Twelve recently weaned Hereford crossbred heifers weighing 227 kg (12 kg SD) and aged 230 d (8 d SD) on d 0 were used to investigate physiological responses associated with compensatory growth. Six heifers were allotted to ad libitum intake (ADLIB) and six were restricted to a maintenance diet for 95 d followed by realimentation (REST). Plasma collected from all heifers during feed restriction (d 0, 20, 48) and realimentation (d 104, 125, 153, 195) was analyzed for growth hormone (GH), insulin-like growth factor I (IGF-I), thyroid hormones (thyroxine [T4] and triiodothyronine [T3]), insulin, glucose, nonesterified fatty acids (NEFA), blood urea nitrogen (BUN), and 3-methyl histidine (3-MH). Resting metabolic rate (RMR) was measured 5 d before and 15 and 36 d after the beginning of realimentation. Feed restriction was associated with higher (P < .05) plasma concentrations of GH and NEFA and lower (P < .05) concentrations of IGF-I, T4, T3, insulin, and glucose. The BUN concentration was lower (P = .05) in REST than in ADLIB heifers on d 48, whereas 3-MH was not affected during the first 48 d of feed restriction. The RMR was lower (P < .05) in REST than in ADLIB heifers during feed restriction. During realimentation, the ADG of REST heifers was higher (P = .001) than that of ADLIB heifers. Concentrations of IGF-I, insulin, glucose, and NEFA in REST heifers increased and no differences (P > .05) between treatments were observed on d 104 (d 10 of realimentation) and thereafter. Conversely, GH concentration in REST heifers remained elevated through d 104 but dropped to ADLIB levels by d 125 (d 31 of realimentation). The T4 and T3 concentrations remained lower (P < .05) in REST than in ADLIB heifers after 10 d of realimentation but rose to control levels by d 31 of realimentation. The RMR was lower (P < .05) in REST than in ADLIB heifers 15 d into realimentation; however, no difference was found between treatments by d 36 of realimentation. These results indicate that enhanced growth rates in the early phase of compensatory growth are associated with the physiological response of the GH-IGF-I-insulin axis coupled with reduced maintenance requirement due to slower metabolic rate in restricted-refed heifers.

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to study the effects of mild, chronic feed restriction followed by refeeding on some longissimus muscle fiber characteristics. Five animals were slaughtered on day 1 for analysis of initial muscle fiber characteristics. The remaining 48 animals were randomly penned in groups of 6 and assigned to treatments as follows: three pens to ad libitum feeding; three pens to 2 mo of feed restriction followed by refeeding, and two pens to 4 mo of feed restriction followed by refeeding. Animals in one ad libitum and one restricted pen were slaughtered after 2 mo and those in one pen from each treatment after 4 mo, and the remainder at the final slaughter weight of about 410 kg. Two rnonths of feed restriction had no effect on the proportions of longissimus muscie fiber-types, ''red " (0R), "white'' (aW), and ''intermediate" (aR), but fiber diameters were smaller (P<0.05) in the restricted than in the ad-libitum-fed animals. Four months of feed restriction was associated with a relatively higher (P<0.05) proportion of BR fibers and lower (P < 0.05) proportion of .yW fibers than ad libitum feeding. Muscle fiber diameters were larger (P<0.05) in the ad-libitum-f'ed than in the restricted heifers. No significant f'eeding treatment differences were found in fiber-type proportions or fiber diameters at the final slaughter weight.

. 1996. Glycogen metabolites and meat quality in feedrestricted re-fed beef heifers. can. J. Anim. Sci. 76: stl-siz. Twenty-four Hereford crossbred heifers weighing2Z2 kg (22 kg SD) and aged226d (13 d SD) on day 0 were used to investigate the efiects.of feed restriction (period 1) followed by realimentation (period 2) on hepatic and longissimus muscle glycogen iretabolites.and meat quality' The heifers were randomly assigned in equal numbers to either ad libitum"feeding (ADLIBj or m"aintenance feeding for 92 d followed by realimentation (REST), and serially slaughtered over a wide range of liveweights (200-460 kg). The concentrations of glycogen, its metabolites, and the total glucidic potential (Gp) were deteniined frorn p6.tioni of the ciudate lobe of the liver and the longissimus lumborum (LL) (p < 0,05) chez les genisses au regime ADLIB, le PG suivant une evolution analogue (P < 0,07). Dans le LL' on n'observait pas de diff6rence significative entre les deux regimes relativement aux concentrations de glycogdne ou de ses metabolites' Les g6niss-es abattues dans la phase I avaient moins de glycogdne (P = 0,!a) et plus de. lactate (P < 0,0 1 ) dans le muscle que celles abattues dans la phase 2. Les b6tes au r6gime REST pesaieni moins ir l''abittage et pr6sentaient une noix de c6te plus petite (P = 0,03), une moindre concentration de gras i-ntramusculaire (p < 0,01) et une plui forti teneur en eau de la viande (P < 0'01) que les gdnisses ADLIB. Ind6pendamment"du poids d l'abattage, leur viande avaii des pertes d'egouttage plus elev6es (P = 0,05) et une valeur L* plus basse (p = 0,01). 11 ressort de ces observitions que le rationnement temporaire influe sur les reserves en glycogdne du foie et ne produit que des effets benins sur la qualite de la viande, rien de comparabie en fait au grave d6faut de la viande DFD (viande noire).Mots cl6s: Rationnement, remise d I'alimentation ir volont6 muscle longissimus, foie potentiel glucidique, quaiite de la viande GP is the sum of glycogen and its major metabolites from anaerobic glycolysis (glucose, glucose-6-phosphate, and lactate For personal use only.