Animal conversion efficiency

It has long been established that the sexual status of an animal controls and coordinates its growth rate and speed of fattening. Bulls grow faster and lay down more lean meat in the carcass than steers, whereas steers grow faster with a higher feed conversion efficiency than cows. These beneficial effects on animal performance are due to the sex steroids produced in the testes. 

More than 97% of the available soybean meal is used for feed where extensive heat treatment is necessary to maximize feed conversion efficiency by livestock. Toasting inactivates protease inhibitors (especially trypsin and chymotrypsin inhibitors) and the enzyme urease, and improves protein digestibility. None of these objectives can be obtained without protein being denatured and loss in water solubility however, depending on the method used, meals with great differences in protein solubilities or dispersibilities can be produced. The optimum amount of heat treatment in toasting soybean meal is still debated among animal nutritionists. 

Typha and other similar aquatic marsh plants have nutrient concentrations as % of dry matter of about 0.5-3% N, 0.1 -0.3% P, and 1.6-3.5% K (1 ). The actual nutrient concentration depends on the part of plant analyzed, the season (or age of plant), and, most importantly, on the nutrient supply to the plant. Nutrient limitation reduces light conversion efficiency and productivity. However, the minimal concentrations required to maintain healthy growth are not well characterized. Critical nutrient tissue levels (at which nutrient deficiency sets in) are 0.09% for P and 2.5% for K in a Typha hybrid (52) for nitrogen it is likely between 0.5-1.0%. For supply of such nutrient levels on a large-scale a number of sources can be considered — agricultural fertilizers, sewage and animal wastes, and recycled nutrients from a processing plant. 

The growth rate and feed conversion efficiency are higher in intact males than in castrated animals. A number of different approaches may be taken to improve the conversion of animal feed into meat one of which is the application of hormones. The hormonal approach includes administration of anabolic sex steroids to either support the animal s steroid production rate or to replace steroids lost through castration. The growth hormone is another hormone used in animal production. 

The Need for Increased Surveillance of the Exposure of Man to lonophores. From the lipid soluhllity of monensln and other lonophores, we would predict they should have no trouble equilibrating across biological membrane systems including the gut. This Is certainly the case for the two diverse species observed, the dog, a carnivore, and the rabbit, a herbivore. Accordingly, we infer that there Is ample opportunity for monensln and other carboxylic lonophores administered orally to livestock to distribute systemically and exert a pharmacological effect on the recipient animal. Furthermore, the resultant physiological effects may be part of the mechanism by which lonophores produce their Improved feed conversion efficiency. 

Bacitracins (BCs) are peptide antibiotics produced by Bacillus subtilis and Bacillus licheniformisP They exhibit an inhibitory activity against Gram-positive bacteria and are most commonly used as animal feed additives for domestic animals, such as calf and swine, for preventing bacterial infection and/or improving feed conversion efficiency. Over... 

Methionine was first reported from casein in 1922 by Mueller. It is a limiting amino acid in the monogastric s feed and the addition of synthetic methionine in animal feed started from the 1950s. The addition of amino acids in the feed increases the nutritional quality and conversion efficiency of low protein feed and hence lowers the feed cost. Methionine is commercially produced by either chemical synthesis, enzymatic methods or microbial fermentation. Methionine has an advantage that it can be supplied to animal feed as a chemically produced racemate or a racemic mixture as the mammals are able to convert it to utilizable form with a methionine racemase enzyme. Chemical production uses harmful chemicals and production from protein hydrolysates requires several separation steps. Chemical synthesis produces a racemic mixture and is acetylated to produce L-methionine. Microbial fermentation overcomes these difficulties and has added advantages over the racemate that it helps optimal nutrient utihzation. 

Assays of available amino acids may be made by measuring the liveweight gain or food conversion efficiency of animals given the intact protein as a supplement to a diet deficient in a particular essential amino acid. Certain microorganisms have amino acid requirements similar to those of higher animals and have been used for protein evaluation. 

Pig and poultry diets based on cereals and vegetable protein sources are now routinely supplemented with L-lysine hydrochloride (supplying 780 g lysine/kg), dl-methionine and L-threonine. A diet for a finishing pig, which has to contain 10 g lysine/kg, required a combination of 750 g barley and 250 g soya bean meal/kg, and this mix has a crude protein content of 185 g/kg (see Appendix 2, Table A.2.2.2). With the inclusion of 2 g of lysine hydrochloride, the same lysine content can be achieved with a mix of 808 g barley and 190 g soya bean meal, and the protein content is reduced to 165 g/kg. Such reductions in crude protein content have maintained a balanced supply of amino acids and resulted in improved rates of liveweight gain and food conversion efficiency. It is important that the supplementary acids are not used excessively to satisfy the animal s requirements, since this may bring about an undersupply of other essential amino acids. 

Reasons proposed for the relatively poor conversion efficiency of ALA to EPA and DHA are that a substantial proportion of the ALA is diverted to P-oxidation (discussed above), that ALA is found distributed throughout all major tissue lipid pools (adipose, carcass, skin), and that in animals ALA might be excreted onto the fur (as discussed above). In addition, LA is the major dietary PUFA and is a competitive inhibitor of the metabolism of ALA to 18 4n-3 (commonly known as stearidonic acid see Chapter 9), a precursor of long-chain n-3 PUFA (see Figure 1). Furthermore, diets rich in LA decrease expression of the hepatic A -desaturase compared with fat-free diets this presumably also reduces the possibility of conversion of ALA to 18 4n-3 and of 24 5n-3 to 24 6n-3 (Cho et al, 1999a). 

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