After reviewing the positive effects of betaine in laying hens and pigs, this review describes the effects of betaine supplementation on ruminant performance.
Besides being a methyl donor, betaine acts as an osmolyte. Betaine, as zwitterion (dipolar ion), has a net neutral charge, but has a region of positive and negative charges. This allows betaine to hold water molecules (intracellular) against a concentration gradient (Hall et al., 2016). Studies with bacteria during high osmolarities, show that betaine restores protein denaturation, saving enzymes, and stabilises and assists in thermoprotection.
Additional functions of betaine are functioning as molecular chaperone, decreasing susceptibility of microbial populations to stress, being an antimicrobial agent to some bacteria, such as Salmonella typhimurium and betaine can be used as a nutrient.
Positive influence on fermentation
In ruminants, betaine also has a positive influence on fermentation, it increases total volatile fatty acid (VFA) production and increases the ratio of acetate to propionate (A:P). Betaine serves as a source of ruminal available nitrogen, increasing microbial fermentation rate and altering fermentation patterns.
Many authors describe how betaine is converted to acetate in the rumen, which can be used for milk fat synthesis. An in vitro trial with rumen fluid showed a betaine degradation of 6% after 12h of incubation and 15% after 24h of incubation, suggesting betaine partially survives the rumen. Betaine is highly water-soluble, dissolving immediately in the rumen fluid after ingestion and it was shown that more than 80% reaches the duodenum within 12h. This explains positive results on ruminant performance, similar to what is already seen in poultry and pigs (see previous review articles).
Cost of heat stress
Research to the effects of climate change on milk production have estimated that the negative effects of heat stress to milk production result in a cost of up to US$ 2 billion per year in the US or over € 400 per cow/year.
Heat stress is mostly expressed by the term Temperature Humidity Index (THI). The principle behind the THI is that when it increases, with higher environmental temperature and/ or relative humidity, cattle will experience more difficulty to cool themselves, decreasing body comfort. For dairy cattle, a THI > 72 is considered as mild heat stress. A THI > 78 is seen as moderate heat stress with markedly reduced milk production and other physiological effects.
Cows with (very) high milk yields, suffer more from heat stress than low producing dairy cows, therefore THI threshold for cows producing more than 35 kg milk/d is revised from 72 to 68. This indicates that depending on Relative Humidity, onset of heat stress in high producing dairy cows occurs at temperatures between 21˚C (RH of 75%) to 24˚C (RH of 25%). Heat stress can be measured by respiration rates, with increasing heat stress, respiration rate also increases from low (20-60 breaths/min) to high (80-120 breaths/min) or even severe (>150 breaths/min).
To alleviate the heat stress burden, the hypothalamus reduces secretion of appetite and energy metabolism hormones T3 and T4, this causes a decrease in dry matter intake (DMI). The hypothalamus also decreases progesterone and prolactin secretion, reducing milk secretion and decreasing milk production. Next to reduced milk production (due to reduced feed intake and to post-absorptive glucose and lipid homeostasis, heat stress also changes the milk quality, by reducing milk lactose and protein levels (Zhang et al., 2014).
Heat stress has a negative effect on the formation of endogenous free radicals, causing a reduction in antioxidant capacity of animals. During heat stress, negative energy balance (NEB) is prolonged, liver activity declines and peripheral fat mobilisation increases, causing lower plasma cholesterol and triglyceride levels.
Effects of heat stress on production
Milk production can decrease between 10-15% and up to 50% during extreme heat events. A trial with dairy cattle for 1 week in thermal neutral zone and 2 weeks thereafter in heat stress conditions showed decreasing milk yields from 32 to 27 and 23 kg/d during wk 1 and 2 of heat stress (P<0,001; Figure 1). Dry matter intake (DMI) was decreased from 25.5 kg/d to 20.2 and 18.8 kg/d during wk 1 and 2 of heat stress (P<0,001). Milk fat and protein% and -yields were decreased after 2 weeks of heat stress. The heat stress increased both rectal temperature and respiration rate (P<0,001).
