PHOTO: CRV LAGOA
PHOTO: CRV LAGOA
Holstein x Gyr crosses are spreading all over central and south America, Africa and South Asia.
calculation model was used to convert EBW to BW and thus calculate requirements of the minerals in milligrams per kilo- gramme of BW per day when necessary, in order to compare studies that present requirements as milligrammes per kilogramme of BW per day.
No effect of breed The calculations made by the researchers resulted in the net requirements for maintenance for Ca, P, K, Mg, and Na and di- etary requirements (g/d) of Ca, P, K, Mg, and Na based on the estimates proposed by this study base (Table 1). For most of the minerals the researchers propose levels that are lower than the levels in BR-CORTE and NRC. For Sodium (Na) the newly proposed levels are a bit higher. The effect of breed was not observed on net requirements for maintenance and gain or on the predicted retention coefficient (RC). The RC is the percentage of the mineral intake that is actually deposit- ed in the animal’s body. Dietary mineral requirements were considered similar for both breeds. Similarly, a breed effect was not observed on BW, ADG, MI, RM, and final body mineral content. The effect of breed might not have been observed because the study used similar diets, management, and cli- mate conditions and the same methodology for estimating MI and RM and for mineral analysis. The researchers suspect that these effects are more likely to affect macromineral re- quirements compared with breed effects. However, BR-CORTE (2016) reported differences in mineral requirements for gain of different beef cattle breeds with an average BW of 315 kg. It is likely that mineral requirement differences might be ex- pressed in other phases of gain but not in pre-weaned dairy calves. Therefore, it is consistent to recommend the estimates obtained in this study for both breeds (Holstein and Hol- stein×Gyr) in pre-weaned dairy calves up to 100 kg of BW.
22 ▶DAIRY GLOBAL | Volume 6, No. 2, 2019
Conclusion In summary, breed did not affect dietary requirements of mi- crominerals for pre-weaned dairy calves. The possible exist- ence of a climatic effect on the mineral requirements is evi- dent; however, it is not known what physiological factors are involved in metabolic and requirement changes. Thus, due to the absence of information regarding mineral requirements for pre-weaned dairy calves, this study is a major advance in this field. However, large differences were observed among the proposed recommendations for pre-weaned dairy calves compared with those of BR-CORTE (2016) and NRC (2001), suggesting that further studies on mineral requirements for pre-weaned calves are still necessary to validate the observed estimates and verify long-term effects.
This article is a summary of the original paper: Determination of macromineral requirements for pre-weaned dairy calves in trop- ical conditions, published in the April edition of Journal of Dairy Science.
The Gyr breed is a type of zebu cattle originating in South Asia. An intense genetic programme was developed for this breed in late 80s with a focus on milk production.
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