Effects on wool growth of the infusion of mixtures of amino acids into the abomasum of sheep

Abstract

SUMMARYMerino sheep were given abomasal infusions of either mixtures of amino acids or protein during periods of 8 or 12 days. Effects on wool growth were measured using autoradiography and a clipping procedure which allowed time for the emergence of the wool fibres. Estimates of volume growth rate, from the autoradiographic measurements, and of mass of wool grown, from clipping, were in good agreement.An infusion of a standard mixture of 13 amino acids, which included ten essential amino acids in approximately the proportions in casein, consistently stimulated wool growth. The mean increases in volume and mass of wool grown, during 30 infusions, were 66 and 67% respectively. A mixture of ten essential amino acids alone appeared to be as effective as the standard mixture for stimulating wool growth, and there were no significant differences between the effects on wool growth of casein and the standard mixture of amino acids.The omission of methionine from an infusion of the standard mixture of amino acids, or from a mixture of essential amino acids only, inhibited wool growth rate; both fibre diameter and length of wool grown per day were reduced to below the control values. In addition, the strength of the fibres was considerably reduced.Infusions of zein and of an amino acid mixture simulating the essential amino acid composition of zein both inhibited wool growth rate, due to a reduction in fibre diameter. Similar effects on wool growth were observed when any one of three essential amino acids (lysine, isoleucine or leucine) was omitted from an infusion of the standard mixture of amino acids. The omission of five other essential amino acids (arginine, histidine, phenylalanine, threonine or valine) from the infusion, or variations in the proportions of leucine, lysine or methionine, had no appreciable effects on wool growth.

Impact of Adding Rumen Protected Lysine or/and Methionine on Some Wool Characteristics in Barki Sheep

“…Furthermore, the fiber length was higher in all treatments after 6 months compared with 3 months of experiment. Our results are in agreement with several authors (Reis and Tunks, 1978;Reis et al, 1991), who found that the omission of methionine from a mixture of amino acids reduced wool growth and decreased length growth rate. Methionine has specific effects on wool growth, it may be related to the formation of S-adenosyl-Lmethionine.…”

Seasonal variation in fibre diameter and length in wool of grazing Merino sheep with low or high staple strength

“…In our experiment, the decline in liveweight started about 6 weeks after wool growth had begun to decline, based on the [ 35 S] fibre diameter and length measurements. This lag is comparable with that observed when protein or amino acid infusions were stopped in pen experiments (Reis and Schinckel 1964;Reis and Downes 1971;Reis and Tunks 1978) and suggests that the protein supply from pasture was sufficient to maintain liveweight after pasture senescence but was insufficient to maintain wool production. Revell et al (1994) estimated that the amount of nitrogen apparently digested by grazing sheep declined by at least 50% at the end of spring with pasture senescence in the Mediterranean environment of south-west Australia.…”

“…The break of season in autumn begins the pasture growth cycle with an abrupt increase in feed quality followed by quantity. At the break of season, liveweight and wool production changes were closely matched and within the time frame for responses recorded from a base diet with protein and amino acid supplementation regimes (Reis et al 1973;Reis and Tunks 1978;Hynd and Allden 1985). Grazing Merino wethers had a large and statistically significant variation in L : D ratio, in line with that recorded for Romney sheep (Woods and Orwin 1988).…”

“…A range of factors has been shown to alter the L : D ratio of wool in housed sheep. Infusion of zein or amino acids mixtures deficient in lysine increased length growth rate while depressing fibre diameter (Reis and Tunks 1978) and was corrected by the addition of lysine to the diet (Reis and Tunks 1976). Hypothyroid sheep have fibre length growth suppressed (Ferguson et al 1965;Hynd 1994) and in hyperthyroid sheep there were non-significant increases in fibre diameter and fibre length growth leading to a significant increase in patch wool production (Hynd 1994).…”

Mitotic Activity in Cells of the Wool Follicle Bulb

“…The rate of wool growth of the sheep on the high-protein ration in this experiment was exceptional (19'6 g/day), and would almost certainly be approaching the genetic maximum for this strain of animal. The ration must have supplied a large amount of sulphur-containing amino acid to the intestines to achieve this rate of fibre production (Reis and Tunks 1978). Preliminary data obtained using the technique described in this paper have revealed that cystine increases wool output not only by providing substrate for keratin synthesis but also by stimulating the rate of follicle bulb cell division (unpublished data).…”