The study included 1013 gilts representing 28 one-way crosses among Yorkshire (Y), Landrace (Ld), Lacombe (Lc), Hampshire (H), Duroc (D), Berkshire (B), Large Black (LB) and Tamworth (T) breeds of swine. The crosses were distributed among five cooperating stations and were mated to Poland China boars to evaluate sow reproductivity based on the performance of the first two litters. The traits studied were weight at 112 days of age, age at puberty, percentage farrowing, litter size and weight at farrowing and at 3 weeks. Significant differences between crosses were found for all traits except farrowing percentage. The most prolific crosses were LdxY, HxLd and D x Y which gave birth to 11·0, 11·0 and 10·8 pigs per litter respectively, compared to the overall mean of 9·7 Ld x Y, LB x Lc and H x Ld crosses weaned litters 7·4, 5·3 and 4·9 kg heavier than the 40·5 kg mean for all crosses. Using percentage farrowing multiplied by litter 3-week-weight for the two litters as a measure of sow productivity, Ld x Y and LB x Lc crosses ranked highest. The breeds that had the best combining abilities for 3-week litter weight were Ld, Y, LB and Lc, however their specific combining abilities are important and hence not all crosses between these breeds produced superior performing crossbred sows. Overall, the Ld x Y was the most precocious, farrowed and weaned the greatest number of pigs per litter and had the heaviest litters at 3 weeks post-farrowing.

The possible use of superovulation and embryo transfer in selection programmes in cattle is investigated theoretically, in terms of both rates of response and inbreeding.

In a selection programme for growth rate, it should be possible to achieve about twice the response of a conventional performance testing programme, so that 400-day weight, for example, could be increased by 16 rather than 9 kg per year.

The improvement of reproductive performance by the use of laparoscopy to measure the natural ovulation rate of animals over several oestrous cycles followed by superovulation of selected animals is investigated. The rate of progress is dependent upon the incidence of twin ovulations in the base population and is unlikely to exceed 0·6% per year unless the initial frequency is 8% or more.

First lactation records from 971 daughters of 93 Red Danish Milk-breed bulls exported as pregnant heifers from Denmark to 4 Bulgarian and 21 Czechoslovakian herds were analysed and compared to results from corresponding half-sib groups under Danish field progeny tests. Average butterfat production in East European tests was 75% of that in Danish tests.

The results indicate that the true genetic variance and the heritabilities for milk yield, fat content and butterfat yield are higher under the Danish conditions than under the corresponding East European conditions. The genetic correlations between the two environments are estimated to be 0·91, 0·97 and 0·79 for milk yield, fat content and butterfat yield, respectively. Because of insufficient correction for environmental effects, these estimates are considered to be lower than the true parameters.

It is concluded that selection of proven sires in the Danish main population for use in the small East European subpopulations will result in a higher genetic improvement rate than will sire testing and selection within the subpopulations.

Reproductive and production traits were studied in a crossbreeding experiment involving Red Danish cattle, Indian milch breeds and native Zebu cattle in various combinations.

Frequency of abortions and postnatal mortality were higher for Red Danish than for Indian milch breeds and crossbreds, age at first calving was higher for Indian milch breeds than for other groups, calving interval was longer for purebreds than for crossbreds. Milk and butterfat production in first and second lactation increased with increasing proportion of genes from Red Danish cattle. The range of milk production in first lactation was from 987 kg for Indian milch breeds to 3445 kg for Red Danish imported from Denmark.

The optimum proportion of genes from Red Danish for the environmental conditions prevailing in the present crossbreeding experiment is considered to be 60 to 80%.

With the object of comparing the energy requirements of cattle of different breeds a total of 108 animals, representing three maturity types, were individually fed at two levels of intake over three 12-week periods commencing at 250, 375 and 500 kg live weight in a co-ordinated experiment. The three breeds compared were Aberdeen Angus cross, Hereford × British Friesian and British Friesian. Animals were offered a 50:50 hay: concentrate ration at two levels of feeding; one level was designed to give 0·7 kg gain daily and the other 75 to 80% of this intake.

Though the relative performance of breeds differed at the three centres, overall average live-weight gain did not differ significantly between breeds. Feed conversion efficiency dropped from 8·55 kg dry matter per kg gain in the first period to 16·95 kg in the third period, but differences in conversion ratio between breeds were not significant.

Carcass measurements taken at slaughter immediately after the third test period indicated higher killing-out percentages and higher fat percentages in the Angus cross than in the British Friesian with Hereford × Friesian intermediate. Differences in energy needs for gain among the three breeds, predicted by apportioning ME intake to maintenance and gain using a multiple regression technique, were greater than differences calculated from carcass composition and published energy requirements for fat and protein deposition. The limitations of the use of the multiple regression technique for this purpose are discussed.

Suckled cows (average 70 days post partum) and British Friesian dairy heifers (13 to 24 months of age) were injected intramuscularly with prostaglandin F2α (PGF2α) on two occasions 12 days apart, to synchronize oestrus and ovulation. The cattle were inseminated twice, 70 and 88 hr after the second injection.

Injections of 20, 30 or 40 mg of PGF2α were equally effective in 59 heifers; after the first injection, 11 failed to show oestrus during the following 10 days and 10 began oestrus within 36 hr. The majority of the heifers (59%) began oestrus during the 3rd or 4th day after the first injection of PGF2α. After the second injection of PGF2α, all but two heifers showed oestrus and the majority (88%) began oestrus in 3 to 6 days.

Injections of 30 or 60 mg of PGF2α were equally effective in 66 suckled cows; after the second injection of PGF2α, 68% of the cows began oestrus from the 3rd to the 6th day but 10 (15%) cows failed to show oestrus.

Fertility was highest among heifers and cows which began oestrus during 3 to 5 days after the second injection of PFG2α, 54% of the treated heifers and 42% of the treated cows calving during the expected intervals. Nineteen of the 20 control heifers were mated and 25 of 33 control cows were observed in oestrus and inseminated during 3-week or 25-day breeding periods. Eleven (55%) control heifers and 14 (42%) control cows calved during the expected intervals. Thus, fertility of the treated cattle inseminated at predetermined intervals after PGF2α was equivalent to that in the controls.

In two experiments a high dry-matter silage (36·8% DM) was offered ad libitum, together with a supplement of a conventional concentrate or cobs of dried grass, to young British Friesian castrated male (steer) calves. The silage was readily acceptable to the calves and was preferred to the dried grass. Intakes of silage DM were significantly higher (P<0·001) when supplemented with dried grass than when supplemented with concentrates, but daily gains were significantly (P<0·001) lower by 0·15 kg. The lower daily gains supported by the silage/dried grass diet were related to lower intakes of digestible organic matter (DOM); efficiency of utilization of silage/dried grass DOM was similar to that of concentrate/silage DOM. The results are discussed in relation to recommended levels of production for calves in a semi-intensive beef system.

The growth of 12 linear body measurements in Ayrshire cattle was analysed by least-squares methods. Measurements were taken at 3-monthly intervals up to 48 mo of age. Adjustments were made for month and year of birth and for type of birth (twin-born animals comprised 40% of the data). The state of pregnancy or lactation in heifers was also taken in account. Growth curves were fitted to the mean values at the 16 ages and were found to give a close fit. Residual deviations, though small, did show a systematic pattern. The estimated degree of maturity at birth ranged from about 25% for measures of width to 50% for measures of height, body length being intermediate at 40%.

To a large extent the different body measurements maintained a uniform pattern of maturing and their ranking for earliness of maturity tended to remain constant throughout the growth period. The application of allometry to the measurements is examined and the error introduced by extrapolating an allometric relationship between characters of different maturing rates is illustrated.

Correlations and regressions between estimated breeding values for 122 day part-lactation, 1st and 2nd lactation yield (part, 1st, 2nd) were estimated from 106 sire progeny groups, each with at least 60 effective daughters.

The genetic correlations between part, 1st and 2nd kg milk were 1·0 and 0·84 respectively, and the regressions of 1st on part and of 2nd on 1st test were 2·40 and 0·82 kg/kg milk, respectively. Selection by one standard deviation between sires on part-lactation tests would improve 1st lactation yields by an average of 204 kg milk with a standard deviation of 84 kg. Selection on 1st lactation yields by one standard deviation would increase 2nd lactation yields by an average of 183 kg milk with a standard deviation of 156 kg, indicating that some bulls so selected could have below average 2nd lactation yields.

Two sire selection models were simulated differing in the selection criterion; 1 st yield in model 1, and 1 st followed by 2nd yields in model 2. The contribution of proven sires to the rate of genetic improvement in lifetime production was greater from model 2 than from model 1 by about 15% without any additional costs for bull maintenance.

1. In three experiments, 112 7-day-old British Friesian male calves were used in performance and digestibility trials to evaluate dried cooked potato in liquid and creep diets.

2. A 15% depression in growth rate for each 10% inclusion of cooked potato flour in liquid diets was recorded from 4 to 21 days and the faeces of potato-fed calves also tended to be less solid. Over the whole feeding period, liquid diets containing up to 20% potato did not significantly depress performance to weaning at 35 days.

3. Only when a liquid diet containing potato starch was introduced prior to 4 weeks of age was daily live-weight gain markedly depressed.

4. Incorporating potato starch in milk diets did not influence creep intake.

5. Calves offered a creep diet containing 40% cooked potato flake ate less, but grew faster than calves given a diet containing 40% flakedmaize. At constant intakes of creep, daily gains were 14 to 18% greater on the diet containing potato flake.

6. The apparent digestibility of gross energy and nitrogen was 0·67 and 0·66 for the flaked maize creep and 0·71 and 0·69 for the potato creep. Digestible energy and digestible nitrogen values were 12·7 MJ and 18·2 g/kg dry matter for the maize diet and 13·0 MJ and 19·0 g/kg dry matter for the flaked potato diet.

7. The incidence of bloat was higher for calves fed on potato than for those fed on maize.

An attempt to evaluate a group of 72 beef carcasses, in retail terms, is described, resulting in a comparative measure of retail value that takes account of saleable fat and of the distribution of lean amongst the different cuts. Changes in the general level of beef prices can be discounted, provided the ratios of the prices of different joints remain the same. It was found that the index of retail value was poorly correlated with the commonly used ratio of high-priced to low-priced parts, but highly correlated with total proportion of lean. The index could best be predicted from a multiple regression on side weight and proportional area of muscle determined from photographs of the cut surface after quartering.

Data on 2208 parturitions involving 3594 kids were used to study the inheritance of polledness and its relationship with intersexuality in the Damascus breed of goat.

The percentage of horned kids in the offspring of polled × polled and horned × horned matings was 26·8 and 100·0, respectively. The corresponding value for matings having one parent horned was 50·3%.

There was a consistent excess of males in the sex ratios. Males comprised 53·8, 52·4, 60·2 and 54·0% of the offspring of polled x polled, polled x horned, horned x polled and horned × horned matings respectively. The corresponding proportions for the intersexes were 6·2, 0·3, 0·0 and 0·0%. The incidence of intersexes was not affected by type of birth (single, twin or multiple) or sex of littermates.

It was concluded that the data from the Damascus breed of goat conform with the current theory on the behaviour of the P gene concerning polledness (direct dominant effect) and intersexuality (pleiotropic recessive effect) in the Swiss breeds of goat.

Observations were made on a commercial herd of female pigs (sows) where a managemental system was employed which enabled sows to be served during lactation. The system involved grouping between 2 and 8 sows together with their litters about 3 weeks post partum. The sows were fed ad libitum from grouping, and the piglets had ready access to creep food. After one day a male pig was introduced to the group. No exogenous hormone therapy was used.

Results from 39 batches, comprising 180 sows, suggested that sows kept under these conditions will exhibit oestrus, and conceive during lactation with a high degree of predictability. Lactational oestrus was shown by all sows and conception to first service was 84·9%. The number of days between grouping and oestrus, and parturition and oestrus, were 11·15 ±0·28 and 35·53 ±0·47 respectively. Litter size and performance did not appear to be adversely affected by the concurrent lactation and pregnancy, either at the present or subsequent parturition. The average farrowing interval of 153 days allowed a performance of 2·35 litters/sow per year, and, with 9·47 piglets weaned/litter, a productivity of 22 piglets/sow per year.

Three changeover experiments, each with 16 milking cows, were conducted to evaluate the effects of stage of growth of lucerne, level of feeding of lucerne or ryegrass and level of inclusion of barley. The artificially dried and processed forages were in the form of cobs and given to cows in addition to a basal ration of hay. Late-cut lucerne (organic matter digestibility, OMD, 55%) promoted significantly lower milk yields than early-cut lucerne (68% OMD). When offered ad libitum in two meals each day both forages were eaten in quantities of about 13 kg dry matter. Ryegrass cobs (79% OMD) produced more milk than lucerne cobs (59% OMD) but gave similar milk yields per unit of digestible organic matter. Production rations supplying similar amounts of digestible organic matter and composed of different proportions of lucerne cobs and rolled barley gave similar milk yields. It is concluded that the relative milk-producing value of processed forages depends on their content of digestible organic matter. However, their bulk may limit their value and the inclusion of cereal with the dried forage may be worth while.

The productivity of cows grazing on veld was studied over four breeding seasons. Different amounts of concentrates were given to three groups of cows during winter and up to 8 weeks post partum. Half of the cows in each group had their calves weaned early (150 days) and the others at the normal time (240 days). Cows given concentrates produced more calves than those given none but time of weaning had no consistent effect on successful conception rates (as judged by subsequent calving rate).

Probit analyses were used to determine the relationship between seasonal body-weight change in the cow and the probability of successful conception. The estimated percentage body-weight changes from autumn peak to mean body weight at the beginning and end of the mating season, which would be followed by successful conception rates of 50%, 75% and 90%, were −14%, −6% and +1% of autumn body weight, respectively.

The practical implications of these results are discussed.

Records for 6012 inseminations of cows were analysed to determine the effect of the stage of oestrus at the time of insemination on conception rates for three groups of sires. All inseminations were completed between 8.30 hr and 11.30 hr using 2·5 million total spermatozoa in 0·5 ml of ‘Caprogen’ extender containing catalase. The designation of the stage of oestrus was based on the milking or milkings relative to the time of insemination at which each cow was observed in oestrus. Data from cows returning to service less than 18 days after insemination were excluded.

The average conception rates (18 to 49 day% non-return rate) for the three groups of sires were 72·9% (7 sires of above average fertility), 70·5% (5 sires of average fertility), and 68·3% (6 sires of below average fertility). With inseminations in early oestrus, the comparable results were 74·3, 62·7 and 58·4% respectively. In contrast, the results for the three groups of sires with post-oestrous inseminations were 73·3, 71·13 and 73·8% respectively.

The average interval from insemination to ovulation and fertilization is related to the stage of oestrus at insemination. This interval was the major factor contributing to the fertility differences between the groups of sires included in this experiment. These differences were also reflected in the percentage and distribution of normal (18 to 24 day) return intervals.

Three groups each of 14 cows, balanced for stage of lactation and potential milk yield, were kept either on a control treatment C, grazing within a rigid rotational grazing system, or on a leader (L) and follower (F) grazing system operated within a similar system. The stocking rate of treatment C was 5·76 cows/ha, the same as the overall stocking rate of treatments L and F. In Experiment 1, a 10-week continuous-type randomized block experiment was preceded by a 4-week uniformity period; in Experiment 2, a 3 × 3 Latin square design was adopted with periods of 4 weeks. Herbage intake and milk yield were only slightly, and not significantly (P > 0·05), higher in the leader than control cows, whilst the performance of cows on treatment F fell significantly (P< 0·001) below the other treatments. In treatment L, cows in early lactation responded to the extra opportunity for herbage selection with significantly (P< 0·01) more milk than those in late lactation. The mean milk production of the leader and follower cows was similar to that of the control cows. It is suggested that the potential value of a ‘leader and follower’ grazing system is unlikely to be greater than that of a conventional rotational grazing system.

1. Forty-eight early-weaned lambs were used in an experiment in which whole barley was gradually replaced by whole oats in order to produce different types of rumen fermentation.

2. The type of rumen fermentation promoted by whole barley did not give rise to excessively soft fat in female lambs; in males, however, some carcasses were unacceptable. An increase in the proportion of propionic acid in the rumen liquor was associated with an increased proportion of odd- and branched-chain fatty acids and a decreased proportion of stearic acid in carcass fat. When the molar proportion of propionic acid in the rumen liquor was above 30%, three out of every five carcasses from the entire male lambs had excessively soft fat.

3. Assessment of food utilization was complicated by lower daily intakes of digestible organic matter (DOM) when more than about 15% of barley was replaced by oats and also influenced by changes in gut contents. With 100% whole barley the mean gut fill was 4·7 kg while with 100% oats it was 9·4 kg.

Assuming a maintenance requirement of 100 kcal metabolizable energy/kg0·75, it was calculated that the digestible organic matter of oats was utilized more efficiently than that of barley to produce empty-body gain. Most of the differences in utilization disappeared if an adjustment was made for differences in gut contents. The results indicate that the maintenance requirement/kg0·75 decreases with increasing gut content.

In the first experiment, 10 ewes (¼ Finnish Landrace: ¾ Clun Forest) were maintained under natural daylength conditions and 10 were exposed to a constant daylength of 8 hr from 22 December until 1 June. No difference was demonstrated between treatments in dates of cessation of oestrous activity. It was concluded that oestrous activity will eventually cease, whether or not daylength increases after the shortest day.

In the second experiment, 40 similar ewes were mated at first oestrus of the natural breeding season (mean 7 September) and lambed in January. Twenty ewes suckled lambs and 20 had lambs removed within 24 hr of birth. No sucked ewes showed oestrus before the end of the breeding season, but 9 non-sucked ewes showed oestrus at a mean interval of 37·5 days after lambing and 4 of these subsequently lambed. Suckling appeared to inhibit oestrous activity and conception in ewes at this time of year.

The behaviour of sows in tether stalls with and without straw was studied in two experiments. Sows lay down more when 1 kg of straw was provided daily, especially when it was chopped and mixed wet with the food (dietary effect). Sows without straw performed avariety of stereotyped oral and other activities which were greatly reduced by the provision of loose straw that could be chewed and manipulated throughout the day (recreational effect). Sows were frequently seen standing or sitting motionless with the head drooping, probably in a state of drowsiness. This behaviour was virtually eliminated by full straw bedding (bedding effect). Certain ‘comfort movements’, barbiting at feeding time, and biting the neighbouring sows, were not influenced by straw. It is concluded that the dietary, recreational and bedding aspects of straw are all significant, but influence different aspects of the animals' behaviour. The significance of bar-biting and other activities is discussed.