Milk metabolites differ with feed efficiency during early lactation but not during feed restriction
Abstract
The objective was to study associations among indicators of feed efficiency and selected milk metabolites during early
lactation, and in response to experimental feed restriction (FR) for the discovery of non-invasive proxies. 28 cows
divergent in phenotypic residual feed intake (RFI; positive or negative) were selected, each RFI group composed of 14
Holstein and 14 Montbéliarde cows. Energy balance (EB) and conversion efficiency (ECE; NEL secreted/intake) were
calculated. Early lactation RFI (RFIearlylact) was measured during the first 10 wks of lactation. Starting at 87±9 DIM,
cows underwent four 4-day periods of FR to meet 50% of individual energy requirements (FR1-FR4). Mid-lactation
RFI (RFImidlact) was measured during 5 wks following FR4, as described (doi.org/10.1016/j.anscip.2022.07.181).
Milk isocitrate, glucose, glucose-6-phosphate, malate, glutamate and free amino groups (NH2-groups) were measured
on wk 1, 2, 3, 4, 6 and 8, and daily during FR1 only. Data was analysed using mixed models with repeated measures,
and spearman correlations. RFIearlylact ranged from -0.44 to -2.39 for negative RFIearlylact (i.e. more efficient),
and from 0.42 to 2.34 kg DMI/d for positive RFIearlylact groups. Early lactation ECE was higher, whereas EB,
plasma glucose, milk glucose, NH2-groups and glutamate were lower for the negative RFIearlylact group. Average
early lactation milk glutamate and NH2-groups from wk1 to 8 were correlated with RFIearlylact (r= 0.44 and 0.41),
but not with RFImidlact. No milk metabolite RFI group differences were observed during FR1. Weekly EB was
positively correlated with milk glucose and malate (r=0.30 and 0.32), and negatively correlated with milk isocitrate
and NH2-groups (r=-0.25 and -0.17), and the inverse correlations were observed for ECE. RFIearlylact associations
with plasma glucose, milk glucose, NH2-groups and glutamate during early lactation may reflect in prioritization
of nutrients towards milk secretion in more efficient cows. Conversely, these effects may be due to the lower EB
experienced by cows with negative RFIearlylact.
Domains
Animal production studiesOrigin | Files produced by the author(s) |
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