Effect of nutritional management on somatotrophic reproductive axis maturation and its relationship with early puberty onset

• Grant number: 08/04363-2
• Support Opportunities: Scholarships abroad - Research
• Start date: February 01, 2009
• End date: May 31, 2009
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding
• Principal Investigator: Alexandre Vaz Pires
• Grantee: Alexandre Vaz Pires
• Host Investigator: Michael L Day
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
• Institution abroad: Ohio State University, Columbus, United States

Abstract

Age at puberty directly influences the performance of the animal in future years. There has been considerable research on nutritional influences on puberty in heifers, but a majority of this has focused on the period after traditional weaning (after 7 months of age). Onset of puberty is gated by an activation of the neuroendocrine system that leads the onset of ovarian activity. Several reports indicate that the nutritional status of the animal plays an important role during the onset of puberty. However, the exact metabolic mechanisms that occur near the puberty are still unknown. Somatotropic axis has been involved in many different physiological processes; and might be the link between the metabolic status of the animals and the activation of the reproductive system. This system is composed by many interactions between different organs and hormones that regulate physiological events such as growth, fat deposition, mammary development and also during post partum period to resume the ovarian activity due the relationships between the energetic balance. Reproductive processes are regulated by the interaction of different organs and systems in the body, such as neuroendocrine, digestive, metabolic and reproductive systems. The impact of nutrition beginning at 3-4 months of age on these interactions, and the resulting onset of reproductive cycles is the focus of this project. We have shown that feeding a high-concentrate diet beginning at 3 to 4 months of age will induce precocious puberty in heifers. This experiment will test both qualitative and quantitative effects of diet from 3 to 10 months of age on reproductive and metabolic characteristics, with the long term aim of identifying the metabolic signals that activate the reproductive axis to cause puberty in heifers.Thirty six animals will be weaned at 79 ± 11.4 days of age and 125.32 ± 21.39 kg. Heifers will be fed with a receiving diet for three weeks. After the receiving period, animals will be transitional onto the experimental diet for seven days. Heifers will be divided randomly in three groups of twelve animals each one, High starch diet (HIGH-S), low starch diet (LOW-S) and control diet (CONT). Target gain for HIGHS and LOWS is 1.50 kg/d, and for the CONT diet is 0.75 kg/d, with diets fed approximately 2.5% of BW (as fed). However, an increase of this percentage will be adjusted to achieve the gains expected and relative body weight between treatments. Age at puberty will be defined as 7 days before the date of collection of the first plasma sample that contained >2 ng/ml progesterone or 7d before the date of collection of the first of 2 consecutive blood samples that each have >1 ng/ml progesterone additionally precocity will be considered as an animal reaching puberty before 300 days of age. Blood samples (10 ml) will be collected by jugular venipuncture once a week to assess progesterone and IGF-1, concentrations in the blood; beginning at 170 days of average age for all of the groups until animals reached puberty. To assess concentrations of LH and GH, serial blood samples will be obtained monthly from approximately 200 d of age until 300 days of age. Serial blood samples will be obtained every 15 minutes for 12 h. This sampling frequency and duration are necessary to detect the pulsatile secretion pattern of these hypophyseal hormones such as LH (Day et al., 1984, 1986, 1987). At the same time, in order to assess the physiological response of heifers to the diets, blood samples will be collected for Insulin and Glucose before feeding (T0), and every hour after feeding (T1, T2, T3, T4) and finally, one sample after two hours from T4 (T5). (AU)