Neuendorff, Don A.

Randel, R. D.

Tatman, S. R.

Wilson, T. W.

English

Texas A&M University

Influence of Season of Birth on Reproductive Development of Brahman Bulls

Texas A&amp;M Repository

    PUBLICATIONS 2002 INFLUENCE OF SEASON OF BIRTH ON REPRODUCTIVE DEVELOPMENTOF BRAHMAN BULLSS. R. Tatman, D. A. Neuendorff, T. W. Wilson, and R. D. RandelBackground: Research has shown that Brahman cattle exhibit decreased reproductive potentialduring the winter months. Brahman females have a shorter duration of estrus and increased incidence ofanestrus, while the Brahman male has decreased semen quality, sperm concentration, and decreasedtesticular size during the winter. Due to these seasonal differences in reproduction, this trial evaluated theeffect of season of birth on the growth and reproductive development of Brahman bulls. Eight fall born(born between August and October) and 10 spring born (born between March and May) purebredBrahman bulls, from a common breeding herd, were studied. Bulls were maintained together and fed acom/soybean meal (3: I) ration supplemented with 200 mg lasalocidlhdlday fed at 1.5% of body weight.Bulls had free access to water, Coastal bermudagrass hay, and a salt/mineral supplement. Measurementsregarding growth (body weight), body condition score, reproduction (scrotal circumference), and spermconcentration were taken at every two weeks. Measurements began prior to reaching 21 cm scrotalcircumference. Upon attainment of 21 cm scrotal circumference, bulls were electroejaculated for semenanalysis. Measurements continued through puberty (classified as an ejaculate with ~ 50 X 106 sperm with~ 10% motility), concluding with the attainment of sexual maturity (classified as an ejaculate with ~ 500X 106 sperm with ~ 50% motility).Research Findings: No differences were found for body weight, body condition score, or scrotalcircumference between fall- and spring-born born bulls at first sperm or puberty. However, age at sexualmaturity was delayed in fall-born bulls when compared to spring-born bulls. Due to their increased age atsexual maturity, fall-born bulls tended to be heavier, have higher body condition scores, and larger scrotalcircumference than their spring-born counterparts. Evaluation of the interval from puberty to sexualmaturity revealed that fall-born bulls required approximately 39 additional days to reach sexual maturitycompared to spring-born Brahman bulls, although, daily interval gain for all measured traits during thisperiod was similar between the fall and spring born bulls.59Table 1 Growth traits of spring/fall bulls at different stages of developmentSuperscripts that differ wlthm column: P<.07; P<.05.First sperm Puberty Sexual maturityFall Spring Fall Spring Fall SpringAge (days) 4lHl3a 38l±12ll 455±l6a 427±15a 527±l3a 453±12cBW (Ib) 792±34a 763±31 a 865±44a 867±39a I034±40a 920±37cBCS 5.9±.l a 5.5±O.l b 6.7±.6a 5.7±.6a 6.3±.1 a 5.7±.lcSC (em) 25.4±.8a 24.8±.7a 28.0±.9a 28.0±.8a 32.8±.9a 30.2±.9ball ."Table 2 Interval change in traits from puberty to sexual maturitySuperscripts that differ wlthm column: P<.07; P<.05.Interval gain Daily interval gainFall Spring Fall SpringAge (days) 72 ±l2a 3Hll DBW (Ib) 170±24a 66±23b 2.4±.3 2.0±.3SC (em) 4.8±.9a 2.4±.8b .O7±.O2 .O6±.O2dU' de,Application. Fall born Brahman bulls undergo a delay in their sexual development during theinterval from puberty to sexual maturity. This delay did not occur in spring born bulls as they reachedthis period during the warmer months with longer photoperiods, whereas fall-born bulls reached thisinterval during the colder months which have shorter photoperiods. Although the fall born bulls appearedto grow and develop normally from a phenotypic standpoint (daily gain for all measured traits was similarbetween the groups), reproductive development was delayed. This could affect both producers andbreeders who plan on using/marketing young Brahman bulls in their breeding programs.60

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Influence of Season of Birth on Reproductive Development of Brahman Bulls

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Texas A&M University

Texas A&M Repository

Influence of Season of Birth on Reproductive Development of Brahman Bulls

Abstract

Similar works

Full text

Available Versions

Texas A&M University

Texas A&amp;M Repository

Texas A&M Repository