Energy and protein requirements for growth of Holstein × Gyr heifers

Abstract

SummaryThere is little information regarding the nutritional requirements for dairy heifers, leading the majority of nutrient requirement systems to consider dairy heifers to be similar to beef heifers. Therefore, we evaluated the muscle protein metabolism and physical and chemical body composition of growing Holstein 9 Gyr heifers and estimated the energy and protein requirements. We performed a comparative slaughter experiment with 20 Holstein 9 Gyr heifers at an initial body weight of 218 AE 36.5 kg and an average age of 12 AE 1.0 months. Four heifers were designated as the reference group, and the 16 remaining heifers were fed ad libitum. The 16 heifers were distributed using a completely randomized design in a 2 9 2 factorial arrangement with two roughages (corn silage or sugarcane) and two concentrate levels (30 or 50%) for 112 days. Greater (p < 0.05) values for fractional rates of muscle protein synthesis, degradation and accretion were observed for heifers that were fed 50% concentrate. The following equations were obtained to estimate the net energy for gain (NE g ) and net protein for gain (NP g ): NE g (Mcal/day) = 0.0685 9 EBW 0.75 9 EBWG 1.095and NP g (g/day) = 203.8 9 EBWG À 14.80 9 RE, respectively, in which EBW is the empty body weight, EBWG is the empty body weight gain and RE is the retained energy. We concluded that increased rates of protein turnover are achieved when a greater quality diet is provided. In the future, these results can be used to calculate the nutritional requirements for growth of Holstein 9 Gyr heifers after equation validation rather than using the recommendations provided by other systems, which use values developed from beef heifers, to determine the nutritional requirements of dairy cattle.

Energy requirements for pregnant dairy cows

“…Nonetheless, we recommend a k g of 41.9% for Holstein × Gyr adult cows. We also suggest, based on our results and previous literature [35,36,37] that the k g reported in NRC [6] should be reviewed, because it might overestimate k g for transition cows. The efficiency of utilization of body store reserves for milk production in early lactation is markedly higher than the efficiency of utilizing dietary metabolizable energy for tissue energy gain [32,38].…”

“…Nonetheless, Oss et al [ 34 ] and Silva et al [ 35 ] evaluating energy requirements of Holstein × Gyr bulls and heifers, reported a k g of 30.5% (average body weight of 235 kg) and 40.8% (average body weight of 218 ± 36.5 kg), respectively. Therefore, our k g was closer to values reported for growing animals, which have greater rates of energy deposited as protein than as fat.…”

Energy requirements of Holstein, Gyr, and Holstein × Gyr crossbred heifers using the respirometry technique

“…Silvestre et al 10.3389/fanim.2022.919515 chambers. We suspect that the estimation method plays a crucial role in those numbers, and the reason for that difference may be linked to how the support metabolism (H i E v ; Silva et al, 2018) is accounted for in each methodology. The H i E v increases energy demand when the animal changes from a maintenance state to a growing or production state.…”

“…respirometry, as described above. Silva et al (Verstegen et al, 1987) used the comparative slaughter technique to estimate their animals' requirements, which reflected in a lower k g to account for the support metabolism (Silva et al, 2018).…”