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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. The first 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 the 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. Pregnancy: Dietary fatty acids: Piglet tissue fatty acidsBoth pre-and immediate postweaning mortality of piglets are important sources of losses to the pig industry (Varley, 1995). Furthermore, poor growth in the same periods results in longer-term reductions in performance (Mahan & Lepine, 1991). Long-chain essential fatty acids (chain length .18) of the n-6 and n-3 series are important for brain development and function (Uauy et al. 2000). Docosahexaenoic acid (22 : 6n-3) is a major constituent of synaptic end sites and may be necessary for the formation of mature synaptosomes, while arachidonic acid (20 : 4n-6) may be a second messenger (Kurlak & Stephenson, 1999). In the pig, as in the human subject (Clandinin et al. 1980), brain growth and therefore accretion of 22 : 6n-3 is greatest in the last third of pregnancy (Sweasey et al. 1976; Passingham, 1985) and continues into postnatal life. Since commercial pig diets are based on cereals that do not contain long-chain n-3 fatty acids, a contributory factor to low piglet viability at birth and subsequent growth may be an imbalance or deficiency of these acids in the diet of the pregnant sow. Rooke et al. (1998Rooke et al. ( , 1999 showed th...

Two experiments were conducted to compare the performance and behaviour of lactating sows and piglets in farrowing pens with crates or multisuckling systems (group housing of sows and piglets in the second half of lactation). All sows were farrowed in commercial accommodation based on farrowing pens with crates. In experiment 1, fifteen purebred Landrace or Large White sows and litters were recorded in crates as a control (C). Three replicates of six sows and litters were recorded in a multisuckling system (M) in which the sows and litters were group-housed from 2 weeks after farrowing until weaning. Experiment 2 involved 30 Manor Meishan sows (0·25 Meishan genes). The sows and litters were arranged into three treatments and two replicates with five sows and litters in each group. Treatments comprised a control farrowing pen with crate system and two multisuckling systems differing in degree of accessibility of the piglet creep area. Multisuckling 1 (Ml) had a solid creep front with an open doorway (0·5 X 0·9 m) for piglet access. In multisuckling 2 (Ml), the lower 30 cm of the solid creep front was removed to facilitate piglet access and allow visual contact with the sows. Piglets were weaned at 31 days in experiment 1 and 29 days in experiment 2. After weaning, piglets were moved to controiled-environment, fully slatted accommodation and monitored for 7 days in experiment 1 and for 12 days in experiment 2. Mortality rate in the two systems was not significantly different. However, some piglets in the M system were crushed after grouping (0·3 and 0·2 piglets per litter in experiments 1 and 2, respectively). Growth rate was reduced in M piglets in the week after grouping (256, 184 (s.e.d. 21·4) g/day, P < 0·01 for C and M respectively in experiment 1 and 243, 150 and 209 (s.e.d. 12·2) g/day, P < 0·01 for C, Ml and Ml respectively in experiment 2) but was higher after weaning (271, 313 (s.e.d. 35·7) g/day, P > 0·05 for C and M respectively in experiment 1 and 148, 280 and 222 (s.e.d. 15·0) g/day, P < 0·01 for C, Ml and Ml respectively in experiment 2). In consequence, piglet live weight at 1 week after weaning did not differ between treatments (9·33, 9·74 (s.e.d. 0·36) kg for C and M respectively in experiment 1 and 9·30, 914 and 9·53 (s.e.d. Oil) kg for C, Ml and Ml respectively in experiment 2). Sucking behaviour of M piglets in both experiments was severely disrupted (P < 0·01) on the day of grouping and the day after grouping. Despite synchronized suckling, M litters had a high incidence of cross suckling (> 50%) throughout lactation. M piglets spent more time than C outside the creep area, even with a more open creep (Ml). The Meishan sows tended to be more docile and fought less at grouping than the white breeds (0·39 and 1-71 fights per sow per h). Immediately after weaning, C piglets spent more time fighting (8·0 and 1·0 (s.e.d. 0·99) % of time, P < 0·01 for C and M respectively in experiment 1 and 4·51, 0·09 and 0·09 (s.e.d. 019) % of time, P < 0·01 for C, Ml and M2 respectively in experiment 2). These studies demonstrate that, in a multisuckling system, piglets achieved similar overall growth rate to C piglets, since both received checks in growth at different times and for different reasons.

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