You've probably heard that. Or a heavy milking cow may get this done even if sires are not genetically larger. Or you might not wean until 9 or 10 months, risking loss of cow body condition and poor rebreeding. Here the picture is different. This should be kept in mind when designing genetic programs.
Conventional wisdom holds that heavy muscling adversely affects reproduction.
A recent analysis of 2055 heifers from Limousin association records was reported by Colorado and Michigan researchers. Higher yearling weight was associated with earlier puberty, particularly in leanest heifers. There was a tendency for heifers with higher muscling scores to reach puberty earlier. It appears that heavier muscled heifers can satisfactorily attain puberty if body condition is adequate, at least within Limousin. However, in comparing breed-types, most research has shown heavier muscled, leaner types to be somewhat later in puberty and lower in conception rates.