Striking similarities are known to exist in the growth processes of different mammalian genotypes. Two genetic size-scaling rules formally summarize these well-established similarities. In consequence, experimental results in one breed or species can often provide an excellent quantitative guide to biological relationships in other species. Despite strong genetic similarity, much genetic diversity usually remains.

The genetic size-scaling rules recently proposed by the author are used to derive genetically standardized growth equations.

Progesterone profiles were obtained from 533 dairy cows during the interval from calving to the re-establishment of pregnancy by twiceweekly radioimmunoassay of milk progesterone. The importance of abnormal patterns of ovarian activity on herd fertility was determined. Animals were divided into five categories based on profile analysis: A, normal; B, delayed start to ovarian cycles; C, cessation of cycles; D, prolonged luteal activity; and E, silent oestrus. Animals in categories B to E were subdivided into treatment groups: categories B and C either (i) untreated controls, (ii) single injection 0·5 mg luteinizing hormone-releasing hormone (Hoechst) or (iii) progesterone-releasing intravaginal device (Abbott Laboratories Ltd) inserted for 14 days; categories D and E either (i) untreated controls or (ii) single injection 0-5 mg cloprostenol (Imperial Chemical Industries).

The proportion of cows in each category was: A 77·5%; B 4·9%; C 5·1%; D 1·9%; and E 10·7%. The incidence of ‘normal’ cows was 75% (first lactation), 80% (2nd to 5th lactations) and 69% (5th to 11th lactations). For normal cows (no. = 413) the interval to the start of cyclicity varied significantly with season but was not correlated with either the intervals to first insemination or to conception. In categories B to E the open period, the number of services per conception, and the days from first insemination to conception were greater than in category A, but only in category C were any differences significant. None of the treatments reduced calving-toconception intervals.

The effects of three levels of crude protein in the diet, 10, 12 and 14 %, on the performance of entire Israeli Friesian male cattle (bulls) during fattening, was studied in two experiments.

The bulls were 5 months old and 200 kg live weight, and 7·5 months and 250 kg, at the start of Experiments 1 and 2, respectively, and were slaughtered after 178 to 268 days (Experiment 1) or 156 to 166 days (Experiment 2) on trial, at a live weight of 430 to 480 kg.

In Experiment 1 mixed diets of two metabolizable energy concentrations (11·1 and 10·5 MJ metabolizable energy/kg dry matter) were used, each containing concentrates with 10, 12 or 14% crude protein content. In half of the treatments the crude protein content of the concentrate was increased by two percentage units for the first 61 days of the experiment. Daily live-weight gain was significantly higher at 14% and 16% crude protein than at 10% and 12% crude protein during the first 61 days for animals on the high energy diet, but liveweight gain was not affected by crude protein content on the low energy diet over this period, or at either energy concentration from 62 days to slaughter.

In Experiment 2 the diet consisted of concentrate, wheat straw and cotton hulls, giving a metabolizable energy concentration of approximately 10·55 MJ/kg dry matter. Daily live-weight gain did not differ significantly between concentrates containing 10, 12 or 14% crude protein, but carcass weight gain was higher at 12% and 14% crude protein than at 10% crude protein.

It is concluded that in order to ensure the best performance of bulls of the Israeli Friesian breed, diets with a high concentration of energy should contain 14% crude protein when fed to animals with a body weight of 200 to 300 kg, and 12% crude protein for heavier animals.

Measurements of live weight and of ultrasonic (Scanogram) fat depth and m. longissimus cross-sectional area at the 12th/13th rib were taken at 4— to 6-week intervals from 10 to 35 months of age (23 occasions) on 15 Hereford males (bulls), 15 castrate males (steers) and 15 females (heifers) managed under grazing conditions.

Mean rates of live-weight change throughout the measurement period (0·51, 0·47 and 0·39 kg/day for bulls, steers and heifers, respectively) were significantly different. When compared at the same ages, fat depth was similar in the steers and heifers, beginning at about 3 mm and increasing to 11 mm. Fat depth changed little in the bulls, beginning at 1·7 mm and increasing to 3 mm. At the same age, bulls had larger m. longissimus cross-sectional areas than steers and steers had larger muscle cross-sectional areas than heifers.

Absolute variation within sex groups increased throughout the experiment in live weight and fat depth, but not in m. longissimus crosssectional area. Simple correlation coefficients, pooled within sex groups, of relationships between the same measurements at various measuring occasions, indicated that measurements of fat depth and of muscle cross-sectional area at 10 to 12 months of age are poor indicators of these measurements at periods of 6 months or more later in life.

When compared at the same live weights, heifers had the greatest and bulls had the smallest fat depth and, within animals, fat depth was closely related to live weight. At any live weight, m. longissimus cross-sectional area was less in heifers than in steers and bulls, which were not significantly different from each other in this trait. Equations relating fat depth and muscle area to live weight are presented and, under the conditions of this study, indicate that there is no basis for adjustment of fat depth for live weight in bulls subjected to contemporaneous selection.

Progeny of younger dams grow more slowly than those of older dams. When the environmental effects of dam age are not allowed for in selection for growth rate, selection differentials and genetic responses to selection are reduced.

In a model herd, with cows aged 2 to 8 years, it was found that neglecting the dam age effects reduced genetic gains by about 15% when selection is for weaning weight, and by 11 to 7 % when selection is at an age of 12 to 20 months. Much of the reduction occurs because of the selection of higher proportions from genetically inferior groups.

If genetic differences among dam age groups are small the reduction is only 7% at weaning and less at older ages. The effect of ignoring calf age was also estimated. It was found that if calves born within a period of 33 days were compared and calf age was neglected, the response to selection for weaning weight would be reduced by about 6%.

Factors influencing reproductive performance and calf and dam live weights were examined for two indigenous breeds, Angoni and Barotse, and an introduced breed, Boran, under ranching conditions in Zambia.

Over 5 years, 675 Angoni, 731 Barotse and 815 Boran records gave calving percentages of 82·5, 78·1 and 75·4 respectively. Year was an important influence on calving and weaning percentages in all breeds; age of dam had little effect and status at mating was only important in the Angoni breed, in which lactating dams produced more calves than dry dams.

Mean calf weaning weights were 147·3, 167·0 and 169·5 kg for the Angoni, Barotse and Boran dam breeds respectively. Hereford, Friesian and Boran bulls sired heavier progeny than Angoni and Barotse. Dam age and status did not influence calf weights, which were positively correlated with dam weights and negatively correlated with dam weight change during lactation.

Dam live weights at the beginning of the breeding season were 313, 357 and 348 kg for the Angoni, Barotse and Boran breeds respectively. Angoni and Boran dams reached maximum live weight at 7 years and Barotses at 9 years. Subsequent calving rate was not influenced by live weight at the beginning of the breeding season nor, in lactating dams, by live-weight change between the autumn peak and mid breeding season.

Live weights from birth to 3·5 years are reported for beef cattle reared under ranching conditions in Zambia. The 809 cattle were purebred Africanders, Angonis, Barotses and Borans and the reciprocal crossbreds of the latter three breeds born in 2 years. All animals born in the 1st year and half the males born in the 2nd year grazed natural grassland. The remaining males and all females born in the 2nd year received, in addition, dry season supplementary feed from 1·5 years of age.

The interaction of genotype with year-of-birth was important but not the interactions of genotype with management or sex. Purebred progeny of the introduced Africander breed were heavier than the progeny of the indigenous Angoni and Barotse breeds in both year-of-birth groups, but only heavier than progeny of the introduced Boran breed in the first group. On average, the Africander progeny had live-weight advantages of about 16% and 10%, and the Boran progeny advantages of about 12·5% and 5·5% over the purebred Angoni and Barotse progeny respectively. Heterosis estimates tended to increase with age, reaching levels of about 5 to 6% in the Barotse/Boran crosses at and after 1·5 years. Heterosis was not shown by the other crosses. The Barotse and Boran breeds had similar maternal effects which were superior to those of the Angoni breed.

Carcass characters for 365 male castrate cattle of the Africander, Angoni, Barotse and Boran breeds, and the reciprocal crossbreds of the latter three breeds, are reported. In each of the two year-of-birth groups, different slaughter-age/management regimes were used. For all carcass characters, except those related to size, the two sanga breeds, Africander and Barotse, were very similar, as were the two zebu breeds, Angoni and Boran. The introduced breeds, Africander and Boran, which had similar carcass weights, had heavier carcasses (+18 kg, +10%) than the indigenous Barotse and Angoni breeds.

The sanga breed carcasses had less fat cover than those of the zebu breeds. Maternal effects were not important for carcass characters and the Angoni/Barotse and Angoni/Boran crosses showed no heterosis. In the Barotse/Boran crosses, slaughter and carcass weights and eyemuscle area gave between 8% and 9·5% heterosis, and the linear carcass measurements between 2% and 3%.

It was concluded from the management comparisons that there was no economic advantage in delaying slaughter to the later of the two ages compared in the two year-of-birth groups.

Masham ewes were mated at three stages of the breeding season, early (15 September to 20 October), mid (20 October to 24 November) and late (15 December to 19 January), at two different body condition scores, 4 and 2, for 3 successive years. The mean scores achieved for body condition 4 were 3·6, 3·7 and 3·9 for early, mid and late respectively and for body condition 2 were 2·4, 2·3 and 2·2. In the late lambing flock more ewes were marked by vasectomized rams and less ewes were barren than in the early and mid flocks. The ewes in higher body condition at mating had significantly more triplets and fewer singles, and a higher lambing percentage (183 versus 165). This effect of body condition on litter size distribution was significant at each time of mating, with the ewes at the late mating producing significantly fewer triplets and more singles; this difference was caused by a reduction in the performance of the body condition 4 ewes in the late group.

Young ewes in the body condition 4 group produced significantly fewer triplets and more singles than the mature ewes in the same body condition group, but at the lower body condition age had no effect on litter size distribution.

Data on 2120 lambs produced over 7 years in the Animal Breeding Research Organization synthetic Dam Line (49% Finn, 22% East Friesian, 16 % Border Leicester and 13 % Dorset Horn) were analysed by least squares. The effects of sex, age of dam, year of birth, birthrearing class, and age of lamb on weights at birth and at 4, 8, 12 and 16 weeks of age were all appreciable. However, pooled within-year correction factors should be adequate in adjusting records for selection. Heritability estimates for weights at the five ages ranged from 0·17 to 0·24 by the sire component method and from 0·18 to 0·28 by regression of offspring on dam. Previous reports of differences in heritability in singles and in twins were not confirmed. Estimates of the genetic correlations among the various lamb weights were high (0·62 to 1·04) indicating that selection for weight at one age should result in increased weights at all ages.

Data on 792 Chios lambs born during the 1972/73 and 1973/74 lambing seasons were used to estimate genetic and phenotypic parameters for birth weight, weaning weight, age at weaning, pre-weaning daily gain, body weight at 5, 10, 15 and 20 weeks of age, and postweaning daily gain. Body weight at 15 weeks of age had the highest heritability estimate (0·73 ± 0·17) and that of post-weaning daily gain was also high (0·56 ± 0·15). Selection for either weight at 15 weeks or post-weaning daily gain would be expected to yield a greater response than selection for pre-weaning daily gain or weaning weight. Genetic correlations among weights and/or gains were positive (approximately 0·20). Phenotypic correlations among weights and gains were generally higher than genetic correlations. However, the correlation between pre— and post-weaning daily gain was small (0·08). Likewise, post-weaning daily gain had low correlations with all weights before 10 weeks. Age at weaning had moderate negative associations with all weights but a very low positive correlation with post-weaning daily gain.

Data from 1447 pigs from 438 litters were used to estimate heritability, breeding and mating system differences and heterosis of atrophic rhinitis. Yorkshire, Landrace and Lacombe breeds and their crosses were represented. Rhinitis was measured by necropsic examination of the degree of degeneration of the nasal turbinates. Two traits were considered: rhinitis incidence, based on whether or not pigs showed any nasal turbinate degeneration; and rhinitis score, which ranged from zero to four, based on the percentage of nasal turbinate degeneration exhibited. Heritabilities of rhinitis incidence and score were 0·12±0·09 and 0·03±0·02, respectively. Mating system differences were significant but differences between crosses within mating system were not. Estimates of heterosis of two-breed, backcross and three-breed cross pigs over purebreds were respectively, 1·1, 3·4 and 22·1% for rhinitis incidence and 10·1, 13·2 and 28·5% for rhinitis score.

A preliminary trial established a subclinical level of infection with Oesophagostomum dentatum capable of affecting the performance of growing pigs. Thereafter a slightly higher level of infection (100 000 larvae) was administered to each of 24 individually- and scale-fed pigs to investigate the effect of O. dentatum on performance, digestibility and nitrogen retention over the live-weight range 32 to 64 kg. Worm-free but otherwise similar pigs served as controls. Infection reduced growth rate (12·9 %) and decreased efficiency of feed conversion to body weight (14·9%). There was no effect on killing-out percentage or area of eye muscle in cross-section, but infected pigs had relatively lower backfat depths (5·5 to 12·5 %). Infection did not influence nitrogen retention, but apparent digestibility of the dry matter, organic matter, nitrogen, gross energy and crude fibre was reduced. Possible explanations for these effects are discussed in relation to tissue changes associated with larval development in the large intestine.

Twenty-six groups of four or eight pigs of mean initial weight 23·2 kg and mean age 84 days were exposed to environmental temperatures of 8, 12, 16 or 20°C under still-air conditions (wind-speed = 0·1 m.s−1) or of 12CC with wind-speeds of 0·45 or 0·8 m.s−1. The animals were fed at a fixed level close to three times their maintenance requirement, with water ad libitum, and were weighed weekly over a 7-week period. Variation in temperature between groups from 8 to 20°C had no significant effect on weight gain, but increasing wind-speed to 0·8 m.s−1 at 12°C resulted in reduced weight gain.

In the year ending September 1977, 242 British Friesian cows were recorded as having produced more than 10 000 kg in a 305-day lactation. The model y(n) = anbe−cn was fitted to the monthly test day yields of each lactation (a, b, c are constants, e the base of natural logarithms and y(n) the average daily yield in week n). The model explained 87·7% of total variation in the loge y(ri), and the mean constants were 31·8, 0·3160 and 0·0373. Seasonality of production was confined mainly to a spring peak of about 10% above an approximately constant level of production during the rest of the year. These lactations generally peaked later, were more persistent and showed less response to seasonal variation than average.

In two experiments young British Friesian cattle were allowed restricted access to maize silage on a self-feed system. Restrictions were imposed by either limiting the width of feed face per animal or by reducing the time available for feeding.

The social order of each group of cattle was determined by observing dominance-submission interactions between pairs of individuals. Dominance rank and angular dominance values were calculated for individuals in each group and related to silage intake, feeding time and rate of eating. Silage intake and rate of eating increased significantly with dominance value, and feeding time decreased although not significantly.

Soay ewes were mated to a Soay or a Dorset Down ram. Live-weight changes of the ewes, birth weights, growth rates and carcass production of the lambs were recorded, and the food consumption of the ewes and lambs was measured. The use of the Dorset Down ram resulted in significantly heavier birth weights, higher growth rates and heavier carcasses. Under conditions of good nutrition the Soay ewes proved to be capable of carrying very high foetal burdens and it was estimated, from lamb live-weight gains, that they produced a large quantity of milk, relative to their size, particularly when crossed with the Dorset Down ram.

Sixteen male and 16 female lambs were used to compare the performance and carcass composition of Texel- and Suffolk-sired lambs out of Finnish Landrace × Dorset Horn ewes. Lambs were weaned at 6 weeks of age and individually fed an all-concentrate diet ad libitum to slaughter at 30 kg (females) and 36 kg (males). At slaughter, offal weights were recorded and carcass left sides jointed and dissected.

Breed types did not differ in weight at weaning, growth iate, age at slaughter, daily feed intake or feed conversion rate. Texels had heavier carcasses (17·2 v. 16·4 kg: P <0·01) and higher dressing percentages (50·7 v. 49·2: P <0·05) than Suffolks. Texel-cross carcasses had 2·9% more lean (P <0·05), but 3·8% less total fat CP <0·01).

The results indicate the suitability of Texel-sired lambs for intensive lamb production.