The potential conflict between reproductive functions and the drive to deposit body protein may impair productive performance in modern gilts of lean genotype. To study the response of the gilt to this conflict, a choice-feeding experiment was carried out to measure the nutrient intake selected by breeding gilts and responses in reproductive and lactation performance. Using a 2×2 factorial design, gilts of two different genotypes (24 of NPD 402, expected higher body protein/lipid ratio (L) or 24 of Camborough 23, expected lower body protein/lipid ratio, (F)) were either choice-fed (C) by offering both a low (120 g crude protein (CP)/kg) and a high protein (218 g CP/kg) feed during rearing and pregnancy or fed conventionally (R) single feeds, ad libitum during rearing and restricted during pregnancy. Choice-fed gilts selected mainly the low protein feed (0.92 of total feed intake) regardless of genotype and had lower protein intakes than R gilts prior to puberty. However, in pregnancy, due to higher feed intakes, C gilts had higher dietary protein and energy intakes than R gilts. C gilts were heavier, and had greater back-fat and eye muscle depth at farrowing than R gilts, but had smaller litter sizes (P<0.01). During lactation, dietary treatments were reallocated so that gilts received either a low (LE, maintenance+45 MJ/day) or a high (HE, maintenance+67 MJ/day) digestible energy intake. Litter size was standardised within 2 days of farrowing. LE gilts had greater decreases in weight and back-fat and eye-muscle depth during lactation than HE gilts, but dietary lactation treatment had no effect on litter performance. The choice-feeding regime which resulted in heavier gilts with greater back-fat and eye-muscle depth at farrowing did not produce any advantage in terms of partitioning of nutrients towards milk production, as indicated by litter performance, irrespective of gilt genotype. F gilts had greater piglet growth rates than L gilts and also had a higher milk protein concentration. A greater number of L than F gilts failed to complete the experiment for health reasons. Treatment effects on glucose tolerance at day 13 of lactation were not significant. Choice-feeding was therefore not found to be suitable for determining nutrient requirements of modern lean-genotype gilts which would improve reproductive performance.

To examine the relationships between passive acquisition of immunoglobulin G (IgG) by piglets from colostrum and concentrations of plasma IgG at weaning, IgG concentrations in the blood plasma of piglets naturally suckling the sow were measured in the first week of life and at 28 days of age in three experiments. In two experiments the quantities of specific antibodies (anti-Newcastle disease virus, NDV) transferred from the sow to the piglet in colostrum were also quantified. The concentrations of IgG in piglet plasma at 28 days of age were significantly and positively related to concentrations in plasma at 2 and 7 days of age. NDV–IgG in piglet plasma declined more rapidly than total IgG between 7 and 28 days of age, but not between 2 and 7 days of age. In one experiment, concentrations of IgG in piglet plasma at 28 and 35 days of age were related to the diet the sow received during pregnancy, with diets including marine oil giving higher values. Estimates were made of the total amount (rather than concentration) of IgG in piglet plasma at different ages and these showed that amounts of IgG increased between 7 and 28 days of age, but not between 2 and 7 days; a similar conclusion was made from the dilution of NDV IgG in piglet plasma. Therefore, these estimates suggested that naturally suckling piglets begin synthesising IgG from 7 days of age and that the amounts of IgG synthesised are positively correlated with the amounts of IgG absorbed from colostrum.

The intake of immunoglobulin G (IgG) by sucking piglets from colostrum was estimated over the first 24 h of sucking by the weigh-suck-weigh technique using experimentally determined correction factors for metabolic and urinary losses and was related to appearance of IgG in piglet plasma. Colostrum immunoglobulin G (IgG) concentrations declined rapidly from 61 mg/ml at the start of sucking to 9.0 mg/ml after 24 h sucking. IgG was first detected in piglet plasma after 4 h sucking, increased to a maximum after 12 to 16 h sucking and thereafter declined. In piglets allowed to suck from birth, there was no significant relationship between estimated IgG intake and plasma IgG concentration suggesting that IgG intake did not limit acquisition of IgG by the piglet. When sucking was delayed by 8 or 12 h, colostrum intakes by piglets were not different from piglets allowed immediate access to the udder but IgG intakes were significantly (P < 0.001) decreased. Total plasma IgG (g/kg live weight) did not decline significantly as a result of delayed sucking. In conclusion, under the experimental conditions employed, the appearance of IgG in piglet plasma was limited by factors other than by colostrum IgG intake.

The effects of different energy Sources in the lactation diet on sow and piglet performance were assessed in association with effects on the metabolic state of the sow around peak lactation. Either maize starch (S) or soya-bean oil (F) was added to a basal diet to provide 0.34 of total digestible energy (DE) intake, such that the experimental diets provided the same daily intakes of DE and crude protein. Twenty-four multiparous sows were allocated between two groups at farrowing, each given one of the two dietary treatments for a lactation period of 28 days. Sow weight and backfat (P-2) as well as individual piglet weights were measured on a weekly basis. Litter sizes were standardized to 10 piglets. Milk samples were collected from sows on days 8, 12, 17, 21 and 25 of lactation to measure milk composition and prolactin concentrations. Blood samples were taken via an ear vein catheter from a subsample (7 S, 6 F) of sows on day 14 of lactation; two pre- and seven post-feeding samples were taken at 60-min intervals to measure plasma prolactin, insulin, glycerol, triglyceride, non-esterified fatty acid, urea, beta-hydroxybutyrate and glucose concentrations. There was no effect of energy source on sow weight or P2 loss or on subsequent weaning-to-oestrus interval. Sows offered starch weaned more piglets than sows offered soya-bean oil (9.4 v. 8.4. P < 0.05). Litter weight gains were higher for S than F sows in week 3 of lactation (2.2 v. 1.7 kg/day, P < 0.05), irrespective of litter size. Significantly increased plasma urea and beta-hydroxybutyrate concentrations and lower post-prandial increases in plasma glucose and insulin concentrations were observed in F sows around peak lactation. Neither milk nor plasma prolactin concentrations were significantly affected by dietary treatments. The metabolic indices indicated that the F diet was more limiting in dietary glucose availability, which was associated with impaired milk yield as indicated by poorer litter performance. In conclusion, this study suggests that starch is superior to fat as an energy source in sow lactation diets, particularly in the later stages of lactation.

Salmon oil (16.5 kg /t), a source of long-chain polyunsaturated n-3 fatty acids, was included in diets offered to multiparous sows during pregnancy and lactation to measure responses in pre-weaning mortality and performance of piglets in two studies. Thefirst study, carried out under commercial conditions, included 196 sows which were offered salmon oil and control diets from immediately post service until weaning. The same diets were also offered to 10 sows per treatment from day 58 of pregnancy in a controlled nutritional study which measured the effects of salmon oil on piglet tissue fatty acid composition. Offering salmon oil to the sow significantly increased gestation length and decreased individual piglet birth weight but had no effect on litter size at birth. Overall, salmon oil reduced pre-weaning mortality from 11(.)7% to 10(.)2% mainly by reducing the incidence of deaths from crushing by the sow. More detailed analysis of mortality using a general linear mixed model and 2294 piglet records, demonstrated that [lie incidence of pre-weaning mortality was significantly decreased with increasing individual piglet birth weight and by inclusion of salmon oil in the diet; the incidence of mortality increased with average piglet birth weight in a litter. Salmon oil inclusion had no effect on weight of litter weaned, sow lactation food intake or subsequent reproductive performance. In both studies, dietary salmon oil increased the proportions of long-chain n-3 polyunsaturated fatty acids in colostrum to a similar extent. In the nutritional study, inclusion of salmon oil reduced the proportions of 20 : 4 n-6 in piglet liver and brain at birth and increased the proportions of long-chain n-3 polyunsaturated fatty acids. Therefore, despite reducing piglet birth weight, offering sows salmon oil reduced pre-weaning mortality of piglets. The nutritional study showed that the amount and type of marine oil used may not have been optimal.

In an attempt to prevent decreases in piglet 20 : 4n-6 status at birth while increasing 22 : 6n-3 status, multiparous sows (eight per treatment) were allocated to one of three different treatments: a basal diet fed from day 63 of pregnancy to term; basal diet supplemented with tuna oil (17.5 g/kg) from day 63 to day 91 and then basal diet alone from day 92 to term; basal diet alone from day 63 to day 91 and then basal diet supplemented with tuna oil from day 92 to term. Tuna oil supplementation increased mainly 22 : 6n-3 intake. Supplementation with tuna oil between day 92 and term increased 22 : 6n-3 to a greater extent in all piglet tissues (brain, liver, retina and the remaining carcass) at birth than supplementation with tuna oil between days 63 and 91. However, while piglet 20 : 4n-6 decreased to a greater extent in liver and carcass when diets were supplemented with tuna oil between days 92 and term than between days 63 and 91, in the brain and retina, the reverse was true; 20 : 4n-6 was decreased to a greater extent between days 63 and 91 than between 92 and term. The effect of pregnancy nutrition on the growth of piglets until 7 d postweaning (35 d of age) was assessed after removing any residual effects of pregnancy treatment by cross-fostering some piglets at birth. Piglets, the diets of whose dams had been supplemented with tuna oil during pregnancy, grew faster during the first 35 d of life than the progeny of sows fed only the basal diet. Feeding tuna oil to sows at different times during pregnancy therefore did not prevent decreases in piglet 20 : 4n-6 status at birth, but did suggest that changes in piglet brain 20 : 4n-6 status between days 63 and 91 of pregnancy were not reversible by later nutrition. Supplementing the diet of the pregnant sow with tuna oil had beneficial effects on postnatal piglet growth.

Addition of marine oils containing long-chainn-3 polyunsaturated fatty acids to the diet of pregnant sows may reduce piglet mortality. In previous experiments, when marine oils have been fed to pregnant sows, improvements in piglet tissue 22 : 6n-3 status have been accompanied by potentially undesirable decreases in 20 : 4n-6. The objective of the present experiment was to establish an amount of dietary salmon oil which would enhance piglet 22 : 6n-3 status while minimising reductions in 20 : 4n-6. Twenty-four pregnant multiparous sows were used in the experiment which began on day 60 of pregnancy (gestation length 115 d). To give four diets, salmon oil was added in increasing amounts (0, 5, 10 and 20 g/kg diet) to a basal diet; the diets were made isoenergetic by adding palm oil to each diet to give a total of 20 g oil/kg diet. Diets were offered to the sows in fixed amounts (2·5 kg/d) until parturition. Piglet tissue samples (brain, liver and retina) were obtained at birth before consumption of colostrum. The greatest increase in piglet tissue 22 : 6n-3 proportions occurred between 0 and 5 g salmon oil/kg diet, with only small increases between 10 and 20 g salmon oil/kg diet. In contrast, tissue 20 : 4n-6 proportions declined progressively as the amount of salmon oil fed to the sow increased. In brain, the change in the value 22 : 6n-3/22 : 5n-6 was greatest between 0 and 5 g salmon oil/kg diet, whereas in liver the value increased linearly with added salmon oil. In addition, piglet brain weight (g/kg live weight) increased to a maximum at 10 g salmon oil/kg diet. The optimum amount of supplementary salmon oil in the current experiment, defined as that which gave the greatest response in brain 22 : 6n-3 proportions with minimum reduction in 20 : 4n-6,was 10 g salmon oil/kg diet. This corresponds to an intake of approximately 2·4 g 20 : 5n-3 plus 3·6 g 22 : 6n-3/d or 0·6 % digestible energy.

Previous studies (e.g. Cia et al. 1998) have shown that modification of body composition of the prepubertal gilt has effects on responsiveness of gilts to exogenous gonadotrophin. Growing pigs are able to select a diet from different foods differing in protein:energy ratio (Dalby 1998); however there is little evidence of what effect the conflicting nutritional demands of growth and reproduction have on diet selection. The objectives of the experiment were to quantify the effects of choice feeding on responsiveness of gilts to exogenous gonadotrophin (Cia et al. 1998) and to investigate the effect of protein source on diet selection as Jones et al.(2000) have observed selection by breeding gilts against a high protein diet containing fishmeal.

The extent to which young sows, which still have a strong drive to continue maternal growth, partition nutrients from body reserves towards milk production, may be influenced by their genetic growth target. Modern genotype sows, with a high mature body protein mass, are thus particularly challenged. It has been suggested that to optimise their metabolic state for expressing lactational potential they will have to achieve a satisfactory proportion of their mature body protein mass before farrowing. This could be constrained by current feeding and breeding regimes. To test this hypothesis, gilts of genotypes differing in their body protein:lipid content were given the choice between a low and a high protein diet during rearing and pregnancy, and their intake, subsequent performance and metabolic state in lactation were measured.

Reproductive performance of modern lean genotypes of pig has been shown to be particularly sensitive to dietary protein (Sinclair et al. 1996, Cia et al. 1998). This experiment examined the effect of modifying body protein : lipid ratio at different absolute protein mass on ovarian function in lactating gilts. A partial weaning technique was used to increase the potential sensitivity of the reproductive axis to differing lactational dietary protein levels.A 3x2 factorial experiment involving 60 first parity sows compared 3 different pregnancy feeding strategies and 2 lactation diets. During pregnancy, sows were fed from day 42 either a set quantity (mean of 2.27 kg/day) of basal diet (5 g lysine, 13 MJ DE/kg[C]), or basal diet + energy (maize starch + soya oil in 3:1 ratio [E]), or additional basal diet supplying both protein and energy [P]. Lactation diets provided either high (180 g CP/kg, 9g lysine/kg [H]) or low lysine (120 g CP/kg, 6g lysine/kg [L]) and were formulated to be isoenergetic (14.5 MJ DE/kg) and fed to appetite. From day 21 of lactation, sows were separated from their litters and housed next to a boar for 8 hours each day; final weaning occurred on day 31.

Previous experiments have indicated that reproductive function in lean, modern genotypes may be more dependent on body protein mass than, as previously believed, on body lipid reserves. This was investigated in a 3 x 2 factorial arrangement of treatments, involving 60 first-parity sows, comparing three pregnancy feeding strategies and two lactation diets. During pregnancy, sows were fed either a basal diet (5 g lysine/kg, 13 MJ of DE/kg [C]) or the same quantity of basal diet + energy source [E], or additional basal diet supplying both protein and energy [A]. The level of supplement for E and A was adjusted weekly to achieve a backfat thickness measurement (P2 position) of 28 mm at farrowing. Isoenergetic lactation diets were fed to appetite and provided either high (180 g CP/kg, 9 g lysine/kg [H]) or low lysine (120 g CP/kg, 6 g lysine/kg [L]). From d 21 of lactation, sows were separated from their litters and housed next to a boar for 8 h each day; final weaning occurred on d 31. Pregnancy treatment differences in backfat and weight were achieved, with C sows having less backfat on d 1 of lactation than E and A sows (E = 28.1, A = 28.0, C = 22.7 kg, P < 0.001). Sows fed additional basal diet were heavier than E sows, which were heavier than C sows (E = 190, A = 201, C = 178 kg, P < 0.001). Average feed intake over lactation showed a pregnancy feeding effect, with E sows eating less than A or C sows (E = 4.9, A = 5.2, C = 5.4 kg/d, P < 0.005). Total lactation weight loss was affected by pregnancy feeding (E = 18.0, A = 19.0, C = 8.4 kg, P < 0.05) and by lactation diet (L = 19.0, H = 11.3 kg, P < 0.05), whereas total lactation backfat loss was affected only by pregnancy treatment (E = 6.9, A = 6.5, C = 4.6 mm, P < 0.05). No pregnancy treatment or lactation diet effects were observed for litter performance. Lactation diet affected weaning-to-estrus interval, with more sows on the H diet coming into estrus within 6 d of partial weaning (P < 0.05), but there was no pregnancy treatment effect. Therefore, voluntary feed intake during lactation was suppressed by increased fat reserves at a limited body protein mass but not when body protein mass was also increased. Partial weaning-to-estrus interval was increased by reduced dietary protein.

An adequate intake of colostrum by the newborn piglet allows the piglet to acquire passive immunity and develop active immunity. Many studies have looked at the uptake of IgG by piglets in artificial situations rather than by natural suckling. Therefore we investigated the uptake of IgG by piglets whilst suckling naturally and estimated the time of gut closure.A total of 8 multiparous sows (Newsham - Large White x Landrace) were induced to farrow on day 114 of gestation. Colostrum/milk was sampled, using oxytocin where necessary, at 0, 4, 8, 12, 16, 20, 24h and 2, 5 and 7 days after farrowing. Female piglets (average 3 per litter) were fitted with umbilical catheters to allow blood sampling at 0, 4, 8, 12, 16, 20, 24 and 48h; samples were taken at 5 and 7 days of age by venepuncture.

N-alkanes are components of plant cuticular wax which have been successfully used as markers for the estimation of grass intake and digestibility in grazing ruminants (Dove and Mayes, 1991). Natural n-alkanes are predominately odd chain, and a known dose of an artificial even chain n-alkane (normally c32 or c36) is used to enable intake to be measured. Dietary n-alkanes may behave differently in the gastro-intestinal tract of ruminants and non-ruminants (Mayes et al, 1995). Therefore, in order to utilise this methodology in studies of outdoor pigs, this experiment was carried out to validate the faecal recovery of n-alkanes in this species. Since n-alkanes are soluble in lipid, which is often incorporated at high inclusion levels in pig diets, the experiment was also designed to determine whether n-alkane recovery is influenced by dietary lipid content.

Starch and fat are the two major energy sources available for sow lactation diets. Fat is more energy dense and can be used to maximise energy intakes, particularly in sows with low appetite. However, the quantity of milk produced in sows has been associated with milk lactose production and the main precursor for lactose is glucose, for which dietary starch is the major source. It is therefore important to know the consequences of using a glucose deficient energy source, such as fat, compared to starch in lactation diets. The following experiment was designed to assess energy sources in lactation diets at an isocaloric level in determining sow and piglet performance, in association with the effects of dietary glucose availability on the metabolic state of the sow around peak lactation.