has drastically improved animal performance and possibly al- tered nutrient requirements. Moreover, feeding management of dairy calves has changed drastically from a traditional management of 10% of body weight in litres of milk to vol- umes greater than eight litres per day or ad libitum milk supply. This lack of knowledge has been the incentive for Bra- zilian researchers to delve deeper into this issue. The re- searchers hypothesised that macromineral requirements of Holstein calves are different from those of Holstein×Gyr crossbred calves raised under the same conditions. In addi- tion, the research team hypothesised that the estimates of di- etary mineral requirements from NRC (2001) and BR-CORTE (2016) are not suitable for dairy calves. Therefore, a me- ta-analysis was developed to estimate the macromineral re- quirements of Ca, P, K, Mg, and Na for maintenance and gain of Holstein and crossbred Holstein×Gyr dairy calves raised under tropical conditions.
Calculating the mineral requirements In the study, data from five studies developed at the Universi- dade Federal de Viçosa (Viçosa, MG, Brazil) were used. For all studies, the comparative slaughter technique was used to es- timate body composition of each animal. Briefly, a group of
animals (baseline group) were slaughtered at the beginning of the experiment to estimate initial EBW and initial mineral composition of the animals that remained in the studies (n = 210). The group of 210 calves was separated into two breeds: purebred Holstein calves (animals with a Holstein pedigree higher than 87.5%) and Holstein×Gyr crossbred calves (ani- mals with a Holstein pedigree lower than 87.5%). The Gyr breed is a type of zebu cattle originating in South Asia. An in- tense genetic programme was developed for this breed in late 80s with a focus on milk production. The Holstein breed will bring the productivity of a Holstein cow and the Gyr will bring the adaptability of a Gyr cow, but with a good potential for milk production. That is the reason the Holstein x Gyr crosses are spreading all over central and South America, Afri- ca and South Asia. Brazil exports Gyr genetics to several coun- tries in the world because of this intense genetic programme. In each study, individual information of each mineral (Ca, P, K, Mg, and Na) was collected for mineral intake (MI; g/d), re- tained mineral (RM; g/d), and mineral body content. In addi- tion, breed data (Holstein or Holstein×Gyr), initial empty bod- yweight (EBW; kg), final EBW (kg), empty body gain (EBG; kg/d), and average daily gain (ADG (kg/d)) were collected and assessed from individual animal. For all requirements, a
▶DAIRY GLOBAL | Volume 6, No. 2, 2019
The only nutri- ent require- ments devel- oped for cattle living under tropical condi- tions are those of BR-CORTE (2016).
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