Abstract
The objective of this study was to evaluate the effect of high or low energy intake on carcass composition and expression of hypothalamic genes related to the onset of puberty. Twenty-four prepubertal Nellore heifers, 18-20- months-old, with 275.3±18.0 kg body weight (BW), and 4.9±0.2 (1-9 scale) body condition score (BCS) were randomly assigned to two treatments: high-energy diet (HE) and low-energy diet (LE). Heifers were housed in two collective pens and fed diets formulated to promote average daily gain of 0.4 (LE) or 1.2 kg (HE) BW/day. Eight heifers from each treatment were slaughtered after the first corpus luteum detection - considered as age of puberty. The 9-10-11th rib section was taken and prepared for carcass composition analyses. Samples from hypothalamus were collected, frozen in liquid nitrogen, and stored at −80 °C. Specific primers for targets (NPY, NPY1R, NPY4R, SOCS3, OXT, ARRB1, and IGFPB2) and control (RPL19 and RN18S1) genes were designed for real-time PCR and then the relative quantification of target gene expression was performed. High-energy diets increased body condition score, cold carcass weight, and Longissimus lumborum muscle area and decreased age at slaughter. High-energy diets decreased the expression of NPY1R and ARRB1 at 4.4-fold and 1.5-fold, respectively. In conclusion, the hastening of puberty with high energy intake is related with greater body fatness and lesser hypothalamic expression of NPY1 receptor and of β-arrestin1, suggesting a less sensitive hypothalamus to the negative effects of NPY signaling.
Highlights
The onset of puberty is characterized by the first ovulation, preceded by a gradual increase in luteinizing hormone (LH) pulse frequency, inducing ovulation of a dominant follicle (Rawlings at al., 2003)
Changes in energy intake can alter secretion of neuropeptide Y (NPY), which acts as an inhibitor of gonadotropin-releasing hormone (GnRH)
Diets were formulated according to NRC (2000) to promote an average daily gain (ADG) of 0.4 kg/d (LE) or 1.2 kg/d (HE) and both diets were offered at ad libitum intake (Table 1)
Summary
The onset of puberty is characterized by the first ovulation, preceded by a gradual increase in luteinizing hormone (LH) pulse frequency, inducing ovulation of a dominant follicle (Rawlings at al., 2003). Day et al (1986) reported that restriction of dietary energy intake prevents the prepubertal rise in secretion of LH and delays the initiation of puberty. Changes in energy intake can alter secretion of neuropeptide Y (NPY), which acts as an inhibitor of gonadotropin-releasing hormone (GnRH). Besides alteration on NPY, acute and chronic changes on the animal energetic status can alter expression of other genes in the hypothalamus-pituitary-gonadal axis (Allen et al, 2012). The identification of the key mediators signaling the nutritional status of the animal to the hypothalamus at the time of puberty is important for the development of nutritional, pharmacological, and breeding strategies aiming to reduce the age of first calving in the Brazilian herd
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