Evaluation of the effects of sire and dam calving group on age at first calving in Brahman heifers
Introduction
Within the beef industry there has been an emphasis for Bos taurus heifers to calve at two years of age [1]. Calving at two years of age has become the desired standard in the United States in Bos taurus cattle since it has been shown that heifers which calve at younger ages have on average higher annual life-time production compared to heifers that calve at older ages [2,3]. Also, in contrast to heifers initially calving at older ages, heifers that initially calve at younger ages tend to also calve earlier in the calving season throughout their productive life, giving them the ability to produce calves with greater weaning weights due to differences in calf age at weaning [4,5]. Therefore, this emphasis on age at first calving has caused the trait of early maturity to become important economically [6]. By having heifers calve at two years of age rather than three years producers can save at least a year on maintenance costs and the heifers will on average produce an extra 0.7 calves over their reproductive lifetime [7,8]. According to one study with Bos taurus cattle, earlier calving cows tended to be more efficient both economically and biologically by reducing maintenance costs due to a majority of their yearly cycle being in a productive mode [5]. Based on another study of Bos taurus cattle, having heifers calve at a younger age and earlier within the calving season would improve overall profitability due to the positive effect of calf age at weaning on weaning weight [9,10].
The age of a heifer at puberty is essential for determining the reproductive capability of the female and is controlled by a decline in estradiol negative feedback [11]. However, Bos indicus breeds of cattle, such as Brahman, reach puberty and calve at later ages than their Bos taurus breed counterparts, which makes it difficult for Brahman heifers to calve at two years of age [6]. For example, to calve as a two-year-old Brahman heifers must reach puberty by 438 days of age; however, Brahman heifers may need an additional 150 days to attain puberty [12]. Patterson et al. [13] determined that Bos taurus and Bos indicus crossbred heifers, must reach at least 65% of their expected mature body weight to attain puberty. We recently reported that Brahman heifers which calved at or before 800 days of age became pubertal at 66% of their mature body weight, whereas heifers that calved at later ages reached puberty at 75%–84.5% of their mature body weight [14].
Age at puberty and age at first calving in dairy and beef breeds may be affected by sire. Specifically, selection of Angus bulls for larger scrotal circumference as yearlings reduced the age at which their daughters reached puberty by 21.3 days [15]. Also in Angus beef cattle, a negative linear relationship was discovered between sire milk expected progeny difference (EPD) and age at first calving of their daughters, where an increase of 113 kg in milk EPD would decrease age at first calving by 21 days, equivalent to one estrous cycle length [16]. In Poland, heifers sired by elite Holstein-Friesian dairy bulls, which are bulls that have high genetic indexes for production, pedigree, fertility, and longevity, calved 15–25 days younger compared to heifers sired from proven and unproven AI bulls [17].
Brahman heifers have been documented to be capable of calving at two years of age [14]. Based on this information we hypothesized that Brahman heifers that reached puberty early would produce a greater proportion of female offspring that were capable of calving early. Therefore, a study was designed to evaluate the possible influence of calving group of the dam on age at first calving in Brahman heifers. The specific objectives of this study were to evaluate the effects of sire and dam calving groups on age at first calving in Brahman heifers.
Section snippets
Animals
All procedures were in compliance with the Guide for the Care and Use of Agricultural Animals in Research and Teaching and approved by the Texas A&M University Institutional Animal Care and Use Committee [18]. A total of 570 purebred Brahman heifers that were born between 2004 and 2017 at the Texas A&M AgriLife Research Center in Overton, TX were used in this study. The heifers were sired by 47 different Brahman bulls and produced by 360 Brahman cows. Heifers were not supplemented while nursing
Dam calving group effect
Dam calving group did not affect (P > 0.10) age at first calving of heifers (Fig. 1). All of the least square means for heifer age at first calving within each dam calving group fall within the intermediate range of the calving group criteria (intermediate = 900–1086 d). There was a year of birth effect (P < 0.01) on daughter age at first calving and calving group, whereas season of birth did not have a significant effect (P > 0.10) on daughter calving group or daughter age at first calving (
Discussion
This study evaluated the influence of dam calving group, sire calving group, dam calving group by sire calving group interaction, season of birth, and year of birth on age at first calving and calving group in Brahman heifers. There was no interaction detected between dam calving group and sire calving group. Season of birth did not significantly affect daughter age at first calving or calving group, whereas there was a significant year of birth effect. Overall, age at first calving and the
Conclusion
Based on the results of this study of purebred Brahman cattle the initial hypothesis that heifers which reach puberty early will produce greater proportions of daughters capable of calving early compared to heifers that reach puberty later must be rejected. Instead it can be concluded that the mean age at first calving of heifers born from sires belonging to the early calving group was decreased, while the proportions of heifers calving early increased if born from sires belonging to the early
CRediT authorship contribution statement
A.L. Earnhardt: Formal analysis, Data curation, Writing – original draft, analyzed the data, and wrote the manuscript. D.A. Neuendorff: Managed the cattle, assisted with data collection, reviewed results. C.R. Long: Writing – review & editing, Reviewed and interpreted the results, edited the manuscript. T.H. Welsh: Writing – review & editing, Reviewed and interpreted the results, wrote and edited the manuscript. R.D. Randel: Conceptualization, Writing – review & editing, designed the study and
Declaration of competing interest
The authors declare the absence of economic or other types of conflicts of interests.
Acknowledgements
This work was supported by Texas A&M AgriLife Research, Western Regional project TEX03212, Hatch project H-9022.
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