Weight, height, and relative-reliability indicators as a management tool for reducing age at first breeding and calving of dairy heifers

In Québec first calving occurs on average at 27mo, whereas the target is 23 to 24.5mo to maximize herd profitability. The aim of this study was to quantify current and future heifer growth using individual heifer random regressions and to generate indicators (such as heifer weight and height at 15 and 24mo, average daily gain before and after 15mo, age at which optimal weight for breeding is attained, i.e., 55% of mature weight, and reliability of the 15- and 24-mo weight predictions) that could be used as a practical on-farm tool. Dairy heifer weight estimated by heart girth circumference and height measured at the withers (from 0 to 27mo) were obtained from the Valacta database (DHI agency, Ste-Anne-de-Bellevue, QC, Canada) from 1995 to 2012. Indicators were calculated based on the current situation of Holstein (HO), Ayrshire (AY), Jersey (JE), and Brown Swiss (BS) heifer growth in Québec. Heifers with less than 2 records were excluded from the analysis. Mature weights were determined by weight at calving of cows from third or greater lactation for a given breed and were 710kg for HO, 625kg for AY, 470kg for JE, and 670kg for BS. Estimated weights at 15 and 24mo were 425 and 627, 334 and 482, 297 and 429, and 379 and 560kg for HO, AY, JE, and BS, respectively, which are heavy enough for breeding and calving, except for AY. Relative reliabilities of the 15- and 24-mo weight predictions were on average 89 and 60%, respectively, based on measurements up to 15mo. For HO, AY, JE, and BS, wither heights at 15 and 24mo were 134 and 143, 125 and 134, 122 and 131, and 130 and 140cm, respectively. Age at optimal breeding weight was 13.6, 15.5, 12.6, and 14.5mo for HO, AY, JE, and BS, respectively. These data suggest that it is realistic to expect a first calving at 24mo for HO, JE, and BS. A growth delay was observed for AY; average daily gain was 655 and 538 g/d before and after 15mo, respectively. The average daily gain before and after 15mo was 848 and 747 g/d for HO, 603 and 486 g/d for JE, and 775 and 662 g/d for BS, respectively. These indicators could be calculated for an individual heifer and on a herd-level basis and used on farm as a management tool for reducing age at first breeding and at first calving.