the effect of nutritional levelon on advancingage at puberty in nelore heifers

Abstract

The objective of this study was to verify the effect of nutritional level on advancing age at Renata puberty in Nelore heifers. Thirty-one animals at 6 months of age were randomly assigned in two groups: GI, or control, with 15 heifers that received a basal diet, and GII, or supplemented, with 16 heifers that received a diet with higher energy and crude protein levels. The development of the animals was accompanied by weighing them at 21-day intervals to verify the daily weight gain from 6 months to puberty. The diets were readapted when necessary. The reproductive status was monitored by ultrasound every two days; and by progesterone concentrations from blood samples drawn twice a week. The ovulation was determined when progesterone concentrations were higher than 1 ng/mL in three consecutive samples, and by ultrasound images of corpus luteum; and oestrous behavior in some animals. The GII group manifested puberty at 16.33 ±0.89 months of age and GI at 20.58 ±1.83 months of age (p less 0.05). The mean weight at puberty was 302.33 ±21.31Kg for GI and 326.19 ±27.78Kg for GII. The daily weight gain was 0.647 ±0.08Kg for GII and 0.447 ±0.03Kg for GI (p < 0 .05). Progesterone levels at puberty were 2.7801 ±0.27 ng/mL for GI and 2.5747 ±0.26 ng/mL to GII. Only 13% of all heifers manifested oestrous behavior. The nutritional supplementation decreased the age of puberty onset in GII and both groups manifested puberty earlier than heifers feeding only on pasture in Subtropical conditions. It is possible to have an earlier puberty onset in Nelore heifers through nutritional supplementation, without negative effects on their reproductive physiology.