Plasma progesterone concentrations as puberty criteria for Brahman-crossbred heifers
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abstract
Plasma progesterone concentrations greater than 1.0ng/mL are often used as puberty criterion for heifers. However, prepubertal Brahman-crossbred heifers may experience progesterone concentrations greater than 1.0ng/mL as result of their excitable temperament. The objective of this experiment was to evaluate three different puberty criteria (1.0, 1.5, and 2.0ng/mL of plasma progesterone) on the proportion of heifers incorrectly classified as pubertal (false positives). Blood samples were collected, immediately after transrectal ovarian ultrasonography, from 37 Braford and 43 Brahman Angus heifers on days 0 and 10, 40 and 50, 80 and 90, and 120 and 130 of the experiment. Across breeds, heifer mean body weight and age were, respectively, 253kg and 269days at the beginning (day 0), and 326kg and 399days at the end of the experimental period (day 130). Puberty was confirmed once a corpus luteum and plasma progesterone concentrations greater than 1.5ng/mL were concurrently detected in one or both evaluations performed on a 10-day interval. Prepubertal heifers were classified as false positive if, at least once during the experimental period, their plasma progesterone concentrations were greater than the adopted puberty criterion in two samples collected 10days apart but no luteal tissue was concurrently detected. Approximately 55% of the Brahman Angus and 86% of the Braford heifers experienced progesterone concentrations above 1.0ng/mL before reaching puberty (breed effect; P < 0.01). Increasing puberty criterion from 1.0 to 1.5ng/mL decreased (P = 0.03) the proportion of false positive Brahman Angus heifers (25.0 versus 8.3%, respectively, SEM = 5.5), whereas increasing puberty criterion from 1.0 to 1.5ng/mL and from 1.5 to 2.0ng/mL decreased (P = 0.01 and 0.05, respectively) the proportion of false positive Braford heifers (57.1, 31.4, and 11.4%, respectively; SEM = 7.4). In conclusion, plasma progesterone concentrations greater than 1.0ng/mL is a common occurrence among prepubertal Brahman-crossbred heifers. Further, 1.5 and 2.0ng/mL of progesterone may be more appropriate values for puberty assessment in Brahman Angus and Braford heifers, respectively, particularly if blood samples are collected infrequently. 2008 Elsevier B.V. All rights reserved.
