Summary

An experiment was conducted to determine the effects of altering the omega-6 () to omega-3 (n-3) fatty acid (FA) ratio in the diets of high producing sows on whole body metabolism.

Results demonstrated that sows consuming diets with an n-6:n-3 ratio below 5:1 were more likely to be in a state of negative energy balance and body fat mobilisation relative to sows with a greater n-6:n-3 ratio, with potentially negative consequences on reproductive performance and sow longevity.

Introduction

Improved genetics and management practices over several years have led to dramatically increased litter sizes. Pre-weaning mortality however, has increased at even greater rates, suggesting that sows may not be able to keep up with the increased energy demands of the litter.

At farrowing, sows undergo many metabolic changes associated with milk production which can put them into a negative energy balance. Hypophagia at farrowing contributes to the sows’ inability to meet the energy demands for milk production. Over subsequent parities, severe negative energy balance and the loss of body condition have negative impacts on subsequent rebreeding performance and may lead to early culling.

Altering the FAs in adipose tissue can affect lipolytic activity and the ability of the animal to mobilise body fat. Omega-3 FAs alter lipid metabolism, and may also affect feed intake. Moreover, it is possible that the ratio of n-3 FAs in relation to n-6 FAs will differentially affect body fat mobilisation in the sow.

The overall objective of a series of experiments is to improve the reproductive and productive functions of high producing sows. In this specific experiment, the objective was to determine how altering the n-6:n-3 FA profile of sow diets affects whole body metabolism and the ability to provide nutrients and energy to her off spring. Milk energy output, piglet growth rate, sow feed intake, plasma leptin and mobilisation of fatty acids from sow adipose tissue in response to an epinephrine challenge were measured.

Materials and Methods

The experiment used five dietary treatments, each divided into a gestation and lactation ration. Total fat concentration (five per cent crude fat) was the same among diets, but the ratio of n-6 to n-3 FAs varied. Treatment groups consisted of a control (tallow), three diets with plant oil based n-6:n-3 ratios (10:1, 5:1 and 1:1) and a 5:1 fish oil diet.

Sows (n=100) farrowing more than 11 piglets and nursing more than 10 piglets were assigned to one of the five diets. Piglet growth rate and sow feed intake was determined throughout lactation. Milk samples were collected on days 4 and 16, and the dry matter (DM), nitrogen and energy output of milk was estimated based on piglet growth.

On day 5 of lactation, eight sows from each of the 10:1 and 1:1 groups had jugular catheters inserted and were challenged with a single injection of epinephrine (epi) followed by serial blood collections to determine the effect of diet on maximal body fat mobilisation. Blood was collected for leptin (a hormone which controls appetite and is negatively correlated with feed intake) analysis on days 5 and 15.

Figure 1. Average daily feed intake of sows consuming diets with varied omega-6 to omega-3 fatty acid ratios during lactation (kg/d)

Results and Discussion

There was no effect of treatment on the number of piglets born or weaned. Piglets raised by sows consuming the 5:1 plant diet had higher birth and weaning weights, while those nursing sows on the fish based diet had the lowest (P<0.05). Control and 5:1 plant fed sows consumed the most feed, while the 1:1 and fish diet sows consumed the smallest amount (P=0.05; Figure 1). Sow body weight was unaffected by dietary treatment; however, sows consuming the 1:1 diet had greater amounts of backfat when compared to the sows consuming the other diets (P<0.05; Figure 2). Piglet growth rates were unaffected.

Altering the n-6:n-3 FA ratio in sow diets did not affect milk composition or output, suggesting that sows will compensate for changes in feed intake through body fat mobilisation. Prior to any form of metabolic challenge, sows consuming the 1:1 ratio diet appeared to be in a state of body fat mobilisation when compared to those consuming the 10:1 ratio (Table 1). Both NEFA and glycerol concentrations (indicators of body fat breakdown) were more than doubled in sows fed the 1:1 diet relative to those fed the 10:1 diet, however the variability associated with this determination was very high and thus significance was not reached. Leptin levels were also elevated in mid lactation in the 1:1 diet sows, which had reduced feed intakes relative to the 5:1 and control diet sows.

When sows were submitted to a metabolic challenge with exogenous epi, the researchers found that the sows consuming a ratio of 10:1 had a greater response, indicated by a lower area under the response curve for glucose (P<0.05) and tendencies for higher area under the curve responses for NEFA and glycerol concentrations. They hypothesised that, since the 1:1 ratio sows were mobilising more body fat prior to the challenge, they were less sensitive to a dose of exogenous epi. than the 10:1 ratio sows.

Figure 2. Backfat thickness (mm) of sows consuming diets with varied omega-6 to omega-3 fatty acid ratios at farrowing and weaning

Conclusions

Reducing the n-6:n-3 FA ratio below 5:1 put sows into a state of increased body fat mobilisation, which may have negative impacts on body condition and longevity. In order to ensure producers are not increasing their cull rates and cost of production due to body condition loss, diet formulations including n-3 FAs should be formulated relative to n-6 FAs.

With the costs of raising replacements increasing, sow longevity is a key factor for producers to maximise profits. Producers can keep their most productive sows in the herd longer, and reduce the costs of raising replacements. When included correctly into diets, n-3 FAs may help reduce the severity of the negative energy balance which occurs in early lactation.

Acknowledgements

Strategic programme funding was provided by Sask Pork, Alberta Pork, Manitoba Pork Council and Saskatchewan Agriculture and Food Development Fund. Specific funding for this project was provided by Vandeputte s.a., Belgium and the National Pork Board.

July 2012