Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The objective of this study was to determine the physiological, endocrine and productive response in lactating dairy cows under several series of artificial cooling at the beginning of the summer (June to July, 2011). Fourteen multiparous Holstein cows were assigned in one of two treatments: Cooling (C) before milking (0700 and 1700 h) and additional cooling (AC) each 2 h (from 0700 to 1700h) in the holding pen of the milking parlor. Milk yield (MY), and serum levels of prolactin (PRL) and IGF1 were measured. Rectal temperature and respiratory rate were registered and included as physiological markers of heat stress. Ambient temperature and relative humidity were also collected and used to calculate temperature-humidity index (THI). Both markers of heat stress showed a significant interaction (P<0.001) between treatment and time/week, which were lower in AC treatment (-3.8 breaths per minute and -0.2 °C) during wk 6 and 7. Serum levels of PRL were higher under additional cooling (AC: 35.1 vs C: 29.4 ng/ml; P=0.004), while  IGF1 serum levels showed variation only through the sampling weeks (P=0.014). The MY increased (P<0.05) in AC only during wk 6 (+3.1 kg/d) and 7 (+3.1 kg/d). It was concluded that additional cooling at the beginning of the summer reduced heat stress in dairy cows allowing a better productive performance at the end of the study because such effect relied on the variable time/week.

Macroeconomic policies adopted by Mexico caused modifications in the productive structure of national and local livestock sector. The aim of the research was to determine the growth of livestock activities and regional specialization in eight regions of Mexico (Northwest NW, North NR, Northeast NE, Central West CW, Central East CE, South SU, East E and Yucatán Península PE) and assess its economic dynamics from 1994 to 2013. Regional analysis techniques such as location quotient and modified differential-structural method were used. The results indicated that in 1994, 2003 and 2013, the regions NW, NE, CE, SU and E specialized in beef, and the last region in conjunction with CE in chicken also. NR region specialized in milk; and NW, CW and PE regions was pork. NE, CW and CE regions also specialized in chicken egg. From 1994 to 2003, the NR, SO, CE and NW regions were dynamics, because the growth of the regional livestock sector (19.94, 11.59, 7.04 and 6.59 %) was higher than the national growth (4.08 %); the rest of the lagged behind regions. From 2003 to 2013, the regional livestock sector dynamics changed. The CW, EA and PE lagging regions in the previous period, became dynamic in this period and which were dynamic (NW, NR, CE and SO), they behaved behind. The NE region remained behind during the two periods. It concludes that the livestock sector showed a different dynamics and specialization between regions in Mexico.