A total of 56 sheep, 28 Clun and 28 Southdown were slaughtered, five of each breed, at birth, 50, 100, 150 and 200 days and three of each breed at 415 days of age. The left half of each carcass was separated anatomically into individual muscles, bones and fat depots. For the purposes of analysis, individual muscles were assigned to one of eight muscle groups, depending upon their anatomical location.

The relative growth of some individual muscles was found to change over this age range, as indicated by a significant squared term in the quadratic allometric equation: this was true for proportionately 0·33 of the muscles in Clun and for proportionately 0·44 of those in Southdown, accounting for proportionately 0·33 and 0·47 of total muscle weight in Clun and Southdown respectively.

Principal components analysis (PCA) was used to derive the multivariate analogue of the quadratic part of quadratic allometry: the sign of the loading on the second principal component had the same sign as the change observed in bq, the quadratic relative growth coefficient. Thus, PCA offers the potential to identify simultaneously, and independently of shape or conformation, all those muscles whose relative growth coefficients change over the period examined. It could be applied successfully to breed comparisons of conformation.

The cumulative effects of changing relative growth rates of muscles were small. Muscle weight distribution appears to be almost fixed within the first few weeks after birth. Despite their differences in conformation and mature size, Clun and Southdown lambs had similar distributions of muscle weight at the same age; the high valued muscles constituted 513·8 g/kg total muscle in Clun and 514·7 g/kg total muscle in Southdown lambs at 200 days of age.

Forty Large White ♂ × (Large White (f × Landrace ♀) pre-pubertal gilts were used to study the influence of five different doses of parenteral oestradiol benzoate (OB) on the attainment of puberty. Five gilts from eight litters were treated at 140 days of age with either 5, 10, 15, 20 or 25 μg OB per kg body weight (BW). The doses were split equally into three bolus injections given on consecutive days. Daily boar contact commenced on the day that the first oestrogen injection was given and continued until the gilts were mated. All gilts were slaughtered at either 20 days post coitum or at 235 days of age for those gilts not exhibiting a second oestrus.

The numbers of gilts which ovulated within 10 days after OB injection were: 5/8, 7/8, 8/8, 6/8 and 5/8 for treatments 5 ng/kg BW through to 25 fig/kg BW, respectively. These differences were not significant (P > 0·05). The duration of behavioural oestrus after OB injection was positively correlated to the dose of oestrogen administered (r = 0·98, P < 0·01). There were no significant differences in age at puberty between treatments, and no significant differences were found in the subsequent reproductive performance.

It is a popular belief, supported by several scientific studies (Vaughan, 1971; McPhee and Laws, 1976; Fredeen and Sather, 1978; Sather and Fredeen, 1982) that leg weakness will diminish in young stock of breeding age after they are transferred from confinement housing to pasture lots. However, Nakano, Aherne and Thompson (1981) working with boars from the Canadian Swine ‘Record of Performance’ (ROP) testing programme found that no improvement in gait resulted after the animals were transferred from confinement housing with solid concrete flooring to pasture lots. The number of animals in the study was limited. All of these reports dealt only with the recovery of pigs from leg weakness and did not include pigs with sound legs at the beginning of the pasture period (approx. 90 kg live weight).

A group of 16 Romney wether sheep fitted with rumen and abomasal cannulae and aged 11 to 12 months was allocated to either high or low crude protein (CP) pelleted diets (220 (HP) and 120 (LP) g CP per kg) to give four daily intakes of dry matter (356, 711, 1067 and 1422 g) within each diet, giving two sheep per treatment. Diets were given hourly for 40 days during which time growth rates, plasma concentrations of insulin (I) and growth hormone (GH) were determined, a glucose tolerance test was performed and relative rates of fatty acid (FA) synthesis were determined.

Live-weight changes ranged from –46 to 215 g/day and wool growth ranged from 86 to 210 mg per 100 cm2 daily.

Plasma GH concentrations were significantly higher (P < 0·001) in sheep given LP diets (21·2 (s.e. 4·2) μg/1) than in those given HP diets (10·1 (s.e. 1·8) μg/1) and negatively correlated with both energy (E) (r = –0·62; P < 0·01) and nitrogen (N) (r = –0·63; P < 0·01) intakes which proportionately accounted for 0·47 of the variance in plasma GH concentration (P < 0·01). Plasma I concentrations were higher (P < 0·05) in sheep given HP diets (2·77 (s.e. 0·34) μg/1) than in sheep given LP diets (1·86 (s.e. 0·23) μg/1). Intakes of E and N proportionately accounted for 0·38 of variance in I concentration which was primarily determined by N intake.

After intravenous infusion of glucose (150 mg/min) for 30 min, significant differences in the rate at which plasma glucose and I concentrations declined to pre-infusion levels were evident with different daily intakes of the pelleted diets.

Synthesis of FA in adipose tissue was on average 1·7 times more rapid in sheep given HP than in sheep given LP diets (P < 0·05) and increased approximately three-fold with increasing intake. Partial correlations showed differences in E and N intakes were able to account for 0·73 (P < 0·01) of the variance in FA synthesis rates, with N intake having a greater influence than E intake (partial correlations: r = 0·53; P < 0·05 and r = 0·35; P > 0·05 respectively).

Two experiments employing 72 and 48 pre-pubertal Large White ♂ × (Large White ♂ × Landrace ♀) gilts respectively were carried out to investigate the involvement of various boar stimuli in the induction of precocious puberty in the gilt. Experiment 1 consisted of the following treatments commencing at 165 days of age: (1) contact with an androgenized, castrated male; (2) contact with an androgenized castrated male plus a recording of boar chants; (3) as treatment (2) plus exposure to a solution of 16-androstene steroids, 3α-androstenol (5α-androst-16-en-3α-ol) and 5α-androstenone (5α-androst-16-en-3-one); and (4) contact with an entire boar. In experiment 2, additional exposure to boar urine occurred in treatments (2) and (3).

Exposure of gilts to tactile, visual and auditory cues from the boar had little effect on puberty attainment. The additional exposure to 16-androstene steroids did stimulate puberty but was not as efficacious as boar exposure. Additional exposure to boar urine improved the puberty-stimulating effect of the castrated males, and further additional exposure to 16-androstenes produced a response approaching that obtained by boar exposure.

These results confirm the involvement of olfactory cues from the boar in stimulating puberty in the gilt. The olfactory cues appear to be 16-androstene steroids present in boar saliva and some undefined compound(s) present in boar urine. These experiments suggest that olfactory stimuli from the boar require the simultaneous exposure to tactile and possibly also visual and auditory cues from the boar in order to stimulate the onset of puberty in the gilt.

cues from the mature boar are also involved in mediating the stimulation of puberty. Exposure of gilts to isolated sources of androstene pheromones was ineffective in stimulating puberty (Kirkwood et al., 1983), whereas exposure to contact with a sialectomized boar order to stimulate the onset of puberty in the gilt.

Despite the low heritability (0·1) for litter size in pigs, quite high rates of genetic improvement are predicted theoretically using conventional selection methods. The highest rates are predicted from schemes with rapid generation turnover (1 year) and with selection of both males and females at breeding age on a family selection index. This index would combine litter records (two on each relative) of the dam, her full sibs and half sibs, and of the sire's dam and his full sibs and half sibs. Annual rates of genetic change of up to half a pig per litter (a proportion 0-05 of the mean) are predicted. This rate is substantially greater than the proportional rates of genetic change possible for growth and carcass traits. These predictions are fairly insensitive to maternal and rearing environmental effects which may affect litter performance. High response rates are also predicted from two-stage selection of males, first on family index as before and then on progeny test of daughters in a large artificial insemination bred population. Intense screening in a large population for females with high litter records (hyperprolific females) can be an effective way to start an improvement programme for litter size. However, continuous screening of hyperprolific females is less effective because of the long time taken to generate enough descendants needed for the next round of intense selection. Despite the high rate of genetic change possible for litter size, omission of the trait from an index which includes growth and carcass traits would result in only small losses (proportionally less than 0·05) in economic improvement of general purpose stocks under United Kingdom market conditions. However, the losses would be higher (proportionally 0·10 to 0·18) in specialized dam stocks and inclusion of litter size in an index when selecting such stocks would be worthwhile.

A performance test of pigs was conducted according to an adapted version of the ‘Kielanowski system’ in which the feeding level and the termination point of the test period were changed. A total of 119 pigs of six genotypes (participants in the Commercial Pig Evaluation in The Netherlands, 1981) averaging 22 kg weight, were fed for 17 weeks on a scheme according to days on test. The regime was such that not all the pigs could consume their total allocation of food. The fast-growing pigs were expected to be more efficient and therefore the leanest.

Forty-eight pigs consumed their total food allocation, whereas the remainder left an average of 5·89 kg food. Pigs that consumed their total allocation of food had a significantly better food conversion ratio (0·07 kg/kg; P < 0·01) and a higher daily gain (33 g/day), but they had significantly less lean (10 g/kg; P < 0·05) in their carcasses than pigs that could not consume their whole allocation. The ranking of genotypes for average daily food intake closely agreed (rs = 0·94) with the ranking in another trial with ad libitum feeding, which points to the possibility for selection on food intake capacity in the proposed system. For the other variates, the ranking correlations were moderate.

Among the pigs that consumed the total amount of food offered, a moderately strong relation (r = 0·70) was found between daily gain and lean tissue growth rate. With the system tested, it was not possible to determine leanness simply by weighing the pigs afterwards. Nevertheless, the results of the modified Kielanowski system show some interesting aspects which contribute to the design of a test system for a genetically unbiased comparison among pigs.

Beef producers no longer emphasize excessive fat deposition in market cattle. Recent research findings in human health suggest that our diets should contain less fat because of the cardiovascular diseases that seem associated with greater intakes of fat. Large-frame cattle slaughtered at the same chronological age as small-frame cattle have leaner carcasses and a correspondingly greater proportion of carcass protein (Arnold, Hentges and Trenkle, 1985). Determining early in life whether a type of cattle will become obese, therefore, would be of great benefit to cattle producers. Arnold et al. (1985) reported that, at 6 months of age, large-frame steers were significantly leaner than small-frame steers.

The initial work of Brooks and Cole (1970), which showed that a mature boar advances the onset of puberty in gilts, has become known as the ‘boar effect’, and this phenomenon has now been confirmed in numerous studies as reviewed by Hughes (1982), and Kirkwood and Hughes (1982).

The potential problems concerning the use of manioc, from the processed roots of cassava (Manihot esculenta), have been reviewed by Oke (1978) and Walker (1983). Although current legislation has ensured that in recent years the levels of cyanogenic glucoside in imported cassava have been negligible (Walker, 1985), there is still conflicting evidence on the maximum level of manioc which can be included in pig diets without adverse effects on digestion and performance. In a previous study (Partridge, 1985), 300 g manioc per kg tended to increase the proportion of energy apparently absorbed from the large intestine compared with lower levels. This may have been partially responsible for some of the digestive upsets found with young pigs by O'Grady and Hanrahan (1979). Evidence of the effect of manioc on performance can be misleading due to palatability problems and therefore lower food intakes (Müller, Chou and Nah, 1975; Papodopoulos, Ziras and Kalaissakis, 1983).

A study of the effects of low birth weight on muscle cellularity was performed on 48 pedigree Large White pigs selected, from a total of 17 litters, on the basis of their weight at birth. Where possible, the largest male (mean birth weight of 1544 g), smallest male (1135 g), and runt (776 g) littermates were chosen. Fresh frozen, whole mid belly, sections of m. semitendinosus and samples of m. trapezius from each animal were stained for the demonstration of acid pre-incubated myosin adenosine triphosphatase. The use of this stain demonstrated groups of positively stained, slow-contracting, myofibres which were each surrounded by a compliment of negatively stained, fast-contracting, fibres which together constituted ‘metabolic bundles’. The positions of metabolic bundles are indicative of the presence of single primary myofibres in the foetal muscle, all the other myofibres in the metabolic bundles being derived from subsequently formed secondary fibres. Determination of total myofibre number and primary fibre number were made for m. semitendinosus together with an estimation of the secondary to primary fibre-number ratios for both this muscle and for m. trapezius. Low birth weight was associated with a permanently reduced total muscle fibre number, proportionately in the order of 0·19 (P < 0·001) between large and runt littermates. A reduced muscle fibre number was not always associated with low birth weight, but when this was the case it was generated through a reduced secondary to primary fibre-number ratio (P < 0·01). Primary fibre number was not significantly affected in low birth-weight pigs except in extreme cases of runting.

The native fat-tailed Awassi and the imported German Mutton Merino (GMM) sheep are well adapted to semi-arid conditions (Degen, 1977; Degen and Shkolnik, 1978). This enables these sheep to graze large areas of the Negev Desert in Israel that is marginal for farming. However, under extensive conditions both these sheep breeds yield low lamb crops producing fewer than 1·0 lamb per ewe per year.

Ileal digesta are often sampled from the pig through either re-entrant or simple T-piece cannulas. There is conflicting evidence, however, concerning the effects of cannulation on nutrient digestion and absorption. In several studies with the pig, cannulation has not influenced overall protein digestibility (Furuya, Takahashi and Omori, 1974; Sauer, Stothers and Parker, 1977; Taverner, 1979; Huisman, Weerden, Leeuwen, Hof and Sauer, 1984) or energy metabolism (Close, Heavens, Stephens and Sambrook, 1984) while in other studies (Laplace and Borgida, 1976; Sauer, Aherne and Thacker, 1979) there have been indications of adverse effects of cannulation on nutrient digestibility. Livingstone and McWilliam (1985) showed an effect of simple ileal cannulation on pig growth which may have been due to decreased nutrient digestibility or utilization.

In formulating a genetic index for use in cow and sire evaluation, there is a need to account for all environmental factors which influence an animal's yield. To this end, milk production records are currently adjusted for, amongst other things, age at calving and month of calving. In Norway, Sweden and West Germany, records are corrected for calving interval, i.e. the number of days between subsequent calvings (Philipsson, Dommerholt, Fimland, Gaillard, Gjøl-Christensen, Lederer, McClintock and Mocquot, 1978), but in Britain no account is taken of calving interval or days dry. Analysis has shown (McClintock, 1982) that both these factors have a significant effect on yield, and hence further investigation into the value and methods of adjusting for these factors was required.

It has been demonstrated with Australian breeds and conditions that active immunization of ewes against androstenedione can induce increases in lambing rate of 20 or more lambs per 100 ewes mated (Cox, Wilson, Scaramuzzi, Hoskinson, George and Bindon, 1982; Geldard and Scaramuzzi, 1983). More recent work (Geldard, 1985) involving active immunization against androstenedione (Fecundin®, Coopers Animal Health, UK) has shown that similar results can also be achieved with some United Kingdom breeds. However, the successful application of this product in practice requires a knowledge of the patterns of reproductive response that can be obtained with a much wider range of genotypes and production systems.