Insulin—glucose interactions characterised in newly hatched broiler chicks Y. TOKUSHIMA, B. SULISTIYANTO, K. TAKAHASHI AND Y. AKIBA Graduate School of Agricultural Science, Tohoku University, Sendai, Japan Abstract 1. A study was conducted to identify the specificity of insulin—glucose interactions in newly hatched broiler chicks. 2. Plasma insulin concentrations in fed chicks at one day post-hatch were lower than those at later ages and tended to increase up to d 7, while the concentrations from 1 to 7 d of age were lower than those in chickens of 10 to 28 d of age. 3. Plasma glucose concentrations were lowered for 60 min by injection of insulin at 10 and 40 mg/kg body weight (BW) in both 1- and 21-d-old chicks, showing that the hypoglycaemic effect of exogenous insulin is of larger magnitude but shorter duration in 1-d-old chicks. 4. The decrease in plasma glucose concentration at 60 min after insulin injection (10 and 40 mg/kg BW) was larger in 1- to 7-d-old chicks than in 14- to 21-d-old chickens. 5. These results indicate that newly hatched broiler chicks are under the control of specific insulin—glucose interactions characterised by low plasma insulin concentrations with high sensitivity to insulin. INTRODUCTION Improvements in growth rates of broiler chickens over the last few decades have emphasised the importance of growth and metabolism during the post-hatch period (up to around 7 d after hatching) (Akiba and Murakami, 1995). Residual egg yolk in the abdomen of post-hatched chicks provides approximately 30% of the energy required for the first 3 d after hatching (Murakami et al., 1992), even when newly hatched chicks initiate ingestion of carbohydrate-rich diets. It has been noted that during the few days post-hatch when the transition of nutrients from residual yolk to exogenous feed occurs, the gastrointestinal tract, secretion of digestive enzymes, absorption of nutrients and dietary energy metabolism are not yet well developed in chicks (Akiba and Murakami, 1995; Murakami et al., 1995; Noy and Sklan, 1997; Sulistiyanto et al., 1999). The transition of nutrient sources with ontogeny of ingestion of carbohydrate-rich diets may trigger species-specific changes in insulin—glucose interactions in chickens. Chickens have blood glucose concentrations that are twice as high as in humans and have a marked resistance to insulin injection (Hazelwood, 1986; Simon, 1989; Akiba et al., 1999). While persistent hypoglycaemia lasting for 5 d has been experi- mentally induced by continuous insulin infusion or repeated administration of tolbutamide in broiler chickens (Akiba et al., 1999; Seki et al., 2001), the hypoglycaemic state influences carbo- hydrate metabolism (including key enzymes involved in gluconeogenesis and glycolysis) to only a small extent (Chida et al., 2000). Other ‘anomalies’ in insulin—glucose interactions have also been reported. Joseph et al. (1996) reported that White Leghorn chicks showed increased insulin sensitivity and attenuated glucagon responsiveness during the first 2 weeks post- hatch compared with 4-week-old chickens. Also, the insulin content in the pancreas increases from d 14 to d 20 of embryonic development and then falls at hatching (Langslow, 1975). In egg-type chicks, plasma insulin concentrations increase with age after hatching (Raheja et al., 1972; Leibush et al., 1984), whereas insulin bind- ing to plasma membranes in erythrocytes and skeletal muscles decreases (Leibush et al., 1984; Kolychev and Leibush, 1987). In broiler chickens, body weight gain per day has been improved by approximately 40% from 1972 to 1990 (Savory, 2002). Fat-line broiler Correspondence to: Yukio Akiba, Animal Nutrition, Graduate School of Agricultural Science, Tohoku University, Aoba-ku, Sendai 981-8555, Japan. Tel: þ81-22-717-8689. Fax: þ81-22-717-8691. E-mail: akiba@bios.tohoku.ac.jp Accepted for publication 30 April 2003. British Poultry Science Volume 44, Number 5 (December 2003), pp. 746–751 ISSN 0007–1668(print)/ISSN 1466–1799(online) ß 2003 British Poultry Science Ltd DOI: 10.1080/00071660310001645758