Browsing by Author "Velasquez, Alejandro"

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    In vitro protein breakdown by enzyme extracts of rumen origin: comparison with methods in situ and proteases of Streptomyces griseus
    (2010) Velasquez, Alejandro; Pichard, Gaston
    A. Velasquez, and G. Pichard. 2010. In vitro protein breakdown by enzyme extracts of rumen origin: comparison with methods in situ and proteases of Streptomyces griseus. Cien. Inv. Agr. 37(3): 57-70. Proteolytic activity of enzymatic extracts generated from rumen microorganisms cultivated in vitro was evaluated. The incubation of rumen fluid used different substrates to generate a higher enzyme concentration and promote a broad spectrum of hydrolytic activity. The composition of the substrates used in the cultivation of the fluid was enriched in protein, starch or cell wall. Enzyme preparations were evaluated by incubating in 30 mL of buffer 50 mM Tris-HCl (pH 6.5) at 39 degrees C during 48 hours, 100 mg of crude protein from feeds soybean meal, canola meal, sunflower meal, gluten feed, dehydrated alfalfa meal, berseem clover, oat forage and perennial ryegrass. Enzyme extracts from cultivated rumen fluid showed an average protein breakdown of 75.5%, in eight feed samples tested. This value was very close to that measured with the technique of proteases from Streptomyces griseus (74.6% CP), but significantly lower (P <= 0.05) than the one obtained by the in situ methodology (84.8% CP). The technique with extracted rumen enzymes showed higher level of proteolysis in the early hours of incubation (6 H) compared to the other techniques. These results suggest that the enzyme preparations of ruminal origin have the ability to predict degradability of feed proteins in the rumen, particularly in the first phase when most of proteins are hydrolyzed and become available for microbial utilization.
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    Physiological and behavioural response of two dairy cows' genotypes during summertime in the central region of Chile
    (2018) Arias, Rodrigo A.; Herrera, Camila; Larrain, Rafael; Gonzalez, Fernando; Mader, Terry L.; Velasquez, Alejandro
    Heat stress has been recognised as a serious problem in dairy farms. The study goal was to assess the effects of climatic conditions on physiological and behavioural responses of dairy cows in Central Chile. Data of tympanic temperature (TT), panting score, respiration rate (RR), and shade utilization of cows from two genotypes, Holstein (H) and Holstein x Montbeliarde (HM), were collected twice per day (AM/PM) during three periods of the summer season in Central Chile. Moreover, three thermal comfort indices: Comprehensive climate index (CCI), temperature humidity-index (THI), and adjusted THI were estimated using meteorological data. The hour of each day was classified as "Normal" or "Stressful" based on CCI threshold of 25 degrees C. Statistical analysis included ANOVA, repeated measures analysis and Chi square test (alpha=0.05). There was an interaction of genotype x CCI condition x period (P=0.0026) with the highest TT of both genotypes under a stressful condition within each period. In addition, interactions of genotype x hour (P<0.0001) and genotype x CCI condition (P<0.0002) were also observed. The HM cows showed greater TT than H cows in both CCI conditions. The RR was higher during the afternoon and a greater proportion of cows used shade at "Mild" and "Moderate" CCI categories (P<0.001). Both genotypes showed some degree of heat stress, but cool nights and shade seem to be enough to allow to cows' cope with the challenging diurnal conditions observed in the summer season. A study of these effects on milk production is necessary to confirm or discard the previous.