Twenty-seven castrate male cattle were used in two nutritional balance and slaughter experiments to measure the effects of increasing levels of dietary protein (9 to 15% in the dry matter) at two levels of feeding (approximately 16 and 22 MJ metabolizable energy (ME)/100 kg live weight (LW) per day) on digestibility, nitrogen (N) balance and carcass growth and composition over the LW range 130 to 390 kg.

The higher level of feeding increased LW gain and carcass gain (CG) but higher protein intake increased LW gain and CG only at the higher feeding level as a result of its favourable effect on digestibility. N balance tended to overestimate carcass N retention at higher levels of protein intake.

The higher level of feeding increased the separable fat and total fat in the carcass. Increased protein intake had no effect on the lean meat content but increased the percentage protein in the edible portion of the carcass. LW gain, CG and carcass energy deposition were related to ME intake only but N balance and carcass protein gain were related to both ME and digestible crude protein intake.

Carcass composition and growth patterns for muscle, fat and bone were compared among 277 young male progeny of eight sire breeds, serially slaughtered at 300 kg live weight, 12 months and 15 months of age. The sire breeds were Simmental (SIM), Charolais (CHA), Danish Red and White (DRK), Romagnola (ROM), Chianina (CHI), Hereford (HER), Blonde d'Aquitaine (BDA) and Limousin (LIM). Tissue growth patterns among breeds were examined by regression estimates from the allometric growth equation (Y = axb) and compositional differences were estimated from the intercepts. No significant sire breed differences were found in the regression of muscle, fat or bone on various size dimensions. In regressions involving fat, however, the fattest (HER) had higher regressions and the leanest (BDA) fattened more slowly relative to muscle and bone growth. Breeds differed significantly in amount of muscle, fat and bone when compared at standard weights.

Sire breed ranking for muscle at common bone weights was LIM, BDA, CHA, SIM, HER, ROM, DRK and CHI, while at common carcass weights the ranking was BDA, CHA, LIM, CHI, ROM, SIM, DRK and HER, reflecting differences in fatness. Minor changes in ranking occurred when comparisons were made at a common live weight reflecting differences in dressing percentage. For fat at standard muscle, carcass or live weight the breeds ranked HER, LIM, DRK, SIM, ROM, CHA, CHI and BDA.

Starlings had free access to cattle food placed in open troughs in a calf yard. During the winters 1974/75, 1975/76 and 1976/77 birds took 1·49, 1·70 and 1·991 of calf food respectively, this ranging from 6·4 to 12·4% of the food given to the calves. These losses were eliminated using enclosures made of Terylene netting or PVC strips. Both enclosures kept starlings out of the yard: the latter was more manageable to farm staff, and calves within grew significantly faster than controls, probably due to a combination of the absence of bird competition for food and the elevated temperature within the enclosed area.

Designs of open nucleus breeding schemes, which comprise a nucleus having the best males and females and a base comprising the remainder, with some base-born individuals used in the nucleus and vice versa, are studied.

Steady-state genetic responses, optimum transfer rates between nucleus and base in both sexes, and genetic differences between nucleus and base are estimated for a range of age structures, selection either within or among age groups (selection methods), nucleus sizes, mating ratios, fertility rates and survival rates appropriate to sheep and cattle populations. With optimum transfer rates between layers maximum or near maximum genetic responses are obtained with nucleus sizes varying from 2 to 15% of the population. Optimum transfer rates are fairly stable for nucleus sizes larger than about 5% and where the same selection procedures are used in both layers. However, a small nucleus with more efficient age structures and selection procedures and more accurate selection than in the base is economically desirable, and then almost no base-born females should be selected as nucleus replacements and up to 70% of male replacements for the base should come from the base. Optimum age structures differed markedly between selection methods.

Although few ‘rules of thumb’ about optimum age structures and transfer rates are sufficiently robust to be widely recommended in commercial situations, the nucleus breeding system behaves according to a few basic principles that can be used to predict the direction if not the magnitude of effects of changes in structure.

Records of piglet mortality were taken on 775 first and 657 second litters farrowed at four locations and representing 28 combinations of two-breed crosses involving eight breeds. All the sows were mated to Poland China boars. Overall mortality was 18% of which 4·2% occurred at birth, 13·2% between birth and 21 days and 1·2% from 21 to 42 days. Landrace x Yorkshire dams had the lowest mortality rate (10·4%) followed by Duroc x Lacombe (12·3%) whereas the highest rate was found in the Hampshire x Lacombe sows (21·6%). Piglets with Tamworth and Yorkshire ancestry had the lowest mortality (16·2 and 16·7%) while those with Berkshire ancestry had the highest (20·0%). Mortality rate was slightly (2%) higher in first than in second parity litters, and highest in summer and similar in the three other seasons. Mortality rate was highest in very small and very large litters and among the lightest and the heaviest piglets. The results showed a linear relationship between mortality rate and homogeneity of piglet weights at birth within litter, mortality rising with the increase in intra-litter variation. The effect of sires on piglet mortality was significant in one, and non-significant in the three other locations.

Eight-hundred-and-fifty-two pigs were weaned at 5 weeks of age, and at an average weight of 8·5 kg were allocated in pens of 14 or 15 to diets having 13·6 or 14·6 MJ digestible energy (DE)/kg combined with 11·0 or 11·8 g lysine per kg.

Over a 5-week experimental period, pigs receiving the diet with the higher DE content had a lower daily feed intake, improved feed conversion efficiency (FCE) but a similar rate of gain to those getting less DE/kg. Efficiency of utilization of energy was poorer when DE content was higher.

Increasing lysine level increased daily feed intake and rate of gain while improving FCE. There were significant energy x lysine interactions. At the lower energy density, increasing the lysine level resulted in increased daily feed intakes whereas the reverse was the case at the higher energy density. Daily gain increased when lysine level was increased at the lower energy density but was unaffected at the higher density. Efficiency of energy utilization was improved by increasing lysine at the higher but not at the lower energy level.

Twenty-four Suffolk cross lambs, the progeny of three sires, were reared artificially under standardized conditions and slaughtered at 40 kg live weight.

The tritiated water technique as a means of estimating carcass composition in vivo was evaluated and carcass composition was established using both physical dissection and chemical analysis. Live-weight gain of the lambs from weaning was 389 g/day but the carcasses were lean. Dissected fat, lean and bone percentages were 20·5, 58·4 and 18·9 respectively. Differences between progeny groups were non-significant.

Fat percentage was the most variable body component, although lower than in many other reported studies. The CV for dissected fat was 15·2% and for chemically analysed fat 15·9%. The correlation between estimates for the two methods was high (r = 0·90) despite there being quantities of other constituents in the dissected fat. It was not possible to demonstrate any relationship between reciprocal of tritiated water count and fat percentage or any other measurement of the composition of the whole carcass. Other measurements made on the live animal, such as fasted live weight and ultrasonic determinations of fat thickness and area of m. longissimus dor si were also not related to carcass composition.

It is concluded that neither tritiated water count nor any of the other measurements of the live animal would be sufficiently accurate to be of value in performance testing.

Between July 1971 and June 1973 a flock of between 60 and 100 Finn-Dorset ewes were mated at 6-monthly intervals in July and January each year following oestrus synchronization. The conception rates at each mating were:

July 1971—51 from 67 mated (76%) using hand-mating with a follow-up of paddock mating (1 ram: 9 ewes);

January 1972—6 from 63 (10%) using artificial insemination only; July 1972—98 from 102 (97%) using paddock mating (1 ram: 10 ewes);

January 1973—28 from 80 (35%) using pen mating (1 ram: 10 ewes).

Satisfactory breeding performance was achieved at the July matings in both years, resulting in production of lambs for the early spring market. The very poor results of the January 1972 mating were associated with the problems of artificial insemination in the recently lambed ewe. The conception rate achieved at the January 1973 mating provided a clearer indication of the difficulty of achieving satisfactory remating within 40 days post partum, which is necessary to achieve a true 6-monthly lambing pattern.

The early initiation of the synchronization technique (7 days post partum) followed by mating only at the second oestrus in January 1973 appeared to offer some encouragement. While a number (48) of ewes were induced to lamb at least once at 6-monthly intervals, only one ewe lambed four times in 24 months.

Two hundred and thirteen Suffolk × (Cadzow Improver × Scottish Blackface) young female sheep were mated either after the natural occurrence of puberty or at 140, 182 and 224 days of age in Year 1 and 140 and 182 days of age in Year 2 after treatment with progestagen (MAP) and 750 i.u. PMS; 90 to 100% of sheep ovulated after hormone treatment. Few sheep were found with embryos or live lambs in Year 1, possibly because of inadequacies in artificial insemination. In Year 2, after natural mating, the incidences of cleaved ova, live embryos 26 days after mating and live lambs born were 82, 33 and 23% respectively for sheep mated at 140 days; 100, 31 and 23% respectively for sheep mated at 182 days; and 100, 62 and 31% respectively for sheep mated after puberty. The occurrence of a second post-treatment ovulation in sheep without embryos at 26 days increased with age at treatment.

Fifty-six young female Suffolk × (Cadzow Improver × Scottish Blackface) sheep were used in a 2 × 2 × 2 factorial experiment investigating: (i) change in daylength (constant C v. reduced R), (ii) level of feeding (to appetite, H, v. 75% of that allowance, L), and (iii) age at hormone treatment (20 v. 28 weeks). At the appropriate age, the sheep were treated with a progestagen (MAP) and 750 i.u. PMS, inseminated, and slaughtered 26 days later. In a second experiment, change in daylength and level of feeding only were investigated. Hormone treatment took place at 20 weeks of age. In both years, all sheep showed oestrous behaviour and ovulated. A greater number of sheep yielded embryos on C than on R treatments (P<0·05 in Year 2), but no effect of feed level or age was found. Of those sheep not yielding embryos, a greater number on R than on C treatments showed a second ovulation at 20 weeks but not at 28 weeks.

The coat of 16 Wiltshire × Wensleydale lambs was investigated and all were woolly, with no halo hairs on the back. The bulk of the coat consisted of curly-tip fibres, and most lambs had Valley (8) or Plain (6) fibre-type arrays, only two having Ravine arrays.

There was little difference in diameter between the primary and secondary fibres in the skin, and some evidence of ‘checking’ in the central primaries. The secondary/primary follicle ratio of 4·26 compared with a mid-parent value of 4·5. There was less latticed medullation in the crossbreds than in the Wiltshire.

The adult fleeces were visually similar to those of the Wensleydale and were intermediate in weight and staple length between the parent breeds. These findings could have practical application in the improvement of ‘hair’ sheep, in that a first cross with the Wensleydale would have a fleece of medium wool lacking hair or kemp.

Thirty-five Assaf intact male lambs were divided into three groups and offered an all-concentrate pelleted diet based on barley and maize and supplemented with either toasted soya bean meal, herring meal or toasted soya bean meal plus methionine to contain 20% crude protein. The live-weight gains to a slaughter weight of 57 kg were 425, 440 and 394 g/day, and the feed conversion ratios were 3·12, 3·07 and 3·38 kg dry matter/kg gain, respectively. It is concluded that, with toasted soya bean meal as the protein supplement, it is possible to obtain high growth rates that do not diifer significantly from those obtained with herring meal.

The results of studies into penial, scrotal and testicular development of Icelandic male lambs indicate relatively early attainment of physiological puberty. This stage of sexual maturity is generally reached by 4 months of age, with marked variation in both puberal age and body weight. Testicular and epididymal weights were more closely associated with body and carcass weights than with age of the lamb. It is a common practice to use Icelandic male lambs for breeding at 7 months of age.

Eight British Friesian bulls and eight steers were compared in terms of performance and levels of metabolites and hormones in circulating blood. Under conditions of generous nutrition the bulls grew significantly more quickly, exhibited a superior feed conversion efficiency and had lower levels of serum albumin and plasma urea and higher levels of serum growth hormone and prolactin than the steers. Differences in levels of plasma glucose and free fatty acids and serum total protein and insulin were not significant. It is suggested that the superior growth performance of the bulls is due, at least partially, to hormonally mediated differences in nitrogen metabolism that result in a greater deposition of lean tissue and hence increased weight gain.

The relative efficiency of voluntary consumption, chemical composition, digestibility in vitro and in vivo, was tested for predicting the nutritive value of five forages: berseem (Trifolium alexandrinum); green oat (Avena sativa); oat hay; cow pea (Vigna spp.) and maize (Zea mays). The digestibility coefficients of dry matter (DM), crude protein, acid-detergent lignin and energy were significantly correlated with DM intake. Digestibilities in vitro of DM and cellulose after 12-h incubation were significantly related to digestibilities in vivo of DM and energy. The values for cellulose digestibility in vitro at 24 h were similar to those for digestibility of energy in vivo. Significant correlations were obtained between the crude protein content of forages and the voluntary DM intake and digestibility of nutrients. Increased cellulose and acid-detergent fibre contents were each related with decreased DM intake and digestibility of nutrients.