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Physiological performance and grazing behaviour of Senepol, Brahman and Holstein heifers in Puerto Rico A.I. Hernandez, D. Cianzio and T. Olson Objectives of the study were: To evaluate the physiological response of Brahman, Charbray and Senepol to the hot climate conditions of the island, and To study their grazing behavior as it relates to changes in diurnal temperatures. The study was conducted: Isabela Substation, north coast of Puerto Rico Months of July – November In three years, 1992, 93, and 94 Three breeds, Charbray, Brahman and Senepol 15-17 yearling heifers per breed Heifers grazed togehter in rotational grazing paddocks with Guinea grass as the predominant species and a rate of 1.3 acres/heifer Data was collected every 15 days, done from 10 am to 2 pm Variables recorded Animal – Live weight – Respiratory rhythm – Rectal temperature – Grazing behavior Environment – Temperature under the sun and under the shade, dry and black bulbs – Index temperature- humidity was calculated Rectal temperature and respiratory rhythm Breeds # Heifers Rectal tem. °C Resp./rhyth. Insp./min. Senepol 49 39.1¹ 53.8² Brahman 47 39.4² 39.5¹ Holstein 49 39.9³ 81.3³ Mean of rectal temperature - heifers by breed and year 38.4 38.6 38.8 39 39.2 39.4 39.6 39.8 40 1991 1992 1993 1994 Year Rectal temp °C Senepol Brahman Holstein Ambient and rectal temp in heifers Ambient temp °C No. of observation Rectal temperature (°C) Senepol Brahman Holstein 29 4 38.9 39.2 39.4 30 11 39.1 39.3 39.7 31 9 39.1 39.4 40.0 Ambient temp and respiratory rythm in heifers Ambient temp °C No. of observation Respiratory rhythm (insp./min.) Senepol Brahman Holstein 29 7 49.6 36.5 70.4 30 9 51.6 38.2 73.7 31 8 56.5 42.6 94.5 Liveweight changes in heifers by breed Heifer breed Initial weight Final weight Weight increase Daily gain ------------------------kg---------------------- Senepol 261 308¹ 47¹ 0.46¹ Brahman 223 280¹ 57¹ 0.58¹ Holstein 230 258² 28 0.28² Hourly grazing of heifers by breed 40 50 60 70 80 90 100 110 7 8 9 10 11 12 13 14 15 16 17 Hours % heifers grazing Senepol Brahman Holstein Hourly %´s of heifers under shade by breed -10 0 10 20 30 40 50 60 70 80 90 7 8 9 10 11 12 13 14 15 16 17 Hours % heifers under shade Senepol Brahman Holstein Effect of black bulb temperature and breed on % of grazing heifers 0 20 40 60 80 100 120 31 32 33 34 35 36 37 38 39 40 41 Black bulb temperature C % heifers grazing Senepol Brahman Holstein Conclusions The study supports the capacity of the Senepol breed to tolerate and perform well under the hot-humid climate conditions of northern Puerto Rico. The Senepol cattle appears as an interesting alternative to be considered as purebred or in crossbreeding systems to improve beef production in the tropics. Thank you all Muchas gracias Grazie mile