Feed Additives

Feed additives are for the prevention, not treatment, of animal health issues related to feeding. They are not a substitute for good feeding management but can play a role in maintaining animal health and production.

Macro minerals

A balanced supply of minerals in feed is essential for animal health and production in all classes of dairy cattle. The three main minerals to consider when formulating diets for dairy cows are calcium, phosphorus, and magnesium. Of these, it’s most likely that calcium may need to be added to the feed of high-producing lactating dairy cows in Australia. This is because pasture and cereal grains alone may not meet the animal’s calcium needs. Ground limestone is generally the most cost-effective source of calcium to help maintain animal health and production.

Phosphorus requirements of lactating dairy cows are often met through a diet of pasture and concentrates, so further supplementation of this mineral may not be needed. Meanwhile, the need to boost magnesium intake varies greatly and depends on the composition of a cow’s diet. Supplementation will be determined by individual circumstances, which need to be assessed regularly depending on the farm and season.

Trace nutrients

As the name suggests, trace nutrients are present in the diet of dairy cows in ‘trace’ amounts of milligrams per day. The main trace nutrients they require are zinc, copper, manganese, selenium, iodine, and cobalt and the vitamins (A, D and E). All are frequently supplied in the form of a premix which can be added to concentrate feeds on-farm or in the feed mill following manufacturer recommendations for rates of inclusion.

Buffers and neutralising agents

Buffers and neutralising agents can play a role in managing the risk of acidosis associated with low effective fibre and high grain or concentrate diets. Commonly used buffers and neutralising agents include sodium bicarbonate, magnesium oxide, and sodium bentonite.

Rumen modifiers

Rumen modifiers such as monensin (e.g. Rumensin™), tylosin (e.g. Tylan™), and virginiamycin (e.g. Eskalin™) are not buffers or neutralising agents. They act by directly altering the balance between the different populations of microbes in the rumen and the proportions of the volatile fatty acids they produce. Consult your vet and nutritionist before feeding rumen modifiers to ensure that they are suitable for your herd.

Additives for heat stress

Yeast, betaine, and vitamin B3 (niacin) can be used to help reduce the effects of heat stress in dairy cows. Yeast and yeast metabolites increase fibre digestibility. They use up lactic acid and break down rumen contents into glucose from propionate, a volatile fatty acid commonly produced by gut bacteria. Some evidence suggests that increased glucose levels can help cows manage their metabolic heat loads during heat stress events.

Betaine helps to maintain feed intake, reduce the energy needed to stay cool and the continuation of normal metabolic processes. Remember, it can provide effective relief in heat stress situations, but only if the dosage is correct. It’s important to consult a nutritional advisor on using betaine because in some situations it’s not advised. Vitamin B3 has been shown to play a role in energy metabolism, so additional supplementation may be helpful in hot conditions.

Dietary supplementation with extra fat is a good way to help increase the energy density of the cow’s diet and maintain daily energy intake during hot conditions. Supplementary fat sources like vegetable oil and commercial bypass fat supplements are an option, provided they are used correctly. Feeding fat has an additional advantage - it’s digested and used by the cow more efficiently than starches and fibre and produces less metabolic heat. However, too much fat interferes with microbial action in the rumen, and this can depress feed intake. It’s recommended that a maximum of five to seven per cent of the cow’s diet (on a dry matter basis) is fat, depending on the type of fat used.

Due to the nutritional challenges posed by heat stress, cows may need additional protein in their diet to maintain rumen microbial function and maintain a good supply of amino acids to the udder for milk protein production. This can be achieved by including higher-quality protein sources such as soybean meal and linseed meal in the diet during summer. Canola meal and cottonseed meal are less suited for this purpose.