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.

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.

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.

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.

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.

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.

An investigation was undertaken to evaluate the crossbred boar per se, and also to assess the value of including the American Hampshire into a first-cross sire. Groups of three boars were placed on each of 20 farms. Each group contained a purebred white (Landrace or Large White), a crossbred white and a crossbred Hampshire boar. Co-operators were asked to obtain at least six litters by each boar, record their performance to weaning, and provide a sample of the progeny of each boar to be reared under standard conditions to slaughter at 90 kg live weight. Breeding of the boars did not affect either the level or variability of litter performance. Differences in performance and carcass traits between the progeny of purebred and whitecross boars were found only for ‘eye-muscle’ area and fat depth ‘C’. Pigs sired by Hampshire-cross boars had carcasses which were 2% shorter than those from white boars.

The discounted gene flow method was used to study the effect of varying financial discount rates and accounting period on the present value of the genetic merit conferred by each insemination.

Over the range from 8% to 16%, each 1% increase in the discount rate reduces the value of the dairy and beef consequences of an insemination by about 5% and 4% respectively, Virtually all of the economic benefit arising from an insemination is complete within 20 years, with about 90% of it being realized in the first 10 years and 98% in the first 15 years.

A total of 178 castrated male cattle (steers), the progeny of Charolais, Hereford and Limousin bulls mated to Holstein-Friesian and Ayrshire cows, were raised from 8 months of age to 545 kg (slaughter weight) on fast- or slow-gaining regimes. The steers on the fast gaining regime were fed a grain mixture with little hay, while those on the slow-gaining regime grazed all summer and were wintered on hay supplemented with a little grain.

The steers on the fast-gaining regime were more efficient in feed conversion ratio, had 0·42 kg per day higher live-weight gain, reached slaughter weight 306 days earlier, and had 2% higher dressing-out percentage, 5·7 mm thicker fat and 5 mm2 larger area of m.longissimus thoracis than those on the slow-gaining regime.

Charolais-sired steers on both regimes had the fastest gain and were the first to reach slaughter weight. Limousin-sired steers raised on the fast-gaining regime had the highest dressing-out percentage, and the largest area of m. longissimus thoracis on both regimes. Hereford-sired steers had the thickest fat cover and the smallest area of m. longissimus thoracis. Little difference was found between the steers from Holstein and Ayrshire cows.

Twelve Ayrshire cows which had reached or just passed peak lactation were selected and divided into two balanced groups. One group was fed strictly according to yield. The other was fed overall according to yield, but was subjected to a 4-day cycle of energy intake. For 2 days energy intake was 12·2% above calculated requirements and for the next 2 days intake was 12·2% below calculated requirements. The treatment was imposed for 10 weeks and milk yield and composition, body weight and blood composition were measured in both groups of cows. A significant variation in daily milk yield and daily solids-not-fat yield was found to follow the feed cycle. Blood composition showed no significant variation.

Digestibility of dry matter, energy and cell wall was measured in two series of digestibility trials in which sheep were fed on pelleted mixed rations containing either 32·0 or 22·6% cell wall at various levels of intake. There were significant depressions in digestibility of all nutritive components as the level of intake increased. The ration lower in cell wall showed smaller declines in dry matter and energy digestibility but a greater decline in cell wall digestibility. The results indicate that the cell wall fraction of concentrate-supplemented rations for sheep is a primary factor in the decline in digestibility observed with increase in level of intake.

An ‘indicator muscle’ (m. flexor digiti V brevis) was removed in its entirety from several Large White and Landrace pigs of varying fat depth (measured over the eye-muscle area). The total muscle fibre number was measured in transverse sections for each muscle. Significant inverse relationships were found between this fibre number and fat depth measurements. These and other results suggest that fibre number is related to lean meat content. Fibre number was also shown to be highly correlated with fibre density and as thinner fibres (i.e. higher fibre density) are associated with more tender meat, fibre number may be associated with quality as well as quantity of meat.

Sixteen cross-bred male lambs were assigned to either a group- or a single-rearing treatment up to 150 days of age. After this time the single-housed rams were penned together and all rams were tested weekly for their abilities to successfully mate with ewes for a further 10 weeks. There were no marked differences in the development of sexual behaviour between the two treatments.