Intake, performance, and feeding behavior of Holstein and Holstein x Gyr heifers grazing intensive managed tropical grasses during the rainy season

Holstein × Gyr and Holstein are the primary dairy breed used in tropical systems, but when rearing under pasture, feed intake, behavior, and performance might differ between them. This study aimed to evaluate the voluntary intake, nutrient digestibility, performance, and ingestive behavior of Holstein and Holstein × Gyr (½ Holstein × ½ Gyr) heifers managed in an intermittent grazing system of Guinea grass ( Panicum maximum Jacq. cv. Mombaça). The experiment was conducted during the summer season throughout four periods of 21 d. Two 8-heifers (four Holstein and four Holstein × Gyr) groups, averaging 258.6 ± 24.8 kg and 157.1 ± 24.99 kg body weight, were used. Each group grazed a separate set of 16 paddocks, and all heifers received a concentrate supplement daily. Heifers were weighed at the beginning and end of the experiment. Fecal, forage and concentrate samples were evaluated for their dry matter (DM), crude protein (CP), crude fat, ash, neutral detergent fiber (NDF), and indigestible NDF. Feeding behavior was evaluated through 24 h of live observation for 48 h of each experimental period. Grazing, ruminating, resting, and intake of concentrate times were recorded, and rumination criteria, bout criteria, mealtime, meal frequency, and meal duration were estimated. There was no difference in dry matter intake (DMI). The Holstein × Gyr heifers had greater NDF intake and average daily gain (ADG), and feed efficiency tended to show greater CP and NDF digestibilities. The forage DMI of Holstein × Gyr was 11.70% greater than the Holstein heifers. Holstein grazed less than Holstein × Gyr heifers in the afternoon. Ruminating time was 18.43% lower for Holstein than Holstein × Gyr heifers, and rumination criteria were greater for Holstein heifers. Holstein heifers presented more prolonged rumination bouts and resting time than Holstein × Gyr heifers. Holstein × Gyr can ingest and ruminate greater amounts of fibrous material. Holstein heifers select lower fiber material, and they need to spend more time ruminating small portions of feed. Overall, we do not recommend using young Holstein heifers in tropical pasture conditions because their ADG is low because of its lower adaptability to fibrous feed and heat stress. However, this management condition is appropriate for Holstein × Gyr heifers and results in an adequate performance. Implications This study was the first to evaluate the performance and behavior of young Holstein × Gyr and Holsteins heifers in tropical grazing systems under the same nutritional and environmental conditions. Crossbreed and purebred heifers interacted differently with the pasture; however, without noticeable variation in grazing time. As expected, Holstein heifers’ performance in the tropical pasture was impaired by a reduction in intake and grazing time. The greater performance observed for Holstein × Gyr heifers was assigned to greater forage intake, rumination time, and efficient forage nutrient use, showing animal’s adaptability to management conditions. ### Competing Interest Statement The authors have declared no competing interest.