Micronutrients in livestock production: vitamin E and mineral advances reviewed

Why the review looked beyond deficiency prevention#

Johnson opens by noting that nutrition research had moved on from working out the minimum levels of vitamins and minerals needed to avoid clinical disease. Instead, attention had shifted to what happens when these micronutrients are fed at levels well above requirement, particularly in intensive pig and poultry systems where margins are tight and disease pressure is constant.

The paper argues that changes in animal genotype were partly behind this shift. As genetic selection pushed poultry and pigs toward faster growth or leaner carcases, their responses to vitamins and minerals changed too, and in some cases certain nutrients could offset undesirable side effects of selection. Johnson also points to new delivery methods that target specific tissues with particular nutrients, offering production gains beyond basic weight gain or feed efficiency.

The review is explicitly not a full literature survey. Johnson instead selects a handful of areas - immunity, stress, skeletal problems, egg quality, vaccine response and carcase quality - to illustrate how far thinking on micronutrients in livestock production had advanced by the early 1990s.

Vitamin E and the immune system#

A substantial part of the paper deals with vitamin E and immunity. Johnson cites work summarised by Rice and Kennedy showing that feeding vitamin E at very high levels, in the order of 100 to 450 mg/kg, improved immune measures compared with the 10 to 15 mg/kg typically stated as sufficient to prevent deficiency. Vitamin E deficiency itself was known to leave phagocytic cells less able to deal with invading pathogens and to weaken the body's antibody-based defences.

In pigs, the focus has been on sow diets, since piglets rely heavily on maternal colostrum for early immunoglobulins. Several studies cited by Johnson found that lifting sow dietary vitamin E to 50 to 70 mg/kg, compared with 10 mg/kg, improved the humoral immune response of piglets. Mahan examined vitamin E at 0, 16, 33 or 66 IU/kg across three parities and found that supplemental levels below 16 IU/kg were inadequate for reproducing sows; pig mortality in the first week fell and litter size rose as dietary vitamin E increased, with the effect becoming larger in sows of higher parity.

In poultry, early work by Tengerdy and Brown showed that broilers given vitamin E at 150 to 300 mg/kg suffered markedly less mortality after exposure to Escherichia coli. Franchini and colleagues later found that doses above 300 mg/kg lifted antibody titres to Newcastle Disease Virus in turkeys and raised interferon levels in broiler chickens. Johnson is careful to note that responses across studies have been inconsistent, and that no firm conclusion on economic benefit could yet be drawn, a caution attributed to Kornegay.

Testing micronutrients in livestock production at commercial scale#

Rice and Kennedy had proposed that the degree of disease challenge on a property would determine whether high vitamin E supplementation paid off, and that only large commercial-scale trials could properly test this idea. Johnson treats the subsequent study by Kennedy and colleagues as a partial test of that proposal.

That analysis covered a large number of broiler flocks, totalling around 3 million birds, comparing diets containing 180 mg/kg against 50 mg/kg vitamin E. The higher level produced an 8.4% improvement in income, which Johnson attributes to gains in both how efficiently birds converted feed and how quickly they put on weight. Johnson notes that commercial vitamin E supplementation in broiler diets had increased over the preceding three to five years, but not to the levels shown in this trial to be necessary for the immune and economic benefits observed.

Stress responses in pigs, poultry and feedlot cattle#

Some pig genotypes carry porcine stress syndrome, a predisposition to a rapid and fatal rise in body temperature under stress, identifiable through Halothane anaesthesia testing. Johnson cites Duthie and Arthur, who found that high dietary vitamin E (235 mg/kg) reduced markers of free-radical cell damage, such as creatine kinase and malonaldehyde, in stress-susceptible pigs subjected to transport stress, compared with untreated stress-susceptible and stress-resistant animals.

In heat-stressed poultry, vitamin C supplementation improved both egg production and broiler growth. Njoku reported that broiler growth rose in step with the amount of ascorbic acid added to the diet as temperatures climbed between 35 and 38 degrees Celsius, to the point that a supplementation rate of around 200 mg/kg could pay for itself under hot conditions. Separately, Ferket and Qureshi found that supplementing vitamins and electrolytes via drinking water during two periods of acute heat stress at 35 degrees Celsius improved body weight gain, feed efficiency and antibody response to sheep red blood cells in broilers.

For feedlot cattle, Johnson reviews work on mineral proteinates, minerals chemically bonded to amino acids or peptides. Chirase and colleagues found organic zinc and manganese improved recovery rates in disease-stressed calves, while Ward and colleagues found that trace minerals supplied in organic complex form, including zinc methionine and copper lysine, lifted how much newly arrived feedlot cattle ate and grew during the early stress period after entering the yards.

Vitamin D3 compounds and egg shell quality#

Leg disorders in broilers, and poor shell strength in older laying hens, are described by Johnson as significant economic concerns for their respective industries. Edwards found that feeding 1,25-dihydroxycholecalciferol or a related trihydroxycholecalciferol compound brought about a reduction in both how often and how badly broilers developed tibial dyschondroplasia, an effect that grew stronger as the dose increased, while higher levels of ordinary vitamin D3 produced no such benefit. Johnson suggests fast-growing broilers may struggle to convert enough vitamin D3 into its active metabolite to support calcium absorption and bone formation, and notes that Glahn and colleagues found aflatoxins reduced plasma concentrations of this active metabolite, raising a possible link to leg problems where feed aflatoxin contamination is more common.

For laying hens, declining egg shell quality with age may relate to reduced production of the same active vitamin D3 metabolite. Results from supplementing it directly have been inconsistent, with toxicity a risk if dietary vitamin D3 is already adequate. Johnson points instead to novel synthetic analogues designed to act on specific tissues without the same side effects as showing promise. A separate finding, from Moreng and colleagues, showed that chelated zinc, in the form of zinc methionine added at 0.2 g/kg of diet, improved shell quality in hens drinking saline water compared with hens given saline water alone.

Carcase quality across species#

Johnson reviews vitamin E's role in meat stability, since lipids in muscle cell membranes are vulnerable to oxidation and this is described as a major cause of quality loss during storage. In broilers, Bartov and Frigg found that supplementing vitamin E either early in life or later, in birds fed a diet containing soyabean oil, improved how well the meat resisted deterioration by 7 weeks of age. In turkeys, Franchini and colleagues showed that vitamin E fed across a range of doses for 140 days raised muscle alpha-tocopherol content and improved the stability of carcase fat during five months of frozen storage.

In beef, Faustman and colleagues gave Holstein steers a daily supplement of 370 mg alpha-tocopherol acetate for 10 months. This roughly doubled the amount of alpha-tocopherol measured in muscle tissue relative to unsupplemented animals, and slowed both the browning reaction that spoils meat colour and the breakdown of fats during storage of fresh and frozen cuts. Mitsumoto and colleagues found similar improvements in colour stability and reduced fat breakdown in crossbred and Holstein steers given daily supplements of 1200 mg alpha-tocopheryl acetate.

A separate thread concerns chromium picolinate. Page and colleagues reported that pigs fed small amounts of chromium as chromium picolinate developed a noticeably larger loin eye, carried more lean muscle and less fat over the tenth rib, an effect not produced by the same amount of chromium given as chromium chloride. A follow-up study testing chromium picolinate across two genetic strains of pigs found that the size of the response depended heavily on which strain was fed.

How much weight these findings carry#

Most of the trials Johnson reviews are individual studies in specific species, breeds or production systems, often using vitamin or mineral doses well above standard commercial practice, and the paper itself flags inconsistency between studies on vitamin E and immunity as an open problem. We would treat the broiler flock-level finding on vitamin E as the strongest evidence in the review, simply because of its scale, while regarding the chromium picolinate and vitamin D3 analogue results as promising leads rather than settled practice, given the paper's own acknowledgement that further work was needed to understand how they act.

Johnson's broader point is that nutritionists and farm managers needed to stop treating vitamins and minerals purely as tools to prevent deficiency, and start weighing their production and economic effects directly. The breadth of species covered - pigs, broilers, turkeys, laying hens and feedlot cattle - suggests this was a pattern across intensive livestock production generally, even though each result rests on its own trial conditions.

Two other catalogue records from the same proceedings touch on related intensive-production nutrition questions: one on protected amino acids for wool and growth in sheep, and another on an acidifier trial in weaner pigs. Both sit alongside this paper in the Recent Advances in Animal Nutrition collection, which gathers conference papers from this period of Australian livestock nutrition research.

Sources and further reading#

• Trove library search: find a library that holds the paper
• Animal Genetics and Breeding Unit
• Feedipedia animal feed database: an open-access database of animal feeds
• Poultry Hub Australia: poultry science information

Questions#

— The Livestock Library team