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SUMMARYIn two experiments carried out on 36 crossbred growing lambs the effect of purified bovine somatotrophic hormone (STH) on wool production and some qualitative fleece characters was studied. Food intake during and after the hormonal treatment was also examined. STH, injected in a dose of 1 mg/kg of body weight in 10- or 15-day intervals to growing lambs from 2 to 100 days of age, increased fleece weight significantly. This increase was accompanied by considerably higher daily food intake both during the hormonal treatment and 15 weeks after cessation of STH injections. No significant effect of STH on qualitative fleece characters was found.

The aim of the study was to evaluate the relationship between the litter size and plasma progesterone (PP) concentration during the breeding season and pregnancy in some prolific sheep breeds. Investigations were performed during two consecutive reproductive cycles. PP concentrations were determined in Finnsheep (n = 16), Polish Heath (n = 13), Friesian (n = 10), Zelazna (n = 12) and Karakul (n = 14). Prolificacy was 3.14, 2.0, 2.0, 1.8 and 1.12, resp. Highly significant differences in PP levels during pregnancy were found between the prolific breeds and breed with the lowest litter size. There was also a significant effect of pregnancy stage on the PP concentration. Breed differences in PP levels during the oestrus cycle were the most pronounced on the 10th day of the cycle. However, due to a considerable variation within breeds they were statistically insignificant.

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In two series of experiments plasma thyroxine and triiodothyronine concentration were examined in 56 adult hens and 139 meat type chickens of Biała Brwinowska strain fed up to 7 weeks of age a diet containing "OO" rape seeds, wheat and barley (diet B) or maize, soyabean meal and wheat (diet C). Relationship between reproductive performance of adult hens and plasma thyroid hormone concentration was assessed.At the age of 7 weeks, chickens fed diet B had significantly lower body weight (except of males in 1994) and, despite of its low (0.7-0.9 /rniol/g) glucosinolate content, significantly higher plasma thyroxine concentration than control birds. No significant diet-related difference was found in their plasma T 3 level and T 3 /T 4 ratio. Also no differences were found in reproductive perfomance of one year old hens related to the diet fed in the first 7 weeks of life. In addition, in both series of experiments plasma T 4 concentration was positively correlated with egg fertility (P ;£ 0.05) while T, negatively to the hatchability rate (P^O.01).