Experiments were carried out in Nepal and Costa Rica to compare voluntary dry-matter intake (DMI) by oxen of diets based on poor quality hay (Costa Rica) and rice straw (Nepal) supplemented with different levels of concentrate foods when the animals were working and not working. Values for the apparent digestibility of the diets, rates of passage of solid and liquid phases ofdigesta and nitrogen balance are also reported.

Amounts of work calculated to raise daily energy expenditure to 1·3 to 1·6 × maintenance were associated with the following effects. (1) A depression of proportionately 0·11 and 0·14 in the DMI of oxen given a diet based on rice straw plus 18 and 27 g/kg live weight of concentrate respectively during work. No depression of DMI was seen with the hay diets which had slightly higher metabolizable energy but less nitrogen than the rice straw diets. (2) An increase in intake in the weeks following work on both the hay and rice straw diets. (3) Variable effects on apparent digestibility of food probably related more to the changes in DMI. (4) A tendency for gastro-intestinal mean retention time to be increased in working weeks particularly on the more fibrous diets.

Ewes of the Segureña breed were allocated to groups and were group-fed different diets composed of concentrates and roughage (lucerne hay in experiment 1 and barley straw in experiment 2), in late pregnancy and lactation. The concentrates were formulated with sunflower cake and barley, either alone (control group) or partly replaced with olive cake (OLC) and olive molasses (OLM) in a 5:1 ratio. The OLC was either untreated or was treated with NaOH or ammonia. Concentrates were given to provide proportionately 0·4 and 0·7 of calculated metabolizable energy (ME) requirements in experiments 1 and 2 respectively. In experiment 2 a further group grazed pasture and was given barley at a reduced rate.

In experiment 1, the mean ME intake during late pregnancy (5+1 weeks pre-lambing) for all treatment groups was about 796 kj/kg M0·75 per day and largely exceeded their average energy requirements, whereas it was close to requirements (601 kj/kg M0·75 per day) in experiment 2. During lactation, ME intake was adjusted to the theoretical needs for ewes suckling a single lamb (835 to 870 kj/kg M0·75 per day) and was slightly deficient (990 to 1020 kj/kg M0·75 per day) for ewes with twins, irrespective of both treatment (except the group at pasture) and experiment.

Minor differences in animal performance, attributed to the type of concentrate offered, were found. In pregnancy, alkali treatment of OLC significantly improved live-weight gains (P < 0·01). Live-weight gains of ewes in experiment 2 were lower than those in experiment 1 in accordance with their lower ME intake, the lowest gains being found in the group at pasture (P < 0·05). Weight losses in lactating ewes in experiment 1 were 17 to 100 and 9 to 165 g per ewe per day for ewes suckling single and twin lambs respectively. In experiment 2 ewes with twins gained weight, while those with single lambs showed little weight change, although differences between experiments were too small to attain statistical significance. No differences in barley straw intake by pregnant ewes were found between treatment groups. However, the intake of barley straw by lactating ewes in the groups offered concentrates containing OLC and OLM was significantly higher than that by controls (P < 0·05).

Birth weight of lambs tended to be higher in experiment 2 when ewes consumed less ME during pregnancy, although variations were not statistically significant. The most important cause of growth rate variation was the number of lambs born to a ewe (P < 0·001). The growth rate of lambs in the outdoor group was significantly lower than that of lambs in the indoor groups (P < 0·05).

Ten Holstein bulls, 4 to 5 years old were used to study the effect of cooling the bulls on their semen quality. Five bulls were sprinkled with water for 15 min five times a day throughout a 6-week period of the summer season (hot-dry) in Saudi Arabia, and the other five bulls acted as the control and were not sprinkled with water. Semen quality was improved significantly during the cooling period. This improvement was evident from the significant increase in sperm motility (P < 0·01) and decrease in the percentage of both dead and morphologically abnormal (primary and secondary) spermatozoa per ejaculate of cooled bulls (P < 0·01). The effect of cooling was more marked through the last 3 weeks than during the first 3 weeks of the experimental period. Ejaculate volume, sperm concentration and hence total sperm counts did not differ significantly between the cooled and the non-cooled bulls. Concerning the type of abnormal spermatozoa, the overall secondary abnormality was higher than the primary in both the cooled and the control groups, with higher values for the control (P < 0·01). Only the mid piece showed higher primary defects than the secondary. The pyriform heads, the coiled mid pieces and tails and the bent tails were the main sources of variations (P < 0·01) in the incidence of sperm abnormality between the cooled and the non-cooled bulls. Cooling the bulls during the heat stress period also lowered their rectal temperature and increased blood haemoglobin level without affecting the packed cell volume

The objective of the study was to assess the usefulness of providing shade for beef cows grazing summer dry Mediterranean -pasture and supplemented with a food high in non-protein nitrogen (poultry litter). Two groups of 30 cows each, in the last trimester of pregnancy, were placed on 1 June in two paddocks of similar grazing pressure, topography, vegetation cover and botanical composition. In one of the sub-units the cows had free access to a large shaded area, provided by 10 to 12 large eucalyptus trees, whereas in the second sub-unit, access to shade was denied until 31 August. Respiration rate, used as an index of heat stress, was much higher in the non-shaded cows (102 breaths per min) than in the cows with access to shade (62 breaths per min). In response to the much higher heat stress in the non-shaded cows, total body water and haematocrit value (an index of plasma volume) were higher than in the cows with access to shade. Metabolizable energy (ME) intake was apparently much lower in the non-shaded cows, as reflected in a much higher non-esterified fatty acid concentration in plasma. Consequently, large differences in live weight gradually developed during the course of the trial, the cows with access to shade becoming much heavier than those with no access to shade. An increase in the consumption of poultry litter by the non-shaded cows was interpreted as an effort to reduce internal heat load by avoiding grazing and by preferring food which induces a lower heat increment upon ingestion and digestion. Above-normal serum concentrations of cholesterol and alkaline phosphatase support previous results that the combination of low ME intake and high ammonia load induces a toxic effect on the liver. Although all the cows were pregnant at the onset of the study, successful parturition was recorded in 26 of the 30 cows having access to shade, and in only 20 of the 30 (F < 0·05 by t test) of the non-shaded cows. It is concluded that providing shade for beef cows under summer Mediterranean conditions will reduce the danger of embryonic loss. However, an interaction with metabolic burden, such as ammonia load and a negative energy balance, can make the situation much worse.

With the objective of determining genetic × environmental interaction for beef production under direct grazing conditions, measured as both individual average daily gain (ADG) and per ha (PROD), 160 steers were utilized through 2 years, from two breeds of different growth potential, and four stocking rates (SR) tending to establish different nutritional environments. The breeds were Aberdeen Angus (A) and high-grade Limousin crossbred (L) and the SRs established were 2·25, 2·87, 3-50 and 4·13 steers per ha. The pasture where the steers grazed was Festuca arundinacea. Response variables were analysed by least-squares using a fixed model of year, breed, SR and their two-way interactions. There were highly significant effects (P < 0·01) of the interaction of breed × SR for ADG and PROD. Quadratic and linear regressions (P < 0·01) were adjusted for PROD and ADG on SR respectively using the least-squares means. The proportional superiority of L on A at the lowest SR was 0·27, while at the highest SR the situation was reversed, A gained proportionately 0·32 more weight than L. These results indicated that under limiting conditions of nutrition as generated at the highest SR in this experiment, the small-sized individuals tended to produce meat more efficiently both individually and per ha, the opposite situation being true when nutritional conditions were not restrictive.

Two experiments were designed to test the hypothesis that young growing pigs between 7 and 25 kg live weight are capable of selecting a diet which closely matches their changing requirement for amino acids, when offered a choke between two balanced foods differing only in their protein content. In the first experiment, three single-food treatments (8·6,11·7 and 17·4 g lysine per kg food) and one choice-feeding treatment (8·6 v. 17·4 g lysine per kg food), were used. In the second experiment, three foods of similar nutrient composition (approx. 14·7 g lysine per kg food) were formulated using different ingredients (fish meal, soya-bean oilcake meal and a combination of sunflower-, cottonseed- and groundnut-oilcake meals). These were fed either alone or as a choice with each other or with a low protein food (8·3 g lysine per kg food) to test whether palatability or anti-nutritional factors would override the selection based on protein alone. In both experiments, 10 pigs were housed per pen, with males and females being penned separately. One food bin with a central partition was supplied per pen, and an initial 6-day training period was used, in which pigs experienced each of the two foods on offer, separately, at daily intervals. All pigs were weighed weekly, as was the amount of food consumed in each pen. The conclusions reached were that growing pigs are able to differentiate successfully between two foods on the basis of their amino acid contents, and of changing the selected diet to match their changing requirement for dietary amino acids. However, one of the foods on offer appeared to contain either anti-nutritive factors or unpalatable components, and whereas the piglets performed as well on this as on the other foods of similar nutrient content when these foods were offered as the sole source of food, they actively selected against this food when it was offered as a choice, even if this meant their growing at a significantly slower rate than that of which they were capable.

One hundred and twenty spring-born steers comprised of 40 Friesians (FR), 40 Canadian Hereford × Friesians (HF) and 40 Simmental × Friesians (SM) were reared together from shortly after birth to slaughter after a mean period of 740 days. During the finishing winter there was a 3 (breed types) × 2 (3 and 6 kg supplementary concentrates per head daily with grass silage ad libitum) × 2 (222- and 225-day finishing periods) factorial arrangement of treatments. One side from each of 96 carcasses (eight per treatment) was completely separated into bone, muscle, intermuscular fat and subcutaneous fat and a 10th rib sample of m. longissimus was chemically analysed.

Carcass weights per day of age and carcass weights were 404, 433 and 449 (s.e. 4·6) g and 301, 320 and 330 (s.e. 3·4) kg for FR, HF and SM, respectively. Corresponding proportions of carcass muscle were 602, 577 and 628 (s.e. 4·8) g/kg. FR and HF had similar proportions of their total muscle in the hindquarter, whereas SM had more of their muscle in the hindquarter. M. longissimus lipid concentrations for FR, HF and SM were 36, 39 and 26 (s.e. 1·96) g/kg. Increasing supplementary concentrate level from 3 to 6 kg/day increased side weight by 7 kg, of which proportionately 0·48 was fat. Extending the finishing period from 121 to 225 days increased side weight by 22 kg of which proportionately 0·45 was fat. Both the higher concentrate level and the longer finishing period reduced carcass muscle and bone proportions, and increased carcass fat proportion. Allometric regression coefficients for side muscle, bone and fat weights on side weight were 0·75, 0·51 and 2·13, respectively. It was calculated that FR, HF and SM would have similar carcass fat proportions at approximate carcass weights of 320, 290 and 380 kg, respectively.

Seventy-two, 4-month-old, British Friesian steers were used to investigate the effects of feeding a supplement of fish meal on the voluntary intake and live-weight gain by young growing cattle given a well preserved ryegrass silage. The silage was offered either alone or mixed with 50,100 or 150 g fish meal per kg silage dry matter (DM) and the diets were offered either ad libitum or intakes were restricted to 16, 19 or 22 g dietary DM per kg live weight (LW). Intakes were recorded daily, LW weekly and in vivo apparent digestibility over one 7-day period during the 132-day trial.

For animals fed ad libitum, the absolute intake of dietary DM increased linearly with an increase in the level of fish-meal supplementation such that intake when the highest level of fish meal was given was significantly higher (P < 0·01) than when silage was given alone. However, DM intake per unit LW (approx. 24 g DM per kg LW) was not affected significantly (P > 0·05).

Inclusion of fish meal in the diet did not affect the apparent digestibility of dietary DM, organic matter, acid-detergent or neutral-detergent fibre (NDF) although there was a trend for slightly higher (P > 0·05) gross energy apparent digestibility when fish meal was given. Increasing the level of feeding reduced NDF digestibility. The coefficients measured at the 22 g and ad libitum levels of intake were lower (P < 0·01 and P < 0·05 respectively) than that measured at the 16 g DM per kg LW level.

Animals given silage alone to appetite achieved LW gains of 0·6 kg/day. LW gains increased linearly with increasing level of feeding (P < 0·001) and increasing level offish-meal supplementation (P < 0·001).

The effect of recombinantly derived bovine somatotropin (bST) administration on wool follicle populations, wool growth and body growth was examined in young lambs. Romney × (Border Leicester × Romney) lambs were treated with bST at doses of 0·1 or 0·3 mg/kg live weight per day, or with excipient, commencing on the day of birth and continuing at weekly intervals until the last injection was given at 11 weeks of age. Concentrations of immunoreactive somatotropin in plasma were 19·2 (s.e. 2·1), 65·2 (s.e. 2·8) and 74·7 (s.e. 4·8) μgll in the control, low dose bST and high dose bST groups, respectively. Somatotropin treatment did not alter the density of primary (P) or secondary (S) follicles in the skin, or the S/P ratio, as measured by histological examination of mid-side skin biopsy samples at 14 weeks of age. Mid-side greasy and clean wool growth during weeks 2 to 14 of the study were increased (P < 0·05) in bST-treated lambs but treatment had no effect on wool growth during the immediate post-treatment period (weeks 14 to 22), or on yearling fleece weight or wool quality characteristics. Body growth was not altered by bST administration. It is concluded that bST treatment stimulates wool growth even in very young lambs but, contrary to the results of a previous study, does not alter the development of wool follicle populations.

A total of 63 primiparous hybrid sows were used in two experiments to study the effect of different fat and α-tocopherol levels in the lactation diet on the performance and milk production of sows and on the performance of sucking piglets. In experiment 1, the major differences in energy sources in the lactation diets were tapioca starch or animal fat. Fifteen sows received the low-fat diet (starch and fat content: 396 and 43 g/kg dry matter (DM)) and 16 sows were given the moderate-fat diet (starch and fat content: 286 and 75 g/kg DM) during 4 weeks of lactation. In experiment 2,16 sows were given a low-fat diet (diet 1: starch and fat content: 418 and 37 g/kg DM) and 16 were given a high-fat diet (diet 2: starch and fat content: 266 and 125 g/kg DM) during 4 weeks of lactation. In diet 2, 68 g animal fat replaced the 200 g starch present in diet 1. The mean α-tocopherol contents of foods in experiment 1 were 14 and 126 mg/kg diet and in experiment 2, 22 and 151 mg/kg diet. The live weight, backfat thickness and milk production of sows were not significantly affected by the different dietary fat levels (P > 0·05). The high dietary fat level increased the DM, fat and energy content of milk and the daily gain of piglets in the second part of lactation in experiment 2 (P < 0·05). The correlation between piglet growth and milk fat and milk energy intake (r) in experiment 1 were: 0·57 and 0·66 and in experiment 2 were 0·41 and 0·40 respectively. The utilization of whole milk and DM, fat, protein and energy content of milk for piglet growth was not influenced by dietary fat level. Varying the level of dietary α-tocopherol did not affect the variables investigated.

Development of new systems of lamb finishing for the late winter/spring market involving an extended housed store period on a predominantly straw diet are constrained by unacceptable reduction in muscle mass arising from inadequate protein supply during dietary adaptation from grass to straw. Problems with subsequent finishing on forage brassicas fedin situ arise from carcass contamination due to soiled wool of crossbred lambs which grow long fleeces over the extended store I finishing period. In order to study the effect of fish-meal supplementation on dietary change over from grass to straw 116 Mule wether lambs were allocated to four treatments, three of which received a supplement of 100 glday fish meal for 28 days from housing and introduction of a diet of straw ad libitum and 225 glday grain distillers' dark grains, the fourth group received no fish meal and was unshorn (No F/US). Shearing treatments of shorn (F/S), unshorn (F/US) and crutched (F/C) were applied to fish-meal supplemented group's. After 112 days, the housed lambs were grazed outside on swedes (Brassica napus) and effects of treatments on performance and bacterial contamination of carcasses (shearing treatments only) were studied. Fish-meal supplementation significantly reduced weight loss on dietary change by 2·2 kg after 45 days (P< 0·001). Of fishmeal supplemented lambs 83% eventually ‘finished’ (defined as Meat and Livestock Commission fat class 3LI3H) v. 34% of unsupplemented lambs. Shearing or crutching had little effect on store or finishing performance indicating adequate fleece regrowth for insulation purposes after turn-out. Shorn and crutched lambs had lower levels of bacterial carcass contamination with reductions of 0·06, 0·42 and 0·40 in counts for colony forming units per cm2, coliforms and Escherichia coli on leg sites (P < 0·05). Economic evaluation indicated financial advantage from fish-meal supplementation with an increase in margin over food costs of €3·50 as a result of heavier carcass weight and a reduced need for remedial concentrate feeding in the store period.

A biological growth model was developed to study economic values for average ad libitum food intake capacity (FIC) in growing pigs. The model was based on the linear/plateau relationship between protein deposition and food intake. Input variables were: minimum fat to protein deposition ratio (R), maximum protein deposition rate (Pdmax)and food intake (FI). Output variables were production traits and production costs.

Economic values (under commercial conditions with ad libitum feeding) were derived with the growth model for each of the traits FIC, R, and Pdmax keeping the other two traits constant, for three alternative levels of FIC. If FIC was too low to realize Pdmax, FIC had a positive economic value, R had a negative economic value and the value of Pdmax was zero. If FIC was higher than necessary to realize Pdmax, economic values were negative, zero and positive for FIC, R, and Pdmax respectively. If FIC was just sufficient to realise Pdmax, the lowest production costs occurred. Now, R had a negative economic value and Pdmax had a positive economic value.

With a restricted feeding regimen under commercial conditions a daily food supply just sufficient to realize Pdmax should be pursued. It was concluded that use of a biological growth model to estimate economic values for FIC would give more insight into correct selection strategies than would the use of an economic model.

Seven groups of five or six Holstein-Friesian male calves were transported to an experimental farm at 2 to 3 days of age. At 6 days of age, heat production (HP) and metabolizable energy (ME) intake were measured for an 8-day period. During this period, calves were exposed to various ambient temperatures: 6, 9, 12 and 15°C. Ambient temperature was constant within days, but changed between days. Calves were fed below (four groups) or near (three groups) the maintenance requirements (290 or 460 kJ ME per kg M0·75 per day).

From 6 to 14 days of age the lower critical temperature (Tc) was 12·5°C and HP increased by 8·4 kJ/kg M0·75 per day per °Cfall in ambient temperature below Tc. Both Tc and increase in HP below Tc were not affected by feeding level. Rectal temperature was lower at low ambient temperatures. The decrease in rectal temperature with ambient temperature was greatest at the low feeding level.

During the experimental period, calves were not in a steady-state regarding energy metabolism. Heat production decreased with time. This decrease was affected by feeding level and ambient temperature. After arrival, the influence of both ambient temperature and feeding level on the energy metabolism of young calves increased with time.

Four experiments examined the chemical composition, intake, dry matter (DDM) and organic matter (DOM) apparent digestibilities and rates of disappearance from nylon bags of hand-separated leaf and stem fractions of straw from four genotypes of barley: Arabi Abiad, Beecher, C63 and ER/Apam. In experiment 1, 900 g leaf from each genotype was offered to three or four wethers together with 200 g soya-bean meal (SBM), and in experiment 2 the leaf from the same four genotypes was offered ad libitum with 200 g SBM. In experiment 3, 500 g stem from Arabi Abiad and Beecher was offered with 100 g SBM to six wethers in two groups. Experiment 4 measured the rate and extent of disappearance of the leaf and stem fractions from nylon bags incubated in the rumen of wethers. The genotypes had widely contrasting morphological characteristics. Stems contained about half as much ash and crude protein as leaves and differences within fractions were small. The leaf and stem fractions of the two-rowed barleys Abiad and Apam contained less modified acid-detergent fibre than the six-rowed Beecher and C63 genotypes.

When leaf was offered with SBM, both restrictedly and ad libitum, the DDM and DOM of this fraction were similar between genotypes (P > 0·05) and in experiment 2 the intake of leaf was also similar between genotypes (P > 0·05). The apparent digestibility of stem differed significantly between Arabi Abiad and Beecher in experiment 3 (P < 0·05). Significant differences were apparent between genotypes in the extent and rate of disappearance of leaf and stem from nylon bags after 48 h incubation in the rumen.

Sheep of three hill breeds, Scottish Blackface, Cheviot and Welsh Mountain and the reciprocal crosses among these breeds were inbred (mostly by parent × offspring mating) for four generations to five levels with inbreeding coefficients ofO, 0·25 (I1), 0·38 (I2), 0·50 (I3) and 0·59 (I4). Inbred females were also mated to unrelated inbred males of the same breed type to produce line crosses (LC). Each type of dam (except LC and I4) was mated to produce lambs of up to three different inbreeding levels thus allowing the effects of the individual's own inbreeding to be separately assessed from the effects of maternal inbreeding. This study examined body weight at a sequence of ages from birth to 4 years of age with 2369 animals (ages up to 78 weeks old) or 1062 animals (2 to 4 years old) contributing to the analyses.

Inbreeding of the individual had a highly significant retarding effect on body weight and growth rate up to the I2 level for weights of lambs up to 24 weeks old, with a slight recovery in performance thereafter. For the later ages examined, the maximum depression was reached at the I3 stage. The partial recovery in performance at the higher levels of inbreeding for lambs less than 24 weeks of age was also noted within lines and did not therefore appear to arise only from a loss of lines as inbreeding proceeded. The effect of dam's inbreeding was to depress growth up to the I3 level and at most ages up to I4. Line-cross lambs were generally heavier (but not significantly so) than non-inbred (F2 and the pure equivalent, O2) and progeny of line-cross dams were similar in weight to those from other non-inbred (F1, or F2 and O1, or O2 dams) or slightly better. The more highly inbred the individuals the more, in general, they fell behind the weights of the corresponding non-inbreds as they grew older. Inbreeding may thus have permanently stunted the sheep.

There were no significant differences between purebred and crossbred sheep in the rate of inbreeding depression. Only at the ages of 3 and 6 weeks was there a significant difference between the three pure breeds in the changes in weight attributable to inbreeding. Up to the age of weaning (15 weeks) the changes with inbreeding of individuals could not be explained statistically in terms of dominance effects alone and non-allelic interactions may therefore also be involved. At all ages the effect of inbreeding of the dam was consistent with dominance effects alone.

Optimum selection directions for average ad libitum food intake capacity (FIC) in growing pigs were derived by means of a biological growth model based on the linear/plateau relationship between protein deposition and food intake. Breeding goal traits were minimum fat to protein deposition ratio (R), maximum protein deposition rate (Pdmax) and FIC. The selection index included FIC, daily weight gain (DG), backfat thickness and proportion of lean meat in the carcass of a full-sib.

Selection indexes were developed for three alternative levels of FIC. If FIC was too low to realize Pdmax, the economic weight of FIC was positive and optimal selection emphasis should be mainly on FIC, resulting in a rapid increase of DG. If FIC was higher than necessary to realize Pdmax, the economic weight of FIC was negative, and short-term selection resulted in increase of carcass leanness but decrease of FIC and DG. If FIC was just sufficient to realize Pdmax, selection should be for R and Pdmax. In this third alternative, the gain in FIC should follow the gain in R and Pdmax in an optimal way and selection should best be carried out with a desired gains index, which results in improvement of DG and carcass leanness.

It was shown that, in cases where FIC was higher than necessary to realize Pdmax, selection with a desired gainsindex should be preferred because this was more profitable in the long term. From the model calculations, it followed that future profit from selection of growing pigs for production traits is likely to decline because of the necessity to increase FIC.

Four sheep (live weight 39 to 42 kg) fitted with rumen cannulas were offered ammonia-treated barley straw alone (control) or supplemented with unmolassed sugar-beet pulp or rolled barley at 0·20 or 0·40 of the total diet on a fresh weight basis (SBP20, SBP40, B20 and B40, respectively) using a 4 × 5 randomized block design. Total diet intakes were 710, 873, 1054, 843 and 1021 g dry matter per day for control, SBP20, SBP40, B20 and B40 respectively. The intake of straw was depressed significantly with SBP40 and B40 (P < 0·05). Rumen pH and ammonia concentration decreased, and total volatile fatty acid concentrations increased (P < 0·05) with increasing level of supplementation for both supplements. Rumen liquid outflow rate was affected little by the supplementation although this measurement for B40 was significantly higher than that for the other treatments. Microbial protein supply, estimated from urinary excretion of purine derivatives, increased significantly with the increasing amounts of supplements (4·5, 6·7, 8·5, 7·1 and 9·0 (s.e.d. 0·73) g N per day for control, SBP20, SBP40, B20 and B40 respectively) (P < 0·05). The calculated efficiency of microbial protein production was 12·8, 14·2, 14·3, 15·7 and 14·5 (s.e.d. 1·45) g N per kg digestible organic matter intake (DOMI) for the five treatments. Although this value was lowest with the control, differences between treatments were not significant (P > 0·05). It seems that microbial protein yield per unit DOMI for a diet based on ammonia-treated straw could not be improved substantially by supplementation with sugar-beet pulp or barley.

The nutrient partitioning of growing pigs was altered through nutrition and castration in order to investigate the relationship between serum insulin-like growth factor 1 (IGFl) and protein deposition and serum cholesterol and fat deposition. In a 2 × 2 factorial experiment 18 entire and 18 castrated male pigs, of 20 kg initial live weight, were given either 2·25 (low) or 3·4 (high) times maintenance energy requirements to a scale based on live weight. Nitrogen and energy balances were measured over 7-day periods when the pigs reached about 30, 60 and 90 kg. Fasting blood samples were taken at each weight and serum was analysed for IGFl and insulin and total- and high density lipoprotein (HDL)-cholesterol. Protein and fat deposition, IGFl and cholesterol concentrations were higher for pigs given the high, as opposed to the low, feeding level. Protein deposition and IGFl concentrations were higher for entire males, as opposed to castrated males, whereas fat deposition and cholesterol concentrations were higher in castrated than in entire males. IGFl and protein deposition increased with age for entire but not for castrated males. Conversely, fat deposition increased with age in castrated but not in entire males. There was no effect of age on serum cholesterol. Serum IGFl was correlated with protein deposition at 30, 60 and 90 kg (r = 0·40, r = 0·63 and r = 0·67; P < 0·05, P < 0·002 and P < 0001 respectively, no. = 36). Serum total cholesterol and low density lipoprotein (LDL)-cholesterol were correlated with fat deposition at 60 and 90 kg (r = 0·65 and r = 0·54; both P < 0·001 for total cholesterol; r = 0·66 and r = 0·50; both P < 0·001 for LDL-cholesterol). Insulin levels were similar for pigs in all treatment groups. It is concluded that serum IGFl and cholesterol may give a useful indication of protein and fat deposition in pigs of between 60 and 90 kg live weight.

Sheep of three hill breeds and the crosses among them were closely inbred for four generations to create five levels with inbreeding coefficients 0·0 (F2/O2), 0·25 (I1,), 0·375 (I2), 0·50 (I3), and 0·59 (I4). Inbred females were also mated to unrelated inbred males of the same breed or crossbred type to produce line-crosses (LC). Mating was arranged so that the effects of inbreeding on the individual could be differentiated from maternal inbreeding. A total of 2369 animals were available up to 78 weeks of age and 1062 to the age of 4 years. This study examines the effects on six linear body dimensions and draws comparison with the effects on body weight. There were significant reductions in the size of the body dimensions with increasing inbreeding but the maximum depression was usually at the I2 stage for individual inbreeding and the I3 stage for maternal inbreeding. Most of the linear and many of the non-linear effects of inbreeding of the individual were significant and the effects of maternal inbreeding were also significant in a majority of cases. Inbreeding effects were more marked for relatively late-maturing parts (shoulder and hook widths) than for early-maturing (cannon bone and tibia lengths) with head width and body length intermediate but closer to the early-maturing parts. This was seen separately at each age, and in the effects of advancing age. By 78 weeks of age, the effects of inbreeding of the individual on absolute size had increased with age and by 4 years of age, in spite of a small recovery in size relative to F2/O2, was still greater than in early life. The effects of maternal inbreeding became progressively less with advancing age relative to non-inbreds. The changes with inbreeding could not be explained by dominance effects alone and epistasis is therefore likely also to be involved.

The effects of four generations of inbreeding, to achieve inbreeding coefficients (F) of 0·25, 0·375, 0·50 and 0·59, on conception rate, prolificacy, litter weight at birth and survival of breeding females, have been studied in sheep. Crosses of inbred lines were also examined. Three breeds, Scottish Blackface, Cheviot and Welsh Mountain, and the crosses among these breeds, were involved. Analyses were carried out both for the data overall and within inbred lines.

Conception rate at the first oestrus at which the ewe was mated (in each year) declined almost linearly from 0·71 (F2 generation - inbreeding F = 0·0) to 0·44 (F = 0·59) with line crosses showing 0·78 conception rate. The corresponding results following up to three rounds of services at successive oestrous periods were 0·91, 0·74 and 0·97 respectively. Analyses within lines showed a steeper rate of decline in conception rate to 0·33 (F = 0·59) following first services and 0·63 following up to three successive periods. This indicates that the lines with the best conception rates survived the inbreeding process better.

Prolificacy, the number of lambs born per ewe lambing, dropped from 1·73 (F = 0·0) to 1·37 (F = 0·25) and thereafter more slowly to 1·24 (F = 0·59). Line crosses were no better than the initial non-inbred generation (F2 and the purebred equivalent O2). Within-line analysis gave the same results.

The effects of inbreeding on litter weight at birth mirror closely those for prolificacy.

Ewe survival declined linearly with inbreeding. There was a 1·2-fold increase in the risk of death for every increase in the inbreeding coefficient (F) of 0·1 (analysed by using a proportional hazard model).

In general, there were no significant differences between purebred and crossbred sheep in the effects of inbreeding. For conception rate, prolificacy and litter weight (for which the point was examined) the changes with inbreeding could not be explained, statistically, in terms of dominance alone, suggesting, therefore, that epistasis is also involved.