Comparison of physical body growth and metabolic and reproductive endocrine functions between north and south climates of Japan in trained Thoroughbred yearling horses

Abstract

This study aimed to compare body growth, metabolic, and reproductive hormonal changes in trained Thoroughbred yearling horses under different climate conditions with and without light supplementation (LS). Thoroughbred yearlings raised at research centers of the Japan Racing Association in Hokkaido (north) or Miyazaki (south) were divided into control and LS groups. In the LS groups, 44 colts and 47 fillies from Hokkaido and 11 colts and 11 fillies from Miyazaki were exposed to LS with an extended photoperiod of 14.5 hr of daylight and 9.5 hr of darkness. One week before and once a month after LS, circulating total thyroxine (T4), insulin-like growth factor-I (IGF-1), prolactin (PRL), cortisol, and progesterone (P4) concentrations were measured by radioimmunoassay and fluoroimmunoassay, respectively. Growth parameters, including body weight, height, girth, and cannon bone circumferences, were measured monthly. Hair coat (HC) condition was scored. Under natural conditions, the T4 concentrations of Hokkaido yearlings tended to be higher, whereas the IGF-1 (colt) and PRL levels were significantly lower than those of yearlings in Miyazaki. Growth parameters and HC scores were lower in Hokkaido yearlings. With LS, the PRL and P4 concentrations in Hokkaido and Miyazaki were higher, and the first ovarian activity tended to be earlier than in the controls. Only LS Hokkaido yearlings showed significantly higher HC scores than the controls. Comparing the different climates among the LS yearlings, the levels of PRL and P4 and the HC scores in Hokkaido yearlings increased and reached levels similar to those in Miyazaki yearlings. The body weight and girth increment percentages of Hokkaido yearlings in January dramatically decreased and then eventually increased to levels similar to those of Miyazaki yearlings. This suggested that yearlings in naturally colder Hokkaido exhibit higher basal metabolism to maintain homeostasis. However, providing LS may help to improve growth and early development of reproductive function in Hokkaido yearlings to levels equal to those of Miyazaki horses.

<b>Avaliação do uso de undecilenato de boldenona em potros</b>

“…Sua expressão é controlada por GH e o fator de crescimento epidermal (EGF). Outros fatores que podem influenciar em sua liberação são temperatura, umidade e medicamentos (SCANES, 2003b;TANGYUENYONG et al, 2017).…”

“…IGF-1 estimula a síntese deste hormônio (SCANES, 2003b). Em potros recém-nascidos, são encontrados valores mais altos de cortisol nos primeiros dias com acentuada queda conforme o animal vai se desenvolvendo, provavelmente, porque este é importante para a maturação e adaptação dos diversos sistemas fisiológicos (MURRAY & LUBA, 1993 (SCANES, 2003b;TANGYUENYONG et al, 2017).…”

“…Há evidências que a prolactina é necessária para o crescimento normal, mas o seu mecanismo de ação ainda não está bem definido (SCANES, 2003b). Em equinos jovens, a suplementação com luz em períodos de inverno aumenta as quantidades circulantes do hormônio (TANGYUENYONG et al, 2017).…”

“…Quando produzida, estimula as células eritrogênicas para o aumento das hemácias (SCANES, 2003b). O controle do crescimento em equinos é crucial para tomadas de decisão e pode ser feito através da mensuração de peso, altura de cernelha, perímetro torácico, perímetro de canela, altura à anca, largura de anca, largura de tórax, altura de tórax, altura do jarrete, altura do joelho, entre outros (MOTA et al, 2010;RAMOS et al, 2014;COSTA et al, 2015;TANGYUENYONG et al, 2017). Além dos hormônios, muitos outros fatores estão envolvidos no processo de desenvolvimento, precisando ser considerados.…”

“…Ainda, temperaturas frias podem levar ao desenvolvimento de animais menores. A suplementação com luz seria uma opção para tentar melhorar a taxa de desenvolvimento nesses casos (TANGYUENYONG et al, 2017). Porém, em estudo com Quarto-de-Milha no Brasil, animais nascidos no fim do inverno possuíam médias de tamanho superiores a animais nascidos em outras estações do ano (MOTA et al, 2010).…”