Study shows that Omega-3 from fish oil can help increase sow litter size

Wednesday, August 10, 2011

But more work is needed to determine the possible mechanisms behind this response

by JANICE MURPHY

Research has shown that diets which supplement Omega-3 polyunsaturated fatty acids (PUFA) from fish oil can improve reproductive performance in dairy cows and ewes, but there is little known about its effects in sows.

A research paper from 1970 reported an increase in litter size born in first and second parity sows when diets containing fish meal were fed during the first two parities. However, other studies have yielded inconsistent results.

Linoleic and linolenic acids are essential fatty acids in mammals since they lack the necessary enzymes to manufacture longer-chain PUFA from shorter-chain fatty acids. These longer-chain PUFA, including arachidonic acid and eicosapentaenoic acid (EPA), are building blocks in the production of prostaglandins. In cows, EPA and docosahexaenoic acid (DHA) have been linked to increases in follicle size and elevated DHA levels in the conceptus and endometrium, which may play an important role in early embryo development in sows.

Increasing Omega-3 PUFA prior to farrowing and during lactation could improve oocyte quality and embryo survival, and consequently improve conception rate and litter size. To test this theory, researchers at the University of Adelaide in Australia set out to feed sows Omega-3 PUFA from fish oil prior to farrowing up to the end of lactation to assess the impact on sow productivity by measuring subsequent farrowing rate and litter size.

From day 107.7 of pregnancy, 328 Large White x Landrace F1 sows ranging in parity from 0 to 7 (average parity 1.95) were fed either a control diet containing tallow or an Omega-3 diet. Diets were formulated to contain the same amount of digestible energy (13.9 MJ/kg), crude fat (54 g/kg), and crude protein (174 g/kg). The diets were based on wheat, barley, dehulled lupins and also included tallow, rice pollard (bran) and wheat middlings.

The Omega-3 sows (159) were fed a similar diet supplemented with 3.3 grams of fish oil per kilogram of diet sourced from salmon as a partial replacement for tallow. Sows were fed three kilograms daily for eight days prior to farrowing and continued on treatment diets ad libitum until weaning at 18.7 days of lactation.

After weaning, all sows were housed in gestation stalls and fed a commercial gestation ration, with no fish oil or fish meal, once a day (12.9 MJ DE/kg; 130 g crude protein/kg; 5.6 g total lysine/kg) at 2.7 kilograms per day and were mated on their first observed post-weaning estrus. Sows were fed 2.5 kilograms of the commercial gestation ration once a day from day two of gestation until they entered the farrowing unit for their subsequent litter.

The experimental results showed that the length of dietary treatment before farrowing was not different between treatment groups (8.2 days). The litter size born and average piglet birth weight at the initial farrowing were not affected by dietary treatment (see Table 1). Litter size born increased significantly and birth weight tended to increase with parity.

Because all the sows started on treatment diets on the same day prior to farrowing and finished on the same day at weaning, the length of treatment feeding from late pregnancy to weaning was identical – 27 days for both treatments. Dietary treatment prior to farrowing and during lactation did not have any effect on piglet weight gain, weaning weight or litter size weaned.

There were no differences between dietary treatments in the proportion of sows mated within seven days following weaning (83.7 per cent versus 90.2 per cent for control and Omega-3 sows, respectively). Weaning to estrus interval was also similar between treatment groups of sows (Table 1). In total, 147 control sows and 132 Omega-3 sows were mated on their first post-weaning estrus.

Treatment did not affect conception within 30 days and farrowing rate to term (Table 1). Of the total number of sows on the study, 41 control sows and 35 Omega 3 sows failed to maintain pregnancy to full term. Reproductive failure – described as return to estrus (day 0 to 30), negative pregnancy test by ultrasound (day 30 to 42), abortion or late-term pregnancy loss (day 42 to 114) – accounted for the majority of losses (38 control sows versus 33 Omega-3 sows) and was similar regardless of treatment.

The number of piglets born alive from Omega-3 sows was significantly greater in the subsequent parity (10.3) than control sows (9.3; Table 1). Subsequent total litter size born was also significantly greater in sows on the Omega-3 diet.

The researchers hypothesized that the dietary response to Omega-3 PUFA they observed may have been due to a large effect on embryo survival in sows compared to other studies in gilts where responses were not evident. This effect would be more pronounced in older parities, which have been reported to have a lower embryo survival than gilts and parity 1 sows.

As there was no difference in sow feed intake, the researchers concluded that the response in subsequent litter size was due to the nature of the fat source, rather than a response based on energy density of the diet. There was no immediate effect of feeding Omega-3 fatty PUFA diets prior to farrowing on piglet viability, lactation, feed intake of sows, piglet weaning weight, or number of piglets weaned.

Increases in neonatal growth and weaning weight have been reported in other studies where fish oil was included at three to four per cent of gestation diets during the last trimester. However, in this study, lower levels (0.3 per cent) of fish oil were used as the diets were designed for ad libitum intakes during lactation.

The mechanism responsible for increased litter size in sows fed diets containing Omega-3 PUFA from fish oil is not clear. In studies where gilts were fed diets containing Omega-3 PUFA from fish oil sources, EPA and DHA also increased in embryos and endometrium. In those experiments, dietary treatments continued during early pregnancy. In this study, dietary changes ended at weaning, so the response noted in subsequent litter size is more likely to be attributable to improvements in follicular development or oocyte quality.

In the pig, follicle and oocyte quality influences embryonic development and survival and this, in turn, influences litter size. Therefore, feeding Omega-3 PUFA-enriched diets during lactation, when follicle growth and oocyte development are occurring, may explain the response in litter size.

This study was the first of its kind to demonstrate that feeding sows a diet containing Omega-3 PUFA from fish oil fed before farrowing and during lactation increased litter size in the subsequent parity, independent of energy intake. Follow-up studies are currently underway to determine the possible mechanisms for this response. BP

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.

Source:
R.J. Smits, B.G. Luxford, M. Mitchell and M.B. Nottle. 2011. Sow litter size is increased in the subsequent parity when lactating sows are fed diets containing Omega-3 fatty acids from fish oil. J. Anim. Sci. published online May 24, 2011.