Talk:Hoof Tape
This page, and references LaShell et al [2], Parish et al[3], and Pruit et al [5] are focused on relationships between hoof circumference (or birth wt projected from hoof circumference) and scale-measured birth weight. Shouldn't we be looking at relationships between hoof circumference and calving ease? What are phenotypic and genetic correlations between hoof circumference and calving ease - is hoof circumference a decent indicator of calving ease?
Toser et al. developed a model to predict calving difficulty, first predicting birth weight from hoof circumference, then predicting dystocia from birth weight and pelvic width. They show hoof circumference increased with calving difficulty score, but standard deviations around the mean circumference for each score overlap. Presumably Ko et al [1] show something similar but I cannot a copy of that paper.
Pruit et al reported a "poor" correlation between hoof circumference and birth wt (R^2 = 0.46) that is near the ballpark of other estimates (R^2 ~ 0.57 to 0.78). Their mean circumference is larger (18.9 cm) than means reported in other work (around 17.5 cm), and the tape they used is apparently different than the widely used Calfscale tape. Pruit et al also allude to research showing birth wt is a better predictor of calving difficulty than other body measurements. Citations to that research are not provided.
Colburn et al. (1997) found a 0.52 phenotypic correlation between hoof circumference and calving difficulty, slightly weaker than their 0.57 correlation between birth wt and calving difficulty. The correlations are a bit curious - mean birth wt increased with calving difficulty and means were significantly different for each category. Mean hoof size bounced around - hard pulls had the numerically smallest feet, not statistically different from easier pulls or unassisted calves. C-sections and easy pulls had the largest feet, different than unassisted. Sires ranked the same by birth wt EPD and calf foot size (lightest EPD/smallest feet ... heaviest EPD/largest feet). The high birth wt EPD/big foot bull also had the most calving difficulty - incidence, mean score, c-section rate. These results suggest hoof circumference might be a useful indicator, but genetic correlation estimates among calving ease, hoof circumference and birth wt are needed to incorporate hoof circumference into calving ease EPD. For this, hoof circumference should be reported as hoof circumference (in cm), not a projected birth weight corresponding to the circumference measurement.
Birth weights projected from hoof circumference may be useful to adjust weaning wt to 205 d. While the tape "weights" might be off (light calves overestimated, heavy calves underestimated), those weights may be closer to actual birth weight than an assumed standard birth weight used in 205 d adjustment when birth weight is missing.
