Regulation of the transforming growth factor beta (TGFβ) superfamily by gonadotrophins in swine follicular cells is not fully understood. This study evaluated the expression of steroidogenic enzymes and members of the TGFβ superfamily in prepubertal gilts allocated to three treatments: 1200 IU eCG at D −3 (eCG); 1200 IU eCG at D −6 plus 500 IU hCG at D −3 (eCG + hCG); and the control, composed of untreated gilts. Blood samples and ovaries were collected at slaughter (D0) and follicular cells were recovered thereafter. Relative gene expression was determined by real-time PCR. Serum progesterone levels were greater in the eCG + hCG group compared with the other groups (P < 0.01). No differences were observed in the expression of BMP15, BMPR1A, BMPR2, FSHR, GDF9, LHCGR and TGFBR1 (P > 0.05). Gilts from the eCG group presented numerically greater mean expression of CYP11A1 mRNA than in the control group that approached statistical significance (P = 0.08) and greater expression of CYP19A1 than in both the eCG and the control groups (P < 0.05). Expression of BMPR1B was lower in the eCG + hCG treatment group compared with the control (P < 0.05). In conclusion, eCG treatment increased the relative expression of steroidogenic enzymes, whereas treatment with eCG + hCG increased serum progesterone levels. Although most of the evaluated TGFβ members were not regulated after gonadotrophin treatment, the downregulation of BMPR1B observed after treatment with eCG + hCG and suggests a role in luteinization regulation.

The use of altrenogest (ALT) supplementation for oestrous synchronization improves subsequent reproductive performance of gilts and sows. However, the causes of this improvement in reproductive performance after ALT treatment are not fully/clearly understood. The objective of this study was to evaluate the effects of ALT supplementation for oestrous synchronization in gilts on the endometrial glands and embryonic development characteristics at 28 days of pregnancy. Pregnant gilts were divided into two experimental treatments: Control (did not receive ALT; n = 9 gilts) and ALT (ALT feeding at 20 mg/day for 18 days; n = 9 gilts). At 28 days of pregnancy, six gilts from each treatment were slaughtered, and reproductive tracts were immediately evaluated. There was no statistical difference (P > 0.05) between treatments regarding ovulation rate, number of embryos, number of vital embryos and number of non-vital embryos. Embryo weight, length and embryonic vesicle weight were lower in ALT treatment compared with Control (P < 0.01), and it was lower in the cervical uterine region compared with apex uterine region, respectively (P < 0.05). Higher values of gland duct area, gland duct perimeter, percentage of the glandular area and total endometrial area were observed in ALT treatment compared with Control (P < 0.05). The use of ALT during 18 days for oestrous synchronization in gilts increased the gland duct area, perimeter and total endometrial area but did not increase the embryo number and embryo size at day 28 of pregnancy.

The British monetary authorities tried to encourage lower long-term interest rates through their government debt management operations between 1962 and 1964, following the Radcliffe report's recommendation that they should have an objective for long-term rates, and with the intention of supporting the government's pursuit of faster economic growth. The implementation of the policy was complicated by the Bank of England's role as a market maker in the government securities market, and beset by misunderstandings among the monetary authorities. The policy was abandoned when the conditions of strong market demand for bonds on which it depended changed. The article describes how the policy was developed and implemented, and the impact of political preferences on it.

The objective of the present study was to investigate the effects of dietary-induced insulin enhancement during the late luteal phase on subsequent fertility of gilts. Fifty-two littermate cyclic gilts were subjected to dietary treatments where two energy sources were tested: corn starch (T1) and soybean oil (T2). The experimental diets were supposed to provide similar amounts of dietary energy, but from different sources. Gilts were fed ad libitum, starting day 8 of the estrous cycle, until the next standing heat. Blood sampling was performed in a subgroup of 20 gilts on days 14 and 21 of the cycle for analyses of glucose and insulin, and after ovulation detection until 18 h after ovulation for progesterone. All gilts were slaughtered on day 28 of pregnancy and the reproductive tracts recovered for further analysis. T1 gilts showed higher postprandial insulin peak on days 14 and 21 and lower glucose levels 4 h after feeding on day 14 (P<0.05), however, there were no treatment effects on plasma progesterone concentrations. Dietary energy sources did not affect average daily feed intake, body weight and backfat on day 28 of pregnancy. Estrous cycle length, estrus duration and time of ovulation were not affected by previous nutritional treatments either. T1 gilts showed higher ovulation rates, number of embryos, embryo weight and placental weight (P<0.05). There were no treatment effects on pregnancy rate, embryo survival rate and volume of amniotic fluid. A positive correlation between progesterone concentration 18 h after ovulation and ovulation rate was observed (r=0.75; P<0.01). These results suggest that it is possible to manipulate dietary insulin response in cyclic gilts and, thus, improve reproductive efficiency when feeding starch as the main energy source during the late luteal and follicular phases of the cycle.

Actuarial models of the market in conventional British Government Stocks, also known as the Gilt-Edged market, are reviewed and contrasted with the methods which have been developed, during the last twenty years, by financial economists.

Following the Treasury's announcement in May 1995 (regarding the taxation of institutional bond holdings), the so-called ‘coupon effect’ has largely disappeared and gilt prices can now be fitted very closely by using the same simple discounting functions for both income and capital flows. A new model suitable for the calculation of yield indices is proposed and is contrasted with the model currently underlying the FTSE Actuaries Government Securities (FTSEAGS) Yield Indices. A number of new possible applications of the reformulated yield indices, such as forward pricing, asset/liability matching and stochastic simulation, are discussed. An analogous model for index-linked gilts leads to applications involving the forward market in the retail prices index.

A survey of professional users of the FTSEAGS Indices is described, and a revised presentation for the published yield indices is suggested. A summary of current statutory references to the indices is presented.

Lactational performance was measured in Large White gilts from lines that had been divergently selected over seven generations for daily food intake (DFI), lean food conversion ratio (LFC), lean growth rate with ad-libitum (LGA) or restricted (LGS) feeding during performance test. Control line gilts were included in the study. During the lactation period of 21 days, gilts were given to appetite five isoenergetic diets differing in ileal digestible lysine: energy (0·40, 0·58, 0·76, 0·94 and 1·12 g/MJ digestible energy). The study consisted of 223 gilts with a similar number of animals in each selection line.

Live-weight loss was greater in the low LFC and LGA lines than in the high lines and food intake was significantly lower in the low LGA line than in the high line. Litter-weight gain of the low LFC and high LGA lines were greater than in the complementary selection lines. Prediction equations for nutrient utilization were used to express the effect of diet and selection line in terms of energy and protein inputs and outputs. Selection on DFI or LGS resulted in gilts that did not mobilize lipid during lactation as sufficient energy for milk and maintenance was provided by dietary intake. In contrast, there was insufficient dietary energy with selection on LFC or on low LGA so lipid mobilization was required to achieve energy balance. The energy required to excrete excess protein and energy from lipid mobilization increased as the dietary lysine energy ratio increased, but there were no other dietary effects on energy and protein utilization. Genotype with nutrition interactions were detected for energy intake and lipid mobilization, which were due to the lines selected for low DFI and LGA. The general absence of genotype with nutrition interactions for lactational performance in gilts selected for components of efficient lean growth and the lack of significant dietary effects on energy utilization indicated that the consequences of changing nutritional inputs will be broadly similar for genotypes within the set of genotypes studied. Selection strategies which result in reduced food intake during lactation should be avoided if lipid mobilization is then required to attain energy balance and there are resultant negative effects on subsequent reproductive performance.

Previous studies examining the effect of age on gilt reproduction have generally failed to discriminate between chronological (i.e. days) and physiological age (i.e. number of oestrous cycles experienced) and the importance of each factor remains unclear in the pig. The present investigation tested the hypothesis that the physiological age at which gilts are bred in a dynamic service system (DSS) affects their reproductive behaviour and performance. A hundred and ninety gilts were randomly allocated between two treatments. They were introduced into the service pens of a DSS to be bred at the same age (215 days) but either at second (2H; no. = 96) or third (3H;no. = 94) post-pubertal heat period. The sexual behaviour of half of them was continuously recorded over a 13-week period and reproductive data from all the gilts were collected. Gilts of 2H treatment were significantly heavier at entry into the service pens (123 v. 119 kg; P < 0·05) than 3H gilts, but there was no significant difference in their backfat thickness. Treatment failed to affect the quality and frequency of mating attempts (MAs) gilts received or oestrus duration. Conception rate to first oestrus in the DSS (82%) was not affected by treatment. Litter size and number of piglets born alive was similar for 3H and 2H gilts (12·0 v. 11·7, s.e.d. 0·40 and 11·5 v. 11·0, s.e.d. 0·4 respectively; all P > 0·05). It is concluded that the reproductive behaviour and performance of gilts that had experienced either two or three oestrous cycles prior to mating at a constant age does not differ significantly in a DSS. More studies are needed in order to clarify the possible interactive influence of repeated and frequent services, which are common in a DSS, on gilt reproduction.

Ages at first behavioural oestrus and at elevated plasma progesterone concentration were measured in three selection groups, after seven generations of divergent selection for lean growth rate (LGA), lean food conversion (LFC) and daily food intake (DFI) in a population of Large White pigs. First physiological oestrus was defined to have occurred when a blood plasma progesterone concentration of at least 1 μg/l was detected from weekly sampling of gilts. The study consisted of 146 gilts, which were given 0·75 , 0·81 , 0·88 , 0·94 or 1·0 g/g of daily ad-libitum food intake during performance test and then 1.9, 2.05, 2.2, 2.35 or 2.5 kg/day, respectively, until conception, to determine if there were differences between selection lines in their sensitivity to changes in nutritional inputs.

Responses in oestrus and performance test traits were dependent on selection group. First physiological oestrus was later with selection for high LFC than for low LFC (234 v. 215, s.e.d. 9.1 days) but there was no significant response within each of the LG A (224 v. 226 days) and DFI (218 v. 206 days) selection groups. The probability of exhibiting oestrous behaviour signs at first physiological oestrus was significantly lower in the high LG A line (0·62 v. 0·93 or 0·5 v. 2.5, s.e.d. 0·75 on the logit scale) than in the low line but there were no responses in the LFC and DFI groups. For animals exhibiting oestrous behaviour signs at first physiological oestrus, there were no significant responses in oestrous behaviour score for the three selection groups. Live weight at first physiological oestrus in the LFC and LG A selection groups was greater in the high lines than in the low lines (120 v. 109 and 123 v. 112, s.e.d. 4.3 kg) but not in the DFI selection group (116 v. 111 kg). Responses in ultrasonic backfat (-7.3, -8.2 and 5.0, s.e.d. 1.5 mm) and muscle depth (4.9, 6.1 and -3.5, s.e.d. 1.4 mm) at first physiological oestrus were of similar magnitude in the LGA, LFC and DFI selection groups.

Increasing the ration (amount of food offered) did not have a linear effect on performance test traits and reproductive development, such that ration had to be included in the model as a fixed effect, rather than a covariate. There was no significant effect of ration or of selection line with ration interaction for traits associated with first oestrus.

Selection for lean growth rate had no adverse effect on reproductive development, unlike selection for lean food conversion. Detection of first oestrus with oestrous behaviour signs combined with physiological assessment may be required in genotypes selected exclusively for lean growth rate, rather than relying only on observed behavioural signs of oestrus.

Ages at first behavioural oestrus and at elevated plasma progesterone concentration were measured in three selection groups, after seven generations of divergent selection for lean growth rate (LGA), lean food conversion (LFC) and daily food intake (DFI) in a population of Large White pigs. First physiological oestrus was defined to have occurred when a blood plasma progesterone concentration of at least 1 μg/l was detected from weekly sampling of gilts. The study consisted of 146 gilts, which were given 0·75 , 0·81 , 0·88 , 0·94 or 1·0 g/g of daily ad-libitum food intake during performance test and then 1.9, 2.05, 2.2, 2.35 or 2.5 kg/day, respectively, until conception, to determine if there were differences between selection lines in their sensitivity to changes in nutritional inputs.

Responses in oestrus and performance test traits were dependent on selection group. First physiological oestrus was later with selection for high LFC than for low LFC (234 v. 215, s.e.d. 9.1 days) but there was no significant response within each of the LG A (224 v. 226 days) and DFI (218 v. 206 days) selection groups. The probability of exhibiting oestrous behaviour signs at first physiological oestrus was significantly lower in the high LG A line (0·62 v. 0·93 or 0·5 v. 2.5, s.e.d. 0·75 on the logit scale) than in the low line but there were no responses in the LFC and DFI groups. For animals exhibiting oestrous behaviour signs at first physiological oestrus, there were no significant responses in oestrous behaviour score for the three selection groups. Live weight at first physiological oestrus in the LFC and LG A selection groups was greater in the high lines than in the low lines (120 v. 109 and 123 v. 112, s.e.d. 4.3 kg) but not in the DFI selection group (116 v. 111 kg). Responses in ultrasonic backfat (-7.3, -8.2 and 5.0, s.e.d. 1.5 mm) and muscle depth (4.9, 6.1 and -3.5, s.e.d. 1.4 mm) at first physiological oestrus were of similar magnitude in the LGA, LFC and DFI selection groups. Increasing the ration (amount of food offered) did not have a linear effect on performance test traits and reproductive development, such that ration had to be included in the model as a fixed effect, rather than a covariate. There was no significant effect of ration or of selection line with ration interaction for traits associated with first oestrus. Selection for lean growth rate had no adverse effect on reproductive development, unlike selection for lean food conversion. Detection of first oestrus with oestrous behaviour signs combined with physiological assessment may be required in genotypes selected exclusively for lean growth rate, rather than relying only on observed behavioural signs of oestrus.

From 74 to 180 days of age, a complete diet was offered either ad libitum (AL) or at proportionately 0·8 of the observed consumption (R) to two groups of purebred Yorkshire gilts, comprising 128 and 127 animals, respectively. Half of the animals in each group was served at the first detected oestrus, and the other half at the third detected oestrus, according to a plan defined at the start of the experiment. Animals which failed to show oestrus before 240 days of age were culled.

At 100 kg live weight (LW), AL gilts were younger (-20 days) and had thicker backfat (+2.3 mm) than R gilts. At the first detected oestrus, AL females were also younger (198 v. 203 days), heavier (127 v. 117 kg LW) and fatter (17·8 v. 14·7 mm backfat thickness) than R gilts. No difference between feeding treatments during rearing was observed in the percentage of females detected on heat before day 240. Seventy-three animals were culled from the start of the experiment until service, half of them (54%) failing to show oestrus. At service, LW and backfat thickness in the four treatments ranged from 117 to 148 kg LW and 14·9 to 19·7 mm, respectively. The body fatness, estimated from the ratio of backfat to LW, was higher in AL than in R gilts (0·14 and 0·12 , respectively), whereas no difference was observed between E1 and E3 gilts (0·13 on average). After the first service 15% of the gilts came back into heat but the conception rate was not affected by feeding treatment during rearing.

A 3 × 2 factorial experiment was used to investigate the influence of the breed type of gilts (Meishan synthetic 50% (M), purebred Large White (LW) and purebred Landrace (LR)) on response to insoenergetic diets of differing protein levels (180 g crude protein (CP) per kg, 9 g lysine per kg; or 240 g CP per kg, 12 g lysine per kg) offered to appetite over a 28-day lactation. Body fat reserves were adjusted during pregnancy by supplementing a set quantity of basal diet (131 g CP per kg, 12·7 MJ digestible energy (DE) per kg) with an energy source (maize starch + soya oil), to attain a backfat at P2 (6·5 mm off midline at last rib) of 25 mm at farrowing for all breeds. There were no significant diet effects or breed ×diet interactions on lactational performance. On day 1 of lactation, backfat was: M = 25·9, LW = 24·9, LR = 23·9 mm (P < 0·005). M gilts were lighter at farrowing (M = 173, LW = 192, LR = 182 kg; P < 0·001) and had more piglets than LW and LR. LR gilts had heavier piglets at birth (M = 1·13, LW = 1·18, LR = 1·38 kg, P < 0·001) than M and LW gilts. M gilts had a higher food intake (M = 6·4, LW = 5·2, LR = 5·1 kg/day; P < 0·001) but higher fat (M = 4·1, LW = 2·2, LR = 2·9 mm; P < 0·05) and weight (M = 15·9, LW = 1·0, LR = 4·7 kg; P < 0·001) loss over lactation than LW and LR gilts. LW gilts had a lower lactation output as reflected by lower litter weights at weaning than M and LR gilts (M = 73·7, LW = 59·3, LR = 75·2 kg; P < 0·002). It is concluded that lactation of gilts is not improved by provision of a very high protein diet (240 g CP per kg) and that performance still differs between breeds when backfat levels are standardized.

Forty first cross hybrid gilts were used to study the effect of dietary protein during lactation on free amino acid, protein and total oestrogen concentrations in colostrum and milk. The diets were formulated to contain similar levels of digestible energy (DE) but with either 236 or 186 g protein per kg and 13·3 and 8·1 g lysine per kg air-dried diet respectively. Both diets were offered at 2·5 kg/day for 1 week prior to farrowing and ad libitum throughout a 24-day lactation (no. = 20 gilts per treatment). Colostrum and milk were collected manually at 3h (colostrum), 3, 7, 14 and 22 days (milk) post partum. Free amino acid concentrations in colostrum and milk were determined by high-performance liquid chromatography following derivatization of the amino acids by 9-fluorenylmethyl chloroformate. The lysine and glutamic acid concentrations in colostrum were the most abundant free amino acids followed by tryptophan and taurine in order of decreasing abundance. Milk free taurine concentrations increased to the greatest extent among all free amino acids over the 21 days of lactation. Gilts' mature milk was rich in free taurine, glutamic acid, glycine and lysine. During the first 3 h post partum, the protein content of colostrum was unaffected by dietary protein. However, milk protein content over 7 to 21 days of lactation was significantly higher in gilts offered the higher protein diet (P < 0·001). Total solids in colostrum and milk was not significantly affected by dietary protein. At 3h and 3 days post partum the concentrations of total oestrogen in colostrum and milk, determined by radioimmunoassay, were significantly higher in gilts offered the high protein diet (P < 0·05). These finding indicate that a high protein diet in late gestation and during lactation can influence protein content, amino acid and oestrogen concentrations of milk in gilts.

Fifty-four lean genotype crossbred gilts were allocated at 118 days of age among three diets with different protein concentrations to give lysine: energy (g/MJ digestible energy) ratios: high (0·9), medium (0·6) and low (0·3) given twice daily at 2·9 × maintenance energy. At 160 days of age, gilts were treated with exogenous gonadotropin (PG600™) and animals were examined daily for signs of oestrus. Animals were slaughtered after the second oestrus, if they had shown behavioural oestrus, or at the age of 212 days. Reproductive tracts were recovered for counting of corpora lutea and albicantia. L gilts were lighter than M or H gilts at puberty induction (80, 95, 97 (s.e. 0·73) kg for L, M, H respectively, P < 0·001), with greater backfat thickness (10·8,10·0, 9·2 (s.e. 0·21) mm P2,P < 0·001), lesser longissimus muscle depth (57·4, 65·9, 64·3 (s.e. 0·77) mm, P < 0·001) and poorer food conversion ratio during rearing (3·87, 2·48, 2·42 (s.e. 0·098) kg food per kg gain, P < 0·001). There was no statistically significant difference in the total number of animals that responded to the puberty induction, although L had a greater latency to oestrus than H. Ovulation rate at this induced oestrus was significantly lower in L gilts than in M or H gilts (12·5, 17·3, 21·5 (s.e. 1·32), P < 0·02). A lower proportion ofL, compared with M or H gilts showed spontaneous ovulation in a subsequent cycle (0·15, 0·75, 0·77, %2 = 12·72, P < 0·005). It proved possible, by means of low protein (lysine) diets, to increase body fat reserves in breeding gilts but protein restriction in the rearing phase negatively affected aspects of reproductive performance.

This study examined the temporal relationships between behavioural activity and hormones associated with stress in gilts farrowing in two environments. Thirty-one Large White × Landrace gilts with indwelling jugular catheters were blood sampled daily (08.00 and 16.00 h) from 10 days before their expected parturition date (EPD). Five days before EPD they were moved to either a farrowing crate (C) with no bedding, or a pen (P) (2·5 m × 3·0 m) with straw provided and were blood sampled daily at 08.00, 12.00 and 16.00 h. Around 12 h before the onset of farrowing an extension was fitted to the catheter and blood samples were taken remotely at 30-min intervals. The posture of the gilts was recorded using 5-min scan samples over the 24 h pre-farrowing. The proportion of scans standing (an index of activity) was strongly affected by time (P < 0·001) with peak levels at approximately 8 h pre-farrowing in both treatments, and by treatment (0·25 v. 0·33 (s.e.d. 0·03) for C and P gilts respectively; P < 0·05). Plasma cortisol concentrations also increased before farrowing (P < 0·001) reaching a peak at 12 to 6 h pre-farrowing. Crated gilts had higher cortisol concentrations than, penned gilts (overall mean 41·5 v. 30·7 (s.e.d. 3·8) [μg/l for C and P gilts respectively; P < 0·05) at 24 to 12 (P < 0·05), 12 to 6 (P < 0·01) and 6 to 2 (P < 0·05) h pre-farrowing. Plasma ACTH concentration showed a similar pattern to cortisol over the pre-parturient period, peaking at 12 h pre-farrowing in both treatments (time: P < 0·001); crated gilts had significantly higher concentrations of ACTH at 6h pre-farrowing only (P < 0·05). Plasma β-endorphin concentrations also showed a gradual rise (P < 0·001) towards parturition; however no treatment differences were seen. These results suggest that the pituitary-adrenal (PA) axis is stimulated during pre-farrowing activity irrespective of farrowing environment. Crates, without bedding, further stimulate the PA axis over the pre-farrowing period perhaps by preventing nest-building. The rise in Q-endorphin may be involved in an endogenous defence against parturition pain.

A study was conducted to evaluate increasing dietary levels of threonine on performance and carcass quality of growing gilt pigs (live-weight period of 50 to 95 kg; no. = 384) by using two different types of basal diets. One basal diet (basal A) was composed of highly digestible food ingredients and the other diet (basal B) of less well digested food ingredients. Before starting the growth trial, Heal apparent digestibility ofamino acids of both basal diets was determined in an in vivo digestibility trial with pigs. Both basal diets were composed in such a way as to obtain equal contents for net energy and Heal digestible threonine, lysine, methionine + cystine and tryptophan. The content of Heal digestible threonine in both basal diets was approximately 3·3 g/kg, corresponding with a total threonine content of 4·8 g/kg in basal diet A and 5·4 g/kg in basal diet B. To both diets three graded dose levels (0·4, 0·8 and 1·2 g/kg) of L-threonine were added, providing at the highest supplemented level 4·5 g/kg Heal digestible threonine. The requirement for Heal digestible threonine was estimated to be 4·1 g/kg regardless of diet composition. This estimated requirement was mainly based on the results for food conversion efficiency. For obtaining maximum weight gain, the requirement for Heal digestible threonine was found to be somewhat higher than for maximum efficiency of food utilization. The estimated requirement figure of 4·1 g Heal digestible threonine corresponded with approximately 5·6 g total threonine per kg in basal diet A and 6·2 g/kg in basal diet B. Carcass quality was not affected by the content of threonine in the diets.

A study was made to investigate the influence of pregnancy feeding level (ad libitum (AL) and restricted (R); 2·0 kg food per day) and lactation length on growth, carcass, meat quality and processing characteristics of pregnant gilts (P) slaughtered after weaning on day 0 (P·0), day 10 (P·10) or day 35 (P·35) after farrowing. Non-pregnant (NP) control gilts were slaughtered at live weights of approximately 95 kg (NP-L), 135 kg (NP-M), and 160 kg (NP-H). P gilts were mated at an average age of 172 days and an average live weight of 97 kg. Pregnancy per se reduced live weight and lean growth rates compared with NP-H animals which were slaughtered at a similar age to the once-bred animals. Weight loss during lactation tended to increase with lactation length and was higher for gilts given food ad libitum during pregnancy compared with restricted animals. The weight of closely trimmed lean in the carcass was similar for the P·0, P·10 and P·35 groups (59·5 v. 62·2 v. 58·8 kg respectively; average s.e. 2·42) and all once-bred gilt groups virtually doubled trimmed lean yields during pregnancy and lactation. Curing yields were similar for P and NP gilts. As lactation length increased, the fat content of the longissimus dorsi and of the overlying subcutaneous fat layers tended to decrease and the moisture content of these two tissues increased. The major impact offeeding level was on fat levels which were significantly higher for AL animals. Trimmed lean yields were also higher for AL gilts suggesting that lean growth rates were not being maximized on the R feeding regime. Subjective muscle colour scores indicated that the longissmus dorsi from P gilts was darker than from NP-L animals and muscle colour tended to become darker with increasing lactation length. There were few significant differences between treatment groups for eating quality. Meat from once-bred gilts was generally judged to be tougher than that from NP-L animals and toughness generally increased with lactation length. This study confirms the potential of the once-bred gilt as an efficient producer of pig meat but raises issues regarding meat quality that require further research.

Growth modelling was used to characterize the response to digestible lysine in two experiments (114 gilts in experiment 1 and 96 gilts in experiment 2) from 34 to 72·5 kg and 72·5 to 136 kg, respectively. Maize-soya-bean meal diets were formulated to assure that lysine (5·4 to 10·4 and 5·4 to 9·4 g digestible lysine per kg for experiments 1 and 2, respectively) was the first limiting amino acid. Analysis of variance was used to test linear and quadratic responses in cumulative weight gain on test as digestible lysine increased. A time × digestible lysine interaction (linear, P < 0·001) was detected, indicating that a separate regression equation for each lysine level was necessary. In experiment 1, average daily gain (ADG) and carcass crude protein (CP) accretion were maximized for gilts given 10·4, 9·4 and 8·4 g digestible lysine per kg from 34 to 44 kg, 44 to 54 kg, and 54 to 72·5 kg, respectively. Lipid accretion was minimized for gilts given 7·4 to 8·4 g digestible lysine per kg. In experiment 2, ADG was maximized by feeding 8·4 g/kg from 72·5 to 92·5 kg and 7·4 g/kg from 92·5 to 136 kg. Carcass CP accretion was maximized by feeding 9·4 g digestible lysine per kg, whereas lipid accretion was minimized for gilts given 8·4 g digestible lysine per kg from 72·5 to 136 kg. If feeding graded levels of digestible lysine resulted in parallel lines for protein accretion, mean values would result in accurate data evaluation. However, responses to digestible lysine changed over the feeding period. Therefore, the use of body weight and compositional growth curves offers an approach to more accurately characterize the growing pig's response to increased digestible lysine.

A study was conducted to evaluate the effect of decreasing age of puberty on lifetime productivity in sows. Two lines of gilts from the Nebraska Gene Pool population were used in this study: a line that had been selected for decreased age at puberty (AP) and a line in which selection had been random (RS). The study was conducted in two parts. In part one, 75 gilts were mated at second oestrus and the productivity measured over five parities. A second experiment utilizing 68 gilts was conducted to provide further data for comparing litter size at parity 1, and also to compare ovulation rates in the two lines at second oestrus. Results showed that litter size was similar in both lines across parities. After five parities the percentage of sows farrowing relative to parity 1 was 58-8% for the AP line but only 39·4% for the RS line (P = 0·17). Litter birth weight, litter size and weight at 21 days, number weaned, and lactation food consumption were similar for both lines. Lactation weight loss was not significantly different between the two lines (60·9 (s.e. 5·9) v. 527 (s.e. 5·0) kg, for RS and AP gilts, respectively) but was consistent with the slightly longer weaning to remating intervals in the RS line (7·8 (s.e. 0·7) v. 6·6 (s.e. 0·7) days, P = 0·22). Ovulation rate at second oestrus did not differ between the two lines (14·1 (s.e. 0·9) v. 14·3 (s.e. 0·5), for RS and AP gilts, respectively). The regression of mean accumulative productivity on time was in favour of the AP line (P = 0·05). These results suggest that reproductive performance is not impaired in gilts which have been selected to reach puberty at earlier ages, and productivity at a specific age may be enhanced.

In four experiments, 189 gilts either received PMSG antiserum around the time of a PMSG- (experiments 1, 2 and 3) or PMSG/hCG-induced (experiment 4) oestrus or served as controls. Ovulation rates were not affected by treatment. There was no treatment effect on pregnancy rate (experiments 2, 3 and 4). In experiment 2, numbers of embryos in PMSG-treated control gilts were quite low and were higher (P < 0·05) in those gilts subsequently receiving anti-PMSG treatment. In experiment 3, the mean number of embryos in control gilts were higher than in experiment 2 and there was no effect of immunoneutralization of PMSG. No treatment effect was evident in PMSG/hCG treated gilts (experiment 4). These data indicate that the immunoneutralization of PMSG is unlikely to improve the reproductive performance of gilts following a gonadotropin-induced oestrus except in gilts that otherwise would have poor performance.

Two experiments were performed to evaluate the influence of relaxin on the fertility of gilts inseminated with aged boar semen. For experiment 1, oestrus was induced in 43 Yorkshire × Landrace gilts by injection of 400 i.u. PMSG plus 200 i.u. hCG. At 24 h after oestrus detection, gilts were inseminated with fresh semen (1 to 2 day old; no. = 15), aged semen (5 to 6 days old; no. = 15) or aged semen containing 400 fig/l of relaxin added at the time of semen extension (no. = 13). Pregnancy rates 24 days after insemination were lower in gilts receiving aged semen (P < 0·05), an effect not prevented by added relaxin. There was no effect of either semen age or relaxin on numbers of embryos. In experiment 2, the ejaculates of eight boars were extended with or without the addition of 400 fig/I relaxin and motility monitored for 7 days. Fresh sperm motility decreased from 87-5 (s.e. 2·5)% at collection to 71-2 (s.e. 3·3)% after 7 days. The attenuation of sperm motility was not affected by relaxin.

In a dissection trial in The Netherlands two subpopulations were distinguished: gilts and castrated males. The sampling scheme, which emphasizes extreme values for the proportion of lean meat in the carcass, was followed for the two sexes separately, to ensure sufficient accuracy for a comparison between them. Significant differences between the prediction formulae for the lean meat proportion for the two sexes were found. Since it is not possible to use separate prediction formulae for the sexes in Dutch slaughterhouses, the formulae had to be combined into one overall prediction formula. In this paper it is shown how the separate prediction formulae for the sexes may be combined, utilizing additional data, not involving dissection, which were easily collected on the slaughterline, at little extra cost. The method can be extended to cover any number of subpopulations. Two objectives can be achieved at the same time: subpopulations may be compared accurately on the basis of a stratified sample and from the results of the comparison an efficient, unbiased, overall prediction formula may be distilled.