Abstract

PACHECO, Francisco; DEPABLOS, Luis; MARTINEZ, Gonzalo  and  VARGAS, Daniel. Non Genetic and Breed Group Factors Affecting Birth Weight in a Beef Cattle System Production. Rev. Fac. Cienc. Vet. [online]. 2013, vol.54, n.1, pp.35-46. ISSN 0258-6576.

To evaluate the effect of non-genetic factors and of breed group on birth weight (BW), 5136 records of calves born in a dry tropical forest were analyzed. The data was analyzed using an additive linear model by the restricted maximum verisimilitude method, that included the fixed effects of: year of birth (YB; 2001,..., 2007); month of birth (MB; January, February, October, November, December); age of the mother at calving (AM; 3.., 11 years or more); sex (S; female - male); breed group of the calf (BG1: Crossbred Bos taurus of the breeds Angus, Braunvieh, Carora, Holstein, Simmental, Romosinuano, Senepol; BG2: mainly Bos indicus of the breeds Brahman, Nelore, Guzerat and Gyr). The YB, MB, AM and S affected (P<0.05) the BW. The effect of BG was not significant. All interactions were studied, including in the final model only the significant ones (P<0.05) such as YB*MB, YB*AM, YB*BG, MB*BG, S*BG. The average BW was 32.1±0.20 kg (mean± standard error) considered normal for a suitable survival of both the calf and cow. The variables that most affected BW were YB (there were difference of 5.35 kg; 17.8 % between extreme years), S (males were 0.64 kg; 2 % heavier) and AM (the major difference was seen in cows of six and eleven years or more with 1.93 kg; 5.9 %). As time elapsed, heavier animals were born, which prompted a necessary revision of these values that could be due to failure at the time of registration of BW or  to genetic changes in the herd. The results showed genotype by environment interactions (YB and MB by BG).

Keywords : Birth weight; environmental factors; animal genetics; Bos taurus; Bos indicus.

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