Effects of zinc-methionine on performance of Angora goats
R. Puchala, T. Sahlu, and J. J. DavisSmall Ruminant Research 33:1-8. 1999.
The essential amino acids lysine, methionine (Met), and cyst(e)ine stimulate wool and mohair growth. Omission of Met reduces wool growth and decreases both length growth rate and diameter. Skin and fiber (wool, mohair) impose heavy demands on the utilization of circulating sulfur amino acids. It has been predicted that 80% of the total free blood pool of combined cysteine and Met would be used for fiber growth. Being responsible for the initiation of protein synthesis, Met is important in fiber growth. Met can be converted to cystine mainly in the liver, but also to some extent in other tissues. Supplementation with specific amino acids has influenced mohair growth in Angora goats. It may be cost effective to increase absorption of most limiting amino acids such as Met through dietary supplementation of specific amino acids, rather than increasing absorption of a large number of amino acids through increasing of the total dietary CP level. Apart from the major nutrients such as protein, many vitamins and trace elements are essential for fiber growth. Zinc (Zn) functions directly in the process of wool growth; thus, Zn deficiencies can seriously affect wool growth. Zinc is needed for the functions of over 100 enzymes, and essential for DNA, RNA, protein synthesis and, as such, cell division. It has been suggested that primary impact of Zn deficiencies on wool growth is through impaired protein synthesis. Commercially available Zn-Met complexes provide both Zn and Met. If Zn-Met is absorbed and transported without modification, the complex may provide a means of increasing tissue supply of Met, which should increase animal productivity when Met is limiting. Therefore, objectives of this study were to investigate effects of dietary supplementation with Zn-Met (Zinpro 40, Edina, MN) or zinc oxide on mohair growth, BW gain, and concentrations of blood metabolites in Angora goats. Dietary inclusion of supplemental Zn-Met, regardless of level increased live weight gain in yearling Angora goats, but only numerically increased mohair production with a basal diet adequate in Zn. Live weight gain was greater for goats supplemented with the same quantity of Zn in the form of Zn-Met vs ZnO, even though plasma Zn concentration was similar. In conclusion, with an 11% crude protein, Zn-adequate diet, 1 g Zn-Met may offer little or no potential to improve fiber production by Angora goats.
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