Fats (ether extract): are another group of CHOs that occur naturally in most common feeds. The broad groupings for fats are monosaturated (MUFA), polyunsaturated (PUFA), and saturated fatty acids (SFA). Any dietary MUFA and PUFA will be biohydrogenated (or saturated) by the rumen bugs and upon intestinal absorption, can be utilised as a source of energy or for incorporation into milk fat. Absorbed fats deliver around two times the metabolisable energy of other CHO forms. However, it must be noted that they do not contribute to blood glucose production, but they can spare glucose from being used for maintenance energy.
Lactating rations are typically formulated to have an ether extract content not exceeding 60g per kg DM. Research often shows declining total DMI once total ether extract exceeds 50g/kg DM, especially when in the form of MUFA and PUFA. Protected fat products are often used to increase energy density for cows in peak lactation and show some promise in assisting reproductive performance. However, it may be wise to avoid feeding fat supplements to lactating cows during periods of weight loss in order to lessen the effects of hepatic oxidation and reduce the risk of fat accumulation in the liver (which is our primary blood glucose plant).