Growth performance and intestinal morphology in broiler chickens produced from hyperthyroid breeder hens A. Akhlaghi A,F , M. J. Zamiri A , Y. Jafari Ahangari B , M. R. Mollasalehi C , H. Shojaie C , H. Atashi A , B. Navidshad D , A. A. Akhlaghi E and M. Dadpasand A A Department of Animal Science, College of Agriculture, Shiraz University, 71441-65186 Shiraz, Iran. B Faculty of Animal Science, Gorgan University of Agricultural Science and Natural Resources, 49189-43464 Gorgan, Iran. C Babolkenar Arian Line Breeding Center, 47561-64397 Babolkenar, Iran. D Department of Animal Science, University of Mohaghegh Ardabili, 56199-11367 Ardabil, Iran. E Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, 21889-89127 Tehran, Iran. F Corresponding author. Email: aakhlaghi@shirazu.ac.ir; amirakhlaghi837@gmail.com Abstract. An association between induced maternal hyperthyroidism and a decreased incidence of cold-induced ascites in broiler chickens has been reported recently. There are also reports suggesting that thyroid hormones have an effect on intestine, a high oxygen-demanding organ. The present study aimed to determine whether the ascites-attenuating effect of maternal hyperthyroidism is associated with morphological changes in intestine and with probable adverse effects on growth performance in progeny chicks. Eighty-eight broiler breeder hens were allotted to control or hyperthyroid [HYPER; thyroxine-treated] groups, and artificially inseminated. Hatching eggs (n = 924) were incubated and day-old male chicks (n = 288) were reared for 42 days under standard or low ambient temperature. Plasma thyroxine was higher in the HYPER hens and their embryos at internal pipping. Maternal hyperthyroidism did not adversely affect the feed : gain ratio and carcass weight, whereas cold stress impaired them. A higher relative weight was found at 42 days of age for all intestinal regions at low ambient temperature. The duodenal and jejunal crypt depths (CD) were lower in HYPER group at 7 days of age. Cold exposure decreased the duodenal and jejunal villus height and CD, and increased the ileal goblet cell number at 21 days. On Day 42, higher values were recorded for CD, goblet cell number, and epithelial thickness of different intestinal regions in cold-exposed birds. In conclusion, growth performance was not adversely influenced by maternal hyperthyroidism and its minimal early effect on intestinal morphology does not appear to be the underlying mechanism for decreased incidence of ascites in broilers. Additional keywords: broiler, cold stress, intestinal morphology, maternal hyperthyroidism, performance. Received 23 August 2012, accepted 23 January 2013, published online 12 April 2013 Introduction Thyroid hormones (TH) contribute to various physiological functions, including intestinal development (Black 1988; Suvarna et al. 1993). The gastrointestinal tract requires a large supply of O 2 (Yen et al. 1989), which may further reduce the availability of O 2 for other organs during hypoxemic conditions, as observed during the ascites syndrome (Julian 1993). The syndrome is believed to be caused by a high oxygen requirement of rapidly growing tissues in the contemporary meat-type chickens (Julian 1993). Our previous study suggested an association between maternal hyperthyroidism and a decreased incidence of ascites in cold-exposed broiler chicks produced from hyperthyroid (HYPER) breeder hens (Akhlaghi et al. 2012). The finding raises the question on the probable underlying mechanism(s) for the lower incidence of ascites in these birds. A hypothesis was tested that induced maternal hyperthyroidism would affect the intestinal morphology of the broiler in favour of a lower oxygen consumption, thereby helping the bird to better tolerate the ascites-inducing condition (cold exposure). A lack of information on association between maternal hyperthyroidism and intestinal morphology in progeny chicks prompted the present study, which aimed to investigate the effects of induced maternal hyperthyroidism on intestinal morphology in progeny chicks reared under conditions of a standard or low ambient temperature. Practically, it would also be of high priority to determine the probable effects of maternal hyperthyroidism on growth performance in broilers (possibly the adverse effects) before making any recommendation. Therefore, the study also aimed to unmask the probable adverse effects of maternal hyperthyroidism on growth performance during a 42-day grow-out period in progeny chicks. The study provides CSIRO PUBLISHING Animal Production Science, 2013, 53, 1046–1051 http://dx.doi.org/10.1071/AN12302 Journal compilation Ó CSIRO 2013 www.publish.csiro.au/journals/an