The potential advantages of early weaning have been listed by Dr Braude in his introduction. In practice, however, piglet mortality can reduce or eliminate these potential improvements in number of piglets per sow per year, and in overall efficiency of feed energy utilization for piglet production (Table 1).

The principal objective to date in packaging dried forages into wafers, cobs or pellets has been to improve handling and storage. Over 80% of the dried forage produced in the UK is still used as a component in pig and poultry rations, for which a milled and pelleted product is the most suitable. However there is evidence that the different forms of package are not of the same nutritive value to ruminants. With the increasing interest in the use of dried forages for ruminant feeding it is important to examine packaging in these dual rôles, as both mechanical and nutritional treatments.

The factors involved in meeting the beef requirements of our expanding population range from biological and economic to social in nature. It was decided to restrict this paper to those biological and economic factors which are directly involved in achieving the targets of beef production within low cost systems.

Under this very broad title we have selected three aspects of current and recent work which have a bearing on our understanding of the interpretation of findings dealing with muscle-weight distribution. The first is a justification of the anatomical approach, the second a confirmation of, and elaboration on, some earlier work, and the third a suggestion for some future thinking.

For the purpose of the present discussion I will define commercial cutting as the cutting of carcasses into commercial wholesale or retail cuts, and the trimming of some fatty tissue and bone from these to commercial specifications. I assume that this will be done by a commercially trained butcher. I also assume that the cutting and trimming will be done in commercial premises.

The most important metabolic disease associated with intensive grassland production and utilization in Northern Ireland is grass tetany. Grass tetany or hypomagnesaemic tetany was recognized in the early decades of this century in Europe and probably appeared in the British Isles in the early 1920's. There has been a steady increase in incidence over the years, and this would seem to be related to an increase in productivity, both in terms of output from the animal and from pasture.

In general the energy supply is the main factor limiting the output of milk by the dairy cow from most food sources. Under Northern Ireland conditions grass produces a greater energy output per unit area than any of the other major crops grown there. Furthermore Lowe (1970) has estimated the relative production costs per unit of dry matter for cereals and root crops to be twice and eight times respectively those incurred with grass. Therefore it is apparent that both on a basis of energy output per unit area, and per unit cost input, grass must continue to provide the maximum possible proportion of the food supply for the dairy industry within Northern Ireland.

I think it is extremely important that when we are making comparisons of the advantages and disadvantages of artificial rearing, as compared with other systems of rearing, that the comparisons should be made on a valid basis.

There are three ways in which the systems can be compared: firstly, they can be compared on a basis of the biological targets of the system. These represent a limit to production in the appropriate systems. Secondly, they can be compared on a basis of maximum performance under laboratory conditions, or in those situations in which scientific personnel have clear control over the system being undertaken. Thirdly, systems can be compared on the basis of the best performance achieved under purely practical conditions. This point can be illustrated by three examples:

1. Number of pigs born per sow per year

Since gestation length cannot be affected, the important factors involved in the number of pigs born per sow per year are: number of pigs born, length of lactation period and the interval between weaning and service.

The potential value of carcass chemical analysis in a variety of animal research studies is not only in the specific information it alone can provide, but in particular as a means of substantiating and augmenting data obtained from other experimental approaches. For example, it may be used in conjunction with in vivo nutrient balance studies and with physical dissection in carcass quality assessment studies. Realization of the full potential value of carcass chemical analysis depends entirely, however, on the ability to produce, from the initial highly heterogeneous carcass material, a fully representative sample that is sufficiently homogeneous to enable valid analyses to be made using the desired analytical techniques. Macro-analytical techniques may be acceptable when the numbers of samples involved are relatively small and /or when the analytical resources available are not critical. Under such conditions a lower degree of homogeneity will be acceptable in the material to be analysed than that required when micro-analytical techniques are used.

Two trials were carried out to investigate the effects of increasing calorie: protein (C:P) ratios of high iso-nitrogenous diets on the performance characteristics, nutrient digestibility, carcass quality and organ weights of 67 growing pigs of the Yorkshire and Landrace breeds, reared in a tropical environment on concrete-floored pens from 9 to 56-8 kg live weight before slaughtering and grading. The dietary protein content was approximately 24 % of dry matter in all cases, and the C:P ratios ranged from 153 to 184 kcal digestible energy/g in both trials. Results showed no consistently significant differences in gain and feed intake due to increasing C:P ratio, but feed conversion ratios consistently improved with increasing C:P ratio. Digestible energy consumed per kg of body weight gained also increased with increasing C:P ratio. The nutrient digestion coefficients did not appear to be significantly affected by the C:P ratio. With respect to carcass quality measurements, there were nonsignificant differences in dressing percentage and average backfat measurements, but significant differences in percentage trimmed fat with increase in C:P ratio. The carcass length, loin eye area, and percentage lean cuts decreased as the C:P ratios increased, the last two showing significant differences only in the second trial. The organ weights showed no significant differences due to increases in C:P ratio.

1. Eight British Friesian male calves were fitted with rumen cannulae at 4 weeks of age, and were given either chopped or pelleted dried grass to appetite. After weaning at 6 weeks the animals were allowed to eat to appetite, or the appropriate food material was added via the cannula, or digesta removed, at the rate of 20 % (dry-matter basis) of voluntary food intake, in alternating periods of 7 days.

2. The addition of food material resulted in a depression in drymatter intake (DMI) which was greater than the increase in DMI following the removal of digesta, and the difference approached significance in the small number of comparisons possible.

3. The response in voluntary food intake increased significantly with age, and reached or exceeded ‘adult’ levels within 6 weeks from weaning. It is postulated that oropharyngeal factors associated with the development of eating behaviour control the initial development of solid food intake; the influences of physical or metabolic limitations upon food intake increase with time.

Sixteen energy and N-balance trials with six sows were performed to study the energy requirement and protein gain of the animals during different stages in the second half of pregnancy. Energy and N-balances were measured during periods of 1 week and gaseous exchange was measured in a respiration chamber. The animals received 2·0,2·5,2·75 or 3 0 kg/day of a normal concentrate ration for sows. In one experiment, one animal had a negative energy balance on the 2 kg ration in the sixth week of pregnancy but in the other experiments the dietary energy intake was sufficient for positive energy balances until a few days before parturition. The N-balances were about 20 to 32 g/day in the second half of the gestation period. With 2·5 and 2·75 kg feed there was a negative deposition of fat at about 2 weeks before parturition. Heat production increased during pregnancy, but at a greater rate during the last 2 weeks. Until 2 to 3 weeks before parturition 2·5 to 2·75 kg of feed seemed to be adequate to meet the energy requirement of a pregnant sow of 180–200 kg live weight. During the last 2 weeks 3 kg was sufficient.

Ewes of seven breeds (Oxford Down, Border Leicester, Finnish Landrace, Southdown, Welsh Mountain, Tasmanian Merino and Soay) were treated with progestagen-treated sponges to synchronize oestrus for an egg-transfer experiment. Ewes of five of the breeds were treated with superovulating doses of pregnant mare serum gonadotropin (PMSG). Mean body weight ranged from 89 kg for Oxford Downs to 20 kg for Soays. Interval from sponge withdrawal to oestrus differed significantly between breeds, ranging from 1·83 days in Finnish Landrace to 3·00 days for Soays, but was not consistently related to ewe weight. Treatment with PMSG prior to sponge removal reduced the interval to oestrus; fertilization rate at the first synchronized oestrus was low. There were marked differences among breeds in proportion of ewes showing oestrus following PMSG treatment, total follicular response, and proportion of follicles ovulated. Ewes of the Finnish Landrace breed, with the highest natural fertility, were equal or superior to the other breeds in every component of response, and yielded more than double the number of fertilized eggs per ewe of the next best breed. Finnish Landrace females 6 to 9 months old made very satisfactory donors. Natural ovulation rates of adult recipient ewes were as follows: Welsh Mountain (23 ewes)—1·43; Border Leicester (15 ewes)—2·00; Finnish Landrace (26 ewes)—3·31.

Twenty-one Finnish Landrace × Polled Dorset Horn female sheep approximating 8 months old were individually penned from 3 to 4 weeks after mating until parturition. They were allocated to one of three diets containing either 12·3, 14·1 or 16·5% crude protein and 2·1 Meal metabolizable energy per kg dry matter, offered at a level of 85 g/kg W0·75 per day. A series of nitrogen balance trials was carried out on all lambs during the last 100 days of gestation.

The mean age at parturition was 382 days and the mean litter size 1·52. The live-weight gain (mean value 152 g/day) was not significantly affected by the level of protein intake. There was a tendency (005 < P < 0·10 for singletons) for lamb birth weight to decrease and the body-weight change of the dam to increase with increasing protein concentration in the diet. There was a significant linear increase in nitrogen retention both with stage of gestation and level of protein intake.

The partition of nitrogen between the foetal and maternal body is discussed in relation to the estimated nitrogen content of the maternal live-weight gain.

A comparison was made of beef-type and dairy-type suckler cows in 17 herds by forming pairs when cows of both types calved within 7 days of each other in the same herd. Cows and calves were weighed within 14 days post partum and when turned out to grass. The calves were weighed again at weaning. Winter food intakes were recorded by weighing feeds on one day of each month. Sixtynine pairs of cows were formed and 23 different levels of winter food input to the cows were computed.

Calves out of dairy-type cows were significantly heavier at turn-out (8-4 kg) and at weaning (8-3 kg). These differences were greater at higher levels of winter food intake per cow.

Two groups of 24 Landrace × Large White gilts were allocated at puberty to two feeding regimes during oestrus. The control group received 1·8 kg food/day throughout the oestrus period, while the flushed group had an additional 1·8 kg immediately after mating on the first day of oestrus. The treatments were imposed at the first post-puberal heat (second heat) and at the post-weaning oestrus in the second and third parities. The sows remained on the same treatment throughout the experiment. Litter performance was measured in the first two parities. The sows were slaughtered on day 25 of their third gestation to provide data on ovulation rate and embryo mortality. Increasing feed intake to 3·6 kg on the day of mating did not significantly affect the number of piglets born, number born live, or mean piglet weight, in either the first or second parity. In the third parity, ovulation rate, embryo number at 25 days of gestation and embryo mortality were unaffected by treatment.

In-lamb ewes were given 38, 58 and 82 g of digestible crude protein daily at a constant energy intake of 1600 kcal ME per head daily during the last 6 weeks of gestation. There were no significant differences between treatments in live-weight gain of the ewes, lamb birth weight or ewe net body-weight change (the difference between live-weight gain over the experimental period and live-weight loss at lambing).

Digestibility coefficients for the diet components and nitrogen balances were determined on three ewes per treatment during weeks 15-16 and 19·20 of gestation. No differences in the apparent digestibility of the diet components were observed between the two periods. The apparent digestibility of crude protein increased significantly (P > 0·001) with increase in crude protein intake. A significant linear relationship (P<0·01) was found between digestible crude protein intake and nitrogen retention; daily N retention increased by 0·19 g per kg W0·73 for every 1 g per kg W0·73 of apparent digested nitrogen intake per day.

Several groups of eight fattening (18 kg to 91 kg) Large White pigs containing both immature female and castrated male animals were established, were fed twice a day on a commercial dry ration, were observed at feeding time and their social orders (linear dominance hierarchy) worked out. Individual pigs were removed, one at a time, from different places in the social order, isolated for varying periods of time, and then replaced in their groups. It was found that the removal of a pig from any rank in the dominance order altered neither the basic social hierarchy nor the amount of aggression within the remainder of the group. The duration of time that an animal could be removed, isolated and returned without being attacked by the rest of its group varied with its social rank. Top-ranking animals could be safely returned even after 25 days' isolation, but lowranking animals were severely attacked after only 3 days' absence.