Effects of feather wear and temperature on prediction of food intake and residual food consumption.

Heat production, which accounts for 0.6 of gross energy intake, is insufficiently represented in predictions of food intake. Especially when heat production is elevated (for example by lower temperature or poor feathering) the classical predictions based on body weight, body-weight change and egg mass are inadequate. Heat production was reliably estimated as [35.5-environmental temperature (degree C)] x [Defeathering (=%IBPW) + 21]. Including this term (PHP: predicted heat production) in equations predicting food intake significantly increased accuracy of prediction, especially under suboptimal conditions. Within the range of body weights tested (from 1.6 kg in brown layers to 2.8 kg in dwarf broiler breeders), body weight as an independent variable contributed little to the prediction of food intake; especially within strains its effect was better included in the intercept. Significantly reduced absolute values of residual food consumption were obtained over a wide range of conditions by using predictions of food intake based on body-weight change, egg mass, predicted heat production (PHP) and an intercept, instead of body weight, body-weight change, egg mass and an intercept.

Relationship between the thyroidal and gonadal axes during the estrous cycle of ewes of different breeds and ages.

In order to define the patterns of TSH, T4, T3, rT3, GH and cortisol during the estrous cycle of sheep, pluriparous and primiparous ewes were synchronized with progestagen-impregnated pessaries (Veramix) at the start of the normal breeding season. After the pessaries were removed (day 0), daily blood sampling was carried out in cannulated ewes during the ovulatory cycle. Hormonal analyses of TSH, T4, T3, rT3, GH, cortisol, LH and progesterone (P) were performed by RIA. P and LH levels during the cycle were conform to the literature and were not different between the primiparous and pluriparous ewes of different breeds used in this study. Neither age nor breed influenced the hormone patterns. A significant negative correlation was found between TSH and P during the cycle, although the correlation between P and T4 was not significant; during the estrous period, low P levels were paralleled by high T4 levels, whereas the reverse was observed during the luteal phase. Higher T3 levels and T3/T4 ratios were observed during the luteal phase. No obvious pattern of rT3 and cortisol during the cycle was found. The GH concentration increased during the 17 days of the cycle. A positive correlation with P was calculated. During the estrous cycle obvious changes in thyroid hormones, GH and TSH occurred. However, this study shows no causal relationship between the thyroid and the gonadal axes.

Thyroid function in newborn lambs: influence of prolactin and growth hormone.

Lambs originating from Suffolk, Milksheep and Texel crossbreeds were injected with saline, 500 micrograms ovine prolactin or 500 micrograms ovine GH within 30 min of parturition (n = 10). Birth weight was negatively correlated with plasma concentrations of reverse tri-iodothyronine (rT3) but not with thyroxine (T4), free T4 (expressed as the free thyroxine index) or cortisol. At birth, T3 and T4 plasma concentrations were high and remained high during the 3-h observation period. After 3 h a significantly lower rT3 concentration was found. The cortisol concentration at birth was also high (100-400 nmol/l) but decreased rapidly to basal values after 1 h. An injection of 500 micrograms prolactin after parturition did not influence the hormonal parameters studied except for rT3 where, after 2 h, lower plasma concentrations were found compared with controls. Growth hormone raised T3 levels from 4.80 +/- 0.44 (S.E.M.) nmol/l at birth to 6.74 +/- 0.42 nmol/l at 1 h after birth (P less than 0.01) and to 6.51 +/- 0.42 nmol/l after 2 h (P less than 0.05). At both times these values were significantly (P less than 0.001) different from saline-injected controls. GH decreased rT3 from 6.77 +/- 0.71 nmol/l at birth to 5.42 +/- 0.54 nmol/l after 1 h (P less than 0.05) and to 5.10 +/- 0.45 nmol/l after 2 h (P less than 0.01; values were also significantly different from saline controls at P less than 0.05 and less than 0.005 respectively). At the same time total and free T4 concentrations were increased. No influence of prolactin or GH injection on plasma cortisol concentrations was seen.(ABSTRACT TRUNCATED AT 250 WORDS)