Feeding efficiency

Increased hormonal levels have resulted in better mminant animal performance. Fstrogen-containing compounds, eg, zearalenone [17924-92-4], 18 22 5 available to improve growth and feed efficiency. These estrogens are given as ear implants. Melengestrol acetate [2919-66-6] (MGA),... 

C25H32O4, an additive that is a synthetic progesterone, suppresses estms in heifers and results in increased weight gain and feed efficiency (5). 

One technology uses bovine somatotropin (bST) produced by recombinant technology (38). Somatotropin [9002-72-6] is a growth hormone. The bST-supplemented cows provide an increase in milk output per cow or an increased feed efficiency. Recombinant bST, also known as recombinant bovine growth hormone (rBGH) is the synthetic analogue of a natural hormone that increases milk production in cows (39). The use of recombinant technology was approved by the FDA in 1993. The Commission of the European Community has recommended that the moratorium on commercial use of BGH be delayed until the year 2000. 

Tin. The widespread use of caimed foods results in a daily intake of tin that is ca 1—17 mg for an adult male (154). At this level it has not been shown to be toxic. Some grains also contain tin. Too much tin can adversely affect 2inc balance and iron metaboHsm. EssentiaUty has not been confirmed for humans. It has been shown for the rat. An enhanced growth rate results from tin supplementation of low tin diets (85). Animals on deficient diets exhibit poor growth and decreased feed efficiency (155). 

A distinct concern arises in the area of veterinary dmgs because of the possibiUty that dmg residues may be conveyed to humans by the food-producing animals. Therefore, dmg residues and their safety in human food remain a central issue for the Center for Veterinary Medicine (CVM). Animal dmgs also include those products which promotional Hterature claims to improve feed efficiency and increase milk production. An animal food product is regulated under the 1968 Animal Dmg Amendments if it contains a dmg used in feed or premixes (25). 

In the United States, 100 times more bacitracin by weight is used as a feed additive than for human medicine. Most of this is BMD but some is the zinc salt. BMD can be used in subtherapeutic nutritional dosages for increase in feed efficiency and for growth promotion in poultry, swine, and feedlot cattie at concentrations of 2.6—33 g/t of feed (78,81,82). Prophylactic or therapeutic medicinal dosing at higher concentrations is used for necrotic enteritis in chickens, transmissable enteritis in turkeys, ulcerative enteritis in quail, dysentery in swine, and Hver abcess in cattie (see Feeds and feed additives). 

The polyether antibiotics were first recognized as a separate class with the pubHcation of the structure of monensia ia 1967 (1). Several members of the group have siace found commercial appHcation as anticoccidials ia poultry farming and ia improvement of feed efficiency for mmiaants (see Feeds and FEED additives). 

The polyether antibiotics exhibit a broad range of biological, antibacterial, antifungal, antiviral, anticoccidial, antiparasitic, and insecticidal activities. They improve feed efficiency and growth performance in mminant and monogastric animals. Only the anticoccidial activity in poultry and catde, and the effect on feed efficiency in mminants such as catde and sheep are of commercial interest. 

Salinomycin (180) and narasin (128) have been reported to be effective in improving feed efficiency but neither has been marketed for this use. Laidlomycin propionate (Syntex, Inc.) and tetronasin (Coopers Animal Health, Inc.) have been under investigation in cattle and sheep (181,182). 

The total world market for the use of ionophores for feed efficiency improvement in mminants is approximately 80— 90 million. The United States is the largest market. Lasalocid and monensin are the only members of this class cleared for use. Outside the United States, salinomycin is used in limited quantities. Worldwide usage is about 1.5 million kg. 

Agricultural Use. Citric acid and its ammonium salts are used to form soluble chelates of iron, copper, magnesium, manganese, and zinc micronutrients in Hquid fertilizers (97—103). Citric acid and citrate salts are used in animal feeds to form soluble, easily digestible chelates of essential metal nutrients, enhance feed flavor to increase food uptake, control gastric pH and improve feed efficiency. 

Another matrix diffusional implant consists of an outer layer of micronized, crystalline 17P-estradiol dispersed in siUcone mbber over a nonmedicated, cylindrical siUcone mbber core. The system, implanted subcutaneously in the ears of cattie, releases estradiol for up to 400 days with kinetics to improve growth rate and feed efficiency (83). 

Copper compounds are used as feed additives in Europe and the United States primarily for chickens and swine (see Feeds and feed additives) (90,91). Copper increases the rate of gain and feed efficiencies of the animals. It is unclear whether this results from overcoming animal deficiencies or by enhancing preservation of feedstuffs. 

A second focus for chemical engineers in agriculture is the improvement of veterinary pharmaceuticals (e.g., peptide hormones that promise to stimulate growth, fecundity, and feed efficiency in farm animals) and vaccines. The prospects for improvement of these compounds parallel the bright prospects for human pharmaceuticals and vaccines, and the requirements for chemical engineering expertise are similar. 

Jensen, et al. (2002) experimented in Denmark with a tented system, plus access to grassland, and recorded growth rates of 780 g per day from 14kg to 99kg, with 8.9 weaned pigs per litter and a feed efficiency of 2.7 kg feed per kg of gain. 

As 3 or As 5 Fed diets of 120-1600 mg As/kg for 8 weeks Growth depression, food avoidance, and impaired feed efficiency at all levels 9... 

A great many antibiotics used in animal agriculture (for growth promotion and increased feed efficiency, subtherapeutic treatments, as well as for disease treatment) have also been used in human medicine, often at much higher levels then in agriculture. Many of those compounds that are not used in human... 

Diethylstilbestrol, mentioned in Chapters 5 and 9 as a synthetic estrogen that is also a human carcinogen, was used in the United States from the 1950s until 1979 as a growth promoter in sheep and cattle. Small amounts of this drug, added to animal feed or implanted in the flesh of animals ears, increase feed efficiency, and it was very widely used for this purpose. 

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