PRODUCTIVE PERFORMANCE, NUTRIENTS INTAKE AND DIGESTIBILITY OF GRAZING BEEF HEIFERS RECEIVING INCREASING LEVELS OF PROTEIN SUPLEMENT AT PERIPARTUM AND POSTPARTUM PERIODS

The low perfomance of pregnant beef heifers is usually due to low energy intake, protein and limited body reserves, in addition to the growth of the foetus in the last third of gestation, which increases their nutritional requirements, as well as the intensity of negative energy balance postpartum. Some studies have shown that different levels of protein supplementation have a positive effect on forage dry matter intake, digestibility, body weight (BW) and body conditions score (BCS). Thus, prepartum and postpartum protein supplementation for beef heifers, fed low-quality tropical forages may improve their forage intake and digestibility, nutrient concentrations in the rumen, crude protein (CP) intake, availability of dietary energy, BCS, metabolic status and animal performance. Therefore, the objective of this study was to evaluate the effect of increasing levels of peripartum and postpartum protein supplementation on nutrient intake, digestibility and productive performance of Nellore heifers on tropical pasture. The experiment was carried out at the Beef Cattle Section of Universidade Federal de Viçosa, Brazil, May to November, which is the dry and dry-rainy season transition. Twenty-eight Nellore heifers with initial average 5.4 ± 0.50 months of gestation, 3.1 ± 0.74 years old, 459.7 ± 6.8 kg of BW and 5.8 ± 0.10 of BCS, kept in four 7-ha paddocks formed by Brachiaria decumbens Stapf. provided with covered drinkers and troughs were used in a completely randomized design with 4 treatments and 7 replicates. The treatments consisted of increasing levels of protein supplement: 0.0 (Control = CON), 0.4 (LOW), 0.8 (MEDIUM) and 1.2 (HIGH) kg/animal.day of protein supplement containing 25% CP. All the animals received a mineral mixture ad libitum. The experiment lasted 180 days, and weight and BCS of heifers were measured at the start, at calving and the end of the experiment. Similarly, the calves were weighed at birth and the end of the experiment. The BCS was evaluated by 4 raters using the 1 to 9 scale as recommended by the NRC (1996). A 9-day digestibility trial was conducted beginning at day 40 of the experiment to evaluate the nutritional characteristics of the diet of the heifers. The supplementation level increased the intake of all evaluated nutrients, digestibility of organic matter, neutral detergent fibre corrected for ash and protein, as well as higher average daily gain prepartum and body weight of calves at birth (P <0.05). Protein supplement at the levels evaluated did not affect body condition score (P >0.05). It was concluded that the supply of up to 1.2 kg/day of protein supplement for grazing heifers optimizes forage intake and average daily gain before calving, and increases the body weight of calves at birth.