Suárez-Rodríguez, José

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    Efecto del sistema de alimentación sobre parámetros productivos y fisiológicos de corderos criados en estrés por calor
    (2019-05-15) Suárez-Rodríguez, José; Rodríguez-Carías, Abner A.; College of Agricultural Sciences; Fernández Van Cleve, John; Pagán Riestra, Suzika; Department of Animal Science; Cortés Figueroa, José
    In tropical regions such as Puerto Rico, sheep are exposed to high temperatures and high relative humidity levels (THI > 72). In addition, the producers feed their sheep mostly by grazing systems using crossbred animals and naturalized pastures (NP) without any agronomic management. It is important to characterize and document extensive and confinement feeding systems and the use of crossbred and purebred sheep so the farmers can use as point of reference for future management decisions. The objective of this study was to determine the physiological parameters (rectal temperature = RT, respiratory rate = RR, heart rate = HR) and production parameters (dry matter intake = DMI, water intake = WI, average daily gain = ADG and feed conversion = FC) of crossbred and Katahdin lambs reared in rotational grazing and in confinement under heat stress conditions. To characterize the extensive system, 9 crossbred lambs (average initial weight = 19.4 kg) were used and fed in a rotational grazing system (pastures with an average area = 610 m2) for 70 days with periods of occupation and rest for 7 and 21 days respectively. In the paddocks, Paspalum virgatum, Sporobolus indicus, Paspalum millegrana and Rhynchospora ciliata NP predominated. One of the pastures had access to a protein bank of Leucaena leucocephala (210 m2). The lambs had daily access to the grazing area during 4 to 6 hours, ad libitum grass hay and water, daily supplement of 100 g of commercial concentrate and a nutritional block. For the confined system, 6 lambs of the Katahdin breed (average initial weight = 27.3 kg) were used, which were fed with total mixed rations (TMR) for 28 days with a diet containing 30% grass hay, 15.4% soybean meal, 54.6% corn grain and mineral block. The diet contained 15.8% CP and 72.4% TDN and was formulated for an ADG of 200 g. The offered and rejected feed was quantified every day (4% BW/DMB) to determine the DMI and the volume of water offered and rejected to determine the WI. To validate the stress conditions, the maximum environmental temperature and relative humidity were monitored to calculate the THI and the RT, HR and RR of the 15 lambs were determined. The lambs were weighed every 7 days. In both experiments, the THI oscillated between 78 and 80. The lambs were not under heat stress conditions (THI x̅ = 79) during both studies. The averages of HR and RT for the extensive system were 118.0 beats per minute and 38.6° C, while the averages for the confinement system were 108.6 beats per minute and 39.4° C, respectively. The average RR (53.6 and 62.6 breaths per minute, in grazing and in confinement, respectively) was greater than the normal value considered for thermal comfort. Respiratory rate was the main mechanism used by lambs to dissipate heat. The heart rate also showed slightly higher values than those reported for animals in the comfort zone. However, the rectal temperature values were constant. As expected, crossbred lambs fed under extensive conditions had a low ADG (55.6g). Nevertheless, Katahdin lambs fed in confinement with TMR had a DMI of 935.4g/day (3.14% BW/DMB), a WI of 3.5L/day, a FC of 4.74 and an ADG of 226.2g. In conclusion, raising crossbred sheep in rotational grazing of NP without any type of agronomic management results in ADG that could not be considered viable in traditional production systems. The introduction of pure breeds and feeding them in confined systems with a TMR results in a pre-determined ADG (200 g/day) and is an alternative that can be evaluated economically for its practical implementation.