Role of betaine in preventing heat stress

By Henk Enting and Jaco Eissen

Betaine, which is a
trimethyl derivate of the amino acid glycine, is found in many cells and has two
main physiological functions. First, betaine can serve as a donor of methyl
groups. For this reason, the substitution of methionine and choline as a methyl
donor by betaine has been subject of many studies. Experiments showed
consistently that choline can be

replaced by betaine, but not always indicated that methionine can be replaced
by betaine. The latter might be due to the fact that this substitution also
depends on the level of cystine in the feed (Eklund et al., 2005). More
evidence is coming to light that betaine is a valuable nutrient in itself. A
part of this is related to the fact that betaine helps to maintain cellular
osmolarity, which is the second main physiological function of betaine.

Stress conditions

A number of experiments show that the addition of betaine to the feeds in
particular improves performance under stress conditions that affect cell
osmolarity. A coccidiosis infection (Tiihonen et al. 1997; Waldenstedt et al.,
1999; Klasing et al., 2001) and heat stress (Zulfiki et al., 2004)
are examples of this. It seems that betaine helps to maintain metabolic
functions of cells under different types of osmolaric pressure. Furthermore,
studies with pigs also indicate an effect of betaine in energy metabolism.
Schrama et al. (2003) found a reduction in maintenance requirements when betaine
was included in the feed and Huang et al. (2007) demonstrated that betaine
increases growth hormone levels significantly. These findings might also stress
the importance of betaine as a nutrient itself, rather than possibly replacing
part of methionine and choline in feeds.

Due to an increased body weight gain of broiler chickens through the years,
temperatures that optimise performance tend to decrease (Gous and Morris, 2005).
Earlier performed research indicates that modern broiler chickens are more
sensitive to high temperatures and suffer more frequently from heat stress (Lin
et al., 2006). Alongside adverse effects of increased

temperatures on feed intake, growth rate and feed conversion ratio, higher
temperatures also result in a decreased body protein deposition and in an
increased body fat deposition (Geraert et al., 1996). Since betaine can have a
positive effect on carcass yield and quality in both poultry (McDevitt et
al., 1999; Esteve-Garcia and Mack, 2000; Noll et al., 2002; YiZhen,
2000) and pigs (Campbell et al., 1997; Fernandez-Figares et al.
2002) and due to its effect on cell osmolarity, the addition of betaine to feed
or drinking water might help to overcome the negative effects of heat stress on
performance and carcass quality (Kidd et al., 1997).

Broiler experiment

In order to test the hypothesis that betaine can improve performance and
carcass quality of broiler chickens during heat stress, an experiment was
carried out at the Nutreco Poultry and Rabbit Research Centre. The experiment
included 300 male and 300 female Ross 308 broiler chickens and was performed
from 0-40 days of age. Broilers were housed in floor pens with 25 male or female
chickens per pen. Feed and water were provided ad libitum. Heat stress was
introduced by increasing the temperature to 35°C for 10 hours a day from 2 days
of age on. During the other hours, a standard temperature schedule was followed.
The experiment included 3 treatments, in which the same basal feeds with betaine
(TNIbetain, Trouw Nutrition International) were provided at 0 (control), 1 or 2
g/kg. Starter feeds were provided from day 0-14 as 2 mm pellets and grower (day
15-31) and finisher (day 32-40) feeds as 3 mm pellets. Amino acid levels in the
experimental diets were according to CVB (1996). This indicates that the diets
were not limiting in methionine and methionine+cystine. The total analysed
choline content in the diets amounted to 2.4 g/kg, which is above requirements
(Whitehead and Portsmouth, 1989; NRC, 1994). Effects of the addition of betaine
to the feeds would therefore be due to an effect of betaine itself and not to
the replacement of methionine or choline. At the end of the experiment, carcass
and meat quality was measured for 10 birds per pen.

Results

The addition of betaine to feeds sufficient in methionine, methionine+cystine
and choline resulted in significant improvement of the feed conversion ratio in
the period from day 0-14 (Table 1). During the entire experimental
period, betaine provided an increase in body weight, which was significantly
different from the control group for the highest inclusion rate. Feed conversion
ratio improved significantly with the highest amount of betaine. No differences
in mortality were observed among treatments. The addition of betaine did not
affect carcass percentage and abdominal fat percentage significantly. In male
broiler chickens, both inclusion levels of betaine provided a significant
increase in the percentage of breast meat (Figure 1).

Why it works

The results of this experiment demonstrate that betaine has a positive effect
on the performance of broiler chickens and carcass quality. This positive effect
of betaine may be related to the osmolyte function of betaine that prevents
dehydration. Moreover, a lower maintenance requirement, as was found in pigs
when betaine was added to the feed (Schrama et al., 2003), might
contribute to a lower heat production, which helps to maintain feed intake and
hence weight gain during heat stress as observed in the present experiment.
Zulfiki et al. (2004) observed a reduction in body temperature of broiler
chickens when betaine was added to the feed under heat stress conditions.
Therefore, both the osmolyte effect and the effect of

betaine on maintenance requirements may explain the more pronounced positive
effects of betaine on performance and carcass quality during heat stress
conditions.

Betaine has been reported to reduce fat composition in non-challenged broiler
chickens (Saunderson and MacKinlay, 1990; Hassan et al., 2005). However,
this does not seem to be the case in heat-stressed birds as was found by Zulfiki
et al. (2004) and in the present experiment. With heat stress, body
protein deposition decreases and fat deposition increases due to hormonal
changes (Geraert et al., 1996). Results reported by Zulfiki et al.
(2004) indicated that betaine may reduce stress hormone levels, which would
favour protein deposition over fat deposition. However, these changes are
probably not big enough to counteract the negative effects of heat stress on fat
deposition. In the present experiment, no clear reduction in mortality was
observed when betaine was added to the feed. Zulfiki et al. (2004)
reported a reduction in mortality with the addition of betaine to the feed.
Mortality in that experiment was clearly higher than in the current experiment
(26.5 % in the control group vs. 10.5 % in the present experiment).

Therefore, effects might become more pronounced with higher mortality
levels.

Conclusion

Although betaine did not provide a clear reduction in abdominal fat and
mortality in the present experiment, it is clear that betaine has a positive
effect on broiler performance and carcass quality under heat stress conditions,
even when feeds are adequate in methionine,

methionine+cystine and choline. This indicates that betaine is an essential
nutrient by itself and is a valuable component in poultry
feeds