Feed Additives, Minerals & Vitamins
Feed additives, minerals and vitamins can support animals when nutritional deficiencies exist or there is an increased risk for health issues or productive decline. They are not a substitute for good feeding management but can play a role in maintaining animal health and production.
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 is 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 and stage of lactation. Supplementation will be determined by individual circumstances, which need to be assessed regularly depending on the farm and season.
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 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.
Antibiotic rumen modifiers such as monensin, tylosin, and virginiamycin 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. An appropriate approach to the use of antibiotic rumen modifiers in-feed (including non-Schedule 4) is summarised in the Australian Veterinary Association Antimicrobial Prescribing Guidelines for Dairy Cattle and must be reviewed at least annually.
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 can increase fibre digestibility and improve gut function. This class of additive has been demonstrated to promote feed intake in hot weather, increase fibre digestion, increase microbial yield and result in more energy being generated per kilo of feed.
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 is important to consult a nutritional advisor on using betaine because in some situations it is 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 is 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 is recommended that a maximum of five to seven per cent of the cow’s total 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 canola meal, soybean meal and linseed meal in the diet during summer.