Can supplemental fat in lactation diets offset the effects of high temperatures?

Monday, April 2, 2012

Research suggests that, in the modern prolific sow, the use of additional dietary fat increased feed disappearance and energy intake. But, while adding fat to lactation diets for P3+ sows improved litter growth rate, it was not beneficial for first and second parity sows

by JANICE MURPHY

The lactating sow is a veritable power plant, requiring vast amounts of nutrients for milk production, including upwards of 78 per cent of her net energy requirement, and also producing heat in the process.

High ambient temperatures can have a negative impact on sow feed intake. Previous research has reported a 46 per cent reduction in feed intake in sows exposed to a temperature of 29 C compared with sows maintained at 18 C. This reduction in intake is the sow's attempt to control her body temperature. Since the heat produced during digestion and metabolism adds to the burden, reducing intake helps to dissipate the effects of extreme ambient temperatures. Unfortunately, the side-effects include body weight loss, decreased mammary size, reduced milk output and reduced litter growth.

Improvements in energy intake are possible through fat supplementation of diets, since fat has a lower heat increment associated with digestion and metabolism compared to corn. Fat supplementation has been proven to have positive effects on the modern sow, but the optimal dietary level of fat has not yet been defined.

Researchers at North Carolina State University set out to evaluate the effects of varying levels of a supplemental animal-vegetable fat blend on sow and litter performance, subsequent reproductive performance and sow heat stress when exposed to high ambient temperatures (27 C, plus or minus three degrees).

Data were collected from 337 mixed parity sows during the summer months (July-September) in a 2,600-sow commercial unit in Oklahoma. Corn-soybean meal based diets were formulated with 7.5 per cent corn distillers dried grains with solubles and six per cent wheat middlings, and contained 3.24 grams standardized ileal digestible Lys/Mcal ME. The animal-vegetable fat blend was supplemented at a rate of zero, two, four or six per cent. Sows were balanced by parity, with 113, 109, and 115 sows representing parity 1, 2, and 3+ (3 to 7), respectively.

Daily feed disappearance during lactation increased at a linear rate when fat was added to the diet (see Table 1). This higher feed disappearance and energy density of fat in the diets resulted in a linear increase in the apparent daily energy intake. Parity 2 sows consumed more feed than parity 1 sows, but not more than P3+ sows. Supplemental fat did not affect the weight of sows at weaning.

Overall, sows in all treatments lost weight during lactation, ranging from -0.13 to -0.01 kilograms a day, but there were no statistical differences between treatments. As expected, P3+ sows were heavier and exhibited higher average daily gain (ADG) throughout the experiment than the first and second parity sows.

The addition of supplemental fat has been known to have a detrimental effect on the pellet durability index. In this experiment, pellet durability suffered dramatically, decreasing to 69 from 94 per cent when fat was added at six per cent. This reduction in pellet quality may explain, in part, the increase in feed disappearance because, as pellet durability decreases and the concurrent amount of fines in the diet increases, feed waste inevitably increases.

When feed intake is limited, lactating sows mobilize a greater proportion of fat from the body, which may be prevented with dietary supplementation of fat. In this experiment, the addition of fat tended to decrease backfat loss. Parity 3+ sows seemed to mobilize less fat from the body than first and second parity sows, but there were no significant differences.

The loss in backfat during lactation in sows in the present study, regardless of treatment, indicates that sows were in negative energy balance. It appears that the supplemental fat provided in the diet was not used for sow body weight gain, but rather for milk fat synthesis in the mammary glands. In addition, first and second parity sows mobilized more body fat from the body than P3+ sows. Presumably, young sows may have to use more nutrient reserves to support lactation since their body reserves are lower.

The addition of fat in diets for parity 1 sows had a negative effect on piglet mortality. The results showed that the number of pigs weaned per litter decreased linearly as supplemental fat increased.

Supplementation of fat did not improve litter weight at weaning for first and second parity sows. However, improvements were observed in litters from P3+ sows. Similarly, addition of fat improved ADG of litters from P3+ sows, but did not affect growth rate in litters from younger sows.

The researchers suggested that improvements in weaning weights with fat supplementation may carry forward into the post-weaning period, since there was evidence of improved post-weaning survival and ADG in pigs from sows fed supplemental fat.

Important improvements in subsequent reproductive performance were achieved for sows fed supplemental dietary fat (see Table 2). More sows – 25 per cent more on average – were bred within the first eight days after weaning when fat was added to their diets. Also, conception and farrowing rates improved with the addition of fat. Wean to breed interval was not affected by supplemental fat.

During the course of the experiment, 53 sows were culled mainly due to health issues, such as lameness, and reproductive issues, such as sows not exhibiting heat or failing to conceive. The number of sows culled after weaning was greater for sows that did not receive supplemental dietary fat.

The bottom line is that, in the modern prolific sow, the use of additional dietary fat increased feed disappearance and energy intake. While adding fat to lactation diets for P3+ sows improved litter growth rate, it was not beneficial for first and second parity sows.

The efficiency of feed and energy utilization offered to sows was negatively affected by fat supplementation, which may have been related, at least partially, to the reduction in pellet quality and the subsequent increase in the amount of feed wastage.

It is clear from these data that the sow's use of body reserves when fat was not supplemented (below two per cent) would compromise return to estrus and subsequent reproductive performance, especially in first parity sows. BP

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

Source: D. S. Rosero, E. van Heugten, J. Odle, R. Cabrera, C. Arellano and R. D. Boyd. 2011. Sow and litter response to supplemental dietary fat in lactation diets during high ambient temperatures. J. Anim. Sci. 2012, 90:550-559.