CALVING TRAITS 2.0 – Reevaluating your Dairy’s Strategy for Calving Traits

Marj Faust

  • Decades of industry wide advancements in management and genetics have driven significant improvements for calving traits.
  • U.S. Calving Trait evaluation results were rescaled to better align with their application and use for on farm genetic selection and decision making.
  • Strategies aimed at ensuring continued improvements in calving pens should be reevaluated and tailored for each dairy’s on-farm scenario.

How We Got to Now

During the past 30+ years, dairies and the wider industry have incorporated a number of practices to improve improve results in calving pens, thereby increasing the number of live calves and reducing undesirable impacts on dams’ subsequent performance and health.  These practices have been wide ranging, including using calving ease sires when breeding heifers, specialized training for staff, dedicated calving pens, and managing body condition

 





 

during late gestation.  Developments in management and genetics have paid off, and today incidence rates of difficult calvings is a fraction of rates experienced in the past.  As summarized by Cole and co-workers (2020), by August 2020 fewer than 2.5% of Holstein heifers and ~3.0% of Brown Swiss heifers required considerable assistance (force) for bull calves.  The dramatic progress made over time in reducing the percent of difficult births to Holstein heifers is illustrated in Figure 1.

Figure 1. Difficult births to Holstein heifers. From: Cole and co-workers.  2020.

After industry wide examination of the April 2020 genetic evaluations, it became evident that the numerical scales used to represent Calving Ease and Stillbirth traits for Holsteins and Brown Swiss had not been updated to keep pace with on farm performance.  In response, research was conducted over the past few months and resulted in the development of more up to date numerical scales for these traits.  The August 2020 Genetic Evaluations release includes these rescaled evaluation results for Sire Calving Ease (SCE), Daughter Calving Ease (DCE), Sire Stillbirth (SSB), and Daughter Stillbirth (DSB) for Holsteins and Brown Swiss.  Dairies can expect that the rescaled results for calving related traits better align with their application and use for on farm management and decision making.  Today, this means that dairies can benefit from reevaluating how these trait data are used for genetic selection and decision making.

 





 

 Interpreting August 2020 Calving Related Trait Evaluations

Beginning in 2005, U.S. Calving Trait evaluations were centered on genetic averages in target Holstein populations of 8% for SCE, DCE, SSB, and DSB.  With the rescaling, August 2020 trait averages for both Holstein and Brown Swiss are considerably lower and better reflect on farm performances seen by dairies.  Other noticeable effects of the rescaling are the shrinking of differences between animals and that of the overall spread.  For example, in April 2020 for SCE, generally Holstein sires ranged from 4% to 12%.  However, after rescaling for August 2020, SCE for these same Holstein sires ranged from 1% to 4%.  Brown Swiss and Holstein trait base averages beginning with the August 2020 evaluations are in Table 1.

Are Animal Rankings Impacted by Rescaling

Rescaling is a straightforward process for adjusting animal trait values to the average and variability for the new scale.  Rescaling does not add new information to genetic computation for individual animals, and as a result, does not lead to changes in rankings for sires and dams in evaluations.  On the other hand, rankings of animals for the genetic selection indexes, Net Merit $ (NM$), Cheese Merit $ (CM$), Fluid Merit $ (FM$), Grazing Merit $ (GM$), and Holstein Association USA’s TPI® may change slightly as a result of adjustments made to the index formulas to account for the effects of rescaling the calving traits.

Tailoring the Strategy Using Rescaled Calving Trait Results

As a result of the industry wide progress for Calving Traits, it is acutely necessary to reevaluate and update how these traits are used by dairies for genetic selection and decision making going forward.  To aid dairies experiencing a range of on farm scenarios for calving related traits, Table 2 outlines tailored strategy options including genetics and management actions.  These actions include a genetics toolkit that is somewhat expanded over more traditional toolkits by including the trait, Gestation Length (GL).  As a reminder, GL trait values represent Predicted Transmitting Abilities (PTAs) for the number of additional/fewer days that a sire’s mate will carry the calf.  While dairies recognize from experience that excessively long gestation lengths are undesirable, researchers have reported that overly long and overly short gestation lengths are undesirable.  For most breeds, sire PTA GL range from -5 (fewer) days to +4 (more) days of gestation.

Summary

Beginning with the August 2020 U.S. Genetic Evaluations, Calving Trait results have been rescaled to better align with their application and use for on farm genetic selection and decision making.  Dairies can benefit greatly by reevaluating on farm calving related performance and use of Calving Ease, Stillbirth, and even Gestation Length traits, and designing a strategy tailored to the on farm scenario.

Sources

.2020Cole, J. B. and co-workers.  U.S. Council on Dairy Cattle Breeding.  https://www.uscdcb.com/wp-content/uploads/2020/06/NAAB-CDCB-HAUSA-Calving-Traits-June-2020-August-2020-Calving-Trait-Adjustment-06_2020.pdf

Cole, J. B. and co-workers.  2020.  U.S. Council on Dairy Cattle Breeding.  https://www.uscdcb.com/cdcb-changes-to-evaluation-system-august-2020/

Eaglen, S. A. E. and J. B. Cole.  2020.  U.S. Council on Dairy Cattle Breeding.  https://www.uscdcb.com/wp-content/uploads/2020/05/Microsoft-Word-NAAB-CDCB-What-is-going-on-with-calving-ease-05_2020-NAAB-CDCB-What-is-going-on-with-calving-ease-05_2020.pdf

Lawlor, T. L.  2020.  Adjusting the Calving Trait Component of the TPI® Formula.  Holstein Association USA.  July.

Meyer, C. L. and co-workers.  2001.  J. Dairy Sci.  84:1246.

Norman, H. D.  2017.  CDCB Connection.  July.  https://queries.uscdcb.com/News/gestation_length_07_06_2017.htm

VanRaden, P. M.  2020.  U.S. Council on Dairy Cattle Breeding.  https://www.uscdcb.com/cdcb-changes-to-evaluation-system-august-2020/ 

Editor’s note:Marj Faust has extensive experience in dairy genetics,  both in academia and the AI industry. Based near Madison, Wis., she may be contacted at: +1 608.219.1834 and
marj.faust@gmail.com

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