Experiments were designed to exchange rumen contents and vary the volumes of rumen contents between two pairs of rumen fistulated cows from herds selected for high (HS) or low (LS) susceptibility o t bloat. After exchanges between HS and LS cows the animals were tested on bloat-potent lucerne. The volume of rumen contents was lower in LS than in HS cows by 3·05 1. Increasing the volume of rumen contents of LS cows caused them to bloat to a degree never previously attained. The degree of bloat (i.e. score) was related to the volume of rumen fluid (r = 0·71) regardless of its origin (HS or LS) or the susceptibility of the recipient cow. The results implied that LS cows from this selection experiment did not bloat because they had a lower relative volume of rumen digesta than HS cows.

Changes in the partitioning of both dissected and chemical fat were examined from birth to maturity, in rams and ewes from flocks of Merino sheep selected for high (weight-plus) and low (weight-minus) weaning weight and from a randomly bred control flock. The partitioning of fat between six dissected and 11 chemical fat partitions in the body was examined in 34 mature animals, and the maturing patterns for these fat partitions calculated relative to the weight of total body fat, using the mean values for the mature animals and individual data from 106 immature animals.

Strain had no effect on the partitioning of dissected fat in the mature animals, but did affect the partitioning of chemical fat in the bone and pelt partitions. Mature ewes had greater proportions of dissected subcutaneous and kidney fat, and lower proportions of dissected intermuscular and scrotal/udder fat, than the mature rams.

There were significant strain and sex effects on maturing patterns for dissected subcutaneous and intermuscular fat. Strain and sex effects were also significant for the maturing patterns of some chemical fat partitions.

Selection for high or low weaning weight had little effect on the partitioning of either dissected or chemical fat when compared at the same stage of maturity of total fat. There were large differences in the partitioning of both chemical and dissected fat between the rams and the ewes when compared at either the same weight of total fat, or the same stage of maturity of total fat in the body.

Thirty-two kid goats of the Granadina breed were used in four trials of three factors: milk type (goat milk and milk replacer), intake level (1·86 and 2·48 maintenance) and slaughter age (15, 30, 45 and 60 days). Weaning was carried out between the 31st and 45th days. The composition of the carcass and its different cuts and the development of the stomach compartments were studied.

Both the high intake level and use of goat milk produced a statistically greater fat proportion in the carcass. At 30 days of age in kids given goat milk at the high intake level the fat proportion of the carcass was 130 g/kg. The variations in bone proportions were inverse to those for fat. The muscle proportions were affected by age, overall. The tissue composition of the different cuts showed similar responses to those in the carcass. The stomach compartments were affected most by age.

The results show that kids of the Granadina breed have a good fattening capacity. The feeding and weaning system used here produced kids by 60 days of age with stomach compartments similar in proportion to those of adult goats.

An experiment was conducted to examine factors affecting the length of the post-partum anoestrous period and associated effects on LH, FSH and prolactin. Forty-six cows (24 Hereford × Friesian and 22 Blue-Grey) ranging in body condition score at calving from 1·50 to 2·75 were used. They were individually fed chopped barley straw and concentrate at either 50 (low) or 91 (high) MJ metabolizable energy per day from calving. At 34 days post partum half the cows were separated from their calves for 48 h. The duration of the post-partum anoestrous period was estimated from progesterone concentrations in thrice weekly blood samples. Blood samples were collected every 20 min for 10 h periods immediately prior to calf separation, during the last 10 h of calf separation and 1 week later. All samples were analysed for LH, and every third sample was analysed for FSH and prolactin.

There were no significant effects of genotype, feeding level or calf separation on the length of the post-partum anoestrous period. There was a negative association between body condition score at calving and the length of the anoestrous period, with each unit increase in body condition score reducing the anoestrous period by 43 (s.e. 20) days. There was some evidence that feeding level affected the number of thin cows (body condition score ≤2·25 at calving) which were still acyclic at the end of the experiment, but not the number of fat cows (body condition score ≥2·5 at calving).

FSH levels were not affected by any of the factors examined. Prolactin concentrations were higher in fatter cows, in cows on the higher level of feeding and in Blue-Grey cows. Prolactin concentrations decreased during the period of calf separation. Genotype and feeding level had no effect on LH concentration or LH pulse frequency. LH pulse frequency was increased (P < 0·05) during the period of calf separation, but there was no effect 1 week later. There was a significant positive relationship between LH puise frequency and body condition score at calving in two of the three sampling periods.

It is suggested that the effect of body condition on the duration of the post-partum anoestrous period i s mediated through effects on LH pulse frequency.

Thirty-one newborn lambs were allocated to four treatments involving subcutaneous or slowly administered intravenous injections of noradrenaline (a natural predominantly a-agonist) or isoprenaline (a synthetic pure ($-agonist). The thermogenic effect of these treatments, attributed to brown adipose tissue, was assessed by changes in metabolic rate and rectal temperature. The objective was to define the optimum treatment for studying genetic variation between lambs in the thermogenic activity of brown adipose tissue. After all treatments, metabolic rate increased significantly by about 7 W/kg to a peak averaging 2·3 times the resting metabolic rate. Rectal temperature increased significantly by about 1°C. Both drugs administered at 150 [ig/kg were similar in potency with noradrenaline producing slightly, but not significantly, greater responses; subcutaneous injections gave significantly larger and more prolonged responses than intravenous injections. Subcutaneous isoprenaline produced the longest sustained response with peak metabolism difficult to define. Subcutaneous noradrenaline injections provided the simplest satisfactory treatment for large scale experiments.

The effects of dietary supplements of iron, molybdenum and sulphur on copper metabolism in calves were examined. In one experiment, 27 castrated male pre-ruminant Friesian calves were given a milk-substitute ration containing 0·9, 4·5 or 9 mmol iron per kg dry matter for 8 weeks. The iron supplements had no effect on liver copper retention. When 24 of these calves were then given a diet based on barley grains and barley straw containing 0, 4·5, 9 or 13·5 mmols iron per kg for up to 24 weeks, liver and plasma copper concentrations were greatly reduced in all iron-supplemented animals but no clinical signs of copper deficiency developed. Reduction in the dietary sulphur concentration from 88 o t 47 mmol/kg after 12 weeks did not prevent the iron-induced reduction in liver copper concentrations n i animals given 9 or 13·5 mmol iron per kg. Plasma copper concentrations increased in all iron-treated calves given the low-sulphur diets, except in animals given 13·5 mmol iron per kg. The results indicate that iron is a potent antagonist of copper metabolism in weaned calves and that its effects are probably independent of dietary sulphur supply.

In a second experiment 20 Hereford × Friesian female calves were given diets with supplements of 2·7 mmol iron and 20 μmol molybdenum per kg, separately and together, for 41 weeks. Both supplements reduced liver and plasma copper concentrations but only in the molybdenum-treated animals were live-weight gains reduced. The rate of decline in liver and plasma copper concentrations tended to be greatest in animals given both supplements, indicating that additive action of these antagonists is possible.

Genetic size-scaling accounts for most of the variation found among mammalian species in food intake and growth rate, with food conversion efficiency independent of the body size of the species. Is the same true of breeds and strains within species?

Animals from Soay, Welsh Mountain, Southdown, Finish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and from a breed of feral goats were grown to 0·40, 0·52, 0·64 or 0·76 of the mean mature weight of their breed and sex. Food was offered ad libitum and individually recorded.

Allometric growth coefficients were obtained for fleece weight, femur weight and femur length. Fleece was late maturing and femur early.

Breed and sex size-scaling coefficients, obtained by regression of breed and sex means on mature size, were similar to those found at the species level for age from conception to slaughter, time taken to mature and food conversion efficiency. Coefficients were higher than expected for total and daily food consumption, especially at early stages of maturity. Most breed coefficients were close to expectation while sex coefficients were somewhat higher than expected.

There were significant breed deviations: Welsh Mountain, Oxford Down and probably Soay sheep required less time and Jacob sheep and feral goats required more time to mature than expected from differences in mature size. Soay and Welsh Mountain sheep appeared to be more efficient and feral goats and Jacob sheep less efficient food converters over the same maturity interval.

Newborn Scottish Blackface lambs from lines previously selected for high (H) or low (L) resistance to body cooling were tested for their metabolic response (O2 consumption) to cold exposure in a water bath or to subcutaneous injections of exogenous noradrenaline as a measure of non-shivering thermogenesis (NST). Six rams from the H line and six rams from the L line were used to produce lambs such that each sire had both cold-tested (no. = 48) and noradrenaline-tested (no. = 86) progeny.

The mean elevations in metabolic rate produced by cold exposure and by noradrenaline were, respectively, 3·4 times and 2·4 times resting (thermoneutral) metabolic rate. H lambs showed significantly greater cold resistance and metabolic response to cold than L lambs. H lambs showed greater NST than L lambs but the difference was not significant. There were significant sire effects on NST, indicating genetic variation. There was a significant correlation between the metabolic responses to cold and those o t noradrenaline among the sire progeny groups. NST capability appears to be a phenotypic component of neonatal cold resistance which would respond to genetic selection, but this genetic variation is not a major component of that determining cold resistance.

Dutch Friesian purebred and Holstein Friesian-Dutch Friesian crossbred veal calves were used to study effects of genotype and feeding level on carcass composition. Carcass analyses were carried out on a total of 56 calves of two genotypes. Calves were reared for 22 weeks and given food dependent on age. From 1 to 16 weeks calves were given the same amount of milk replacer. At week 16, calves were assigned to either a high or low feeding level. Total energy intakes for the two groups were 5062 MJ metabolizable energy (ME) and 5408 MJ ME, respectively. Carcass weight and carcass composition traits showed no significant interaction between genotype and feeding level. Dutch Friesians had higher lean: bone ratios than Holstein Friesian crossbreds (3·85 v. 3·67). Differences between the two genotypes for fat and lean proportions in the carcass were not significant. Average proportions for lean and fat were 653 and 134 g/kg.

Differences between the two feeding levels for carcass composition were significant. Calves on the low feeding level had 655 g lean and 131 g fat per kg, while calves on the high level had 645 g lean and 143 g fat per kg.

The influence of the dissection technique on the differences in lean and muscle proportion between groups was studied on 18 carcasses using a standardized butcher's method (the Institute of Animal Husbandry (IVO) standard method) and the European Economic Community (EEC) reference method for beef. Average proportion of lean was 640 g/kg by the IVO method and of muscle was 557 g/kg by the EEC method. The difference between the two genotypes for lean proportion was smaller by the' EEC method due to the more complete separation between muscle and fatty tissue. Dutch Friesians had more intermuscular fat than Holstein Friesian crossbreds. Results of the EEC reference method indicate differences between the two feeding levels for fat as well as for protein deposition.

Animals from Soay, Welsh Mountain, Southdown, Finnish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and a breed of feral goats were slaughtered when 0·40, 0·52, 0·64 or 0·76 of mature body weight. The effects of stage of maturity, breed and sex were examined in the following traits: gut content as a proportion of slaughter weight; blood, omental plus mesenteric fat, perirenal fat, alimentary tract, ‘remainder’ of non-carcass parts and hot carcass, each as a proportion of fleece-free empty body weight; also shoulder, rib, loin and gigot joints and their commercially higher-valued (prime) and lower-valued cuts, each as a proportion of carcass weight.

As a proportion, gut content declined as animals matured, as also did blood, alimentary tract, ‘remainder’, prime shoulder, shank and prime gigot. Increasing proportions were internal fat depots, the hot carcass, rib, loin and gigot flank. Males accumulated significantly less internal fat and more shoulder than females.

When equally mature in live weight, males had proportions that were significantly lower for perirenal fat, rib and gigot and higher for shoulder and pelt plus head, feet and organs.

There were significant inter-breed regressions on mature body weight. The proportion of blood, alimentary tract, pelt plus head, feet and organs, and prime gigot declined with breed size, while hot carcass, brisket, rib and loin proportions increased. These regressions were attributed to a non-random sample of breeds. The small Soay breed had proportions of internal fat and hot carcass which were well below average, and higher proportions of blood, alimentary tract and ‘remainder’. Soay sheep also had a higher proportion of commercially higher-valued cuts in the carcass. In contrast, the large Oxford Down breed had low proportions of non-carcass components (except alimentary tract) and high proportions of lower-priced cuts and prime rib. Feral goats had a greater, and Southdown sheep a smaller, proportion of gut content than other breeds.

Adipose tissue cell volume, lipolytic rates, Iipoprotein lipase (LPL) and acetyl CoA carboxylase (ACC) activities were determined in biopsy samples taken from the back, shoulder, rump and groin subcutaneous fat depots of 17-month-old female sheep (no. = 24). Half of the sheep had received a copper (Cu) supplement at 6 weeks of age. Biopsy samples were taken after fasting overnight.

Differences in cell volume and ACC activity were apparent between sites. Supplementation with Cu at 6 weeks of age led to a proportional increase of between 0·24 and 0·45 in adipose cell volume and a proportional increase in lipolysis which varied from 0·70 to 2·27 depending on site and hormone addition. Correlations between sites for cell volume and lipolytic activity were not high in general but those for ACC and LPL activities were higher (for ACC r = 0·40 to 0·79). Overall the best correlations were between the back and rump sites. Correlations between the various metabolic measurements and cell volume were not apparent within treatment groups.

Males and females from Soay, Welsh Mountain, Southdown, Finnish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and a breed of feral goats were slaughtered when they reached 0·40, 0·52, 0·64 or 0·76 of the mean mature body weight of their breed and sex. Total weight of dissected muscle was close to 0·30 times fleece-free empty body weight, or 0·24 times live weight, for all breeds and stages of maturity. The growth of 12 individual muscles or muscle groups dissected from the commercially higher-valued joints of the carcass, was examined in relation to live weight and total muscle weight. Limb muscles matured early. All 12 muscles, when combined, also matured early so that the proportion of lean tissue from the higher-valued joints declined as live weight increased.

There were small but significant sex differences in the relative growth rate of some muscles. The abdominal muscles were early maturing for males and average for females. There were also sex differences in muscle weight distribution. The proportion of muscle in the hind limb of females was 1·055 times that in males, while the 12 muscles from higher-valued cuts constituted 0·403 of total carcass muscle for females and 0·389 for males, a proportional difference of 0·035.

Muscle weight distribution was unrelated to breed size with the possible exception of m. gastrocnemius which appeared to be relatively smaller in genetically larger breeds. After accounting for differences in mature weight, there remained small but significant breed deviations in muscle weight distribution. Southdowns had the most attractive distribution. Feral goats and Jacob sheep, although they had the highest proportion of total muscle, had a much less attractive distribution.

Thirty-five Charolais × Blue-Grey and Charolais × (Hereford × Friesian) weaned suckled calves which had been reared as either singles or twins and 19 single-reared Luing and Charolais × Luing weaned suckled calves were given silage ad libitum supplemented with either 0·75 or 2·5 kg rolled barley per day during the post-weaning winter. During summer the cattle continuously grazed perennial ryegrass swards. The high level of barley supplementation increased winter live-weight gain by 0·25 kg/day (P < 0·001). During summer the cattle from the low level of feeding gained weight at 0·09 kg/day (P < 0·05) faster than those from the high level of feeding. However, by the end of the summer grazing period the cattle on the low level of feeding were proportionately only 0·97 the weight of the animals on the high level of feeding.

During winter the performance of all genotypes was similar, but at pasture the Luing cattle gained less weight (P < 0·01) than the single-reared Charolais-cross genotypes.

Twin-reared cattle took 55 days longer to reach slaughter condition, but produced carcasses of equal weight and fatness to those from single-reared cattle.

The twin-reared cattle on the high level of feeding and the single-reared cattle on the low level of feeding attained a similar weight, body condition and ultrasonic backfat at turn-out. Thereafter, their herbage intakes and live-weight gains were identical suggesting that previous level of feeding per se is unimportant in determining an animal's subsequent intake and performance. Rather it is the body composition at a given age, irrespective of the pathway followed to attain that composition, that determines performance thereafter. It is also suggested that the inability of cattle to compensate for a reduction in level of nutrition during the first 3 to 4 months of life is due to the lack of potential for fat deposition, and there is thus limited opportunity for nutritional manipulation of body composition at that age.

Six breeds differing widely in body size and milk yield were compared for growth and food intake between 24 and 120 weeks of age in a time-controlled feeding system based on Calan-Broadbent electronic feeding gates activated by time clocks to give six meals a day of length 4, 5 or 6 min. The breeds were South Devon, Charolais × British Friesian, British Friesian, Hereford, Aberdeen Angus and Jersey. Each breed was represented by 12 animals, with four allocated to each meal length.

At every age, voluntary food intake was strongly determined by meal length. For each meal length, and after adjustment for breed size, most breeds closely followed the same intake curve. Thus, when intake was restricted (either slightly or severely) by uniformly limiting the time available for eating, the reduced voluntary daily intake of a breed, like its ad libitum intake, was largely genetically determined by breed size. A time-controlled feeding system thus allowed acceptable breed comparisons under conditions of restricted nutrition.

The mean growth rates resulting from a wide variety of different time-controlled voluntary intakes were all adequately explained by a linear equation based on a constant maintenance efficiency and a partial efficiency of growth that declined linearly with degree of maturity in body weight.

Eating rate was surprisingly similar for the three different meal lengths. When averaged over breeds, it increased from 1 MJ metabolizable energy (ME) per min between 6 and 12 months of age up to about 2 MJ ME per min at 2 years of age. Over this range, eating rate could be expressed as an allometric function of degree of maturity in body weight. In consequence, time-controlled daily intakes could be predicted from eating rate within ad libitum limits, as could the total eating time needed to achieve a given growth rate.

In a 2 × 2 × 2 experiment, 296 Scottish Blackface ewes were fed to achieve one of two levels of body condition (high: condition scores ^2·75; low: condition scores ^2·50) by 2 weeks before joining with rams. Half of the ewes of each condition score were fed dried grass pellets ad libitum and 300 g hay per head daily, between 2 weeks before and 8 days after joining, while the remaining ewes were offered a live-weight maintenance ration comprising 750 g pellets and 400 g hay per head daily. From 8 days after joining the intake of all ewes was gradually changed, over a 2-week period, to 1250 g pellets and 400 g hay per head daily. Two days before joining, half of the ewes of each condition/intake group were passively immunized against testosterone. A total of 99 ewes were slaughtered 18 days after joining and their ovulation rate at the first mating determined. Ovulation rates were significantly affected by immunization (immunized: 2·31, control: 1·86, pooled s.e. = 0·055; P < 0·01) and food intake (ad libitum: 2·24, maintenance: I 92, pooled s.e. = 0·055; P < 0·05) but not by body condition at mating (high: 2·15, low: 2·02, pooled s.e. = 0·059; P > 0·05). Lambing rates were dependent on treatment (immunized: 1·82 control: 1·62, pooled s.e. = 0·044; P < 0·01), food intake (ad libitum: 1·85, maintenance: 1·59, pooled s.e. = 0·043; P < 0·01) and body condition (high: 1·82, low: 1·62, pooled s.e. = 0·044; P < 001). In ewes in a high body condition at mating, the effects of intake and immunization were additive but in ewes in low condition, immunization induced little improvement in performance in ewes fed ad libitum. Circulating antibody titres were lower in ewes fed ad libitum than in ewes offered a maintenance ration (1: 416 v. 1: 534, pooled s.e. = 14; P < 0·001), but ovulation rates and litter sizes were not related to titres.

Three hundred and sixty male and female Californian ♂ × New Zealand White ♀ growing rabbits were used to study the influence of nine types of fat at 30 or 60 g/kg diet on growth and apparent digestibility. The fats used were: beef tallow (T), pork lard (L), sunflower oil (SO), two by-products from the oil-refining industry, sunflower oleins (O) and soya-bean lecithin (S), and 2: 1 (w/w) mixtures of T + S, L + S, O + S and T + O. All diets, including a diet without added fat, were formulated to a 190 g/kg acid-detergent fibre (ADF) level and to a 100 kJ digestible energy per g digestible protein ratio.

As O level in the diet increased, growth was significantly impaired (P < 0·001) but the other fats had no significant effect on this variable (P > 0·05). A maximum oleins concentration in the diet of 10 g/kg is suggested. Excluding diets with more than 10 g oleins per kg, a significant improvement in food conversion ratio was recorded for diets containing 60 g added fat per kg (P < 0·05). This improvement was related not only to a higher gross energy concentration of added-fat diets but also to a significantly (P < 0·001) higher energy digestibility (0·653 v. 0·602 for 60 g/kg added-fat diets and control diet respectively). Fat addition both at 60 and 30 g/kg also improved significantly (P < 0·001) dry matter, organic matter, crude protein and ether extract (EED) digestibilities. As a result, the use of ether extract in addition to ADF for estimating the energy value of diets including added fat, is proposed.

An increase in the degree of unsaturation of dietary ether extract increased significantly EED (P < 0·001), but did not affect other variables studied.

Maximum eating rate, rmax in kj metabolizable energy per min, at a given body weight W kg, can be predicted in normally growing cattle when adult body weight, A kg, is known, by the formula of Taylor and Murray (1987) as rmax = 31μ0·86 A0·73 where u = W/A is degree of maturity in body weight. When the pattern of normal growth is disturbed by fluctuating levels of food intake, a better prediction can be obtained in terms of incisor arcade breadth. This paper gives the allometric relationship between degree of maturity in body weight, u, and degree of maturity in incisor arcade breadth uD, fo r both cattle and sheep, as uD = u0·29.

Combining this allometric relationship with that of Illius and Gordon (1987) gives the following formula for incisor arcade breadth, Du(mm), in the rth species at age, t, in relation to degree of maturity in body weight, uit, and adult body weight, Aikg): Dit = 7·8 uit0·29Ai0·36. Substituting uD and adult arcade breadth, Dadult, for u and A in the formula of Taylor and Murray (1987) gives the following more robust formula for predicting maximum eating rate, namely, rmax = 0·53 u3DD2adut.

Selection indices to improve lean meat production of terminal sire breeds of sheep were derived. An aggregate breeding value which comprised growth rate, killing-out proportion and carcass lean proportion was examined. Selection criteria included growth rate and ultrasonic or X-ray computer tomography (CT) estimates of carcass composition. Correlations betwen the index and the aggregate breeding value were about 0·38 for indices using ultrasonic fat measurements, and about 0·40 for those using CT measurements. Dropping ultrasonic or CT measurements from the indices reduced the correlations with the aggregate breeding value by only about 0·01 and 002 respectively, indicating that selection on growth rate alone under current economic conditions was highly efficient. Changes in economic weights, and genetic parameters had little effect on the efficiency of selection. The total national discounted value of returns from a single round of selection on the indices was expected to be between £6 and £30·5 million, depending on penetration rates of improved stock, the breeding scheme used, and with a time horizon of 20 years.

Dromedary camels (Camelus dromedarius) inhabit and are well suited to semi-arid and arid areas of north Africa, south-east Asia and India. Little attention has been given to their husbandry although they are an important livestock species in some areas. One of the limiting factors in camel production is the 2- to 3-year interval between calvings. In this study, three female calves (birth weight 32·5 kg) were weaned onto artificial milk 30 days after birth and the she-camels (400 to 500 kg) were mated 10 to 14 days later. Between 30 and 120 days of age the calves received mainly artificial milk and between days 120 and 180 they received concentrates and lucerne hay. While the calves sucked milk, intake averaged 6·9 l/day, metabolizable energy intake (MEI) averaged 19·5 MJ/day and average daily gain (ADG) was 0·87 kg. Ratios of conversion of milk intake (l/day) and MEI (MJ/day) to body-mass gain (kg/day) were 8·0: 1 and 22·4: 1, respectively, and to total body solids gain (kg/day) were 22·3: 1 and 62·7: 1, respectively. From days 30 to 120, ADG was 0·67 kg, and from days 120 to 180 ADG was 0·61 kg. The calves averaged 155 kg at 180 days and ADG to that age was 0·68 kg. All three she-camels conceived 10 to 14 days post weaning.

This study demonstrated that camel calves can be weaned early and that high growth rates can be achieved. In addition, she-camels can be mated shortly after parturition so that calving intervals can be reduced to 15 months.

An experiment was carried out at Bahia Blanca (38°44' S, 62°10' W) to estimate the seasonal variation in ovulation rate and its components shown by Lincoln ewes of constant live weight.

Twenty-three 5-year-old ewes were subjected to nine 17-day observation periods which were evenly spaced within 405 days.

Percentage of ewes showing oestrus and ovulation, incidence of multiple ovulations and ovulation rate were estimated for each period by using vasectomized rams and performing iaparoscopies.

Traits showed a similar seasonality which was presumably induced by the natural light regime to which the ewes became exposed before and during each observation period.

A significant and periodic relationship was found between each trait and the number of days elapsed from the longest day.

The predicted maximum values for each parameter were reached about 40 days before the shortest day. Prior to and after this date both the percentage of ewes showing oestrus and ovulation and the incidence of multiple ovulations declined so that the expected ovulation rate values became zero for a period of about 3 months before the longest day.