Bull prolificacy in multi-sire herds (updated Feb 2/23)

Application of DNA paternity tests to evaluate bull prolificacy in Multi-Sire Cattle Herds and the Differences in their Offspring

Performance

Lead Scientist – Dr. Obioha Durunna Duration – 2019 to 2023

Background

Herd bulls have significant impacts on beef productivity and profitability. Multiple bulls can be used to increase reproductive rates, especially when artificial insemination is not practical due to cost or infrastructure limitations. Beef producers implementing natural mating schemes prefer bulls with the genetic potential for production, desirable carcass traits, and improved reproductive efficiencies. Bull prolificacy under multi-sire breeding groups is required to ensure the efficient use of feed and other farm resources. Because it is difficult to predict the number of calves each bull in a multi-bull herd will sire, identifying the calves sired by each bull can be achieved through DNA paternity testing

DNA paternity testing allows for potential sires to be linked to potential calves using commercial genetic marker panels The information on bull prolificacy enables owners to make informed culling and purchasing decisions based on their performances, especially on the bulls that did not meet expectations These sire-progeny matches also support accurate pedigree information and record-keeping that enhance selection, breeding, and management decisions.

Commercial herds in Alberta typically run multiple bulls with their cows and replacementheifers. Knowing the average prolificacy of bulls can help producers understand their bulls’ current and future contributionsto productivity, profitability andsustainability. This information will also create helpful industry benchmarks that will guide producers in decision-making.

Objectives

This project demonstrated how commercial beef producers who typically operate multi-sire breeding programs can:

• use a handy tool (e.g., Q-Link) to collect tissue/DNA used in determining sire-progeny matches

• implementor improve record-keeping

• track offspring data to make informed breedingdecisions.

This project aims to equip producers with practical information andmethodsthat will demonstrate the use of paternity testing tools to assess sire prolificacy in multi-sire breeding pastures

Materials and Methods

DNA extracted from ear tissues was used in paternity analysis via a commercial panel of approximately 96 single nucleotide polymorphisms (SNPs). The calves were matched to bulls over 4 consecutive years (2019 to 2022) in six commercial herds across Alberta (VC, OS, CF, KF, DIF and DEF) Figure A shows the distribution of the farms The study evaluated 2,265 calves, potentially from 69 bulls and 2,109 cows, across six (6) sites in Alberta. Approximately 187 calves did not have dam records.

Bull prolificacy was determined by the proportion of calves matched to each bull within each breeding group. The differences in body and growth performance of calves were analyzed with linear mixed models

Results and Discussion

Using the Q-Link tools (QGI tags and tagger/applicator), the calves were matched to potential bulls (Table 1). Table 1 also shows the number of classes of cattle evaluated within each herd. The calves without dam records were likely omitted during processing by the owners. It is also likely that some of the calves were abandoned or that their dams lost their visual tags making it difficult for owners to record the information Some calves were not matched to the existing bulls, because some bull candidates or their potential sires were not available (died or sold) prior to the collection of tissue samples or hair. The inability to match calves to sires results in incomplete pedigree information and may also be caused by other unidentified factors.

Complete pedigree information promotes accurate assessment of genetic merit in replacement candidates or the current parent bulls and cows. Sire verification tools also help assess the prolificacy of herd bull(s). Table 2 and Figures 1 to 3 show the differences in the proportion of calves matched to bulls in different herds (as an indicator of prolificacy). There was variability in the proportion of calves assigned to bulls within each herd, ranging from 0.09% (CF) to 75.44%

Figure A: Distribution of herds evaluated in the study

(VCR2; LLC; Fig.2). There are several factors that affect bull prolificacy. These would range from the innate /physical breeding ability of the bull to environmental factors (e.g. ambient temperature) or management factors such as rotation of bull turn-in. Further, clean-up bulls following a prolific bull are less likely to sire many calves. Prolificacy also determines the impact a bull has in a herd, through the propagation of his genes through the generations.

The economic implications of bull prolificacy help producers identify underperforming bulls. It may cost over $2500 for the annual maintenance of bulls. Fewer-than-expected calves increase the production costs for producers, e.g. a bull that sired only two calves in a year attracts greater cost per calf ($1250/calf) compared to one that sires 25 calves ($100/calf). Bulls that sire more calves are preferred and are more economical for beef producers.

The ages of the bull (where available) were not related (P > 0.05) to the observed prolificacies. There were also differences in the birthweights and the weaning weights among the bulls (where some records were available). Figures 4 to 6 show the average birth weights in different herds while Figures 7 to 10 show the average weaning weights. Differences were not observed (P > 0.05) in the VCC (Fig. 4) and VCR (Fig. 5) groups for the average birthweight of the calves, but some bulls in the OS herd (Fig. 6) showed some differences in the average birth weight of their calves. There were no differences (P > 0.05) for the weaning weights in VCC and VCR (Fig. 7) but the other herds recorded differences among sires for average weaning weights. Recording production information (such as the birthweight or weaning weight) reinforces or confirms the genetic potentials of such bulls, especially those purchases that were based on the bull’s genetic merit (EPD) of the bull. The lack of keeping progeny production records (e.g. birth and weaning weights) limits the abilities of producers to assess their bull batteries or cowherds.

The lack of feed costs and other maintenance costs limited the economic information deduced from this study. Such information supports the financial management of the operations and may also help identify potential cost-reduction factors.

Table 1. Summary of Bulls, Dams and Offspring in the different herds.

Note: 187 calves have no record of dams

Table 2. Sire Prolificacy (%) across the Years

Fig.3:

Different superscripts indicate significant differences at P < 0.05

Fig. 4: Average Birth Weights of Calves (kg) across 4 Years in VCC Group (Commercial)

Fig. 5: Average Birth Weights of Calves (kg) by Sire in the VCR Group (Research)

Fig. 7: Average Weaning Weights (kg) of Calves by Sire in the VCC and VCR Groups

Fig.

Conclusions

There were variations in prolificacy among the bulls evaluated in this study

There were differences in production performance among the offspring from different bulls in some herds

There is a need to assess the economic implications of the management decisions of culling and replacing bulls that perform below expectation

The drivers of prolificacy across the years were unclear