Correlations between body weight and scrotal circumference with age at puberty in zebu steers raised under tropical conditions — ASN Events
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  3. Correlations between body weight and scrotal circumference with age at puberty in zebu steers raised under tropical conditions

Correlations between body weight and scrotal circumference with age at puberty in zebu steers raised under tropical conditions (#406)

Jorge Chacon 1 , Alejandra Arias 1 , Karla Barrantes 1 , Bernardo Vargas 1
  1. Research Program on Applied Animal Andrology, Vet School, Universidad Nacional, Heredia, Costa Rica

Body weight (BW) and scrotal circumference (SC) were measured from 609 zebus (Brahman; n=486 and Nellore; n=123) aiming to determine their correlations with age at puberty. Bulls were measured monthly from weaning (7 months) to 12 months (period 1) (P1) and then bimonthly until 2 yrs of age (period 2) (P2). All bulls were raised in tropical Costa Rica, grass feed and supplemented with minerals. Puberty attainment was defined as the age when an ejaculate contained ≥50 millions spermatozoa with ≥10% motility. All males were electro-ejaculated starting at 16 months and then every 60 days if necessary until they reached puberty.

No differences were observed between breeds for BW, SC and age at puberty. Consequently, variables under study were analyzed as a pooled data set. Mean age, BW and SC at puberty were 18.57±2.67 months, 394.08±68.34 kg and 26.65±4.0 cm, respectively). Monthly BW gain in P1 was 30.75% lower than P2 (13.10 kg vs. 18.87 kg respectively). The same pattern was observed for the monthly growth in SC which was 30.82% lower during P1 (0.80 cm vs. 1.17 cm respectively). This difference could be the result of the considerable stress suffered by the calf during the early post weaning period.

Interestingly, the correlation between BW and SC in P1 was higher than that observed in P2 (r=0.64 and 0.42 respectively, P<0.001). Even though the correlations between BW and age at puberty in P1 and P2 were similar (r= -0.29 and -0.24 respectively, P<0.001), the correlation between SC and age at puberty in P1 was 4 times that observed in P2 (r= -0.49 vs. -0.12 respectively, P<0.001). This fact would be linked to the onset of spermatogenesis in Bos indicus cattle, which has been determined based on histological analysis of the testis parenchyma to start around 9 to 11 months of age3 .

Similarly as it has been repeatedly reported for Bos taurus2, this results underline that scrotal circumference is the most reliable and highest correlated variable with age at puberty in Bos indicus breeds. Sadly, selection in this genotype by this characteristic has been ignored in tropical areas1. Attention should be kept during early post weaning period on those factors affecting scrotal growth at this stage.

  1. Chacón J (2009) Manejo reproductivo y diagnostico andrológico del toro en ganaderías extensivas del tropico centroamericano [Breeding management and andrological diagnosis in bulls extensively reared in tropical Central América] Memories XXI meeting of Latin American Association of Animal Production (ALPA) 17 14-29
  2. Coulter G and Foote R (1979) Bovine testicular measurements as indicators of reproductive performance and their relationship to productive traits in cattle Theriogenology 11 297-311
  3. Igboeli G and Rakha A (1981) Puberty and related phenomena in Angoni (Short horn zebu) bulls Journal of Animal Science 33 647-653