The long-term genetic contributions were calculated for 219 Finnish Ayrshire bulls born between 1958 and 1964 to 707 Finnish Ayrshire bulls made available for artificial insemination and born between 1986 and 1988. Three strategies were employed:(i) using all known pedigree information; (ii) ignoring information on the dam of females; (iii) only using information on sires. Expected contributions were calculated using gene flow matrices.

The contributions from strategies 1, 2 and 3 were only 0.6 (1 and 2) or 0.7 (strategy 3) of those expected. The causes of this shortfall for strategies 2 and 3 were identified as (i) the use of an imported sire and (ii) generation skipping. For strategy 1, 0.2 of the expected pathways remained unaccounted for and were ascribed to missing pedigree information.

Of the 219 ancestors, only 86 made positive contributions to the descendants. Only 10 ancestors made contributions more than the average, and one bull accounted for 0.3 of all pathways traced on strategy 2. There was general agreement in the relative contributions of individual bulls when assessed using the three strategies.

The rate of inbreeding (ΔF) estimated by regression from 1974 to 1988 and using known pedigrees was 0.0018 per year and the average coefficients of additive genetic relationship among cohorts was increasing by 0.0030 per year. AF was estimated using the contributions calculated by strategies 1, 2 and 3 to be 0.0147, 0.0151 and 0.0125 per generation respectively. These were converted into rates per year by assuming a generation interval of 6.5 years taken from both published and new information on generation intervals in the Finnish Ayrshire population. This gave annual rates of 0.0023, 0.0023 and 0.0019. The estimates from strategy 3 were obtained without the use of any pedigree information pertaining to dams.

A dynamic programming model was used to derive economic values for the goal traits milk, fat and protein yield and longevity. The economic values derived were £3.37 per % cows surviving to complete lactation four (conditional on having a milk record in the first lactation) and £-0.03, £0.60 and £4.04 per kg for milk, fat and protein yield respectively. In terms of genetic standard deviations the weight for protein, fat, milk and longevity were 1.0, 0.21, —0.25 and 0.55, respectively. Using economic values and genetic (co) variances, weights were derived for milk fat, protein and four linear type traits (chosen out of fifteen on the basis of the genetic correlation with longevity): angularity (angular), foot angle (steeper), udder depth (shallower) and teat length (shorter). Three additive indices were derived, assuming that the breeding goal was for: (i) yield only (PIN), (ii) longevity only (LIN) or (ii) yield and longevity, hence economic merit (ITEM). Selection on ITEM is expected to give a 2% higher annual rate of genetic progress compared with selection on PIN. Efficiency of using ITEM was larger than 0.97 compared with the optimum index, when the real individual economic values increased or decreased by a factor 1.5 or 2.0. Weights for ITEM were calculated assuming that predicted transmitting abilities (PTAs) from complete multivariate analysis were used as index measurements. In the practical situation that index measurements came from (i) separate univariate best linear unbiased prediction (BLUP) evaluations or (ii) two multivariate BLUP evaluations (one for type and one for yield), efficiency of ITEM (compared with the optimum index) decreased with decreasing accuracy of the PTAs and with increasing ratio between number of records for type and yield, or vice versa, but remained close to 100%. Only in the (not practical) situation where accurate PTAs for type and inaccurate information for yield were combined, did the efficiency of ITEM drop as low as 0.44, due to a change of sign for udder depth in the optimal index.

Thirty-six Holstein/Friesian cows were used in a 3 × 2 factorial design randomized-block experiment to evaluate the production and nutrient utilization responses of animals of three genetic indices (cow genetic index 90 (CGI); 950, 650 and 550), each given either a complete diet (CD) or concentrate separate from grass silage through out-ofparlour feeders (OPF). The experiment included days 11 to 160 of lactation. On the CD treatment the diet was offered ad libitum with a concentrate proportion of 0.64 (dry matter (DM) basis), while on the OPF treatment the grass silage urns offered ad libitum and the allowance of concentrate was made equal to the mean concentrate intake of the CD treatment during the previous week. The concentrate was based on barley, maize gluten, molassed sugar-beet pulp, citrus pulp, soya-bean meal, fish meal and protected fat. During the experiment eight blocks each of six animals were used in metabolism studies to determine total ration digestibility, nitrogen balance and energy utilization.

No significant feeding method × genetic index interactions were found in terms of food intake, milk production or nutrient utilization. Although CGI had no significant effect on total DM intake, silage DM intake increased linearly as the cow CGI increased (P < 0.01) across the CD and OPF treatments. The high CGI cows produced respectively 6.60 and 8.25 kg/day more milk fP < 0.001) than the medium and low CGI animals without altering milk concentrations of fat and protein, but with on average a negative live-weight change with the high CGI cows. Although nitrogen digestibility was significantly higher with the low than medium CGI cows (P < 0.05), cow CGI had no significant effects on DM and energy digestibilities, daily methane energy output, heat production or the efficiency of utilization of metabolizable energy for lactation fk,) in the metabolism study. The results indicated that higher milk production with the high CGI cows was mainly attributed to an alteration in nutrient partitioning between milk energy and body energy retention.

Across the three genetic indices, feeding method had no significant effect on total DM intake, although silage DM intake was 0.46 kg/day higher (P < 0-05) on the OPF treatment. However feeding the complete diet resulted in 3.04 kg/day more milk CP < 0.05) than feeding concentrate separate from silage without altering milk concentrations of fat and protein. In the nutrient metabolism study whole tract digestibilities of DM (F < 0.001), nitrogen (P < 0.05) and energy (P < 0.01) were higher on the OPF treatment, but methane energy output and heat production were similar between the two treatments.

Two groups of eight Charolais heifers were used to examine the effect of feeding level during the post-weaning winter on the grazing behaviour and herbage intake over three periods during the first 2 months of grazing. The winter diets (L and H) were given to achieve a mean difference of 50 kg between groups at turn-out. The heifers were set-stocked together on a hill pasture where sward height was maintained at 12 cm.

The winter live-weight gains were 0·31 and 0·70 (s.e. 0·032) kg/day for L and H heifers respectively, and spring gains 1·94 and 1·66 (s.e. 0·082) kg/day respectively. Intakes increased throughout the spring grazing for both groups. Absolute intakes were lower for L than for H heifers only during the first period (P < 0·05). Intake per kg live weight was higher in L than in H heifers (23·0 v. 21·1 (s.e. 0·54) g organic matter (OM) per kg live weight). Bite weights of H heifers were constant throughout (434, (s.e. 12·9) mg OM), while bite weights ofL heifers only reached those of H heifers in the last period. Bite weight was linearly related to live weight. Bite rates were not different between groups, but L heifers compensated for lower bite weight by grazing longer and they increased their grazing time after turn-out faster than H heifers. Grazing time was mainly responsible for higher relative intakes in L heifers, and thus, partly, for compensatory gain observed.

Data from two experiments are reported which test the hypothesis that nutrient and/or dry-matter intake and body condition may interact to modify hypothalamic opioidergic activity and thus influence the pulsatile release of LH during the early post-partum period and during the oestrous cycle. Experiment 1 involved 16 multiparous, twin-suckling beef cows, and was a 2 × 2 × 2 factorial design in which the factors were level of post-partum energy intake (80 v. 130 M) metabolizable energy (ME) per day), the digestible undegradable protein (DUP) content of the post-partum diet (14 v. 31 g/kg dry matter), and treatment with either 200 mg or 400 mg naloxone hydrochloride. Blood samples were collected at 15-min intervals for 4h at weeks 4 and 7 post partum. Naloxone was administered intravenously after the eighth sample. Experiment 2 involved 16 cyclic maiden heifers and was also arranged in a factorial manner, with two levels of body condition at the start of the experimental period (2·50 and 3·16 units) and two levels of energy intake thereafter (40 and 80 MJ ME per day). Seven blood samples were collected at 15-min intervals on 4 days consecutively during the mid-luteal phase of the oestrous cycle. On the first 2 of these 4 days naloxone was administered, whilst on the last 2 days a gonadotropin-releasing hormone agonist (buserelin; GnRH) was administered, both after the fourth sample. Plasma from both experiments was assayed for LH and prolactin (Prl).

In experiment 1, cows on 130 MJ ME per day returned to oestrus and ovulated earlier than cows on 80 MJ ME per day (44·5 v. 55·0 days; s.e.d. = 3·93; P < 0·05). At week 4 post partum the proportional increase in plasma LH following naloxone challenge was greater for cows on 130 MJ ME per day than cows on 80 MJ ME per day (1·38 v. 1·12; P < 0·05), but the converse was true at week 7 (1·15 v. 1·68; P < 0·05). Cows on the high DUP diet required a higher dose of naloxone to elicit an LH response. Few heifers in experiment 2 exhibited an LH response to naloxone. In contrast, there were significant dietary treatment effects on the LH response to GnRH (P < 0·01). Relatively thin heifers on 40 MJ ME per day exhibited the lowest proportional increases in plasma LH to GnRH challenge, whereas heifers on 80 MJ ME per day and given the higher dose of GnRH produced the greatest plasma LH responses. Mean Prl concentrations before and after feeding in experiment 2 were respectively 13·2 and 10·2 ng/l (P < 0·01).

Suckled cows given a high energy diet during the early post-partum period can overcome the opioid mediated block on LH release and resume oestrous cycles earlier than cows given a low energy diet. LH would appear to be inhibited by a non-opioid mechanism in mid-luteal phase heifers. Total pituitary reserves ofLH may be influenced by the animals nutritional status.

Alternative closed breeding schemes for beef cattle are analysed using stochastic computer simulation. Multiple ovulation and embryo transfer (MOET) schemes are compared with conventional schemes (schemes without MOET) with an equal expected number of progeny born per year. Schemes are compared for genetic gain and inbreeding obtained after 25 years of selection. The trait considered, evaluated in both sexes, has an initial heritability of 0·35. Different population sizes and numbers of sires selected are evaluated. Current realistic parameters for embryo production are assumed in MOET schemes.

After 25 years of selection, and with no control on inbreeding, cumulative genetic gains are about 50% higher in MOET schemes compared with conventional schemes. The benefit from MOET is mostly due to increased selection intensities in females. The rate of inbreeding increases by up to nearly 300% when MOET is used. This maximum percentage increase in inbreeding following the use of MOET can be reduced to about 100% when selection and mating strategies for controlling inbreeding are used. The effect of the number of sires used on the inbreeding obtained is more important than the effect of the size of the herd. In MOET schemes, increasing the number of sires selected by a factor of three, leads to reductions in inbreeding rates of 40%. When schemes of the same size are compared at similar acceptable inbreeding levels, MOET schemes give around 30% higher genetic progress than conventional schemes.

Reproductive performance of purebred Angus (A) and Criollo (C) cows and crossbred CA and AC cows in the temperate area of Buenos Aires, Argentina, was assessed through the study of reproductive rates, calving date, first insemination date, number of inseminations and weight related variables. The herd was grazed on pastures all year round. Matings were by artificial insemination with visual oestrus detection, from October to December. Heifers first calving was at 3 years of age. All traits were analysed with general linear models including, as corresponded, fixed effects of dam and calf genetic groups, calving year and month, dam physiological status, calving age and first order interactions. Female genetic group adjusted means were used to estimate direct (gl) and maternal (gM) breed differences and heterosis (hl) effects on reproductive traits. Weaning rate was mostly determined by oestrons detection rate. Due to the inhibitory effects of nursing on reproduction, female genetic group effects were significant for suckling cows only: mean oestrous detection rate was higher (P < 0·05) for crossbred cows (AC: 91·2 (s.e. 5-1) %; CA: 88·4 (s.e. 2·9) %) than for A (76·3 (s.e. 2·0) %) and C (49·9 (s.e. 3·3) %); direct breed effects favoured A (glA - g1c = 26·4 (s.e. 3·7) %; P < 0·001) and h1 was 26·7 (s.e. 3·4) % (P < 0·001). When only oestrous-detected cows were considered, direct breed effects were significant only for pregnancy rate fg1A —g1c = 8·5 (s.e. 4·4) %) whereas h1 was significant for pregnancy (8·3 (s.e. 3·8) %), calving (9·3 (s.e. 4·1) %) and weaning (10·1 (s.e. 4·1) %) rates (P < 0·05). Criollo cows calved later than crossbred (≍19 days) and A (≍15 days) cows mainly due to longer post-partum anoestrous. For calving date, direct breed effects favoured A (g1A — g1c = 20·8 (s.e. 5·9) days; P <0·0·001) and h1 was 11·4 (s.e. 2·8) days (P < 0·001). Low reproductive performance in C was not associated with live iveight at the beginning of mating. This genetic group was the latest in showing oestrous behaviour, even when not suckling. Number of inseminations was similar for the four genetic groups. These results sustain the principle of utilizing Fl Criollo-Angus cows to improve beef herd productivity, whereas they do not support the recommendation of using purebred Criollo females under this type of production system.

A comparison of the patterns of LH and FSH secretion was undertaken in lines of Finn sheep selected for and against high ovulation rate. Mean ovulation rate was significantly higher in the high line ewes (mean 4·1) compared with both the control (mean 2·5) and low line (mean 2·7) ewes (P <0·01). The pre-ovulatory LH peak occurred significantly earlier in the high line ewes (mean 52·1 h) compared with both the control (mean 65·0 h) and low line (mean 59·0 h) ewes (P < 0·05). While mean LH pulse frequency and overall mean LH concentrations were both significantly higher during the follicular compared with the luteal phase of the cycle (P < 0·05), there were no consistent relationships between patterns of pulsatile LH secretion and ovulation rate among the three selection lines. Plasma FSH concentrations remained significantly higher over the entire follicular phase of the oestrous cycle in the high line ewes compared with both the control and low line ewes (P < 0·05). It is suggested that the ovulation rate achieved by high line ewes may be causally related to their higher follicular phase FSH concentrations.

One hundred and thirty-two ewes of the Merino (M), Finn × Merino (FLXM), Border Leicester × Merino (BLXM), Bleu de Maine × Merino (BMXM), Texel × Merino (TXM), Cheviot × Merino (ChXM) and Merino Landsheep × Merino (MLXM) were evaluated for efficiency of lamb production. Individual food intakes of every ewe and also of her lamb(s) were determined over a complete production cycle. Efficiency of lamb production (kg lamb marketed at 35 kg live mass per kg food consumed by the ewe and her lamb(s)) indicated that the FLXM was the most efficient, followed by the TXM, Merino, MLXM, BLXM, ChXM and the BMXM was the least efficient. No significant differences (P < 0·05) were found between genotypes for efficiency of lamb production for ewes producing and rearing singletons until 35 kg live mass with ewe mass included as a covariate. Efficiency of wool production of the Merino was significantly (T < 0·001) higher than that of the other crosses. These results emphasize the importance of reproduction traits in improving efficiency of lamb production.

Information on the chemical composition of Suffolk × Blackface lambs was collected and used to predict empty body (EB) component weights from empty body weight (EBW) and non-carcass (NC) component weights. EBW accounted proportionately for 0·94, 0·89 and 0·95 of the variation in EB crude protein, fat and energy content. A combination of NC component weights accounted proportionately for 0·94, 0·95 and 0·96 of the variation in EB crude protein, fat and energy content. EBW and a combination of NC component weights together accounted proportionately for 0·97, 0·97 and 0·98 of the variation in EB crude protein, fat and energy content. Chemical analysis of NC components is cheaper and easier than whole body analysis and provides a viable alternative to sample joint or specific gravity analysis.

Eiues on grass silage-based diets were offered, during the last 6 weeks of pregnancy, an increasing allowance of a barley-soya-fish meal concentrate (400 g/day in weeks 15/16; 600 g/day in weeks 17/18; 800 g/day in weeks 19/20) as either one, two or three feeds daily or as a complete mix with silage. Silage dry-matter intake increased with concentrate feeding frequency (P < 0·01) and was greatest with the mixed diet at an average of 1·38 of that with a single daily concentrate meal. The effect on silage intake was evident even at the lowest level of concentrate supplementation during weeks 15/16 and was independent of silage quality. Ewes gained more live weight (P < 0·01), and maintained a higher live weight post partum, as a result of increasing the frequency of feeding of concentrates but mean lamb birth weight was unaffected. Maternal serum metabolites were measured in weeks 17/18 and 19/20 only. Mean [i-hydroxybutyrate was higher, but not significantly so, in weeks 19/20 despite the increased concentrate allowance and was higher overall (P < 0·05) in ewes offered concentrates once daily compared with those receiving concentrates three times daily or mixed with the silage. Insulin-like growth factor 1 (IGF-1) was higher in serum of ewes given frequent concentrate meals compared with those offered concentrate once daily (P < 0·05). Serum albumin and globulin increased as concentrate intake increased between weeks 17/18 and 19/20 (P < 0·05) and also, when concentrates were offered more than once daily (P < 0·05). Serum urea level was higher with more frequent concentrate meals (P < 0·01) and was affected by silage quality (P < 0·001).

The efficiency of utilization of absorbed essential amino acids (AA) was studied in wether lambs (35 to 40 kg live weight) given dried grass and dried grass: barley pelleted diets over an intake range from maintenance (M) to 2·5 M energy intake. Each animal was prepared with a duodenal and Heal simple (T-shaped) cannulafor the collection of digesta entering and leaving the small intestine and with a catheter into the abomasum for the infusion of digesta phase markers (103Ru phenanthroline and 51 Cr ethylene diamine tetra acetic acid). The efficiencies of utilization of total AA and individual essential AA (EAA) were calculated from the ratios of the regressions describing AA retention per unit nitrogen (N) intake (assessed using the N retention data obtained in the present study and the AA composition of N retention derived during an accompanying comparative slaughter experiment) and AA absorption per unit N intake. These ratios for total EAA were 0·5 for the grass diet and 0·59 for the grass plus barley diet. Values for individual EAA ranged from 0·32 for threonine in sheep given the grass diet to 0·88 for arginine in sheep given the grass: barley diet. Whilst the ratios for total and individual EAA were generally higher for the grass: barley diet the very wide 95% confidence limits associated with these derived values make any between-diet or between-EAA comparisons equivocal. The data appear to support the introduction by the Agricultural and Food Research Council (1992), of a scaling factor to reduce the high efficiency of utilization of AA used previously.

A well fermented grass silage was mixed with 9·3 g lactic acid per kg silage supplied either as the free acid (lactic acid) or partially neutralized to pH 5·2 with sodium hydroxide (sodium lactate) to give three dietary treatments. Treatment with lactic acid reduced silage pH (P < 0·05) from 4·03 to 3·80 and increased (P < 0·01) the amount of sodium hydroxide required to raise silage pH to 6·5 (neutralizing value) from 167 to 261 mmol/kg silage and osmolality (P < 0·01) from 712 to 854 mosmoljkg silage; sodium lactate treatment increased (P < 0·05) silage pH to 4·15 and osmolality (P < 0·01) to 964 mosmoljkg silage but did not change neutralizing value.

Wlien fed in a randomized-block design to either six intact lambs or to four rumen fistulated sheep lactic acid treatment reduced (P < 0·05) silage dry matter (DM) intake (g/kg weight0·75) from 34·7 to 27·8 for intact sheep and from 35·5 to 29·9 for fistulated sheep. Intakes of the sodium lactate-treated silage tended to be higher (39·2, intact and 40·1, fistulated sheep, g/kg weight0·75) than the control silage. Silage DM intake was correlated more closely with neutralizing value (r2 = 0·34) than pH (rz = 0·24).

Treatment of silage with lactic acid or sodium lactate did not change rumen pH, volatile fatty acid patterns or osmolality. Blood pH, pCO2 and bicarbonate concentrations were not changed by the diets offered and were within normal ranges. Urine acid-base balance was not affected by lactic acid treatment whereas urine pH, and bicarbonate and sodium excretion were (P < 0·01) increased by sodium lactate treatment of the silage.

The intestinal production of skatole and its deposition in backfat was investigated in 35 uncastrated crossbred male pigs. The pigs were fed five purified non-commercial diets containing either casein or brewers yeast slurry as protein source. The yeast slurry diet was used alone or supplemented with either wheat bran (200 g/kg), sugar-beet pulp (200 g/kg), or soya oil (100 g/kg).

Skatole concentrations in backfat, and in digesta in different sections of the gastro-intestinal tract were measured at slaughter (mean weight 112 kg). There were large variations in skatole concentrations in the hind gut of different animals given the same diet. Although there was some correlation between skatole in intestinal contents and deposition in adipose tissue, there were also large variations between individual animals in their response to intestinal skatole. Nevertheless, there was a clear effect of diet on both intestinal skatole production and skatole deposition in backfat. The use of casein as a protein source decreased microbial skatole production, the total amount in the gut, and the concentration in the backfat. Addition of sugar-beet pulp to the yeast slurry diet increased microbial activity in the intestine (measured as ATP content, concentration of short-chain fatty acids, and lowering of digesta pH). There was a decreased rate of skatole production during in vitro incubations of intestinal content, and less skatole in the hind gut and backfat.

In vitro fermentations of freeze-dried Heal effluent inoculated with faecal bacteria, and addition of substrates to in vitro incubations of intestinal contents, demonstrated that tryptophan availability rather than microbial activity was the limiting factor for skatole production.

The results show that skatole production depends on the amount of protein entering the hind gut and the proteolytic activity of the intestinal microbiota. Protein fermentation in the hind gut can be decreased either by using more readily digestible protein sources (for example casein rather than yeast slurry) which reduce the amount of protein passing through to the hind gut, or by adding an alternative energy source which is more readily metabolized by the hind gut microbiota (for example supplementation of the yeast slurry diet with sugar-beet pulp). This provides a basis for the rational design of diets which will decrease skatole concentrations in the carcass.

Forty days after mating, 16 pregnant sows were randomly allocated to two diets containing either sugar-beet pulp (SBP) or wheat straw (WS) each offered at two levels (1·0 or 1·5 × maintenance energy requirement (M), where M = 460 kJ digestible energy (DE) per kg0·75 per day). Diets were iso-nitrogenous, and contained similar levels of DE together with 260 g non-starch polysaccharides (NSP) per kg dry matter (DM) largely derived from either the SBP or the WS. A 7-day NSP and DM balance was made between day 60 and 100 of gestation. During lactation sows had ad libitum access to a conventional sow diet which contained neither SBP or WS.

Outputs of both fresh and dry faeces from sows given diet WS were significantly greater than the outputs from sows given the corresponding SBP diets (P <0·05), and outputs were significantly greater at the higher feeding level for both diets (P < 0·05). There was a tendency for higher urinary outputs from sows given diet WS, but these were variable and not significantly different from those from sows given diet SBP. The apparent digestibility and retention of DM was significantly greater for the SBP diet than for diet WS but were not significantly affected by feeding level. The apparent digestibilities of the total NSP and each of the individual constituent monomers were significantly higher for diet SBP than for diet WS (P < 0·001), but were independent of feeding level (P> 0·05). Xylose was the most poorly digested NSP constituent from both diets. Apparent digestibility coefficients for the remaining NSP constituents in diet SBP were > 0·8 and were > 0·52 in diet WS, with the uronic acids and mannose being the most highly digested NSP fractions from diets SBP and WS respectively.

The requirement for a training period prior to a choice feeding regime was assessed using 36 weaned piglets whose initial live weight was 6·2 (s.d. 1·21) kg. Two foods (H and L) were offered ad libitum as the choice and these were similar in energy but differed in crude protein (CP) concentration (291 g/kg and 155 g/kg fresh matter respectively). The pigs ivere subjected to one of three training treatments: treatment ALTERNATE allowed piglets the two foods separately on alternate days for 6 days, followed by a free choice of the two foods; treatment THREE allowed 3 days of one food followed by 3 days of the other prior to the free choice; treatment CHOICE gave the animals free choice immediately. Piglets on a fourth treatment, CONTROL, were given a single food M (242 g CP per kg fresh food) as a control. Weight gain (0·60, 0·59, 0·59 and 0·61 (s.e. 0·005) kg/day) and food intake (0·776, 0·752, 0·771 and 0·747 (s.e. 0·010) kg/day) did not differ significantly between treatments ALTERNATE, THREE, CHOICE and CONTROL respectively in the 19-day post-training period. A significant difference was seen in the protein consumption (0·145, 0·150, 0·139 and 0·177 (s.e. 0·005) kg/day). This together with a tendency for the proportion of food H selected to decline as the growth period progressed, indicated that newly weaned piglets are capable of regulating their protein intake when offered a free choice of two foods differing in their CP concentration, without a necessity for an initial training period.

Two experiments were performed to examine the effects of immunoneutralizing PMSG at the onset of oestrus on the reproductive performance of sows. In experiment 1, 12 multiparous sows received 750 i.u. PMSG at weaning and six sozus acted as controls and were injected with saline. At 84 h after PMSG injection, all sows received an injection of 500 i.u. human chorionic gonadotropin (hCG) and six of the PMSG-treated sows also received an injection of 750 i.u. of a monoclonal anti-PMSG serum. The ovaries of all sows were examined by real time ultrasonography at 60-min intervals from 36 to 48 h after hCG injection for evidence of ovulation. In sows observed to ovulate, there was no significant effect of treatment on the interval from hCG injection to the start of ovulation, the duration of ovulation or subsequent litter size. In experiment 2, 253 primiparous sows received injections at weaning of 750 i.u. PMSG (no. = 134), 400 i.u. PMSG plus 200 i.u. hCG (no. = 69) or served as controls (no. = 50). At breeding, 67 of the PMSG-treated sows received an injection of 750 i.u. of monoclonal anti-PMSG serum.

More gonadotropin-treated than control sows were bred by 7 days after weaning (P < 0·05). Farrowing rates were higher in sows receiving the PMSG followed by anti-PMSG and PMSG plus hCG than in controls (P < 0·05), with those receiving PMSG alone being intermediate. There was no effect of treatment on subsequent litter sizes. These data indicate that the reproductive performance of primiparous sows may be improved by gonadotropin administration at the time of weaning. However, there was no advantage to using any particular hormone combination or anti-PMSG.

A pedigree originally designed for pig genome mapping was used in order to study carcass and muscle development as well as meat quality of F2-crosses between the European Wild Pig and the domestic Large White pig (no. = 191). As a marker for the influence of genes inherited from the ‘wild’ and domestic grandparents, grouping based on the length of the small intestine was used. The pigs were also typed for genetic polymorphism at the calcium release channel (CRO locus controlling halothane susceptibility in pigs, and one of the Wild boars was found to be a carrier of the halothane mutation. At assessment, the carcasses were divided into cuts, the back and ham were defatted, and m. longissimus dorsi and the large muscles of the ham were weighed separately.

Wlien grouped according to length of the small intestine, those animals with a short small intestine were more similar to Wild Pig, e.g. they were older at slaughter and had a slower growth rate than the other group. Their carcasses contained less lean meat, more flare fat and more subcutaneous fat. No difference in meat quality could be discerned between the groups, except for a tendency to greater pigment content and higher shear force value in the group with a short small intestine.

The effect of the halothane mutation at the CRC locus was very prominent, although no animals had the gene in homozygous form. Carriers of the gene were leaner and had a higher reflectance value, lower water-holding capacity, lower pHu, higher protein denaturation and higher shear force value.

The growth hormone-insulin-like growth factor (GH-IGF) axis is involved in the control of postnatal growth in all animals studied to date. At birth, blood levels of IGF-1 are low, although levels of GH are high. Thus a switching occurs during the postnatal period, which involves an increase in liver GH-receptors (GHR). This study investigates the changes in serum IGF-1 and IGF-1 and GHR mRNA in liver and skeletal muscle of growing pigs. The period from birth to 20 days of age showed a gradual increase in both IGF-1 and GHR mRNA expression by the liver, thus accounting for the gradual increase in serum IGF-1. The IGF-1 mRNA expressed was found to be predominantly class 1 transcripts with very few class 2 transcripts. There was a plateau of liver IGF-1 mRNA levels after 20 days and up to 140 days, even though the expression of GHR mRNA continued to increase. The levels of expression of the two genes were found to correlate in the first 20-day period (r = 0·76, P < 0·005), but not in the later period (r = 0·44, P > 0·05).

Levels of expression of both genes in the LD muscle were highly variable, with no age related changes being observed. However, a significant negative correlation of expression of the two genes was observed (R = 0·60, P < 0·001), with the correlation still being significant in the two age periods.

The data are consistent with a likely initial dependence for postnatal growth upon GH-stimulated IGF-1 mRNA expression by the liver, up to 20 days of age. After this time, hepatic expression of IGF-1 mRNA reaches a plateau, even though the serum IGF-1 and hepatic GHR mRNA levels continue to rise. A possible explanation for this could be an increase in either turn-over or stability of IGF-1 mRNA, giving rise to increased levels of peptide with no apparent change in mRNA level. Another possibility is that an increased expression/production of the IGF-binding proteins leads to an increase in the half-life of the peptide in the circulation.

Two lines of pigs that had been selected for five generations for lean tissue growth rate (LTGR) on a high (HP) or low (LP) protein diet were evaluated on a commercial diet (165 g crude protein per kg diet). The growth characteristics of 534 animals were measured, and carcass data were obtained on 405 animals. Differences between lines were tested for significance taking genetic drift into account. The animals from the HP-line grew faster both before and during the test and were 6·5 days younger at slaughter than the LP-line pigs. The HP-line pigs had a higher lean content (587 v. 558 g/kg) and a thinner backfat layer (17·8 v. 22·7 mm) than the LP-line. LTGR was higher in the HP-line (374 v. 347 g/day). No significant differences between lines were found in meat quality or in the incidence of osteochondrosis in elbow or knee. The realized differences between lines confirm that selection for LTGR on a high protein diet was more effective in improving both leanness and growth rate compared with selection for LTGR on a low protein diet.