Pregnancy testing: using results

Mick Sullivan
Department of Agriculture and Fisheries

Pregnancy testing is a very valuable management tool. To ensure that the returns outweigh the effort and cost, it is essential to establish objectives to determine how the pregnancy testing results will impact management decisions. Pregnancy testing does not offer redemption from poor management; sound management usually must be in place before pregnancy testing can offer significant returns.

Uses of pregnancy testing

  • Identification of non productive breeders and heifers for culling. Pregnancy testing increases the efficiency of culling non performing females: heifers, mature and aged breeders. Cows which don’t provide a calf each year should be replaced by cows/heifers that do.
  • Management of surplus females. A pregnancy diagnosis can indicate the most appropriate management to achieve maximum returns for culls. Certified pregnancy status can attract a premium.
  • Identification of productive breeders. Cows that regularly conceive while lactating, are exhibiting a reasonably heritable trait. Identifying these breeders may be useful for future heifer selection.
  • Estimating calving distribution and numbers for management. Weaning to manage cow body condition and supplement program management can be better planned if preg testing is used to estimate calving distribution.
  • Segregation of high risk cows. In herds where mating is uncontrolled preg testing enables producers to identify, separate and manage high risk cows due to calve in the late dry season.
  • Infertility and disease investigations. These require serial pregnancy testing with detailed records to determine if there are delayed or poor conceptions.
  • AI programs. Pregnancy testing is used in AI programs to assess suitability of cattle (not pregnant, cycling, no reproductive abnormalities or disease), and to differentiate sires.

The critical considerations when looking at pregnancy testing data are:

  • What was the pregnancy rate or conception rate?
  • What was the pattern of conceptions over the mating period?
  • What does the pregnancy data mean for future planning and management?
  • What does the pregnancy data mean for future business performance?

What was the pregnancy rate?

Pregnancy testing occurs closer to mating than branding or weaning and provides an excellent measure of mating performance provided all animals are tested. Not testing cows that ‘look calfy’ produces data of little value, because there is no way of knowing whether the ‘calfy’ cows were in fact pregnant.

Pregnancy testing provides a set of figures from which losses to branding, and to weaning, can be calculated and consequently overall breeder performance determined. However, the value of the data depends on the accurate pregnancy testing/foetal aging of all animals, and on good records to define the number of cows mated to produce the calves. A problem can be the time between mating and weaning leading to miscalculations. A cow that conceives in November 2011 will not wean that calf until April-June 2013.

It is important to know the conception rate and conception pattern of maiden heifers, first calf cows (cows on their second mating) and mature cows. If conception rates are low knowing the conception pattern of these three groups can help diagnose the problem.

The overall conception rate is useful for calculating potential sale numbers in future years.

Joiner heifers. Joiner heifers are the most critical animals in the breeder herd because if they get off to a good start their lifetime performance will be better. If heifers are joined at two years they should be achieving a 90% conception rate in four months. Many well managed herds achieve 90% conception in three months. Joiner heifers need to be managed as a separate group to receive special attention in poor seasons and ensure they have the maximum opportunity to re-conceive.

Yearling joining. Yearling joining is attempted on better land types. With yearling joining conception rates tend to be lower and more variable. Yearling heifer conception rates on properties which participated in a central Queensland project were in the range 60–85% over four months. On tougher country where heifers struggle to achieve good mating weights (300kg plus) a poor maiden conception is often followed by very low conceptions as first calf cows. In deciding whether to yearling mate performance over the first two joinings is important. If a majority of yearling mated heifers’ only produce one calf by the time they are three year old there is little economic advantage and the practice should be questioned. On all but the very best country these heifers will need special attention to ensure a satisfactory conception at their second mating.

First calf cows. This group has the lowest conception rates due to the combined stress of lactation and their requirements for growth. Conceptions rates are generally 10–40% below that of the maiden heifers. Identifying conception rates in this group will highlight management issues which may need to be addressed. Recording of condition score is particularly important with this group.

Wet and dry cows. In herds with year round mating or where empty cows were retained the previous year there will be dry cows at the pregnancy test. These dry cows should conceive early in the mating period and should be culled if found empty. The dry cows have been under far less pressure than those which have raised a calf. Consequently, it is important to record the lactation status of cows at pregnancy test so that the pregnancy rate of wet and dry cows can be assessed separately.

What was the conception pattern over the mating period?

Of equal importance to the overall pregnancy rate of each group of cows is the conception pattern. The conception pattern of a herd indicates;

  • The most fertile cows are those that conceive early in the mating period and while lactating. Where possible replacement heifers should be kept from cows that conceive and calve early.
  • A disease or body condition problem. A large percentage of late pregnancies can indicate a disease problem in the herd or that the cows were not in good enough body condition at the start of mating.

Early conceptions indicate a more productive and profitable herd. The aim is to have as many conceptions as possible early in the mating season. This means that calves will be older and bigger at any given time of the year and can be the difference between finishing and sale in the current year or having animals held over (Table 1).

Table 1. Impact of conception date on calving date, weaner weight and value for 2011 calves based on weaning date of 1 June 2011

Days from start of mating (1/12/2009) Conception date Calving date Weaning age (months) Estimated weaner weight (kg)1 Estimated weaner value @
$1.90/kg ($)
1 1/12/2009 10/09/2010 8.8 245 466
60 30/01/2010 9/11/2010 6.8 197 374
120 31/03/2010 8/01/2011 4.8 149 283
180 30/05/2010 9/03/2011 2.8 101 192

1Calculated on birth weight of 34kg and calf growth rate of 0.8kg/day

Fertility diseases. Delayed conceptions in the mating period can arise due to diseases such as vibriosis and trichomoniasis with animals aborting then re-conceiving later in the joining period. The graph below shows the delayed conceptions and lower overall conception for a herd in 1998 when vibriosis was detected, compared to 1999.

Figure 1 conception rates.
Figure 1. Cumulative conception rates for maiden heifers in 1998 and 1999

Other data to collect when preg testing

Heifer growth rates. The principal cause of delayed conceptions in maiden heifers is not being heavy enough at joining. For further information on critical mating weight see Heifer management. Heifer weights should be monitored from weaning to ensure they will achieve the target or critical mating weight. This allows early intervention if the heifers growth fall below the desired level.

Weighing maiden heifers at the pregnancy test is useful because it shows how well they have grown and if mating weights were high enough. Data in Table 2 demonstrates the impact of heifer weights on conception rates.

Table 2. Heifer weights at pregnancy test and conception rates for a north west Queensland property in 1999 and 2002

Year 1999 2002
Pregnancy test date 12/05/1999 21/05/1999
Average heifer weight (kg) 402 388
Pregnancy rate (%) 91 79

Data collected from properties participating in a central Queensland group fertility management PDS showed much lower conception rates in heifers under 360–380kg. These lighter heifers spent much of the joining period reaching puberty and conceived late or failed to conceive.

Breeder body condition. Breeder body condition prior to calving is the major determinant of conception rates. The graph below shows how cows in body condition score (BCS) 3 and 4 conceived quicker and achieved higher pregnancy rates than those in BCS 2.

Figure 2 conception rates.
Figure 2. Cumulative conception rates for cows in a range of body condition scores at pregnancy test

Recording BCS at pregnancy test assists evaluation of the results and planning. If there are significant numbers of breeders in BCS 2, dry season supplementation should be considered to prevent these animals slipping further. Drafting off these animals at pregnancy test enables targeted supplementation as cows in BCS 3 or 4 may require no dry season supplementation.

If a large proportion of the breeder herd is in BCS 2 at pregnancy test, it indicates that changes in mating management, time of weaning and grazing management may be required to help cows maintain body condition. For more information see Nutritional management of breeders.

What does pregnancy data mean for future planning?

Good pregnancy testing data enables better planning for the next 12 months. Data from pregnancy testing can be used into calving summary tables like the example in Table 3. Knowing what cows will calve when assists:

  • Grazing management
  • Planning branding
  • Planning weaning to manage cow body condition
  • Supplement program management (if some cows calve in the dry season).

Table 3. Estimated 2005 calving data for Swans Lagoon CRC Brahman Cows

Calving Data
Pregnancy test date 1/06/2004
Gestation length (days) 290
Estimated breeder mortality (%) 1
Estimated foetal and calf losses (%) 6
Mean birth weight (kg) 31
Mean calf growth rate (kg/hd/day) 0.8

 

Table 4. Estimated cow and calf numbers, losses, calving dates and calf ages at 30/05/2005

Pregnancy status No. of cows Calving
date
Calf numbers Age of calves Mean calf weight
(months) (days) (months) (kg)
2 5 17 January 2005 5 133 4.4 137
2.5 21 2 January 2005 20 148 4.9 149
3 36 18 December 2004 34 163 5.4 161
3.5 97 3 December 2004 90 178 5.9 173
4 69 18 November 2004 64 193 6.4 185
4.5 30 3 November 2004 28 208 6.9 197
Total 258 240 175

 

Table 5. Estimated cow numbers at weaning

No %
Wet cows 240 94
Dry cows (lost calf) 15 6
Total cows 255 100

 

The information in Table 3 also assists at branding to identifying the likely number of cows which will have lost their pregnancy or calf and can be drafted off for sale. These animals are usually in good condition and as well as generating cash flow early in the year their sale will reduce the stocking rate for the latter part of the growing season.

What does pregnancy data mean for future business performance?

Collecting and using pregnancy test data puts businesses in a much better position with financiers for whom the reliability of future cash flow is a critical consideration. If turnoff numbers are going to be down, there is time to identify opportunities to fill the gap. This type of planning is even more critical in herds with a younger turnoff as there is less time to fill income gaps.

In many herds, there is considerable opportunity to tighten the calving period and increase the selection for fertility by culling the 5-10% of animals which conceive in the last month of joining. Joiner heifers are an excellent group to implement this approach with as the late calvers are less fertile and the animals most likely to have trouble re-conceiving as a first calf cow.

Key points

  • Pregnancy testing with accurate foetal ageing is critical for assessing reproductive performance.
  • Body condition scoring provides additional valuable data for managing weaning, grazing strategies and supplementation.
  • Pregnancy test data allows better planning of grazing management, weaning and cull cow turnoff for the next 12 months.
  • The forward planning of weaning and turnoff, which pregnancy test data enables, is critical for business planning and financial management.