Residual feed intake in dairy ewes: an evidence of intraflock variability

Abstract

This study examined the intraflock variability of feed efficiency in dairy ewes, through monitoring residual feed intakes (RFI). Primiparous lactating ewes (n=43; 57.7{+/-}0.91 kg body weight [BW] at lambing), representative of a French Lacaune dairy flock, were allocated in an equilibrated 2 x 2 factorial design experiment, lasting for 63 days during mid-lactation and combining 2 litter sizes (singletons, SING or twins, TWIN) and 2 daily milking frequencies (once, ONE or twice, TWO). Ewes were individually fed a diet based on ryegrass silage, local hay and supplements. Individual DMI was recorded daily and further used to evaluate (and compare) differences in RFI between ewes at 35, 42, 49, 56, 63, 70, 77, 84, 91 and 98 days relative to lambing (DIM). Total (BW) and metabolic (BW0.75) body weight, BCS, milk yield and plasma NEFA were monitored weekly. Differences in DMI were mainly due to the lactation stage and litter size and were 11% higher in ewes with TWIN compared to SING. This was positively correlated to milk yield and consistent with differences in RFI which varied due to litter size and to the milking frequency x lactation stage interaction. Ewes that lambed SING showed higher feed efficiency ({square}0.13{+/-}0.020 vs. 0.08{+/-}0.015 kg DM/ewe/d of RFI in SING vs. TWIN, respectively), whereas there was no differences in BW or BCS. Milking frequency did not affect DMI but milk yields were higher in TWO, which was related to a higher feed efficiency in this group (0.04{+/-}0.017 vs. {square}0.10{+/-}0.018 kg DM/ewe/d of RFI in ONE vs. TWO, respectively). Average RFI was affected (P <0.0001) by the ewe, thus allowing a ranking among individuals to be established. High (n=22) or low (n=21) feed efficiency ewes averaged {square}0.17{+/-}0.09 or 0.18{+/-}0.09 kg DM/d RFI, respectively. Estimates of RFI were not correlated to the individual milk production potential. Even if no differences in BW, BW0.75 or BCS were detected, high efficiency ewes mobilised almost two-fold their body reserves when compared to the low efficiency group. The observed intraflock variability in feed efficiency of this dairy ewes flock was affected by litter size and milking frequency but also by evident differences between individuals physiologies.