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The effect of antibiotic ionophores on milk production and composition in Angora goats

 

P. R. King and D. Wentzel

Grootfontein College of Agriculture, Middelburg CP, 5900

 

Ionophores are organic compounds capable of forming complexes with cations. The antibiotic property of the ionophores lies in their ability to carry cations across cell membranes very effectively, thereby changing the electrolyte balance within the cell. This change in electrolyte balance leads to the destruction of the cell membrane. At least one hundred ionophores have been identified up to date. Some are metabolites of micro-organisms while others are synthetic compounds.

Monensin, a product of the fungus Streptomyces cinnamonensis, was the first antibiotic ionophore to be isolated. Monensin has a coccidiostatic ability and was originally used in chicken rations to control coccidiosis. During the early sixties, it was discovered that ionophores included in fattening rations for ruminants decrease feed intake while improving feed conversion and weight gain. This is the result of ionophores inhibiting the gram positive organisms which mainly produce acetic acid, lactic acid and buturic acid in the rumen, while the gram negative organisms, producing mainly propionic acid, flourish. Propionic acid is of more value as a source of energy than the other volatile fatty acids produced in the rumen.

The ingestion of large quantities of starch by ruminants can lead to the excessive production of lactic acid in the rumen which, in turn, can lead to acidosis. This problem was addressed firstly by alkalinizing the grain and secondly by the inclusion of an ionophore to limit the production of lactic acid. In practice, however, the allegation was made that these ionophores cause the production of "watery" milk. In the dairy industry it was found that cows with low production rates of acetic acid in the rumen tend to produce less butter fat. Because ionophores also tend to decrease acetic acid production, it is theoretically possible that lactating small stock receiving chocolate grain produce less butter fat.

To investigate this possibility, lactating Angora does were given a basal diet containing either no ionophores, lasalocid (Taurotec), salinomycin (Salocin) or Monensin-Na (Rumenson). The does were milked at 14, 42 and 90 days after parturition. In each case the kids had been removed from their mothers for a 16 hour period before milking. The milk volume was recorded and a representative sample was taken for each doe. Milk samples were analyzed for protein, fat, phosphorus, calcium and ash content (Table 1).

 

No significant differences in any of the determined parameters between the various groups were found. In accordance with these results, Slippers (1990), using Dohne Merino ewes, also found no significant differences in protein and fat content of the milk between the control group receiving no ionophores and the experimental group receiving ionophores, but the milk production of the experimental group was 29,4 % higher than that of the control group.

These results demonstrate that ionophores do not have any detrimental effects on either milk production or milk composition. When lactating ewes receive a chocolate grain supplement it is essential that they receive sufficient roughage. Special attention should be given to using the correct ingredients and the precise procedure for the preparation of chocolate grain in order to prevent the incidence of acidosis - a condition which will obviously have serious detrimental effects on both milk production and milk composition in any lactating animal.

 

REFERENCE

SLIPPERS, S.C., 1990. The effect of Lasalocid-sodium in lactation diets on production and composition of ovine milk. Proceedings of the 29th congress of the South African Society of Animal Production, 27-29 March 1990, Stellenbosch.

 

Published

Karoo Agric, Vol4, No 3, 1991 (21-22)