The present value of future genetic improvement in a closed population is taken to be proportional to the sum of discounted changes in the population mean. It is shown that, if T animals are available for selection and R is the discount rate per generation, the selection intensity which maximizes present value is a function of TR. If TR is greater than 15, under 10% of the population should be selected. It is then shown how T can be chosen to maximize profit if the value of genetic improvement and cost of testing are known. The theory is illustrated by a numerical example.

A method of selection for two or more traits is investigated, where the selected individuals have to be the highest performing for any one trait, but not necessarily for several traits. The efficiency of selection of extremes is contrasted with the methods of culling levels and tandem selection. It is shown to be superior to culling level selection when the proportion of individuals retained for breeding exceeds 0·5. At higher selection intensities, the effectiveness of selection of extremes falls between that of culling levels and tandem selection.

Based on the Agricultural Research Council's feeding system, equations were developed that allow the calculation of the metabolizable energy requirements for maintenance and weight gain by cattle, separately or combined. A general equation was developed for the straight-forward calculation of the total metabolizable energy requirements of growing and fattening cattle for any combination of body weight, rate of weight gain, age, level of muscular work, and metabolizable energy concentration of the diet. The estimates of energy requirement made by the use of this equation are in excellent agreement with those made by the Agricultural Research Council using an iterative method.

In addition to avoiding the awkward iterative process, the equations proposed are readily adaptable to computer use.

A study was made of the chemical composition and energy value of the whole, empty body, and of the relative size of certain organs in 11 ponies ranging in full-body weight from 81 to 259 kg. The fatty acid composition of various adipose tissues was examined in three ponies.

Ingesta-free body weight (Y) was found to be highly predictively related (r2 = 0·) to the full-body weight (X) in accordance with the equation, Y = 0·9678X–10·41. The gastrointestinal contents constituted 9·65 ± 3·44% of the full-body weight.

Despite the heterogeneous nature of the population examined and the small range in body fatness (6·6% to 18·9% of ether-extractable lipids in the empty body), 93·3 % of the variation in the concentration of body fat was associated with the variation in the concentration of water. The mean fat-free, empty body contained 70·7 % of water, 22·6 % of protein and 6·0 % of ash. Of the variation in the weights of water, fat, protein, ash and energy, 97·0%, 64·5%, 91·0%, 85·2% and 87·0%, respectively, were ascribable to the variation in empty-body weight.

For the conglomerate body, the calorific values of protein and fat were 5·381 and 9·311 kcal/g, respectively.

The ranges for the mean percentage contents of major individual acids in the fatty acids of five adipose tissues were: oleic, 29·5–33·3; palmitic, 26·1–28·0; linoleic, 17·1–24·0; palmitoleic, 6·2–9·5; and linolenic, 3·8–10·2. In one animal the depot fats contained relatively high concentrations (8·6–12·0 %) of linolenic acid; the concentrations of palmitic and linoleic acids were correspondingly lower than those of the depot fats of the other horses.

Tissue weights of various segments of the gastrointestinal tract were linear functions of body weight. About 87 % and 82 % of the variation in the weights of liver and kidneys respectively, was associated with the variation in full-body weight.

Sixty gilts by Landrace sires out of Large White × Landrace females were allocated on the basis of litter relationship and initial weight to six treatments involving the individual feeding of six dietary protein levels, 15·5%, 17·4%, 20·2%, 22·3%, 25·3% and 27·3% crude protein (CP), at a common energy level of approximately 3500 kcal/kg DE, from 23 to 59 kg live weight. Amino acid balance was maintained relatively constant with synthetic lysine, methionine and tryptophan. There were significant increases in growth rate and efficiency of feed conversion from the 15·5% to the 17·4% CP diets and significant reductions in both from the 25·3 % to the 27·3 % CP diets. Carcass lean by dissection increased linearly (r = 0·976) and fat decreased linearly (r = −0·992) with dietary protein increment over the full range studied. As best growth performance and maximum lean content were attained at different dietary CP levels, a combined measure of daily lean deposition was calculated; this indicated that maximum rate of lean growth and efficiency of feed conversion to lean were reached on the 22·3% CP level. In terms of efficiency of utilization of nutrients, maximum retentions of both DE and DCP in the edible part of the carcass appeared to be attained on the two lowest dietary protein levels.

Forty-eight gilts by Landrace sires on Large White × Landrace females were randomly allocated to eight pens and within pens to six treatment groups involving three diets and two levels of feeding from 23 to 59 kg live weight. All diets were formulated to have approximately the same ratio of digestible energy to crude protein (160 kcal DE/unit % CP) but different energy and protein concentrations: (A) 3500 kcal/kg DE and 21 % CP, (B) 3150 kcal/kg DE and 19% CP, and (C) 2800 kcal/kg DE and 17% CP. Amino acid balance was maintained relatively constant with synthetic lysine, methionine and tryptophan. The levels of feeding were such that the lower level of diet A allowed an intake of energy and protein similar to the higher level of diet B, and the lower level of B was similar to the higher level of C.

On the lower level of feeding, growth rate, efficiency of feed conversion and carcass fat content increased linearly with each increment in nutrient concentration; on the higher level of feeding growth rate and EFC increased from diet C to B but not from B to A, whereas carcass fat content increased linearly with diet from the lowest to the highest concentration. There was a non-significant tendency for the higher density diets at a similar level of nutrient intake to give better EFC and fatter carcasses than the lower density diets.

Feeding trials were carried out at different times of the year to determine the optimum crude protein requirements of weaner and growing pigs, using principally the locally available ingredients. The animals used were 96 weaners and 113 growing pigs of the Large White and Landrace breeds of average initial weights of about 9 kg and 41 kg respectively. Test diets contained protein levels ranging from 12% to 24% on a dry-matter basis, and the pigs were mostly group-fed ad libitum except for one trial. Average daily gains, efficiency of feed utilization, apparent nitrogen retention and digestibility, and feed cost per kg of body gain were measured. In a humid tropical environment, such as Ibadan, the optimum crude protein requirement for weaner pigs from 9 kg to 34 kg live weight is between 22 % and 24 % of dry matter, while that for the fattening pigs from 41 kg to 82 kg live weight is between 18% and 21% of dry matter.

Two experiments were conducted to compare the milk-producing value of dried forages in the form of cobs and pellets as replacements for a standard dairy concentrate. Four levels (0·33, 0·44, 0·55 and 0·66 kg/kg milk) of dried forage or standard dairy concentrate were offered in addition to a basal ration of 6 kg hay and 2 kg standard dairy concentrate. In both experiments the rate of eating by the cows of cobs was significantly slower (P<0·05) than that of pellets. No significant difference was found between the cobs and pellets in either experiment in their value for milk production. In Experiment 2 the standard dairy concentrate had a non-significantly higher (P>0·05) milk-producing value than the dried lucerne. Level of feeding had a significant positive effect on the milk yield (P< 0·001) of cows offered the dried grass and lucerne and on the milk solids- not-fat content (P<0·05) and live weight (P<0·01) of cows offered the dried grass, lucerne and standard dairy concentrate.

1. For four consecutive years, each one of four herds of 13 cows and calves grazed land stocked and fertilized at one of the following combinations of rates (ha/cow, kg N/ha): 0·61, 82; 0·51, 82; 0·51,203 and 0·40, 203.

2. The Devon and Devon × British Friesian cows present in each herd reared calves by Devon bulls. Calving occurred indoors over the period February to April, the cows having been housed in early December.

3. Live-weight gains of calves to weaning in mid-October did not differ between herds in any year. Live-weight increase of cows over the grazing season was similar and substantial in all herds. On average pure-bred calves were 25 kg lighter at weaning than the cross-bred calves.

4. The main difference between treatments was in quantity of grass conserved and it was only in the herd kept at 0·51 ha/cow, 203 kg N/ha that enough was made to supply all the energy needs of the herd for a 150-day winter.

5. Gross margins/ha were greatest at the higher rate of nitrogen application but no further improvement was evident at the maximum stocking rate. The importance of maximizing output/animal is discussed.

Grazing and stall-feeding experiments were conducted to examine the effect of giving different amounts of cereal-protein concentrate with grass on the live-weight gain of cattle initially 6 months of age. The effect of level of concentrate on grass intake was also studied in the indoor trial. Experiment 1 took place at pasture, with two stocking rates (high and low) and three levels of supplementation at each stocking rate. The response to supplementation, and rate of live-weight gain by the unsupplemented groups was similar at both stocking rates for a 101-day period from late April to mid-August. The results are discussed in relation to other pasture supplementation experiments, and to those obtained in the indoor experiment. Experiment 2 (stall-feeding) consisted of five levels of concentrate feeding from zero to 100% of the diet. There was little increase in total intake as the proportion of concentrate in the diet increased, and the relationship between grass intake and concentrate intake was rectilinear.

Gut fill estimates are presented for each level of concentrate feeding, and results for empty body-weight gain are discussed in relation to live-weight gains. There was a linear increase in weight gain with increasing proportion of concentrate in the diet. Empty body-weight gain is recommended as a less biased assessment of the response of cattle to concentrates given with pasture or forages.

Three experiments were conducted to compare the performance of 9-month-old Friesian steers wintered in three environments, (a) conventional cattle houses, (b) wind-sheltered roofless sawdust pads and (c) unsheltered roofless sawdust pads. Within each environment animals were fed on two planes of nutrition.

In each experiment, winter live-weight gains of animals accommodated on the three winter environments were similar as were weight changes during the subsequent four weeks at grass in Experiments 2 and 3.

No interaction on live-weight gain was found between plane of nutrition and winter environment. Health of outwintered animals was good throughout. The response to feeding barley with hay in these experiments (obtained by comparing low-plane with high-plane treatment groups) showed that on average 5·5 kg of barley dry matter were required to produce 1 kg of additional live-weight gain above that obtained from hay fed alone.

Live-weight gains of two groups of 9-month-old Hereford × Shorthorn steers wintered in either roofless cubicles or indoor cubicles were compared during the winter of 1968/69, and during a subsequent 29 days at pasture. The animals were fed 1·82 kg concentrates per head daily and both treatment groups received equal quantities of silage.

No significant difference was found between treatments in winter live-weight gains or subsequent weight changes at pasture. The health of all animals was excellent throughout.

Field beans were compared with fish meal and soya bean meal as a protein source for young calves, and the effect of processing beans and barley on the digestibility of the diet was measured with older, castrated male cattle.

In calves given equal nitrogen intakes, apparent nitrogen digestibility was lower with field beans than with soya bean meal or white-fish meal, but nitrogen retention (g/day and percentage of intake) in calves given beans was between that obtained with fish meal and soya bean meal. The dry-matter digestibility of diets containing 20 % whole or rolled beans together with rolled barley was 80 % but fell to 74 % if the barley was given whole.

Thirty-four pregnant Shorthorn cows were fed during the winter either grass silage from first crop material or rapeseed silage, both low in selenium content (less than 33 nanogram/g DM). Serum glutamic oxalacetic transaminase (SGOT) determinations were performed before and after the calves went to the pasture. There was no evidence either clinically, biochemically (SGOT) or at post-mortem examination, of any nutritional muscular dystrophy (NMD) disorder in the 34 calves, despite very low plasma selenium levels (4 to 5 ng/ml plasma).

An implantation technique using a slow-release selenium pellet also was evaluated as a means of controlling the disease. Fifteen calves from a total of 33 calves born to cows given a dystrophy-producing hay during the winter, were implanted a few days after birth with a pellet containing 15 mg of selenium. Four out of 18 calves in the control group showed clinical symptoms of NMD and two died with NMD lesions. SGOT levels in the implanted calves were normal during the experiment and none was affected by NMD. Plasma selenium levels in the implanted calves were significantly higher than in the deficient controls at each sampling period, but within normal ranges previously reported.

Data on the protein content of the empty body were obtained for 44 young Polish Black-and-White Lowland bulls ranging from 10-day- old calves to bulls more than 400 kg live weight. The percentage of protein of the empty body was found to be practically constant (19–19·5%) over the weight range investigated. Less than a half (up to 48 %) of the total protein content was found in the edible parts of the carcass.

Records on lamb survival were available for 757 lambs, the progeny of 33 rams. Purebred lambs were of the Nali and Lohi breeds and crossbred lambs were produced by mating Nali ewes to Nellore or Mandya rams, and Lohi ewes to Nellore rams. For the flock as a whole 93% of those born survived to 14 days of age and 86% to weaning. A least-squares analysis of variance showed that among the factors investigated only lamb's weight at birth significantly affected survival to 14 days of age, and lamb's weight at birth, ewe's weight at lambing and the year of birth had significant effects on lamb survival from 15 days to weaning. Heritability estimates for lamb survival were based on half sib correlations. For the period from birth to 14 days of age the estimates were 0·08 for pure Nali lambs and 0·03 for the whole flock, and for the period from 15 days to weaning the estimates were 0·10 and 0·26 for the two groups respectively.

Eighty pregnant ewes, housed in December approximately 14 weeks before lambing, were offered grass silage to appetite. The factors considered were breed (Greyface or North Country Cheviot), concentrate level during the final 7 weeks of pregnancy (‘normal’ or ‘high’) and clipping (clipped at housing or left undipped at housing). Silage intakes were affected by level of concentrate supplementation, the higher level tending to reduce intakes during the final weeks of pregnancy but no effect of clipping on silage intakes was detected. Level of concentrate had no effect on lambing performance, but ewes clipped at housing produced lambs which were 1 kg heavier (P<0·05) at birth than lambs from undipped ewes. Time of clipping had a significant effect on wool yields but no effect on wool grades.

The fatness of 34 non-pregnant Scottish Blackface ewes was estimated subjectively by lumbar palpation. The sheep were separated into groups of ‘fat’ (more than 27 % body fat) and ‘thin’ animals (less than 20% body fat). The voluntary intake of dried grass by these sheep was measured over a 6-week period.

The mean daily dry-matter intake by the thin sheep was 1·9 kg or 106 g/kg W0·73 and by the fat sheep was 1·4 kg or 68 g/kg W0·73.