Attributes of lactation and weight of components of the empty body were analysed to evaluate relationships between performance potential of various breeds or breed crosses and the proportion of empty-body components relative to slaughter weight. Differences in major internal organs attributable to breed, breed cross, level of food intake, mature body size and milk production potential were observed. Milk yield was positively related to proportion of lung tissue, tended to be positively related to head and liver tissues but was negatively related to the proportion of warm carcass. As estimated from a three breed diallel, significant additive breed direct effects were observed for several empty-body components. In general, heterosis tended to be non-significant for all proportions of body components with the exception of proportion of head, fore and hind feet and lung tissue. Breed crosses characterized as having greater potential for mature weight were heavier at slaughter and had a greater proportion of structural components such as head, hide and fore and hind feet. Differences among visceral organs associated with production potential for size and milk production are discussed relative to the possible effect on basal energy expenditure and the effect these differences may have on the energy requirements for a cow/calf livestock enterprise.

A selection experiment with Scottish Blackface sheep was used to compare predicted and realized responses to selection. Three closed lines, of approximate annual size of 270 ewes and 10 rams, were maintained between 1956 and 1974, in which selection was at random, or for high and low values of an index of cannon-bone length at 8 weeks of age adjusted for body weight at the same age. An unselected base flock (1954-55) and the randomly selected line were used to estimate base population parameters, while the selected lines were used to estimate realized responses to selection.

Heritabilities and genetic correlations were obtained in the unselected lines from a variety of collateral and ancestral relationships. The important components of phenotypic variance were estimated and likely responses to selection predicted for the index and its two component traits. Realized responses to selection were estimated from the regression of response on selection differential. The expected variance-covariance matrix of observed responses was included in generalized least-squares estimates of these regressions.

The realized heritability of the index under selection, estimated from the divergence of selected lines, was 0·52 (s.e. 0·02). After allowing for the expected reduction in heritability arising from linkage disequilibrium, this was very similar to the base population estimate of 0·56 (s.e. 0·04). The responses in the component traits of the index were also very close to those expected from base population parameters

The reproductive performance of female Magra and Marwari sheep of the desert areas of north-western India was studied in relation to intermittent water deprivation, for a period of 39 months during which four breedings were completed. The control group received an ad libitum supply of water every day, while the water-restricted group was provided with water on the same 2 days each week only throughout the experimental period, except during the monsoon season. All the ewes were maintained on cultivated Cenchrus ciliaris pasture. No ill effect was noticed on the general health of the animals. Reproductive measures such as incidence and duration of oestrus, length of the oestrous cycle, conception rate, lambing rate, length of gestation, post-partum interval, inter-lambing period, post-lambing weight of ewes and birth weight of lambs were not significantly affected by the imposed water deprivation. The dailywatered ewes had a slightly, but not significantly higher gain in body weight than the water-restricted ewes. It wa^ concluded that ewes of these two breeds could be maintained on a twice weekly watering schedule for prolonged periods of time without having any adverse effect on their reproductive performance.

Energy expenditure, food intake and some physiological reactions of Brahman and Brahman × British Friesian cattle working on an inclined treadmill at 33°C were studied. The effect of work at a lower ambient temperature (15°C) and local cooling of the head region while at 33°C were also investigated. Whilst walking up a 6° gradient at 1 m/s, animals expended about four times as much energy as when standing. Heat production during work (W/kgM0·75) was similar in both breeds and was not influenced by the treatments imposed. Crossbred animals showed significantly higher respiration rates and sweating rates than the Brahmans immediately after working for 30 min at 33°C. Food intake and body-weight changes in the crossbreds at 33°C compared with Brahmans provided further evidence that these animals were less tolerant of the conditions. Head cooling during work appeared to reduce depression in food intake associated with work at 33°C in both breeds although it had no effect on physiological changes.

The dry-matter degradation of 19 varieties of barley, 14 varieties of wheat, 11 varieties of oats and one variety of triticale straws, both untreated and ammonia treated were studied using the nylon-bag technique. There were significant differences between the untreated varieties of all the types of cereal straw studied with respect to dry-matter loss (DML) values. When the barley and wheat straws were treated with ammonia, the differences between the varieties were also significant although ammonia treatment tended to improve those with lower values to a greater extent than those with higher values. There were also significant differences between the DML values of the oat straws when they were treated with ammonia but only after 48-h incubation. There was a significant negative relationship between the 48-h DML values of the untreated oat straws and the improvement in the DML values with ammonia treatment (r = −0·65; P < 0·05). Grain yield, straw length and nitrogen concentration had no significant relationship with the DML values of the untreated straws. Barley and oat straws had generally higher DML than the wheat and triticale straws.

A selection experiment with Scottish Blackface sheep was used to compare predicted and realized correlated responses to selection. Three lines were maintained between 1956 and 1974 in which selection was either at random or for high and low values of an index of cannon-bone length at 8 weeks of age adjusted for body weight at the same age.

There was no evidence of asymmetrical responses in any trait. Selection for increased cannon-bone length, adjusted for body weight, resulted in (i) increased body weights at all ages between birth and maturity, (ii) increased reproduction rate, principally from increased litter size but also from small responses in ewe fertility and lamb survival and (iii) decreased survival of adult ewes. The realized genetic correlations were relatively small (up to 0·3) but mostly significantly different from zero, whereas base population genetic correlation estimates were very imprecise. The realized responses in reproduction rate were probably a consequence of the genetic response in body weight.

In a multibreed experiment 306 females from 25 British breeds of cattle were given a standard pelleted diet ad libitum. Correlations of food conversion efficiency (FCE) with body weight, weight gain, and food intake were studied over 12-week and longer periods from 12 to 72 weeks of age. Inter-age correlations of FCE with itself and the other traits were also studied over age intervals separated by 12, 24, 36 and 48 weeks. The between-breed correlations were genetic while the within-breed correlations were phenotypic.

Between breeds, FCE measured over the full age range from 12 to 72 weeks appeared to be very highly correlated with FCE measured over the 12-week period between 24 and 36 weeks of age. Correlations of 12 to 72 week FCE with traits not requiring measurement of food intake were much lower, being at most 0·77 for weight gain, 0·73 for weight gain per unit body weight and 0·57 for body weight. The pattern of correlations implied that over constant age ranges the larger faster-growing breeds with high intakes tended to be more efficient; however, these correlations were generated primarily at early ages between 12 and 36 weeks and FCE at later ages could not be predicted from other traits measured at earlier ages. Nevertheless, between-breed selection to improve FCE by indirect selection on body weight and weight gain could be effective but there would appear to be no advantage in waiting beyond 1 year of age.

Within breeds, correlations of 12 to 72 week FCE with FCE measured over 12-week periods increased with age from 0·24 to 0·61. Correlations of FCE with weight gain in the same 12-week periods were quite high (0·49 to 0·89) and those with weight gain per unit weight were invaribly higher (0·68 to 0·90). However, as a predictor of FCE in any subsequent period, weight gain per unit body weight was poor and weight gain of no value whatsoever. There was no strong association of FCE with body weight.

Two varieties of barley straw, Corgi and Gerbel, which varied in degradability when incubated in the rumen in nylon bags, were chosen for further examination of botanical fractions and to see how each fraction responded to treatment with ammonia. The straws were separated into leaves, internodes, nodes and chaff. The average proportions of these fractions were respectively 0·499, 0·380, 0·055 and 0·065 in Corgi straw and 0·404, 0·512, 0·059 and 0·025 in Gerbel straw. For both varieties the degradability of the botanical fractions were leaves > chaff > nodes > internodes.

Despite a similar chemical composition, the dry-matter loss (DML) values of leaves, internodes and nodes of Corgi were higher than those of Gerbel straw.

The differences between varieties were larger for internodes and nodes than for leaves. The difference in DML of the two varieties at 48-h incubation was 132 g/kg DM. Of this difference, 25 g were due to differences in distribution of the botanical fractions and 107 g to differences in DML of the fractions.

Ammonia treatment significantly increased the DML of all fractions except the nodes. The overall improvement due to ammonia treatment of the different fraction was internode > chaff > leaves > nodes.

A study was made of the levels of oestrous activity of two indigenous breeds of sheep (Somali and Nandi) and three exotic breeds of sheep (Merino, Karakul and New Zealand Romney Marsh) over a period of 3 years, in an equatorial environment. Breed was the only significant source of variation for the length of the oestrous cycle (P < 0·01). The mean lengths of the oestrous cycle were 17·2 (s.d. 3·21), 17·5 (s.d. 2·24), 17·9 (s.d. 2·99), 17·5 (s.d. 2·57) and 16·5 (s.d. 3·41) days for the Somali, Nandi, Merino, Karakul and Romney Marsh breeds, respectively.

The mean percentage of ewes of the different breeds showing oestrus in 20-day periods were 69·8 (s.d. 22·57), 49·9 (s.d. 18·67), 63·4 (s.d. 25·70), 79·2 (s.d. 20·30) and 33·2 (s.d. 23·50) % for the Somali, Nandi, Merino, Karakul and Romney Marsh breeds, respectively. Time-series analysis did not detect any evidence of seasonal variation in oestrous activity, although there was an indication that the Merino and Romney Marsh breeds showed a marked increase in oestrous activity following, the introduction of rams. It was concluded that the variation in level of oestrous activity was short term and random.

Two groups of 19 Border Leicester cf × Scottish Blackface 9 ewes were fed so that ewes of one group were in a very high level of body condition at mating (mean score 3·35) and had a high level of intake. Ewes of the second group were in moderately high condition (mean score 2·74) and were given a live-weight maintenance ration. Ewes in the high group had a higher ovulation rate than those of the moderate group (3·36 v. 2·33) but a lower number of embryos per ewe mated (1·16 v. 1·42). Mean follicle stimulating hormone profiles were similar for ewes of the two groups during the luteal and follicular phases of the cycle before mating and during the subsequent oestrus. Mean prolactin concentrations were higher in ewes of the high group during the follicular phase and oestrus but not during the luteal phase. Mean luteinizing hormone (LH) concentrations were higher in ewes of the high group during the follicular phase and oestrus but not during the luteal phase. Mean LH concentrations were similar for the two groups at all times but the frequency of LH pulses was higher in the high group during the follicular phase.

Ewes that were not pregnant at slaughter had abnormal progesterone profiles following mating, abnormal pre-ovulatory LH surges or failed to show oestrus. These abnormalities were not related to gonadotrophin profiles prior to oestrus.

Twenty-eight Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged 47 days and weighing 17 kg on average were allocated to be sham-implanted controls (group C) or implanted with trenbolone acetate (TBA) combined with oestradiol-17β (OE) as follows: 17·5 mg TBA + 2·5 mg OE (group TO1); 35 mg TBA + 5 mg OE (TO2); 52·5 mg TBA + 7·5 mg OE (TO3). The lambs were offered ad libitum a diet containing (per kg dry matter) an estimated 12·5 MJ metabolizable energy and 0·16 kg crude protein. They were slaughtered 60 days following implantation.

On average hormonal treatment resulted in significant increases in (a) live-weight gain, food intake and gut fill, (b) proportions of perinephric and retroperitoneal fat in empty body, (c) carcass lean proportion, and (d) proportion of lean in shoulder and rib joints. Variable changes in the weights of m. semitendinosus, m. gastrocnemius and m. supraspinatus were recorded.

Hormonal treatment, on average resulted in significant reductions in (a) killing-out proportion, (b) proportions of total fat and subcutaneous fat in carcass and (c) proportions of fat in the shoulder, rib and hind leg joints. Treated lambs had smaller thymus glands but larger accessory vesicular glands. Penile tissue was also increased in treated lambs. The proportional differences in live-weight gain and carcass fat content were 0·15 and 0·12 respectively.

Differences in dose level had little effect on growth and carcass characteristics.

Two experiments were designed to study the effect of rearing method, female company, and repeated libido and semen tests on the pattern of sexual development of ram lambs. Four artificial rearing treatments (AR) were compared with natural rearing (NR) in one experiment and four artificial compared with three natural rearing treatments in a second experiment. Lambs on AR treatments in both experiments, as well as naturally reared lambs in the second experiment, were reared with or without females either before and/or after weaning. Half the lambs in the second experiment were libido and semen tested, and their mean plasma testosterone level was also measured, while the rest were only tested at the end of the experiment. The effect of method of rearing and female company on body growth, testes diameter, libido and semen quality were also investigated.

A close relationship was found between body weight and sexual characteristics (for example, testis diameter, semen traits, libido, testosterone level and age at the onset of sexual maturity). NR resulted in faster growth than AR but was not appreciably different from early weaned-naturally reared treatments. It was also observed that mating performance improved steadily with advancement in age and increase in body weight. The onset of sexual maturity was attained at a minimum of 23 kg body weight and a minimum of 198 days of age. However, the heavier the lamb when sexually mature, the better its mating performance.

Previous libido tests of ram lambs improved their subsequent mating performance, but had no effect on semen quality. However, libido tests did not improve the performance of those ram lambs which did not exhibit initial libido.

It is suggested that early weaning at 2 months of age could be a suitable system for ram lambs weaned off their mothers for breeding purposes. These lambs should be reared as an all-male group but libido tested at monthly intervals commencing at 3 months of age. The criteria for selecting these lambs at an earlier age should be body weight and testis diameter.

On a hill farm, the reproductive performance of Scottish Blackface ewes increases annually with increasing age up to 6 years and is positively related to pre-mating live weight. A group of Scottish Blackface ewe lambs was, from 5 months of age, preferentially managed over a 2-year period to accelerate the achievement of mature size, in order to study the relative importance of age and size to reproductive performance. Ovulation rate and early embryo mortality of these ewes at 31 months of age were compared with those of adult ewes of similar body size and condition at 79 months of age which had been reared conventionally in the same hill flock. Two comparisons were made, one between different age groups in the same year and the other retrospectively between different ages of the same age group. In the first comparison, the adult ewes had a slightly greater reproductive response which suggested a small effect of age per se but there was also the possibility of a genetic difference. In the second comparison, there was no difference in ovulation rate or potential lambing rate per pregnant ewe, but a trend towards greater wastage of twin-shed ova in the heavier and fatter younger ewes again suggested a small effect of age. At both ages, however, these ewes performed close to their adult genetic potential which suggested that the treatment of the young ewes was sufficient to overcome most of the limitations associated with age or size. Reproductive performance normally associated with young animals is therefore mainly an expression of their size relative to their maturity and the removal of the size limitation by higher levels of nutrition and more rapid growth can largely eliminate their poorer performance.

To evaluate passive and active methods for rewarming hypothermic lambs, the rectal temperature of 19 neonatal lambs (4·9 (s.e. 0·34) kg) was reduced to 35°C by cold water immersion. Metabolic responses and change in rectal temperature were monitored as the hypothermic lambs recovered with added insulation in a 20 to 25°C air environment, or with thermal assistance provided by an infrared heat lamp, or through immersion in 38°C water. During the first 12 min of rewarming, the rise in rectal temperature in all treatment groups was linear, however it was more rapid with the lambs immersed in warm water (0·26°C/min; P < 0·05) as compared with the insulated lambs (0·21°C/min) and the lambs rewarmed with a heat lamp (0·22°C/min). During this 12-min period, the insulated lambs produced metabolic heat more rapidly than did the warm-water lambs, 13·6 v. 11·1 (s.e. 0·67) W/kg, respectively (P < 0·05). These data indicate that there was a substantial influx of heat which contributed to the increase in body temperature of the lambs immersed in warm water. Stabilization of rectal temperature occurred after 18 to 20 min in all treatment groups. The lambs recovered in all treatment groups, in addition, no clinical problems were observed in any of the lambs during the tests or subsequently when they were returned to their dams.

Ultrasonic measurements of fat thickness and m. longissimus depth 25 and 50 mm lateral to the mid line at the last rib and 100 mm caudally to the last rib were made, before slaughter, on 273 ram lambs using two probes: the Scanogram and Krautkramer. The lambs were from three strains: a meat-type sire strain and two fecund dam strains. They weighed on average 37·3 kg at scanning, (range 29·0 to 51·3 kg), well within the weight range over which Canada Al-grade lambs are marketed in Canada. Their carcasses contained on average 437 g trimmed boneless meat per kg (s.d. pooled within strain = 24·1 g/kg).

The precision with which the ultrasonic measurements combined with live weight at scanning predicted trimmed boneless meat (weight and proportion) was examined. Fat thickness measurements had no predictive value (P > 0·05). The residual standard deviations for the prediction of trimmed boneless meat in the half carcass (weight and proportion) from weight at scanning were 0·29 kg and 21·5 kg, respectively; the addition of the m. longissimus depth measurement reduced the residual standard deviations by 0·02 kg and 1·1 g/kg, respectively. The weight of trimmed boneless meat was predicted with more precision than the proportion of trimmed boneless meat. Strain, location of measurement site or type of instrument did not change the precision of prediction.

It is concluded that prediction of trimmed boneless meat in young ram lambs based on live animal ultrasonic measurements made with the Scanogram or Krautkramer lacks the level of precision necessary for practical application.

Border Leicester × Scottish Blackface (Greyface) ewes of three groups, each comprising 118 animals in a wide range of body condition scores, were mated at a synchronized oestrus in mid October. The ewes were passively immunized against testosterone (group P), actively immunized against androstenedione (group F), or not treated (group C). All ewes were slaughtered at return to service or at 35 to 45 days of pregnancy and ovulation rates and numbers of embryos present were determined. Mean ovulation rates of ewes in group P were higher than in those in group C (P < 0·05) and this difference was evident at most levels of body condition. The absolute increase in ovulation rate, compared with the control group, was similar at all condition scores. Mean ovulation rates of ewes in group F were higher than those in group C (P < 0·001) and the magnitude of the increase was greater in ewes in higher condition scores. The incidence of ova wastage was variable but differences between treatments in mean ovulation rate were generally reflected in mean litter size. The conception rates of immunized ewes were depressed compared with those of control animals, particularly in ewes with a body condition score less than 3·0 at mating. Consequently, there was no improvement in the potential lambing rate of immunized ewes following only one cycle of mating. Circulating antibody titres were not related to conception rate or body condition at mating and were related to ovulation rate only in group F ewes. It is concluded that immunization against steroids, using either passive or active techniques, can improve the reproductive performance of individual ewes but improvement in the performance of the flock as a whole may only be achieved under optimal conditions of nutrition and season.

Mortality and its causes were studied during two consecutive years in a total of 934 lambs. The lambs were from two lines of sheep genetically selected for low (L) and high (H) concentrations of copper (Cu) in plasma within an interbred Scottish Blackface × Welsh Mountain population and from unselected Scottish Blackface (B) and Welsh Mountain (W) breeds. The lambs grazed improved hill pastures. Half of the lambs in each line or breed were given an oral Cu supplement by 7·5 weeks of age.

Mortality from birth to 24 weeks in H was less than half that in L; mean proportional mortalities were L 0·28, H 0·12, B 0·37 and W 0·07, with a similar distribution in each year. Swayback accounted proportionately for 0·26 deaths in year 1, but proportionately for only 0·02 in year 2. The majority of other losses involved a variety of microbial infections.

Genetic type (W < H < L < B) was a major determinant of, and Cu supplementation a protection against, swayback and non-swayback losses. For non-swayback losses L lambs were about twice (P < 0·01) and B lambs about four times (P < 0·001) more vulnerable than H and W lambs respectively. Unsupplemented lambs were more than twice as vulnerable to non-swayback causes of death in the 1st year (P < 0·05) and four times as vulnerable in the 2nd year (P < 0·01) as were Cu-supplemented lambs. There were no cases of swayback in supplemented lambs even though Cu treatment was in some lambs as late as 7·5 weeks after birth.

Such marked differences in mortality rate, particularly between the selected lines, had not been apparent in the 5 years preceding pasture improvement, suggesting a genotype × environment interaction affecting survival.

The results provide the first definitive evidence that decreased resistance to infection is a clinical consequence of ovine Cu deficiency in the field, amenable to control by Cu treatment and genetic selection.

One hundred and ninety-two individually fed pigs, half of them castrated males and half females, were used to examine the effects of reducing the concentration of dietary lysine below the value of 0·84 g/MJ digestible energy suggested by the Agricultural Research Council (1981). Lysine was varied by altering the inclusion of either free lysine hydrochloride or soya-bean meal. Over the whole experiment from 18 to 65 kg live weight, there were significant reductions in live-weight gain and increases in food: gain ratio in response to reducing lysine concentration; these changes were greater with soya-bean meal than with free lysine. During later growth (45 to 65 kg) alterations in lysine concentration had no significant effect.

For pigs given soya-bean supplements, both the live weights after fasting and the carcass weights were significantly lower than for those given free lysine hydrochloride, suggesting that at least part of the difference in growth between pigs given free lysine hydrochloride and soya-bean was attributable to this difference. The food required per kg carcass weight gain, or per kg lean tissue gain, was not affected by the source of lysine.

In a subsidiary experiment using nitrogen balance, supplements of five amino acids in addition to lysine did not increase nitrogen retention, providing further evidence that lysine was the only amino acid responsible for the response seen with soya-bean meal. It was concluded that for growing pigs with daily food intakes of 1·5 to 1·8 kg, a lysine concentration of at least 0·81 g/MJ digestible energy is required to maximize performance.

Sixty Landrace × Large White piglets were removed from their mothers at birth and allocated to one of five treatments. Treatment A piglets were controls and did not receive any form of passive immunity after birth. Treatment B piglets were given by intraperitoneal injection 20 ml equine serum derived from horses previously hyperimmunized against porcine pathogens. Treatment C piglets received the same equine serum given orally. Treatment D piglets were given 20 ml pooled pig plasma by intraperitoneal injection. Treatment E piglets received the same pig plasma given orally. All piglets were reared to 2 weeks of age in an artificial-rearing device and were automatically fed a liquid diet every hour. Overall survival to 2 weeks of age was 90% (54/60) but treatment did not affect survival. The overall survival after 6 weeks of age was 47% (22/47) deaths being due to a variety of systemic disorders. Overall daily gain to 2 weeks of age was 143 g/day and the food/gain ratio was 0·88. Treatment did not affect performance. The concentrations of immunoglobulin class G (IgG) in the blood were measured at 42, 49 and 56 days of age. There were no differences between the treatment groups in IgG concentrations.

Halothane positive and negative selection lines were established to estimate the effects of the halothane gene on performance in British Landrace pigs. Incidences of positive reaction diverged from 0·12 in the foundation generation to 0·93 in the positive and to 0·02 in the negative line in generation 4. Differences in litter productivity as a trait of the dam were estimated from a total of 399 positive × positive and negative × negative parity 1 and 2 matings in generations 1 to 4.

Compared with negative contemporaries, positive females showed non-significant reductions in litter size at birth (−0·10, s.e. 0·26) and at 42 days (−0·28, s.e. 0·26), accompanied by significant reductions in average piglet weights at birth (−0·11, s.e. 0·02 kg) and 42 days (−0·4, s.e. 0·2 kg). There were no differences in conception rate or adult live weights. A subsample of 69 parity 2 and 3 sows slaughtered 30 days after mating showed no significant difference in ovulation rate or embryo survival, but for positive dams the length of embryos was significantly reduced (−3·1, s.e. 1·1 mm).

The study suggests that the principal effect of the halothane gene was in reducing foetal growth rather than litter size. However, the phenotypic difference is expected to under-estimate the genetic difference between homozygotes, and it was not possible to distinguish the effects of dam and offspring genotypes. The present economic loss of roughly £4·70 per positive litter would be unlikely to justify elimination of the gene from a purebred maternal Landrace herd.