A numerical model of male and female replacement processes is developed and used to construct a matrix which specifies the numbers of lactations of different parities expressed in a given time period by daughters of bulls used in artificial insemination (AI).

Populations resulting from newly established AI breeding programmes contain an unduly high proportion of offspring by young bulls. Subsequently an equilibrium is reached in which offspring of young and tested bulls are present in proportions determined by the relative usage of the two types of sire and by differences in replacement rates amongst their progeny. Once an equilibrium has been reached the numbers of progeny sired by bulls lacking a progeny test proof is extremely small.

The use of the technique to solve a number of specific planning problems is demonstrated.

Groups of individually-fed pigs, each of three gilts and three castrates of mean live weights 18, 31, 46, 58, 72 and 80 kg, were given for 20 days feed allowances based on the ARC estimates of energy required for maintenance, assuming an efficiency of utilization of digestible energy (DE) of 77% for maintenance. As the actual diet used had a higher DE value than that calculated before the start of the experiment, DE intakes (260·3 W056) were about 4·0% above the ARC values.

There was no statistically significant change in live weight over the period of study. This supports the validity of the ARC estimates, if maintenance is defined as a lack of change in body weight.

The metabolizable energy (ME) intakes (248·3 W0·56) which maintained weight were also close to other estimates of ME requirements.

Allowances of about 1·4M, 1·8M, 2·2M, 2·6M, 3·OM, and 3·4M (M = feed required for maintenance) were compared for pigs growing over the live-weight ranges 20·40, 40·60, 60·80, and 80·100 kg, with feed conversion efficiency (FCE) as the main response criterion.

Response to increased digestible energy (DE) allowance was curvilinear; FCE improved rapidly up to 2·2M-2·6M, and changed much less with intakes above 2·6M. It is concluded that optimum FCE occurs at about 2·7M for pigs of 30 kg and at about 3·OM for pigs of 50, 70 and 90 kg.

Allowances of dietary DE suggested by the Agricultural Research Council correspond to 2·56M, 2·95M, 3·04M and 3·08M for pigs of 30, 50, 70 and 90 kg live weight, respectively. It appears that these are near to the optima in promoting the best FCE.

Changes of −25%, −15%, −5%, +5% and +15% in daily intake around the optimum levels caused FCE to deteriorate by averages of about 13%, 4·5%, <1%, <1% and 4·5% respectively. Daily weight gains would then change by about −34%, −18%, −5%, +4% and +10%, respectively.

Three diets were given separately, each at four levels of digestible energy (DE) intake, to gilts, castrates and boars growing from 21 to 92 kg live weight. The energy levels were those suggested by the Agricultural Research Council, compared with a 5% increase or 10% or 20% decreases in daily allowance. One diet (ME 18) had 3·0 Meal DE/kg and 18·2% crude protein; the other two (HE 16 and HE 19) had 3·26 Meal DE/kg and 16·1% or 19·3% crude protein.

They were given unchanged throughout the experiment. Responses to change in daily DE intake were not affected by sex or diet, except in shoulder fat thickness. Feed eaten per kg gain did not vary by more than 4% over the intake levels investigated, and no difference was significant. On average, each reduction in daily intake below the ARC+5% allowance led to an increase of 1·2 percentage units of carcass lean and a decrease of 1·3 percentage units of carcass fat.

In comparison with HE 16, the higher protein diet HE 19 gave improved feed conversion efficiency and growth rate, particularly in gilts. It did not cause significant changes in carcass measurements. In comparison with ME 18, HE 19 gave more efficient conversion of DE to weight gain, and faster growth.

Boars required less feed per kg gain and had faster growth rates and leaner carcasses than gilts, which were superior to castrates. There was a high incidence of unpleasant odour in fat from boars, but some was also detected in that from gilts and castrates.

The transport of protein across the small intestine of the newborn pig was measured in vitro. The transport of both bovine immune globulin and bovine plasma albumin showed a large variation between piglets. The polycations poly-ornithine, poly-arginine and poly-lysine stimulated both the transport of globulin and albumin. Protamine, histone and arginine were without effect on protein transport. Poly-ornithine became bound to albumin and to the piglet intestinal mucosa. The amount of poly-ornithine needed to stimulate albumin transport was of the same order as that needed to change the electrophoretic mobility of brush border membranes and some 30 times less than that needed to change the charge on the protein. It is concluded that polycations stimulate protein transport by a direct action on the brush border membrane of the pig intestinal mucosa.

Twelve sows (F) were fed 7·3 kg/day and twelve (T) 3·7 kg/day of a 16% crude protein (CP) diet for the last 5 weeks of an 8-week lactation, so that at the subsequent service F sows were heavier (16%) and in better condition.

From service to slaughter 70 days later, sows received either 3·7 kg/day (H) or 1·8 kg/day (L) of a 15% CP diet, giving four treatment combinations; FH, FL, TH and TL.

In pregnancy H sows gained more weight than L sows and, on the low plane, F sows gained more weight than T sows. Ovulation rate as measured by corpora lutea count at slaughter was higher for TH than TL sows and for FL sows than FH sows. A combination of low ovulation rate and high mortality rate gave fewer foetuses (10·0) in the TL sows than in sows on the other treatments (13·5). Similarly mean foetal weight and thus foetal litter weight was least in TL sows. Foetal membranes, uterine fluids and uterine wall were lighter at slaughter in T sows than F sows and lighter in L sows than H sows, those of TL sows being appreciably the lightest.

The results indicate that when the sow is in poor condition at service, body reserves being depleted, the uterus and its contents become more vulnerable to adverse pregnancy nutrition.

The performance of Israeli-Friesian male calves on six rations, including two levels (15% and 30%) of ground wheat straw and oatvetch hay in pelleted mixtures, and the same two levels of ground straw in non-pelleted mixtures, was examined.

Daily live-weight and carcass gain were higher on the lower level of both roughages. The differences in performance on hay and straw were insignificant. Feed intake was higher on the 15% level of both roughages when pelleted but the energy conversion ratio was higher on pelleted rations of both levels of straw.

The dressing percentage was higher for animals on pelleted rations. There was no significant difference in percentage fat trim, percentage bone or percentage saleable meat in the carcasses. There was 20% more kidney, pelvic and cod fat on the lower level of roughage.

The digestibility of organic matter was higher on rations with the lower level of roughage, and on the pelleted rations compared with the non-pelleted at equal level of roughage. This was not the case for the digestibility of crude fibre. Nitrogen retention was significantly higher on the lower levels of straw and on the pelleted rations of a similar level, and was higher on hay rations than on straw rations. Ration differences in the molar proportions of volatile fatty acids in the rumen liquor were detected.

Pelleting appeared to improve the nutritive value of straw.

In two experiments the effects of several levels of supplementary energy and of protein on the voluntary intake of long straw by young cattle of 200 to 300 kg weight were studied.

In Experiment 1, 40 cattle were used to compare 4 protein levels and 5 energy levels. At the lowest protein level (diets containing 6·6% crude protein or less) intake of straw was low at all energy levels and the live-weight gain of the cattle was not increased by the energy supplements. There was no difference in performance between the other 3 protein levels, which gave whole diets containing 8·8% crude protein or more in the dry matter. Supplements of 5 to 9 g concentrates per kg live weight reduced straw intake only a little, and increased gains.

In Experiment 2, 40 cattle were used to compare barley and oat straw alone and with 2 levels of protein and 2 levels of energy supplement; one of the latter was higher, 12 g concentrate per kg live weight, than any in Experiment 1. The digestibility of the diets was determined. The results showed no difference in animal performance between oat and barley straw and agreed in general with Experiment 1. The low-protein, high-energy combination (6·4% crude protein in the whole diet) was frequently refused and gains on this treatment were low; at the higher protein level, when protein supply was adequate, straw intakes were less than on the lower energy level with adequate protein. Long straw could supply 35 to 45% of the daily energy requirements of young growing cattle.

An experiment was carried out using lambs reared from 1 day to 23 days of age on milk substitute given either ad libitum or at a restricted rate of 250 g dry matter per day, in rooms maintained at three temperatures, 7, 14 and 21°C.

Lambs fed milk substitute ad libitum showed similar growth rates (about 365 g per day) at all environmental air temperatures. Total dry-matter intake of milk substitute per lamb over 22 days was slightly higher in those kept in an environmental air temperature of 7°C. The efficiency of lambs in the 7°C environment was lower than those in the 14 and 21°C environments.

When dry-matter intake was held constant, at the restricted level, growth rate increased linearly between 237 and 265 g per day as the environmental air temperature was increased.

At each of these temperature levels the restricted-rate lambs were more efficient than the respective lambs fed ad libitum.

1. Groups of 12 male and 12 female lambs, early weaned and individually fed, were used at six centres in Great Britain to determine the effect of dietary protein concentration on growth rate and feed utilization from weaning to 37 kg live weight. Three diets varying in the proportion of rolled barley to white-fish meal were used to give 13·5, 16·0 or 18·5% crude protein in the dry matter. The diets were pelleted and offered ad libitum.

2. The male lambs showed significantly poorer growth rates and feed conversions on the low-protein than on the other diets. Results for the females were more variable so that although the mean values showed similar trends these were not statistically significant.

3. Female lambs had about 19% lower growth rates than male lambs. The mean food conversion (kg dry matter/kg gain) with the diet containing 16% crude protein was 2·67 for the males and 3·30 for the female lambs. Food utilization differed significantly between centres, the centres using lambs of Finn Dorset breeding having lower growth rates and poorer food utilization than Suffolk crosses.

1. Calorimetric evaluation of the nutritive value of feeds for ruminants has, of necessity, involved using mature sheep isolated in respiration chambers. This experiment was designed to examine how such information relates to growing lambs reared in different ways.

2. Lambs were either completely isolated, individually fed, or fed in groups. Two lambs in each group were fed to gain 100 g/day (medium) and two to gain 200 g/day (high). Calorimetric measurements were made on individuals or groups at intervals over 20 weeks.

3. All lambs fed to gain 100 g/day consumed their entire ration, isolated lambs gained on average 123 g/day and the others 160 g/day. On the ‘high’ ration isolated lambs ate less than the others and gained 178 as against 228 g/day.

4. Metabolizable energy intake, heat production and thus energy retention were similar in all groups offered the ‘medium’ ration. Differences in energy retention on the ‘high’ ration were related to differences in intake.

5. The net availability for weight gain of the diet (kf) estimated from energy balance trials conducted throughout the growth period (0·61) agreed well with that predicted from its content of metabolizable energy (0·63).

6. Estimates of the caloric density of the weight gain suggested that on the ‘medium’ ration the isolated lambs retained substantially more energy as fat than those reared in groups. These observations are discussed in relation to the design and interpretation of calorimetric experiments to predict the nutritive value of feeds for growing lambs.

A flock of Polled Dorset Horn ewes joined with three Polled Dorset Horn rams were observed during the hours of daylight, for 17 days, when all the ewes were known to be showing oestrus regularly. The number of approaches, mounts and serves made by the rams and the identities of the ewes involved were recorded.

The mean and SE for the number of services per ewe in oestrus was 4·2 ± 0·3. There were no significant differences in sexual performance between the rams apart from the number of mounts and the mount to service ratio. The number of ewes served per ram and the number of services per ewe in oestrus declined significantly over the 17-day period. Ram performance was significantly related to the number of ewes in oestrus and to the time that the rams had been joined with the same group of stimulative animals (e.g. multiple regression of number of services x with time y and number of ewes in oestrus z is: x = −0·72y + 1·3z + 8·8).

Sheep ate significantly faster during the first 30 min after being offered fresh food when they were fed on ground, pelleted dried grass than when fed on long hay; chopped dried grass was eaten at an intermediate speed. Rate of eating of the unground diets was negatively related to mean retention time and positively related to total voluntary intake.

In a second experiment, rate of eating during the 30 min after feeding was significantly faster when hay was fed at two-thirds of the ad libitum rate than when it was fed ad libitum, irrespective of whether penning was individual or in groups of six.