How does your herd measure up: Part 1: Non-Pregnancy Rates

One of the most important economic criteria that determines profitability is the calf crop percentage. This is defined as the percentage of cows weaned per cow exposed to the bull.

Obviously, having a live calf to sell is the ultimate objective of most cow-calf enterprises and a failure to produce a calf can have a major impact on the bottom line. Weaning weights, annual costs of maintaining cows and selling prices of calves also have significant impacts on profitability, but the calf crop percentage is an easily measurable productivity trait.

The calf crop percentage can be affected by a number of factors including reproductive fertility or pregnancy rates, abortions, and calf death losses.

A recent paper published in the scientific journal PLOSONE gives important benchmarking data that affects calf crop percentage for cow-calf herds in Western Canada. Benchmarking data helps to define what is normal and what is a reasonable goal or target for some of these important productivity measures.

This study summarizes the productivity findings from the Western Canadian Cow-Calf Surveillance Network, which followed about 100 cow-calf herds located on the prairie provinces from 2014-17. This project was funded by the Canadian Cattlemen’s Association through the Beef Cattle Research Council and also received research funding from Saskatchewan Agriculture.

Dr. Cheryl Waldner and colleagues from the Western College of Veterinary Medicine authored this particular study, which resulted from this project.

Cow-calf herds were recruited from across Manitoba, Saskatchewan and Alberta to match the geographical distribution of beef herds in these regions and to match the distribution of smaller herds with 100-300 cows, and larger herds of more than 300 cows in those regions based on the 2011 Census of Agriculture.

All of the herds had at least 100 cows at the time of enrollment in the study.

I’d like to focus on the pregnancy testing results from the herds in this study.

Cows and heifers that are identified as not pregnant at the time of pregnancy testing is an important factor when determining the calf-crop percentage.

Producers in the study were asked to record the number of animals that were identified as non-pregnant when pregnancy testing occurred each year. Only herds that performed whole herd pregnancy testing were included in the results of the study.

When we look at the overall average over the four years of the study, the median percentage of cows identified as non-pregnant was 6.2 percent. This is based on a total of 94 herds and 276 individual herd observations over this time period.

The median percentage of heifers testing non pregnant was slightly higher at 8.3 percent. There was a great deal more variation in the non-pregnancy percentages of heifers reported in these herds when compared to the non-pregnancy percentages of cows.

This probably suggests that there is more variability in how cow-calf producers manage and select heifers, which might explain some of this greater variation in the heifer non-pregnancy rates.

So what is a reasonable goal or target for pregnancy percentages in cows and heifers? The herds in this study all worked closely with a veterinary practice and were probably fairly well managed herds overall. If we look at the data, over 75 percent of the herd observations included pregnancy rates for cows above 90 percent and more than 50 percent of the herd observations exceeded 90 percent pregnancy rates for heifers. The top 25 percent of herds tended to achieve pregnancy rates greater than 95 percent for both cows and heifers, which would suggest that this is indeed an attainable goal.

The authors also looked at some of the factors that influenced pregnancy rates in the study. The variation in non-pregnancy percentages between herds was always greater than the variation from year to year, which suggests that herd management plays an important role in pregnancy rates.

There was some geographic variations in pregnancy rates between provinces, but this wasn’t consistent and probably is simply due to climate and precipitation effects on forage production.

The most interesting finding was that those herds that timed their breeding season later in the year (July or August) tended to have significantly higher rates of non-pregnancy for both cows and heifers. Producers in Western Canada that have moved their breeding season later in the year have actually previously commented that they thought they were experiencing slightly lower pregnancy rates and the data in this study demonstrated that this was indeed true.

The differences in non-pregnancy rates were not dramatic, but they were statistically significant. The theory that may explain this is that herds that have a breeding season in July and August may now be breeding cows when the quality of pasture is declining somewhat. This may result in cows with poorer nutritional status and therefore slightly lower pregnancy rates.

This is probably especially important in a geographic region that is limited by moisture.

Obviously breeding later in the year means calving later in the year and some of these decreases in pregnancy rates were offset to some degree by better calf survival rates.

Making decisions on breeding and calving seasons is a classic example of a decision that can have multiple economic and productivity consequences.

This project provides us with some benchmarks in non-pregnancy rates so that we can compare the productivity measurements in our own herd.

If you’d like to read the article, it is available as an open access online article at the following link https://doi.org/10.1371/journal.pone.0219901.

John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.

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