic foundation population.

The effects of a moderate level of undernutrition on the release of luteinizing hormone (LH) at oestrus and after luteinizing hormone releasing hormone (LHRH) treatment was investigated. Plasma levels of glucose, non-esterified fatty acids (NEFA), cortisol and prolactin were also investigated.

During the early breeding season 10 mature ewes were placed on either a maintenance (M) or a restricted (R) diet. After 50 days of dietary treatment their oestrous cycles were synchronized and blood samples were taken over the oestrous period. Eight days later LHRH was administered and blood samples were taken for the following 6 h.

After 50 days of treatment mean body- weights were 66 (s.e. 4) and 53 (s.e. 3) kg, and mean body condition scores were 3·5 and 2·0 for the M and R groups respectively. The pre-ovulatory and LHRHinduced LH peaks were similar in both groups as were the prolactin profiles. However, plasma NEFA levels were elevated and glucose and cortisol levels were reduced in the restricted group.

It is concluded that the reduction in energy intake achieved in this experiment, although sufficient to cause significant metabolic changes had no effect on the release of LH either at oestrus or after LHRH treatment.