INFLUENCE OF THE PHOTOPERIOD AND A LIGHT REVERSE PROGRAM ON METABOLICALLY ACTIVE HORMONES AND FOOD-INTAKE IN DOMESTIC PIGS COMPARED WITH A WILD BOAR

The pattern of food intake, IGF-I and testosterone secretion were moni tored in entire and castrated domestic boars (n = 4/group) either unde r a light program simulating changes of the natural photoperiod (''nat ural photoperiod'') or a light program simulating the natural photoper iod with a shift of 6 mo (''light reverse program'') over a 14-mo peri od. For comparison, a European wild boar was also investigated under a light reverse program for 23 mo. Under decreasing and short daylength , testosterone secretion increased in the wild and the domestic boars. During the testosterone maximum, the wild boar refused food for about 6 wk (25% weight loss). In parallel, IGF-I concentrations decreased b y 50%, whereas under long daylength, IGF-I concentrations reached thei r seasonal maximum of about 200 ng mL(-1). In domestic boars and barro ws, lowest IGF-I concentrations (boars: 105 ng mL(-1), barrows: 76 ng mL(-1)) were measured under early increasing daylength (natural photop eriod: February/March; light reverse program: August/October). In boar s, IGF-I concentrations started to increase under long daylength and r eached a maximum of 155 ng mL(-1) in October (photoperiod) or April (l ight reverse program). In barrows, maxima (105 ng mL(-1)) were measure d in September (photoperiod) or March (light reverse program). In dome stic boars, IGF-I secretion was stimulated by gonadal steroids even if the food intake was significantly reduced by testosterone.