Based on experimental and empirical evidence, it can be argued that dietary supplementation with pure betaine can slightly improve nutrient digestibility and lead to enhanced growth and feed conversion in broilers, turkeys, and ducks. In addition, betaine in poultry diets may lead to less carcass fat and more breast meat. Of course, the exact magnitude of such effects can be very variable. In addition, under practical conditions, it can be accepted that the relative bioavailability of betaine compared to methionine is 60 percent, or in other words, it can be said that 1 kg anhydrous betaine can replace 0.6 kg of added methionine. In regards to choline, it has been estimated that on average betaine can replace about 50 percent of added choline in broilers, and 100 percent in laying hens.
Nevertheless, following a more conservative approach that allows for the fact that choline has further biological roles, it is recommended to replace no more than 25 percent of added choline with pure betaine.
A meta-analysis of the effects of dietary betaine supplementation on pig performance and carcass characteristics, including 19 studies, indicated that betaine did not significantly affect growth rate, but it did improve significantly feed efficiency (2-8 percent) and carcass yield, while reducing backfat deposition (10-20 percent). The methionine and choline sparing effect of betaine in pigs is not well documented and as such it is not considered of practical significance at the moment.
There is no doubt that betaine can offer substantial benefits to animals stressed by the lack of water, which will benefit the most from betaine. These include (1) heat-stressed animals, especially broilers during the summer months, (2) lactating sows that almost always consume less water than they need, and (3) all animals drinking saline water.