To cull cows early or not?

To cull cows early or not?

There seems to be a common perception among some local dairy farmers that cows may be culled earlier than their expected production lifespan when using high genetic merit bulls. This implies that daughters from such bulls would in first lactation produce more milk than older cows. In some herds cows are therefore culled after they had completed only three lactations. Although possible it is not common for first lactation cows to produce more or similar amounts of milk than older cows. It may just indicate that the present older cows producing less milk than first lactation cows may be of lower genetic merit which should have been culled as heifers or during first lactation because of lower than group average milk yield levels. Although the correlation between genetic merit and milk yield is positive, higher milk yield levels are not necessarily the result of improved genetic merit. A better diet, housing conditions and overall management may also result in the improvement of the milk yield of cows. The improvement in milk yield over time due to these environmental factors should not be confused with a change in genetic merit.

Genetic merit

The genetic merit of a dairy herd is determined through participating in the national milk recording scheme. This requires that the milk yield of all lactating cows in a dairy herd is recorded on specific days during a calendar year. Ten dates are usually provided for the recording of the milk yield of cows. Cows must be more than 5 days in milk. Usually, 8-10 test days per lactation are required to estimate the lactation milk yield of cows. On such milk recording days a milk sample is also collected from each cow to be analysed later at a central laboratory for its fat, protein, and lactose contents. The somatic cell count and milk urea nitrogen content of the milk may also be determined from this sample.

This information together with each cow’s identity and that of her dam and sire are used to estimate the breeding value for cows, heifers (progeny of cows) and bulls that have been used in the herd. Genetic trends for milk, fat and protein yield, fat and protein percentage, somatic cell count, herd life and calving interval are presented as a genetic profile for the herd. From this information the change in genetic merit for production parameters can be estimated using linear or quadratic regression equations. These trends for the herd can be compared to that for the breed (or national herd). In the following table milk production parameters is presented for all the cows in a specific Jersey herd for birth years from 2007 to 2017.

Birth year Milk (kg) Fat (kg) Protein (kg) Fat (%) Protein (%)
Herd Breed Herd Breed Herd Breed Herd Breed Herd Breed
2007 -34 -109 -0.7 -3.2 -0.7 -3.7 0.01 0.04 0.01 0.01
2017 152 165 5.5 9.2 5.9 7.0 -0.04 0.02 0.00 0.02
Change/year 24.2 26.5 0.86 1.25 0.91 1.05 -0.005 -0.0007 0.0001 0.0007

This shows that estimated breeding values for production traits for this herd increased from 2007 although being lower compared to the national herd. Fat and protein percentages differed little over time. This may indicate that the breeding objective for the herd was not strong on milk yield performance.

The mean genetic merit for milk yield of all bulls used in the herd was 221 kg varying from -727 to +1522 kg. Of all bulls 57% had breeding values lower than the overall mean for all bulls. Most (74%) of these were “home-bred” bulls. In addition to the breeding value of bulls, the number of daughters of each bull contributes greatly to the genetic merit of the herd. One bull had 33 daughters ranging from -290 to 1045 kg for milk yield while some bulls only had a few daughters. To ensure ongoing genetic progress bulls with positive genetic merit values for milk, fat or protein yield should be used to service cows and heifers. Selecting sires using breeding values for protein yield would prevent affecting fat and protein percentages negatively.The full article is for subscribed members only. To view the full article please subscribe. It’s FREE!Log In Register

 

Author

  • Research Associate, Faculty of Animal Sciences, University of Stellenbosch

[printfriendly]

Please share this article with your friends!

Related Articles

All
  • All
  • Awards
  • Business
  • Crops
  • Education
  • Energy
  • Featured Article
  • Finance
  • Health
  • Hospitality
  • Human Resources
  • Irrigation
  • Latest News
  • Lifestyle
  • Livestock
  • Recipes
  • Soil
  • Uncategorized
  • Under cover farming
  • Water
Better breeding improves financial results

Better breeding improves financial results

All dairy farmers are breeders although breeding aims may differ among herds. Some farmers breed show cows while others produce sires for the artificial insemination...
WordPress › Error

There has been a critical error on this website.

Learn more about troubleshooting WordPress.