# Effect of Day Length on Growth and Gonadal Development in Meishan Male Pigs

## TL;DR

This study shows that longer day lengths improve growth and testicular development in Meishan male pigs, possibly through a specific melatonin receptor.

## Contribution

The study reveals a novel link between day length, melatonin receptor MT2, and steroid synthesis in male pig gonadal development.

## Key findings

- Longer day lengths increased body height, chest circumference, and testicular size in Meishan male pigs.
- Longer day lengths elevated fecal testosterone and cortisol levels and altered steroidogenesis proteins like MT2, CYP19, and SF1.
- The effect of day length on growth and gonadal development may be mediated through melatonin receptor MT2.

## Abstract

Day length is a critical environmental factor for gonadal development in animals. However, related studies on male pigs are limited. The present study investigated the effects of different day lengths on behavior changes, growth parameters, testicular size, testosterone secretion, steroidogenesis proteins, and melatonin receptors in Meishan male pigs. The results indicated that a long day length (LDL, 14 h light/10 h dark, 14L/10D) could increase the lying time, decrease the exploring time, and increase the body height, chest circumference, testicular length, testicular weight, crude protein digestibility, and fecal testosterone and cortisol contents compared to a short day length (SDL, 10L/14D) in Meishan male pigs, accompanied by the changes in sex hormone synthesis proteins and melatonin receptor 1b (MT2), but with no change in melatonin receptor 1a (MT1). This suggests that the effect of day length on growth and gonadal development in male pigs may be conducted via MT2 and influence steroid synthesis and secretion in the testis, and proper day length should be provided in male pig breeding.

Day length is a critical environmental factor for regulating animal growth and development. This study aimed to investigate the effects of different day lengths on the developmental changes of growth parameters, testicular sizes, testosterone secretion in Meishan male pigs, and steroidogenesis proteins and melatonin receptors. Fourteen Meishan male pigs (10 weeks (wks) of age) with the same parity, paired in litter and body weight (BW), were evenly allocated into a short-day-length group (SDL, 10 light/14 dark) and long-day-length group (LDL, 14 light/10 dark). After 12 wks of the experiment, the LDL-treated boars had more lying time and less exploring time. The LDL treatment led to significant increases in body height, chest circumference, testicular length, testicular weight, crude protein digestibility, and fecal testosterone at the 10th and 12th wks of the experiment, and cortisol at the 10th wk, compared to the SDL treatment, with no differences in the final BW, testicular width, and epididymis weight. Furthermore, the LDL treatment significantly increased the protein levels of melatonin receptor 1b (MT2), aromatase (CYP19), and steroidogenic factor 1 (SF1) in the testis, with no differences in the protein levels of melatonin receptor 1a (MT1), steroidogenic acute regulatory (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), and cholesterol side-chain cleavage enzyme (P450scc). The present study suggests that day length has an effect on the growth and gonadal development in male pigs maybe via MT2 and influences steroid synthesis and secretion in the testis. Therefore, proper day length should be considered in male pig breeding.