When testing facilities are limited and the number of breeds and/or crosses to be tested is potentially large, then multibreed designs which involve a large number of breeds with only a few animals per breed give the optimum allocation of animals within and between breeds for various objectives. Multibreed designs could therefore form a useful adjunct to existing breed testing and selection programmes. How far such designs should be introduced would depend, among other things, on the degree of confidence in existing information, on the success of existing testing schemes, and on the relevance of the selection criteria currently being used. In this, the first of a series of papers on multibreed designs, the general approach is outlined, and designs for measuring between-breed variation are considered.

To estimate the extent of between-breed variation, the best overall design is to have four unrelated animals per breed and as large a number of breeds as possible. Valuable experimental work on breed variation can therefore be done without vast facilities.

An analysis is undertaken of the effect of errors in estimates of parameters on the response to selection for an economically important trait (trait 1) when one or more additional traits are added in a selection index. The detailed analysis is confined to one additional trait (trait 2) which contributes useful information unless the genetic and phenotypic regressions of trait 1 on trait 2 are equal.

If there are errors in parameter estimates the extra response obtained by including trait 2 will usually be over-predicted. When trait 2 actually contributes no useful information the predicted benefit equals the real loss in efficiency from its inclusion.

The loss in efficiency from poor estimation of parameters, whether or not the second trait makes a contribution, is roughly one-quarter of the squared coefficient of variation of a heritability estimate of trait 1 in the same experiment.

Sheep from the Soay, Finnish Landrace, Southdown and Oxford Down breeds were serially slaughtered at about 40, 50, 60 and 70% of their estimated mature body weight. Breed and sex comparisons were made at these degrees of maturity. Large differences were found in the weight of muscle, fat and bone, total muscle ranging from a mean of 3·3 kg in the Soay to 13·0 kg in the Oxford Down; the corresponding range for dissected fat was 1·2 to 9·2 kg.

Most of the breed and sex differences observed at the same degree of maturity disappeared when expressed as a percentage of body or carcass weight. Thus both sexes had almost the same body and carcass composition in terms of fat, muscle and bone percentage. There were breed differences in fat percentage, with the Soay significantly less fat than the other breeds. Total muscle as a percentage of body weight was remarkably close to 28·5% in all breeds in both sexes, and at all four stages of maturity.

The relationship between two methods of sire evaluation (Bar-Anan and Sacks's cumulative difference method (CD) and Henderson's best linear unbiased predictor method (BLUP)) is shown. This relationship suggests a modification, with more theoretical justification, to the CD method.

Optimal designs are given for estimating some of the genetic parameters needed to describe a population of breeds when testing facilities are limited and the number of breeds to be tested is potentially large. The best design for estimating the relative proportion of genetic variation within and between breeds is to have a large number of breeds, a few sires per breed, and a few offspring per sire, the total number of animals per breed being of the order of 10 to 20.

Records from a selection flock of Galway ewes collected over a 6-yr period (1966 to 1971) were used to obtain estimates of the phenotypic and genetic parameters of ewe productivity. The number of lambs born (NLB) and weaned (NLW), the weight of lamb weaned (WLW), ewe body weight (EBW) and greasy fleece weight (GFL) were used as measures of productivity, mean values being 1·25, 0·88, 25·6 kg, 52·8 kg and 2·8 kg, respectively. Each ewe's annual performance was adjusted to a 4-yr-old ewe equivalent and expressed as a deviation from the appropriate flock × year subgroup mean; these deviations were combined into a single index value for each ewe for NLB, NLW and WLW. Records for 975 individual ewes representing 84 sires which had three or more progeny were used in a half sib analysis of variance.

Estimates of heritability were 0·18, 0·24 and 0·25 for NLB, NLW and WLW based on index record and 0·07, 0·16 and 0·30 respectively for 2-yr-old ewes. Heritability estimates of EBW and GFL were 0·73 and 0·52 respectively. The genetic correlations between EBW and NLB2, NLW2, WLW2 and GFL were 0·85, 0·42, 0·62 and 0·53 respectively; those between EBW and index records were slightly negative. Phenotypic correlations were generally lower than the corresponding genetic ones.

Ewes born as multiples were more productive than singles. They were 1·8 kg lighter (P < 0·01) at 18 mo and weaned 2·5 kg more lamb (P < 0·05) at 2 yr of age. The repeatability of NLB ranged from 0 to 0·2.

Dissection data from 643 carcasses of castrated male cattle (steers) of 15 breed-type × feeding system groups were used to examine the distribution of total fat (TF) between subcutaneous (SF), intermuscular (IF), kidney knob and channel (KKCF) and cod fat depots. The breed-type groups, which were from cereal or grass/cereal feeding systems, included Ayrshire, Simmental × Ayrshire, British Friesian and Friesian crosses with Aberdeen Angus, Hereford, Limousin, Charolais, South Devon and Simmental. Means for percentage TF in side ranged from 21·4 to 36·2 with a pooled within group SD of 3·87.

The growth of each depot relative to TF was examined using the allometric equation. Significant but not large differences existed between groups for the growth coefficients of SF and IF while the coefficients for KKCF differed widely among groups. The coefficient for SF was greater than that for IF in every group (pooled within-group b values±SE were 1·20±·02 and 0·87±0·01 respectively).

At constant TF weight, carcasses from Ayrshire and Ayrshire crosses tended to contain less SF and more IF+KKC F than those from Friesian and beef breed × Friesian. Important differences in distribution were recorded between the various beef breed × Friesian groups. The proportion of SF was lower for cattle fed on grass/cereal diets than for cattle of the same breed type fed on cereal diets.

The differences in fat distribution led to substantial bias for some groups when the percentages of IF and TF in the side were predicted from percentage SF. The bias was less when both KKCF and SF were used as predictors.

The susceptibility of whole and rolled cereal and legume seeds to microbial attack within the rumen of cows was examined by incubating seeds in nylon bags in the rumen for 24,48 and 72 hr. With whole, intact seeds the husked cereal grains were less susceptible than naked grains and legume seeds. Inter-varietal differences were observed with maize, oats and barley. Breaking the cereal grains before incubation considerably increased the losses of dry matter. Digestibility trials with non-lactating cows confirmed that barley, sorghum, wheat and oats were poorly digested when given whole, and considerable variation was recorded between individual cows in their ability to digest whole grains. Rolling the grains before feeding made the greatest improvement in digestibility with sorghum, wheat and barley and the least with oats.

1. Weaned single-suckled calves (castrates) were housed at 260·7 kg live weight. Six genotypes, all two- or three-way crossbreds, were represented. A diet of bruised barley, wet distiller's grains, swedes and grass silage was offered until the required minimum live weight (363 kg) and body composition was reached. The cattle were then slaughtered (treatment A), or retained for 8 (treatment B) or 16 weeks (treatment C). During the period when treatment B and C animals were retained their diet was 53% bruised barley and 47% wet distiller's grains offered ad libitum.

2. Live weights at slaughter were 418·2, 458·6 and 496·1 kg (P < 0·001), carcass weights 240·5, 266·2 and 295·7 kg (P < 0·001), and killing-out percentages 57·5, 58·1 and 59·6 (P<0·01) for treatments A, B and C respectively. Daily live-weight gain did not decline during the 8 or 16 weeks cattle were retained on treatments B and C.

3. Retaining the cattle to slaughter points B and C caused increases in the percentage of low-value joints in the carcass, carcass fat percentage, dry matter and fat contents of the dissected m. longissimus dorsi; and decreases in the percentage of high-value joints, carcass lean and bone percentage, crude protein and ash contents of m. longissimus dorsi. The carcass composition was 55·6, 53·5 and 51·4% lean (P<0·001); 30·7, 33·3 and 36·2% fat (P<0·001); 13·7, 13·2 and 12·4% bone (P< 0·001) for treatments A, B and C respectively.

4. The results are discussed in relation to the choice made by beef producers between slaughter and retention of cattle which have reached suitable live weight and condition for marketing.

The nutritional value of a pelleted fattening concentrate mixture, in which heat-sterilized poultry litter (PL) was included at rates of 0, 15, 25 and 35%, was studied. A digestion and nitrogen balance trial was carried out with rams, and a feeding trial was carried out with intact male cattle from the age of 8 mo to slaughter at 14 mo.

Digestibility of crude protein was related inversely to PL content of the diet. This decrease in digestibility was not accompanied by a decrease in the quality of the protein digested.

Gross and digestible energy contents of the diets were related inversely to their PL content. There were no significant differences in blood urea concentration. A concentrate mixture containing 1% urea but otherwise similar to the control, was included in the feeding trial.

There were no significant differences in rate of live-weight or carcass gain between treatments. The differences in degree of fatness of the carcasses tended to be related inversely to PL% in the diet, but they were small and reached significance only with the extreme treatments. Feed intake on PL-containing diets was higher than on the control diet, but feed conversion efficiency was impaired when the proportion of PL exceeded 25%. No significant correlations were found between total volatile fatty acids in rumen liquor and daily live-weight gain.

1. Two series of energy balance trials were conducted with British Friesian veal calves. In the first, calves were given a milk replacer diet at three different planes of nutrition. In the second, calves were raised from about 80 to 180 kg at four air temperatures, 5°, 10°, 15° and 20°.

2. The net efficiency of utilization of the milk replacer diet for growth was 0·72. The effect of body size on heat production in growing calves was best expressed by an exponent of body weight slightly but not significantly below W0·75.

3. Measurements of heat production estimated from respiratory exchange and heat loss measured by direct calorimetry agreed exactly at all planes of nutrition. Heat production at zero energy retention was 675 kJ/kg W0·75 per 24 hr.

4. Average daily live-weight gain and total heat loss were the same at all air temperatures. Changes during growth in the partition of heat loss into its sensible and evaporative components indicated that calves acclimated progressively to the air temperatures to which they were exposed.

1. Fifty-four weaned single-suckled steer calves aged 11 to 14 mo were individually fed 2 kg wet distiller's grains, 10 kg swedes and an average of 11·5 kg grass silage daily. The quantity of silage offered was adjusted during the experiment in accordance with a live weight related scale. There were six treatments differing in the physical form, moisture content and level of barley grain offered. A nil barley supplement was compared with 2·5 kg barley dry matter daily offered either whole or bruised having been prepared for storage by drying (84·6% DM) and by treatment with propionic acid (79·9% DM); dried barley was also offered whole (at approximately 50% DM) after soaking in water for 24 hr. Each replicate of six cattle, one animal from each treatment, was slaughtered when all its members were subjectively estimated to have the required minimum body condition and minimum estimated carcass weight (186 kg) for marketing.

2. A supplement of barley grain caused increases in daily live-weight gain, slaughter weight, carcass weight and carcass fat content; and reduced carcass lean and bone content. These effects were increased if the barley grain was processed by bruising compared to being consumed unprocessed (whole). There was no indication that the method of preparation for storage or the moisture content of the barley grain when consumed affected the results of the experiment. It was concluded that the costs of processing barley grain by bruising for feeding to growing cattle for slaughter will be exceeded by the value of the additional animal performance obtained in comparison to feeding whole barley grain.

1. Eight British Friesian and eight Jersey calves were fed fresh milk during the period from 3 days to 40 days of age, at two levels of feeding.

2. Energy and nitrogen balances were measured twice for each calf.

3. Fasting heat production (FHP) (MJ/day), which was measured on these occasions, was related to live weight (kg) by FHP = 0·435 W0·75. There was no significant difference in FHP/kg0·75 between the breeds but previous level of feeding and the duration of fast had significant effects.

4. The data for heat production, metabolizable energy (ME) intake and energy retention were interpreted to provide estimates of ‘true’ net energy required for maintenance of 0·23–0·27 MJ/kg0·75 daily.

5. Pooled values for ME required for maintenance and for the net efficiency of utilization of ME above maintenance were 0·39 or 0·42 MJ ME/kg0·75 daily, and 0·67 or 0·72 determined by simple or multiple regression techniques respectively; there were no significant differences between the breeds. Pooled values for the partial net efficiencies of utilization of ME for the synthesis of protein and fat were 0·54 and 0·79 respectively.

6. ME required above maintenance was estimated to be 11·3 and 13·6 MJ ME/kg of live-weight gain for the lower and higher rates of gain respectively.

7. A small experiment revealed no major differences between diets of milk alone or milk plus solid food, with regard to maintenance requirement or net efficiency of utilization of ME by calves.

The effects of diets containing variable percentages of roughage and moisture on depot fats were studied. Treatments were 25 and 45% roughage in the complete fattening diet, and 10, 50 and 75% moisture content of the diets. Depot fats collected post-slaughter from kidney, pelvic, ruminal, cod and trim fats in the carcass (mostly subcutaneous and some intermuscular) were weighed and analysed for their fatty acid composition.

Increasing the quantity of roughage in the diet (from 25 to 45%) significantly decreased ruminal fat deposition. Moistening the feed significantly increased the deposition of kidney, pelvic and cod fat, and significantly reduced the deposition of fat trim in the carcass. The content of unsaturated triglyceride fatty acids was significantly greater in calves fed on the 25% roughage diet. Calves fed on the soaked diets had significantly higher contents of unsaturated fatty acids than the controls.

The content of unsaturated acids was greater in cod fat and carcass trim than in kidney, pelvic or ruminal fat.

Hydrogenation in vitro of fatty acids by ruminal micro-organisms decreased with increasing level of moisture in the diet.

It is suggested that the increased unsaturated fatty acid content of the depot fats of animals fed on soaked diets might be due to a reduction in the hydrogenation of dietary lipid by rumen micro-organisms.

1. Hereford × British Friesian castrate male cattle, growing from about 80 to 500 kg, were given equal amounts of metabolizable energy (ME) from dried grass pellets or from a pelleted diet of barley and a protein supplement. Two animals on each diet were fed close to appetite (High) and two at a level mid-way between maintenance and appetite (Medium). The rations for all animals were reduced to approximately maintenance for 4 weeks on three occasions equally spaced throughout the experiment. Measurements of energy and nitrogen balance were made for each animal at intervals of 6 to 8 weeks. Total body-water content was estimated from D20 dilution at intervals of 110 kg live weight.

2. Values for the metabolizability of the gross energy of the dried grass and barley/protein diets were 0·55 and 0·67.

3. Metabolic heat production during growth was closely related to body weight to the power 0·75. Predicted basal metabolism was 395 kJ/kg 0·75 per 24 hr.

4. Estimates of the net efficiency of utilization of ME for growth were unaffected by small variations in the exponent of W used to describe the effect of body size on heat production. Both diets were utilized above maintenance with a net efficiency close to 0·62.

5. Nitrogen balance trials seriously overestimated nitrogen retention. Gains in fat-free body mass estimated from D2O dilution were combined with calorimetric measurements of energy retention to predict the relationship between energy retention and weight gain. The agreement between observed and predicted live-weight gain was good at the lower body weights and on the lower ration. For fatter animals eating the high ration at higher body weights, live-weight gains were less than predicted.

Thirty-six British Friesian entire male calves were reared from 100 kg live weight (LW) to slaughter at 450 kg LW. They were offered maize silage ad libitum plus supplements of minerals and a protein concentrate or urea in three treatment diets: protein concentrate (P), urea (U) and (P/U) in which protein and urea each provided 50% of the supplementary N up to 200 kg LW followed by urea alone. Levels of N × 6·25 in the diet dry matter (DM) were 16% from 100 to 200 kg LW, 14% from 200 kg to 300 kg, and 12% thereafter. Barley was given to all the cattle over 12 mo of age at 1% of LW daily.

Live-weight gain in the 280-day period prior to the introduction of barley averaged 899, 684 and 580 (±31·0) g/day for P, P/U and U, respectively, and was greater for P than for the other two treatments (P<0·05). After the introduction of barley, gains were similar between treatments, averaging 1275, 1333 and 1270 (±43·2) g/day, resulting in mean ages at slaughter of 15, 16·5 and 17 mo for P, P/U and U, respectively.

Substitution of protein concentrate by urea was reflected in a reduced content of metabolizable energy (ME) in the diet and a reduced intake of DM and ME in period 1. Although the contents of ME in the diets were similar in period 2, when barley was given to the cattle, there was little evidence of compensatory growth in treatment P/U and U compared with treatment P. Live-weight gains predicted from ME intake showed good agreement with actual gains. However, reduced intakes and gains by treatments P/U and U compared with treatment P meant that the target weight and age at slaughter of 450 kg and 15 mo of age was met only by treatment P. For the complete system the cattle consumed an average of 2·3 t DM per head of which maize silage DM comprised 78%. Efficiency of feed use averaged 15·5 kg live-weight gain per 100 kg total DM eaten.

1. Three pure breeds, Aberdeen-Angus (AA), Ayrshire (AYR) and British Friesian (FR), and three crossbreds, Aberdeen-Angus × Ayrshire (AA × AYR), Aberdeen-Angus × British Friesian (AA × FR) and British Friesian × Ayrshire (FR × AYR) were studied. Each breed type was represented by 12 male castrates which were the progeny of at least seven sires in each case.

2. The purebred cattle of dairy type (FR and AYR) were faster growing (P < 0·001), heavier at slaughter (P < 0·001) and produced heavier carcasses (P < 0·001) than the pure beef breed. There were no significant differences between the breeds in the lean contents of their carcasses and there was no indication of any systematic breed effect on the distribution of lean within the carcass. The AA had carcasses with a higher fat content (P < 0·05), a lower bone content (P < 0·001) and a higher lean:bone ratio (P < 0·001) than the FR and AYR.

3. In general the values for performance and carcass data of the crosses between the three purebreeds fall mid-way between their parent values or do not differ significantly from this value. The hypothesis that crossbred cattle produce carcasses with higher muscle: bone ratios than purebred cattle is refuted by these data.

Components of reproductive efficiency of Zebu-type and Charolais × Zebu-type (1/2, 3/4 and 7/8) females were compared. Zebus had longer mean intervals from calving to first service (57·8 days) and from calving to conception (46·0 days). Least squares means for both traits were respectively 129·8 and 145·1 days. Correspondingly, in the Charolais cross group 26·4% more cows were detected in oestrus within 180 days of calving, and 31·4% more conceived in the same period. Least squares means for these traits were respectively 80·7 and 50·5%.

No significant differences were found between the two breeding types either in number of services per conception or in the percentage conceiving by artificial insemination (of those showing oestrus) both for lactating and dry females. A higher percentage of oestrus cycles of normal duration was found in Charolais cross (72·9 %) than in Zebus (63·1%). Gestation lengths of Zebus (Indu-Brasil sires) and Charolais cross (Charolais and Simmental sires) were respectively 288·8 and 283·1 days.

The main difference between breed types was the longer lactation anoestrus shown by Zebus. These were very sensitive to seasonal effects, showing a cyclical time trend with peaks of shorter anoestrous periods for cows calving in January–February–March, and longer ones for cows calving in July–August–September. Related traits followed parallel cycles. Charolais cross cows showed less variation than Zebus.

Thirty-nine British Friesian lactating cows were used to study the effects on milk production of supplementation of maize silage offered ad libitum during two 3-hr periods each day. During weeks 11 to 24 of lactation a comparison was made of (i) no supplement, (ii) 183 g/day of a mixture (2: 1) of urea: urea phosphate, (iii) 5 kg/day of barley plus 183 g/day of the urea: urea phosphate mixture, (iv) 7 kg/day of dried grass and (v) 10 kg/day of dried grass. The corresponding treatment mean values were: milk yield (kg/day), 10·0, 9·9, 13·4, 15·1, 16·8; fat content (%), 3·43, 3·80, 3·98, 3·92, 3·61; solids-not-fat content (%), 7·95, 8·03, 8·45, 8·51, 8·49; energy intake (MJ/day), 71·2, 76·9, 130·3, 132·7, 138·6; intake of dry matter as maize silage (kg/cow per day), 7·1, 7·7, 8·3, 7·7, 6·5. With the exception of fat content, the differences between treatments 1 and 2 were not significant but the values for these two treatments were significantly lower than those for the other three treatments.

A technique for evaluating beef carcasses in terms of their retail value, has been applied to 132 half-carcasses from seven groups of cattle (Jersey, Hereford, Polled Hereford, Lincoln Red, Devon, South Devon and Charolais × Jersey) to test the general applicability of the method, in particular the regression equations for predicting retail value. Significant differences in retail value were found between the groups of animals, South Devon and Charolais × Jersey having a high retail value per kg side weight, and Jerseys a low one. There was a very high correlation between retail value per kg side weight and the proportion of muscle in the side. Relationships between retail value and proportion of fat in the side were also investigated. It is not possible to decide, from these data, whether the differences found in retail value are a true breed effect, or whether they are due solely to differences in composition.