Abstract
ABSTRACT The transition period is often a great challenge for dairy cows and mineral imbalances are frequent. With the aim to better understand the mineral profile of F1 Holstein x Gyr dairy cows and their performances under the different conditions of summer and winter, we collected blood samples to measure calcium, magnesium and phosphorus. Samplings were performed during summer and winter, on 15 and 13 pluriparous F1 Holstein x Gyr dairy cows, respectively. Blood sampling started 4 weeks prior to the expected calving date until 30 days postpartum. The mean concentrations of all three minerals had a different pattern during the transition period in each season, representing the interaction time x season. Calcium concentration was lower in winter and more animals suffered from subclinical hypocalcemia (100%) then in summer (38.46%). Magnesium concentration was also lower in winter and 46.67% of animals had hypomagnesemia, contributing for the higher hypocalcemia frequency observed in the same season. A high proportion of animals had hyperphosphatemia what can represent an environmental problem and more attention should be given to it. The high frequency of animals with subclinical hypocalcemia is alarming once that can lead to greater consequences.
Highlights
Crossing specialized Bos taurus breeds with Bos indicus has been practiced for more than 70 years in the tropical areas
Regarding the differences between seasons serum calcium, concentration was higher after calving in summer when compared to winter, while magnesium concentration was always higher in summer
Season has a great impact on mineral metabolism and winter surprisingly represented the most challenging season with lower concentrations of calcium and magnesium, and greater frequency of hypocalcemia and hypomagnesemia
Summary
Crossing specialized Bos taurus breeds with Bos indicus has been practiced for more than 70 years in the tropical areas. Dairy production in Brazil is mainly based on grazing systems, but, in most parts of the country, supplementation with other source of roughage and concentrate is often necessary during the dry period. This variation in feed supply due to climate implies in two distinct managements and have a great influence on the performance of animals (Moreira et al, 2015). F1 Bos taurus x Bos indicus dairy cows are becoming more popular because of their increased production in the last few years, due to genetic selection, combined with high heterosis and longevity (Madalena, 1998; Madalena and Junqueira, 2004). The higher production levels currently achieved by the crossbreed cows can lead to an increase in the occurrence of metabolic alterations (Fleischer et al, 2001)
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