The growth of adipose tissue was investigated in lines of mice selected for high and low body weight at 5 and 10 weeks of age, by dissecting and weighing individual fat depots from mice aged 5, 7·5, 10 and 15 weeks. At fixed ages most depots were heavier in the High lines and lighter in the Low lines. Depots grew at different rates and the rate of total fat deposition relative to gain in body weight was greater in High than in Low lines. At about 20g live weight High and Low lines had similar proportions of total fat; at lower weights the High lines were relatively leaner. These correlated effects of selection were more pronounced in the faster growing depots of the kidneys and gonads. In consequence, the High an d Low lines had different fat distributions at fixed ages, at fixed body weights and at fixed weights of fat.

A study of the factors that influence the age at first oestrus has been made with 57 Friesian heifers reared on high planes of nutrition in a partially-controlled environment. Although animals born during the period of increasing daylength reached puberty approximately 2 months earlier than those born during decreasing daylength, there was also a marked influence of live weight at 182 days of age and of the phase of the moon at the time of oestrus.

Frequency of occurrence of first oestrus and of conception showed four distinct peaks at approximately 7-day intervals within the lunar cycle; this association between conception and lunar phase appeared to decline with increasing parity. Frequency of occurrence of artificial insemination, which reflected all suspected instances of oestrus, was also related to lunar phase. This effect of the lunar phase appears to be associated in the young heifer with 7-day cycles of oestrous activity positioned in time by the occurrence of the full moon.

The fibrous roughages, wheat straw (WS) and cotton stalks (CS), were left untreated or treated with 30 g sodium hydroxide per kg, and residual alkali was either neutralized with sulphuric acid or left unneutralized. All roughages were pelleted and used either in complete feeds or separately. The effects of these treatments on the nutritive value of the roughages were examined in digestibility trials in vitro and in vivo, and in a 7·month feeding trial of a factorial arrangement of 2 × 3 × 2, in which the roughages constituted 350 g/kg of the diets. Approximately 150 g/kg of the neutral-detergent fibre (cell wall) constituents of both roughages was solubilized by sodium hydroxide treatment, while the changes in acid-detergent fibre components (cellulose and lignin) were much smaller, although evident.

In vitro-dry matter digestibility of wheat straw was 22 % higher than that of cotton stalks, and its increase due to NaOH treatment was 50% and 30% for wheat straw and cotton stalks, respectively. In vivo digestibility of organic matter of wheat straw was increased from 0·47 to 0·59, and that of cotton stalks from 032 to 037. The increase was evident in all components except protein, in which digestibility was reduced. The increase in the metabolizable energy values of wheat straw from 6·86 to 7·45MJ/kg dry matter and that of cotton stalks from 4·77 to 5·10MJ/kg dry matter following sodium hydroxide treatment was not reflected in daily live-weight or carcass-weight gain in the feeding trial. The animals offered NaOH-treated roughages had significantly more fat trim, and more fat in the large depots. Including roughages in complete feeds revealed no advantage in metabolizable energy conversion into live weight.

Seventy-two British Friesian cows, with a mean calving date of 21 January, were used in a 3 × 2 factorial design experiment to assess the effects of the interval between harvest and wilting on the value of grass silage for milk production. Three regrowth intervals of 5, 7 and 9 weeks were used with each material ensiled both unwilted and after wilting to a dry-matter content of approximately 450g/kg. The six silages were offered ad libitum in addition to 7·6 kg concentrates per day, from day 8 of lactation until 13 April, with a mean experimental period of 67·5 days. The mean intakes of silage dry matter were 11·2, 9·8 and 8·7 kg/day for the 5-, 7 and 9-week regrowth intervals respectively and 9·6 and 10·2kg/day for the unwilted and wilted silages respectively. Regrowth interval significantly affected milk yield with mean yields of 24·7, 24·2 and 22·5 (s.e. 047) kg/day being obtained for the 5-, 7- and 9-week intervals respectively. Wilting significantly depressed milk yield with mean yields of 24·8 and 227 (s.e. 0·39) kg/day being recorded with the unwilted and wilted materials respectively. Live weight at the end of the experiment was not significantly affected by any of the treatments but the rate of live-weight loss, calculated by linear regression over the experiment, and loss in body condition score both significantly increased with increasing regrowth interval. Wilting had no effect on live weight or body condition. Increasing the regrowth interval also significantly reduced the solids-not-fat and protein contents of the milk produced during the final week of the experiment but no other significant effects were recorded on milk composition.

Blood analysis data are presented: blood urea was the only component affected by the treatments and decreased significantly as regrowth interval increased.

The performance of groups of Holstein-Friesian, Dutch-Friesian and Friesian × Africander heifers in the coastal belt of Mozambique was compared over a 3-year period. The three groups of heifers were kept together under a reasonable level of management and feeding, and measurements were made of age at first calving, milk yield, days i n production, milkability, udder wearability, mastitis incidence, calving difficulties, reproductive efficiency, disease incidence, parasitic resistance and mortality.

The highest milk production was obtained with the Holstein-Friesians followed by the Dutch-Friesians. Last came the Friesian × Africander which also showed older age at first calving, poorer milkability, fewer days in production and more udder wear. No significant differences were found in calving difficulties, disease incidence, parasitic resistance, mastitis incidence and mortality. The fertility level was relatively low in all groups.

The results corroborate reports made by several workers that acclimatized European breeds can produce milk efficiently in the not-too-harsh areas of the tropics and sub-tropics if they are properly managed and fed. The main problem seems to be the relatively low fertility rates that are common in these areas regardless of breed.

In a trial of a changeover design, 12 British Friesian castrates (steers) were offered both grass silage and crushed swedes (Brassica napus) ad libitum so that they could show their preference for these feeds on a free-choice basis. Two additional dietary treatments were provided by the supplementation of either swedes or grass silage with 2 kg of rolled barley. Steers consumed 0·32 of their dry-matter intake as silage when offered a free-choice of crushed swedes and grass silage. Supplementing the diet with 2 kg of rolled barley significantly increased daily dry-matter intake but the increase was not affected by the location of the supplement, on either the silage or the roots.

In a grazing experiment, the organic matter digestibility of herbage selected by sheep grazing at two stocking rates was determined at monthly intervals over a 9-month period by (i) the in vitro determination of organic matter digestibility of the material collected from sheep fitted with an oesophageal fistula, and (ii) derivation from the prediction of digestible organic matter intake with a faecal nitrogen regression. A comparison of the two techniques confirms the view of other workers that faecal nitrogen indices based on pen feeding trials of green herbage are unreliable for predicting digestibility of green herbage in the field. The bias which is produced by faecal nitrogen regression appears to be associated with the time spent grazing by the animal each day. Relating organic matter digestibility directly to nitrogen content of faeces of grazing sheep (N, g nitrogen/100 g faecal organic matter) and their grazing time (T,h) yielded the following equation:

The expression has standard errors (±2·6) similar to those involved in an in vitro determination. It provides a simple technique for estimating digestibility of herbage eaten by grazing sheep, but this may only be applicable to the particular sward conditions.

Field estimates of digestibility over summer and autumn by this equation were found to be similar to estimates by a faecal nitrogen expression established from hand feeding sheep with dry summer herbage.

Twenty-four prenatal (15 female), and 15 postnatal female Romney sheep, comprising a weight range from 3g to 60 kg, were dissected into their major carcass tissues. Adipose tissue was not dissectable from foetuses aged less than 80 days. The growth rates of the dissected adipose tissues and their chemical components, deoxyribonucleic acid, protein, and total lipid subdivided into phospholipid, cholesterol and triglyceride, were compared relative to the growth of the total carcass wet weight. Total side (half-carcass) adipose tissue grew at a rate substantially greater than total carcass weight. The subcutaneous adipose tissue of the forequarter grew at the fastest rate while that from the shoulder, sternum and internal cavity of the forequarter grew slowest, at rates which were not significantly different from that of the carcass. Of the chemical components, triglyceride and cholesterol grew at the fastest rate, deoxyribonucleic acid grew at the slowest rate, and phospholipid and protein grew at intermediate rates; all grew faster than the carcass. Predictions were made of the distribution of triglyceride in the carcass of the sheep at different stages of growth.

The diameter of adipocytes from subcutaneous, intermuscular and internal cavity fat depots of 5 pre- and 14 postnatal Romney female sheep was measured, the volume calculated, and the number per depot computed from the weight of triglyceride in the depots.

The rates of increase of adipocyte volume relative to the increase in weight of total side adipose tissue, and of the fat depots and their chemical components, were calculated using linear regression analyses of the natural logarithmic transformed data. These logarithmic regression equations were used to estimate the volume of adipocytes in sheep at different stages of development. The total numbers of adipocytes at each stage of growth were estimated using linear double logarithmic regressions of adipocyte number on carcass weight.

The growth of total adipose tissue and of each of the fat depots occurred mainly by an increase in the adipocyte volume, which increased over 70-fold from 120 days gestation to 5 years of age. The increase in adipocyte volume during growth occurred at similar rates in all of the fat depots and no significant differences between the volumes of adipocytes from the fat depots were found within sheep of similar carcass weight. During the same growth period the total number of adipocytes increased about 6-fold. Differences in the relative rates of growth of the fat depots were attributed to cellular multiplication rather than to cellular enlargement.

The value of a selection index for 8-week litter weight as a trait of the ewe, combining information on the ewe and on five classes of female relatives, was considered. Adding records on the dam and on paternal half sibs to those of the ewe gives increases of 10 to 50% in the rates of genetic response. The index can be simplified with little loss in efficiency by weighting all records equally for relatives with 1, 2 or more records within each class of relative. In selecting breeding replacements, information on the parents of the sire of the individual being selected may increase the rates of response by a further 20 to 30 %.

The lipolytic activity of porcine lipid mobilizing factor, a pituitary peptide, was potentiated by porcine serum when measured in a rabbit fat-cell suspension. The potentiation caused by sera from 54 individual pigs which had been bred using backfat thickness and growth rate as selection criteria was examined. No significant correlation was found between the potentiation and either of these parameters.

Seventy-two Large White × (Large White × Landrace) weaner pigs in each of three experiments were scale-fed diets containing 850 g barley per kg which had been processed by either cold rolling (R) or grinding through 1-56 mm (O) or 468 mm (T) screens. In experiments 1 and 2 barley (0-868 dry matter) was used and group feeding was practised for 55 and 100 days respectively. In experiment 3 barley (0-838 dry matter) was used and individual feeding was practised for 107 days. In experiment 1 gastric pH was recorded at slaughter. In all experiments the stomachs of all pigs were examined for gross and histological abnormalities.

In experiments 1 and 2 growth rates and efficiencies of feed conversion were not significantly different for pigs fed the R-, O- and T-based diets. In experiment 1 the pH in the pylorus, but not in the fundus, was significantly higher in pigs fed the O-diet compared with the T-diet, and on the T-diet compared with the R-diet. Growth rates and efficiencies of feed conversion in experiment 3 were significantly poorer in pigs fed the R-diet compared with the T-diet, and on the T-diet compared with the O-diet. In experiment 1 one pig from each of the three diets showed hyperplastic changes in the pars oesophagea of the stomach. In experiment 2 no gastric abnormalities were found, but bile staining was present in the pyloric zone of one pig fed each of the three diets. In experiment 3 hyperplastic lesions of the pars oesophagea (and bile staining) were present in 19 (14), 10 (7) and 4 (1) pigs fed diets O, T and R respectively.

An adverse reaction in pigs to the anaesthetic halothane at approximately 8 weeks of age appears to be controlled by a single recessive gene affecting stress susceptibility, lean content and reproductive performance. In a survey of British nucleus herds, a total of 2998 pigs between 5 weeks of age and 28 kg live weight were given 3-min halothane tests during visits to 17 breeders or companies. There were no positive halothane reactions among 764 Large Whites from 7 herds. The frequency of positive reaction among 1538 Landrace from 14 herds averaged 11%, with a range from 0 to 23 % in individual herds. Frequencies in other pure breeds or synthetic lines varied from 0 to 88%. British and foreign breeds are compared, and the possibility of eliminating the halothane gene is discussed.

When sows and their litters were grouped 21 days after farrowing, the introduction of a boar 4 days later stimulated lactational oestrus in only 2 of the 21 sows (seven groups of three sows and litters) exposed to the boar, while none of the sows in the control groups showed lactational oestrus. The boar presence in lactation affected the subsequent weaning to first service interval. This interval was 228 days for the sows exposed to a boar and 10·0 days for the control groups, the difference approaching significance (0·05<P<0·10). None of the sows in the boar treatment groups had a weaning to oestrus interval exceeding 9 days.

Fifty-one cattle were allocated into five groups varying in time of starvation (0, 17, 24, 41 and 48 h). Most of the loss in fasted live weight, stomach and intestinal contents occurred within 24 h. Weights of water, dry matter and potassium present in the stomach showed a significant decrease in the first 24 h, although the percentage of water in the stomach contents rose slowly over a 48-h period. It is suggested that cattle from pasture need be starved for no more than 24 h to minimize the effect of gut fill for body composition studies.

A procedure has recently been developed for estimating economic values which employs a profit function implying that animals with mean values for variates in the profit function give the most profit. However, the proposed index selects extreme animals, a paradox which is explained by showing that the index is appropriate for only part of the profit function. More appropriate selection indices are developed and illustrated graphically.