A theoretical analysis of open nucleus breeding systems, in which there is some introduction of breeding females to the sire breeding nucleus, is presented. Numerical analysis of a discrete generation model shows that the rate of genetic gain may be increased by 10 to 15% by opening the nucleus when selection intensity in females is low. In sheep and beef cattle breeding the optimal structure would be to have about 10% of the population in the nucleus, to get half of the nucleus female replacements from the base population, and to use all nucleus-born females not needed as nucleus replacements for breeding in the base population. The genetic gain, however, is not very sensitive to variation in these parameters. The rate of inbreeding in such an open nucleus would be about half that in a closed nucleus of the same size.

1. Gestation diets formulated to contain A, 9; B, 11; C, 13 or D, 15% protein, and lactation diets with C, 13 or E, 17% protein provided eight treatment combinations. They were given at seven centres at 2 kg/day in gestation and approximately 5·7 kg/day in lactation to sows which remained on experiment for three to five parities and produced in total 468 litters. Mean results for parities one to four are given in this summary.

2. For gestation diets A to D mean litter size at birth was 9·7, 10·1, 10·3 and 10·4 live pigs, and at weaning (at 6 weeks), 8·2, 8·7, 8·8 and 8·8. Sows which received lactation diets C and E subsequently produced 10·4 and 10·3 pigs at birth and 8·9 and 8·3 at weaning.

3. Gestation diets had no consistent effects on piglet weights. During lactation, however, diet E gave heavier pigs than C, by 0·2 kg at 3 weeks and 0·5 kg at weaning.

4. Extra protein for either gestation or lactation had a positive effect on sow weight at that stage, but a negative effect in the following stage. There were no direct treatment effects on the time required for re-conception.

5. Twenty experimental sows at the Rowett Institute, together with an additional group given diet A for both gestation and lactation, showed strong positive relationships between lactation protein intake and milk yield or composition.

6. The treatment combination AC (i.e. 9% protein in gestation and 13% in lactation) gave the lowest weight of weaned pigs per litter, and CC gave the highest. The remaining treatments gave similar weights; of these BC (nominally 11 with 13, but actually 11·5 with 13·5% protein) was concluded to provide the lowest protein intake consistent with satisfactory performance.

Data for 432 litters of pigs were collected from 1965 to 1975 inclusive, at the Fasola Stock Farm, near Oyo in the Western State of Nigeria. The breeds represented were Large White, Duroc and Hampshire, and their crosses. The main objective was to investigate the effects of certain identifiable environmental sources of variation on litter performance characteristics such as litter size, mortality and weight at birth, 3 weeks and 8 weeks of age. Breed and year effects were significant for the litter size traits, but parity of dam, season and breed × season effects were significant only for litter size at birth which increased up to the fifth parity and then declined steadily in subsequent parities. Postnatal pig mortality was affected significantly by breed, litter size at birth and breed × season interaction. It was found that the larger the size of litter at birth the higher the postnatal mortality. Average pig weight at birth was reduced by approximately 0·01 kg for each additional pig in the litter.

1. Of 80 gilts reared on a restricted plane of nutrition, 75 were allocated to one of four groups. Group 1; 17 gilts mated at puberty were slaughtered after farrowing their first litter. Group 2; 20 gilts mated at puberty were observed for three parities. Group 3; 18 gilts mated at second oestrus were observed for three parties. Group 4; 18 gilts mated at third oestrus were observed for three parities. Group 5; nine additional gilts reared on feed ad libitum and mated at first oestrus were observed for three parities. All animals received the same ration after the first mating.

2. The mean age (±SD) of the restricted gilts at puberty was 186 ± 17 days at a weight of 89 ± 9 kg. The gilts fed ad libitum were significantly (P<0·01) older and heavier at puberty (203 ± 15 days and 120 ± 27 kg).

3. Conception rates were 83, 86, 94 and 82% for Groups 1 and 2 combined, 3, 4 and 5 respectively.

4. Gilts mated at first, second and third oestrus produced, respectively, 7·8, 9·8 and 10·4 ± 2·2 piglets in the first parity. Group 5 gilts had 11·0 ± 2·2 piglets. All significant differences were confined to the first parity.

5. By the end of the third parity there were no differences between the restricted gilts mated at first, second or third oestrus in total number of piglets born or reared.

6. The gilts slaughtered (at 135 kg) after producing one litter yielded carcasses which were heavier but leaner than those from contemporary maiden gilts grown to 120 kg on a semi-restricted feeding scale.

Herbage intake and grazing times were measured in four experiments in which adult sheep grazed short and long pastures. The digestible organic matter (DOM) intake of adult wooled Merino and Corriedale wethers was higher, both absolutely and per kg live weight, when they were lower in live weight due to prior under-nutrition. The relative differences were similar on both abundant and scant pasture and were proportional to the relative differences in live weight. The higher intakes were achieved by differences in the time spent grazing and in the rate of intake per hour of grazing. DOM intake of shorn sheep was increased by up to 44% per kg live weight within 5 weeks of shearing in two experiments when the mean temperature was 8°C but no increase in DOM intake was observed in four other experiments when the mean temperature was 11°C. Shorn sheep achieved higher intakes on both abundant and scant pastures by increasing intake per hour of grazing.

1. Oxygen consumption was measured in two experiments using castrated Romney male sheep both shorn and unshorn. The sheep were fed either ground hay or dried grass. An ambient temperature of 13°C ± 1°C was maintained at all times. In Experiment 1, oxygen consumption was measured with eight sheep using a respiration chamber and in Experiment 2, oxygen consumption was measured with four sheep using a ventilated hood. The times spent standing, lying, eating and ruminating were measured in Experiment 2. Heat production was calculated from the measured values for oxygen consumption.

2. Heat production increased following shearing in both experiments. In Experiment 1, heat production of the sheep receiving dried grass was significantly greater (P<0·05) on days 1, 8 and 16 following shearing, compared with pre-shearing values. For sheep receiving ground hay, heat production was greater on day 1 (P<0·05) and day 8 (P<0·01) following shearing, compared with pre-shearing values. The mean maximum increase in heat production following shearing was 2·3 MJ/24 hr (25% increase) for sheep receiving dried grass and 1·2 MJ (17%) for those receiving ground hay.

3. The patterns of change in heat production following shearing in Experiment 2 were similar to those observed in Experiment 1 although the maximum increases were smaller: 21% for the sheep receiving dried grass and 13% for those receiving ground hay.

4. The time spent standing increased considerably after shearing and this change in behaviour made a large contribution to the increase in energy expenditure after the sheep were shorn.

The patterns of seasonal variation in reproductive activity were observed over a period of 15 mo for approximately 15 females of each of three breeds: Finnish Landrace (Finn), Tasmanian Merino (Merino) and Scottish Blackface (Blackface). The incidence of oestrus was measured by teasing with vasectomized rams, and the incidence and rate of ovulation were determined frequently by laparoscopy. Luteal function was assessed from peripheral venous blood progesterone concentration on days 7 and 11 of the oestrous cycle. Nutritional status was monitored by recording body weight and plasma-free fatty acid levels throughout the study.

The breeding seasons differed significantly: Finn, October to May; Merino, September to February; and Blackface, October to February. Variation in the incidence of ovulation was similar to that in the incidence of oestrus for each breed. The incidence of silent ovulation varied with the breed, being greatest in the Merino and least in the Finn. The ovulation rate varied among breeds (Finn, 2·99; Merino, 1·08 and Blackface, 1·30), and during the breeding season (e.g. Finn: November, 3·5; March, 2·6). Follicles were observed in each breed throughout the period of study.

The pattern of variation in progesterone concentration was similar for each breed despite their different breeding seasons. In addition to breed differences in ovulation rate and in onset and end of the breeding season, the sensitivity to oestrogen was apparently such that, with the Finn if oestrogen secretion was high enough to stimulate ovulation it would usually also stimulate oestrus, whereas with the Merino ovulation often occurred without oestrus; this suggests that in the Merino the centres controlling ovulation are more sensitive to oestrogen than those controlling behaviour.

Body size was estimated for 255 Greyface ewes using five linear body dimensions. On the basis of this calculated measure combined with a subjective measure of body size 50 small and 50 large ewes were selected for use in the experiment. Precise ovulation data were obtained by endoscopy and this technique allowed the ewes to be mated subsequently.

Body size did not affect the mean ovulation rate of the ewes although, at the same level of body condition, the large ewes were 25% heavier than the small ewes. The ovulation rates and the numbers of lambs born were influenced by changes in live weight and body condition. For these reasons live weight per se was not a good indicator of ovulation rate as ewe live weight was a combination of both body size and body condition. At the same live weight small ewes in improving body condition had a significantly higher ovulation rate than large ewes in reducing body condition.

The onset of the breeding season of the ewes was not affected by their body size. The mean date of onset of oestrous activity for both large and small ewes was 17 October 1972 at a latitude 55° 52′ N.

One hundred and forty-two kids of the Damascus breed of goat were used over a 10½-mo period to study the effects of early castration (at 7 days of age) on growth, feed conversion efficiency and carcass quality and late castration (at 7½ mo of age) on the presence or absence of taint in goat meat.

Intact male kids grew faster and used feed more efficiently than castrates until they were about 9 mo old (56 kg live weight). There- after intact kids exhibited strong sexual activity and as a result their growth ceased completely whereas castrates continued growing. Early castrates produced fatter carcasses than those of intact kids. Castration of male kids at the age of about 7½ mo (44 kg live weight) was not successful in this trial and the kids performed very poorly. A taint of varying intensity was present in the meat of intact goats but not in that from any of the early or late castrates.

In two experiments with steers (initial live weight 339 kg) the effect of dried grass, barley and concentrates on the intake of ‘wilted’ and unwilted grass and whole-crop barley silage was investigated.

In both experiments there was no significant effect of silage type on silage dry-matter intake when given alone or with a supplement. In Experiment 1, supplementation significantly reduced (P<0·05) the intake of silage dry matter (DM) from unwilted and whole-crop barley silage. Total DM intake was significantly higher (P<0·05) for the ‘wilted’ silage diet than for either the unwilted or whole-crop barley silage diets. In Experiment 2, supplementation had no significant effect on total DM intake. Digestible energy intake was significantly higher (P < 0·05) from whole-crop barley silage supplemented with concentrate rather than barley or dried grass and was significantly lower (P<0·05) from unwilted silage diets (P<0·05) when dried grass rather than concentrate or barley was given. In the second experiment, ration digestibility and rate of passage of digesta results are reported.

Teat diameters of 144 British Friesian cows were measured (1) at the proximal end of the teat and (2) 20 mm above the distal end before and after milking. Proximal minus distal diameter—‘teat diameter gradient’is used to describe shapes varying from cylindrical to funnel-shaped. Proximal and distal teat diameters and teat diameter gradient had higher values before milking than after milking. Teat diameter, teat diameter gradient and difference in gradient before and after milking, were positively correlated with milk yield and negatively correlated with somatic cell count.