Lactating goats and sheep were fitted with catheters in the external pudendal arteries supplying both mammary glands. Saline was infused continuously into one artery whereas the other artery received continuous infusions, over successive 4-day periods, of either saline or growth hormone (GH)-doses increasing twofold between successive periods from 100 to 400 ltg/day in goats and 400 to 3200 Itg/ day in sheep.Local infusion of GH at up to 1600 ltg/day in sheep did not affect milk yield or composition nor peripheral plasma concentrations of GH, insulin, glucose, urea and non-esterified fatty acids (NEFA). Infusion of GH at 3200 ltg/day in sheep increased peripheral plasma concentrations of GH, tended to increase milk yield and peripheral plasma NEF A but there were no changes in peripheral plasma insulin, glucose and urea. It is concluded that GH does not exert direct effects on the mammary glands of sheep and goats in situations where the hormone is administered over short periods.
The effects of daily administration of 10 mg of highly purified ovine growth hormone (GH) for a period of 4 weeks on wool growth have been measured in 12 Merino ewes fed either a calculated maintenance energy intake or 1·6 times this amount (six on each ration). Concentrations of hormones, glucose, urea, a-amino N and amino acids in the blood were monitored and faeces and urine collected for measurement of nitrogen balance.Wool growth rate decreased by 200/0 during the 4 weeks of GH treatment in sheep fed the high energy diet, largely because of reduced wool fibre diameter. This was followed by restoration of normal growth and then an increase of up to 20% above control levels, a response which persisted for 12 weeks following cessation of GH administration, and which was due to increases in both fibre length and diameter. GH administration caused marked increases in plasma concentrations of GH, insulin and somatomedin C, glucose and free fatty acids, all of which returned to basal levels following cessation of GH administration. No consistent changes in plasma concentration of T 3 , T 4 , cortisol, prolactin or a amino N were detected. Plasma urea and methionine levels decreased during GH treatment and returned to, or were raised above, basal levels after the GH treatment period. GH injection also resulted in a net retention of N during treatment, followed by a transient period of net N loss.The GH-induced changes in wool growth may be caused by a change in the partitioning of amino acids between the muscle mass and the skin. No other contributing factor(s) were identified.
Forty-eight crossbred wethers [Dorset Horn X (Border Leicester X Merino)] were injected subcutaneously each day for 42 to 133 days with recombinant bovine growth hormone (rebGH) at doses of either 0,50,150 or 250 pg rebGH kg-1 liveweight day-1 from 22 kg liveweight (LW) until slaughter at either 34, 42 or 50 kg LW. The lambs were fed ad libitum pellets consisting of (g kg-1 as fed) 850 lucerne, 100 barley and 50 cotton seed meal.Injections of rebGH exerted anabolic effects which were dose dependent. Overall, there were linear increases (P<0.001) in liveweight gain (LWG), total non-carcase weight, weights of heart, liver, skin, reticula-rumen, loin eye area, carcase crude protein, non-carcase crude protein, carcase ash and noncarcase ash, as well as plasma concentrations of insulin and glucose (P<0.01). There were linear decreases (P< 0.001) in feed conversion ratio, carcase weight, tissue depth (GR) and subcutaneous fat depth at the 12th rib, carcase fat and non-carcase fat as well as plasma urea. Significant interactions of dose rate with liveweight groups indicated that overall, the effects were larger in sheep grown to 50 kg than to 34 kg LW, or occurred only in the former in respect of weights of carcase, heart, liver and reticula-rumen. The same was true for depth of tissue, depth of subcutaneous fat and loin eye area at the 12th rib and also carcase and non-carcase weights of CP, fat and ash.
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