Minerals are extremely important in animal nutrition. However, there is lack of information regarding mineral requirements for pre-weaned dairy calves raised under tropical conditions. Here we take a closer look at what Holstein and Gyr crossbred calves need in terms of macrominerals.
Minerals play essential functions in the body (i.e., structural, physiological, catalytic, regulatory, and immune response), although they are found in small concentrations compared with other nutrients such as fat and protein. Therefore, a deficiency in minerals can compromise the productivity and reproductive performance of livestock. However, there is not a lot of information available regarding the mineral requirements for pre-weaned dairy calves raised under tropical conditions. In practice, diet formulation is hence based on mineral requirements reported by international councils, where NRC (2001) is the most commonly used publication for formulating diets for growing dairy calves. The NRC (2001) suggests fixed recommendations of mineral concentrations in the diet of pre-weaned dairy calves regardless of bodyweight, genetic makeup, or animal performance. The only nutrient requirements developed for cattle living under tropical conditions are those of BR-CORTE (2016). However, this system only estimates the nutrients for beef breeds and estimates the net mineral requirements for growing Zebu calves up to 180 days of age and not for calves below 90 kg.
Diet formulation, based on assumptions and old studies from the 1950s, 70s and 80s, is not recommended and never leads to the best possible diet. In addition, dairy cattle have undergone intense genetic selection over the last decade, which has drastically improved animal performance and possibly altered 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 volumes greater than eight litres per day or ad libitum milk supply. This lack of knowledge has been the incentive for Brazilian researchers to delve deeper into this issue. The researchers hypothesised that macromineral requirements of Holstein calves are different from those of Holstein × Gyr crossbred calves raised under the same conditions. In addition, the research team hypothesised that the estimates of dietary mineral requirements from NRC (2001) and BR-CORTE (2016) are not suitable for dairy calves. Therefore, a meta-analysis was developed to estimate the macromineral requirements of Ca, P, K, Mg, and Na for maintenance and gain of Holstein and crossbred Holstein × Gyr dairy calves raised under tropical conditions.
In the study, data from five studies developed at the Universidade Federal de Viçosa (Viçosa, MG, Brazil) were used. For all studies, the comparative slaughter technique was used to estimate 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 (animals with a Holstein pedigree lower than 87.5%). 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. 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, Africa and South Asia. Brazil exports Gyr genetics to several countries 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), retained mineral (RM; g/d), and mineral body content. In addition, breed data (Holstein or Holstein × Gyr), initial empty bodyweight (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 calculation model was used to convert EBW to BW and thus calculate requirements of the minerals in milligrams per kilogramme of BW per day when necessary, in order to compare studies that present requirements as milligrammes per kilogramme of BW per day.
The calculations made by the researchers resulted in the net requirements for maintenance for Ca, P, K, Mg, and Na and dietary 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 deposited 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 climate 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 requirements 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 expressed 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 Holstein × Gyr) in pre-weaned dairy calves up to 100 kg of BW.
In summary, breed did not affect dietary requirements of microminerals for pre-weaned dairy calves. The possible existence of a climatic effect on the mineral requirements is evident; 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 tropical conditions, published in the April edition of Journal of Dairy Science.