A specific double antibody radioimmunoassay for ovine and caprine growth hormone (CH) is described in wh ich a comparison is made between the results obtained with purified preparations of ovine and caprinc GH as the labelIed antigens. Measurement of the circulating levels of GH in plasma taken from four lactating female, tour castrated male and four virgin female goats showed no significant differences between the levels of GH in lactating and non-Iactating animals. Marked variations in plasma GH were found between sampIes from different goats and between sampIes from the same goal. Possible reasons for these variations are discussed.

Physiological differences between cows in hormone and metabolite concentrations were sought that may account for genetic differences in milk production.Two groups of New Zealand Friesian cows, differing in genetic merit for fat production (high breeding index (HBI) and low breeding index (LBI)) by approximately 23 breeding index units (20 kg fat on the United Kingdom improved contemporary comparison scale), were each divided into two further groups, one of which was given freshly cut pasture to appetite and in the other intake was restricted to 70% of appetite. Eighteen blood samples were collected over a 24-h period from each of 16 cows fitted with indwelling jugular catheters. Samples were analysed for growth hormone, insulin, free fatty acids and P-hydroxybutyrate. Mean concentration of insulin was significantly higher in the HBI underfed group than in any other group (P < 0-01). Glucose concentration was significantly lower in the LBI group (P < 0-05), whose intake was restricted. The concentration of (3-hydroxybutyrate was significantly higher in the cows whose intake was restricted (P < 0-01) and the concentration fell markedly after feeding. Growth hormone concentrations were higher in the cows on restricted intake (P < 0-05) and in HBI cows but the differences were not statistically significant.It was concluded that different patterns of blood metabolites and hormones are associated with cows that differ in genetic merit. Aspects of insulin and glucose metabolism, particularly at low planes of feeding, appear to offer most promise as indicators of high milk-solids production.

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A group of 16 Romney wether sheep fitted with rumen and abomasal cannulae and aged 11 to 12 months was allocated to either high or low crude protein (CP) pelleted diets (220 (HP) and 120 (LP) g CP per kg) to give four daily intakes of dry matter (356, 711, 1067 and 1422 g) within each diet, giving two sheep per treatment. Diets were given hourly for 40 days during which time growth rates, plasma concentrations of insulin (I) and growth hormone (GH) were determined, a glucose tolerance test was performed and relative rates of fatty acid (FA) synthesis were determined.Live-weight changes ranged from -46 to 215 g/day and wool growth ranged from 86 to 210 mg per 100 cm 2 daily.Plasma GH concentrations were significantly higher (P < 0-001) in sheep given LP diets (21-2 (s.e. 4-2) Hg/1) than in those given HP diets (10-1 (s.e. 1-8) ng/1) a n d negatively correlated with both energy (E) (r = -0-62; P < 0-01) and nitrogen (N) (r = -0-63; P < 0-01) intakes which proportionately accounted for 0-47 of the variance in plasma GH concentration (P < 001). Plasma I concentrations were higher (F < 0-05) in sheep given HP diets (2-77 (s.e. 0-34) (ig/1) than in sheep given LP diets (1-86 (s.e. 0-23) Hg/1). Intakes of E and N proportionately accounted for 0-38 of variance in I concentration which was primarily determined by N intake.After intravenous infusion of glucose (150 mg/min) for 30 min, significant differences in the rate at which plasma glucose and I concentrations declined to pre-infusion levels were evident with different daily intakes of the pelleted diets.Synthesis of FA in adipose tissue was on average 1-7 times more rapid in sheep given HP than in sheep given LP diets (P < 0-05) and increased approximately three-fold with increasing intake. Partial correlations showed differences in E and N intakes were able to account for 0-73 (P < 0-01) of the variance in FA synthesis rates, with N intake having a greater influence than E intake (partial correlations: r = 0-53; P < 0-05 and r = 0-35; P > 0-05 respectively).

The changes in the rate of growth in area and in arborescence of the duct system of intact and ovariectomized female mice of the CHI strain have been measured by objective means.The duct system of intact mice grows in area at a rate isometric with (body weight) \ m=2/ 3\ until the mice are about 24 days old, when the rate of growth becomes positively allometric. The number of junctions in the duct system is almost constant before the phase of rapid growth in area begins, but increases rapidly for a time, then more slowly until the mice are between 56 and 84 days old when little further increase is seen. These changes do not occur in ovariectomized mice less than 84 days old, but by 1 year such mice showed evidence of stimulation of the mammary glands (mammae) and uteri, the source of the stimulating factor being presumably hyperplastic tissue in the adrenal cortices.The duct system of ovariectomized mice 42 days old, given 0\m=.\055 \g=m\g oestrone daily in 0\m=.\1ml. arachis oil, did not differ significantly from that of intact controls, either in area or arborescence, and increasing the dose of oestrone to 0\m=.\1 \g=m\gdaily caused no further change in area or arborescence. Ovariectomized mice given 0\m=.\01 \g=m\g oestrone daily showed duct systems which were double the area of those of ovariectomized controls, but considerably smaller than those of intact controls.Weaning at 15 instead of the normal 21 days did not affect either normal or oestrone-induced growth of the mammae. The mammae of intact, suckling mice between 10 and 15 days old did not respond to oestrone or progesterone, but showed a slight growth in response to unfractionated anterior-pituitary suspension and a greater response when this suspension and oestrone (0\m=.\01\g=m\gdaily) were given together. A combination of anterior-pituitary suspension and progesterone caused a great increase in duct branching, but little if any increase in area of the duct systems. There was no response in area or branching when these mice were given oestrone and progesterone together, but a slight thickening of the ducts was observed, although this was less than in mice given unfractionated anterior-pituitary extract.