Robustness of suckling cows at herd level is associated with cows’ productive longevity
Résumé
Reproductive failure is one of the main reasons for involuntary culling in beef cattle herds. Consequently, individual
cows’ productive longevity (PL, 1st calving to culling interval), a proxy of their robustness, is highly determined by their
ability to conceive and recalve within the time window defined by the farmer. One indicator to measure this ability is
the calving-to-calving interval (CCI). At the herd level, robustness can be defined as the ability to maintain performance
stable across time. The objective was to verify whether the herds’ robustness was associated to cows’ robustness. We
used time-series from 89 herds (min. size of 20 cows) of Charolais suckling cows with individual dates of birth, calving
and culling for at least 10 years (max. 36 years). Primiparous and multiparous cows that did not manage to complete
pregnancy were attributed a theoretical CCI calculated as the max. herd CCI at a given year plus 1.5 times inter-quartile
range. For each herd, robustness was assessed by the standard error of mean PL (SE_PL) and mean CCI (SE_CCI)
across time. Links between herd and cows’ robustnesses were studied via the correlations between SE_PL and the
average PL of cows present in a farm across the studied period and between SE_CCI and the average CCI. Between
herds time averaged PL and CCI were negatively correlated (-0.28, P=0.008). Correlations between log(SE_CCI) and
log(SE_PL) with PL and CCI were negative and positive (-0.18, P=0.09; 0.35, P=0.0009), respectively. PL stability
(log(SE_PL)) was positively associated with CCI stability (log(SE_CCI)) as well (0.40, P=0.0001). When herds
were grouped based on these four variables, two clusters (CL1 and CL2) emerged that presented distinct properties as
follows: CL1 had significantly higher PL than CL2 (PLCL1=2,213±35 d; PLCL2=2,004±47 d; P=0.0005), associated
with significantly lower SE_CCI and higher SE_PL (P<0.0001), respectively. On the other hand, CL2 presented
significantly higher CCI than CL1 (CCICL1=389±1 d; CCICL2=401±1 d; P<0.0001) and presented significantly higher
and shorter SE_CCI (P<0.0001), respectively. In conclusion, robustness traits observed at the individual scale seem
to have been transmitted to the herd scale.