Recent advances in estimating protein and energy requirements of ruminants

Abstract

Considerable efforts have been made in gathering scientific data and developing feeding systems for ruminant animals in the past 50 years. Future endeavours should target the assessment, interpretation and integration of the accumulated knowledge to develop nutrition models in a holistic and pragmatic manner. We highlight some of the areas that need improvement. A fixed metabolisable-to-digestible energy ratio is an oversimplification and does not represent the diversity of existing feedstock, but, at the same time, we must ensure the internal consistency and dependency of the energy system in models. For grazing animals, although data exist to compute energy expenditure associated with walking in different terrains, nutrition models must incorporate the main factors that initiate and control grazing. New equations have been developed to predict microbial crude protein (MCP) production, but efforts must be made to account for the diversity of the rumen microbiome. There is large and unexplained variation in the efficiency of MCP synthesis (9.81–16.3 g MCP/100 g of fermentable organic matter). Given the uncertainties in the determination of MCP, current estimates of metabolisable protein required for maintenance are biased. The use of empirical equations to predict MCP, which, in turn, is used to estimate metabolisable protein intake, is risky because it establishes a dependency between these estimates and creates a specificity that is not appropriate for mechanistic systems. Despite the existence of data and knowledge about the partitioning of retained energy into fat and protein, the prediction of retained protein remains unsatisfactory, and is even less accurate when reported data on the efficiency of use of amino acids are employed in the predictive equations. The integrative approach to develop empirical mechanistic nutrition models has introduced interconnected submodels, which can destabilise the predictability of the model if changed independently.

Relationships of retained energy and retained protein that influence the determination of cattle requirements of energy and protein using the California Net Energy System

“…In contrast, the correlation between observed and predicted RP was much lower when using observed RE to predict RP ( r = 0.679; Figure 1B ) than when using predicted RE to predict RP ( r = 0.939). These disturbing findings were initially reported by Tedeschi and Fox (2018) and discussed in a subsequent review of advances in estimating protein and energy requirement of ruminants ( Tedeschi et al, 2017 ). These authors also highlighted additional areas of research that need clarifications.…”

“…Failures in data collection and analysis at the experimental level might partially explain the inadequacy in predicting RP and RF ( Tedeschi et al, 2017 ). Most of the experiments used in the evaluation of RE ( Figure 1A ) and RP ( Figure 1B ) used the comparative slaughter technique in which the amounts of RE (Mcal) and RP (kilograms) are determined by difference (final minus initial amounts over a feeding period of at least 30 d), assuming a predetermined initial body composition of the animals slaughtered at the end of the feeding period, and RE and RP are computed by difference.…”

“…The greater correlation between observed and predicted RP when using predicted RE ( r = 0.939) to predict RP vs. using observed RE ( r = 0.679) is, by itself, a concern because it indicates a clear interdependency between predicted RP and predicted RE that is needed to predict RP with a higher precision. These internal offsetting errors result in an apparent overall adequacy of the CNES to predict net energy (NE) and net protein (NP) requirements, thereby potentially destabilizing the predictability of nutrition models when submodels are changed independently ( Tedeschi et al, 2017 ). The second concern was previously raised by Tedeschi (2001) and recently discussed by Tedeschi et al (2002) , Williams and Jenkins (2003b) , and Tedeschi et al (2004) .…”

Does the Effect of Replacing Cottonseed Meal with Dried Distiller’s Grains on Nellore Bulls Finishing Phase Vary between Pasture and Feedlot?

“…During the finishing phase, the animal leaves puberty and there is an increase in the adipose tissue deposition and a decrease in the muscle tissue deposition [ 39 ]. These changes result in an increased energy requirement for gain, since the deposition of adipose tissue is less efficient per unit of mass than that of muscle tissue [ 46 ]. During the finishing phase, the proportion of fat deposited in the carcass is directly related to energy intake [ 39 ].…”

How nutrition influences the distribution and abundance of chital deer (Axis axis) in northern Queensland

“…Although the conversion is influenced by the quality of forage that animals receive (Galyean et al 2016), this was not a factor in this study which compared different ruminants accessing the same forage. For cattle the conversion factor of 0.82 is reliable in the absence of predictions of energy loss through urine and methane (Tedeschi et al 2017) and ranges in deer species from 0.83 to 0.88 (Dryden 2011).…”