Grouping crossbred Holstein x Gyr heifers according to different feed efficiency indexes and its effects on energy and nitrogen partitioning, blood metabolic variables and gas exchanges

Abstract

The objectives of this study were: i) to classify animals into groups of high and low feed efficiency (FE) using three FE indexes (Residual feed intake (RFI), Residual weight gain (RG) and Feed conversion efficiency (FCE)), and ii) to evaluate whether crossbreed Holstein x Gyr heifers divergent for FE indexes exhibit differences in nutrient intake and digestibility, energy partitioning, heat production, methane emissions, nitrogen partitioning and blood parameters. Thirty-five heifers were housed in a tie-stall, received ad libitum TMR (75:25, corn silage: concentrate) and were ranked and classified into high (HE) or low efficiency (LE) for RFI, RG and FCE. The number of animals for each HE group were 13 (< 0.5 standard deviation (SD) for RFI, 11 for RG and 11 for FCE (> 0.5 SD) and for the LE were 10 (> 0.5 SD) for RFI, 11 for RG and 12 for FCE (< 0.5 SD). Gas exchanges (O 2 consumption, CO 2 and CH 4 production) in open-circuit respiratory chambers and whole tract digestibility trial was performed. A completely randomized experimental design was used and the data were analyzed by ANOVA and correlation study. High efficiency animals for RFI produced less CO 2, consumed less O 2 and had lower heat production (HP). Methane production was positively correlated with RFI. High efficiency RG had higher O 2 consumption and CO 2 production in relation to LE-RG. High efficiency FCE had greater NFC digestibility, higher positive energy balance (EB) and excreted (11.4 g/d) less nitrogen in urine. High efficiency RG and FCE groups emitted less CH 4 per kg of weight gain than LE animals. Animals HE for RFI and FCE had lower β-hydroxybutyrate and higher glucose concentrations, respectively. The differences in intake, digestibility, energy and nitrogen partition, CH 4 emission, blood metabolic variables and heat production between the HE and LE groups varied according to the efficiency indexes adopted. The HP (kcal/d/BW 0.75) was lower for HE animals for RFI and FCE indexes.

Evaluation of Ingestive Behavior, Ruminal and Blood Parameters, Performance, and Thermography as a Phenotypic Divergence Markers of Residual Feed Intake in Rearing Dairy Heifers

“…No differences were observed in glucose, insulin, and IGF-1 concentrations, and the glucose:insulin ratio between HE and LE groups for RFI (Table 3), was corroborated in research that found no difference in glucose concentration between HE-RFI and LE-RFI [29]. However, a moderate correlation was observed between glucose and DMI (0.33; p = 0.0017) and between glucose and ADG (0.35; p = 0.0009) (Table 4).…”

Common and diet-specific metabolic pathways underlying residual feed intake in fattening Charolais yearling bulls

“…However, milk N secretion is easier to measure than N accretion in growing animals. In growing cattle, most studies have failed to prove this link through N balance measurements 24 , 25 . However, results from our team using a novel isotopic approach applied to this same experimental setup (n = 48) suggested that more efficient animals in terms of RFI also show higher N use efficiency compared to less efficient RFI animals 26 .…”

Residual Feed Intake as an Efficiency Metric for Pre-Weaning Dairy Calves: What Do We Know?

“…The lack of correlation between rumen fermentation parameters and RFI in the pre-weaning phase is probably related to insufficient rumen function in milk-fed animals, as neonatal calves have an underdeveloped rumen until close to weaning [ 16 ], and differences in rumen fermentation products have been reported for RFI-divergent animals in later life [ 39 , 40 ]. In fact, β-hydroxybutyrate levels have been pointed out as a potential marker for the identification of high-efficiency heifers post-weaning [ 40 ]. It is possible that gene expression in rumen epithelium [ 41 ] and epithelium-associated bacteria [ 42 ], rather than fermentation, might be involved in improved efficiency in pre-weaning calves, as it has been indicated for older cattle.…”