Butterfat is increased by increasing the number, and protecting the conditions which are beneficial to cellulose digesting, acetate producing,bacteria in the rumen.
Don't over feed supplement.
Supplement should not exceed 50% of the diet. In their effort to make more milk, producers will often overfeed supplement. This reduces butterfat, especially when the supplement to forage ratio approaches2:1. Concentrates are too quickly digested and with the correspondent drop in the need for saliva production, you get a drop in rumen pH, which is harmful to the microbes that produce butterfat.
Feed roughage before you feed grain in the morning.
Again, having hay in the rumen first will slow down digestion, ensure adequate saliva production and keep the rumen pH at a favorable level for acetate-producing microbes.
Take the total amount of supplement the goats need to eat during a day, and feed it in several small meals instead of giving it in only two larger meals at milking time..
Again, this optimizes the conditions beneficial to microbes. It takes time to feed more often, so producers will have to decide how badly they want higher butterfat.
Provide good ventilation, plentiful water and multiple smaller meals when it is hot outside. Goats eat less when it is hot, so you will often see a drop in butterfat in the summer due to a drop in intake of feed.. Anything you can do to help them eat more will increase butterfat. Increased intake increases the heat of digestion in the rumen, and that in turn increases acetate production and raises the level of butterfat.
Feed good quality forage. If you have only poor quality forage, add buffer to the diet.
Low-roughage fiber intake lowers butterfat. Supplement the diet with buffer at a rate of 4% of the amount of supplement fed per day to increase butterfat production when feeding poor quality forages. (Note:many goats do not like buffer in their feed, and will completely refuse to eat the ration with it in there, but will take it readily when it is offered free-choice in the barn or lot.
Feed larger quantities of dried brewer's grain.
Research show that distillers grains contain yeast by-products that stimulate rumen cellulose digestion, which results in acetate formation, thereby increasing butterfat.
Breed for high butterfat as well as high milk production.
When selecting breeding stock, if you select for high milk production alone, don't pay attention to butterfat levels, you will gradually see decreased butterfat from one generation to the next..
Link: Variations in Milk Fat Composition: Why do my milk processorand DHIA tests not always agree? http://extension.usu.edu/files/publications/newsletter/pub__4960713.htm