Five Karan Swiss cows were allowed to calve spontaneously and served as controls (Group A), while another 10 were induced to calve about 1 month prior to expected term using either 25 mg dexamethasone alone (Group B) or 25 mg dexamethasone in combination with 25 mg stilboestrol dipropionate (Group C). Blood samples were collected prior to, and for 50 days following, parturition for subsequent hormone analysis, and observations were made on the occurrence of retained placentae.

Parturition was successfully induced in all treated cows within 72 h of drug administration. Placental membranes were retained for 24 h in all treated animals and were manually removed in the farm veterinary clinic. No incidence of placental retention occurred in control cows.

Mean plasma oestradiol-17β in control cows showed a gradual rise from days 30 to 5 pre partum, followed by a sharp increase to peak value 1 day before calving. The rise in mean oestradiol-17β levels in the 2 days before parturition in controls was significantly greater than that recorded for the treated animals. A precipitous drop in plasma oestradiol-17β level occurred following parturition in all groups, with the levels staying low for the rest of the sampling period. Drug administration to animals in groups B and C resulted in a rapid and significant drop in plasma progesterone concentrations to a level similar to that for control animals at parturition. Subsequently, the plasma progesterone remained low in all treatment groups. Mean plasma cortisol levels showed a significant but transient increase at calving in control cows, but were suppressed for at least 48 h following drug administration in treated cows before exhibiting a rebound phenomenon to reach high values after calving.

It is concluded that for normal placental expulsion, oestradiol-17β levels are more critical than progesterone, and that the rise in oestradiol-17β and fall in progesterone levels pre partum must be gradual.

The performance of 38 Friesian cows with either high or low breeding indexes was measured during the whole lactation and in short-term experiments where the cows were individually given cut pasture in stalls, or grazed on pasture.

Cows with high breeding indexes produced more milk fat than did cows with low breeding indexes in the short-term experiments, and during the whole lactation. There was close agreement between the expected differences (predicted from breeding indexes) and the measured differences in milk fat yield. When fresh cut pasture was given ad libitum in stalls the intake per cow was the same between genotypes. However, when intake was expressed per unit of metabolic weight, the mean pasture drymatter intake of the high breeding index cows was 1·05 of that of the low breeding index cows, but the difference was significant in only one of the four indoor feeding experiments.

The difference between genotypes in size was not regarded as significant because the differences in mean live weight at calving (high breeding index – low breeding index) of the animals purchased in the 1st and 2nd years were –28 and 9 kg respectively. During the whole lactation, low breeding index cows gained significantly more live weight and lost significantly less body condition than did the high breeding index cows. No significant differences in live-weight and body-condition changes could be detected during the shorter periods (4 to 5 weeks) of the indoor feeding and grazing experiments.

It can be calculated that the higher milk production of the high breeding index cows could be explained partly because they eat more (per unit metabolic live weight) and more importantly because they divert a higher proportion of the food they eat to milk production and a lower proportion to live-weight gain than do the low breeding index cows.

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.

Six lactating Friesian cows (three high and three low breeding index cows) were subjected to a total of 28 complete energy and nitrogen balances during early and late lactation. In addition, 12 non-lactating Friesian cows (six high and six low breeding index cows) were offered individually pasture indoors for 62 days, beginning at approx. 180 days of pregnancy. Cows within each genotype were randomly allocated to feeding levels which were nominally equivalent to their requirements for maintenance or twice maintenance. Eight of the 12 cows (four high and four low breeding index) were each subjected to two energy balance periods at approx. 210 (period 1) and 230 (period 2) days of pregnancy.

When offered pasture ad libitum during lactation, cows with high breeding indexes consumed significantly more gross energy per unit of metabolic live weight (P < 0·05) than did cows with low breeding indexes, but the two genotypes did not differ in their ability to metabolize the gross energy of the food, or in the individual losses of energy in faeces, urine or methane.

There were no significant differences between genotypes in their heat production at a common energy intake except during restricted feeding in early lactation when high breeding index cows produced less heat than did low breeding index cows (P < 0·05). During lactation high breeding index cows retained a higher proportion of their total energy retention (milk + body tissue energy) as milk in late lactation (P < 0·01) but not in early lactation.

For non-lactating cows, both genotypes required similar amounts of metabolizable energy to maintain zero maternal body energy retention, 0·79 and 0·80 MJ/M0·75 for periods 1 and 2 respectively. The efficiency with which metabolizable energy was converted to net energy (kg) was similar for both genotypes at both stages of pregnancy, the mean value being 0·52. The metabolizable energy required to maintain body condition was estimated to be 0·78 and 0·71 MJ/M0·75 for high and low breeding index cows respectively. The metabolizable energy required in excess of maintenance to promote a gain of one unit of body condition was estimated to be 2290 MJ. This is equivalent to 27 MJ energy retained per kg live-weight gain.

For lactating and non-lactating cows the differences between genotypes in their utilization of nitrogen were small and inconsistent.

Haryana and crossbred (Holstein × local Haryana) bullocks were subjected to work under heavy loads in summer. During the work, bullocks exhibited distress symptoms. After work, rectal temperature, respiration rate, heart rate and minute volume increased significantly, the average pO2 content increased, muscle lactic acid increased and creatine phosphate level declined. From the results it was evident that oxygen availability in blood improved during work. Despite the enhanced oxygenation of blood, there was accumulation of lactic acid in muscle. This indicated a certain degree of tissue hypoxia, which probably brought about fatigue earlier.

Compositional and acidity changes in fermented normal or antibiotic milk, and the effects of feeding jch milk on the growth, food conversion efficiency and overall health of dairy calves were studied, Type of milk (normal or antibiotic) did not significantly affect pH, lactose, crude protein, fat and free (H3—N content of milk. Lactose content and pH values decreased with time whereas free NH3—N lcreased. Higher room temperatures were associated with lower pH; values below 5 were obtained after weeks of fermentation in winter, 2 weeks in spring, 1 week in autumn and less than 1 week in jmmer. Overall pH values and lactose content declined until week 4 and remained constant thereafter, calves fed fermented antibiotic milk gained less weight from birth to weaning than those on fresh milk, put post-weaning growth rates were similar. Incidence of scouring was higher among calves fed antibiotic lilk, but no deaths occurred. Milk intake was similar, and consumption of dry food (pre and post eaning) differed slightly.

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 empirically based equation for voluntary food intake, obtained from a multibreed cattle experiment, was used to develop formulae for evaluating the overall efficiency of food utilization of beef production n i a production unit consisting of a dam and her progeny. With these formulae the dependence of overall efficiency on degree of maturity at slaughter was studied, with reproductive rate, dam food costs, terminal sire size and number of calvings per dam allowed to vary.

The formulae were used to study efficiency of food utilization in a traditional beef production system. Maximum efficiency values ranged from 2·3 to 3·5 g of lean tissue per MJ of metabolizable energy. These maximum values were affected to a small extent when progeny were slaughtered much earlier or later than the optimal degree of maturity. In a single-sex, bred-heifer (SSBH) system, the maximum value that could be attained with high technological efficiency and a reproductive rate of unity was 5·2 g, which was 0·5 times more efficient than the highest achievable traditional value. With a reproductive rate of 0·85, the highest efficiency value in an SSBH system was 4·8 g.

Overall efficiency of food utilization was also examined in a sex-controlled system where all offspring for slaughter were male and in a modified traditional system where every surplus female was bred once. Both these systems could give higher efficiency (up to 1·08 times) than in a traditional system, but neither could compete with a well-operated SSBH system.

Formulae to deal with multiple births, partial sex control and other factors are given in the APPENDIX.

In a multibreed experiment, 292 heifers from 25 British cattle breeds were fed a standard pelleted diet ad libitum from 12 to 72 weeks of age. Inter-age correlations involving body weight, weight gain, average daily food intake and cumulated food intake were measured across traits at the same age and within and across traits at ages separated by an interval of 12, 24, 36 and 48 weeks. Within-breed correlations were phenotypic but between-breed correlations were genetic.

The between-breed inter-age correlations involving body weight, cumulated intake and average daily intake were all very high (range 104 to 0·94) and declined only gradually as the intervening age interval increased from 12 to 48 weeks. Inter-age correlations involving weight gain were lower but usually above 0·7. The within-breed correlations by contrast were invariably lower and declined much more rapidly as the age interval increased. Although the between-breed and within-breed correlations differed in magnitude there was a similarity in their overall pattern.

For breed samples, body weight at young ages provided very accurate rankings at later ages for body weight, cumulated intake and average daily intake. Body weight was almost as reliable as food intake itself for predicting cumulated intake.

For individuals within breeds predicted rankings at later ages were not very accurate for body weight or cumulated intake and they became worse as the age interval increased. Neither weight gain nor average daily intake could be predicted with any reliability.

Inter-age correlations while dependant on age interval did not depend on age itself in the case of body weight and cumulated intake, although they were age-dependant for weight gain and to a lesser extent for average daily intake. Reciprocal correlations between body weight and cumulated intake were very symmetrical whereas those involving weight gain and daily intake were asymmetrical.

An attempt is made to meet the need for a single standardized growth equation to cover the entire period from conception to adulthood in a wide range of mammalian species. It is suggested that an ideal equation is one which adequately describes the overall shape of a growth curve and, in addition, can be extended or modified to give greater flexibility and higher precision as necessary. The structure of such an equation is discussed and results in the derivation of a logistic relationship between adjustable ‘flexibility’ functions of size and time.

Data from eight species are examined and in both its basic and extended forms the equation is found to give acceptable fits to individual species and to provide a useful mean standardized growth curve for mammals.

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.

An abrupt fall in live weight of grazing cattle occurs at the beginning of the growing season in the seasonally dry tropics. In an experiment with grazing crossbred bulls in central Tanzania designed to monitor changes in gut fill, 16 were slaughtered in the dry season and 14 in the early wet season. Bulls were measured and weighed before, and weighed after, a 20-h fast and then slaughtered. Gut fill was measured and empty body weight (EBW) calculated.

During fasting, the ratio gut fill/EBW fell from 0·291 to 0·217 in the dry season and from 0·207 to 0·119 in the wet season. Heart girth/EBW1/3 was 0·2577 and 0·2567 m/kg1/3 in the dry and wet seasons respectively.

It was concluded that live weight before or after fasting is seriously affected by season and can give biased predictions of EBW change. On the other hand, heart girth is little affected by season and can be used to monitor relative increases or decreases of EBW within animals.

The Milk Marketing Board beef shape (BS) score for a sire is derived from the beef conformation assessments made during the routine inspection of his first lactation daughters in the Dairy Progeny Testing Scheme. The trial compared the scores for seven Friesian/Holstein sires with the beef characteristics of their steer progeny. Two groups of cattle, 189 in total, all out of Friesian dams, were used in the trial. The dams were assessed for BS. The cattle were reared on a standard grass/cereal system designed to achieve an overall target live-weight gain of 0·85 kg/day and slaughtered at 530 kg live weight. An assessment of BS was made at seven points during the lifetime of each animal. Carcass classification and assessment together with dissection of the shin joint was undertaken by the Meat and Livestock Commission. In addition to this, 40 carcasses representing high and low BS scores were taken for full dissection of the left side.

The BS score of the dam had no significant effect on the score of the calf at any point during its life. The relationship between the sire BS score and the calf score did not become significant until the calf was 12 months old (P < 0·01) and was still significant immediately prior to the slaughter of the calf (P < 0·05). Carcass conformation scores showed highly significant progeny group differences (P < 0·001). The regression of the sire progeny group means, corrected for estimated proportion of subcutaneous fat, on the sire BS scores was significant (P < 0·001). The carcasses in the high BS score group had a significantly greater weight of lean than those in the low BS score group.

Thirty-six individually-penned ewes (mean live weight 69 kg), each suckling two lambs, were given one of three diets containing either 128 (low), 155 (medium) or 186 (high) g crude protein (CP) per kg dry matter. All diets contained (g/kg), milled hay, 570; molasses, 95; and a barley/fish meal concentrate, 330. The three protein concentrations were achieved by adjusting the proportions of barley and fish meal in the concentrate. Each diet was given at daily metabolizable energy (ME) intakes of 19, 23 and 27 MJ. Mean daily yields of milk in weeks 3 to 8 of lactation for ewes given the diet with the low concentration of crude protein increased from 2·32 kg at 19 MJ ME to 2·53 kg at 27 MJ. Corresponding values for the medium concentration of CP were 2·49 and 2·67 kg and for the high concentration 2·52 and 3·09 kg (P < 0·05 for differences between ME intakes and differences between dietary protein concentrations). For milk composition, interactions between the concentration of dietary protein and level of ME intake were not statistically significant but the main treatment effects were significant, with the protein concentration in milk increasing from 49·6 g/kg for ewes given the low concentration of dietary protein to 54·1 g/kg for those given the high (P < 0·001). Corresponding values for protein concentration in milk for the lowest and highest energy intake were 51·2 and 53·4 g/kg (P < 0·05). Losses of tissue protein were variable but decreased from 26 g/day for ewes given the low-protein diet to 8 g/day for those given the high. In discussing the responses in milk yield to dietary protein and ME intake attention is drawn to the modifying influence of the energy contributed from body tissue.

Male lambs were selected annually at 18 and 24 weeks of age for high or low concentrations of copper in plasma to produce two closed lines. The difference between the high and low lines increased to approx. 0·5 mg/1 after 5 years when the experiment ended, indicating appreciable additive genetic variation for the concentration of Cu in plasma. The selection lines were derived from a population of Scottish Blackface × Welsh Mountain crosses which had been interbred for many generations. The two parental breeds contributing to the cross normally differ in a number of aspects of Cu status with that of the Welsh higher than that of the Blackface. Both pure breeds were kept as controls. In the final year, Cu concentrations of the high selection line exceeded the values of the Welsh and the low selection line had values below those of the Blackface. Differences between the selection lines persisted at all ages.

There were indications of changes in the frequency of the Hb alleles, associated with the selection for Cu concentrations, but there were no correlated changes in body weight, reproductive performance or lamb mortality during the 5-year selection period when dietary supplies of Cu were not particularly restrictive.

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.

Two experiments were conducted in successive years with, respectively, 112 and 194 mature Scottish Blackface ewes to study the effects of shearing during pregnancy on lamb birth weight and subsequent growth. In each year half the ewes were shorn approx. 10 weeks before lambing. Shorn and unshorn ewes were offered and consumed equal quantities of food.

In both years the shorn ewes lost approx. 2 kg of live weight shortly after shearing (making allowance for the weight of wool removed); thereafter live-weight differences remained relatively constant. Plasma 3-hydroxybutyrate concentrations indicated that the initial live-weight loss was probably attributable to short-term increases in heat production and energy expenditure.

Respiration rates and rectal temperatures of unshorn ewes were always higher than in shorn ewes, but were not elevated to an extent indicative of heat stress.

Shearing had no effect on the birth weights of single or twin lambs, nor was there any effect on lamb growth rate to 14 weeks of age.

It is postulated that the effects of shearing on lamb birth weight reported by others working with sheep fed ad libitum are most likely to be due to the increased voluntary food intakes of shorn ewes.